Positive electrode active material and preparation method therefor, positive electrode sheet, battery cell, battery, and electrical apparatus

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery cell, a battery, and an electrical apparatus, relating to the technical field of batteries. The positive electrode active material comprises: a positive electrode matrix material having a secondary particle morphology, the secondary particles being formed by agglomeration of a plurality of primary particles; and a coating layer, the coating layer being coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode matrix material, and the coating layer comprising LiaMbOC, where a>0, b>0, and c>0. The ionic radius R of the M element satisfies: 50 pm≤R≤120 pm. The positive electrode active material can improve the cycle performance of a battery cell.

Description

Positive electrode active material and preparation method thereof, positive electrode sheet, battery cell, battery, and electrical device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese patent application No. 202410166615.5 filed on February 5, 2024, entitled “Positive electrode active material and preparation method thereof, positive electrode sheet, battery cell, battery, and electrical device,” and the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery cell, a battery, and an electrical device. Background Art

[0003] With the increasing severity of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor in its development.

[0004] The development of battery technology requires consideration of multiple design factors, such as energy density, cycle life, and reliability. The design of the positive electrode active material in a battery cell is crucial to its performance. Therefore, how to provide a positive electrode active material that improves the cycle performance of the battery cell is a pressing technical issue. Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material to improve the cycle performance of a battery cell.

[0006] In order to achieve the above-mentioned objectives, the present application provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery cell, a battery, and an electrical device.

[0007] In a first aspect, a positive electrode active material is provided, comprising: a positive electrode matrix material having a secondary particle morphology, wherein the secondary particles are formed by agglomerating a plurality of primary particles; a coating layer, wherein the coating layer is coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode matrix material, wherein the coating layer comprises Li a M b O c , a>0, b>0, c>0, the ionic radius R of element M satisfies: 50pm≤R≤120pm.

[0008] An embodiment of the present application provides a positive electrode active material. The morphology of the positive electrode matrix material is secondary particles, and the secondary particles are formed by the aggregation of multiple primary particles. The positive electrode active material includes a positive electrode matrix material and a coating layer covering at least a part of the surface of at least a part of the primary particles of the positive electrode matrix material. The coating layer includes Li a M b O c , and the ionic radius R of the M element satisfies: 50 pm ≤ R ≤ 120 pm. The setting of the coating layer is beneficial to improving the bonding force between the primary particles of the positive electrode matrix material, reducing the risk of cracking of the positive electrode active material, and slowing down the side reaction between the positive electrode matrix material and the electrolyte, thereby improving the cycle performance of the battery cell.

[0009] In a possible implementation, 50 pm ≤ R ≤ 80 pm. The M element with the above ionic radius is convenient for partial embedding into the crystal lattice of the crystal grains, which is beneficial to improving the compressive strength of the positive electrode active material and the cycle performance of the battery cell.

[0010] In a possible implementation, the M element includes at least one of Al, Mg, Sr, Ti, Y, Zr, Nb, Mo, W, or Sb; optionally, the M element includes W or Al. The above M element has a relatively appropriate ionic radius, which is convenient for obtaining a positive electrode active material with high strength.

[0011] In a possible implementation, based on the total mass of the positive electrode active material, the mass content A of the M element in the coating layer satisfies: 0 < A ≤ 0.5 wt%; optionally, 0.25 wt% ≤ A ≤ 0.5 wt%. In this way, it is beneficial to have an appropriate amount of M element between the grain boundaries of the primary particles, which is beneficial to improving the bonding strength between the primary particles, reducing the risk of cracking of the positive electrode active material, and improving the cycle performance of the battery cell; and it can also reduce the adverse effect on the conductivity of the battery cell due to too high content of the M element.

[0012] In a possible implementation, the thickness d of the coating layer satisfies: 0 < d ≤ 20 nm; optionally, 2 nm ≤ d ≤ 9 nm. In this way, the coating layer has an appropriate thickness, which is beneficial to improving the cycle performance of the battery cell and can also reduce the adverse effect on the conductivity of the battery cell due to too thick coating layer.

[0013] In a possible implementation, the compressive strength E of the positive electrode active material satisfies: 85 MPa ≤ E ≤ 100 MPa; optionally, 90 MPa ≤ E ≤ 100 MPa. In this way, the positive electrode active material is not easily cracked, and the battery cell has high cycle stability.

[0014] In a possible implementation, among the secondary particles of the positive electrode matrix material, the number B of the primary particles of the positive electrode matrix material satisfies: 3 particles / μm 2 ≤B≤30 particles / μm 2 ; optionally, 3 particles / μm 2 ≤B≤15 particles / μm 2 .

[0015] By setting the number of primary particles of the positive electrode matrix material per unit area, the primary particles of the positive electrode matrix material have a more appropriate size, which is beneficial to taking into account the cycle performance and rate performance of the battery cell.

[0016] In a possible implementation, the volume average particle size Dv50 of the positive electrode active material satisfies: 3μm ≤ Dv50 ≤ 30μm; optionally, 3μm ≤ Dv50 ≤ 15μm. In this way, the risk of agglomeration of the positive electrode active material can be reduced, and the path length for active ions to escape from the positive electrode active material is more appropriate, so that the battery cell can have higher rate performance.

[0017] In a possible implementation, the tap density P of the positive electrode active material under a pressure of 4T satisfies: 3.0 g / cm 3 ≤P≤3.6 g / cm 3 . The positive electrode active material having a higher tap density is beneficial to improving the volume energy density of the battery cell.

[0018] In a possible implementation, the chemical formula of the positive electrode matrix material is Li d [Ni x Co y Mn z M 1 e O f , where M1 includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Ca, V, Ta or Sr, 0.5 < x < 1, 0 < y < 0.2, 0 ≤ z < 0.5, 0 ≤ e < 0.5, 0.8 < d < 1.2, 1.8 < f < 2.2. By using a ternary material as the positive electrode matrix material, it is beneficial to improve the energy density of the battery cell.

[0019] In a possible implementation, the material of the coating layer is amorphous. In this way, the atoms of the compounds in the coating layer are arranged in a disordered manner.

[0020] In the second aspect, a method for preparing the positive electrode active material in the first aspect and any possible implementation thereof is provided, comprising: adding a positive electrode base material and an additive to a solvent and mixing them to obtain an intermediate product, wherein the additive includes an M element; and sintering the intermediate product to obtain the positive electrode active material.

[0021] The positive electrode matrix material and the additive including the M element are added to the solvent, so that the additive and the positive electrode matrix material can be evenly mixed in the solvent, and the additive is facilitated to penetrate into the primary particles and the spaces between the primary particles of the positive electrode matrix material; the intermediate product is sintered to facilitate the reaction between the positive electrode matrix material (such as the residual alkali on the positive electrode matrix material) and the additive, thereby facilitating the formation of a coating layer between the primary particles and the primary particles of the positive electrode matrix material.

[0022] In one possible implementation, based on the total mass of the positive electrode matrix material and the additive, the mass content C of the additive satisfies the following range: 0.5 wt% ≤ C ≤ 2 wt%; alternatively, 1 wt% ≤ C ≤ 2 wt%. Selecting an additive with a mass content within the above range facilitates the formation of a coating layer with a suitable thickness.

[0023] In one possible implementation, the additive includes at least one of phosphotungstic acid, aluminum sulfate, sodium metaaluminate, niobium pentoxide, niobium oxalate, or strontium hydroxide. This facilitates the reaction of the additive with the positive electrode matrix material, thereby doping the primary particles of the positive electrode matrix material with the corresponding M element.

[0024] In one possible implementation, the solvent includes water. Thus, the additive can be dissolved in water to form a solution, facilitating the additive's infiltration into the spaces between the primary particles of the positive electrode matrix material. Furthermore, after obtaining the intermediate product, excess water can be easily removed by drying or other methods.

[0025] In a possible implementation, the temperature T of the sintering process satisfies: 600° C. ≤ T ≤ 800° C., and / or the time t of the sintering process satisfies: 8 h ≤ t ≤ 12 h.

[0026] By selecting the temperature and time of the sintering treatment, the additive and the positive electrode base material can fully react, and the coating layer can be formed.

[0027] In a third aspect, a positive electrode plate is provided, comprising the positive electrode active material of the first aspect and any possible implementation thereof, and / or the positive electrode active material prepared by the method of the second aspect and any possible implementation thereof.

[0028] In a fourth aspect, a battery cell is provided, comprising the positive electrode sheet described in the third aspect.

[0029] In a fifth aspect, a battery is provided, comprising the battery cell described in the fourth aspect.

[0030] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0032] FIG1 is a SEM image of a positive electrode active material according to an embodiment of the present application;

[0033] FIG2 is an enlarged schematic diagram of a portion of a positive electrode active material according to an embodiment of the present application;

[0034] FIG3 is an enlarged schematic diagram of a portion of a positive electrode active material according to an embodiment of the present application;

[0035] FIG4 is a schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application;

[0036] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0037] FIG6 is a schematic diagram of a battery according to an embodiment of the present application;

[0038] FIG. 7 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] The embodiments of the positive electrode active material and its preparation method, positive electrode sheet, battery cell, battery, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0040] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery, and the battery cell can be the smallest battery unit.

[0045] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, lithium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0046] It should be understood that the "embedding" process described in this application refers to the process in which lithium ions are embedded in the positive electrode active material and the negative electrode material due to electrochemical reactions, and the "extraction" and "deintercalation" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material and the negative electrode material due to electrochemical reactions.

[0047] The development of battery technology must simultaneously consider multiple design factors, such as energy density, cycle life, discharge capacity, charge and discharge rate, reliability, etc. The battery cell includes a positive electrode plate, and the performance of the positive electrode active material in the positive electrode plate is crucial to the capacity, cycle performance, and charge and discharge rate performance of the battery cell. For polycrystalline positive electrode active materials, the positive electrode active material is formed by a plurality of single crystal primary particles aggregated together to form secondary particles. During the charge and discharge process of the battery cell, primary particles are prone to cracking, which in turn leads to the intensification of the side reaction between the positive electrode active material and the electrolyte, and the cycle life of the battery cell is rapidly attenuated. Therefore, how to provide a positive electrode active material to enhance the bonding strength between primary particles, reduce the risk of secondary particles cracking, and thereby improve the cycle performance of the battery cell is a technical problem that needs to be solved urgently.

[0048] In view of this, the present invention provides a positive electrode active material, including a positive electrode matrix material having a secondary particle morphology, wherein the secondary particles are formed by agglomerating a plurality of primary particles, and a coating layer coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode matrix material, wherein the coating layer includes Li a M b O c , a>0, b>0, c>0, and the ionic radius R of the M element satisfies: 50pm≤R≤120pm. The M element can be partially embedded in the lattice of the primary particles of the positive electrode matrix material, while the remaining portion is located in the coating layer. This can enhance the bonding strength between the grain boundaries of the primary particles, thereby reducing the risk of secondary particle cracking and improving the cycling performance of the battery cell.

[0049] [Positive electrode active material]

[0050] The present application provides a positive electrode active material, comprising: a positive electrode base material having a secondary particle morphology, wherein the secondary particles are formed by agglomerating a plurality of primary particles; a coating layer, wherein the coating layer is coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode base material, and the coating layer comprises Li a M b Oc , a>0, b>0, c>0, the ionic radius R of element M satisfies: 50pm≤R≤120pm.

[0051] Figure 1 is an SEM image of the positive electrode active material of an embodiment of the present application, Figure 2 is an enlarged schematic diagram of a partial area of ​​the positive electrode active material of an embodiment of the present application, and Figure 3 is an enlarged schematic diagram of a partial area of ​​the positive electrode active material of an embodiment of the present application. In conjunction with Figure 1, Figure 1 shows a plurality of particles of positive electrode active materials. In conjunction with Figure 2, Figure 2 shows an SEM image of a particle of positive electrode active material. It can be seen in Figure 2 that the particle is a secondary particle, and a secondary particle includes a plurality of primary particles. In conjunction with Figure 3, the primary particles are separated by grain boundaries, and the grain boundaries are enriched with M elements.

[0052] The morphology of the positive electrode base material is secondary particles, which may mean that the positive electrode base material is a polycrystalline material, that is, the positive electrode base material includes a plurality of single crystals.

[0053] Secondary particles are formed by agglomeration of multiple primary particles. For example, secondary particles are generally formed by agglomeration of 10 or more primary particles.

[0054] Primary particles may refer to single crystal grains, that is, primary particles are single crystals. Primary particles may refer to unagglomerated particles.

[0055] The positive electrode matrix material 10 can be a layered transition metal oxide, such as a ternary material or a lithium-rich manganese-based material. During the charge and discharge process of the battery cell, the active lithium ions in the positive electrode matrix material 10 can be released from or embedded in the positive electrode matrix material 10. In other words, the positive electrode matrix material 10 can be a material that provides active lithium ions.

[0056] The coating layer coats at least a portion of the surface of at least a portion of the primary particles of the positive electrode base material. That is, the coating layer may coat a portion of the primary particles in a secondary particle of the positive electrode base material, or may coat all the primary particles in a secondary particle of the positive electrode base material. The coating layer may coat the entire surface of a primary particle, or may coat a portion of the surface of a primary particle. As an example, the coating layer coats the entire surface of at least a portion of the primary particles of the positive electrode base material.

[0057] The surface of the primary particle can be the grain boundary of a single grain of the primary particle. The coating layer is arranged at the grain boundary of the grain, and a coating layer is provided between adjacent grains. The coating layer includes an M element, and the ionic radius R of the M element satisfies: 50pm≤R≤120pm. In this way, the M element can be partially embedded in the lattice of the primary particle of the positive electrode matrix material and partially located at the grain boundary, thereby increasing the bonding strength between the grain boundaries through the M element, reducing the risk of cracking of the positive electrode active material (or secondary particles) along the grain boundary.

[0058] R can be 50 pm, 62 pm, 80 pm, 113 pm, or any value within the above range. When R is greater than or equal to 50 pm, the risk of M element dissolving from the lattice of the positive electrode matrix material and the risk of M element not being able to locate at the grain boundary can be reduced; when R is less than or equal to 120 pm, the steric hindrance effect can be reduced, which is conducive to partially doping M element into the lattice of the positive electrode matrix material, thereby facilitating the improvement of the bonding strength between primary particles.

[0059] The coating layer includes Li a M b O c , a>0, b>0, c>0. Among them, Li a M b O c is an oxide comprising Li and M. The specific values ​​of a, b, and c are not specifically limited. a M b O c The coating layer can be a compound formed by an additive including the element M and residual lithium on the surface of the primary particles of the positive electrode matrix material. This chemical bond connects the element M to the element Li, thereby enhancing the bond strength between the grain boundaries of the primary particles and reducing the risk of cracking in the positive electrode active material. Furthermore, the coating layer isolates the primary particles of the positive electrode matrix material from the electrolyte, reducing the risk of reaction between the positive electrode matrix material and the electrolyte, thereby reducing the risk of electrolyte oxidation and gassing in the battery cells.

[0060] The present invention provides a positive electrode active material, wherein the morphology of the positive electrode base material is secondary particles, and the secondary particles are formed by agglomeration of multiple primary particles. The positive electrode active material includes a positive electrode base material and a coating layer coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode base material, and the coating layer includes Li a M b O c, the ionic radius R of the M element satisfies: 50 pm ≤ R ≤ 120 pm. The setting of the coating layer is beneficial to improving the bonding force between the primary particle cathode matrix material and the primary particle cathode matrix material, beneficial to reducing the risk of cracking of the cathode active material, and slowing down the side reaction between the cathode matrix material and the electrolyte, thereby being beneficial to improving the cycling performance of the battery cell.

[0061] In some embodiments, 50 pm ≤ R ≤ 80 pm. The M element satisfying the above ionic radius is more convenient for partially embedding into the lattice of the crystal grains, so as to obtain a cathode active material with a relatively large compressive strength.

[0062] In some embodiments, the M element includes at least one of Al, Mg, Sr, Ti, Y, Zr, Nb, Mo, W or Sb.

[0063] The ionic radius of the above M element satisfies the range of 50 pm to 120 pm. By selecting the above M element, it is beneficial to obtain a cathode active material with a relatively high compressive strength.

[0064] Optionally, the M element includes W or Al. The ionic radius of the above M element is relatively small, which is more convenient for partial doping of the M element into the lattice of the primary particles of the cathode matrix material, and partial doping is between the primary particles and the grain boundaries of the primary particles.

[0065] In some embodiments, based on the total mass of the cathode active material, the mass content A of the M element in the coating layer satisfies: 0 < A ≤ 0.5 wt%; optionally, 0.25 wt% ≤ A ≤ 0.5 wt%.

[0066] A can be 0.005 wt%, 0.01 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.5 wt% or any value within the above range.

[0067] In this embodiment, 0 < A ≤ 0.5 wt% is beneficial to having an appropriate amount of the M element between the primary particles and the grain boundaries of the primary particles, which is beneficial to enhancing the bonding strength between the primary particles, reducing the risk of cracking of the secondary particles of the cathode active material, and enhancing the cycling performance of the battery cell; and can also reduce the adverse effect on the conductivity of the battery cell due to too high content of the M element (for example, it can reduce the risk of capacity deterioration of the battery cell).

[0068] In some embodiments, the thickness d of the coating layer satisfies: 0 < d ≤ 20 nm; optionally, 2 nm ≤ d ≤ 9 nm.

[0069] The thickness of the coating layer can be the average thickness of the coating layer. For example, the thickness of the coating layer at multiple positions is measured, and the average value of multiple measurement data is taken as the thickness d.

[0070] d can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, 15 nm, 18 nm, 20 nm or any value within the above range.

[0071] In this embodiment, 0 < d ≤ 20 nm, and the coating layer has an appropriate thickness, which is beneficial to improving the cycling performance of the battery cell and can also reduce the adverse effect on the electrical conductivity of the battery cell caused by the excessive thickness of the coating layer.

[0072] In some embodiments, 2 nm ≤ d ≤ 9 nm. In this way, the battery cell can not only have a high capacity retention rate but also reduce the risk of capacity deterioration.

[0073] In some embodiments, in the secondary particles of the positive electrode matrix material, the number B of the primary particles of the positive electrode matrix material satisfies: 3 particles / μm 2 ≤ B ≤ 30 particles / μm 2 ; optionally, 3 particles / μm 2 ≤ B ≤ 15 particles / μm 2 .

[0074] B can reflect the number of primary particles within a certain area inside a single secondary particle.

[0075] When B is greater than or equal to 3 particles / μm 2 , the risk that the number of primary particles of the positive electrode matrix material per unit area is small and the crystal grains of the primary particles are large can be reduced. Thus, the active lithium ions have a relatively appropriate path length when escaping from the primary particles, and the adverse effects on the capacity performance and rate performance of the battery cell caused by too long escape paths can be reduced; when B is less than or equal to 30 particles / μm 2 , the risk that the number of primary particles of the positive electrode matrix material per unit area is large and the crystal grains of the primary particles are small can be reduced, which is beneficial to improving the cycling stability of the battery cell.

[0076] By setting 3 particles / μm 2 ≤ B ≤ 30 particles / μm 2 , the primary particles of the positive electrode matrix material have a relatively appropriate size, which is beneficial to taking into account the cycling stability and rate performance of the battery cell.

[0077] In some embodiments, the particle size of the primary particles of the positive electrode matrix material is 0.1 μm to 1 μm. The particle size of the primary particles can be measured according to the photos taken by SEM.

[0078] In some embodiments, the volume average particle size Dv50 of the positive electrode active material satisfies: 3 μm ≤ Dv50 ≤ 30 μm; optionally, 3 μm ≤ Dv50 ≤ 15 μm.

[0079] Dv50 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 50%, or it can refer to the particle size smaller than it accounting for 50%.

[0080] When Dv50 is greater than or equal to 3μm, the risk of agglomeration of multiple particles due to the small particle size of the positive electrode active material can be reduced; when Dv50 is less than or equal to 30μm, the risk of a long path length for active lithium ions to escape from the particles due to the large particle size can be reduced, which is beneficial to the capacity of the battery cell and improves the rate performance of the battery cell.

[0081] By setting 3μm≤Dv50≤30μm, the particles of the positive electrode active material have a suitable particle size, which is beneficial to improving the rate performance of the battery cell.

[0082] In the case of 3 μm ≤ Dv50 ≤ 15 μm, the positive electrode active material has greater compressive strength.

[0083] In some embodiments, the compaction density P of the positive electrode active material at a pressure of 4T satisfies: 3.0 g / cm 3 ≤P≤3.6g / cm 3 The positive electrode active material has a high compaction density, which is beneficial to improving the volume energy density of the battery cell.

[0084] The compacted density P refers to the compacted density of the powder of the positive electrode active material under a pressure of 4T (4 tons).

[0085] Compared to single-crystal cathode active materials, polycrystalline cathode active materials can have a higher compaction density, which helps improve the volumetric energy density of battery cells. In addition, compared to single-crystal cathode active materials, the use of polycrystalline cathode active materials can also help improve the power performance and rate performance of battery cells.

[0086] In some embodiments, the positive electrode active material is suitable for battery cells with relatively high operating voltages, for example, battery cells with operating voltages greater than or equal to 4.3 V. Under high voltage conditions, due to the high bonding strength between the primary particles of the positive electrode matrix material and the grain boundaries between the primary particles, the positive electrode active material has high strength and is less likely to crack along the grain boundaries. This reduces the risk of cracking and pulverization of the positive electrode active material, and the battery cell can have high cycling stability.

[0087] In some embodiments, the material of the coating layer is amorphous. As an example, Li a M b O c It is amorphous. Li in the coating layer a M b O cIt is amorphous, and the bonding strength between the grain boundaries of the primary particles is relatively high.

[0088] The amorphous state can refer to the compound Li a M b O c without a specific crystalline form. Under a transmission electron microscope, the atoms in the compound Li a M b O c are arranged in a disordered state.

[0089] In some embodiments, 0.5 ≤ a ≤ 3, 1 ≤ b ≤ 3, 1 ≤ c ≤ 5. For example, a is 0.5, 1, 2, 3 or any value within the above range, b is 1, 2, 3 or any value within the above range, and c is 1, 3, 5 or any value within the above range.

[0090] In some embodiments, the Li in the compound Li a M b O c is in a lithium-deficient state. For example, when the M element is the Zr element, the molar content of the Li element is less than the molar content of the Li element in lithium zirconate.

[0091] In some embodiments, the chemical formula of the positive electrode matrix material is Li d [Ni x Co y Mn z M 1 e O f , where M 1 includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Ca, V, Ta or Sr, 0.5 < x < 1, 0 < y < 0.2, 0 ≤ z < 0.5, 0 ≤ e < 0.5, 0.8 < d < 1.2, 1.8 < f < 2.2. By selecting a ternary material as the positive electrode matrix material, it is beneficial to improve the energy density of the battery cell.

[0092] In some embodiments, the positive electrode matrix material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0093] It should be noted that the battery cell will be accompanied by the deintercalation and consumption of Li during the charge and discharge process. The molar content of Li is different when the battery is discharged to different states. The above definition of d includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V). In the enumeration of positive electrode matrix materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode matrix material is applied to the battery system, and the molar content of Li will change after the charge and discharge cycle. In the enumeration of positive electrode matrix materials in this application, the molar content of O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0094] In some embodiments, the compressive strength E of the positive electrode active material satisfies: 85 MPa≤E≤100 MPa. In this way, the positive electrode active material is not easily cracked, and the battery cell has high cycle stability.

[0095] E can be 85 MPa, 90 MPa, 95 MPa, 100 MPa or any value within the above range.

[0096] The compressive strength E of the positive electrode active material may be the strength of the powder of the positive electrode active material.

[0097] In some embodiments, 90 MPa≤E≤100 MPa. In this way, the positive electrode active material can have a higher compressive strength, so that the battery cell has a higher cycle stability; at the same time, it is also beneficial for the battery cell to maintain a higher capacity.

[0098] In some embodiments, the surface of the positive electrode active material is further provided with a coating layer, the coating layer including Li a M b O c , a>0, b>0, c>0, the ionic radius R of element M satisfies: 50pm≤R≤120pm.

[0099] [Method for preparing positive electrode active material]

[0100] FIG4 is a schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application. For example, as shown in FIG4 , a method 100 for preparing a positive electrode active material includes the following steps.

[0101] Step 110 : adding the positive electrode base material and the additive into the solvent and mixing them to obtain an intermediate product, wherein the additive includes the M element.

[0102] The positive electrode matrix material can be a layered lithium-containing transition metal oxide, such as a ternary material. Before preparing the positive electrode active material, the positive electrode matrix material is a polycrystalline material formed by multiple single crystals.

[0103] As an example, the positive electrode base material and the additive including the M element are added to a solvent and stirred to mix uniformly, so that the additive can penetrate into the positive electrode base material (for example, into the primary particles and the grain boundaries of the primary particles), and then filtered and dried to obtain an intermediate product. The intermediate product can be a mixture of the positive electrode base material and the additive.

[0104] Step 120 , sintering the intermediate product to obtain a positive electrode active material.

[0105] Due to the influence of the preparation process of the positive electrode matrix material, there are residual alkalis on the surface of the primary particles of the positive electrode matrix material, such as lithium hydroxide and lithium carbonate. As an example, during the sintering process, the additive including the M element can react with the residual alkali, thereby generating Li-ion batteries at the grain boundaries between the primary particles. a M b O c The coating layer. Because the M element reacts with the residual alkali on the surface of the primary particles of the positive electrode matrix material, the M element and the Li element in the residual alkali are chemically bonded, resulting in a strong bond between the coating layer and the primary particles at the grain boundaries, thereby increasing the bond strength between the grain boundaries. Furthermore, the ionic radius of the M element falls within a suitable range, and some of the M element even enters the crystal lattice of the primary particles, resulting in a high bond strength between the grain boundaries.

[0106] In preparation method 100, a positive electrode matrix material and an additive including an M element are added to a solvent, thereby uniformly mixing the additive and the positive electrode matrix material in the solvent and facilitating the infiltration of the additive into the spaces between the primary particles of the positive electrode matrix material. The intermediate product is then sintered to facilitate the reaction between the positive electrode matrix material (e.g., residual alkali on the positive electrode matrix material) and the additive, thereby facilitating the formation of a coating layer between the primary particles of the positive electrode matrix material. The positive electrode active material prepared by the above method has high strength, reduces the risk of cracking of the positive electrode active material during the charge and discharge cycles of the battery cell, and provides high cycle stability for the battery cell.

[0107] In some embodiments, based on the total mass of the positive electrode matrix material and the additive, the mass content C of the additive satisfies: 0.5 wt % ≤ C ≤ 2 wt %; alternatively, 1 wt % ≤ C ≤ 2 wt %.

[0108] C can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt% or any value within the above range.

[0109] By selecting additives whose mass content meets the above range, it is easy to form a coating layer with a suitable thickness.

[0110] In some embodiments, the additive includes at least one of phosphotungstic acid, sodium aluminum sulfate metaaluminate, niobium pentoxide, niobium oxalate, or strontium hydroxide. This facilitates the reaction of the additive with the positive electrode matrix material, thereby doping the primary particles of the positive electrode matrix material with the corresponding M element.

[0111] In some embodiments, the solvent includes water. This allows the additive to dissolve in water to form a solution, facilitating the additive's infiltration into the spaces between the primary particles of the positive electrode matrix material. Furthermore, after obtaining the intermediate product, excess water can be easily removed by drying or other methods.

[0112] In some embodiments, the temperature T of the sintering process satisfies: 600° C. ≤ T ≤ 800° C.; and / or the time t of the sintering process satisfies: 8 h ≤ t ≤ 12 h.

[0113] T may be 600°C, 700°C, 800°C, or any value within the above range.

[0114] t can be 8h, 10h, 12h or any value within the above range.

[0115] By selecting the temperature and time of the sintering treatment, the additive and the positive electrode base material can fully react, and the coating layer can be formed.

[0116] In some embodiments, before step 110, the preparation method 100 further includes: preparing a positive electrode matrix material. As an example, the precursor of the positive electrode matrix material (for example, (Ni 0.6 Co 0.2 Mn 0.2 )OH2) and LiOH·H2O were mixed in a mixer at a molar ratio of 1.00:1.05, and then sintered at 830° C. in an oxygen atmosphere to obtain a positive electrode matrix material.

[0117] [Positive electrode]

[0118] An embodiment of the present application provides a positive electrode plate, comprising the positive electrode active material of any of the above embodiments, and / or the positive electrode active material prepared by the preparation method of any of the above embodiments.

[0119] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0120] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector may be an aluminum foil.

[0121] The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. 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 substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] The positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0123] The positive electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] [Negative electrode]

[0125] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0126] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0127] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be a negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0128] The negative electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] [Electrolytes]

[0130] The electrolyte conducts ions between the positive and negative electrodes. The present invention does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0131] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0132] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0133] The solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0134] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high or low temperature performance, etc.

[0135] [Isolator]

[0136] The separator is used to separate the positive electrode sheet from the negative electrode sheet. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical and mechanical stability can be selected.

[0137] The separator can be made of at least one of fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. In the case of a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0139] [Battery Cell]

[0140] An embodiment of the present application provides a battery cell, comprising the positive electrode sheet in the above embodiment.

[0141] The embodiment of the present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. The battery cell can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, or the like.

[0142] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application. As shown in FIG5 , the battery cell 3 includes a housing 31 , an end cap assembly 32 , and an electrode assembly 33 . The electrode assembly 33 is disposed in the housing 31 , and the end cap assembly 32 is used to cover the housing 31 .

[0143] The end cap assembly 32 includes an electrode terminal 322 . For example, as shown in FIG. 5 , the end cap assembly 32 includes two electrode terminals 322 , one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0144] The electrode assembly 33 includes an electrode assembly body 331 and a tab 332 extending from the electrode assembly body 331 . The electrode assembly 33 can be made of a positive electrode sheet, a negative electrode sheet, and a separator through a winding process or a lamination process.

[0145] The battery cell 3 further includes a current collecting member 34, which is used to connect the tab 332 of the electrode assembly 33 and the electrode terminal 322. For example, as shown in FIG5 , the battery cell 3 includes two current collecting members 34, one current collecting member 34 for connecting the positive electrode tab and the positive electrode terminal, and the other current collecting member 34 for connecting the negative electrode tab and the negative electrode terminal.

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

[0147] [Battery]

[0148] The present invention provides a battery comprising the battery cells of the above-mentioned embodiment. FIG6 is a schematic diagram of a battery according to an embodiment of the present invention. As shown in FIG6 , the battery 5 may comprise a plurality of battery cells (not shown in the figure).

[0149] The battery cells 3 can be directly assembled into the battery 5 , or they can be assembled into battery modules first, and then multiple battery modules can be assembled into the battery 5 .

[0150] [Electrical devices]

[0151] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0152] Figure 7 is a schematic diagram of an electric device according to an embodiment of the present application. As shown in Figure 7 , the present application provides an electric device 6 including the battery according to the above embodiment.

[0153] Optionally, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., and the embodiments of the present application include but are not limited to the above.

[0154] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0155] [Example]

[0156] Example 1

[0157] The positive electrode active material in Example 1 was prepared by the following steps.

[0158] (1) Preparation of positive electrode matrix material

[0159] The positive electrode matrix material precursor (Ni 0.8 Co 0.1 Mn 0.1 )OH2 and LiOH·H2O were mixed in a mixer at a molar ratio of 1.00:1.05, and then sintered at 800° C. in an oxygen atmosphere to obtain a positive electrode matrix material.

[0160] (2) Preparation of positive electrode active materials

[0161] The positive electrode matrix material LiNi 0.8 Co 0.1 Mn 0.1 O2 and an additive (sodium aluminate) are added to water in a mass ratio of 99:1 and stirred. After mixing evenly, the intermediate product is obtained by centrifugation, filtration, and drying. The intermediate product is sintered at a temperature T of 700°C and a time t of 10 hours to obtain a positive electrode active material.

[0162] In Example 1, the positive electrode matrix material is LiNi 0.8 Co 0.1 Mn 0.1 O2, the coating layer includes Li a Al b O c The ionic radius of Al is 50 μm, the thickness d of the coating layer is 2 nm, and the mass content A of the Al element is 0.05 wt% based on the total mass of the positive electrode active material. The number of primary particles per unit area B is 10 / μm 2 The volume average particle size Dv50 of the positive electrode active material is 10 μm and the compressive strength E of the positive electrode active material is 90 MPa.

[0163] Examples 2-5

[0164] The difference between Examples 2-5 and Example 1 is that the mass content of the Al element is different.

[0165] Accordingly, different mass contents A may be related to the added amounts of the additives.

[0166] Examples 6-8

[0167] The difference between Examples 6-8 and Example 1 is that the additives are different.

[0168] In Example 6, the additive is phosphotungstic acid, which includes the element W, and the W ion radius is 62 μm. In Example 7, the additive is niobium pentoxide, which includes the element Nb, and the Nb ion radius is 70 μm. In Example 8, the additive is strontium hydroxide, which includes the element Sr, and the Sr ion radius is 113 μm. Furthermore, the mass contents of the additives in Examples 6-8 differ from those in Example 1.

[0169] Examples 9-11

[0170] The difference between Examples 9-11 and Example 3 is that the volume average particle size Dv50 of the positive electrode active material is different.

[0171] Examples 12-14

[0172] The difference between Examples 12-14 and Example 3 is that the number B of primary particles of the positive electrode base material per unit area is different.

[0173] Example 15

[0174] The difference between Example 15 and Example 3 is that the positive electrode matrix material is different. The positive electrode matrix material is LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0175] Comparative Example 1

[0176] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material in Comparative Example 1 is a positive electrode matrix material and does not include a coating layer.

[0177] In Comparative Example 1, after the positive electrode base material was prepared, no additional treatment was performed on the positive electrode base material.

[0178] Comparative Example 2

[0179] The difference between Comparative Example 2 and Example 1 is that in step (2) of preparing the positive electrode active material in Comparative Example 2, rubidium hydroxide is added. In the prepared positive electrode active material, the element doped at the grain boundaries of the primary particles is rubidium, and the ionic radius of rubidium is 148 μm.

[0180] Comparative Example 3

[0181] The difference between Comparative Example 3 and Example 1 is that in step (2) of preparing the positive electrode active material in Comparative Example 3, the added substance is boric acid, and the ion radius of B is 20 μm.

[0182] Table 1 Preparation method parameters of Examples and Comparative Examples

[0183] Table 2 Parameters of positive electrode active materials of Examples and Comparative Examples

[0184] Table 3 Performance test results of battery cells of the embodiment and comparative example

[0185] [Preparation of battery cells]

[0186] Preparation of positive electrode sheets: The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent (carbon black) are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5, stirred for 2 hours, and then stirred in a homogenizer at a speed of 1200r / min until uniformly mixed, and then evenly coated on both sides of a 13-micron thick aluminum foil current collector. After coating, it is dried in a drying oven at 120°C, cold pressed, and cut to obtain positive electrode sheets.

[0187] Preparation of negative electrode sheets: Mix the negative electrode active materials graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and acetylene black in a mass ratio of 96:1:1:2, add deionized water, and stir evenly in a blender. Then, coat the slurry on both sides of an 8-micron-thick copper foil, dry it in an oven at 120°C, cold press it, and cut it into pieces to obtain negative electrode sheets.

[0188] Preparation of the electrolyte: Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:2 to obtain a mixed solvent. Then, in an argon atmosphere glove box, thoroughly dried lithium hexafluorophosphate was dissolved in the mixed solvent and mixed thoroughly to obtain an electrolyte. The lithium salt concentration in the electrolyte was 1 mol / L.

[0189] Preparation of lithium-ion battery cells: The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly, wherein the positive electrode sheet and the negative electrode sheet do not contact each other; the electrode assembly is placed in a square aluminum shell, and electrolyte is added. After standing and forming processes, a lithium-ion battery cell is obtained.

[0190] It should be noted that the mass content of the M element in the coating layer of the positive electrode active material, the volume average particle size of the positive electrode active material, the cycle performance of the battery cell, etc. in the embodiments of the present application are common knowledge in the art, have meanings known in the art, and can be measured by test methods and instruments known in the art.

[0191] [Testing of the coating]

[0192] By using a transmission electron microscope (TEM) to analyze and test the positive electrode active material, the coating layer at the grain boundary can be observed. The thickness of the coating layer at multiple locations can be averaged to obtain the thickness d of the coating layer. The element surface distribution can be observed and determined by EDS, and the mass percentage of the element can be determined by ICP testing. After determining the elements in the coating layer, the ionic radius of the element can be determined based on the specific element (for example, the ionic radius of the element can be determined by the periodic table).

[0193] [Volume average particle size test]

[0194] The volume average particle size of the material can be measured with reference to GB / T19077-2016 / ISO 13320:2009 using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer.

[0195] As an example, take an appropriate amount of the sample to be tested (ensure the sample concentration is 8% to 12% shading), add 20 mL of anhydrous ethanol, and sonicate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO13320:2009. To prevent agglomeration during the drying process from affecting the particle size test, take a washed, wet sample for dispersion testing.

[0196] [Test of the strength of the positive electrode active material]

[0197] The particle strength of the positive electrode active material can be measured using a dynamic ultramicrohardness tester (Shimadzu DUH-211S). The particle strength of the material is tested under a 115° triangular pyramid probe and a pressure of 0-20mN. The force and pressure when the material breaks are recorded to obtain the compressive strength of the positive electrode active material.

[0198] [Cycle performance test of lithium-ion battery cells]

[0199] Perform charge and discharge tests on the battery at 25°C, using a constant current rate of 1C for each cycle. The first cycle is designated as C0, and the nth cycle is designated as Cn. The capacity retention rate for each cycle is Cn / C0 × 100%. Repeat the previous process for 1000 cycles. Record the capacity retention rate after 1000 cycles.

[0200] As an example, in this cycle performance test, the battery capacity is 0.15mAh, and it is charged to 4.25V at a constant current rate of 1C (i.e., 0.15mA), and then discharged to 2.80V at a constant current of 0.15mA, and the discharge capacity is recorded each time.

[0201] [Storage gas generation performance test of lithium-ion battery cells]

[0202] At 25°C, first charge the lithium-ion battery cell to 4.25V at a constant current of 1 / 3C, then charge it at a constant voltage with a current of 0.05C to 4.25V. The volume of the lithium-ion battery cell is measured in deionized water using the drainage method, and is V0.

[0203] The lithium-ion battery was stored at 70°C for 40 days, and the volume after 40 days was measured and recorded as Vn.

[0204] The volume expansion ratio (%) of a lithium-ion battery cell after storage at 70° C. is (Vn-V0) / V0×100%.

[0205] In combination with Examples 1-15 and Comparative Example 1, a coating layer is provided on the surface of the primary particles of the positive electrode matrix material, and the coating layer includes Li a M b O c The setting of the coating layer is beneficial to enhancing the bonding force between the primary particles and the grain boundaries of the primary particles. The strength of the secondary particles of the positive electrode active material is higher, the risk of cracking of the secondary particles of the positive electrode active material along the grain boundaries is reduced, and the battery cell has a higher capacity retention rate. The setting of the coating layer can also reduce the risk of side reactions between the positive electrode matrix material and the electrolyte, and reduce the gas production and volume expansion rate of the battery cell at high temperature.

[0206] As shown in Examples 1-15 and Comparative Example 2, when the ionic radius of the M element exceeds 120 pm, it is difficult for the M element to enter the lattice of the primary particles, the strength improvement of the secondary particles is limited, the capacity retention rate of the battery cell is low, and the gas production and volume expansion rate are large.

[0207] As shown in Examples 1-15 and Comparative Example 3, when the ionic radius of the M element is less than 50 pm, the M element is easily dissolved from the positive electrode active material and is difficult to be enriched at the grain boundaries. The improvement in the strength of the secondary particles is limited, the capacity retention rate of the battery cell is low, and the gas production and volume expansion rate are large.

[0208] As shown in Examples 1-5, by setting the mass content C of the additive including the M element to 0.2wt% to 2wt%, a coating layer with a thickness of 2nm to 18nm can be obtained, and the mass content A of the M element in the coating layer is 0.05wt% to 0.5wt%, and the battery cell has a high capacity retention rate and a low volume expansion rate. As shown in Examples 1-5, increasing the mass content of the M element in the coating layer is beneficial to improving the capacity retention rate of the battery cell and reducing the gas production of the battery cell; in addition, setting the mass content A of the M element in the coating layer to 0.05wt% to 0.5wt% is beneficial to reducing the risk of capacity deterioration of the battery cell.

[0209] As shown in Examples 6-8, the additives can be a variety of substances, and in the prepared coating layer, the ion radius of the M element is in the range of 50 pm to 120 pm, and the battery cell has a higher capacity retention rate and a lower volume expansion rate.

[0210] As shown in Examples 9-11, when the volume average particle size Dv50 of the secondary particles of the positive electrode active material meets the range of 3μm to 20μm, the battery cell has a higher capacity retention rate; when the volume average particle size Dv50 of the secondary particles of the positive electrode active material is between 3μm and 15μm, the capacity retention rate of the battery cell can be further improved.

[0211] Combined with the results of Examples 12-14, the number of primary particles meets the requirement of 3 particles / μm. 2 ~30 / μm 2 In this case, the battery cell has a higher capacity retention rate; further, the number of primary particles meets 3 / μm 2 ~15 / μm 2 Under the condition of , the capacity retention rate of the battery cell is further improved.

[0212] As shown in Example 15, the positive electrode active material is suitable for a variety of different positive electrode matrix materials.

[0213] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that include: A positive electrode matrix material having a secondary particle morphology, wherein the secondary particles are formed by agglomeration of multiple primary particles; The coating layer is coated on at least a portion of the surface of at least a portion of the primary particles of the positive electrode base material, and the coating layer includes Li a M b O c , a>0, b>0, c>0, the ionic radius R of element M satisfies: 50pm≤R≤120pm.

2. The positive electrode active material according to claim 1, characterized in that 50pm≤R≤80pm.

3. The positive electrode active material according to claim 1 or 2, characterized in that The M element includes at least one of Al, Mg, Sr, Ti, Y, Zr, Nb, Mo, W or Sb.

4. The positive electrode active material according to claim 3, characterized in that The M element includes W or Al.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that Based on the total mass of the positive electrode active material, the mass content A of the M element satisfies: <A≤0.5wt%。 6. The positive electrode active material according to claim 5, characterized in that 0.25wt%≤A≤0.5wt%.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The thickness d of the coating layer satisfies: <d≤20nm。 8. The positive electrode active material according to claim 7, characterized in that 2nm≤d≤9nm.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that The compressive strength E of the positive electrode active material satisfies: 85 MPa≤E≤100 MPa.

10. The positive electrode active material according to claim 9, characterized in that 90MPa≤E≤100MPa.

11. The positive electrode active material according to any one of claims 1 to 10, characterized in that In the secondary particles of the positive electrode base material, the number B of the primary particles of the positive electrode base material satisfies: 3 particles / μm 2 ≤B≤30 / μm 2 .

12. The positive electrode active material according to claim 11, characterized in that 3 pieces / μm 2 ≤B≤15 pieces / μm 2 .

13. The positive electrode active material according to any one of claims 1 to 12, characterized in that The volume average particle size Dv50 of the positive electrode active material satisfies: 3 μm≤Dv50≤30 μm.

14. The positive electrode active material according to claim 13, characterized in that 3μm≤Dv50≤15μm.

15. The positive electrode active material according to any one of claims 1 to 14, characterized in that The compaction density P of the positive electrode active material under a pressure of 4T satisfies: 3.0 g / cm 3 ≤P≤3.6g / cm 3 .

16. The positive electrode active material according to any one of claims 1 to 15, characterized in that The chemical formula of the positive electrode matrix material is Li d [Ni x Co y Mn z M 1 e ]O f , where M 1 Including at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Ca, V, Ta or Sr, 0.5 <x<1,0<y<0.2,0≤z<0.5,0≤e<0.5,0.8<d<1.2,1.8<f<2.2。 17. The positive electrode active material according to any one of claims 1 to 16, characterized in that The material of the coating layer is amorphous.

18. A method for preparing the positive electrode active material according to any one of claims 1 to 17, characterized in that: include: Adding a positive electrode base material and an additive to a solvent and mixing them to obtain an intermediate product, wherein the additive includes an M element; The intermediate product is sintered to obtain the positive electrode active material.

19. The method according to claim 18, characterized in that Based on the total mass of the positive electrode base material and the additive, the mass content C of the additive satisfies: 0.5 wt % ≤ C ≤ 2 wt %.

20. The method according to claim 19, characterized in that 1wt%≤C≤2wt%.

21. The method according to any one of claims 18 to 20, characterized in that The additive includes at least one of phosphotungstic acid, aluminum sulfate, sodium metaaluminate, niobium pentoxide, niobium oxalate or strontium hydroxide.

22. The method according to any one of claims 18 to 21, characterized in that The solvent includes water.

23. The method according to any one of claims 18 to 22, characterized in that The temperature T of the sintering treatment satisfies: 600° C. ≤ T ≤ 800° C., and / or the time t of the sintering treatment satisfies: 8 h ≤ t ≤ 12 h.

24. A positive electrode plate, characterized in that: The method comprises the positive electrode active material according to any one of claims 1 to 17, and / or the positive electrode active material prepared by the method according to any one of claims 18 to 23.

25. A battery cell, characterized in that: Comprising the positive electrode sheet as described in claim 24.

26. A battery, characterized in that: Comprising the battery cell as claimed in claim 25.

27. An electrical device, characterized in that: Comprising the battery of claim 26.

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