Positive electrode sheet and preparation method thereof, and battery

Abstract

The present invention discloses a positive electrode sheet, a preparation method thereof, and a battery. The positive electrode sheet comprises: a current collector and a positive electrode active material layer provided on at least one side of the current collector, wherein the compacted density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82g / cm 3 The porosity of the positive electrode sheet is 3.5% to 5.5%. By simultaneously controlling the compaction density of the positive electrode active material layer and the porosity of the positive electrode sheet to meet the given range, the volume energy density, the electrolyte's wetting effect on the positive electrode sheet, and the cycling stability can be taken into account at the same time, reducing the electrolyte's damage to the positive electrode active material and the occurrence of side reactions. Using this in a battery can help the battery achieve both high volume energy density and good cycling performance, improving the battery's service life and safety.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and in particular, relates to a positive electrode plate and a preparation method thereof, and a battery. Background Art

[0002] As the demand for electricity continues to grow, batteries have also experienced rapid development. Lithium-ion batteries, for example, have been widely used in military and civilian small appliances due to their high energy, high battery voltage, wide operating temperature range, and long storage life. Large-capacity lithium-ion batteries are already being used in electric vehicles and will become one of the primary power sources for electric vehicles in the 21st century. They will also be used in satellites, aerospace, energy storage, and other fields. Future battery technology development trends will focus on increasing energy density, extending battery life, reducing costs, and enhancing safety. Appropriate positive electrode plate design will significantly impact battery performance. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one object of the present invention is to provide a positive electrode sheet and a method for preparing the same, and a battery, so that the battery has both high volume energy density and good cycle performance.

[0004] In the first aspect of the present invention, a positive electrode sheet is provided, comprising: a current collector and a positive electrode active material layer provided on at least one side of the current collector, wherein the compaction density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82g / cm 3 The porosity of the positive electrode sheet is 3.5% to 5.5%.

[0005] The positive electrode plate of the first aspect of the present invention has at least the following beneficial effects: by simultaneously controlling the compaction density of the positive electrode active material layer and the porosity of the positive electrode plate to meet the given range, the volume energy density, the wetting effect of the electrolyte on the positive electrode plate and the cycle stability can be taken into account at the same time, reducing the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions. Using it in a battery is conducive to making the battery have both higher volume energy density and better cycle performance, improving the battery's service life and safety issues.

[0006] In addition, the positive electrode sheet according to the above embodiment of the present invention may also have the following additional technical features:

[0007] In some embodiments of the present invention, the porosity of the positive electrode sheet is 4% to 5%.

[0008] In some embodiments of the present invention, the ultimate compaction density of the positive electrode active material layer is ≥3.75 g / cm 3 , optional ≥3.8g / cm 3。

[0009] In some embodiments of the present invention, the positive electrode active material in the positive electrode active material layer is single crystal particles.

[0010] In some embodiments of the present invention, in the positive electrode active material layer, the average particle size P of the positive electrode active material 50 is 2.5 μm to 5.0 μm, optionally 3.0 μm to 4.5 μm.

[0011] In some embodiments of the present invention, the median diameter D of the positive electrode active material 50 is 4.5 μm to 8.0 μm, optionally 5.5 μm to 7.5 μm.

[0012] In some embodiments of the present invention, the grain size of the positive electrode active material is optionally

[0013]

[0014] In some embodiments of the present invention, the tap density of the positive electrode active material under a pressure of 20 kN is ≥ 3.45 g / cm 3 , optionally ≥ 3.5 g / cm 3 。

[0015] In some embodiments of the present invention, in the positive electrode active material layer, the positive electrode active material includes A a Ni x M1 y Co z M2 b O 2-c / 2 R c , where: 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 ≤ b ≤ 0.08, 0 ≤ c ≤ 0.1; A is Li or Na; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr and Ti; R is F and / or Cl.

[0016] In some embodiments of the present invention, the positive electrode active material includes Li a Ni x Mn y Co z M2 b O 2-c / 2 R c 。

[0017] In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder, and the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95 to 98):(0.5 to 4):(0.5 to 4).

[0018] In a second aspect of the present invention, a method for preparing the above positive electrode plate is provided, including:

[0019] Disperse the positive electrode active material, the conductive agent, and the binder in a solvent to obtain a positive electrode active paste;

[0020] Coat the positive electrode active paste on at least one side of the positive electrode current collector to form a positive electrode active material layer,

[0021] wherein, the tap density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82 g / cm 3 and the porosity of the positive electrode plate is 3.5% to 5.5%.

[0022] The method for preparing the positive electrode plate in the second aspect of the present invention has at least the following beneficial effects: The prepared positive electrode plate has both an appropriate tap density and an appropriate porosity, can simultaneously take into account the volume energy density, the wetting effect of the electrolyte on the positive electrode plate, and the cycle stability, reduce the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions, and using the prepared positive electrode plate in a battery is beneficial to making the battery have both a high volume energy density and good cycle performance, and improving the service life and safety problems of the battery.

[0023] In some embodiments of the present invention, the positive electrode active material includes A a Ni x M1 y Co z M2 b O 2-c / 2 R c , 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 ≤ b ≤ 0.08, 0 ≤ c ≤ 0.1; A is Li or Na; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr, and Ti; R is F and / or Cl, and the preparation method of the positive electrode active material includes: mixing an alkali metal source, a Ni source, a M1 source, and a Co source and performing a first roasting treatment.

[0024] In some embodiments of the present invention, precursor particles comprising Ni, M1, and Co are used to provide the Ni source, the M1 source, and the Co source. The average particle size P of the positive electrode active material is 50 The median diameter D of the precursor particles is 2.5 μm to 5.0 μm. 50 Satisfied: P 50 / 0.85≤D 50 '≤P 50 / 0.65; and / or, D 50 '≥3.5μm.

[0025] In some embodiments of the present invention, based on the total molar number of Ni, M1, and Co, the relative molar amount of the alkali metal in the alkali metal source is 1 mol to 1.08 mol.

[0026] In some embodiments of the present invention, the temperature T1 of the first calcination process satisfies: x is A a Ni x M1 y Co z M2 b O 2-c / 2 R c The subscript value of Ni in .

[0027] In some embodiments of the present invention, the calcination temperature T1 of the first calcination treatment is 900° C. to 1050° C., the calcination time is 7 h to 20 h, and the calcination atmosphere is an oxygen-containing atmosphere.

[0028] In some embodiments of the present invention, the alkali metal source, the Ni source, the M1 source, the Co source, and the M2 source are mixed to perform the first calcination treatment.

[0029] In some embodiments of the present invention, the method for preparing a positive electrode sheet further includes: mixing the product of the first calcination treatment with a coating agent and performing a second calcination treatment.

[0030] In some embodiments of the present invention, the temperature T2 of the second calcination process is less than or equal to the temperature T1 of the first calcination process.

[0031] In some embodiments of the present invention, the temperature T2 of the second calcination treatment is 250° C. to 1000° C., the time is 5 hours to 20 hours, and the calcination atmosphere is an oxygen-containing atmosphere.

[0032] In some embodiments of the present invention, the coating agent includes one or more of Zr, B, W, Nb, Cd, Pb, Si, Mo, Cu, La, Al, Ce, Er, Ho, Y, Mg, Sr and Ti.

[0033] In some embodiments of the present invention, the coating agent includes an M2 source, and based on the total molar number of Ni, M1, and Co, the relative molar amount of M2 in the M2 source is ≤0.08 mol.

[0034] In a third aspect of the present invention, a battery is provided, comprising: the aforementioned positive electrode sheet, or a positive electrode sheet produced by the aforementioned method. The battery has both high volume energy density and good cycle performance, a long service life, and low safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a scanning electron microscope image of the positive electrode active material particles prepared according to Example 1 of the present invention.

[0036] Figure 2 This is a scanning electron microscope image of the cross section of the positive electrode sheet prepared according to Example 1 of the present invention.

[0037] Figure 3 is a scanning electron microscope image of the positive electrode active material particles prepared according to Comparative Example 1 of the present invention.

[0038] Figure 4 This is a scanning electron microscope image of the cross section of the positive electrode sheet prepared according to Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0040] In the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one of such features.

[0041] In the first aspect of the present invention, a positive electrode sheet is provided, comprising: a current collector and a positive electrode active material layer provided on at least one side of the current collector, wherein the compaction density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82g / cm 3 The porosity of the positive electrode sheet is 3.5% to 5.5%.

[0042] For example, the compaction density of the positive electrode active material layer can be 3.55 g / cm 3 、3.6g / cm 3 、3.65g / cm 3 、3.7g / cm 3 、3.75g / cm 3 、3.8g / cm 3、3.82g / cm 3 etc.; the porosity of the positive electrode sheet can be 3.5%, 4%, 4.5%, 5%, 5.5%, etc. Under normal circumstances, a battery mainly includes a positive electrode sheet, a negative electrode sheet, an electrolyte, a separator, etc. Among them, the positive electrode sheet plays a decisive role in the energy density, cycle life, cost and safety of the battery. A reasonable positive electrode sheet design can significantly improve battery performance. If the compaction density of the positive electrode sheet is too low or the porosity is too high, the following problems may occur: it is easy to cause poor contact of the positive electrode active material, the capacity rate of the positive electrode active material is relatively low, and the electrolyte infiltration is more, the positive electrode active material is more susceptible to corrosion, and it is easy to cause poor cycle performance and safety. If the compaction density is too high or the porosity is too small, the following problems may occur: it is easy to cause insufficient electrolyte infiltration, the capacity of the positive electrode active material is relatively low, and some particles are easily crushed, resulting in poor cycle performance.

[0043] In view of this, the present invention improves the compaction density of the positive electrode active material layer and the porosity of the positive electrode sheet. The positive electrode sheet of the first aspect of the present invention has at least the following beneficial effects: by simultaneously controlling the compaction density of the positive electrode active material layer and the porosity of the positive electrode sheet to meet the given range, it can simultaneously take into account the volumetric energy density, the electrolyte's wetting effect on the positive electrode sheet, and the cycling stability, thereby reducing the electrolyte's damage to the positive electrode active material and the occurrence of side reactions. Using this in a battery can help the battery achieve both high volumetric energy density and good cycling performance, improving the battery's service life and safety.

[0044] According to an embodiment of the present invention, the compacted density of the positive electrode active material layer is: the mass of the positive electrode active material layer (unit: g) / the volume of the positive electrode active material layer (unit: cm 3 ); the porosity P of the positive electrode sheet is:

[0045] P = total volume of pole piece adsorption holes V1 / (pole piece skeleton volume V0+total volume of pole piece adsorption holes V1)×100%,

[0046] Where: pole piece frame volume V0 = sample tube volume – pole piece external volume;

[0047] The total volume of the electrode adsorption pores V1 = the adsorption volume per unit mass of the electrode × the weight of the electrode;

[0048] The test methods for the porosity of the positive electrode sample include: 1. Testing the empty tube volume of the sample tube, which is the volume of the sample tube in cm 3 2. Weigh a certain amount of rolled positive electrode (the volume can be 1 / 2 to 2 / 3 of the sphere at the bottom of the sample tube), record the weight of the electrode in g; 3. Place the electrode into the sample tube and measure the adsorption volume of the electrode in cm 3 / g; and the volume of gas that can be flushed into the sample tube after the electrode is added, which is the external volume of the electrode, in cm 3 In some embodiments, the porosity of the positive electrode sheet can be measured using a Micromeritics Tristar 3020 surface area analyzer. Thin slices of the rolled positive electrode sheet are placed in a sample tube and measured by the electrode sheet adsorption volume and the BJH calculation method for the mesopore distribution.

[0049] In some embodiments of the present invention, the porosity of the positive electrode sheet can be 4% to 5%, for example, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5%, etc. This helps to further reduce the risk of the following problems that may arise due to excessively high porosity of the positive electrode sheet: poor contact of the positive electrode active material, low capacity ratio of the positive electrode active material, and increased electrolyte infiltration, which makes the positive electrode active material more susceptible to corrosion, leading to poor cycle performance and safety; and the risk of the following problems that may arise due to excessively low porosity of the positive electrode sheet: insufficient electrolyte infiltration, low capacity of the positive electrode active material, and some particles being easily crushed, leading to poor cycle performance. Furthermore, using the positive electrode sheet in the battery helps the battery achieve both high volume energy density and good cycle performance, improving the battery's service life and safety.

[0050] In some embodiments of the present invention, the ultimate compaction density of the positive electrode active material layer may be ≥3.75 g / cm 3 For example, the ultimate compaction density of the positive electrode active material layer can be 3.75 g / cm 3 、3.8g / cm 3 、3.85g / cm 3 、3.9g / cm 3 、3.95g / cm 3 , 4g / cm 3 , 4.05g / cm 3 , 4.1g / cm 3 Etc. Making the ultimate compaction density of the positive electrode active material layer meet the given conditions is conducive to further reducing the problems of insufficient electrolyte infiltration, low capacity of the positive electrode active material, and easy crushing of some particles, resulting in poor cycle performance, etc. when the compaction density of the positive electrode active material layer is too high. Then, using the positive electrode sheet in the battery is conducive to making the battery have both high volume energy density and good cycle performance, improving the service life and safety of the battery. Optionally, the ultimate compaction density of the positive electrode active material layer can be ≥3.8g / cm 3 , which is beneficial to further make the positive electrode sheet have better electrochemical performance.

[0051] According to an embodiment of the present invention, the ultimate compaction density of the positive electrode active material layer can be tested by the following method: after rolling and compacting the positive electrode active material layer, several points are taken on the electrode sheet in a direction parallel to the short side, and the thickness difference of the test area is within 1 μm. The straight line of the several points is folded in half for testing, and the compaction density at the fold is calculated according to the thickness of the electrode sheet at the fold. If the fold is not transparent after 10 times, the sample is replaced and the double-sided coating density of the electrode sheet is increased by 0.01 g / cm 2 The above-mentioned operation is repeated during compaction until light is transmitted within 10 folds. The maximum light-proof compaction density is the ultimate compaction density of the electrode.

[0052] In some embodiments of the present invention, the positive electrode active material layer may include single crystal particles of positive electrode active material. Optionally, the positive electrode active material in the positive electrode active material layer may be mainly single crystal particles. For example, the volume proportion of single crystal particles of positive electrode active material in the positive electrode active material layer may be ≥50%, for example, ≥60%, ≥70%, ≥80% or ≥90%, etc. More optionally, the positive electrode active material in the positive electrode active material layer may be single crystal particles. Common positive electrode active material particles are mostly secondary particles formed by the agglomeration of primary particles. In the present invention, the "single crystal particles" refer to particles with less agglomeration and good particle dispersion. The number of agglomerates composed of 3 or more primary particles in all positive electrode active material particles accounts for ≤5%, which can be observed with the help of a scanning electron microscope. Increasing the compaction density of the positive electrode active material layer is beneficial to obtaining a higher volume energy density. At present, the mainstream method to improve the compaction density of the positive electrode active material layer is to use large particle agglomerates mixed with small particle single crystals or agglomerates for the positive electrode active material. However, the compressive performance of the agglomerates is relatively poor. Compared with the method of mixing large particle agglomerates with small particles, the present invention uses single crystal particles to prepare high-compacted positive electrode plates, which is beneficial to avoid the use of agglomerates and can significantly improve the cycle performance and storage stability of the positive electrode plates.

[0053] In some embodiments of the present invention, in the positive electrode active material layer, the average particle size P of the positive electrode active material is 50 It can be 2.5 μm to 5.0 μm, for example, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, etc. Optionally, the positive electrode active material can be mainly single crystal particles. 50 It is the average of the caliper diameters of more than 300 representative particles of the positive electrode sample under a scanning electron microscope. The caliper diameter is equal to the length plus width of the smallest circumscribed rectangle divided by two. Compared with conventional positive electrode sheets whose positive active materials are mainly composed of secondary particles (i.e. agglomerates) composed of primary particles, in positive electrode sheets whose positive active materials are mainly single crystal particles, the average particle size P 50The particle size of the single crystal particles that meet the given range is larger than that of the primary particles and smaller than that of the secondary particles. Not only does it have good particle structure stability, which is conducive to the preparation of high-density positive electrode sheets and obtain higher compaction density, but it can also avoid the use of agglomerated particles, which can significantly improve the cycle performance and storage stability of the positive electrode sheets. In addition, the average particle size P 50 The single crystal particle size that meets the given range is relatively large, the specific surface area is small and the compaction density is large, the electrode porosity is low, and less electrolyte is required during the cycle, which is conducive to further inhibiting the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions, effectively improving the cycle performance and safety of the battery. Therefore, it is not only conducive to obtaining a positive electrode electrode with a compaction density and porosity that meet the given range, but also the use of the positive electrode electrode in the battery is conducive to making the battery have both a higher volume energy density and better cycle performance, improving the battery's service life and safety issues. Furthermore, the average particle size P of the positive electrode active material is 50 It can be 3.0μm to 4.5μm, which is beneficial to further reduce the specific surface area and electrode porosity of the positive electrode active material, inhibit the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions, effectively improve the cycle performance and safety of the battery, and further help the battery have both higher volume energy density and better cycle performance.

[0054] In some embodiments of the present invention, the median diameter D of the positive electrode active material 50 It can be 4.5 μm to 8.0 μm, for example, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, etc. Optionally, the positive electrode active material can be mainly single crystal particles. 50 It can be measured by laser particle size analyzer. In some specific operations, the median diameter D of the positive electrode active material is tested. 50 Before the slurry is removed, it can be ultrasonically treated, for example, the ultrasonic time can be 20 seconds. 50 The positive electrode active materials that meet the given range, especially the single crystal particle positive electrode active materials, are conducive to obtaining a highly compacted positive electrode sheet, and the particles have a small specific surface area and a high compaction density, the sheet porosity is low, and less electrolyte is required during the cycle process, which is conducive to further inhibiting the damage of the electrolyte to the positive electrode active materials and the occurrence of side reactions, improving the cycle performance and safety of the battery, and thus helping the battery to have both a high volume energy density and good cycle performance. Furthermore, the median diameter D of the positive electrode active material is 50 It can be 5.5 μm to 7.5 μm, which is further beneficial for the battery to have both higher volume energy density and better cycle performance.

[0055] In some embodiments of the present invention, the grain size D of the positive electrode active material isXRD Can For example, it can be or Optionally, the grain size D of the positive electrode active material XRD Can be The grain size of the positive electrode active material can be determined using an X-ray diffractometer combined with the included SmartLab Studio II software for material structure refinement and analysis using the Rietveld technique. A relatively large grain size within the given range helps reduce the number of grain boundaries. This not only helps reduce stress concentration and interfacial reactions at grain boundaries, resulting in better structural stability for the positive electrode active material, but also increases the diffusion rate of active metal ions, reduces internal resistance, and thus further improves the battery's cycling performance.

[0056] In some embodiments of the present invention, the compaction density of the positive electrode active material under a pressure of 20 kN may be ≥3.45 g / cm 3 , for example, it can be 3.45g / cm 3 , 3.5g / cm 3 、3.55g / cm 3 、3.6g / cm 3 、3.65g / cm 3 、3.7g / cm 3 、3.75g / cm 3 、3.8g / cm 3 , etc. Optionally, the compaction density of the positive electrode active material under a pressure of 20 kN can be ≥3.5 g / cm 3 The positive electrode active material particles that meet the given conditions are more conducive to obtaining a high-density positive electrode sheet and a low porosity, inhibiting the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions. The use of the prepared positive electrode sheet in the battery is conducive to making the battery have both a high volume energy density and good cycle performance, which can improve the battery's service life and safety issues.

[0057] In some embodiments of the present invention, in the positive electrode active material layer, the positive electrode active material may include A a Ni x M1 y Co z M2 b O 2-c / 2 R c, where: 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 ≤ b ≤ 0.08, 0 ≤ c ≤ 0.1; A is Li or Na; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr and Ti; R is F and / or Cl. Among them, the value of a can be 0.9, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, etc.; the value of x can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, etc.; the value of y can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, etc.; the value of z can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, etc.; the value of b can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, etc.; the value of c can be 0, 0.02, 0.05, 0.08, 0.1, etc., and optionally, the value of c can be 0. The specific type of element A can be selected according to the application scenario of the positive electrode sheet. For example, for the positive electrode sheet used in a lithium battery, A can be Li, and for the positive electrode sheet used in a sodium battery, the alkali metal source can be Na. The positive electrode active material within the given range has a relatively high energy density and working voltage, and relatively good cycling performance. Using it in the positive electrode sheet and the battery is conducive to further enabling the battery to have both a relatively high volumetric energy density and good cycling performance.

[0058] In some embodiments of the present invention, the positive electrode active material A a Ni x Ml y Co z M2 b O 2-c / 2 R c In, the distribution manner of the M2 element is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, it can be dispersed throughout the positive electrode active particles or dispersed on the surface of the positive electrode active material particles in a coated form.

[0059] In some embodiments of the present invention, in the positive electrode active material layer, the positive electrode active material may include Li a Ni x Mn y Co z M2 b O 2-c / 2 Rc , such as can include Li a Ni x Mn y Co z M2 b The positive electrode active material that meets the given range has a high energy density and operating voltage, and relatively good cycle performance, and can be used in the positive electrode of lithium batteries to enable the battery to have both high volume energy density and good cycle performance.

[0060] In some embodiments of the present invention, the positive electrode active material layer may include a positive electrode active material, a conductive agent, and a binder. The mass ratio of the positive electrode active material, the conductive agent, and the binder may be (95-98): (0.5-4): (0.5-4). When preparing the positive electrode active material layer, the positive electrode active material, the conductive agent, and the binder dispersion may be dissolved in an organic solvent (such as N-methylpyrrolidone, etc.) to form a positive electrode active slurry. The positive electrode active slurry is applied to at least one side of the positive electrode current collector, and the positive electrode active material is obtained after drying, cutting, and other processes. The positive electrode active material may be the positive electrode active material described in the aforementioned section or a common positive electrode active material in the art. Those skilled in the art may flexibly select according to actual needs. In addition, the specific types of the conductive agent and the binder are not particularly limited. Those skilled in the art may flexibly select according to actual needs. For example, they may be conventionally selected in the art. In some examples, the conductive agent may include, but is not limited to, one or more of conductive carbon black, graphene, carbon nanotubes, acetylene black, etc., and the binder may include, but is not limited to, polyvinylidene fluoride (PVDF), etc. The specific material and structure of the positive electrode current collector are not particularly limited and can be flexibly selected by those skilled in the art based on practical needs. For example, it can be a conventional choice in the art. In some examples, the positive electrode current collector may include, but is not limited to, aluminum foil. Furthermore, it should be noted that the sources of the positive electrode active material, binder, and conductive agent are not particularly limited and can be prepared or purchased.

[0061] In a second aspect of the present invention, a method for preparing the above-mentioned positive electrode sheet is proposed, comprising: dispersing a positive electrode active material, a conductive agent, and a binder in a solvent to obtain a positive electrode active slurry; applying the positive electrode active slurry to at least one side of a positive electrode current collector to form a positive electrode active material layer, wherein the compacted density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82g / cm 3 The porosity of the positive electrode sheet is 3.5% to 5.5%.

[0062] The method for preparing the positive electrode sheet according to the second aspect of the present invention has at least the following beneficial effects: The prepared positive electrode sheet has both an appropriate tap density and an appropriate porosity, can simultaneously take into account the volumetric energy density, the wetting effect of the electrolyte on the positive electrode sheet, and the cycle stability, reduce the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions, and using the prepared positive electrode sheet in a battery is beneficial to endow the battery with a relatively high volumetric energy density and good cycle performance, and improve the service life and safety of the battery. It should be noted that the characteristics and effects described for the above positive electrode sheet also apply to the method for preparing the positive electrode sheet, and will not be elaborated here.

[0063] In some embodiments of the present invention, the positive electrode active material may include A a Ni x M1 y Co z M2 b O 2-c / 2 R c , 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 ≤ b ≤ 0.08, 0 ≤ c ≤ 0.1; A is Li or Na; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr, and Ti; R is F and / or Cl. The method for preparing the positive electrode active material may include: mixing an alkali metal source, a Ni source, a M1 source, and a Co source and performing a first roasting treatment. Among them, for the positive electrode active material A a Ni x M1 y Co z M2 b O 2-c / 2 R c The composition and beneficial effects have been described in detail in the foregoing part and will not be elaborated here.

[0064] In some embodiments of the present invention, the positive electrode active material particles may be single crystal particles.

[0065] In some embodiments of the present invention, a precursor particle including Ni, M1, and Co may be used to provide the Ni source, the M1 source, and the Co source. For the design requirement of the average particle size P 50 of the positive electrode active material to be 2.5 μm to 5.0 μm, the median diameter D 50 ' of the precursor particle may be controlled to satisfy: P 50 / 0.85 ≤ D 50 ' ≤ P 50 / 0.65; and / or, D [[ID=]] 50'≥3.5μm. Controlling the particle size of the precursor particles to meet the given range is conducive to obtaining positive electrode active material particles of the desired particle size. When the median diameter of the precursor particles meets the given conditions, it is easy to obtain positive electrode active material with an average particle size within the desired range, and thus it is easy to obtain a positive electrode sheet with a high compaction density.

[0066] In some embodiments of the present invention, the relative molar amount of the alkali metal in the alkali metal source is 1 mol to 1.08 mol, for example, 1 mol, 1.02 mol, 1.05 mol, 1.08 mol, etc., based on the total molar number of Ni, M1, and Co. During the calcination process, the alkali metal element is easily evaporated. Controlling the amount of the alkali metal source to meet the given range can be used to compensate for the evaporation loss of the alkali metal element during the calcination process, thereby obtaining a positive electrode active material of the desired composition and reducing the problem of capacity loss caused by the evaporation loss of the alkali metal element.

[0067] In some embodiments of the present invention, the temperature T1 of the first calcination process may satisfy: x is A a Ni x M1 y Co z M2 b O 2-c / 2 R c The subscript value of Ni in the formula is: a Ni x M1 y Co z M2 b O 2-c / 2 R c The appropriate calcination temperature is also affected by the Ni content. By controlling the temperature of the first calcination treatment to meet the given range, it is further beneficial to obtain the average particle size P 50 (2.5μm~5.0μm) and grain size D XRD ( )Single crystal particles of positive electrode active material that meet the expected range.

[0068] In some embodiments of the present invention, the calcination temperature T1 of the first calcination process can be 900°C to 1050°C, the calcination time can be 7h to 20h, and the calcination atmosphere can be an oxygen-containing atmosphere. Among them, T1 can be 900°C, 950°C, 980°C, 1000°C, 1050°C, etc., the calcination time can be 7h, 10h, 12h, 15, 18h or 20h, etc., and the oxygen-containing atmosphere can include but is not limited to air atmosphere, etc. This is conducive to further obtaining the average particle size P 50 and grain size D XRD Positive electrode active materials that meet the expected range.

[0069] In some embodiments of the present invention, the order of adding the M2 source can be selected according to the expected dispersion area of ​​the M2 element in the positive electrode active material. For example, if it is desired to disperse the M2 element in the entire positive electrode active material particle, the alkali metal source, Ni source, M1 source, Co source, and M2 source can be mixed to perform the first calcination treatment. Among them, the relative amounts of the Ni source, M1 source, Co source, and M2 source can be selected according to A a Ni x M1 y Co z M2 b O 2-c / 2 R c Flexible selection of stoichiometric ratio.

[0070] In some embodiments of the present invention, the method for preparing a positive electrode plate may further include: mixing the product of the first calcination treatment with a coating agent and performing a second calcination treatment. In this way, a coating layer can be formed on the surface of the positive electrode active material particles. The coating agent is used to improve the performance of the positive electrode active material, including but not limited to structural stability, electrochemical performance, etc. It should be noted that in the present invention, the type of coating agent is not particularly limited, and those skilled in the art can flexibly select it according to the expected technical effect. For example, in some specific embodiments of the present invention, the coating agent may include one or more elements selected from Zr, B, W, Nb, Cd, Pb, Si, Mo, Cu, La, Al, Ce, Er, Ho, Y, Mg, Sr and Ti.

[0071] In some embodiments of the present invention, the temperature T2 of the second calcination process may be less than or equal to the temperature T1 of the first calcination process, thereby facilitating avoiding destruction of the crystal structure and particle state of the first calcined product during formation of the coating layer.

[0072] In some embodiments of the present invention, the temperature T2 of the second calcination treatment can be 250°C to 1000°C, the time can be 5 hours to 20 hours, and the calcination atmosphere can be an oxygen-containing atmosphere. For example, T2 can be 250°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, etc., the calcination time can be 5 hours, 10 hours, 15 hours, or 20 hours, etc., and the oxygen-containing atmosphere can include, but is not limited to, air. This is beneficial for forming a coating structure on the surface of the positive electrode active material particles and also helps avoid destroying the crystal structure and particle state of the first calcined product during the formation of the coating layer.

[0073] In some embodiments of the present invention, the coating agent may include an M2 source. Based on the total molar number of Ni, M1, and Co, the relative molar amount of M2 in the M2 source may be ≤0.08 mol, for example, 0.01 mol, 0.02 mol, 0.03 mol, 0.04 mol, 0.05 mol, 0.06 mol, 0.07 mol, 0.08 mol, etc. Selecting the M2 source as the coating agent allows the M2 element to be dispersed on the surface of the positive electrode active material particles.

[0074] In some embodiments of the present invention, the specific types of the alkali metal source, Ni source, M1 source, Co source, and M2 source are not particularly limited, and those skilled in the art can flexibly select them according to actual needs. For example, the alkali metal source, Ni source, M1 source, Co source, and M2 source can independently include, but are not limited to, one or more of metals, metal oxides, hydroxides, halides, sulfides, carbonates, bicarbonates, acetates, sulfates, and phosphates. In addition, the specific type of alkali metal element in the alkali metal source can be selected according to the application scenario of the positive electrode sheet. For example, for a positive electrode sheet for a lithium battery, the alkali metal source can be a lithium source, and for a positive electrode sheet for a sodium battery, the alkali metal source can be a sodium source.

[0075] In the present invention, based on the same inventive concept and the purpose of obtaining the above-mentioned high-density and low-porosity positive electrode sheet, the present invention also proposes a positive electrode active material, wherein the positive electrode active material is a single crystal particle, and the average particle size of the single crystal particle is P 50 The average particle size of the single crystal particles is 2.5 μm to 5.0 μm. Compared with the mainstream method of mixing small single crystal particles or agglomerates with large particle agglomerates, the use of single crystal particles with an average particle size larger than that of ordinary single crystal particles and relatively smaller than that of ordinary agglomerates as the electrode active material not only has strong compressive resistance and is conducive to obtaining a higher compaction density; the single crystal particles are relatively large in size, small in specific surface area, and have a high ultimate compaction density, which can obtain a lower porosity electrode. Less electrolyte is required during the charge and discharge cycle of the electrode, which can better inhibit the damage of the electrolyte to the positive electrode active material and the occurrence of side reactions, effectively improving the cycle performance and safety of the battery.

[0076] In order to further improve the performance of the positive electrode sheet made using the positive electrode active material, the positive electrode active material may further meet one or more of the following characteristics:

[0077] The median diameter D of the single crystal particles 50 It can be 4.5 μm to 8.0 μm, and optionally can be 5.5 μm to 7.5 μm;

[0078] The average particle size P of the single crystal particles 50It can be 3.0 μm to 4.5 μm;

[0079] The grain size D of the positive electrode active material XRD can optionally can be

[0080] The tap density of the positive electrode active material under a pressure of 20 kN can be ≥ 3.45 g / cm 3 , optionally can be ≥ 3.5 g / cm 3 .

[0081] The positive electrode active material can include A a Ni x M1 y Co z M2 b O 2-c / 2 R c , such as can be Li a Ni x Mn y Co z M2 b O 2-c / 2R c , and for another example can be Li a Ni x Mn y Co z M2 b O2. Wherein, 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 ≤ b ≤ 0.08, 0 ≤ c ≤ 0.1; A is Li or Na; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr and Ti; R is F and / or Cl.

[0082] Among them, the beneficial effects of the positive electrode active material or the single crystal particles satisfying the above characteristics on the positive electrode sheet have been described in the foregoing part, and will not be elaborated here. In addition, the preparation method of the positive electrode active material A a Ni x M1 y Co z M2 b O 2-c / 2 R c can also refer to the relevant description in the foregoing part, and will not be elaborated here.

[0083] In a third aspect of the present invention, a battery is provided, comprising: the aforementioned positive electrode sheet, or a positive electrode sheet produced using the aforementioned method. It should be noted that the features and effects described for the aforementioned positive electrode sheet and method for producing the positive electrode sheet also apply to this battery and will not be further elaborated here. In general, this battery combines high volumetric energy density with good cycle performance, resulting in a long service life and low safety risks.

[0084] It is understandable that the battery also includes components such as a negative electrode sheet, an electrolyte, and a separator. The specific structure or composition of the negative electrode sheet, the electrolyte, and the separator is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the separator may include, but is not limited to, polyethylene (PE) film, polypropylene (PP) film, PP / PE / PP composite film, composite ceramic separator, and adhesive-coated separator. For another example, the electrolyte may include an organic solvent and an electrolyte salt. For lithium batteries, the organic solvent may include one or more ester solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC). The electrolyte salt may include, but is not limited to, one or more common lithium salts such as lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalatoborate) (LiBOB), and lithium difluorophosphate (LiO2F2). Optionally, additives may be added to the electrolyte. These additives may include, but are not limited to, common additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC). As some specific examples, the electrolyte may also be the electrolyte LBC420H57 or LBC420U67 manufactured by Shenzhen Xinzhoubang Technology Co., Ltd.

[0085] The present invention will be described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way. Where specific techniques or conditions are not indicated in the examples, they are performed according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents or instruments used that do not indicate the manufacturer are conventional products that can be obtained commercially.

[0086] In the following examples, unless otherwise specified, all raw materials are commercially available.

[0087] Unless otherwise specified, the room temperature in the present invention refers to 25±2°C.

[0088] In the following examples and comparative examples, the relevant parameters were obtained by testing using the following methods:

[0089] (1) Particle size test: laser particle size analyzer.

[0090] (2) Morphology and surface roughness test: Scanning electron microscope ERA-9200 model from ELIONIX, Japan;

[0091] (3) Specific surface area test: Micromeritics Tristar 3020 specific surface area meter;

[0092] (4) Electrochemical performance test:

[0093] In the following examples and comparative examples, the electrochemical properties of the multi-element positive electrode materials were measured using a stacked full cell.

[0094] The assembly method of lithium-ion batteries (full batteries) includes:

[0095] Preparation of positive electrode sheet: The multi-element positive electrode active material, conductive carbon black (SP), carbon nanotubes (CNT) and polyvinylidene fluoride (PVDF) were mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 96.7:1:0.8:1.5 to form a uniform slurry. The slurry was coated on aluminum foil. After the drying process, it was punched into 112mm×40mm pole sheets using a die-cutting machine. The loading amount of the positive electrode active material was 370g / m 2 ;

[0096] Preparation of negative electrode sheet: The negative electrode active material, SP, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed with an appropriate amount of pure water in a mass ratio of 96.5:0.5:1.2:1.8 to form a uniform slurry. The slurry is coated on copper foil. After the drying process, a die-cutting machine is used to punch out 115mm×41.5mm electrode sheets. The loading amount of the negative electrode active material is 222g / m 2 .

[0097] Diaphragm: Adhesive coated diaphragm, PE base film + ceramic PVDF mixed coating;

[0098] Electrolyte: The electrolyte used is the LBC420H57 produced by Shenzhen Xinzhoubang Technology Co., Ltd.

[0099] Battery assembly: Z-shaped stacking is carried out in an environment with a dew point of -40°C. The positive and negative pole pieces correspond to each other and are separated by a diaphragm. After the battery cell is assembled, it is vacuum baked at 85°C.

[0100] Liquid injection: Inject 7.5ml of liquid into the assembled battery cell in the glove box and soak it at 45℃ for 24h.

[0101] Electrochemical performance test: The battery is pre-charged and discharged with a small current on a splint. The battery is sealed for the second time to remove the air bag. The battery is then put on the cabinet for charging and discharging at 0.2C, 0.33C, 0.5C, and 1C to complete the battery capacity separation.

[0102] Cycling performance test: The charge and discharge voltage range is controlled at 2.8-4.4V. At a constant temperature of 45°C, the full battery is charged and discharged twice at 0.1C, and then charged and discharged 200 times at 1C to evaluate the high-temperature capacity retention rate of the multi-electrode positive electrode material.

[0103] Example 1

[0104] S1, median diameter D 50 '=5.1μm precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2 particles and lithium hydroxide were mixed evenly, and the first sintering was carried out at 1010℃ for 10 hours, and the mixture was naturally cooled to room temperature, and the mixture was crushed and sieved to obtain the positive electrode active material process product; the positive electrode active material process product was mixed with MgO (nanoparticles), and the second sintering was carried out at 700℃ for 8 hours, and the mixture was crushed and sieved to obtain the single crystal multi-element positive electrode active material: Li 1.06 Ni 0.7 Co 0.2 Mn 0.1 Mg 0.001 O2; average particle size P 50 It is 3.8μm.

[0105] S2: The multi-element positive electrode active material prepared in S1 was fully mixed with SP, CNT and polyvinylidene fluoride (PVDF) in a mass ratio of 96.7:1:0.8:1.5 and N-methylpyrrolidone (NMP) to form a uniform slurry. The slurry was coated on aluminum foil. After the drying process, it was punched into 112mm×40mm pole pieces using a die-cutting machine, wherein the positive electrode active material loading was 370g / m 2 The compaction density of the positive electrode active material layer is 3.70 g / cm 3 .

[0106] Example 2

[0107] The differences between Examples 2 to 10 and Example 1 are detailed in Table 1.

[0108] The main difference between Example 2 and Example 1 is that in step S2, the compaction density of the positive electrode active material layer is 3.60 g / cm 3 , the porosity of the electrode is 4.94%.

[0109] The main difference between Example 3 and Example 1 is that in step S2, the compaction density of the positive electrode active material layer is 3.75 g / cm 3 , the porosity of the electrode is 3.82%.

[0110] The main difference between Example 4 and Example 1 is that in step S1, the precursor Ni0.7 Co 0.2 Mn 0.1 The median diameter D of (OH)2 particles 50 '=5.8μm, the first sintering temperature is 1030℃, the average particle size P of the positive electrode active material prepared in S1 50 =4.7 μm, and the compaction density of the positive electrode active material layer is 3.70 g / cm 3 , the porosity of the electrode is 3.5%.

[0111] The main difference between Example 5 and Example 1 is that in step S1, the precursor Ni 0.7 Co 0.2 Mn 0.1 The median diameter D of (OH)2 particles 50 ' = 4.2 μm, the first sintering temperature is 990 ° C, the average particle size P of the positive electrode active material prepared in S1 50 =3.4 μm, and the compaction density of the positive electrode active material layer is 3.70 g / cm 3 , the porosity of the electrode is 5.15%.

[0112] The difference between Example 6 and Example 1 is that in step S2, the porosity of the positive electrode sheet is 5.45%, and the compaction density of the positive electrode active material layer is 3.55 g / cm 3 .

[0113] The difference between Example 7 and Example 1 is that in step S2, the porosity of the positive electrode sheet is 3.56%, and the compaction density of the positive electrode active material layer is 3.82 g / cm 3 .

[0114] The difference between Example 8 and Example 1 is that in step S1, the first sintering temperature is 980°C, and the finished product particle size P50, median diameter D50, grain size, etc. are all different.

[0115] The main difference between Example 9 and Example 1 is that in step S1, the median diameter D 50 '=5.1μm precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2 particles and lithium hydroxide were mixed evenly, and the first sintering was carried out at 1010℃ for 10h, and then naturally cooled to room temperature, and crushed and sieved to obtain single crystal multi-element positive electrode active material: Li 1.06 Ni 0.7 Co 0.2 Mn 0.1 Mg 0.001 O2.

[0116] The main difference between Example 10 and Example 1 is that in step S1, the precursor is Li1.06 Ni 0.8 Co 0.1 Mn 0.1 Mg 0.001 O2 particles.

[0117] Comparative Example 1

[0118] S1, median diameter D 50 '=5.1μm precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2 particles and lithium hydroxide were mixed evenly, and the first sintering was carried out at 950℃ for 10 hours. The mixture was naturally cooled to room temperature, crushed and sieved to obtain the positive electrode active material process product. The positive electrode active material process product was mixed with MgO, and the second sintering was carried out at 700℃ for 8 hours. The single crystal multi-element positive electrode material: Li 1.06 Ni 0.7 Co 0.2 Mn 0.1 Mg 0.001 O2; average particle size P 50 It is 1.6μm.

[0119] S2: The multi-element positive electrode active material prepared in S1 was fully mixed with SP, CNT and polyvinylidene fluoride (PVDF) in a mass ratio of 96.7:1:0.8:1.5 and N-methylpyrrolidone (NMP) to form a uniform slurry. The slurry was coated on aluminum foil. After the drying process, it was punched into 112mm×40mm pole pieces using a die-cutting machine, where the positive electrode material loading was 370g / m 2 The compaction density of the positive electrode active material layer is 3.47 g / cm 3 .

[0120] Comparative Examples 2-3

[0121] The main difference between Comparative Example 2 and Example 1 is that in step S2, the compaction density of the positive electrode active material layer is 3.50 g / cm 3 , the porosity of the pole piece is 5.73%.

[0122] The main difference between Comparative Example 3 and Example 1 is that in step S2, the compaction density of the positive electrode active material layer is 4.05 g / cm 3 , the porosity of the pole piece is 5.62%.

[0123] Comparative Example 4

[0124] The difference from Example 1 is that

[0125] In S1, part of the positive electrode active material process product is mixed with MgO for a second sintering (the preparation conditions of the positive electrode active material process product, the second sintering conditions, and the amount of MgO are the same as those in Example 1), and the particles are crushed and sieved to obtain an average particle size P 50 2.5μm single crystal multi-element positive electrode active material: Li 1.06 Ni 0.7 Co 0.2 Mn 0.1 Mg 0.001 The other part of the positive electrode active material process product is ground and granulated and then mixed with MgO for the second sintering, crushed and sieved to obtain an average particle size P 50 The multi-element positive electrode active material Li is a large particle agglomerate of 15 μm. 1.06 Ni 0.7 Co 0.2 Mn 0.1 Mg 0.001 The large-particle agglomerate multi-element positive electrode active material and the single-crystal multi-element positive electrode active material are mixed in a mass ratio of 7:3.

[0126] In S2, the mixed multi-element positive electrode active material prepared in S1 was fully mixed with SP, CNT and polyvinylidene fluoride (PVDF) in a mass ratio of 96.7:1:0.8:1.5 and N-methylpyrrolidone (NMP) to form a uniform slurry. The slurry was coated on aluminum foil and, after a drying process, was punched into 112 mm × 40 mm pole pieces using a die-cutting machine. The loading amount of the positive electrode active material was 370 g / m 2 The compaction density of the positive electrode active material layer is 3.52g / cm 3 , the porosity of the pole piece is 6.84%.

[0127] Comparative Example 5

[0128] The difference from Comparative Example 2 is that in step S1, the cathode active material in-process product is not mixed with MgO for the second sintering treatment.

[0129]

[0130] Results and Conclusions:

[0131] In Example 1, single crystal particles with appropriate particle size are used as active materials, and the appropriate electrode compaction density is 3.70 g / cm 3 , porosity 4.09%, the material has good capacity and cycle performance.

[0132] In Example 2, the same active material is used as in Example 1, and the electrode compaction density is reduced to 3.60 g / cm 3The electrode porosity (4.94%) is larger than that of Example 1, and its capacity and cycle performance are slightly lower than those of Example 1. The reasons may be that: the contact of the active material is poor, the capacity in the first week is low, and the porosity is large, the electrolyte corrosion is more, and the cycle is reduced. In addition, due to the low compaction density, the volume capacity density of the material is greatly reduced.

[0133] In Example 3, the same active material is used as in Example 1, and the electrode compaction density is increased to 3.75 g / cm 3 The electrode porosity (3.82%) is relatively small compared to Example 1, and its capacity and cycle performance are slightly lower than Example 1. Analysis shows that the reason may be that the electrolyte infiltration is insufficient and the capacity in the first cycle is low.

[0134] In Example 4, compared with Example 1, the active material particle size P50 is 4.7 μm, which is relatively large, and the electrode porosity (3.50%) is relatively small. Its capacity and cycle performance are slightly lower than those of Example 1. Analysis shows that the reason may be that the relatively large particle size leads to low capacity.

[0135] In Example 5, compared with Example 1, the active material particle size P50 is 3.4 μm, which is relatively small, and the electrode porosity (5.15%) is relatively large. Its capacity and cycle performance are slightly lower than those of Example 1. Analysis of the reasons may be that: the small particle size leads to low capacity, and the large porosity leads to poor cycle performance.

[0136] Example 6: Using the same active material as in Example 1, the electrode compaction density is reduced to 3.55 g / cm 3 The porosity of the electrode (5.45%) is relatively large, and its capacity and cycle performance are slightly lower than those of Example 1. The reasons may be that: the contact of the active material is poor, the capacity in the first week is low, and the porosity is large, the electrolyte corrosion is more, and the cycle is reduced. In addition, due to the low compaction density, the volume capacity density of the material is greatly reduced.

[0137] Example 7, using the same active material as Example 1, the electrode compaction density is increased to 3.82g / cm 3 The electrode porosity (3.56%) is relatively small, and its capacity and cycle performance are slightly lower than those of Example 1. Analysis shows that the reason may be that the electrolyte infiltration is insufficient and the capacity in the first cycle is low.

[0138] In Example 8, compared with Example 1, the first sintering temperature is lower than the temperature calculated by the formula, the particle size of the active material is only 3.1 μm, which is relatively small, the electrode porosity (5.50%) is relatively large, and the cycle performance is lower than that of Example 1. Analysis of the reasons may be that: the relatively small particle size leads to a relatively large electrode porosity, which in turn leads to a slightly poor cycle.

[0139] Example 9, which does not contain a coating layer, has a significantly lower circulation rate than Example 1.

[0140] In Example 10, the molar ratio of Ni, Co, and Mn in the precursor is 8:1:1, the material capacity is improved, and the cycle time is reduced.

[0141] The performance of Comparative Example 1 is poor compared with that of the embodiment. The reasons may be that the particle size P50 is 1.6μm, which is relatively small, and the ultimate compaction density of the pole piece is relatively low, resulting in a low optimal compaction density of the pole piece, low compaction density, low volume energy density, and small active material particle size, resulting in poor cycle.

[0142] Comparative Example 2 uses the same active material as Example 1. The performance is poorer than that of Example 1. The reason may be that the compaction density of the electrode is reduced to 3.50g / cm 3 , the material porosity (5.73%) is relatively large, the electrolyte infiltration is insufficient, the first-week capacity is low, the volume energy density is low, and the cycle is poor.

[0143] Comparative Example 3 uses the same active material as Example 1. The performance is poorer than that of Example 1. The reason may be that the compaction density of the electrode is reduced to 4.05g / cm 3 , exceeding the ultimate compaction density of the electrode, the material circulation rate decreases rapidly and cannot be used in practice.

[0144] The performance of Comparative Example 4 is slightly worse than that of the embodiment. The reasons may be that: since the large particle agglomerates have poor compressive resistance and are easily crushed, the ultimate compaction density of the pole piece is low, the compaction density of the pole piece that can be applied is low, the battery volume capacity density is low, and the agglomerate circulation is poor.

[0145] Comparative Example 5, compared with Comparative Example 2, has no MgO coating and has a worse cycle.

[0146] From Examples 1 to 10 and Comparative Examples 1 to 5, it can be seen that simultaneously controlling the porosity of the positive electrode sheet and the compaction density of the active material layer to meet the requirements of the present invention is conducive to further improving the volume energy density and cycle performance of the battery. In addition, the combination of the embodiments of the present invention and the comparative examples can also illustrate that the dispersion of the single crystal particles of the positive electrode active material is good, which is further conducive to achieving a positive electrode sheet with a porosity and compaction density that meet the requirements of the present invention. Taking Example 1 and Comparative Example 1 as examples, Figure 1 This is the SEM image of the single crystal multi-element positive electrode active material prepared in Example 1. It can be seen from the figure that the average particle size P of the positive electrode active material particles is 50 3.8μm, Figure 2 This is a cross-sectional SEM image of a positive electrode sheet prepared from the multi-element positive electrode active material prepared in Example 1; Figure 3This is the SEM image of the single crystal multi-element positive electrode active material prepared in Comparative Example 1. It can be seen from the figure that the average particle size P of the positive electrode active material particles is 50 1.6μm, Figure 4 This is a cross-sectional SEM image of the electrode sheet prepared from the multi-element positive electrode active material prepared in Comparative Example 1. Figures 1 to 4 It can be seen that the single crystal positive electrode active material has good dispersion in the positive electrode active material layer, and no obvious agglomerated particles are observed. In addition, it can be seen that single crystal particles with a relatively large average particle size are further conducive to achieving a positive electrode sheet with a porosity and compaction density that meet the requirements of the present invention. In addition, in combination with Examples 1, 4-5 and Example 8, Table 1 can also be seen that by adjusting the first sintering temperature and changing the particle size range of the precursor particles, the particle size of the obtained positive electrode active material particles can be changed, thereby affecting the compaction density and porosity of the final positive electrode sheet. In combination with Example 9, it can be seen that the performance of the positive electrode sheet and the battery can be further improved by forming a suitable coating layer material on the surface of the positive electrode active material particles. Furthermore, in combination with Example 10, it can be seen that the relative molar amount of the transition metal elements in the multi-element positive electrode active material can be further controlled to further improve the discharge capacity of the positive electrode sheet and the energy density of the battery.

[0147] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0148] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A positive electrode plate, characterized in that: Comprising: A current collector and a positive electrode active material layer provided on at least one side of the current collector, wherein the compaction density of the positive electrode active material layer is 3.55 g / cm 3 ~3.82g / cm 3 , the porosity of the positive electrode sheet is 3.5% to 4.6%; The positive electrode active material layer is composed of a positive electrode active material, a conductive agent, and a binder, and the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95 - 98):(0.5 - 4):(0.5 - 4); The ultimate compaction density of the positive electrode active material layer is ≥3.8 g / cm 3 The positive electrode active material in the positive electrode active material layer is a single crystal particle; The average particle size P of the positive electrode active material 50 3.4μm~4.5μm; The grain size D of the positive electrode active material XRD for The positive electrode active material is Li a Ni x M1 y Co z M2 b O 2-c / 2 R c ,in: 0.9 ≤ a ≤ 1.1, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 < b ≤ 0.08, 0 ≤ c ≤ 0.1; M1 is Mn and / or Al; M2 is one or more of Ba, Ra, Zr, Fe, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Cu, V, Ta, Cr, La, Al, Ce, Er, Ho, Y, Mg, Sr, and Ti; R is F and / or Cl.

2. The positive electrode sheet according to claim 1, characterized in that: In the positive electrode active material layer, the positive electrode active material satisfies at least one of the following conditions: The median diameter D of the positive electrode active material 50 4.5μm~8.0μm; The compaction density of the positive electrode active material under a pressure of 20 kN is ≥3.45 g / cm 3 .

3. The positive electrode sheet according to claim 1, characterized in that: In the positive electrode active material layer, the positive electrode active material satisfies at least one of the following conditions: The median diameter D of the positive electrode active material 50 5.5μm~7.5μm; The compaction density of the positive electrode active material under a pressure of 20 kN is ≥3.5 g / cm 3 .

4. The positive electrode sheet according to claim 3, characterized in that: The positive electrode active material includes Li a Ni x Mn y Co z M2 b O 2-c / 2 R c .

5. A method for preparing the positive electrode sheet according to any one of claims 1 to 4, characterized in that: Comprising: Disperse the positive electrode active material, the conductive agent, and the binder in a solvent to obtain a positive electrode active paste; Coat the positive electrode active paste on at least one side of the positive electrode current collector to form a positive electrode active material layer, wherein, the preparation method of the positive electrode active material includes: The alkali metal source, Ni source, M1 source and Co source are mixed and subjected to the first calcination treatment, and the Ni source, M1 source and Co source are provided by precursor particles comprising Ni, M1 and Co, wherein the median diameter D of the precursor particles is 50 Satisfied: P 50 / 0.85≤D 50 '≤P 50 / 0.65; The roasting temperature T1 of the first roasting treatment is 900°C to 1050°C, the time is 7h to 20h, and the roasting atmosphere is an oxygen-containing atmosphere.

6. The method according to claim 5, characterized in that The median diameter D of the precursor particles 50 Satisfied: D 50 '≥3.5μm.

7. The method according to claim 5 or 6, characterized in that Satisfy at least one of the following conditions: Based on the total molar amount of Ni, M1, and Co, the relative molar amount of the alkali metal in the alkali metal source is 1mol to 1.08mol; The temperature T1 of the first calcination process satisfies: x is A a Ni x M1 y Co z M2 b O 2-c / 2 R c The subscript value of Ni in ; Mix the alkali metal source, the Ni source, the M1 source, the Co source, and the M2 source and conduct the first roasting treatment.

8. The method according to claim 5 or 6, characterized in that Further comprising: Mix the product of the first roasting treatment with a coating agent and conduct a second roasting treatment.

9. The method according to claim 8, characterized in that Satisfy at least one of the following conditions: The temperature T2 of the second roasting treatment ≤ the temperature T1 of the first roasting treatment; The temperature T2 of the second roasting treatment is 250°C to 1000°C, the time is 5h to 20h, and the roasting atmosphere is an oxygen-containing atmosphere; The coating agent includes one or more of Zr, B, W, Nb, Cd, Pb, Si, Mo, Cu, La, Al, Ce, Er, Ho, Y, Mg, Sr, and Ti; The coating agent includes the M2 source, and based on the total molar amount of Ni, M1, and Co, the relative molar amount of M2 in the M2 source ≤ 0.08mol.

10. A battery, characterized in that: Comprising: The positive electrode plate according to any one of claims 1 to 4, or the positive electrode plate prepared by the method according to any one of claims 5 to 9.

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