Cathode material, preparation method and application thereof

Abstract

The application provides a positive electrode material and a preparation method and application thereof. The positive electrode material is indicated by a gas generation index of the positive electrode material obtained based on a cumulative particle size distribution change rate of the positive electrode material after being pressed under different pressures. The positive electrode material has good structural stability and particle pressure strength, is not easy to break, can reduce the volume expansion of a battery, and improves the performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of energy storage of electrochemical devices, and particularly to a cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] The cathode material is an important component of electrochemical energy storage devices such as lithium secondary batteries. Currently, the existing cathode materials generally have problems such as poor structural stability and low particle pressure resistance, which easily lead to volume expansion of the electrochemical device and affect the performance of the electrochemical device. Summary of the Invention

[0003] The present invention provides a cathode material, a preparation method thereof, and an application thereof. The cathode material has good structural stability and high particle pressure resistance, and can effectively overcome the defects existing in the prior art.

[0004] In one aspect of the present invention, a cathode material is provided, satisfying which represents the gas generation index of the cathode material obtained based on the cumulative particle size distribution change rate of the cathode material after being pressed under different pressures.

[0005] According to an embodiment of the present invention, the cathode material includes a core and a coating layer existing on the surface of the core.

[0006] According to an embodiment of the present invention, the core is Li (1+a) Ni x Co y E w M z O2, where -0.02 ≤ a ≤ 0.06, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w < 0.2, E includes Mn or Al, M includes one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, and the coating layer includes a compound of one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, Li, F, P, Ce.

[0007] According to an embodiment of the present invention, the specific surface area BET of the cathode material satisfies: 0.3 m 2 / g ≤ BET ≤ 0.9 m 2 / g.

[0008] According to an embodiment of the present invention, the particle size of the cathode material satisfies: 5 μm ≤ D50 ≤ 15 μm, and / or, 0.5 ≤ (D90 - D10) / D50 ≤ 1.3.

[0009] According to one embodiment of the present invention, in the X-ray diffraction analysis results of the cathode material, the grain size in the direction perpendicular to the crystal plane of the (104) diffraction peak is D. 104 ,45nm≤D 104 ≤70nm.

[0010] In another aspect, the present invention provides a method for preparing the above-mentioned cathode material, comprising: mixing a precursor containing Ni, Co, and E, a lithium source, and a dopant containing M, performing a first sintering, mixing the resulting product with a coating agent, and then performing a second sintering to obtain the cathode material.

[0011] According to one embodiment of the present invention, the temperature of the first sintering is 700-850°C; and / or, the temperature of the second sintering is 250-700°C.

[0012] According to one embodiment of the present invention, the precursor comprises Ni x Co y E w (OH)2; and / or, the lithium source includes lithium hydroxide; and / or, the dopant includes one or more of oxides, hydroxides, acids, sulfates, and acetates containing M; and / or, the coating agent includes one or more of oxides, hydroxides, acids, sulfates, and acetates.

[0013] In another aspect, the present invention provides a positive electrode sheet comprising the above-described positive electrode material.

[0014] In another aspect, the present invention provides a battery comprising the above-described positive electrode.

[0015] According to one embodiment of the present invention, it further includes a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising graphite.

[0016] According to one embodiment of the present invention, the battery includes a lithium secondary battery.

[0017] The positive electrode material of this invention satisfies It has good structural stability, high particle pressure resistance, and reduces battery volume expansion, especially reducing the volume expansion rate of the battery under high temperature conditions, thereby improving battery performance. Attached Figure Description

[0018] Figure 1 The cumulative volumetric particle size relative difference graph for Example 1 (x-axis is x, y-axis is y);

[0019] Figure 2The images show the cathode material of Example 1 and the scanning electron microscope (SEM) images of the cathode material after being pressed under pressures of 150 MPa, 200 MPa, 250 MPa, 300 MPa and 350 MPa, respectively.

[0020] Figure 3 This is a graph showing the cumulative volumetric particle size relative difference in Example 2 (x-axis is x, y-axis is y). Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] With technological advancements, electrochemical energy storage devices have become widely used. For example, lithium-ion batteries, with their advantages of high energy density, environmental friendliness, and a mature industrial chain, have attracted widespread attention as a clean energy source that reduces carbon dioxide emissions. High energy density and high safety are crucial directions for battery development. Improving the specific capacity of cathode materials and increasing battery charging voltage are the main ways to enhance battery energy density.

[0023] However, current cathode materials generally suffer from poor structural stability and low particle pressure resistance, which can easily lead to volume expansion, especially under high temperature conditions, resulting in more severe volume expansion and thus affecting battery performance and use.

[0024] For example, during the charging, discharging, and high-temperature storage of a battery, the oxygen evolution reaction of the positive electrode material is usually aggravated. The evolved active oxygen will cause the side reactions between the positive electrode material and the electrolyte to intensify, leading to phenomena such as the oxidative decomposition of the solvent and the dissolution of metal ions. The dissolved metal ions will deposit on the negative electrode, thereby destroying the SEI film of the negative electrode and causing the reducing decomposition of the solvent. The whole process will produce gases such as CO2, CO, H2, methane, ethane, ethylene, and propylene, which will cause severe volume expansion of the battery. The volume expansion will cause misalignment between the positive electrode, separator, and negative electrode, resulting in increased battery impedance, decreased cycle performance, and even direct contact between the positive and negative electrodes, which will lead to thermal runaway of the battery due to self-discharge.

[0025] Furthermore, when using positive electrode materials to prepare electrodes, a certain pressure is usually required. This can cause the positive electrode material particles to break, producing cracks or fine powder, resulting in uneven positive electrode material. Moreover, the fracture surface of the particles has poor contact with other components such as binders and conductive agents, leading to an increase in battery impedance. At the same time, the formation of cracks or fine powder in the positive electrode material can also cause more serious side reactions with the electrolyte, increasing the gas production rate and causing the battery volume to expand. Additionally, the positive electrode material is prone to the dissolution of transition metals, which migrate to the negative electrode and are reduced, catalyzing side reactions such as the SEI film of the negative electrode, leading to battery failure or thermal safety issues.

[0026] In view of the above problems, embodiments of the present invention provide a cathode material that satisfies the following requirements. This represents the gas production index of the cathode material, obtained based on the cumulative particle size distribution change rate after the cathode material is pressed under different pressures. The cumulative particle size distribution is a volume-based particle size distribution.

[0027] Specifically, Max and Min are obtained through the following process:

[0028] Obtain n sets of data, and fit each set of data into a curve to obtain a set of curves consisting of n curves.

[0029] Each set of data was obtained through the following process:

[0030] According to the formula Calculate the y values ​​corresponding to different x values ​​to obtain the data set.

[0031] D P0 x This indicates that, in the volume-based particle size distribution, the cathode material particles, starting from the smallest particle size side and reaching a cumulative volume D... P0 x The particle size at that time is x μm, i.e., D P0 x This represents the original volume-based particle size distribution test results for the cathode material, i.e., particle size distribution testing was performed on the cathode material before pressure was applied, and the cumulative volume percentage D of the particles at different x values ​​was obtained. P0 x For example, when D P0 x When x = 10%, x is the particle size D10 (or Dv10) of the cathode material.

[0032] D Pa x This indicates that after the cathode material is pressed under pressure of Pa (i.e., pressed under pressure of Pa), in the volume-based particle size distribution, the cathode material particles, starting from the smallest particle size side and reaching a cumulative volume D... Pax The particle size at that time was x μm.

[0033] D Pb x This indicates that after the cathode material is pressed under the pressure of Pb (i.e., the cathode material is pressed under the pressure of Pb), in the volume-based particle size distribution, the cathode material particles, starting from the smallest particle size side and reaching a cumulative volume D... Pb x The particle size at that time was x μm.

[0034] In practice, the cathode material is pressed under pressure of Pa or Pb. When Pa or Pb is high enough to compress the cathode material powder, it can be further crushed into powder or further dispersed by ultrasonic treatment to avoid agglomeration between cathode material particles. Then, the external particle size / cumulative volume particle size distribution of the cathode material powder is tested to obtain the cumulative volume ratio D of particle size corresponding to different x values. Pa x Or D Pb x .

[0035] In practice, 0.1–0.3 g of positive electrode material can be added to a 50 mL beaker, along with sodium hexametaphosphate and ultrapure water (approximately 20 mL). The mixture is then sonicated for 5 minutes at a power of 120 W and a frequency of 53 Hz to achieve ultrasonic treatment of the positive electrode material.

[0036] After pressing the cathode material under pressure of Pa or Pb, the particle size distribution of the cathode material usually changes. Among them, after pressing the cathode material under pressure of Pa, the rate of change of the cumulative volume ratio of particle size ε1 at any value of x can be expressed by the following formula I:

[0037]

[0038] After pressing the cathode material under Pa pressure, the cumulative volume percentage change rate ε2 of the particle size at any x value can be expressed as the following formula II:

[0039]

[0040]

[0041] Specifically, ε1 and ε2 represent the changes in the cumulative volumetric particle size distribution before 30 μm in the particle size distribution of the cathode material relative to the cumulative volumetric particle size of the original cathode material that has not been pressed, and Δε is the difference in the cumulative volumetric particle size distribution of the cathode material after being pressed under different pressures.

[0042] Furthermore, x∈(0, 30]. Specifically, when fitting any set of data into a curve, the y-values ​​corresponding to different x-values ​​(i.e., the cumulative volume percentage of particles corresponding to different x-values) are measured. Studies show that these x-values ​​are distributed between 0 and 30 (i.e., x∈(0, 30]). For the above-mentioned cathode material, the above n curves have greater distinguishability (i.e., the cumulative particle size change is mainly before 30 μm). Max and min exist in the interval of x∈(0, 30], and when x>30 μm, the y-values ​​corresponding to any x-value of the above n curves are basically not different.

[0043] Arrange these x values ​​in ascending order, with the smallest x value not exceeding 3 (specifically, it can be around 0.5 to 1) and the largest x value not exceeding 30 μm (specifically, it can be between 15 and 25). The difference between two adjacent x values ​​Δx ≤ 2.5.

[0044] For example, these x values ​​can include 5, 10, 15, 20, as well as several values ​​distributed between 0 and 5 (e.g., more than 10), several values ​​distributed between 5 and 10 (e.g., about 4 values ​​greater than 5 and less than 10), several values ​​distributed between 10 and 15 (e.g., about 2 values ​​greater than 10 and less than 15), and several values ​​distributed between 15 and 20 (e.g., at least 1 value greater than 15 and less than 20).

[0045] In addition, when obtaining any set of data, the following conditions must be met: 20Ma≤Pa-Pb≤60MPa (e.g., Pa-Pb=50MPa), 0<Pa≤400MPa, and 0<Pb≤400MPa.

[0046] In addition, when obtaining n sets of data, the n sets are arranged in ascending order of Pa value, and in any two adjacent sets, the Pa value of the previous set is equal to the Pb value of the next set.

[0047] Here, n groups represent multiple groups, which can be integers greater than or equal to 4.

[0048] In practice, n=4, that is, 4 sets of data are obtained (correspondingly, the curve set consists of 4 curves). In the first set, Pa=150MPa and Pb=200MPa; in the second set, Pa=200MPa and Pb=250MPa; in the third set, Pa=250MPa and Pb=300MPa; and in the fourth set, Pa=300MPa and Pb=350MPa.

[0049] When n > 4, meaning at least one new data set is added, with Pa < 150 MPa or Pa > 350 MPa, the resulting curve lies between the curve containing Max and the curve containing Min, without affecting Max, Min, and... value.

[0050] In the above set of curves, the largest y-value is Max, and the smallest y-value is Min.

[0051] Specifically, in a coordinate system with y as the vertical axis and x as the horizontal axis, within the range of x∈(0,30], the curve containing Max shows a trend of first increasing and then decreasing. The y-value corresponding to the vertex of the curve containing Max is Max. The curve containing Min usually shows a trend of first decreasing and then increasing (or it may show a trend of first increasing and then decreasing). The y-value corresponding to the lowest point of the curve containing Min is Min. Min can be a negative or positive value.

[0052] Furthermore, in the ordinate direction of the coordinate system, among the above curve group, the remaining curves, excluding the curve containing Max and the curve containing Min, are located between the curve containing Max and the curve containing Min. Max is not less than the maximum y-value of any of the other curves except the one containing Max, and Min is not greater than the minimum y-value of any of the other curves except the one containing Min.

[0053] According to the inventors' research, the gas production index of the cathode material in the embodiments of the present invention... satisfy The structure is stable, the particles have high compressive strength and are not easily broken, making the positive electrode material particles in the positive electrode sheet more uniform. It also improves the adhesion between the positive electrode material and other components such as conductive agents and binders in the positive electrode sheet, reduces impedance, and reduces the dissolution of transition metals in the positive electrode material and the resulting metal ions migrating to the negative electrode and damaging the SEI film. At the same time, it reduces side reactions between the positive electrode material and the electrolyte, as well as oxygen evolution reactions in the positive electrode material, thereby reducing gas generation in the battery and reducing battery volume expansion. In particular, it can reduce the volume expansion rate of the battery under high temperature conditions. For example, after storage at 70°C for 14 days, the volume expansion rate of the battery is no more than 35%, thereby improving the battery's electrical performance and lifespan.

[0054] In some embodiments, the cathode material may include a core and a coating layer present on the surface of the core, wherein the core may be Li (1+a) Ni x Co y E w M zO2, where -0.02 ≤ a ≤ 0.06, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w < 0.2, E includes Mn or Al, M includes one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, the coating layer includes one or more compounds of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, Li, F, P, Ce, such as boron-containing lithium compounds, boron-containing aluminum compounds, cerium-containing compounds, etc., usually oxides, that is, the above elements in the coating layer usually exist in the form of oxides.

[0055] Specifically, in the above positive electrode material, a high-nickel ternary material (nickel-cobalt-manganese (E is Mn) or nickel-cobalt-aluminum (E is Al)) is used as the matrix, and M is a dopant doped in the matrix to form a core, and then a coating layer is formed on the surface of the core. Among them, by introducing a specific amount of dopant (0 < z ≤ 0.2), the structural stability of the positive electrode material can be further improved, the strength of the positive electrode material particles can be enhanced, and the capacity performance of the positive electrode material during charge and discharge can be taken into account (studies have shown that if there is too much M element, it will affect the capacity performance of the positive electrode material during charge and discharge).

[0056] In the positive electrode material, the coating layer can exist on a part of the surface of the core or on the entire surface of the core (i.e., coating the core). The thickness of the coating layer is very thin, generally not exceeding 50 nm (usually a few nm to 50 nm), and is very small relative to the particle size of the core. Therefore, the influence of the coating layer on the particle size and particle size distribution of the positive electrode material can be basically ignored. That is, the particle size of the positive electrode material is basically equal to the particle size of its core, and the particle size distribution of the positive electrode material is basically the same as the particle size distribution of its core.

[0057] In addition, its core uses a high-nickel ternary material (nickel-cobalt-manganese (E is Mn) or nickel-cobalt-aluminum (E is Al)) as the matrix, and the introduction of the dopant M basically does not affect the particle size and particle size distribution of the core. Therefore, the particle size of the positive electrode material is basically equal to the particle size of the matrix (high-nickel ternary material) of its core, and the particle size distribution of the positive electrode material is basically the same as the particle size distribution of the matrix (high-nickel ternary material) of its core.

[0058] In addition, the BET specific surface area of the positive electrode material can satisfy: 0.3 m 2 / g ≤ BET ≤ 0.9 m 2 / g, and BET is, for example, 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m2 / g or a range consisting of any two of them.

[0059] Studies show that when BET > 0.9m 2 When BET is / g, the contact area between the cathode material and the electrolyte is large, and the reaction is more vigorous. When BET < 0.9m 2 At a density of 0.3 μm / g, an overly dense surface morphology or excessively thick coating on the cathode material can affect electrolyte wetting, resulting in insufficient electrolyte wetting and limited conductivity. Therefore, controlling the surface density to 0.3 μm / g is crucial. 2 / g≤BET≤0.9m 2 / g allows the cathode material (especially its capacity-functional component as the core) to have a more suitable contact area with the electrolyte, thereby improving battery performance.

[0060] The particle withstand strength of the cathode material is related not only to the structural stability of the material itself, but also to the particle size distribution. In some preferred embodiments, the particle size of the cathode material can satisfy: 5μm≤D50≤15μm, where D50 is, for example, a range of 5μm, 8μm, 10μm, 12μm, 15μm or any two of them; 0.5≤(D90-D10) / D50≤1.3, where (D90-D10) / D50 is, for example, a range of 0.5, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3 or any two of them.

[0061] Specifically, the particle size D50 of the cathode material represents the particle size that, in a volume-based particle size distribution, reaches 50% of the total volume from the smallest particle size side. The particle size D90 of the cathode material represents the particle size that, in a volume-based particle size distribution, reaches 90% of the total volume from the smallest particle size side. The particle size D10 of the cathode material represents the particle size that, in a volume-based particle size distribution, reaches 10% of the total volume from the smallest particle size side.

[0062] The cathode material particles are secondary particles composed of multiple primary particles. The particle size distribution of the secondary particles is an important factor affecting the compaction density of the powder. During the preparation of cathode sheets using cathode materials or during the use of cathode sheets, when the cathode material is subjected to a certain pressure, larger particles or structurally unstable secondary particles are prone to breakage, resulting in fine powder or cracks and the formation of fresh surfaces. These fresh surfaces undergo more severe side reactions with the electrolyte, increasing the gas production rate and causing the battery to expand in volume.

[0063] In this embodiment, the positive electrode material particles are secondary particles composed of multiple primary particles, controlling... The cathode material has a more stable particle structure, high pressure resistance, and is not prone to breakage, thereby suppressing the gas generation rate and the volume expansion of the battery, effectively overcoming the above problems. At the same time, controlling the particle size of the cathode material to meet 5μm≤D50≤15μm and 0.5≤(D90-D10) / D50≤1.3 can further alleviate the volume expansion of the battery.

[0064] Specifically, (D90-D10) / D50 characterizes the particle size distribution of the cathode material. When (D90-D10) / D50 < 0.5, the particle size distribution of the cathode material is too narrow, meaning the particle sizes are relatively small. Under pressure, the particles are prone to breakage / spherical formation due to lack of filling. A cathode material with a relatively wide particle size distribution (0.5 ≤ (D90-D10) / D50 ≤ 1.3) contains large, medium, and small particles with significant size differences. During pressure testing, the gaps between large particles are filled by smaller particles, resulting in higher powder compaction. High powder compaction often corresponds to high particle compressive strength, leading to higher overall particle compressive strength in the cathode material. However, if the cathode material has a wide particle size distribution ((D90-D10) / D50 > 1.3), the excessive fine powder leads to severe side reactions between the cathode material and the electrolyte, affecting the battery's cycle performance and gas generation performance (volume expansion).

[0065] Furthermore, in the X-ray diffraction (XRD) analysis results of the cathode material, the grain size in the direction perpendicular to the (104) diffraction peak crystal plane is D. 104 ,45nm≤D 104 ≤70nm, D 104 For example, a range consisting of 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, or any two of them.

[0066] Specifically, D 104 Characterized by the size of primary particles (or primary grains), excessively large primary particle sizes (i.e., D...) 104 If the diameter is too large (greater than 70nm), the internal structure of the cathode material is tightly packed, making it prone to microcracks. Electrolyte can then enter the cathode material, increasing side reactions and leading to increased gas production (i.e., deteriorated gas production performance). This results in battery volume expansion, while D... 104 Too small a size (less than 45nm) is also detrimental to battery capacity; therefore, controlling the size to 45nm ≤ D is crucial. 104 A depth of ≤70nm can further reduce battery volume expansion, especially under high temperature conditions, and improve battery performance.

[0067] The method for preparing the cathode material in this embodiment of the invention may include: mixing a precursor containing Ni, Co, and E, a lithium source, and a dopant containing M (e.g., mixing them at high speed in a ball mill until uniform), sintering once, mixing the resulting product with a coating agent, and then sintering a second time to obtain the cathode material.

[0068] Specifically, after a first sintering, a core material (i.e., a ternary material doped with M) is formed. The core material is then mixed with a coating agent and subjected to a second sintering to form a coating layer on the surface of the core material, thus obtaining the cathode material. This preparation process can yield cathode materials that meet the required standards. The positive electrode material has better structural stability, high particle compressive strength, and is not easily broken.

[0069] The primary sintering temperature can be between 700 and 850℃, for example, 700℃, 780℃, 800℃, 820℃, 850℃, or any combination thereof. When the primary sintering temperature is too low (below 700℃), it easily causes inhomogeneity in the material composition, resulting in incomplete growth of the primary particles, poor crystallinity, and severe Li / Ni mixing, affecting the capacity and other properties of the cathode material. When the primary sintering temperature is too high (above 850℃), it leads to overburning, causing rapid growth of the primary particles constituting the cathode material. Due to the excessively high temperature, surface lithium volatilizes, resulting in severe Li / Ni mixing. Furthermore, because the primary particles are large and tightly packed internally, they are prone to microcracks, affecting structural stability and particle strength, and impacting the capacity, cycle life, and safety performance of the cathode material.

[0070] Generally, the compacted density of powder is mainly related to the true density, particle size distribution, and primary particle morphology of the material, while the true density of the material is mainly related to the main content component of the cathode material (Li). (1+a) Ni x Co y E wThe true density of cathode materials is largely unaffected by the proportion of doping element M and the coating layer. Therefore, cathode materials with the same main content have similar true densities. The primary particle morphology is mainly related to the primary sintering temperature. Lower primary sintering temperatures result in smaller primary particle sizes, while higher temperatures result in larger primary particle sizes. The particle size distribution is essentially determined during the core formation stage of the primary sintering. Narrow particle size distribution matrix particles are relatively uniform in size, exhibiting consistent lithiation during sintering and similar surface activity during the subsequent secondary sintering coating stage, resulting in good coating uniformity. However, due to the small difference in particle size, the particles are prone to fragmentation / spherical breakage under pressure due to lack of filling. Therefore, controlling the primary sintering temperature to 700–850℃ can give the cathode material particles a more suitable particle size distribution (0.5 ≤ (D90-D10) / D50 ≤ 1.3), resulting in higher overall particle compressive strength while maintaining coating uniformity and other properties, further improving the performance of the cathode material.

[0071] Specifically, the primary sintering is carried out in an environment containing oxygen gas, and the oxygen concentration in the gas environment can be greater than or equal to 85%, for example, in a sintering vessel or other equipment.

[0072] After the first sintering, the resulting product can be washed and dried sequentially, then mixed with a coating agent, for example, using a high-speed mixer, and then placed in a box furnace for a second sintering (i.e., re-sintering). The temperature for the second sintering can be 250–700℃. The second sintering is carried out in an environment containing oxygen gas, and the oxygen concentration in the gaseous environment can be greater than or equal to 85%.

[0073] In practice, the amount of coating agent can be adjusted to control the content / thickness of the coating layer in the formed cathode material, thereby controlling the specific surface area of ​​the cathode material (generally, the more coating agent used, the higher the content of the coating layer in the cathode material, and the smaller its specific surface area (more compact), and vice versa).

[0074] Specifically, the precursor containing Ni, Co, and E is the precursor of the matrix (high-nickel material) that forms the core of the cathode material, and may specifically include Ni. x Co y E w (OH)2, for example Ni x Co y Al w (OH)2 or Ni x Co y Mn w (OH)2; the lithium source may include lithium hydroxide (LiOH); the dopant may include one or more of the following: oxides, hydroxides, acids, sulfates, and acetates containing M.

[0075] Furthermore, the aforementioned coating agent may include compounds containing one or more elements selected from Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, Li, F, P, and Ce. For example, it may include one or more of boron-containing compounds, aluminum-containing compounds, boron-aluminum-containing compounds, fluorine-containing compounds, phosphorus-containing compounds, and cerium-containing compounds. These compounds may include, for example, one or more of oxides, hydroxides, acids, sulfates, and acetates. Exemplarily, boron-containing compounds may include boric acid, cerium-containing compounds may include one or more of cerium oxide, cerium hydroxide, cerium sulfate, and cerium acetate, and boron-aluminum-containing compounds may include aluminum borate.

[0076] Generally, during the secondary roasting process, lithium in the core also reacts with boron-containing compounds (i.e., boron-containing coating agents), resulting in some lithium embedding into the coating layer formed on the core surface. This means the coating layer contains lithium in addition to the dopant elements introduced by the coating agent. Specifically, when the coating agent includes a boron-containing compound (i.e., a boron-containing coating agent), the resulting coating layer is typically a boron-lithium compound. Conversely, when the coating agent is a cerium-containing coating agent, the resulting coating layer is typically a cerium-containing compound.

[0077] In addition, after secondary calcination, the coating agent forms the coating layer in the cathode material, and the elements contained therein (one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, Li, F, P, Ce) exist mainly in the form of oxides.

[0078] The amounts of precursors containing Ni, Co, and E, the lithium source, and the dopant are sufficient to form the cathode material core (Li). (1+a) Ni x Co y E w M z The stoichiometric ratio of each element in O2 is as follows: Specifically, the molar ratio of lithium source (calculated as Li), precursor, and dopant (calculated as M element) is (0.98~1.06):1:(0~0.05).

[0079] The positive electrode sheet of this invention includes the above-mentioned positive electrode material, which has advantages corresponding to the above-mentioned positive electrode material, and will not be described in detail hereafter.

[0080] Specifically, the positive electrode sheet may include a positive current collector and a positive active material layer disposed on the surface of the positive current collector, the positive active material layer including a positive electrode material, a conductive agent and a binder.

[0081] The battery in this embodiment of the invention includes the above-described positive electrode sheet, which has advantages corresponding to the above-described positive electrode material, and will not be described in detail hereafter.

[0082] Specifically, the aforementioned batteries may include lithium secondary batteries, specifically lithium-ion batteries.

[0083] The battery also includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes a negative active material, a conductive agent and a binder. The negative active material may include graphite.

[0084] The aforementioned positive electrode current collector and negative electrode current collector can be conventional materials for such current collectors in the art. For example, the positive electrode current collector includes aluminum foil, and the negative electrode current collector includes copper foil.

[0085] The aforementioned conductive agent can be a conventional conductive material in the field, such as carbon black, acetylene black, etc.

[0086] The adhesives described above can be conventional adhesives in the art, such as polyvinylidene fluoride (PVDF).

[0087] The present invention will be further described below through specific embodiments and comparative examples.

[0088] Example 1

[0089] LiOH·H2O, Ni 0.8 Co 0.06 Mn 0.12 (OH)2 and ZrO2 are mixed evenly in a high-speed mixer at a molar ratio of (0.98~1.06):1:0.03, and then placed in a sagger for sintering at 775℃ and an oxygen concentration of more than 85% to obtain the core material.

[0090] After homogenizing the boric acid and the core material, the mixture was placed in a box furnace and subjected to recalcination under an oxygen atmosphere to obtain a core containing (LiNi). 0.827 Co 0.06 Mn 0.12 Zr 0.003 The cathode material consists of O2 and a coating layer (containing boron compounds) on the surface of the core.

[0091] The gas production index of this cathode material was tested according to the following procedure. :

[0092] The external particle size of the above cathode material was tested to obtain the corresponding D values ​​for different x values. P0 x ;

[0093] The above-mentioned cathode material was compacted into powder under pressures of 150 MPa, 200 MPa, 250 MPa, 300 MPa, and 350 MPa, respectively, then crushed, and its external particle size was tested (0.1–0.3 g of cathode material was added to a 50 mL beaker, followed by the addition of sodium hexametaphosphate and ultrapure water (approximately 20 mL), and then sonicated for 5 min at 120 W and 53 Hz, followed by particle size testing). The D values ​​corresponding to different x values ​​were obtained. Pa x D Pb x ;

[0094] Plot curve 1: According to the formula Calculate the y values ​​corresponding to different x values ​​to obtain data set 1, where Pb = 150 MPa and Pa = 200 MPa. These x values ​​are shown in [reference needed]. Figure 1 Then, based on data set 1, fit curve 1 (see...). Figure 1 );

[0095] Plot curve 2: According to the formula Calculate the y values ​​corresponding to different x values ​​to obtain data set 2, where Pb = 200 MPa and Pa = 250 MPa. These x values ​​are shown in [reference needed]. Figure 1 Then, based on data set 2, fit curve 2 (see...). Figure 1 );

[0096] Plot curve 3: According to the formula Calculate the y values ​​corresponding to different x values ​​to obtain data set 3, where Pb = 250 MPa and Pa = 300 MPa. These x values ​​are shown in [reference needed]. Figure 1 Then, based on data set 3, fit curve 3 (see...). Figure 1 );

[0097] Plot curve 4: According to the formula Calculate the y values ​​corresponding to different x values ​​to obtain data set 4, where Pb = 300 MPa and Pa = 350 MPa. These x values ​​are shown in [reference needed]. Figure 1 Then, based on data set 4, fit curve 4 (see...). Figure 1 ).

[0098] As can be seen from Table 1, in the curve group consisting of curves 1 to 4, the largest y-value (the y-value corresponding to the vertex of curve 2) is approximately 6% (i.e., Max = 6%), and the smallest y-value (the y-value corresponding to the lowest point of curve 4) is approximately -4%.

[0099] In addition, from Figure 1 It can be seen that the cumulative particle size change after being pressed under different pressures is basically before 20μm (the range of x < 20μm in the horizontal axis), and the larger change occurs before 10μm.

[0100] In addition, SEM analysis was performed on the above-mentioned cathode material, as well as the cathode material after being pressed and crushed under different pressures. The results are shown in [Figure 1]. Figure 2 As can be seen, at 150 MPa, the larger secondary spheres (secondary particles) break into hemispheres. As the pressure increases, the secondary spheres break and the fine powder generated by the breakage increases. Furthermore, because these fine powders adhere to the secondary sphere particles under high pressure, they cannot be opened even under external ultrasonic treatment (i.e., ultrasonic treatment under the above conditions). Therefore, the particle size of the compressed particles may also show an increasing trend.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that the first sintering temperature is 860°C, while the other conditions are the same;

[0103] Refer to the gas production index in Example 1 The testing process used curves 1 to 4 fitted with the cathode material prepared in Comparative Example 1 are shown in the figure. Figure 3 As can be seen from Table 1, in the curve group consisting of curves 1 to 4, the largest y-value (the y-value corresponding to the vertex of curve 3) is approximately 20% (i.e., Max = 6%), and the smallest y-value (the y-value corresponding to the lowest point of curve 4) is approximately -18%.

[0104] Comparative Example 2

[0105] The difference from Example 1 is that the precursor Ni 0.8 Co 0.06 Mn 0.12 The particle size distribution (i.e., the value of D90-D10 / D50) of (OH)2 is 1.5 (the particle size distribution of the obtained cathode material is also basically 1.5); the temperature of the first sintering is 780℃; the other conditions are the same.

[0106] Comparative Example 3

[0107] The difference from Example 1 is that the sintering temperature is 780°C; the amount of boron-containing coating agent is different (so that the BET of the formed positive electrode material is 1.1 m2 / g), while the other conditions are the same.

[0108] Examples 2 to 15

[0109] Following the preparation process of Example 1, and using appropriate raw materials (such as aluminum borate as the coating agent used in Examples 7-11, and cerium hydroxide as the coating agent used in Examples 12-15) and conditions, a positive electrode material was prepared (its gas production index was tested). Curves 1 to 4 in the process are similar to those in Example 1, and will not be described again. The differences between Examples 2 to 15 and Example 1 are shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same.

[0110] The coating thickness in the cathode materials of Examples 1-15 and Comparative Examples 1-3 was less than 50 nm. The specific surface area (BET), particle size (D50), and particle size distribution (Span, i.e., (D90-D10) / D50) of the cathode materials of each example and comparative example were measured, and the D240 particle size distribution was analyzed by XRD. 104 Gas production index The results are summarized in Table 1.

[0111] In addition, pouch cells with graphite as the negative electrode were fabricated using the positive electrode materials of each embodiment and comparative example, and the full-electric performance of these cells was tested. The test conditions were as follows: the cells were stored at 70°C for 14 days, and their volume expansion rate (referred to as the thermal volume expansion rate at 70°C@14 days) was measured, as shown in Table 1.

[0112]

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized by, Satisfy 0≤ ≤0.3, The gas production index of the cathode material is represented by the cumulative particle size distribution change rate obtained after the cathode material is pressed under different pressures; =Max-Min; where Max is the curve formed by fitting n different particle sizes x corresponding to the volume percentage change rate y, in the particle size interval x∈(0, 30) The maximum volume percentage change rate y within; n≥4; Min refers to the particle size interval x∈(0, 30) The minimum volume percentage change rate y value; n curves are formed by determining n pressure combinations, calculating the y value corresponding to different x for each pressure combination, and then fitting the curves; where each pressure combination includes Pb and Pa, satisfying 20MPa≤Pa−Pb≤60MPa, 0<Pa≤400MPa, 0<Pb≤400MPa.

2. The positive electrode material of claim 1, wherein, The cathode material includes a core and a coating layer present on the surface of the core.

3. The positive electrode material according to claim 2, characterized in that, The core is Li (1+a) Ni x Co y E w M z O2, where -0.02 ≤ a ≤ 0.06, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w < 0.2, E includes Mn or Al, M includes one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, and the coating layer includes a compound of one or more of Al, Ti, Na, Sr, Sb, Mg, Cr, Zr, Y, Ta, Zn, V, Mo, W, B, Cu, Li, F, P, Ce.

4. The cathode material of claim 1, wherein, The specific surface area BET of the cathode material satisfies: 0.3 m² 2 / g≤BET≤0.9m 2 / g.

5. The cathode material of claim 1, wherein, The particle size of the positive electrode material satisfies: 5μm≤D50≤15μm, and / or, 0.5≤(D90-D10) / D50≤1.

3.

6. The cathode material according to claim 1, characterized in that, The grain size in the direction of the crystal face perpendicular to the (104) diffraction peak in the X-ray diffraction analysis result of the positive electrode material is D 104 , 45nm≤D 104 ≤70nm.

7. A method for producing the positive electrode material as claimed in any one of claims 1 to 6, characterized by, include: Containing Ni and Co 、 The precursor of E, the lithium source, and the dopant containing M are mixed and sintered once. The resulting product is then mixed with a coating agent and sintered a second time to obtain the cathode material.

8. The method for preparing the cathode material according to claim 7, characterized in that, The temperature of the first sintering is 700~850℃; and / or, The temperature for the secondary sintering is 250~700℃.

9. The method for preparing the cathode material according to claim 7 or 8, characterized in that, The precursor comprises Ni x Co y E w (OH)2; and / or, The lithium source includes lithium hydroxide; and / or, The dopant includes one or more of the following: oxides, hydroxides, acids, sulfates, and acetates containing M; and / or, The coating agent includes one or more of oxides, hydroxides, acids, sulfates, and acetates.

10. A positive electrode sheet characterized by comprising: Includes the cathode material as described in any one of claims 1-6.

11. A battery, characterized by Includes the positive electrode sheet as described in claim 10.

12. The battery of claim 11, wherein, It also includes a negative electrode sheet, which includes a negative electrode active material, which includes graphite.

13. The battery according to claim 11 or 12, characterized in that, The battery includes a lithium secondary battery.

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