Composite positive electrode material, positive electrode sheet, secondary battery and electronic device

Abstract

An embodiment of the present application provides a composite cathode material, which includes a core containing a cathode active material and a coating layer coated on its surface. The coating layer contains Li x A y MO z material, A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and at least contains at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and at least contains at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, and W; 0 ≤ x ≤ 2, 0

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of secondary batteries, and in particular to a composite positive electrode material, a positive electrode sheet, a secondary battery and an electronic device. Background Art

[0002] The widespread use of lithium-ion batteries in consumer electronic devices (such as mobile phones), electric vehicles, energy storage devices, etc. has driven people to develop lithium-ion batteries with high energy density and long cycle life. Among them, the above-mentioned performance improvements of lithium-ion batteries often rely on the performance improvements of their key component - the positive electrode material.

[0003] Surface coating modification of positive electrode materials is one of the common methods to improve the cycle stability and safety performance of positive electrode materials. Coating can reduce the contact between the positive electrode material and the electrolyte and reduce the side reactions at the interface. Common coating materials include inert oxides (such as aluminum oxide, zirconium oxide) and solid electrolyte materials. However, the conductivity of oxides such as aluminum oxide is very low and the ion conductivity is poor, while solid electrolyte materials are generally electronic insulators. Their presence will degrade the rate performance of the positive electrode material and reduce the capacity, which is not conducive to the improvement of the overall performance of the battery. Therefore, it is urgent to develop a coating material that can take into account good ionic conductivity and electronic conductivity to better improve the performance of the positive electrode material. Summary of the invention

[0004] In view of this, the embodiment of the present application provides a composite positive electrode material. By coating the surface of the positive electrode active material with a specific coating material having both high ionic conductivity and electronic conductivity, the direct contact between the positive electrode active material and the electrolyte can be effectively reduced, thereby improving its cycle stability and safety without affecting its rate performance and high capacity characteristics, and greatly improving the thermal stability of the composite positive electrode material.

[0005] In a first aspect, an embodiment of the present application provides a composite positive electrode material, comprising a core and a coating layer coated on the core, wherein the core comprises a positive electrode active material, and the coating layer comprises at least one general formula of Li x A y MO z A metal oxide, wherein A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and includes at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0≤x≤2,0 <y≤2,0<z≤5。

[0006] The composite positive electrode material of the embodiment of the present application forms a coating layer containing the above-mentioned metal oxide on the surface of the positive electrode active material. The coating layer has both ionic conductivity and electronic conductivity, and will not increase the internal resistance of the composite positive electrode material to cause a decrease in capacity, nor will it reduce the lithium ion diffusion rate to cause a decrease in rate performance. The electrochemical properties of the coating layer are stable, and it can durably block the contact between the positive electrode active material and the electrolyte, inhibit the positive electrode-electrolyte interface side reactions, and improve the structural stability, cycle stability and safety performance of the positive electrode active material.

[0007] In the embodiment of the present application, there is also a diffusion layer between the core and the coating layer, and the diffusion layer includes the positive electrode active material and the metal oxide, and in the diffusion layer, the metal oxide diffuses into the bulk phase and / or the surface of the positive electrode active material to form a TOM bond and / or a TOA bond, and T represents the transition metal element in the positive electrode active material. At this time, the presence of the diffusion layer in the composite positive electrode material can improve the tightness of the bonding between the core and the coating layer, and effectively restrain the release of oxygen species and the dissolution of transition metal elements in the bulk phase of the positive electrode active material, stabilize its lattice structure, and significantly improve thermal stability.

[0008] It should be noted that when the expression "A and / or B" is used in this application, it means "at least one of A and B", that is, A, or B, or A and B.

[0009] In some embodiments of the present application, the M includes at least one of Co, Fe, and Mn. In this case, the general formula is Li x A y MO z The material can have higher electronic conductivity and lithium ion conductivity at the same time, which is more conducive to the rate performance and capacity of the positive electrode active material. Moreover, it is conducive to enhancing the bonding force of the diffusion layer on the core and significantly improving the thermal stability of the core material.

[0010] In some implementations of the present application, the value range of x is: 0.1≤x≤0.6.

[0011] In some embodiments of the present application, the sum of x and y is less than 1. In this case, when x is small, Li x A y MO z The ionic conductivity of the material is better, and the presence of an appropriate amount of y can make Li x A y MO z The material also has excellent electronic conductivity.

[0012] In the embodiment of the present application, the electronic conductivity of the metal oxide at 20°C is ≥10 -5 S cm-1 , lithium ion conductivity ≥10 -5 S cm -1 .

[0013] In the embodiment of the present application, the coating layer completely covers the surface of the positive electrode active material, so as to avoid the presence of uncoated areas of the positive electrode active material becoming active sites for side reactions with the electrolyte, thereby better improving the safety performance and cycle stability of the positive electrode active material.

[0014] In the embodiment of the present application, in the composite positive electrode material, the total mass of the metal oxide accounts for 0.1wt%-10wt% of the total mass of the positive electrode active material. The mass proportion of the metal oxide in this range can better ensure the high specific capacity of the positive electrode active material, and form a coating layer of appropriate thickness to better inhibit the side reaction between the positive electrode active material and the electrolyte.

[0015] In the embodiment of the present application, the coating layer has a thickness of 1 nm-5 μm. A coating layer with a suitable thickness can effectively suppress the side reaction between the positive electrode active material and the electrolyte without reducing the specific capacity of the positive electrode active material.

[0016] In order to better bind the lattice oxygen in the bulk phase of the positive electrode active material, stabilize its skeleton structure, and increase the close connection between the core and the coating layer, in the embodiment of the present application, the thickness of the diffusion layer is 0.1nm-20nm.

[0017] In the embodiment of the present application, the particle size of the positive electrode active material is 50 nm-50 μm. Positive electrode active materials with suitable particle sizes can take into account both higher structural stability and shorter lithium ion diffusion paths.

[0018] In the embodiment of the present application, in the lithium-ion battery, within the operating voltage range of the positive electrode active material, the discharge gram capacity of the metal oxide does not exceed 15% of the discharge gram capacity of the positive electrode active material. At this time, the electrochemical activity of the metal oxide is very low, and the electrochemical properties are relatively stable, so that the structural stability of the coating layer is high, and the contact between the core positive electrode active material and the electrolyte is more stably blocked.

[0019] In order to improve the thermal stability of the positive electrode active material with the coating layer, in the embodiment of the present application, the thermal decomposition temperature of the metal oxide is higher than the thermal decomposition temperature of the positive electrode active material.

[0020] In some embodiments of the present application, the exothermic peak temperature of the composite positive electrode material is at least 5% higher than the exothermic peak temperature of the positive electrode active material. The above exothermic peak temperature can be measured by differential scanning calorimetry (DSC). Compared with the uncoated positive electrode active material, under the combined action of the above diffusion layer and coating layer, the exothermic peak temperature of the composite positive electrode material is significantly higher, indicating that the thermal stability of the material is greatly improved, and thus its safety performance is also significantly improved.

[0021] In some embodiments of the present application, the exothermic peak temperature of the composite positive electrode material is higher than the exothermic peak temperature of the positive electrode active material by more than 15° C. Compared with the uncoated positive electrode active material, the thermal stability of the composite positive electrode material is greatly improved and the safety performance is improved.

[0022] A second aspect of the present application provides a method for preparing a composite positive electrode material, comprising:

[0023] A coating layer is constructed on the surface of the positive electrode active material to obtain a composite positive electrode material; wherein the coating layer includes at least one x A y MO z A metal oxide, wherein A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and includes at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0≤x≤2,0 <y≤2,0<z≤5。

[0024] In the embodiment of the present application, the construction method of the coating layer includes a direct mixing coating method or an in-situ reaction coating method, wherein the direct mixing coating method includes one or more of ball milling, mechanical stirring, mechanical fusion, coating, fluidized bed coating, and spray drying coating methods, and the in-situ reaction coating method includes ball milling, sol-gel, hydrothermal / solvothermal coating, and co-precipitation coating.

[0025] The method for preparing the composite positive electrode material of the embodiment of the present application has a simple process, is easy to operate, and is suitable for large-scale production.

[0026] A third aspect of the embodiment of the present application further provides a positive electrode plate, wherein the positive electrode plate comprises the composite positive electrode material described in the first aspect of the embodiment of the present application.

[0027] The fourth aspect of the embodiment of the present application further provides a secondary battery, comprising the composite positive electrode material described in the first aspect of the embodiment of the present application. The electrochemical device may be a lithium secondary battery.

[0028] Using the above composite positive electrode material as the positive electrode active material of the secondary battery can improve the thermal stability and cycle performance of the secondary battery, and maintain good rate performance and high capacity characteristics, which can better meet the needs of consumer electronic devices for secondary batteries with good thermal stability, long cycle life and high energy density.

[0029] The fifth aspect of the embodiment of the present application provides an electronic device, the electronic device includes the secondary battery described in the fourth aspect of the present application. The electronic device is powered by the secondary battery provided in the embodiment of the present application, which can improve the product's user experience and market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1A A schematic diagram of the structure of a composite positive electrode material provided in an embodiment of the present application;

[0031] Figure 1B Another schematic diagram of the structure of the composite positive electrode material provided in the embodiment of the present application;

[0032] Figure 2 A schematic diagram of the structure of a lithium secondary battery provided in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of the structure of an electronic device provided in an embodiment of the present application;

[0034] Figure 4 Another structural schematic diagram of an electronic device provided in an embodiment of the present application;

[0035] Figure 5 X-ray diffraction (XRD) patterns of the coating materials used in Examples 1-3 and Comparative Example 1 of the present application;

[0036] Figure 6 The scanning electron microscope (SEM) results of the positive electrode active material in Example 2 of the present application before coating (a) and after coating (b);

[0037] Figure 7 The characteristics of lithium ion conductivity and electronic conductivity of the coating layer materials used in Examples 1-3 and Comparative Examples 1-2 of the present application are summarized;

[0038] Figure 8 The differential scanning calorimetry (DSC) curves of the positive electrode materials of Example 1 and Comparative Example 3;

[0039] Fig. 9 The cyclic performance curves of the positive electrode materials of Example 1 and Comparative Example 3 are shown. Detailed implementation manners

[0040] The embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

[0041] Figure 1A FIG. is a schematic structural diagram of a composite positive electrode material 100 provided in an embodiment of the present application. The composite positive electrode material 100 includes a core 10 and a coating layer 20 coated on the core 10. The core 10 includes a positive electrode active material, and the coating layer 20 includes at least one metal oxide with a general formula of Li x A y MO z . Wherein, A is selected from at least one of La, Nd, Pr, Sm, Ba, and Sr, and at least includes at least one of La, Nd, Pr, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and at least includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0≤x≤2, 0<y≤2, 0<z≤5. When the expression "at least one" is involved in the present application, "at least one" means one or more than two.

[0042] For the composite positive electrode material of the embodiment of the present application, by forming the coating layer 20 containing the above metal oxide on the surface of the core 10, the coating layer has both ionic conductivity and electronic conductivity, does not affect the insertion or extraction of Li + into or from the positive electrode active material, ensures the performance of its rate performance, and does not increase the internal resistance of the composite positive electrode material, and thus does not cause a decrease in the battery capacity. In addition, the coating layer material has a relatively high voltage platform for the deintercalation / insertion reaction with respect to Li / Li + . Within the working voltage range of the lithium ion battery, it has almost no electrochemical activity or exhibits a very low charge-discharge capacity, and rarely participates in the deintercalation / insertion / Li + reaction, and has relatively stable electrochemical properties, so that the structure of the coating layer 20 is highly stable. It can persistently block the contact between the core positive electrode active material 10 and the electrolyte, inhibit the side reactions at the positive electrode-electrolyte interface (such as reducing the dissolution of transition metal elements, reducing the release of lattice oxygen, continuous rupture-reconstruction of the solid electrolyte interface, etc.), ensure the good structural stability of the positive electrode active material, and improve its cycle stability and safety performance, especially conducive to improving the cycle performance and safety performance of the positive electrode active material at high voltages.

[0043] In some implementation manners of the present application, refer to Figure 1BThe composite positive electrode material 100 further comprises a diffusion layer 12 between the core 10 and the coating layer 20. The diffusion layer 12 comprises the material of the core 10 (i.e., the positive electrode active material) and the material of the coating layer 20 (i.e., the Li x A y MO z ), and in the diffusion layer 12, the metal oxide diffuses into the bulk phase and / or the surface of the positive electrode active material, and forms a TOM bond and / or a TOA bond, where T represents the transition metal element in the positive electrode active material. At this time, the diffusion layer 12 comprising the material of the core 10 and the material of the coating layer 20 can enhance the transmission of lithium ions and electrons at the interface of the positive electrode active material and improve the tightness of the binding between the core 10 and the coating layer 20. Among them, the above-mentioned coating layer material (especially the M element) diffuses into the bulk phase of the positive electrode active material, which will change the initial valence state of at least part of the transition metal elements in the positive electrode active material and change the coordination environment of the oxygen atoms therein. The temperature required for the TOM bond to break and form an O defect site is higher than that of the TOT bond (corresponding to the energy required for O release). Therefore, the presence of the TOM bond can improve the stability of the coordination form of the oxygen atom, improve the stability of the lattice structure of the positive electrode active material, inhibit the release of its lattice oxygen and the dissolution of the transition metal element, and improve the thermal stability of the system. For the A element, its migration energy is low and it tends to aggregate at the positive electrode interface to form a TOA bond, improve the degree of mixing of the positive electrode Li / transition metal (especially Li / Ni), and enhance the stability of the positive electrode structure. Therefore, under the synergistic effect of the coating layer 20 and the diffusion layer 12, the stability of the core 10 can be more significantly improved, the risk of thermal runaway caused by the release of oxygen from the positive electrode active material and the action of the electrolyte can be reduced, and the safety performance can be significantly improved. It should be noted that the above-mentioned T can be part or all of the transition metal elements that constitute the positive electrode active material. For example, for a binary or ternary positive electrode active material containing Ni, T is usually Ni, rather than other transition metals in its structure.

[0044] In some embodiments of the present application, in the diffusion layer, the metal oxide diffuses into the bulk phase of the positive electrode active material and / or diffuses to its surface to form TOM bonds and TOA bonds. Especially when T is the same as M. At this time, under the synergistic effect of TOA bonds and more TOM bonds, it can better inhibit the surface structural phase change and release of oxygen species of the composite positive electrode material, thereby improving the structural stability and thermal stability. Furthermore, the metal oxide diffuses into the bulk phase of the positive electrode active material and / or diffuses to its surface, and AOM bonds are also formed.

[0045] In the present application, the A includes at least one of La, Pr, Nd and Sm. The presence of lanthanide elements La, Pr, Nd and Sm can reduce the general formula Li x A y MOz When A also includes Ba and / or Sr, it can partially replace the position of La series elements and can be Li + Provides greater migration space and improves Li x A y MO z The ionic conductivity of the material. For example, the above general formula is Li x A y MO z The material can be LaBaMO or LaSrMO system material.

[0046] In some embodiments of the present application, the M includes at least one of Co, Fe, and Mn. In this case, the general formula is Li x A y MO z The material has low oxygen defect formation energy and low lithium migration energy, and can have high electronic conductivity and lithium ion conductivity at the same time, which is more conducive to the rate performance and capacity of the positive electrode active material. In addition, the M elements such as Co, Fe, and Mn are the same as the transition metal elements of some positive electrode active materials. In this case, Li x A y MO z The lattice similarity between the material and the positive electrode active material is high, and epitaxial growth will be formed on the surface of the positive electrode active material, which is more conducive to forming a diffusion layer 12 firmly bonded to the core 10, and better improving the interface thermal stability of the positive electrode active material.

[0047] Furthermore, when M includes at least one of Co, Fe, and Mn, M may also include one or more of Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta. Among them, Ni and V are more conducive to improving Li x A y MO z The electronic conductivity of the material, Cr and Nb are more conducive to improving Li x A y MO z The lithium ion conductivity.

[0048] In some implementations of the present application, the value range of x is: 0.1≤x≤0.6. x A y MO z There are many A-site defects in the structure of the material, and lithium ions can migrate through the A-site defects, so that the material exhibits higher lithium ion conductivity. Wherein, x can be specifically 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.55, etc. In some embodiments, the value range of x is: 0.2≤x≤0.45.

[0049] In some embodiments of the present application, x + y < 1. At this time, when x is small, the ionic conductivity of the Li x A y MO z material is relatively excellent, and the presence of an appropriate amount of y can make the Li x A y MO z material have relatively excellent electronic conductivity. In some embodiments, the value range of y is: 0.2 ≤ y < 0.8. Among them, y can specifically be 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.7, etc. In some embodiments, the value range of y is: 0.2 ≤ y ≤ 0.6. The above values of x and y can be specifically determined according to the valences of A and M.

[0050] In some embodiments of the present application, the range of z is: 0 < z ≤ 3. Among them, when z is less than 3, there are oxygen defect sites in the Li x A y MO z material, which is beneficial to improving its electronic conductivity.

[0051] In the present application, the crystal phase of the metal oxide may include orthorhombic phase, triclinic phase, tetragonal phase, cubic phase, monoclinic phase or hexagonal phase, etc. The specific crystal phase can be determined according to the specific elements of A and M.

[0052] In the embodiments of the present application, the electronic conductivity of the metal oxide at 20 °C ≥ 10 -5 S·cm -1 , and the lithium ion conductivity ≥ 10 -5 S·cm -1 . By regulating the above specific selected elements of A and M and the values of x and y, a metal oxide with desired good electronic conductivity and ionic conductivity can be obtained.

[0053] In the embodiments of the present application, as shown in Figure 1A and Figure 1B , the coating layer 20 completely coats the surface of the positive electrode active material 10. This can avoid the uncoated areas of the positive electrode active material from becoming active sites for side reactions with the electrolyte, and complete coating can better improve the safety performance and cycle stability of the positive electrode active material.

[0054] In the embodiment of the present application, the thickness of the coating layer 20 is 1nm-5μm. The coating layer of suitable thickness can effectively inhibit the side reaction between the positive electrode active material and the electrolyte, while not reducing the reversible capacity of the composite positive electrode material and the energy density of the battery due to the excessive thickness of the coating layer. Specifically, the thickness of the coating layer 20 can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 120nm, 200nm, 500nm, 800nm, 1μm, 2μm or 4μm, etc. In some embodiments, the thickness of the coating layer 20 can be 2nm-100nm. In other embodiments, the thickness of the coating layer 20 is 2nm-50nm. In some other embodiments, the thickness of the coating layer 20 is 5nm-35nm.

[0055] In the present application, the diffusion layer 12 may be formed by a metal oxide Li x A y MO z The diffusion layer 12 and the core 10 are formed by diffusion into the material of the core 10, and have a continuous positive electrode active material phase. This is conducive to the stable combination of the diffusion layer 12 on the core 10, and the diffusion layer 12 is used to establish a connection bridge between the core 10 and the coating layer 20.

[0056] In the embodiment of the present application, the thickness of the diffusion layer 12 mainly depends on the diffusion ability of the A, M and O elements in the metal oxide to the core 10. In order to better bind the lattice oxygen in the bulk phase of the positive electrode active material, stabilize its skeleton structure, and form a close connection between the core 10 and the coating layer 20, the thickness of the diffusion layer 12 can be 0.1nm-20nm. Specifically, it can be 0.2nm, 0.5nm, 1nm, 1.5nm, 2nm, 5nm, 10nm, 15nm, etc. In some embodiments, the thickness of the diffusion layer 12 is 0.2nm-10nm; in some embodiments, the thickness of the diffusion layer 12 is 0.2nm-5nm; in some embodiments, the thickness of the diffusion layer 12 is 0.2nm-2nm.

[0057] Considering the coating material Li x A y MO zIt has almost no electrochemical activity. In order to better ensure the specific capacity of the positive electrode active material and inhibit the release of lattice oxygen and dissolution of transition metal elements of the positive electrode active material, in the embodiment of the present application, in the composite positive electrode material, the total mass of the metal oxide accounts for 0.1wt%-10wt% of the total mass of the positive electrode active material 10. At this time, it can ensure the formation of a coating layer with appropriate thickness and high coating integrity and a certain thickness of the diffusion layer 12, and better inhibit the side reaction between the positive electrode active material and the electrolyte under the premise of ensuring the lithium ion transmission performance, and ensure the good lithium ion transmission performance of the positive electrode active material. In some embodiments, the mass of the coating layer 20 accounts for 0.3wt%-5wt% of the mass of the positive electrode active material 10. In some embodiments, the ratio is 0.5wt%-2wt%.

[0058] In the embodiment of the present application, the lithium removal voltage platform of the metal oxide is greater than the charge cut-off voltage of the positive electrode active material. That is, when the battery is charged to the charge cut-off voltage, the metal oxide does not remove lithium or only removes a very small amount of lithium, and the electrochemical properties are stable.

[0059] In some embodiments of the present application, in a lithium-ion battery, within the operating voltage range of the positive electrode active material, the discharge gram capacity of the metal oxide does not exceed 15% of the discharge gram capacity of the positive electrode active material. This indicates that the electrochemical activity of the metal oxide is very low and the electrochemical properties are relatively stable, so that the structural stability of the coating layer 20 is high. The above-mentioned composite positive electrode active material is generally used in a lithium-ion battery system with a charging cut-off voltage of 3.8-4.5V, and the charging cut-off voltage is generally adjusted according to the core positive electrode active material.

[0060] In the embodiment of the present application, the positive electrode active material as the core may be undoped or modified by doping. The positive electrode active material includes, but is not limited to, one or more of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese oxide, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium vanadium phosphate, and lithium-rich manganese-based positive electrode materials. When the expression "multiple" is involved in the present application, "multiple" means two or more. Among them, the positive electrode active material may be spherical or quasi-spherical.

[0061] In some embodiments of the present application, the positive electrode active material is a positive electrode active material containing Ni. The thermal stability and safety of the positive electrode are strongly related to the release of oxygen atoms in the lattice, and the most unstable oxygen coordination determines the temperature at which oxygen species begin to be released. Taking the Ni-containing ternary positive electrode active material as an example, the aforementioned coating layer material diffuses into the diffusion layer 12 formed in the positive electrode active material. The introduction of the M element will change the initial valence state of Ni, the coordination environment of the O atom and the degree of Li / Ni mixing. The TOA bond and TOM bond (T represents the transition metal element of the positive electrode active material) formed by the A element and the M element in the diffusion layer can improve the stability of the coordination form of the oxygen atom. For example, in the NCM ternary material, when M=Mn or Co, the most unstable (lowest decomposition temperature) Ni-O-Ni bond in the NCM system will be replaced by Ni-O-Mn, Ni-O-Co (these two are originally present in the NCM system, but the proportion is increased) and Ni-O-La (new appearance), thereby improving the stability of the lattice oxygen at the positive electrode interface and restraining the release of the lattice oxygen on the surface of the inner core, thereby ensuring the excellent thermal stability and safety of the composite positive electrode material 100.

[0062] In the embodiment of the present application, the particle size of the positive electrode active material is 50nm-50μm. The particle size of the positive electrode active material is large, its specific surface area is not too large, and its structural stability is high, but the particle size should not be too large otherwise the diffusion path of lithium ions will be lengthened and its rate performance will be poor. In some embodiments, the particle size of the positive electrode active material is 100nm-30μm. In some embodiments, the particle size of the positive electrode active material is 500nm-20μm.

[0063] In the embodiment of the present application, the thermal decomposition temperature of the metal oxide is higher than the thermal decomposition temperature of the positive electrode active material. In this case, after being coated with the metal oxide, the thermal stability of the positive electrode active material can be improved.

[0064] In some embodiments of the present application, the exothermic peak temperature of the composite positive electrode material is at least 5% higher than the exothermic peak temperature of the positive electrode active material. The above exothermic peak temperature can be measured by differential scanning calorimetry (DSC). If the exothermic peak temperature of the positive electrode active material is recorded as T0 and the exothermic peak temperature of the composite positive electrode material is recorded as T1, then (T1-T0) / T0≥5%. Compared with the uncoated positive electrode active material, under the joint action of the above-mentioned diffusion layer and coating layer, the exothermic peak temperature of the composite positive electrode material becomes significantly higher, indicating that its thermal stability is greatly improved and the safety performance can also be significantly improved. However, if the positive electrode active material is coated with only ordinary metal oxides with high thermal decomposition stability, the exothermic peak temperature of the resulting composite material cannot be significantly improved. In some embodiments, (T1-T0) / T0≥8%; in some embodiments, (T1-T0) / T0≥10%; in some embodiments, (T1-T0) / T0≥13%; in some embodiments, (T1-T0) / T0≥15%.

[0065] In some other embodiments of the present application, the exothermic peak temperature T1- of the composite positive electrode material is at least 15°C higher than the exothermic peak temperature T0 of the positive electrode active material. That is, T1-T0≥15°C. Compared with the uncoated positive electrode active material, the thermal stability of the composite positive electrode material is greatly improved and the safety performance is improved. In some embodiments, T1-T0≥20°C, or even ≥30°C.

[0066] The present application also provides a method for preparing the composite positive electrode material, which may include:

[0067] A coating layer is constructed on the surface of the positive electrode active material to obtain a composite positive electrode material; wherein the coating layer includes at least one x A y MO z A metal oxide, wherein A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and includes at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0≤x≤2,0 <y≤2,0<z≤5。

[0068] Among them, the construction method of the above-mentioned coating layer includes but is not limited to direct mixing coating method or in-situ reaction coating method. The direct mixing coating method here refers to taking the prepared coating layer material and compounding it with the positive electrode active material. The in-situ reaction coating method mainly refers to mixing the raw material of the synthetic coating layer material with the positive electrode active material, and obtaining the coating layer material or its precursor through in-situ reaction while achieving the coating of the positive electrode active material. Among them, the direct mixing coating method can include ball milling, mechanical stirring, mechanical fusion, coating, fluidized bed coating, spray drying coating, etc. The in-situ reaction coating method can include ball milling, sol-gel, hydrothermal / solvothermal coating, co-precipitation coating, etc. Generally, after the in-situ reaction coating method, high-temperature sintering treatment is required to promote the crystallization of the coating layer material and enhance the bonding force between it and the positive electrode active material.

[0069] In some embodiments of the present application, the method for preparing the composite positive electrode material may specifically include:

[0070] S01, mixing the positive electrode active material with the raw material for synthesizing the coating layer material, so as to coat the precursor of the coating layer material on the surface of the positive electrode active material, to obtain a first composite material; wherein the coating layer material includes at least one general formula of Li x A y MO z A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and includes at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0≤x≤2,0 <y≤2,0<z≤5;

[0071] S02, sintering the first composite material to transform the precursor of the coating layer material into the coating layer material to obtain a composite positive electrode material; the composite positive electrode material includes a core and a coating layer coated on the core, the core includes a positive electrode active material, and the coating layer includes the metal oxide.

[0072] In step S01, the method of coating the precursor of the coating layer material includes the above-mentioned in-situ reaction coating method, which mainly refers to mixing the raw material of the synthetic coating layer material with the positive electrode active material, and obtaining the coating layer material precursor through in-situ reaction, while achieving coating of the positive electrode active material. The coating layer material precursor can be converted into the coating layer material after the sintering treatment in step S02.

[0073] In some embodiments, a sol-gel method is used to construct a coating layer material precursor, specifically including: adding a lithium source, a raw material of element A, a raw material of element M and a positive electrode active material to a solvent, reacting under stirring conditions at a temperature of 40°C-80°C, then evaporating the solvent to form a coating layer precursor material on the surface of the positive electrode active material.

[0074] Among them, the lithium source, the raw material of element A, and the raw material of element M can be selected from nitrates, oxalates, acetates, sulfates, carbonates, hydroxides, oxides, etc. of the corresponding elements, respectively, and preferably contain oxygen. The molar ratio of lithium element, the raw material of element A, and element M can be determined according to the structural formula of the final required coating material, and considering the loss of Li element during the sintering treatment process in step S02, the molar amount of lithium is generally controlled to be within 10% excess. In addition, the positive electrode active material can be a commercially available product or prepared by itself. In addition, the time of the above stirring reaction can be 20-60min. The solvent used can include one or more of water, ethanol, acetone, etc. The evaporation method of the solvent includes one or more of rotary evaporator drying, water bath stirring, centrifugal drying, and oven drying; the heating temperature used for evaporation is 60℃-100℃.

[0075] In step S02, the first composite material is sintered to promote the reaction of Li, A, and M elements in the coating layer material precursor to transform into the coating layer material, that is, the general formula is Li x A y MO z of metal oxides.

[0076] In some embodiments, the first composite material is sintered to form a diffusion layer between the inner core and the coating layer; wherein the diffusion layer includes the positive electrode active material and the metal oxide, and in the diffusion layer, the metal oxide diffuses into the bulk and / or surface of the positive electrode active material to form TOM bonds and / or TOA bonds, and T represents the transition metal element in the positive electrode active material.

[0077] Sintering can improve the bonding strength between the core cathode active material and the coating layer and promote the x A y MO z The metal oxide and the surface lattice of the positive electrode active material diffuse into each other to form a diffusion layer (also called an interface layer), which enhances the transmission of lithium ions and electrons at the positive electrode interface and promotes the diffusion of the metal oxide into the bulk phase of the positive electrode active material to form TOM bonds and TOA bonds. With the help of this diffusion layer, the release of lattice oxygen in the core and the dissolution of transition metal elements are suppressed.

[0078] The sintering process in step S02 can be carried out in an atmosphere such as oxygen, air, argon, helium, etc. In order to ensure the crystal phase structure required for the formation of the coating layer, ensure the tight combination of the core and the coating layer, and achieve uniform and continuous thickness of the coating layer, the embodiments of the present application set the sintering temperature and holding time during the sintering process. Among them, the sintering temperature in the sintering process can be 400-1000 °C, and the holding time can be 1h-10h. In particular, since too fast heating rate will generate large stress at the interfaces between phases, the heating rate is set to 1 °C / min-5 °C / min in the sintering process of the embodiments of the present application. Exemplarily, the sintering temperature can specifically be 500, 600, 700 °C, 720 °C, 750 °C, 800 °C, 850 °C, 900 °C or 950 °C, etc. In some embodiments, the sintering temperature can be 600-900 °C. The holding time can specifically be 2h, 4h, 5h, 6h, 7h, 8h, 9h or 10h; the heating rate can specifically be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min.

[0079] After sintering is completed, the powder is collected after natural cooling, and the composite cathode material is obtained. In some embodiments, the powder collected after sintering can also be subjected to crushing and refining treatment to obtain the composite cathode material with the required particle size.

[0080] In other embodiments of the present application, the preparation method of the above composite cathode material may specifically include:

[0081] Mix the cathode active material with the coating layer material to coat the coating layer material on the surface of the cathode active material to obtain a first composite material, that is, obtain the composite cathode material; wherein, the coating layer material includes at least one metal oxide with the general formula Li x A y MO z , A is selected from at least one of La, Pr, Nd, Sm, Ba, Sr, and at least includes at least one of La, Pr, Nd and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, Ta, and at least includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, Ta; 0≤x≤2, 0<y≤2, 0<z≤5; the composite cathode material includes a core and a coating layer coated on the core, and the core includes the cathode active material.

[0082] Among them, the method of coating the coating layer material includes the direct mixing coating method. As described above, the direct mixing coating method can include ball milling method, mechanical stirring method, mechanical fusion method, coating method, fluidized bed coating method, spray drying coating method, etc.

[0083] For example, in some embodiments, the ball milling method is used to coat Li x A y MO z The material, wherein the ball milling method can be specifically a dry ball milling method or a wet ball milling method. The ball-to-material ratio for ball milling is (1-3):1, the ball milling time can be 0.5-5h, and the ball milling speed can be 200-500r / min. The ball milling method can realize the simple preparation of the core-shell composite material.

[0084] Furthermore, in some embodiments, after obtaining the first composite material, it also includes: sintering the first composite material to form a diffusion layer between the inner core and the coating layer; wherein the diffusion layer includes the positive electrode active material and the metal oxide, and in the diffusion layer, the metal oxide diffuses into the bulk phase of the positive electrode active material to form TOM bonds and TOA bonds, and T represents the transition metal element in the positive electrode active material.

[0085] As described above, the sintering treatment can promote the mutual diffusion of the coating layer material and the surface lattice of the positive electrode active material to form a diffusion layer (also referred to as an interface layer), enhance the transmission of lithium ions and electrons at the positive electrode interface, and promote the diffusion of metal oxides into the bulk phase and / or the surface of the positive electrode active material to form TOM bonds and / or TOA bonds. With the help of the diffusion layer, the lattice oxygen release of the core and the dissolution of transition metal elements are suppressed. The sintering treatment can also improve the bonding force between the core and the coating layer. The specific sintering treatment can be as described above in this application, and will not be repeated here.

[0086] The method for preparing the composite positive electrode material provided in the embodiment of the present application has low raw material cost, simple process, easy operation, and is suitable for large-scale production.

[0087] The embodiment of the present application also provides a positive electrode plate for a battery, which includes the composite positive electrode material described above in the embodiment of the present application. In some embodiments of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, the positive electrode material layer includes a positive electrode active material, a binder and a conductive agent, and the positive electrode active material includes the composite positive electrode material described above in the embodiment of the present application. The mass proportion of the composite positive electrode material in the positive electrode material layer may be greater than or equal to 80%. In some embodiments, the positive electrode active material may also include other positive electrode active materials that are different from the core of the composite positive electrode material described above, and the selection range of the specific material may be as described above in the present application.

[0088] The positive electrode current collector includes but is not limited to metal foil, alloy foil or metal-plated film, and its surface can be etched or roughened to form a secondary structure, which is convenient for forming effective contact with the positive electrode material layer. Exemplary metal foils can be aluminum foil, carbon-coated aluminum foil or aluminum-plated film, and exemplary alloy foils can be stainless steel foil, aluminum alloy foil or carbon-coated stainless steel foil. Binders can specifically include but are not limited to polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylate, polyacrylamide (PAM), polyimide (PI) and the like. Conductive agents can specifically include but are not limited to one or more of acetylene black, Ketjen black, Supper P conductive carbon black, graphite, graphene, carbon nanotubes, carbon fiber, amorphous carbon and the like. The preparation method of the positive electrode sheet may include: mixing the positive electrode active material, the conductive agent, the binder and the solvent to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode collector, and rolling after drying to obtain a positive electrode sheet.

[0089] See also Figure 2 , the embodiment of the present application also provides a secondary battery 200, which includes the above-mentioned positive electrode plate. The secondary battery 200 can be a lithium secondary battery, which includes a positive electrode 201, a negative electrode 202, an electrolyte 203 disposed between the positive electrode 201 and the negative electrode 202, a diaphragm 204, and corresponding connecting accessories and circuits, wherein the positive electrode 201 includes the above-mentioned positive electrode plate of the embodiment of the present application. The lithium secondary battery has good cycle stability, rate performance and thermal stability within its operating voltage range.

[0090] The negative electrode 202 may include a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, the negative electrode material layer including a negative electrode active material, a binder and an optional conductive agent. Among them, the negative electrode current collector includes but is not limited to metal foil, alloy foil or metal-plated film, and its surface may be etched or roughened to form a secondary structure to facilitate effective contact with the negative electrode material layer. Exemplary metal foils may be copper foil, carbon-coated copper foil or copper-plated film, and exemplary alloy foils may be stainless steel foil, copper alloy foil, etc. The negative electrode active material includes but is not limited to one or more of lithium titanate, metallic lithium, lithium alloy, carbon-based material, silicon-based material, tin-based material, and phosphorus-based material. Among them, the carbon-based material may include graphite (such as natural graphite, artificial graphite), non-graphitized carbon (soft carbon, hard carbon, etc.); the silicon-based material may include one or more of elemental silicon, silicon-based alloy, silicon oxide and silicon-carbon composite material, etc.; the tin-based material may include one or more of elemental tin, tin alloy, etc.; the phosphorus-based material may include phosphorus (such as black phosphorus), phosphorus-carbon composite material, etc. The electrolyte includes a lithium salt and a solvent, and the solvent may include one or more of a carbonate solvent, a carboxylate solvent, and an ether solvent. The separator may be a polymer separator, a non-woven fabric, etc., including but not limited to a single-layer PP (polypropylene), a single-layer PE (polyethylene), a double-layer PP / PE, a double-layer PP / PP, and a triple-layer PP / PE / PP separator.

[0091] The lithium secondary battery of the embodiment of the present application can be used in terminal consumer products such as mobile phones, tablet computers, mobile power supplies, portable computers, laptops, digital cameras and other wearable electronic devices or mobile electronic devices such as drones, electric bicycles, electric vehicles and other products to improve product performance.

[0092] The embodiment of the present application also provides an electronic device including the above-mentioned secondary battery. The electronic device may include various consumer electronic products, such as mobile phones, tablet computers, laptops, mobile power supplies, portable machines, and other wearable or movable electronic devices, televisions, DVD players, video recorders, camcorders, radios, recorders, combination audio systems, record players, laser turntables, home office equipment, home electronic health care equipment, and automobiles and other electronic products. It should be noted that when the above-mentioned secondary battery is applied to an electronic device, it can be accommodated in the electronic device in the form of a battery pack. Generally, the battery pack includes multiple battery modules (a single battery module can include multiple of the above-mentioned secondary batteries) and a battery management system that controls them.

[0093] In some embodiments, see Figure 3 The embodiment of the present application provides an electronic device 300, which includes a housing 301 and electronic components ( Figure 3The housing 301 may include a front cover assembled on the front side of the terminal and a rear housing assembled on the rear side, and the battery 302 may be fixed inside the rear housing.

[0094] In some other embodiments, see Figure 4 , an embodiment of the present application provides an electronic device 400, which can be various movable devices for loading, transportation, assembly, disassembly, security, etc., and can be various forms of vehicles. Specifically, the electronic device 400 may include a body 401, a mobile component 402, and a drive component, the drive component includes a motor 403 and a battery 404, and the battery 404 includes the above-mentioned secondary battery 200 provided in the embodiment of the present application. Among them, the mobile component 402 can be a wheel. The battery 404 can be a battery pack including the above-mentioned secondary battery 200, which is accommodated at the bottom of the vehicle body and is electrically connected to the motor 403, so that the secondary battery 200 can power the motor 403, and the motor 403 provides power to drive the mobile component 402 of the electronic device 400 to move.

[0095] The electronic device provided in the embodiment of the present application adopts the composite positive electrode material provided in the embodiment of the present application as the positive electrode active material of the battery, which can improve the cycle performance, thermal stability, rate performance, etc. of the battery, better meet the needs of various electronic products for good thermal stability, long cycle life, and high energy density of the battery, and improve the user experience and market competitiveness of electronic products.

[0096] The embodiments of the present application are further described below with reference to a plurality of embodiments.

[0097] Example 1

[0098] A composite positive electrode material, the preparation method of which comprises the following steps:

[0099] (1) Preparation of positive electrode active materials

[0100] Weigh 100g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor powder was mixed with LiOH in a molar ratio of 1:1.03, sintered at 700 °C for 5 h in an oxygen atmosphere, and then crushed and sieved to obtain material A, that is, high-nickel ternary LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811) positive electrode active material.

[0101] (2) Preparation of coating material

[0102] According to the coating material Li to be prepared0.35 La 0.6 Molar ratio of Li, La and Mn in MnO3 Lithium carbonate (Li2CO3), lanthanum oxide (La2O3) and manganese oxide (MnO2) were weighed and mixed to obtain a mixture B;

[0103] The mixture B was placed in a ball mill filled with zirconium oxide grinding balls, anhydrous ethanol was added to 70% of the inner wall of the ball mill and sealed, the sealed ball mill was placed in a planetary ball mill, and ball milled at a speed of 350 rpm for 6 hours. After the ball milling was completed, the obtained slurry was poured into a mortar and placed in a vacuum drying oven at 120°C for drying for 480 minutes. The dried raw materials were ground into powder, placed in a crucible and placed in a heating furnace for sintering, and the temperature was increased to 750°C at a heating rate of 5°C / min, and kept at 750°C for 4 hours, and then naturally cooled to 100°C to obtain orthorhombic phase Li 0.35 La 0.6 MnO3, the conductivity data and XRD data of this material are shown in Figure 5 and Figure 6 .

[0104] (3) Using orthogonal phase Li 0.35 La 0.6 MnO3 coated positive electrode active material

[0105] The above material A and orthogonal phase Li 0.35 La 0.6 The MnO3 material is loaded into a ball mill filled with zirconium oxide grinding balls at a mass ratio of 1:1%, anhydrous ethanol is added to 70% of the inner wall of the ball mill and sealed, the sealed ball mill is placed in a planetary ball mill, and the ball mill is milled at a speed of 350rpm for 2 hours. After the ball milling is completed, the obtained ball milled slurry is poured into a mortar, placed in a vacuum drying oven at 120°C for 480min, and then heated to 350°C at a rate of 2°C / min in an oxygen atmosphere, and sintered at 350°C for 4h, and naturally cooled to 100°C to obtain a composite positive electrode material. The composite positive electrode material includes an NCM811 core and a diffusion layer and an orthorhombic phase Li formed on the surface of the core in sequence. 0.35 La 0.6 MnO3 coating layer; the diffusion layer contains NCM811 material and Li 0.35 La 0.6 MnO3 material, and Li 0.35 La 0.6 The MnO3 material is embedded in the lattice phase of NCM811, replacing part of the Ni-O-Ni bonds to form Ni-O-Mn bonds and Ni-O-La bonds. The thickness of the diffusion layer is 0.5-1nm, and the thickness of the coating layer is 8-10nm.

[0106] Preparation of lithium secondary batteries

[0107] The obtained orthogonal phase Li 0.35 La 0.6 The MnO3-coated NCM811 positive electrode active material, the conductive agent acetylene carbon black, and the binder PVDF were mixed evenly in a mass ratio of 96:2:2, and an appropriate amount of 1-methyl-2-pyrrolidone was added. The mixture was stirred in a mixer at a speed of 800r / min for 10 minutes to obtain a positive electrode slurry, which was evenly coated on an aluminum foil, dried at 80°C for 480 minutes, and rolled to form a positive electrode sheet. The metal lithium sheet was used as the negative electrode and assembled into a 2032 button cell. The electrical performance of the button cell can be tested using the Xinwei battery test system later.

[0108] Example 2

[0109] A composite positive electrode material, the preparation method of which comprises the following steps:

[0110] (1) Configuring the coating material

[0111] According to the coating material Li 0.35 La 0.6 Molar ratio of Li, La and Mn in MnO3 Lithium nitrate (LiNO3), lanthanum nitrate (LaNO3) and manganese acetate (Mn(CH3COO)2) were weighed, added to ethanol, and stirred to obtain a mixed solution B;

[0112] (2) According to Li 0.35 La 0.6 The coating ratio of MnO3 is 1wt%, and the NCM811 positive electrode active material prepared by the method described in Example 1 is added to the mixed solution B, stirred at 60°C for 1h, and then dynamically dried by a rotary evaporator for 60min to remove the solvent. The collected precursor material is placed in a vacuum drying oven at 120°C for 480min, and then heated to 750°C at a rate of 2°C / min in an oxygen atmosphere, and sintered at 750°C for 4h, and naturally cooled to 100°C to obtain a composite positive electrode material. The composite positive electrode material includes an NCM811 core and an orthorhombic phase Li coated on the surface of the core. 0.35 La 0.6 A MnO3 coating layer and a diffusion layer between the coating layer and the core.

[0113] The NCM811@orthorhombic phase Li prepared in Example 2 of the present application 0.35 La 0.6 The MnO3 composite positive electrode material was used as the positive electrode active material and assembled into a 2032-type button cell in the same manner as in Example 1.

[0114] Example 3

[0115] A composite positive electrode material, comprising a core-NCM811 positive electrode active material and a diffusion layer and a triclinic phase Li formed on the surface of the core in sequence 0.35 La 0.6 CoO3 coating layer, diffusion layer contains NCM811 material and Li 0.35 La 0.6 CoO3 material, and Li 0.35 La 0.6 CoO3 material is embedded in the lattice phase of NCM811, replacing part of the Ni-O-Ni bond to form Ni-O-Co bond, Ni-O-Co bond and La-O-Co bond; among them, Li 0.35 La 0.6 The mass of CoO3 material is 1% of the mass of NCM811 material; the thickness of the diffusion layer is 0.6-1nm, and the thickness of the coating layer is 8-10nm.

[0116] The method for preparing the composite positive electrode material of Example 3 is different from that of Example 1 in that the manganese oxide (MnO2) in step (2) of Example 1 is replaced with cobalt oxide (CoO2) to prepare the triclinic phase Li 0.35 La 0.6 CoO3 coating material; orthorhombic Li in step (3) of Example 1 0.35 La 0.6 The MnO3 material is also replaced by triclinic Li 0.35 La 0.6 CoO3.

[0117] The NCM811@triclinic phase Li prepared in Example 3 of the present application 0.35 La 0.6 The CoO3 composite positive electrode material was used as the positive electrode active material and assembled into a 2032-type button cell in the same manner as in Example 1.

[0118] Example 4

[0119] A composite positive electrode material, comprising an NCM811 core (the preparation of which is shown in Example 1) and an orthorhombic phase Li coated on the surface of the core 0.35 La 0.6 MnO3 coating layer, and a diffusion layer between the coating layer and the core, the diffusion layer contains NCM811 material and Li 0.2 La 0.55 YO3 material, and Li 0.2 La 0.55 YO3 material is embedded in the lattice phase of NCM811 to form Ni-OY bonds and Ni-O-La bonds; among them, Li 0.2 La 0.55The mass of YO3 material is 0.5% of the mass of NCM811 material, the thickness of the diffusion layer is 0.3-0.5nm, and the thickness of the coating layer is 5-7nm.

[0120] Example 5

[0121] A composite positive electrode material, comprising an NCM811 core (the preparation of which is shown in Example 1) and a Li 0.26 La 0.57 TaO 2.99 The coating layer and the diffusion layer between the coating layer and the core contain NCM811 material and Li 0.26 La 0.57 TaO 2.99 Materials, and Li 0.2 La 0.55 YO3 material is embedded in the lattice phase of NCM811 to form Ni-O-Ta bonds, Ni-O-La bonds and La-O-Ta bonds; among them, Li 0.26 La 0.57 TaO 2.99 The mass of the material is 6% of the mass of NCM811 material, the thickness of the diffusion layer is 2-5nm, and the thickness of the coating layer is 35-40nm.

[0122] Example 6

[0123] A composite positive electrode material, comprising an NCM811 core and a Li coated on the surface of the core 0.45 La 0.45 Ba 0.1 CoO3 coating layer; among them, Li 0.45 La 0.45 Ba 0.1 The mass of CoO3 material is 2% of the mass of NCM811 material, and the thickness of the coating layer is 15-20nm.

[0124] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0125] Comparative Example 1

[0126] A composite positive electrode material, comprising a core-NCM811 positive electrode active material and a tetragonal phase Li coated on its surface 0.35 La 0.6 TiO3 coating, Li 0.35 La 0.6 The mass of TiO3 material is 1% of the mass of NCM811 material. The preparation method of the composite positive electrode material of Comparative Example 1 is different from that of Example 1 in that the manganese oxide (MnO2) in step (2) of Example 1 is replaced with titanium oxide (TiO2) to prepare tetragonal Li 0.35La 0.6 TiO3 coating material; orthorhombic phase Li in step (3) of Example 1 0.35 La 0.6 The MnO3 material is also replaced by tetragonal Li 0.35 La 0.6 TiO3.

[0127] The NCM811@tetragonal phase Li 0.35 La 0.6 The TiO3 composite positive electrode material was used as the positive electrode active material and assembled into a 2032-type button cell in the same manner as in Example 1.

[0128] Comparative Example 2

[0129] A composite positive electrode material comprises a NCM811 positive electrode active material and Al2O3 coated on the surface of the positive electrode active material, wherein the mass of the Al2O3 is 1% of the mass of the NCM811 material.

[0130] The preparation method of the composite positive electrode material comprises the following steps:

[0131] Weigh the NCM811 positive electrode active material prepared by the method described in Example 1, add aluminum nitrate nonahydrate according to the Al2O3 coating ratio of 1w%, stir evenly, and slowly add ammonia water to the above solution, filter the mixed precipitate, and wash to form product B;

[0132] Take an appropriate amount of the dried product B, raise the temperature to 750°C at a heating rate of 2°C / min, and sinter at 750°C for 4 hours. After crushing and sieving, a high-nickel ternary NCM811 positive electrode active material coated with Al2O3 is obtained.

[0133] The NCM811@Al2O3 composite positive electrode material provided in Comparative Example 2 was used as a positive electrode active material and assembled into a 2032-type button cell in the same manner as in Example 1.

[0134] Comparative Example 3

[0135] Take the uncoated high-nickel ternary NCM811 positive electrode active material and assemble it into a 2032-type button battery in the same manner as in Example 1.

[0136] Figure 5 The XRD patterns of the coating materials used in Examples 1-3 and Comparative Example 1 of the present application are shown in FIG. Figure 6 It can be seen that the coating material of the present application has high crystallinity. The coating material Li used in Examples 1-2 0.35 La 0.6 MnO3, the crystal phase is orthorhombic phase, the space group is Pnma; the coating material used in Example 3 is Li 0.35La 0.6 The crystal phase of CoO3 is triclinic, and the space group is R-3c. The coating material Li used in Comparative Example 1 0.35 La 0.6 The crystal phase of TiO3 is tetragonal and the space group is P4 / mmm.

[0137] The morphology of the positive electrode active material of Example 2 of the present application before and after coating was characterized by a scanning electron microscope (SEM). Figure 6 As shown, Figure 6 (a) is uncoated LiNi 0.83 Co 0.11 Mn 0.06 SEM image of O2 positive electrode active material, Figure 6 (b) is a SEM image of the composite positive electrode material obtained. It can be clearly seen that compared with (a), the surface morphology of the particles in (b) is different, and a coating film is formed on its surface, which indicates that the surface of the positive electrode active material is successfully coated with the coating layer.

[0138] The characteristics of lithium ion conductivity and electronic conductivity of the coating materials used in Examples 1-3 and Comparative Examples 1-2 of the present application are summarized in Figure 7 .from Figure 7 It can be clearly seen that the lithium ion conductivity and electronic conductivity of the coating material Al2O3 used in Comparative Example 2 are extremely low, while the coating material Li 0.35 La 0.6 Although the lithium ion conductivity of TiO3 can reach 10 - 5 S cm -1 , but its electronic conductivity is low, only 10 -9 S cm -1 , and the coating layer materials of the composite positive electrode materials in Examples 1-3 of the present application have good lithium ion conductivity and electronic conductivity at the same time, and using them as the coating layer of the positive electrode active material does not affect its rate performance.

[0139] Differential scanning calorimetry (DSC) was used to measure the NCM811@orthorhombic phase Li 0.35 La 0.6 The thermal stability of the MnO3 composite positive electrode material and the uncoated NCM811 positive electrode active material of comparative example 3 were evaluated, and their DSC curves were as follows: Figure 8 As shown, the temperature of the main exothermic peak (ie, the thermal decomposition temperature) is summarized in the following Table 1, and the thermal decomposition temperatures of the positive electrode materials of the remaining embodiments and comparative examples are also summarized in Table 1. Figure 8 As shown in Table 1, the NCM811 positive electrode active material is0.35 La 0.6 After the MnO3 material is coated, its exothermic peak temperature increases significantly, by about 15.7%, which indicates that its thermal stability is significantly improved and its safety performance is improved.

[0140] In order to strongly support the beneficial effects of the embodiments of the present application, the button cells assembled in the above embodiments and comparative examples were subjected to the following electrochemical performance tests:

[0141] a) Cycling performance: Each button cell was charged and discharged at 45°C with a current rate of 0.3C and a voltage range of 3.0-4.25V, and the capacity retention rate after 50 cycles was recorded;

[0142] b) Rate performance: Charge and discharge each button cell at 0.2C rate at 25°C, with a voltage range of 3.0-4.25V, and record the discharge capacity of the second cycle; Charge and discharge each button cell at 25°C with a current of 2C rate at a voltage range of 3.0-4.25V, and record the discharge capacity of the second cycle; The ratio of 2C discharge capacity to 0.2C discharge capacity is used as an indicator to measure the battery rate performance.

[0143] The results of the electrochemical performance tests are summarized in Table 1 below. Fig. 9 The cycle performance curves of the positive electrode materials of Example 1 and Comparative Example 3 are shown. Fig. 9 It can be clearly seen that compared with the uncoated and modified NCM811 positive electrode material, the capacity retention rate of the composite positive electrode material of Example 1 is significantly improved.

[0144] Table 1 Summary of test results of various embodiments and comparative examples

[0145]

[0146]

[0147] As can be seen from Table 1, the positive electrode active material of Comparative Example 3 without coating modification exhibits faster high temperature capacity decay and poor rate performance. 0.35 La 0.6 Although the TiO3 coating modification and the Al2O3 coating modification of comparative example 2 increased the thermal decomposition temperature to a certain extent, it caused the deterioration of the rate performance, discharge capacity and cycle stability. After the coating layer material modification of Examples 1-6 of the present application with good electrical conductivity and ion conductivity was used, the thermal decomposition temperature of the obtained composite positive electrode material was greatly improved, and its initial discharge capacity, rate performance and high temperature cycle stability were also improved.

Claims

1. A composite positive electrode material, characterized in that: The composite cathode material includes a core and a coating layer coated on the core. The core includes a cathode active material, and the coating layer includes at least one metal oxide with a general formula of Li x A y MO z , where A is selected from at least one of La, Pr, Nd, Sm, Ba, and Sr, and at least includes at least one of La, Pr, Nd, and Sm; M is selected from at least one of Co, Fe, Mn, Ni, V, Cr, Nb, Cu, Zn, Y, Mo, W, and Ta, and at least includes at least one of Co, Fe, Mn, Cu, Zn, Y, Mo, W, and Ta; 0 < x < 1, 0.2 ≤ y < 0.8, and x + y < 1, 0 < z ≤ 5.

2. The composite positive electrode material according to claim 1, characterized in that There is also a diffusion layer between the inner core and the coating layer, and the diffusion layer includes the positive electrode active material and the metal oxide. In the diffusion layer, the metal oxide diffuses into the bulk phase and / or the surface of the positive electrode active material to form a TOM bond and / or a TOA bond, and T represents the transition metal element in the positive electrode active material.

3. The composite positive electrode material according to claim 1 or 2, characterized in that: The M includes at least one of Co, Fe, and Mn.

4. The composite positive electrode material according to any one of claims 1 to 3, characterized in that The value range of x is: 0.1≤x≤0.

6.

5. The composite positive electrode material according to any one of claims 1 to 4, characterized in that: The electronic conductivity of the metal oxide at 20°C is ≥10 -5 S cm -1 , lithium ion conductivity ≥10 -5 S cm -1 .

6. The composite positive electrode material according to any one of claims 1 to 5, characterized in that: In the composite positive electrode material, the mass of the metal oxide accounts for 0.1wt%-10wt% of the mass of the positive electrode active material.

7. The composite positive electrode material according to any one of claims 1 to 6, characterized in that: The coating layer has a thickness of 1 nm-5 μm.

8. The composite positive electrode material according to claim 2, characterized in that: The thickness of the diffusion layer is 0.1 nm-20 nm.

9. The composite positive electrode material according to any one of claims 1 to 8, characterized in that: The particle size of the positive electrode active material is 50nm-50μm.

10. The composite positive electrode material according to any one of claims 1 to 9, characterized in that: In a lithium-ion battery, within the operating voltage range of the positive electrode active material, the discharge gram capacity of the metal oxide does not exceed 15% of the discharge gram capacity of the positive electrode active material.

11. The composite positive electrode material according to any one of claims 1 to 10, characterized in that: The exothermic peak temperature of the composite cathode material is at least 5% higher than the exothermic peak temperature of the cathode active material.

12. The composite positive electrode material according to any one of claims 1 to 10, characterized in that: The exothermic peak temperature of the composite positive electrode material is higher than the exothermic peak temperature of the positive electrode active material by more than 15°C.

13. A positive electrode sheet, characterized in that: The positive electrode plate comprises the composite positive electrode material according to any one of claims 1 to 12.

14. A secondary battery, characterized in that: The secondary battery comprises the positive electrode sheet as claimed in claim 13.

15. An electronic device, characterized in that: The electronic device includes the secondary battery according to claim 14.

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