Positive electrode sheet, method for manufacturing the same, battery, and power using device

Abstract

The present application relates to a kind of positive plate and its preparation method, battery and electric device, the positive plate includes current collector and first active layer and second active layer sequentially stacked in the surface of the current collector;The component of the first active layer includes the single crystal type active material of the mass fraction of nickel X1%;The component of the second active layer includes the polymorphic active material of the mass fraction of nickel X2%;X1% And X2% satisfy: X1% > X2%. When the positive plate is used to prepare battery, can reduce the energy density of battery while improving the impedance of battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a preparation method thereof, a battery and an electric device. BACKGROUND

[0002] Secondary batteries are increasingly widely used due to their clean and renewable characteristics, and mainly rely on the movement of active ions such as lithium ions between the positive electrode and the negative electrode to generate electric energy.

[0003] In recent years, with the rapid development of the new energy industry, people's demand for new energy vehicles such as electric vehicles and electric bicycles is increasing, and the requirement for their endurance performance is also increasing. Secondary batteries are an important power source for electric vehicles, so people's demand for the energy density of secondary batteries is also increasing.

[0004] With the increase in demand, the energy density of traditional secondary batteries is increasingly difficult to meet people's needs, and further improvement is needed. SUMMARY

[0005] Therefore, it is necessary to provide a positive electrode sheet, a preparation method thereof, a battery and an electric device, which aims to reduce the battery impedance of the secondary battery and improve the energy density of the battery.

[0006] The present application is achieved by the following technical solutions.

[0007] In a first aspect of the present application, a positive electrode sheet is provided, which comprises a current collector and a first active layer and a second active layer which are sequentially stacked on the surface of the current collector;

[0008] The components of the first active layer include a single-crystal active material with a mass fraction of nickel of X1%;

[0009] The components of the second active layer include a polycrystal active material with a mass fraction of nickel of X2%;

[0010] X1% and X2% satisfy: X1%> X2%.

[0011] In the aforementioned positive electrode, a first active layer and a second active layer are sequentially stacked on the surface of the current collector. Specifically, the first active layer is positioned closer to the current collector surface than the second active layer, and the crystal form of the active material and the molar percentage of nickel in each layer are controlled. The first active layer contains a single-crystal active material with a relatively high nickel content. Increasing the nickel content of the first active layer improves battery capacity and energy density. Furthermore, using a stable single-crystal active material reduces the likelihood of side reactions with the electrolyte. The second active layer contains a polycrystalline active material with a relatively low nickel content. The material employs a polycrystalline structure, giving the second active layer a larger and more complete pore structure, facilitating electrolyte wetting and improving ion transport capabilities. Furthermore, by reducing the nickel content, side reactions between the second active layer and the electrolyte are minimized. Thus, by creatively controlling the crystal form of the active materials in the first and second active layers and the molar ratio of nickel, the two work synergistically to improve the ion transport capability and reduce impedance of the positive electrode while preventing side reactions. When used in battery fabrication, this positive electrode can reduce impedance while increasing the battery's energy density.

[0012] In some embodiments, X1% and X2% satisfy: X1% > (X2+2)%;

[0013] Optionally, X1% ≥ (X2+5)%.

[0014] By adjusting the nickel content ratio of active materials in each layer, the energy density of the battery can be further improved.

[0015] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions (1) to (2):

[0016] (1) X11% is the percentage of nickel content in the single-crystal active material to the total amount of transition metals in the single-crystal active material, and X11 satisfies: 55% ≤ X11% ≤ 97%.

[0017] Optionally, 65% ≤ x 11% ≤ 97%;

[0018] (2) X21% is the percentage of the amount of nickel contained in the polycrystalline active material to the total amount of transition metals contained in the polycrystalline active material, and X21 satisfies: 50% ≤ X21% ≤ 92%.

[0019] Optionally, 55% ≤ x 21% ≤ 92%.

[0020] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions (3) to (6);

[0021] (3) The thickness of the first active layer is 3μm to 60μm;

[0022] Optionally, the thickness of the first active layer is 10 μm to 60 μm;

[0023] (4) The thickness of the second active layer is 20 μm to 100 μm;

[0024] Optionally, the thickness of the second active layer is 40 μm to 100 μm;

[0025] (5) The compaction density of the first active layer is 3.2 g / cc to 3.7 g / cc;

[0026] Optionally, the compaction density of the first active layer is 3.5 g / cc to 3.7 g / cc;

[0027] (6) The compaction density of the second active layer is 3.2 g / cc to 3.7 g / cc;

[0028] Optionally, the compaction density of the second active layer is 3.3 g / cc to 3.6 g / cc.

[0029] By adjusting the thickness of each layer, the transport efficiency of active ions such as lithium ions can be further improved.

[0030] In some embodiments, the single-crystal active material satisfies at least one of the following conditions (7) to (9):

[0031] (7) The volume distribution particle size Dv50 of the single-crystal active material is 1μm to 5μm;

[0032] Optionally, the volume distribution particle size Dv50 of the single-crystal active material is 2 μm to 3 μm;

[0033] (8) The particle size and volume distribution of the single-crystal active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.5;

[0034] (9) In the first active layer, the mass percentage of the single-crystal active material is 90% to 99%;

[0035] Optionally, in the first active layer, the mass percentage of the single-crystal active material is 95% to 99%.

[0036] In some embodiments, the polymorphic active material satisfies at least one of the following conditions (10) to (12):

[0037] (10) The volume distribution particle size Dv50 of the polycrystalline active material is 5μm to 18μm;

[0038] Optionally, the volume distribution particle size Dv50 of the polycrystalline active material is 9 μm to 12 μm;

[0039] (11) The particle size and volume distribution of the polycrystalline active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.5;

[0040] (12) In the second active layer, the mass percentage of the polycrystalline active material is 90% to 99%;

[0041] Optionally, in the second active layer, the mass percentage of the polycrystalline active material is 95% to 99%.

[0042] In some embodiments, under the same pressure conditions, the compaction density of the monocrystalline active material is greater than that of the polycrystalline active material;

[0043] Optionally, both the monocrystalline active material and the polycrystalline active material comprise the cathode material shown in formula (A):

[0044] LiNi z Co y M (1-z-y) O2(A);

[0045] Wherein, 0 < z < 1, 0 < y < 1, 0 < z + y < 1, and M includes at least one of Mn, Al, B, Y, Zr, Sr, La, Ti, Mg, Zn, Fe, Nb, Ge, and Ce. Single-crystal active materials have a higher compaction density, which reduces the porosity of the first active layer, further reducing the probability of side reactions with the electrolyte. Polycrystalline active materials have a lower compaction density, which is beneficial for forming a second active layer with a larger and more complete pore structure, further improving the ion transport capability of the cathode.

[0046] In some embodiments, the positive electrode further includes a base coating layer disposed between the current collector and the first active layer;

[0047] The components of the base coating include a conductive agent and a binder.

[0048] The undercoating layer between the current collector and the first active layer can prevent particulate matter in the first active layer from damaging the current collector, thus playing a buffering and protective role and further improving the stability of the positive electrode.

[0049] In some embodiments, the base coating satisfies at least one of the following conditions (13) to (15):

[0050] (13) The thickness of the base coating is 0.5 μm to 5 μm;

[0051] (14) In the base coating, the mass percentage of the conductive agent is 50% to 80%;

[0052] (15) In the base coating, the adhesive accounts for 20% to 50% by mass.

[0053] A second aspect of the present invention provides a method for preparing the electrode sheet of the first aspect, comprising the following steps:

[0054] A first active slurry and a second active slurry are prepared respectively; the first active slurry is a single-crystal active material with a nickel content of X1% by mass, and the second active slurry is a polycrystalline active material with a nickel content of X2% by mass; X1% and X2% satisfy: X1% > X2%;

[0055] The first active slurry is coated on at least one side surface of the current collector to form a first active layer;

[0056] The second active slurry is used to form a second active layer on the surface of the first active layer away from the current collector to obtain a positive electrode.

[0057] A third aspect of this application provides a battery comprising a positive electrode sheet prepared by the method of preparing a positive electrode sheet according to the first aspect or the second aspect.

[0058] A fourth aspect of this application provides an electrical device comprising the battery of the third aspect. Attached Figure Description

[0059] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0060] Figure 1 This is a schematic diagram of one embodiment of a secondary battery;

[0061] Figure 2 yes Figure 1 Exploded view;

[0062] Figure 3 This is a schematic diagram of one embodiment of the battery pack;

[0063] Figure 4 yes Figure 3 Exploded view;

[0064] Figure 5 This is a schematic diagram of one embodiment of an electrical device in which a battery is used as a power source.

[0065] Explanation of reference numerals in the attached figures:

[0066] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Secondary battery; 41. Housing; 42. Electrode assembly; 43. Cover plate; 5. Electrical device. Detailed Implementation

[0067] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0068] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0069] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0071] In summary, the energy density of traditional rechargeable batteries is increasingly failing to meet people's needs. In traditional technologies, engineers have primarily focused on developing new active materials or improving battery structures, but so far there have been no significant breakthroughs or progress.

[0072] Side reactions between the active material and the electrolyte in the positive electrode can seriously affect battery performance. Traditional technology attempts to set a gradient nickel content in the active layer of the positive electrode, with a higher nickel content in the bottom layer near the current collector and a lower nickel content in the top layer far from the current collector. The aim is to reduce the degree of side reactions between the top layer and the electrolyte compared to the bottom layer, thereby improving stability. It is also believed that setting a single-crystal active material in the top layer can prevent grain breakage between particles, further improving battery performance.

[0073] However, the technical personnel of this application have found in the long-term actual production and R&D process that although setting single crystal active material on the top layer can avoid the breakage of grains between particles, the high compaction density of single crystal active material will reduce the porosity of the top active layer, thereby reducing the transport efficiency of active ions and limiting the improvement of battery capacity.

[0074] Based on this, the technical personnel of this application broke free from the constraints of conventional thinking and explored new avenues. After extensive creative research, they obtained the positive electrode sheet of this application that can reduce the battery impedance of secondary batteries while increasing the energy density of batteries.

[0075] According to one embodiment of this application, a positive electrode is provided, which includes a current collector and a first active layer and a second active layer sequentially stacked on the surface of the current collector; the first active layer is composed of a single-crystal active material with a nickel content of 1% by weight; the second active layer is composed of a polycrystalline active material with a nickel content of 2% by weight.

[0076] X1% and X2% satisfy the condition: X1% > X2%.

[0077] It can be understood that the "first active layer and second active layer stacked sequentially on the surface of the current collector" means that the first active layer is closer to the current collector than the second active layer.

[0078] Single-crystal active materials refer to active materials in which the molecules, atoms or ions contained are arranged in a regular and periodic manner in three-dimensional space. Polycrystalline active materials are active materials composed of multiple small crystallites, and at least two of the small crystallites have different arrangements and orientations.

[0079] Specifically, XRD diffraction tests can be used to distinguish between the two: single-crystal active materials have only one set of diffraction spots in their diffraction patterns, while polycrystalline active materials have different orientations and show multiple sets of diffraction spots in their diffraction patterns.

[0080] In the aforementioned positive electrode sheet, a first active layer and a second active layer are sequentially disposed on the surface of the current collector, and the crystal form of the active material and the molar ratio of nickel in each layer (hereinafter referred to as nickel content) are controlled. The first active layer contains a single-crystal active material with a relatively high nickel content. Increasing the nickel content of the first active layer improves battery capacity and thus energy density. Furthermore, using a stable single-crystal active material reduces the probability of side reactions with the electrolyte. The second active layer contains a polycrystalline active material with a relatively low nickel content. On the one hand, the polycrystalline structure gives the second active layer a larger and more complete pore structure, facilitating electrolyte wetting and improving ion transport capabilities. On the other hand, reducing the nickel content reduces side reactions between the second active layer and the electrolyte. Thus, by creatively controlling the crystal form of the active materials and the molar ratio of nickel in the first and second active layers, the ion transport capability of the positive electrode sheet is improved, impedance is reduced, and side reactions are avoided. When this positive electrode sheet is used to manufacture batteries, it can simultaneously improve the energy density of the battery.

[0081] It should be noted that the current collector in the positive electrode has two surfaces opposite to each other in its own thickness direction. That is, the first active layer and the second active layer are stacked sequentially on either of the two opposite surfaces of the positive electrode current collector, or the first active layer and the second active layer are stacked sequentially on both surfaces.

[0082] In some embodiments, X1% and X2% satisfy: X1 > (X2 + 2)%;

[0083] Optionally, X1% ≥ (X2+5)%.

[0084] By adjusting the nickel content ratio of the active materials in each layer, the energy density of the positive electrode can be further improved.

[0085] In some embodiments, X11% is the percentage of the amount of nickel contained in the single-crystal active material to the total amount of transition metals contained in the single-crystal active material, and X11 satisfies: 55% ≤ X11% ≤ 97%.

[0086] Optionally, 65% ≤ x 11% ≤ 97%.

[0087] In some embodiments, X21% is the percentage of the amount of nickel contained in the polycrystalline active material to the total amount of transition metals contained in the polycrystalline active material, and X21 satisfies: 50% ≤ X21% ≤ 92%.

[0088] Optionally, 55% ≤ X21% ≤ 92%. It can be understood that if the transition metal includes nickel, then based on the total amount of transition metals contained in the single-crystal active material, the percentage of nickel contained in the single-crystal active material is X11%; based on the total amount of transition metals contained in the polycrystalline active material, the percentage of nickel contained in the polycrystalline active material is X21%.

[0089] In some embodiments, in addition to nickel, the transition metal also includes at least one of chromium, manganese, iron, cobalt, nickel, copper, zinc, palladium, silver, and platinum.

[0090] Optionally, the single-crystal active material includes at least one of high-nickel cathode materials and nickel-containing lithium transition metal composite oxides.

[0091] Optionally, the polymorphic active material includes at least one of high-nickel cathode materials and nickel-containing lithium transition metal composite oxides.

[0092] In some embodiments, X11% and X21% satisfy: X11% > X21%; alternatively, X11% and X21% satisfy: X11% > (X21+2)%;

[0093] Optionally, X11% ≥ (X21+5)%.

[0094] Optionally, both the monocrystalline active material and the polycrystalline active material include the cathode material shown in formula (A).

[0095] LiNi z Co y M (1-z-y) O2(A);

[0096] Wherein, 0 < z < 1, 0 < y < 1, 0 < z + y < 1, and M includes at least one of Mn, Al, B, Y, Zr, Sr, La, Ti, Mg, Zn, Fe, Nb, Ge, and Ce.

[0097] Optionally, M includes Mn.

[0098] Further optionally, both the monocrystalline and polycrystalline active materials include components that satisfy: Li d (Ni a Co b Mn cO2, where 0.9≤d≤1.2, 0.5≤a<1, 0<b<1, 0≤c<1, a+b+c=1. In this case, it can be understood that: when X11% is the percentage of nickel content in a single-crystal active material to the total amount of transition metals in the single-crystal active material, X11%=a×100%; similarly, when X21% is the percentage of nickel content in a polycrystalline active material to the total amount of transition metals in the polycrystalline active material, X21%=a×100%.

[0099] It is understood that the single-crystal active material and the polycrystalline active material in this application can be various nickel-containing ternary cathode materials commonly used in the art, such as LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2).

[0100] Optionally, the transition metal in the nickel-containing lithium transition metal composite oxide includes at least one of cobalt, manganese, and aluminum.

[0101] It should be noted that the components of active materials with different crystal forms can be the same or different.

[0102] All of the above-mentioned active materials can be purchased through commercial channels, and the elemental composition of the purchased products is already labeled. Furthermore, the components of the active materials of this application can also be detected by chemical analysis methods commonly used in the field, including but not limited to: complexation titration, precipitation gravimetric method, redox method, differential method, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry. Among these, ICP-AES and atomic absorption spectrometry are convenient and efficient, and their mechanisms are as follows:

[0103] Plasma emission spectroscopy is an analytical method that uses a high-temperature excitation source generated by plasma as the excitation source for atomic emission spectra. Different elements produce different characteristic spectra. These characteristic spectra are projected onto a grating in a spectrometer through a lens. By controlling a motor to rotate the grating, a transmission mechanism accurately positions the intensity of the characteristic spectral lines of the element to be measured at the exit slit after spectral dispersion. A photomultiplier tube converts this spectral intensity into an electric current. After further circuit processing and conversion, the data is processed by a computer to obtain the analytical results.

[0104] Atomic absorption spectrometry (AAS), also known as atomic absorption spectrophotometry, is an analytical method based on the absorption of characteristic radiation (spectral lines) emitted by atomic vapors of the same type of atom. The analytical process involves irradiating the sample solution with atomized and atomized atomic vapors of the sample solution using characteristic radiation emitted by the same type of atom. The gaseous ground-state atoms of the analyte in the vapor absorb the characteristic radiation lines emitted from the light source. Different elements exhibit selective absorption of these characteristic radiation lines, and the concentration of the analyte in the sample is determined by the degree of radiation attenuation.

[0105] In the above "55% ≤ X11% ≤ 97%", the value of X11% includes the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 97%; or any range consisting of any two values. For example, percentages could be 55%–95%, 55%–94%, 55%–93%, 55%–92%, 55%–90%, 55%–85%, 55%–80%, 55%–75%, 55%–70%, 55%–65%, 55%–60%, 65%–95%, 75%–95%, 85%–95%, 60%–95%, 60%–90%, 60%–85%, or 60%–80%.

[0106] Optionally, 65% ≤ x 11% ≤ 97%.

[0107] In the above "50% ≤ X21% ≤ 92%", the value of X21% includes the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 50%, 51%, 52%, 53%, 54%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%; or any range consisting of two values, for example, 50% to 92%, 50% to 91%, 50%–90%, 50%–85%, 50%–80%, 50%–75%, 50%–50%, 50%–60%, 55%–92%, 55%–90%, 55%–85%, 55%–80%, 55%–75%, 55%–70%, 55%–65%, 55%–60%, 65%–95%, 75%–95%, 85%–95%, 60%–95%, 60%–90%, 60%–85%, 60%–80%.

[0108] Optionally, 55% ≤ x 21% ≤ 92%.

[0109] In some embodiments, the thickness of the first active layer is 3 μm to 60 μm.

[0110] Optionally, the thickness of the first active layer is 10 μm to 60 μm.

[0111] In some embodiments, the thickness of the second active layer is 20 μm to 100 μm.

[0112] Optionally, the thickness of the second active layer is 40 μm to 100 μm.

[0113] By adjusting the thickness of each layer, the transport efficiency of active ions such as lithium ions can be further improved.

[0114] The values ​​in "3μm~60μm" above include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm; or any range of two values, for example, 3μm~55μm, 3μm~60μm. m~50μm, 3μm~45μm, 3μm~40μm, 3μm~35μm, 3μm~30μm, 3μm~25μm, 3μm~20μm, 10μm~60μm, 10μm~55μm, 10μm~45μm , 10μm~35μm, 15μm~45μm, 15μm~50μm, 15μm~60μm, 20μm~60μm, 30μm~60μm, 25μm~55μm, 35μm~45μm, 25μm~40μm.

[0115] The range "20μm to 100μm" includes the minimum and maximum values ​​within this range, as well as every value between these two values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm; or any range consisting of two values, for example, 20μm to 90μm, 20μm to 80μm, 20μm to 70μm, 20μm to 100μm. m~60μm, 20μm~50μm, 20μm~40μm, 30μm~60μm, 30μm~70μm, 30μm~90μm, 30μm~100μm, 40μm~100μm, 50μm~100μm, 60μm~100μm, 50μm~ 90μm, 50μm~80μm, 60μm~90μm, 60μm~80μm, 25μm~100μm, 25μm~800μm, 25μm~75μm, 35μm~90μm, 35μm~85μm, 35μm~70μm, 35μm~60μm.

[0116] In some embodiments, the compaction density of the first active layer is 3.2 g / cc to 3.7 g / cc.

[0117] Optionally, the compaction density of the first active layer is 3.5 g / cc to 3.7 g / cc.

[0118] In some embodiments, the compaction density of the second active layer is 3.2 g / cc to 3.7 g / cc.

[0119] Optionally, the compaction density of the second active layer is 3.3 g / cc to 3.6 g / cc.

[0120] In some embodiments, the volume distribution particle size Dv50 of the single-crystal active material is 1 μm to 5 μm.

[0121] Optionally, the volume distribution particle size Dv50 of the single-crystal active material is 2μm to 3μm.

[0122] The smaller particle size of single-crystal active materials can reduce the porosity of the first active layer, thus reducing the likelihood of side reactions between the material and the electrolyte.

[0123] In some embodiments, the particle size distribution of the single-crystal active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.5.

[0124] In some embodiments, the mass percentage of the monocrystalline active material in the first active layer is 90% to 99%.

[0125] Optionally, in the first active layer, the mass percentage of the single-crystal active material is 95% to 99%.

[0126] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline active material is 5 μm to 18 μm.

[0127] Optionally, the volume distribution particle size Dv50 of the polycrystalline active material is 9 μm to 12 μm.

[0128] The larger particle size of polycrystalline active materials is beneficial for forming a second active layer with a larger and more complete pore structure, thereby further improving the ion transport capability of the positive electrode.

[0129] In some embodiments, the particle size distribution of the polymorphic active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.5.

[0130] In some embodiments, the polymorphic active material accounts for 90% to 99% of the mass in the second active layer.

[0131] Optionally, in the second active layer, the mass percentage of the polycrystalline active material is 95% to 99%.

[0132] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline active material is greater than that of the monocrystalline active material.

[0133] In this application, Dv10, Dv50, or Dv90 refer to the particle size corresponding to a cumulative volume distribution percentage of 10%, 50%, or 90%, respectively, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0134] In some embodiments, under the same pressure conditions, the compaction density of the monocrystalline active material is greater than that of the polycrystalline active material.

[0135] The higher compaction density of monocrystalline active materials reduces the porosity of the first active layer, further decreasing the likelihood of side reactions with the electrolyte. Conversely, the lower compaction density of polycrystalline active materials facilitates the formation of a second active layer with a larger and more complete pore structure, thereby enhancing the ion transport capability of the positive electrode. In some embodiments, the positive electrode further includes an undercoating layer disposed between the current collector and the first active layer; the undercoating layer comprises a conductive agent and a binder.

[0136] The undercoating layer between the current collector and the first active layer can prevent particulate matter in the first active layer from damaging the current collector, thus playing a buffering and protective role and further improving the stability of the positive electrode.

[0137] The aforementioned conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0138] The adhesives mentioned above can be commonly used adhesives in the art, and can be selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resins.

[0139] In some embodiments, the thickness of the base coating is 0.5 μm to 5 μm.

[0140] In some embodiments, the conductive agent accounts for 50% to 80% of the mass of the base coating;

[0141] In some embodiments, the binder comprises 20% to 50% by mass in the base coating.

[0142] In some embodiments, the components of the first active layer further include a first conductive agent and a first binder.

[0143] Optionally, the first conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0144] Optionally, in the first active layer, the mass percentage of the first adhesive is 0 to 30 wt%.

[0145] The first adhesive mentioned above can be an adhesive commonly used in the art, and can be selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resins.

[0146] Optionally, the components of the first active layer may further include a thickener; the thickener may be a commonly used thickener in the art, including but not limited to: sodium carboxymethyl cellulose (CMC-Na).

[0147] In some embodiments, the components of the second active layer further include a second conductive agent and a second binder.

[0148] Optionally, the second conductive agent can be a conductive material commonly used in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0149] Optionally, in the second active layer, the mass percentage of the second adhesive is 0-30 wt%.

[0150] The second adhesive mentioned above can be an adhesive commonly used in the art, and can be selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resins.

[0151] Optionally, the components of the second active layer may further include a thickener; the thickener may be a commonly used thickener in the art, including but not limited to: sodium carboxymethyl cellulose (CMC-Na).

[0152] In some embodiments, the "first active layer and second active layer disposed on the surface of the current collector" may be disposed on at least a portion of the surface of the current collector, including but not limited to: disposed on at least one surface of the current collector and disposed on two surfaces of the current collector. The current collector may be a metal foil or a composite current collector. For example, 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 (aluminum, aluminum 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.).

[0153] Another embodiment of this application provides a method for preparing a positive electrode sheet, including the following steps S10 to S30.

[0154] S10. Prepare a first active slurry and a second active slurry respectively; the first active slurry is a single-crystal active material with a nickel content of X1%, and the second active slurry is a polycrystalline active material with a nickel content of X2%; X1% and X2% satisfy: X1% > X2%.

[0155] The selection ranges for X1% and X2% are the same as above, and will not be repeated here.

[0156] S20. The first active slurry is coated on at least one side of the current collector to form a first active layer.

[0157] S30. The second active slurry is coated on the surface of the first active layer away from the current collector to form the second active layer, thereby obtaining the positive electrode.

[0158] The coating process in steps S20 to S30 includes, but is not limited to, printing coating, blade coating, spin coating, or inkjet coating. The slurry is coated onto the current collector, and after processes such as drying and cold pressing, a coating is obtained.

[0159] Furthermore, steps S20 to S30 can be performed simultaneously using a dual-head mold.

[0160] In some embodiments, the positive electrode sheet can be prepared by coating a first active slurry onto a current collector and drying it, then coating it with a second active slurry, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0161] Furthermore, the compaction density of the positive electrode sheet is 3.2 g / cc to 3.7 g / cc, and can be selected as 3.3 to 3.5 g / cm³. 3 The formula for calculating compacted density is:

[0162] Compacted density = surface density / (extruded electrode thickness - current collector thickness).

[0163] The compaction density and areal density of the aforementioned positive electrode sheet have meanings known in the art. The areal density of the positive electrode sheet refers to the weight of the active layer loaded per unit area of ​​the positive electrode sheet, and the areal density per unit area = weight of the active layer / area of ​​the active layer. As an example, the compaction density can be obtained by testing the following steps:

[0164] The positive electrode sheet is cut into 1000mm long films; the positive electrode sheet is then rolled under certain pressure. Due to the ductility of aluminum foil, the film length is 1006mm, and then it is punched into 1540.25mm pieces. 2 The compaction density can be calculated by measuring the weight and thickness of the small circular disc.

[0165] One embodiment of this application also provides a battery, which includes the above-described positive electrode plate.

[0166] The aforementioned batteries have low impedance and excellent energy density.

[0167] Furthermore, the battery described above also includes a negative electrode, a separator, and an electrolyte. Examples of the negative electrode, separator, and electrolyte are provided below, including but not limited to the following.

[0168] Negative electrode plate

[0169] The negative electrode includes a positive current collector and a negative active layer loaded on the surface of the positive current collector.

[0170] The components of the negative electrode active layer include negative electrode active materials.

[0171] The aforementioned negative electrode active material can be any commonly used negative electrode active material described in this application.

[0172] In any embodiment of this application, the aforementioned negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials, and iron-based materials.

[0173] Optionally, specific examples of the above-mentioned negative electrode active materials include, but are not limited to, at least one of the following: interphase carbon microspheres, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fibers, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, and silicon-carbon composites.

[0174] In any embodiment of this application, the mass percentage of the above-mentioned negative electrode active material in the negative electrode active layer is 70% to 99.5%.

[0175] In any embodiment of this application, the components of the above-mentioned negative electrode active layer further include a negative electrode conductive agent and a negative electrode binder.

[0176] In any embodiment of this application, the aforementioned negative electrode conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0177] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode conductive agent in the negative electrode active layer is 0–20 wt%.

[0178] The aforementioned negative electrode binder can be a commonly used binder in the art, and can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS).

[0179] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode binder in the negative electrode active layer is 0–30 wt%.

[0180] In any embodiment of this application, the negative electrode active layer may optionally include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC-Na). Based on the total weight of the negative electrode active layer, the weight ratio of other additives in the negative electrode active layer is 0 to 15 wt%.

[0181] In any embodiment of this application, the current collector in the negative electrode can be a metal foil or a composite current collector. For example, copper foil can 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 can be formed by forming a metal material (aluminum, aluminum 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.).

[0182] In any embodiment of this application, the negative electrode sheet can be prepared by: dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing processes such as drying and cold pressing to obtain the negative electrode sheet. The negative electrode slurry has a solid content of 30wt% to 70wt% and its viscosity at room temperature is adjusted to 2000 mPa·s to 10000 mPa·s; coating the obtained negative electrode slurry onto a negative electrode current collector, and then performing a drying process followed by cold pressing, such as with rollers, to obtain the negative electrode sheet. The anode powder coating has a unit areal density of 75 mg / m³. 2 ~220mg / m 2 The compaction density of the negative electrode sheet is 1.2 g / m³. 3 ~2.0g / m 3 .

[0183] Electrolyte

[0184] Electrolytes include electrolyte salts and solvents.

[0185] In some embodiments, the electrolyte salt may be selected from electrolyte salts commonly used in the art, such as lithium-ion electrolyte salts.

[0186] As an example, lithium-ion electrolyte salts include, but are not limited to, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0187] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] In some implementations, the concentration of the electrolyte salt in the electrolyte is typically 0.5 mol / L.

[0189] ~15mol / L.

[0190] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0191] [Isolation membrane]

[0192] The separator is placed between the positive electrode and the negative electrode.

[0193] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0194] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. 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.

[0195] The thickness of the diaphragm is controlled between 2 μm and 15 μm; optionally, the thickness of the diaphragm is controlled between 2 μm and 13 μm.

[0196] In some embodiments, the battery is a secondary battery; specifically, the battery is a lithium-ion battery.

[0197] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 4.

[0198] In some embodiments, refer to Figure 2 The outer casing may include a housing 41 and a cover plate 43. The housing 41 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 41 has an opening communicating with the receiving cavity, and the cover plate 43 can be placed over the opening to close the receiving cavity.

[0199] The positive electrode, negative electrode, and separator can be formed into electrode assembly 42 by a winding or stacking process. Electrode assembly 42 is encapsulated within a receiving cavity. Electrolyte is immersed in electrode assembly 42. The battery 4 can contain one or more electrode assemblies 42, which can be adjusted according to requirements.

[0200] This application also provides an electrical device that includes the aforementioned secondary battery.

[0201] Furthermore, in the aforementioned electrical device, the secondary battery can exist in the form of a single battery cell, or it can be further assembled into a battery pack.

[0202] Figure 3 and Figure 4 Here is an example of a battery pack 1. The battery pack 1 includes a battery box and one or more secondary batteries 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 being able to cover the lower box 3 and form a closed space for the secondary batteries 4.

[0203] Multiple secondary batteries 4 can be arranged in the battery box in any way.

[0204] The aforementioned secondary batteries or battery packs assembled from them can be used as power sources for electrical devices or as energy storage units for electrical devices.

[0205] The aforementioned electrical devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0206] Figure 5 This is an example of an electrical device 5. This electrical device 5 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device 5, a battery pack can be used.

[0207] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use batteries as their power source.

[0208] The present invention will now be described with reference to specific embodiments. However, the present invention is not limited to the embodiments described below. It should be understood that the appended claims summarize the scope of the present invention. Under the guidance of the inventive concept, those skilled in the art should realize that any changes made to the various embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention.

[0209] The following are specific examples. Specific Implementation

[0211] Example 1

[0212] 1. Preparation of positive electrode sheet

[0213] S1: The first active material, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:2. Then, N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum mixer to obtain the first positive electrode slurry. Then, the first positive electrode slurry is uniformly coated on one of the surfaces of the positive electrode current collector aluminum foil to form the first active layer.

[0214] S2: The second active material, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:2. Then, N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum mixer to obtain the second positive electrode slurry. The second positive electrode slurry is then uniformly coated on the surface of the first active layer to form the second active layer. The mixture is then dried in an oven at 100℃~130℃.

[0215] S3: Repeat the same coating process as S1 to S2 on the other surface of the aluminum foil, and then obtain the positive electrode sheet through cold pressing, die cutting and slitting.

[0216] The types, nickel content, volumetric particle size distribution Dv50, and distribution parameters of the first and second active materials are shown in Table 1. The volumetric particle size distribution (Dv90-Dv10) / Dv50 of the first active material is denoted as T1, and the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the second active material is denoted as T2.

[0217] Wherein, Dv10, Dv50, or Dv90 represent the particle size corresponding to a cumulative volumetric distribution percentage of 10%, 50%, or 90%, respectively, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, referring to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0218] Furthermore, the thickness of each layer in the positive electrode sheet can be tested using methods known in the art, specifically through a profilometer test. The profilometer probe gently glides across the sample surface with extremely small force. The micron- or even nanometer-level undulations on the sample surface are amplified millions of times by a sensor connected to the probe, then converted into electronic signals, input into computer software, and finally displayed in digital and graphical form, as detailed in Table 1. The specific process is as follows:

[0219] First, test the film thickness A1 obtained in step S1, then the thickness of the first active layer = A1 - the thickness of the current collector; then, test the film thickness A2 obtained in step S3, then the thickness of the second active layer = A2 - A1.

[0220] Furthermore, the compaction density of each layer in the positive electrode was tested:

[0221] First, based on the areal density of the first and second active layers in the above-mentioned positive electrode sheet, films with corresponding areal densities are prepared using the first and second positive electrode slurries, respectively. Then, the compaction density of each layer is tested using the following method:

[0222] The membrane was cut into 1000mm lengths; the membrane was then pressed under pressure, and due to the ductility of the aluminum foil, the membrane length was reduced to 1006mm, which was then punched into 1540.25mm pieces. 2 The compaction density can be calculated by measuring the weight and thickness of the small circular discs. The test results are shown in Table 1.

[0223] The areal densities of the first and second active layers are calculated according to the following formula:

[0224] Areal density = mass of active layer / area.

[0225] 2. Preparation of negative electrode sheet

[0226] The negative electrode active material graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to the solvent water in a mass ratio of 96:2:1:1 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried at 85°C, and then cold-pressed to prepare a negative electrode sheet.

[0227] 3. Electrolyte preparation: The organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC, and DEC is 20:20:60. Thoroughly dried LiPF6 is dissolved in the organic solvent in an argon-atmosphere glove box with a water content of <10 ppm. After thorough mixing, the electrolyte is obtained, wherein the concentration of LiPF6 is 1 mol / L.

[0228] 4. Separating membrane: Polyethylene microporous film is used as the porous separating membrane substrate. Inorganic alumina powder, polyvinylpyrrolidone and acetone solvent are mixed evenly in a weight ratio of 3:1.5:5.5 to form a slurry, which is then coated on one side of the substrate and dried to obtain the separating membrane.

[0229] 5. Preparation of lithium-ion batteries: The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound to obtain a bare cell, and then the lithium-ion battery is obtained through processes such as packaging, liquid injection, formation and degassing.

[0230] 6. Performance testing of lithium-ion batteries:

[0231] (1) Perform the battery DC impedance test. The test procedure is as follows:

[0232] The battery was left to stand at a constant temperature of 25℃ for 2 hours. Then, it was charged at 0.33C to 4.2V within the range of 2.8V to 4.2V. Next, it was charged at a constant voltage of 4.2V until the current was ≤0.05C. After standing for 10 minutes, it was discharged at 0.33C to adjust the SoC to 50%. It was then discharged at 1C for 10 seconds. The voltage difference before and after discharge was recorded. The DC internal resistance (DCIR) is the ratio of the voltage difference to the discharge current. The test results are shown in Table 1.

[0233] (2) Battery capacity testing, the testing process is as follows:

[0234] The lithium-ion battery was left to stand at a constant temperature of 25°C for 2 hours. Then, it was charged at 0.33C to 4.2V under a voltage range of 2.8V to 4.2V. Next, it was charged at a constant voltage of 4.2V until the current ≤0.05C. After standing for 10 minutes, it was discharged at 0.33C to 2.8V. The capacity C of the lithium-ion battery was recorded. O The test results are shown in Table 1.

[0235] Examples 2-8

[0236] Examples 2 to 8 are basically the same as Example 1, except for the parameters in Table 1.

[0237] The other steps and conditions are the same as in Example 1. The test results are shown in Table 1.

[0238] Example 9

[0239] Example 9 is basically the same as Example 1, except that in the preparation of the positive electrode in step 1, before step S1, a step S0 for preparing the undercoating layer is also included:

[0240] S0: Polyvinylidene fluoride (PVDF) adhesive and acetylene black conductive agent are mixed at a mass ratio of 40:60, and then N-methylpyrrolidone (NMP) is added. The mixture is stirred evenly under vacuum to obtain a primer slurry. The primer slurry is then uniformly coated onto one surface of the positive electrode current collector aluminum foil to form a base coating. Steps S1 to S3 are then performed sequentially on the base coating surface, and steps S1 to S3 are the same as in Example 1.

[0241] The other steps and conditions are the same as in Example 1. The test results are shown in Table 1.

[0242] Examples 10-11

[0243] Examples 10 and 11 are basically the same as Example 9, except for the parameters in Table 1.

[0244] The other steps and conditions are the same as in Example 9. The test results are shown in Table 1.

[0245] Comparative Example 1

[0246] Comparative Example 1 is basically the same as Example 1, except that the preparation process of the positive electrode in step 1 is as follows:

[0247] The active materials (the first active material and the second active material are mixed in a mass ratio of 1:1), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:2. Then, N-methylpyrrolidone (NMP) is added and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on one of the surfaces of the positive electrode current collector aluminum foil to form a positive electrode active layer.

[0248] The other steps and conditions are the same as in Example 1. The test results are shown in Table 1.

[0249] Comparative Examples 2-5

[0250] Comparative Examples 2-5 are basically the same as Example 1, except for the parameters in Table 1.

[0251] The other steps and conditions are the same as in Example 1. The test results are shown in Table 1.

[0252] The relevant parameters and performance results of each embodiment and comparative example are shown in Table 1. The components of the first and second active materials satisfy the following: Li x (Ni a Co b Mn cO2, where 0.9≤x≤1.2, 0.5≤a<1, 0<b<1, 0<c<1, a+b+c=1. Taking the first active material as an example, the molar percentage of nickel among the transition elements contained in the first active material is denoted as nickel content X11%, X11%=a×100%; the specific values ​​of x, a, b, and c are different depending on the nickel content X11%. Among them, when the nickel content X11% of the first active material is 92%, the components satisfy: Li 1.05 (Ni 0.92 Co 0.06 Mn 0.02 When the nickel content (X11%) is 90%, the composition satisfies: Li 1.05 (Ni 0.9 Co 0.07 Mn 0.03 When O2 and nickel content X11% is 85%, the composition satisfies: Li 1.05 (Ni 0.85 Co 0.1 Mn 0.05 When the nickel content (X11%) is 82%, the composition satisfies: Li 1.05 (Ni 0.82 Co 0.1 Mn 0.08 When the nickel content (X11%) is 80%, the composition satisfies: Li 1.05 (Ni 0.8 Co 0.12 Mn 0.08 When the nickel content (X11%) is 55%, the composition satisfies: Li 1.05 (Ni 0.55 Co 0.2 Mn 0.25 When the nickel content (X11%) is 50%, the composition satisfies: Li 1.05 (Ni 0.5 Co 0.2 Mn 0.3 O2. Further, the molar percentage of nickel in the overall first active material is denoted as nickel content X1%, where X1% = a / 4.05 × 100%.

[0253] Similarly, X2% and X21% have the same meaning as above. When the values ​​of X2% and X1% are the same, and the values ​​of X21% and X11% are the same, the components of the first active material and the second active material are the same, only the crystal forms are different.

[0254] Table 1

[0255]

[0256]

[0257] For the same battery volume, energy density is directly proportional to capacity; that is, the higher the capacity, the higher the energy density. As shown in Table 1, using the positive electrode of this application can reduce battery impedance and increase battery energy density.

[0258] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0259] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a current collector and a first active layer and a second active layer sequentially stacked on the surface of the current collector; The first active layer comprises a single-crystal active material with a nickel content of 1% by weight. The second active layer comprises a polycrystalline active material with a nickel content of 2% by weight. X1% and X2% satisfy the condition: X1% > X2%; Under the same pressure conditions, the compaction density of the monocrystalline active material is greater than that of the polycrystalline active material; the volume distribution particle size Dv50 of the monocrystalline active material is 1μm~5μm; and the volume distribution particle size Dv50 of the polycrystalline active material is 9μm~12μm.

2. The positive electrode sheet as described in claim 1, characterized in that, X1% and X2% satisfy: X1%>(X2+2)%.

3. The positive electrode sheet as described in claim 2, characterized in that, X1%≥(X2+5)%.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, X11% is the percentage of the amount of nickel contained in the single-crystal active material to the total amount of transition metals contained in the single-crystal active material, and X11% satisfies: 55%≤X11%≤97%.

5. The positive electrode sheet as described in claim 4, characterized in that, 65%≤X11%≤97%。 6. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, X21% is the percentage of the amount of nickel contained in the polycrystalline active material to the total amount of transition metals contained in the polycrystalline active material, and X21% satisfies: 50%≤X21%≤92%.

7. The positive electrode sheet as described in claim 6, characterized in that, 55%≤X21%≤92%。 8. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The thickness of the first active layer is 3 μm to 60 μm.

9. The positive electrode sheet as described in claim 8, characterized in that, The thickness of the first active layer is 10 μm to 60 μm.

10. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The thickness of the second active layer is 20μm~100μm.

11. The positive electrode sheet as described in claim 10, characterized in that, The thickness of the second active layer is 40 μm to 100 μm.

12. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The compaction density of the first active layer is 3.2 g / cc to 3.7 g / cc.

13. The positive electrode sheet as described in claim 12, characterized in that, The compaction density of the first active layer is 3.5 g / cc to 3.7 g / cc.

14. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The compaction density of the second active layer is 3.2 g / cc to 3.7 g / cc.

15. The positive electrode sheet as described in claim 14, characterized in that, The compaction density of the second active layer is 3.3 g / cc to 3.6 g / cc.

16. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The volume distribution particle size Dv50 of the single-crystal active material is 2μm ~ 3μm.

17. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The particle size and volume distribution of the single-crystal active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.

5.

18. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, In the first active layer, the mass percentage of the single-crystal active material is 90% to 99%.

19. The positive electrode sheet as described in claim 18, characterized in that, In the first active layer, the mass percentage of the single-crystal active material is 95% to 99%.

20. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The particle size and volume distribution of the polycrystalline active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.

5.

21. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, In the second active layer, the mass percentage of the polycrystalline active material is 90% to 99%.

22. The positive electrode sheet as described in claim 21, characterized in that, In the second active layer, the mass percentage of the polycrystalline active material is 95% to 99%.

23. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, Both the monocrystalline active material and the polycrystalline active material include the cathode material shown in formula (A): LiNi z Co y M (1-z-y) O2(A); Wherein, 0 < z < 1, 0 < y < 1, 0 < z + y < 1, and M includes at least one of Mn, Al, B, Y, Zr, Sr, La, Ti, Mg, Zn, Fe, Nb, Ge, and Ce.

24. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode also includes a base coating layer, which is disposed between the current collector and the first active layer.

25. The positive electrode sheet as described in claim 24, characterized in that, The components of the base coating include a conductive agent and a binder.

26. The positive electrode sheet as described in claim 25, characterized in that, The conductive agent includes at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene.

27. The positive electrode sheet as described in claim 25, characterized in that, The adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, and fluorinated acrylate resin.

28. The positive electrode sheet as described in claim 25, characterized in that, The thickness of the base coating is 0.5μm to 5μm.

29. The positive electrode sheet as described in claim 25, characterized in that, In the base coating, the conductive agent accounts for 50% to 80% by mass.

30. The positive electrode sheet as described in claim 25, characterized in that, In the base coating, the adhesive accounts for 20% to 50% by mass.

31. A method for preparing a positive electrode, characterized in that, Includes the following steps: A first active slurry and a second active slurry are prepared respectively. The first active slurry comprises a monocrystalline active material with a nickel content of X1% by weight, and the second active slurry comprises a polycrystalline active material with a nickel content of X2% by weight. X1% and X2% satisfy: X1% > X2%. Under the same pressure conditions, the compaction density of the monocrystalline active material is greater than that of the polycrystalline active material. The volume distribution particle size Dv50 of the monocrystalline active material is 1μm to 5μm, and the volume distribution particle size Dv50 of the polycrystalline active material is 9μm to 12μm. The first active slurry is coated on at least one side surface of the current collector to form a first active layer; The second active slurry is coated on the surface of the first active layer away from the current collector to form a second active layer, thereby obtaining a positive electrode.

32. A battery, characterized in that, The battery includes a positive electrode sheet prepared by any one of claims 1 to 30 or by the method of preparing a positive electrode sheet as described in claim 31.

33. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 32.

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