Positive electrode active material, positive electrode sheet, secondary battery, and power using device

Abstract

The application provides a positive electrode active material, a positive electrode sheet, a secondary battery and a power device. A ratio of a difference between Dv99 and Dv10 of the positive electrode active material particles and Dv50 of the positive electrode active material particles satisfies: 0.8≤(Dv99-Dv10) / Dv50≤8. By regulating the particle size distribution of the positive electrode active material particles, the positive electrode active material particles of different sizes are matched, the powder compaction density of the positive electrode active material and the compaction density of the positive electrode sheet are improved, and the performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode active material, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, as secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace, the market's performance requirements for secondary batteries have become increasingly higher.

[0003] The performance of cathode active materials plays a crucial role in battery performance. Currently, the performance of cathode active materials cannot meet the application requirements of next-generation electrochemical systems. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material. By controlling the particle size distribution of the positive electrode active material particles, the particles of different sizes of positive electrode active material are matched to improve the powder compaction density of the positive electrode active material and the compaction density of the positive electrode sheet, thereby improving the performance of the battery.

[0005] In a first aspect, this application provides a positive electrode active material, comprising a polyanionic compound, wherein the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to Dv50 of the positive electrode active material particles satisfies: 0.8 ≤ (Dv99 - Dv10) / Dv50 ≤ 8. By adjusting the particle size distribution of the positive electrode active material particles, controlling the difference between Dv99 and Dv10 and the ratio to Dv50 of the positive electrode active material particles to satisfy: 0.8 ≤ (Dv99 - Dv10) / Dv50 ≤ 8, the particle sizes of the positive electrode active material particles can be matched to each other, improving the density of the positive electrode active material arrangement and increasing the space utilization rate. This matching effect between positive electrode active material particles of different sizes allows for full utilization of the packing space of the positive electrode active material, thereby improving the powder compaction density of the positive electrode active material and the compaction density of the positive electrode sheet, and improving battery performance.

[0006] In any embodiment, the difference between Dv99 and Dv10 of the positive electrode active material satisfies: 4.0μm≤(Dv99-Dv10)≤8.0μm.

[0007] Controlling the difference between Dv99 and Dv10 of the positive electrode active material particles within a suitable range is beneficial for utilizing the mutual stacking of positive electrode active materials of different sizes, improving space utilization, increasing the powder compaction density of the positive electrode active material, and thus improving battery performance.

[0008] In any embodiment, the Dv50 of the positive electrode active material satisfies: 1.0μm≤Dv50≤5.0μm.

[0009] Controlling the Dv50 of the positive electrode active material particles within a suitable range can effectively avoid or reduce physical gelation during the slurry coating process caused by excessively small Dv50, which increases the difficulty of coating. It can also effectively avoid or reduce the reduction in the compaction density of the positive electrode active material powder caused by excessively large Dv50, thus balancing the processability and compaction density performance of the positive electrode active material.

[0010] In any embodiment, the positive electrode active material particles are formed by the aggregation of primary particles, and the ratio of the Dv50 of the positive electrode active material to the particle size D of the primary particles satisfies: 0.5≤Dv50 / D≤10.

[0011] Controlling the ratio of the Dv50 of the positive electrode active material particles to the particle size D of the primary particles within a suitable range can effectively control the degree of aggregation of the primary particles, avoiding or reducing the phenomenon of physical gelation of the slurry caused by excessively small particle size of the positive electrode active material, which increases the difficulty of coating. It can also avoid or reduce the phenomenon of excessively large particle size of the positive electrode active material, which reduces its powder compaction density and thus lowers the kinetic performance of the positive electrode active material during charge and discharge, thus balancing processability and electrical performance.

[0012] In any embodiment, the particle size D of the primary particle satisfies: 1μm < D ≤ 1.5μm.

[0013] By controlling the particle size D of the primary particles within a suitable range, the Dv50 of the positive electrode active material particles formed by the aggregation of primary particles can be effectively controlled within a suitable range, and the Na... + The transmission path improves Na + This increases the diffusion rate and improves battery performance.

[0014] In any embodiment, the positive electrode active material comprises a carbon-composite polyanionic compound, which has the following general formula:

[0015] Na x R y (PO4) z (P2O7) k / C

[0016] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4.

[0017] The polyanionic compound in this application has excellent structural stability, safety and a suitable voltage platform, and can be used as a positive electrode active material in sodium secondary batteries.

[0018] In any embodiment, the carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film.

[0019] Carbon materials are coated onto the surface of primary particles of polyanionic compounds in the form of carbon films, which increases the contact area between the carbon materials and the polyanionic compounds, facilitates electron transport, and helps improve the conductivity of polyanionic compounds.

[0020] In any embodiment, the carbon material includes one or more of amorphous carbon, conductive carbon black, carbon nanotubes, and graphene.

[0021] Different types of carbon materials can improve the conductivity of positive electrode active materials.

[0022] In any embodiment, based on the total mass of the positive electrode active material, the mass content of the carbon material in the positive electrode active material is 0.1% to 10%, optionally 0.15% to 2%.

[0023] Controlling the carbon material content within a suitable range can prevent or reduce the decrease in specific capacity of the positive electrode due to excessive carbon content, while also preventing or reducing the effectiveness of improving the conductivity of the positive electrode active material due to insufficient carbon content. A suitable carbon material content balances production costs, processing performance, and electrical performance, resulting in batteries with excellent electrochemical performance and promising application prospects. Further controlling the material content to 0.15%–2% is beneficial for further improving the coulombic efficiency and cycle performance of the battery.

[0024] In any embodiment, after compaction at a pressure of 400 MPa, the compacted density of the positive electrode active material powder is 2 g / cm³. 3 ~2.5g / cm 3 .

[0025] The positive electrode active material provided in this application has a high powder compaction density, which allows for a further increase in the compaction density of its positive electrode sheet. This is beneficial for further optimizing the discharge capacity of the positive electrode active material, and enables the secondary battery to have excellent cycle life and safety during long-term rapid charge and discharge use.

[0026] A second aspect of this application provides a positive electrode sheet comprising a binder, a conductive agent, and a positive electrode film layer, wherein the positive electrode film layer comprises the positive electrode active material described in the first aspect.

[0027] In any embodiment, based on the total mass of the positive electrode film, the mass content of the binder is 1.5% to 3%, optionally 2.0% to 2.5%.

[0028] Controlling the binder mass content within a suitable range provides sufficient bonding strength and is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the binder mass content to 2.0%–2.5% is beneficial for further improving the battery's cycle performance.

[0029] In any embodiment, the conductive agent includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

[0030] The addition of one-dimensional and / or zero-dimensional conductive materials can help increase the conductivity of the positive electrode.

[0031] In any embodiment, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or

[0032] Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%, and can be selected as 0.5% to 0.9%.

[0033] Controlling the mass content of one-dimensional conductive material within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of one-dimensional conductive material to 0.5%–0.9% is beneficial for further improving the battery's coulombic efficiency.

[0034] In any embodiment, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or

[0035] Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%, and optionally 2% to 2.8%.

[0036] Controlling the mass content of zero-dimensional conductive materials within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of zero-dimensional conductive materials to 2%–2.8% is beneficial for further improving the battery's coulombic efficiency.

[0037] A third aspect of this application provides a secondary battery, including the positive electrode sheet described in the second aspect.

[0038] In any embodiment, the secondary battery is a sodium-free secondary battery without a negative electrode.

[0039] In any embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a base coating disposed on at least one surface of the negative current collector, the base coating including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0040] The aforementioned base coating not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the current collector surface, thereby improving the coulombic efficiency and cycle performance of the battery.

[0041] In any embodiment, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0042] The surface density is 5 g / m³ 2 ~50g / m 2 The base coating is beneficial to the uniform distribution of nucleation sites in the negative electrode-free secondary battery, promotes the uniform deposition of metal, and does not affect the electron transport behavior.

[0043] In any embodiment, the thickness of the base coating is 2 μm to 100 μm.

[0044] Controlling the thickness of the undercoat layer to 2μm to 100μm can provide enough nucleation sites for the negative electrode-free secondary battery, which is conducive to the uniform deposition of metal ions and suppresses dendrites.

[0045] A fourth aspect of this application provides an electrical device including a secondary battery as described in the third aspect of this application. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a secondary battery cell according to one embodiment of this application;

[0047] Figure 2 yes Figure 1 An exploded view of a secondary battery cell according to an embodiment of this application is shown.

[0048] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0049] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0050] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0051] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the positive electrode active material, positive electrode sheet, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] The compaction density of the cathode active material is closely related to the performance of the battery. This compaction density is influenced not only by the material's physical properties and surface morphology, but also significantly by its particle size distribution. Therefore, it is necessary to provide a cathode active material with a suitable particle size distribution to improve its compaction density and meet the requirements of next-generation batteries.

[0062] [Positive electrode active material]

[0063] Based on this, this application proposes a positive electrode active material, wherein the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to Dv50 of the positive electrode active material particles satisfies: 0.8≤(Dv99-Dv10) / Dv50≤8.

[0064] In this paper, the term "Dv99" refers to the particle size at which the cumulative volume distribution percentage of particles reaches 99%.

[0065] In this paper, the term "Dv50" refers to the particle size at which the cumulative volume distribution percentage of particles reaches 50%.

[0066] In this paper, the term "Dv10" refers to the particle size at which the cumulative volume distribution percentage of particles reaches 10%.

[0067] In some embodiments, the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to Dv50 of the positive electrode active material particles can be selected as 0.8, 1.0, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a value within the range formed by any two of the above points.

[0068] The Dv99, Dv50, and Dv10 of the positive electrode active material particles can all be measured by any known method, including but not limited to laser diffraction for particle size distribution. As an example, referring to GB / T 19077-2016 Laser Diffraction for Particle Size Distribution, 0.1g–0.13g of the positive electrode active material sample to be tested was weighed into a 50mL beaker, 5g of anhydrous ethanol was added, and a stir bar of approximately 2.5mm was placed inside. The beaker was then sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The tests were performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK. Among them, Dv99 of the positive electrode active material particles is the particle size corresponding to a cumulative volume distribution percentage of 99% for the positive electrode active material particles, Dv50 of the positive electrode active material particles is the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material particles, and Dv10 of the positive electrode active material particles is the particle size corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material particles.

[0069] By controlling the particle size distribution of the positive electrode active material particles, and ensuring that the difference between Dv99 and Dv10, and the ratio of Dv99 to Dv50, satisfy the condition 0.8 ≤ (Dv99 - Dv10) / Dv50 ≤ 8, the positive electrode active material particles have a certain span ratio. This allows for the close packing of the positive electrode active material through the matching of particles of different sizes. This matching effect between positive electrode active material particles of different sizes ensures full utilization of the packing space, thereby improving the powder compaction density of the positive electrode active material and the compaction density of the positive electrode sheet, ultimately enhancing battery performance.

[0070] In some embodiments, the difference between Dv99 and Dv10 of the positive electrode active material particles satisfies: 4.0 μm ≤ (Dv99 - Dv10) ≤ 8.0 μm. In some embodiments, the difference between Dv99 and Dv10 of the positive electrode active material particles can be selected as 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, or a value within a range consisting of any two of the above points.

[0071] Controlling the difference between Dv99 and Dv10 of the positive electrode active material particles within a suitable range is beneficial for utilizing the mutual stacking of positive electrode active material particles of different sizes, improving space utilization, increasing the powder compaction density of the positive electrode active material, and thus improving battery performance.

[0072] In some embodiments, the Dv50 of the positive electrode active material particles satisfies: 1.0 μm ≤ Dv50 ≤ 5.0 μm. In some embodiments, the Dv50 of the positive electrode active material particles can be selected as 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or a value within the range formed by any two of the above points.

[0073] Controlling the Dv50 of the positive electrode active material particles within a suitable range can effectively avoid or reduce physical gelation during the slurry coating process caused by excessively small Dv50, which increases the difficulty of coating. It can also effectively avoid or reduce the reduction in the compaction density of the positive electrode active material powder caused by excessively large Dv50, thus balancing the processability and compaction density performance of the positive electrode active material.

[0074] In some embodiments, the positive electrode active material particles are formed by the aggregation of primary particles, and the ratio of the diameter Dv50 of the positive electrode active material particles to the particle size D of the primary particles satisfies: 1 < Dv50 / D ≤ 10. In some embodiments, the ratio of the diameter Dv50 of the positive electrode active material particles to the particle size D of the primary particles can be selected as 1.1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a value within the range formed by any two of the above points.

[0075] The particle size D of the primary particles in the positive electrode active material can be measured by any known method, including but not limited to SEM testing. As an example, using SEM testing, after cold-pressing the positive electrode active material sample, the sample is cut open using an Ar particle beam to expose the end face. Images of the end face are then obtained using a scanning electron microscope (SEM). The particle size D of the primary particles in the positive electrode active material is measured based on the SEM images.

[0076] Controlling the ratio of the Dv50 of the positive electrode active material particles to the particle size D of the primary particles within a suitable range can effectively control the degree of aggregation of the primary particles, avoiding or reducing the phenomenon of physical gelation of the slurry caused by excessively small particle size of the positive electrode active material, which increases the difficulty of coating. It can also avoid or reduce the phenomenon of excessively large particle size of the positive electrode active material, which reduces its powder compaction density and thus lowers the kinetic performance of the positive electrode active material during charge and discharge, thus balancing processability and electrical performance.

[0077] In some embodiments, the particle size D of the primary particles satisfies: 0.5 μm ≤ D ≤ 1.5 μm. In some embodiments, the particle size D of the primary particles can be selected as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or a value within the range formed by any two of the above points.

[0078] By controlling the particle size D of the primary particles within a suitable range, the Dv50 of the positive electrode active material particles formed by the aggregation of primary particles can be effectively controlled within a suitable range, and the Na... + The transmission path improves Na + This increases the diffusion rate and improves battery performance.

[0079] In some embodiments, the positive electrode active material includes a carbon-based composite polyanionic compound having the following general formula:

[0080] Na x R y (PO4) z (P2O7) k / C

[0081] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4.

[0082] In some embodiments, R includes Fe. In some embodiments, R includes Mo. In some embodiments, R includes V. In some embodiments, R includes Mn.

[0083] In some implementations, x can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 0.4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points; y can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points; z can be selected as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a value within the range formed by any two of the above points; and k can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points.

[0084] The polyanionic compound in this application has excellent structural stability, safety and a suitable voltage platform, and can be used as a positive electrode active material in sodium secondary batteries.

[0085] In some embodiments, carbon material is coated on the surface of primary particles of polyanionic compound in the form of a carbon film.

[0086] Carbon materials are coated onto the surface of primary particles of polyanionic compounds in the form of carbon films, which increases the contact area between the carbon materials and the polyanionic compounds, facilitates electron transport, and helps improve the conductivity of polyanionic compounds.

[0087] In some embodiments, the carbon material includes one or more of amorphous carbon, conductive carbon black, carbon nanotubes, and graphene.

[0088] Different types of carbon materials can improve the conductivity of positive electrode active materials.

[0089] In some implementations, the carbon material is derived from an inorganic or organic carbon source.

[0090] In some implementations, the inorganic carbon source includes one or more of natural graphite, artificial graphite, carbon black, carbon nanotubes, and graphene.

[0091] In some embodiments, the organic carbon source includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polyethylene glycol, and polyvinyl alcohol.

[0092] In some embodiments, based on the total mass of the positive electrode active material, the mass content of carbon material in the positive electrode active material is 0.1% to 10%, optionally 0.15% to 2%. In some embodiments, based on the total mass of the positive electrode active material, the mass content of carbon material in the positive electrode active material is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a value within a range consisting of any two of the above points.

[0093] Controlling the carbon material content within a suitable range can prevent or reduce the decrease in specific capacity of the positive electrode due to excessive carbon content, while also preventing or reducing the effectiveness of improving the conductivity of the positive electrode active material due to insufficient carbon content. A suitable carbon material content balances production costs, processing performance, and electrical performance, resulting in batteries with excellent electrochemical performance and promising application prospects. Further controlling the material content to 0.15%–2% is beneficial for further improving the coulombic efficiency and cycle performance of the battery.

[0094] In some embodiments, after compaction at a pressure of 400 MPa, the compacted density of the positive electrode active material powder is 2 g / cm³. 3 ~2.5g / cm 3In some embodiments, after the positive electrode active material is compacted under a pressure of 400 MPa, the compacted density of the positive electrode active material powder can be selected as 2 g / cm³. 3 2.1g / cm 3 2.15g / cm 3 2.2g / cm 3 2.25g / cm 3 2.3g / cm 3 2.35g / cm 3 2.4g / cm 3 2.45g / cm 3 2.5g / cm 3 The value within the range formed by any two of the above points.

[0095] After the positive electrode active material is compacted at 400 MPa, the compacted density of the powder can be measured by any known method. As an example, referring to GB / T 24533-2009 Powder Compacted Density Method: a certain amount of powder is placed in a special compaction mold, and then the mold is placed on a compaction density instrument. The pressure is set to 400 MPa, compaction is completed, and the pressure is released. The thickness of the compacted powder in the mold is read on the instrument, and the density is calculated using the following formula:

[0096] pC = m / V = m / (S*H)

[0097] Where: pC --- compacted density of powder, g / cm³ 3 m --- Sample mass, g; S --- Mold bottom area, cm² 2 H---Compacted thickness, cm.

[0098] The positive electrode active material provided in this application has a high powder compaction density, which can further improve the compaction density of its positive electrode film layer. This is beneficial to further optimize the discharge capacity of the positive electrode active material, and enables the secondary battery to have excellent cycle life and safety during long-term rapid charge and discharge use.

[0099] [Positive electrode plate]

[0100] The positive electrode sheet includes a positive electrode film layer, which includes a binder, a conductive agent, and a positive electrode active material in some embodiments.

[0101] In some embodiments, the binder content is 1.5% to 3% by mass based on the total mass of the positive electrode film, and can be optionally 2.0% to 2.5%.

[0102] In some embodiments, based on the total mass of the positive electrode film, the mass content of the binder can be selected as 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or a value within a range consisting of any two of the above points.

[0103] Controlling the binder mass content within a suitable range provides sufficient bonding strength and is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the binder mass content to 2.0%–2.5% is beneficial for further improving the battery's cycle performance.

[0104] In some embodiments, the conductive agent includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

[0105] In some embodiments, the positive electrode film layer contains both one-dimensional and zero-dimensional conductive materials. The simultaneous addition of two types of conductive materials is beneficial for further increasing the conductivity of the positive electrode.

[0106] In some embodiments, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0107] In some embodiments, the mass content of the one-dimensional conductive material is 0.2% to 1%, optionally 0.5% to 0.9%, based on the total mass of the positive electrode film.

[0108] In some embodiments, the one-dimensional conductive material includes single-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes multi-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes both single-walled and multi-walled carbon nanotubes.

[0109] In some embodiments, based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material can be selected as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a value within a range consisting of any two of the above points.

[0110] Controlling the mass content of one-dimensional conductive material within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of one-dimensional conductive material to 0.5%–0.9% is beneficial for further improving the battery's coulombic efficiency.

[0111] In some implementations, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black.

[0112] In some embodiments, the mass content of the zero-dimensional conductive material is 1% to 3% based on the total mass of the positive electrode film, and can be selected as 2% to 2.8%.

[0113] In some embodiments, the zero-dimensional conductive material includes Super P. In some embodiments, the zero-dimensional conductive material includes Ketjen Black. In some embodiments, the zero-dimensional conductive material includes both Super P and Ketjen Black.

[0114] In some embodiments, based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material can be selected as 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, or a value within a range consisting of any two of the above points.

[0115] Controlling the mass content of zero-dimensional conductive materials within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of zero-dimensional conductive materials to 2%–2.8% is beneficial for further improving the battery's coulombic efficiency.

[0116] In some embodiments, the positive electrode sheet further includes a positive current collector, which can be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of SuperP, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal materials of the metal foil, carbon-coated metal foil, and porous metal plate are each independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil with a polymer base film.

[0117] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0118] [Negative electrode plate]

[0119] The negative electrode may consist only of the negative current collector and not contain the negative active material. Alternatively, a metallic phase may be pre-deposited on the negative current collector.

[0120] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In some embodiments, the negative electrode sheet includes a negative current collector and a base coating disposed on at least one surface of the negative current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, carbon black, alumina, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0122] The aforementioned base coating not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the current collector surface, thereby improving the battery's cycle performance and safety.

[0123] In some embodiments, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0124] In some embodiments, the areal density of the base coating may be selected as 5 g / m³. 2 10g / m 2 15g / m 2 20g / m 2 25g / m 2 30g / m 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 The value within the range formed by any two of the above points.

[0125] The surface density is 5 g / m³ 2 ~50g / m 2 The base coating facilitates the uniform distribution of nucleation sites, promotes uniform metal deposition, and does not affect electron transport behavior.

[0126] In some embodiments, the thickness of the base coating is 2 μm to 100 μm.

[0127] In some embodiments, the thickness of the base coating can be selected as 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, or a value within the range formed by any two of the above points.

[0128] Controlling the thickness of the base coating to 2μm to 100μm can provide enough nucleation sites to facilitate the uniform deposition of metal ions and suppress dendrites.

[0129] [Isolation membrane]

[0130] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0131] In some embodiments, the material of the separator can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0132] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0133] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0134] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0135] [Rechargeable Battery]

[0136] Secondary batteries can come in various forms, including, but not limited to, individual battery cells, battery modules, and battery packs.

[0137] A battery cell includes a positive electrode sheet, which includes a positive electrode active material in some embodiments or a positive electrode active material prepared by a preparation method in some embodiments.

[0138] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is an example of a square-structured battery cell, 5. Figure 2 This is an exploded view of battery cell 5.

[0139] In some embodiments, the secondary battery cell also includes a negative electrode, a separator, and an electrolyte.

[0140] In some implementations, the secondary battery cell is a sodium-free secondary battery without a negative electrode.

[0141] In a negative electrode-less sodium secondary battery, no negative electrode active material is pre-deposited; it only contains a negative electrode current collector. During the first charge, sodium ions gain electrons on the cathode side and deposit metallic sodium on the surface of the current collector to form a sodium metal phase. During discharge, the metallic sodium can be converted back into sodium ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other sodium secondary batteries, a negative electrode-less sodium secondary battery can achieve higher energy density because it is not limited by negative electrode materials. Moreover, while maintaining high electrochemical performance, it can shorten the battery production cycle, reduce manufacturing costs, and greatly improve production efficiency.

[0142] In some implementations, the CB value of the sodium-free secondary battery is less than or equal to 0.1.

[0143] The CB value is the capacity per unit area of ​​the negative electrode in a secondary battery divided by the capacity per unit area of ​​the positive electrode. Since batteries without a negative electrode do not contain negative electrode active material, the capacity per unit area of ​​the negative electrode is relatively small, and the CB value of the secondary battery is less than or equal to 0.1.

[0144] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0145] [Battery Module]

[0146] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0147] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0149] [Battery Pack]

[0150] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0151] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0152] [Electrical appliances]

[0153] In one embodiment of this application, an electrical device is provided, including at least one of a secondary battery, a battery module, or a battery pack according to any embodiment.

[0154] Electrical devices include at least one of the secondary batteries, battery modules, or battery packs provided in this application. The secondary batteries, battery modules, or battery packs can be the power source of the electrical device or the energy storage unit of the electrical device. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0155] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0156] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0157] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0158] Example

[0159] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0160] I. Preparation Method

[0161] Example 1

[0162] 1) Preparation of positive electrode active materials

[0163] Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:2.9:2 and stirred continuously at room temperature for 30 min to obtain a mixed slurry. This mixed slurry was then milled to an average particle size of 0.2 μm. Subsequently, SuperP and glucose aqueous solution were added and milled for 10 min to obtain the final slurry. The slurry was then spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 109℃. Finally, under a N2 atmosphere, the temperature was increased to 320℃ at a rate of 2℃ and held for 4 h, then increased to 550℃ at a rate of 2℃ and held for 10 h. The sintered product was crushed and sieved by adjusting the frequency of the air classifier to 50 Hz and the induced draft fan frequency to 30 Hz to obtain the positive electrode active material. Based on the total mass of the positive electrode active material, the carbon material content is 1%; the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to the Dv50 of the positive electrode active material particles is 2.03; the particle size D of the primary particles of the positive electrode active material is 1.5 μm; the Dv50 of the positive electrode active material particles is 3.0 μm; the difference between Dv99 and Dv10 of the positive electrode active material particles is 6.1 μm; and the compaction density of the positive electrode active material is 2.15 g / cm³. 3 .

[0164] 2) Preparation of positive electrode sheet

[0165] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), and then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material were added and stirred until homogeneous to obtain a positive electrode slurry. The slurry was uniformly coated onto the surface of a current collector aluminum foil to prepare a positive electrode film layer, and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was then rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode film layer was 2 g / cm³. 3 .

[0166] 3) Preparation of negative electrode sheet

[0167] Single-walled carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was die-cut to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoat layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0168] 4) Electrolyte

[0169] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0170] 5) Separating membrane

[0171] Polypropylene film is used as the separator.

[0172] 6) Battery manufacturing

[0173] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-free secondary battery product of Example 1.

[0174] Examples 2-18

[0175] The batteries in Examples 2-18 are prepared in a similar manner to the battery in Example 1, but the content of carbon material in the positive electrode active material, the particle size D of the primary particles of the positive electrode active material, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles are adjusted (the particle size D of the primary particles of the positive electrode active material is adjusted by controlling the calcination temperature and calcination time, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles are adjusted by controlling the frequency of the airflow pulverizer and the induced draft fan). The specific parameters are shown in Table 1.

[0176] Example 19

[0177] 1) Preparation of positive electrode active materials

[0178] Sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, and manganese nitrate were dissolved in deionized water at a molar ratio of 1:2.8:2:0.1 and stirred continuously at room temperature for 30 min to obtain a mixed slurry. This mixed slurry was then milled to an average particle size of 0.2 μm. Subsequently, Super P and glucose aqueous solution were added and milled for 10 min to obtain the final slurry. The slurry was spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 109℃. Finally, under a N2 atmosphere, the temperature was increased to 320℃ at a rate of 2℃ and held for 4 h, then increased to 550℃ at a rate of 2℃ and held for 10 h. The sintered product was crushed and sieved by adjusting the frequency of the airflow pulverizer to 50 Hz and the induced draft fan to 30 Hz to obtain the positive electrode active material. Based on the total mass of the positive electrode active material, the carbon material content is 1%; the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to the Dv50 of the positive electrode active material particles is 2.03; the particle size D of the primary particles of the positive electrode active material is 1.1 μm; the Dv50 of the positive electrode active material particles is 3.0 μm; the difference between Dv99 and Dv10 of the positive electrode active material particles is 6.1 μm; and the compaction density of the positive electrode active material is 2.18 g / cm³. 3 .

[0179] 2) Preparation of positive electrode sheet

[0180] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), and then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material were added and stirred until homogeneous to obtain a positive electrode slurry. The slurry was uniformly coated onto the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was then rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode film layer was 2 g / cm³. 3 .

[0181] 3) Preparation of negative electrode sheet

[0182] Carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was die-cut to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoating layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0183] 4) Electrolyte

[0184] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0185] 5) Separating membrane

[0186] Polypropylene film is used as the separator.

[0187] 6) Battery manufacturing

[0188] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-free secondary battery product of Example 19.

[0189] Example 20

[0190] The battery in Example 20 is prepared in a similar manner to the battery in Example 19, but the content of carbon material in the positive electrode active material, the particle size D of the primary particles of the positive electrode active material, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles are adjusted (the particle size D of the primary particles of the positive electrode active material is adjusted by controlling the calcination temperature and calcination time, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles are adjusted by controlling the frequency of the airflow pulverizer and the induced draft fan). The specific parameters are shown in Table 1.

[0191] Examples 21-28

[0192] The batteries in Examples 21-28 are prepared in a similar manner to the battery in Example 1, but the x and y values ​​of the positive electrode active material, the carbon content of the positive electrode active material, the particle size D of the primary particles of the positive electrode active material, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles are adjusted by controlling the calcination temperature and calcination time (and by controlling the frequency of the airflow pulverizer and the induced draft fan). The specific parameters are shown in Table 1.

[0193] Comparative Example 1

[0194] The battery in Comparative Example 1 is prepared using a method similar to that in Example 1, but the preparation method of the positive electrode active material has been adjusted, and the preparation method is as follows:

[0195] 1) Preparation of positive electrode active materials

[0196] Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:2.9:2 and stirred continuously at room temperature for 30 min to obtain a mixed slurry. This mixed slurry was then milled to an average particle size of 0.2 μm. Subsequently, SuperP and glucose aqueous solution were added and milled for 10 min to obtain the final slurry. The slurry was then spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 109℃. Finally, under a N2 atmosphere, the temperature was increased to 300℃ at a rate of 2℃ and held for 2 h, then increased to 480℃ at a rate of 2℃ and held for 6 h. The sintered product was crushed and sieved by adjusting the frequency of the air classifier to 50 Hz and the induced draft fan frequency to 20 Hz to obtain the positive electrode active material. Based on the total mass of the positive electrode active material, the carbon material content is 1%; the ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to the Dv50 of the positive electrode active material particles is 7.78; the particle size D of the primary particles of the positive electrode active material is 0.3 μm; the Dv50 of the positive electrode active material particles is 0.9 μm; the difference between Dv99 and Dv10 of the positive electrode active material particles is 8.1 μm; and the compaction density of the positive electrode active material is 1.95 g / cm³. 3 .

[0197] 2) Preparation of positive electrode sheet

[0198] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material were added and mixed evenly to obtain a positive electrode slurry. The slurry was uniformly coated on the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode film layer was 1.9 g / cm³. 3 .

[0199] 3) Preparation of negative electrode sheet

[0200] Carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was die-cut to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoating layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0201] 4) Electrolyte

[0202] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0203] 5) Separating membrane

[0204] Polypropylene film is used as the separator.

[0205] 6) Battery manufacturing

[0206] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-free secondary battery product of Comparative Example 1.

[0207] Comparative Examples 2-8

[0208] The batteries of Comparative Examples 2 to 8 were prepared in a similar manner to those of Comparative Example 1, but the x and y values ​​of the positive electrode active material, the carbon content in the positive electrode active material, the particle size D of the primary particles of the positive electrode active material, and the Dv99, Dv50, and Dv10 of the positive electrode active material particles were adjusted. The specific parameters are shown in Table 1.

[0209] II. Performance Testing

[0210] 1. Testing of positive electrode active materials

[0211] 1) Dv99, Dv50 and Dv10 tests of positive electrode active material particles

[0212] Referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, 0.1g–0.13g of the positive electrode active material sample to be tested was weighed into a 50mL beaker, 5g of anhydrous ethanol was added, and a stir bar of approximately 2.5mm was placed inside before sealing with plastic wrap. The sample was sonicated for 5 minutes and then transferred to a magnetic stirrer, stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The Mastersizer 2000E laser particle size analyzer (Malvin Instruments Ltd., UK) was used for testing. The Dv99 value of the positive electrode active material particles corresponds to a cumulative volume distribution percentage of 99%, the Dv50 value corresponds to a cumulative volume distribution percentage of 50%, and the Dv10 value corresponds to a cumulative volume distribution percentage of 10%.

[0213] 2) Primary particle size D test

[0214] SEM testing was employed: After cold-pressing the positive electrode active material sample, the sample was cut open using an Ar particle beam to expose the end face. Images of the end face of the positive electrode active material were obtained using a scanning electron microscope (SEM). The particle size D of the primary particles in the positive electrode active material was measured based on the SEM images.

[0215] 3) Powder compaction density

[0216] Referring to GB / T 24533-2009 Powder Compaction Density Method, a certain amount of powder is placed in a special compaction mold, and then the mold is placed on a compaction density instrument. The pressure is set to 400MPa, and after compaction, the pressure is released. The thickness of the compacted blank is read on the equipment, and the powder compaction density is calculated.

[0217] pC = m / V = m / (S*H)

[0218] Where: pC---compacted density of powder, g / cm³; m---sample mass, g; S---base area of ​​mold, cm² 2 H---Compacted thickness, cm.

[0219] 2. Positive electrode performance testing

[0220] 1) Compacted density

[0221] According to embodiments of this application, the compaction density PD of the positive electrode film is determined by measuring the areal density (g / cm³) of one side of the positive electrode film. 2 The density of the positive electrode film (PD) is determined by the thickness of the positive electrode film layer on one side (cm) (number of sampling points > 14). Specifically, the compaction density of the positive electrode film layer (PD) = the surface density of the positive electrode film layer on one side (g / cm³). 2 ) / Positive electrode film thickness (cm).

[0222] 3. Battery performance test

[0223] 1) Initial discharge capacity test

[0224] The initial discharge capacity test process is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1C, then charged at a constant voltage of 3.75V until the current drops to 0.05C, and then discharged to 1.5V with a constant current of 1C to obtain the initial discharge capacity (Cd1). The test process for the comparative example and other embodiments is the same as above.

[0225] 2) First Coulomb efficiency test

[0226] The initial coulombic efficiency test procedure is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1 / 5C, and then charged at a constant voltage of 3.75V until the current drops to 0.05C, obtaining the initial charge capacity (Cc1); then discharged to 1.5V with a constant current of 1 / 5C, obtaining the initial discharge capacity (Cd1), and the battery coulombic efficiency is calculated according to the following formula: Initial coulombic efficiency = Initial discharge capacity (Cd1) / Initial charge capacity (Cc1). The test procedures for the comparative example and other embodiments are the same as above.

[0227] 3) Battery cycle capacity retention test

[0228] The battery capacity retention rate test process is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1C, then charged with a constant voltage of 3.75V until the current drops to 0.05C, and then discharged to 1.5V with a constant current of 1C. The resulting capacity is recorded as the initial capacity (C0). The above steps are repeated for the same battery, and the discharge capacity (Cn) of the battery after the nth cycle is recorded. The battery capacity retention rate after each cycle is Pn = Cn / C0 × 100%. A curve is obtained by plotting the 100 points P1, P2...100 as the vertical axis and the corresponding cycle number as the horizontal axis. In this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 100th cycle to n=100. The battery capacity retention rate data corresponding to the examples or comparative examples in Table 2 are the data measured after 100 cycles under the above test conditions, i.e., the value of P100. The test process for the comparative examples and other examples is the same as above.

[0229] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0230] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0231] Table 1

[0232]

[0233] Table 2

[0234]

[0235] Based on the above results, it can be seen that Examples 1 to 20 all include positive electrode active materials. The ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to Dv50 of the positive electrode active material particles satisfies: 0.8 ≤ (Dv99 - Dv10) / Dv50 ≤ 8. A comparison of Examples 1 to 8 with Comparative Examples 1 to 2, Example 19 with Comparative Example 3, Example 22 with Comparative Example 4, Example 25 with Comparative Example 5, Example 26 with Comparative Example 6, Example 27 with Comparative Example 7, and Example 28 with Comparative Example 8 shows that controlling the difference between Dv99 and Dv10 of the positive electrode active material particles and the ratio to Dv50 of the positive electrode active material particles to satisfy 0.8 ≤ (Dv99 - Dv10) / Dv50 ≤ 8 is beneficial for improving the compaction density of the positive electrode active material and the compaction density of the positive electrode film, thereby increasing the initial discharge capacity of the battery and improving battery performance.

[0236] As can be seen from the comparison between Examples 1-8 and Comparative Examples 1-2, controlling the difference between Dv99 and Dv10 of the positive electrode active material particles to satisfy: 4.0μm≤(Dv99-Dv10)≤8.0μm is beneficial to improving the compaction density of the positive electrode active material and the compaction density of the positive electrode film, thereby increasing the first discharge capacity of the battery.

[0237] As can be seen from the comparison between Examples 1-8 and Comparative Examples 1-2, controlling the Dv50 of the positive electrode active material particles to satisfy: 1.0μm≤Dv50≤5.0μm is beneficial to improving the compaction density of the positive electrode active material and the compaction density of the positive electrode film, thereby increasing the first discharge capacity of the battery.

[0238] As can be seen from the comparison between Examples 1-8 and Comparative Examples 1-2, controlling the particle size D of the primary particles to satisfy: 0.5μm≤D≤1.5μm is beneficial to improving the compaction density of the positive electrode active material and the compaction density of the positive electrode film, thereby increasing the first discharge capacity of the battery.

[0239] A comparison of Examples 1-17 with Example 18 shows that controlling the mass content of carbon material in the positive electrode active material to 0.05%-10% is beneficial for improving the compaction density of the positive electrode active material and the positive electrode film, thereby increasing the battery's initial discharge capacity. A comparison of Examples 1-16 with Example 17 shows that controlling the mass content of carbon material in the positive electrode active material to 0.1%-10% is beneficial for improving the battery's coulombic efficiency and capacity retention after 100 cycles. A comparison of Examples 1-12, 15 with Examples 13-14, 16, and Examples 21-23 with Example 24 shows that further controlling the mass content of carbon material in the positive electrode active material to 0.15%-2% is beneficial for balancing the compaction density of the positive electrode active material and the battery's performance.

[0240] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The ratio of the difference between Dv99 and Dv10 of the positive electrode active material particles to Dv50 of the positive electrode active material particles satisfies: 0.8≤(Dv99-Dv10) / Dv50≤8; the Dv50 of the positive electrode active material particles satisfies: 1.0 μm≤Dv50≤5.0 μm.

2. The positive electrode active material according to claim 1, characterized in that, The difference between Dv99 and Dv10 of the positive electrode active material particles satisfies: 4.0 μm ≤ (Dv99 - Dv10) ≤ 8.0 μm.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material particles are formed by the aggregation of primary particles, and the ratio of the Dv50 of the positive electrode active material particles to the particle size D of the primary particles satisfies: 1 < Dv50 / D ≤ 10.

4. The positive electrode active material according to claim 3, characterized in that, The particle size D of the primary particles satisfies: 0.5 μm ≤ D ≤ 1.5 μm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The positive electrode active material includes a carbon-composite polyanionic compound, which has the following general formula: So x R y (PO4) z (P2O7) k / C Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4.

6. The positive electrode active material according to claim 5, characterized in that, The carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film.

7. The positive electrode active material according to claim 5 or 6, characterized in that, The carbon material includes one or more of amorphous carbon, conductive carbon black, carbon nanotubes, and graphene.

8. The positive electrode active material according to any one of claims 5 to 7, characterized in that, Based on the total mass of the positive electrode active material, the mass content of the carbon material in the positive electrode active material is 0.1% to 10%.

9. The positive electrode active material according to claim 8, characterized in that, Based on the total mass of the positive electrode active material, the mass content of the carbon material in the positive electrode active material is 0.15% to 2%.

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that, After compaction at a pressure of 400 MPa, the compacted density of the positive electrode active material powder is 2 g / cm³. 3 ~2.5 g / cm 3 .

11. A positive electrode plate, characterized in that, It comprises a binder, a conductive agent, and a positive electrode film layer, wherein the positive electrode film layer comprises the positive electrode active material according to any one of claims 1 to 10.

12. The positive electrode sheet according to claim 11, characterized in that, Based on the total mass of the positive electrode film, the mass content of the binder is 1.5% to 3%.

13. The positive electrode sheet according to claim 12, characterized in that, Based on the total mass of the positive electrode film, the mass content of the binder is 2.0% to 2.5%.

14. The positive electrode sheet according to any one of claims 11 to 13, characterized in that, The conductive agent includes at least one of one-dimensional conductive materials and zero-dimensional conductive materials.

15. The positive electrode sheet according to claim 14, characterized in that, The one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%.

16. The positive electrode sheet according to claim 15, characterized in that, Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.5% to 0.9%.

17. The positive electrode sheet according to any one of claims 14 to 16, characterized in that, The zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%.

18. The positive electrode sheet according to claim 17, characterized in that, Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 2% to 2.8%.

19. A secondary battery, characterized in that, The positive electrode sheet includes any one of claims 11 to 18.

20. The secondary battery according to claim 19, characterized in that, The secondary battery is a sodium-free secondary battery without a negative electrode.

21. The secondary battery according to claim 19 or 20, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative current collector and a base coating disposed on at least one surface of the negative current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

22. The secondary battery according to claim 21, characterized in that, The areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

23. The secondary battery according to claim 21 or 22, characterized in that, The thickness of the base coating is 2 μm to 100 μm.

24. An electrical appliance, characterized in that, The secondary battery includes any one of claims 19 to 23.

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