Positive electrode material, and preparation method therefor and application thereof

Abstract

Embodiments of the present application provide a positive electrode material, and a preparation method therefor and an application thereof. The positive electrode material comprises a core, and a first shell layer and a second shell layer that sequentially cover the surface of the core. In a thermal runaway environment, the first shell layer material and the second shell layer material can synergistically induce the release of lattice oxygen in the core material so as to suppress the peak heat release of the positive electrode material in the thermal runaway environment and reduce the total heat generation of the positive electrode material in the thermal runaway environment, such that the positive electrode material has high thermal stability while having good intrinsic electrochemical performance, and has high safety performance.

Description

Positive electrode material, preparation method thereof, and application

[0001] This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on July 31, 2023, with the application number 202310955157.9 and the application title "Positive electrode material, preparation method thereof, and application", the entire content of which is incorporated herein by reference. Technical field

[0002] The embodiments of this application relate to the technical field of batteries, and specifically relate to a positive electrode material, a preparation method thereof, and an application. Background technique

[0003] Lithium nickel composite oxides and sodium nickel composite oxides are expected to be widely used in batteries and energy storage systems due to their high energy density and good rate performance. However, the above materials have poor thermal stability in some scenarios (such as thermal abuse, electrical abuse, etc.). For example, they generate heat through side reactions with the electrolyte and release lattice oxygen, and the concentrated release of heat can cause the battery to undergo thermal runaway, which severely restricts the large-scale application of the above materials.

[0004] In order to improve the thermal stability of the above materials, the industry chooses to coat a shell layer on the surface of the above materials, or to perform element doping on the whole material. However, the above solutions are relatively single. The surface shell layer generally suppresses side reactions by inhibiting the contact between the material and the electrolyte, and the improvement effect on the thermal stability of the material is limited; doping with some elements (such as Al) can fix the lattice oxygen of the material to improve the thermal stability, but doping the whole material will affect some intrinsic electrochemical properties of the material while improving the thermal stability, and local doping will also make the scope of action limited, basically only limited to improving the thermal stability of the doped area. Therefore, how to improve the thermal stability while maintaining the intrinsic electrochemical properties of the material is the common demand for solving the safety pain points of the above materials.

[0005] Summary of the invention

[0006] In view of this, the embodiments of this application provide a positive electrode material, a preparation method thereof, and an application. The positive electrode material has high thermal stability and high safety performance while taking into account good intrinsic electrochemical properties.

[0007] In the first aspect of this application, a positive electrode material is provided, which includes a core and a first shell layer and a second shell layer sequentially coated on the surface of the core; the core includes A(Ni 1-x M x )O2, 0 < x < 1, where A is Li and / or Na, and M is at least one of Co, Mn, Nb, Ta, V, Mo, W, and Zr;

[0008] The first shell layer includes A(Ni1-x M x ) 1-a E a O₂, 0 < x < 1, 0 < a < 1, E is at least one of Al and Mg;

[0009] The second shell layer includes a compound having Li - O and X - O bonds, and / or a compound having Na - O and X - O bonds; X is at least one of B, P, and Si.

[0010] In a thermal runaway environment, for the material in the region near the first shell layer in the core, the E element in the first shell layer has a strong polarization effect on the O in the material in this region, and A (Ni 2- has a strong polarization effect, and A (Ni 1-x M x ) 1-a E a The specific atomic arrangement structure of O₂ makes the first shell layer have a first - type induction effect on the lattice oxygen in the above - mentioned region, which can promote its removal; the second shell layer has Li - O bonds and / or Na - O bonds and X - O bonds, which can form Li - O - X bonds and / or Na - O - X bonds, and thus can further form a polyanion structure, which has a second - type induction effect on the lattice oxygen in the above - mentioned core region; therefore, under the dual action of the first - type induction effect and the second - type induction effect, the binding ability of the atoms around the lattice oxygen to it is greatly weakened, so the release of the lattice oxygen in the above - mentioned core region can be promoted (that is, the release kinetics of the lattice oxygen in the corresponding region of the core is improved), and it escapes from the cathode material in the form of oxygen, so that the heat can be dissipated before the battery cell further undergoes thermal runaway, inhibiting the peak heat release caused by the cathode material, thereby reducing the total heat generation of the cathode material, and further improving the thermal stability of the cathode material. At the same time, the small - area doping of the first shell layer hardly affects the intrinsic electrochemical performance of the cathode material. In addition, the above - mentioned second shell layer also has a physical barrier effect, hindering the side reaction between the electrolyte and the active components in the cathode material, reducing the risk of chain side reactions of the cathode material, and improving the cycling performance of the cathode material at room temperature. Therefore, the cathode material provided by the embodiments of the present application can have both good intrinsic electrochemical performance and high thermal stability, and has high safety performance.

[0011] In some embodiments of the present application, the thickness of the first shell layer is less than or equal to 10 nm. In this way, there is enough material in the first shell layer to induce the material in the corresponding region of the core to release lattice oxygen in advance, and it is also beneficial for the distance between the second shell layer and the core to be appropriate, which is conducive to the exertion of the second - type induction effect.

[0012] In some embodiments of the present application, in the first shell layer, the content of element E gradually decreases from the first shell layer towards the core. Further, the thickness of the first shell layer is less than or equal to 1 nm. A suitable thickness can enable the induction effects of both the first shell layer and the second shell layer to be fully exerted.

[0013] In some embodiments of the present application, in the first shell layer, the content of element E first increases and then decreases from the first shell layer towards the core. Such a setting can increase the maximum action depth of the first type of induction effect of the first shell layer material.

[0014] In some embodiments of the present application, in the first shell layer, the distance from the peak position of the molar content of element E to the surface of the core is 50%-80% of the thickness of the first shell layer. A more suitable peak position of the content of element E is conducive to the exertion of the first type of induction effect; at the same time, its action depth has a good overlap with the action depth of the second type of induction effect.

[0015] In some embodiments of the present application, 0 < a ≤ 0.1. This doping concentration can enable the first shell layer to have good electrochemical activity.

[0016] In some embodiments of the present application, any 1 μm 2 The thickness difference within the range is less than or equal to 6 nm. In this way, the second shell layer has high uniformity, so that on the circumferential length of the core, the second type of induction effect it receives is relatively uniform, which is conducive to the lattice oxygen in the corresponding area of the core being released from the cathode material in the form of oxygen in advance.

[0017] In some embodiments of the present application, any 1 μm 2 In the material of the second shell layer with a thickness of 1 nm - 5 nm per unit area, the molar content of element X is within the range of greater than 0 to less than or equal to 13%. In this way, there is an appropriate amount of polyanion structure in the second shell layer, which can not only better achieve the second type of induction effect, but also has good ionic conductivity itself.

[0018] In some embodiments of the present application, the surface layer of the second shell layer includes a plurality of closely arranged nanoparticles, and there are pores between adjacent nanoparticles, and the pore diameter of the pores is less than or equal to 1 nm. In this way, the second shell layer is relatively dense, which can better isolate the electrolyte and further reduce the risk of side reactions between the cathode material and the electrolyte.

[0019] In some embodiments of this application, a cross-composite layer is further provided between the first shell layer and the second shell layer. The cross-composite layer includes the compound having Li-O and XO bonds and / or the compound having Na-O and XO bonds, as well as the element E. The presence of the cross-composite layer makes the combined effect of the first and second type of inductive effects more pronounced, which is more conducive to reducing the total heat generation of the cathode material.

[0020] In some embodiments of this application, the thickness of the cross-composite layer is less than or equal to 2 nm. This facilitates controlling the insertion / extraction path length of active ions in the cathode material within a suitable range.

[0021] In some embodiments of this application, the A(Ni) 1-x M x O2 has a layered structure.

[0022] The second aspect of this application provides a method for preparing a cathode material, which can be used to prepare the cathode material provided in the first aspect of this application, including:

[0023] The substrate is placed in a reaction chamber filled with dry gas, and a first reaction material and a second reaction material are introduced. After atomic layer deposition, a positive electrode material is prepared. The first reaction material includes an A element source, an X element source, and an E element source. The second reaction material includes an O element source.

[0024] The cathode material preparation method provided in this application embodiment generates a first shell layer and a second shell layer in situ on the substrate surface simultaneously through atomic layer deposition. This method has high process reliability and significantly improves the controllability of the thickness and uniformity of the first and second shell layers. It can ultimately obtain a cathode material with both good electrochemical performance and high thermal stability. At the same time, it can realize the large-scale industrial production of cathode materials.

[0025] In some embodiments of this application, when the first reactant is introduced into the reaction chamber, the A element source, the X element source, and the E element source are introduced alternately. This facilitates a more complete reaction of each material source.

[0026] In some embodiments of this application, the reactants after atomic layer deposition are placed in an oxygen environment for heat treatment. This allows element E to diffuse further towards the center of the substrate and form a gradient doping within the second shell, and allows the material of the second shell to be wholly or partially transformed from an amorphous phase into a crystalline phase.

[0027] A third aspect of this application provides a positive electrode sheet, including the positive electrode material provided in the first aspect of this application, or the positive electrode material prepared by the preparation method provided in the second aspect. This positive electrode sheet can be used for lithium-ion batteries or for sodium-ion batteries.

[0028] A fourth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator and electrolyte located between the positive and negative electrode, as provided in the third aspect of this application. This secondary battery exhibits both good electrochemical performance and high safety performance, particularly high energy density and low risk of thermal runaway. The aforementioned secondary battery can be a lithium-ion battery or a sodium-ion battery.

[0029] A fifth aspect of this application provides an electrical device, including the secondary battery provided in the fourth aspect of this application. Because this electrical device uses the secondary battery provided in this application for power supply, it has good market prospects. In some embodiments of this application, the aforementioned electrical device includes, but is not limited to, 3C electronic devices, powered vehicles, etc.

[0030] A sixth aspect of this application provides an energy storage system, including the secondary battery provided in the fourth aspect of this application. Because it uses the secondary battery provided in this application, the energy storage system can have better thermal stability and safety performance. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the structure of a cathode material provided in an embodiment of this application;

[0032] Figure 2 is a schematic diagram of the structure of a positive electrode material provided in another embodiment of this application;

[0033] Figure 3 is a scanning electron microscope (SEM) image of a cathode material provided in an embodiment of this application;

[0034] Figure 4 is a TEM image of the cathode material provided in Embodiment 1 of this application;

[0035] Figure 5 is a TEM image of the cathode material provided in Embodiment 2 of this application;

[0036] Figure 6A shows the DSC curves of the positive electrode materials of Example 1 and Comparative Example 2 in a closed electrolyte system;

[0037] Figures 6B and 6C show the thermogravimetric curves of the cathode materials of Example 1 and Comparative Example 2 of this application, and the curves showing the change of oxygen production with temperature, respectively.

[0038] Figure 7A shows the DSC curves of the positive electrode materials of Example 2 and Comparative Example 2 in a closed electrolyte system;

[0039] Figures 7B and 7C show the thermogravimetric curves of the cathode materials of Example 2 and Comparative Example 2 of this application, and the curves showing the change of oxygen production with temperature, respectively.

[0040] Figure 8 shows the DSC curves of the cathode materials of Comparative Example 1 and Comparative Example 2 in a closed electrolyte system.

[0041] Figure 9A shows the time-of-flight secondary mass spectrometry (TOF-SIMS) test results of phosphorus in the cathode material of Example 1 at different etching times;

[0042] Figure 9B shows the TOF-SIMS test results of aluminum in the cathode material of Example 1 at different etching times;

[0043] Figure 10A shows the TOF-SIMS test results of phosphorus in the cathode material of Example 2 at different etching times;

[0044] Figure 10B shows the TOF-SIMS test results of aluminum in the cathode material of Example 2 at different etching times;

[0045] Figure 11 shows the X-ray photoelectron spectroscopy (XPS) test results of the cathode material in Example 1;

[0046] Figure 12 shows the XPS test results of the cathode material in Example 2;

[0047] Figure 13 shows the X-ray diffraction (XRD) spectra of the cathode materials of Examples 1 and 2, and the cathode material of Comparative Example 2.

[0048] Explanation of the reference numerals: 100 - cathode material; 10 - core; 21 - first shell; 22 - second shell; 23 - cross-composite layer. Detailed Implementation

[0049] To meet the market's high energy density requirements for batteries, lithium nickel composite oxides / sodium nickel composite oxides are expected to be widely used in secondary batteries and energy storage devices. However, the thermal runaway of batteries caused by the poor thermal stability of lithium nickel composite oxides / sodium nickel composite oxides is one of the main reasons hindering the large-scale application of the above materials. Taking the commonly used nickel cobalt manganese ternary cathode material (abbreviated as NCM) for lithium secondary batteries as an example, the high energy density characteristics of NCM are premised on sacrificing thermal stability. The higher the Ni content in the NCM material, the higher the energy density of the material, and the worse the thermal stability and structural stability. During the thermal decomposition process of the NCM ternary material, phase changes occur, and the phase change process is accompanied by the release of lattice oxygen, generating a large amount of heat. At the same time, the NCM material also reacts with the electrolyte to generate free radicals, which will initiate a chain reaction to release heat. When the temperature of the battery cell increases rapidly in a short time, it will trigger the thermal runaway of the cell and even spread to the entire battery, resulting in the thermal runaway of the battery.

[0050] To solve the above problems, an embodiment of the present application provides a cathode material. Please refer to FIG. 1, which is a schematic structural diagram of the cathode material according to an embodiment of the present application. The cathode material 100 includes a core 10 and a first shell layer 21 and a second shell layer 22 sequentially coated on the surface of the core 10; the core 10 includes A(Ni 1-x M x )O2, where A is Li and / or Na, and M is at least one of Co, Mn, Nb, Ta, V, Mo, W, and Zr;

[0051] The first shell layer 21 includes A(Ni 1-x M x ) 1-a E a O2, 0 < x < 1, 0 < a < 1, and E is at least one of Al and Mg;

[0052] The second shell layer 22 includes a compound having Li-O and X-O bonds, and / or a compound having Na-O and X-O bonds; X is at least one of B, P, and Si.

[0053] Exemplarily, the above cathode material 100 is the cathode material 100 for a lithium ion battery. The above core includes Li(Ni 1-x M x )O2. Then, the second shell layer 22 includes a compound having Li-O bonds and X-O bonds; when the core material is in Li(Ni 1-x M xWhen Na is doped at the Li site in addition to O2, the second shell 22 includes compounds with Li-O bonds and XO bonds, and may also include compounds with Li-O and / or Na-O bonds and XO bonds. Similarly, when the above-mentioned positive electrode material 100 is a positive electrode material 100 for sodium-ion batteries, the core includes Na(Ni) 1-x M x If O2 is present, then the second shell 22 includes compounds with Na-O bonds and XO bonds; based on this, when the core material Na(Ni) 1-x M x When the Na site of O2 is also doped with Li, the second shell 22 may also include compounds with Li-O bonds and XO bonds.

[0054] The aforementioned first shell 21 includes A(NiM) 1-x E x O2, E ions (specifically Al) 3+ Mg 2+ For the O in the above kernel region 2- It possesses strong polarization properties. Furthermore, the composition of the first shell 21 is essentially E element doped at transition metal sites in the core material, exhibiting a specific atomic arrangement. When the cathode material 100 is heated (under a thermal flooding environment), the material of the first shell 21 exerts a first-type inductive effect on the material near the first shell 21 region of the core, promoting the release of lattice oxygen in the corresponding region of the core, enhancing the oxygen release kinetics in the corresponding region of the core, and thus increasing the oxygen release amount in the corresponding region of the core. Moreover, compared to overall doping in the prior art, the small-area elemental doping in the cathode material 100 of this embodiment hardly affects the intrinsic electrochemical performance of the material; therefore, the cathode material 100 also possesses a high energy density. Furthermore, the aforementioned E ion doping in A(Ni 1-x M x In O2, lattice oxygen in the first shell material can be fixed, suppressing cation mixing in the first shell 21, while improving the thermal stability and cycle performance of the material in the first shell 21. Figure 13 shows the cathode material 100 and LiNi provided in two embodiments of this application. 0.836 Co 0.104 Mn 0.06 The XRD pattern of O2 (equivalent to the core of cathode material 100) shows that small-area doping of element E did not significantly change the crystal structure of cathode material 100.

[0055] Compounds containing Li-O and / or Na-O and XO bonds in the second shell 22 can form Li-OX and / or Na-OX bonds, thereby further forming a polyanionic structure. When heated, it has a second type of inductive effect on the lattice oxygen in the region of the core 10 near the second shell 22. Under the synergy of the first type of inductive effect from the first shell 21, the binding ability of the atoms around the lattice oxygen in the material of the aforementioned core region is greatly reduced, making the lattice oxygen easier to release, improving its oxygen release kinetics, increasing the amount of oxygen released, thereby reducing heat dissipation before the cell is further heated and runaway, suppressing the peak heat release caused by the positive electrode material 100, thereby reducing the total heat generation of the positive electrode material 100, and thus improving the thermal stability of the positive electrode material 100, controlling and slowing down the heat spread in the battery, and improving the safety performance of the battery. Furthermore, compounds with Li-O and XO bonds, and / or compounds with Na-O and XO bonds, exhibit high ionic conductivity, which can enhance the deintercalation / intercalation rate of active ions on the surface of the cathode material 100, thus improving the rate performance of the battery. In addition, the second shell layer 22, as the surface layer of the cathode material 100 particles, forms a physical barrier between the cathode material 100 and the electrolyte, preventing side reactions between the electrolyte and the active components in the cathode material 100. Simultaneously, it can suppress surface damage and electrical performance degradation caused by side reactions between the electrolyte and the highly delithiated cathode material 100 at room temperature, thereby improving the battery's room-temperature cycle performance.

[0056] Figures 6A and 7A show the DSC test curves of the cathode material 100 in a closed electrolyte system. It can be seen that the total heat release of the cathode material 100 provided in this embodiment is less than that of the cathode material 100 in the prior art (equivalent to a core without the first shell 21 and the second shell 22).

[0057] It should be further explained that, in the direction from the core surface to the core center, the core region with a depth of H1 (H1>0) can increase the oxygen release when subjected to the dual induction effect; at the same time, the core material in the region with a depth of H1+h (h>0) will also be affected by the above reaction, which may also increase the oxygen release, thereby promoting more lattice oxygen pre-decomposition in the core, further dispersing and suppressing the peak exothermic reaction caused by the cathode material 100.

[0058] Please refer to Figures 6B and 7B, which show the weight loss curves of the cathode material 100 provided in this application embodiment as a function of temperature. In the range of 200℃-300℃, the weight loss rate of the cathode material 100 provided in this application embodiment is significantly higher than that of the cathode material 100 in the prior art. This indicates that more lattice oxygen is released from the cathode material 100 provided in this application embodiment within this temperature range, resulting in a higher weight loss rate of the cathode material 100.

[0059] Furthermore, the aforementioned lattice oxygen is in an unstable free oxygen state when it is extracted from the unit cell. However, this free oxygen reacts with each other to generate oxygen during the process of passing through the first shell 21 and the second shell 22. Therefore, the aforementioned lattice oxygen ultimately escapes from the cathode material 100 in the form of oxygen. In this way, it is possible to avoid further side reactions between the free oxygen and the electrolyte, which would lead to heat generation. Please refer to Figures 6C and 7C. The oxygen production of the cathode material 100 provided in this embodiment is significantly higher than that of materials in the prior art in the range of 200°C-250°C.

[0060] In summary, the aforementioned cathode material 100 can improve thermal stability while maintaining electrochemical performance.

[0061] In the embodiments of this application, the presence of Li-O bonds, Na-O bonds and XO bonds can be characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS) or X-ray photoelectron spectroscopy (XPS).

[0062] In this embodiment of the application, Raman spectra can be used to characterize the doping sites of element E.

[0063] In this embodiment, the M element in the core and the first shell 21 are each independently selected from at least one of Co, Mn, Nb, Ta, V, Mo, W, and Zr. The M element in the core and the M element in the first shell 21 may or may not be identical. For example, the value of x can be 0.1, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, etc. Specifically, taking the positive electrode material 100 for lithium-ion batteries as an example, the material of the core includes, but is not limited to, LiNi. 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), etc. Correspondingly, when the core material is NCM811, the material of the first shell 21 can be, but is not limited to, Li (Ni). 0.8 Co 0.1 Mn 0.1 ) 1-x E xO2; specifically, the value of 'a' can be, but is not limited to, 0.001, 0.005, 0.01, 0.02, 0.05, 0.08, 0.09, etc. Similarly, when the core material is other materials, the material of the first shell layer 21 can be analogized according to the above principles, which will not be elaborated here. For example, taking the positive electrode material 100 for sodium-ion batteries as an example, the core material includes, but is not limited to, NaNi. 0.5 Mn 0.5 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2. When using the cathode material 100 for sodium-ion batteries, the material of the first shell layer 21 is also analogous to that of the cathode material 100 for lithium-ion batteries, and will not be described in detail here.

[0064] In some embodiments of this application, the thickness of the first shell layer 21 is less than or equal to 10 nm. Specifically, the thickness of the first shell layer can be 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, etc. By controlling the thickness of the first shell layer 21 within the above range, sufficient material can be induced to release lattice oxygen in the corresponding region of the core, and the effective distance of the second induction effect of the second shell layer 22 material is controlled within a suitable range, thereby facilitating the exertion of the dual induction effect and further promoting the release of the aforementioned lattice oxygen. Furthermore, its proportion within the cathode material 100 is also appropriate, which is beneficial to the intrinsic electrochemical performance of the cathode material 100. The greater the thickness of the first shell layer 21, the more pronounced its first-type induced effect, which may help further reduce the total heat generation of the cathode material 100. However, the distance of its induced effect has an upper limit; simply increasing the thickness of the first shell layer 21 will not necessarily increase the depth of the region in the core that promotes the release of lattice oxygen. In this embodiment, TOF-SIMS can be used to characterize the thickness of the first shell layer 21 by measuring the change in elemental content with depth.

[0065] In some embodiments of this application, the content of element E in the first shell 21 gradually decreases from the first shell 21 towards the core. That is, A(Ni) 1-x M x ) 1-a E aIn O2, the value of a gradually decreases from the first shell 21 towards the core. Specifically, the content of element E in the first shell 21 (the value of a) can decrease linearly or non-linearly from the first shell 21 towards the core. Furthermore, the thickness of the first shell 21 is ≤1 nm. Understandably, the region with a high concentration of element E doping in the first shell 21 (a larger value) has a stronger effect on inducing lattice oxygen release. Controlling the thickness of the first shell 21 to be smaller is beneficial for maximizing the inductive effect of the first shell 21 material in the aforementioned region, and also for increasing the depth of the second type of inductive effect of the second shell 22 material in the core, enhancing its inductive effect. Under the synergistic effect of both, it is more conducive to reducing the total heat generation of the cathode material 100 under thermal flooding conditions. Specifically, the thickness of the first shell 21 can be 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, etc.

[0066] In some embodiments of this application, in the first shell 21, the content of element E first increases and then decreases from the first shell 21 toward the core. That is, A(Ni) 1-x M x ) 1-a E a In O2, the value of a first increases and then decreases from the first shell 21 towards the core. This effectively pushes the maximum depth of the first-type inductive effect towards the core, facilitating the exertion of the inductive effect of the first shell 21 material. Specifically, the content of element E (the value of a) in the first shell 21 can vary linearly or non-linearly with the thickness of the first shell 21.

[0067] In some embodiments of the present application, in the direction from the first shell layer 21 towards the inner core, the content of element E first increases and then decreases. At this time, the thickness of the first shell layer 21 is within the range of 1 nm to 10 nm. Specifically, at this time, the thickness of the first shell layer 21 can be 1 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm, 5.0 nm, 5.5 nm, 6.0 nm, 6.5 nm, 7.0 nm, 7.5 nm, 8.0 nm, 8.5 nm, 9.0 nm, 9.5 nm, etc. At this time, in some specific embodiments, in the thickness direction of the first shell layer 21, the distance from the position of the peak content of element E in the first shell layer 21 (that is, the position of the maximum value of a) to the surface of the inner core is 50% - 80% of the thickness of the first shell layer. Specifically, the distance from the position of the peak content of element E in the first shell layer 21 to the surface of the inner core can be specifically 50.0%, 52.5%, 55.0%, 57.5%, 60.0%, 62.5%, 65.0%, 67.5%, 70.0%, 72.5%, 75.0%, 77.5%, 80.0%, etc. In this way, it is beneficial to exert the first type of induction effect, and at the same time, its action depth has a good overlap with the action depth of the second type of induction effect. In the embodiments of the present application, TOF - SIMS can be used to characterize the position of the peak content of element E from the surface of the inner core.

[0068] In some embodiments of the present application, 0 < a ≤ 0.1. That is, the molar content of element E in the first shell layer 21 is greater than 0 and less than or equal to 10%. Controlling the value of a (the doping amount of element E) within the above range can achieve a good first type of induction effect in the first shell layer 21 without losing the electrochemical activity of the first shell layer 21; at the same time, it can also make the lattice oxygen in the first shell layer 21 be better fixed, prevent cation mixing, be beneficial to the insertion and extraction of active ions in the first shell layer 21, and be beneficial to the rate of active ions in the inner core when passing through the first shell layer 21. Specifically, the value of a can be specifically 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, etc. In some specific embodiments, 0.001 ≤ a ≤ 0.1. In the embodiments of the present application, TOF - SIMS or XPS can be used to characterize the molar content of element E.

[0069] In some embodiments of the present application, for any 1 μm of the second shell layer 22 2 the thickness difference within the range is less than or equal to 6 nm. That is, for any 1 μm of the second shell layer 22 2Within the specified range: the maximum thickness of the second shell 22 minus the minimum thickness of the second shell 22 ≤ 6 nm. This ensures that the thickness of the second shell 22 is relatively uniform throughout, resulting in a more uniform distribution of the second type of induced effect along the circumference of the core in the cathode material 100. This facilitates the release of lattice oxygen in the corresponding region of the core, thereby improving the thermal stability of the cathode material 100. Specifically, any 1 μm thickness of the second shell 22... 2 The thickness difference within the range can be 0, 0.5nm, 1.0nm, 1.5nm, 2.0nm, 2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm, 5.0nm, 5.5nm, 6.0nm, etc.

[0070] In some embodiments of this application, any 1μm of the second shell 22 2 The thickness of the second shell 22 is in the range of 2nm-10nm. Controlling the thickness of the second shell 22 within this range allows for an appropriate amount of material in the second shell 22 to exert its second type of inductive effect on the core material, thereby promoting the release of lattice oxygen in the corresponding region of the core. Simultaneously, the second shell 22 has a suitable thickness, which is beneficial for controlling the insertion / extraction pathways of active ions within a suitable range, while also providing sufficient path length for the oxygen free radicals released from the core to be converted into oxygen and then released to the outside of the cathode material 100. The suitable and uniform thickness of the second shell 22 also facilitates its isolation from the electrolyte, avoiding more side reactions. Specifically, any 1μm thickness of the second shell 22... 2 The thicknesses within this range can specifically be 2.0nm, 2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm, 5.0nm, 5.5nm, 6.0nm, 6.5nm, 7.0nm, 7.5nm, 8.0nm, 8.5nm, 9.0nm, 9.5nm, 10.0nm, etc.

[0071] In some embodiments of this application, any 1μm 2 In the material of the second shell layer 22 with an area of ​​1 nm to 5 nm and a thickness, the molar content of element X is in the range of greater than 0 and less than or equal to 13%. For ease of description, any 1 μm 2In the material of the second shell layer 22 with an area of 1 nm - 5 nm in thickness, the molar content of element X is denoted as b, where 0 < b ≤ 13%. In some specific embodiments of the embodiments of the present application, 0.1% ≤ b ≤ 13%. Controlling the molar content of element X within the above range enables an appropriate amount of polyanion structure in the second shell layer 22, so as to better achieve the second type of induction effect on the material in the corresponding region of the inner core, thereby facilitating the release of the above lattice oxygen; furthermore, it also helps to ensure that the ionic conductivity of the material of the second shell layer 22 is better, which is beneficial to the rate performance of the positive electrode material 100. Specifically, the above b can specifically be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 2.%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, etc.

[0072] In some embodiments of the present application, the material of the second shell layer 22 is an amorphous phase. In some embodiments, the material of the second shell layer 22 is a crystalline phase. In other embodiments, the material of the second shell layer 22 includes a crystalline phase and an amorphous phase. Those skilled in the art can select according to actual application needs.

[0073] In some embodiments of the present application, the surface of the second shell layer 22 includes a plurality of closely arranged nanoparticles. During the preparation process of the positive electrode material 100, if the atomic layer deposition method is used to prepare the first shell layer 21 and the second shell layer 22, it may cause nanoparticles to be arranged on the surface of the second shell layer 22, and pores will be formed between adjacent nanoparticles. In some embodiments of the present application, there are pores between adjacent nanoparticles, and the pore diameter of the pores is less than or equal to 1 nm. Controlling the pore diameter of the above pores within the above range can improve the densification of the second shell layer 22, thereby enhancing the effect of the second shell layer 22 as a physical barrier and further reducing the risk of side reactions between the positive electrode material 100 and the electrolyte. Specifically, the pore diameter of the above pores can specifically be 0.05 nm, 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, etc. In some other specific embodiments of the present application, there are no pores on the surface layer of the second shell layer 22. At this time, it is more conducive to ensuring the densification of the second shell layer 22, thereby further reducing the risk of side reactions between the positive electrode material 100 and the electrolyte.

[0074] In this embodiment, the surface layer of the second shell 22 is densely packed with multiple nanoparticles. The second shell 22 may include a dense bottom layer covered with a single layer of nanoparticles; or the bottom layer may have two or more layers of nanoparticles arranged on it; or a portion of the bottom layer may be covered with a single layer of nanoparticles, while another portion may have two or more layers of nanoparticles arranged on it; however, this is not limited to these embodiments. For a specific morphology, please refer to Figure 3, which is an SEM image of the cathode material 100 according to an embodiment of this application. In this embodiment, the particle size of the nanoparticles may be less than or equal to 10 nm, less than or equal to 100 nm, or less than or equal to 500 nm, but is not limited to these. In this embodiment, the shape of the nanoparticles may be spherical, quasi-spherical, sheet-like, etc., but is not limited to these.

[0075] In some embodiments of this application, referring to Figure 2, a cross-composite layer 23 is further provided between the first shell 21 and the second shell 22. The cross-composite layer 23 includes compounds with Li-O and XO bonds and / or compounds with Na-O and XO bonds, as well as element E. In the cross-composite layer 23, element E tends to form a tetrahedral structure with some compounds containing Li-OX bonds and / or Na-OX bonds, exhibiting a first-type inductive effect on the material in the corresponding region of the core. The other part of the compounds with Li-O and XO bonds and / or compounds with Na-O and XO bonds exhibits a second-type inductive effect on the material in the corresponding region of the core. Therefore, the combined effect of the two types of inductive effects is more pronounced, thus more conducive to inducing the release of lattice oxygen. In some specific embodiments of this application, the composite cross-layer simultaneously contains the materials of the first shell 21 and the second shell 22. In some specific embodiments of this application, the E element in the region of the composite cross layer near the second shell 22 can form chemical bonds with the compounds in the second shell 22 that have Li-O bonds and XO bonds, and / or the compounds that have Na-O bonds and XO bonds, thereby improving the interfacial bonding force between the first shell 21 and the composite cross layer, which is beneficial to improving the structural stability of the cathode material 100.

[0076] In some embodiments of the present application, the thickness of the cross-composite layer 23 is less than or equal to 2 nm. The thickness of the cross-composite layer 23 being less than or equal to 2 nm means that, along the direction from the inner core to the first shell layer 21, the thickness extending from the surface of the first shell layer 21 towards the second shell layer 22 is less than or equal to 2 nm. Controlling the thickness of the cross-composite layer 23 within the above range, its existence will not affect the induction effect of the second shell layer 22 on the material in the corresponding area of the inner core under overheating conditions, and at the same time, it is also beneficial to control the diffusion path of active ions in the positive electrode material 100 within a relatively short range. In some specific embodiments, due to the preparation method, there may be a small amount of element E in the second shell layer 22. In some specific embodiments, the thickness of the cross-composite layer 23 is 0.1 nm - 2 nm. Specifically, the thickness of the cross-composite layer 23 can specifically be 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, etc.

[0077] In some embodiments of the present application, the material of the inner core has a layered structure. For the lithium-ion positive electrode material 100, its layered structure means that the inner core material can be divided into a Li layer and a transition metal oxide layer; for the sodium-ion positive electrode material 100, its layered structure includes a transition metal layer, and sodium ions are located between the layers of the transition metal layer, forming an alternating layered structure.

[0078] In some embodiments of the present application, the inner core material includes A(Ni 1-x M x )O2, where 0 < x ≤ 0.2. Specifically, the value of x can specifically be 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.19, 0.20, etc. Especially for Li(Ni 1-x M x )O2, the molar content of Ni element in the inner core material is greater than or equal to 80%. For example, 80% - 87%, etc. Increasing the molar content of Ni in the inner core can improve the capacity of the positive electrode material 100, so the energy density of the final battery can be improved.

[0079] In the embodiments of the present application, the D of the positive electrode material 100 VThe particle size of Dv50 is in the range of 2μm to 20μm. Those skilled in the art can select the appropriate size based on actual application needs. Specifically, the Dv50 particle size of the cathode material 100 can be 2μm, 3μm, 4μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, or 20μm. Dv50 refers to the particle size corresponding to 50% of the volume distribution of the cathode material 100, and can be measured by a laser particle size analyzer.

[0080] Accordingly, this application also provides a method for preparing a cathode material, which can be used to prepare the aforementioned cathode material 100, comprising:

[0081] The substrate is placed in a reaction chamber filled with dry gas, and a first reactant and a second reactant are introduced. The first reactant includes an A element source, an X element source, and an E element source; the E element includes at least one of Al and Mg; the X element includes at least one of B, P, and Si; and the second reactant includes an O element source. After atomic layer deposition (ALD), a positive electrode material is prepared. Further, in some specific embodiments, the A element in the A element source is the same as the A element in the substrate. It can be understood that when preparing a positive electrode material for lithium-ion batteries, if the A element in the substrate includes Li, then the A element source can be a lithium element source; further, when the material in the substrate is also doped with Na at its Li sites, the A element source can include a Li element source and / or a sodium element source. Similarly, when preparing a positive electrode material for sodium-ion batteries, the above principles can be applied by analogy, and will not be elaborated further here.

[0082] By processing the substrate using the above process, a first shell and a second shell can be formed simultaneously in situ. The resulting cathode material exhibits high compatibility between the first shell and the core, as well as high compatibility between the first and second shells, and good interfacial bonding between them. Specifically, the first reactant is adsorbed onto the substrate surface, and the second reactant reacts chemically with the adsorbed first reactant on the substrate surface, generating a second shell and byproducts on the substrate surface. This allows the spontaneous diffusion of element E from the element source into the surface material of the substrate, achieving small-area doping. This transforms the surface substrate into the first shell and the internal substrate into the core. Furthermore, due to the self-limiting properties of ALD, the chemical reaction automatically terminates after the first reactant has completely reacted, allowing the removal of residual second reactant and byproducts from the system, and enabling atomic-level thickness control. Therefore, the above process can flexibly and precisely control the thickness of the first and second shells, while also ensuring the uniformity of the first and second shells, thus improving the overall performance of the cathode material.

[0083] In some embodiments of this application, since the cathode material is prepared by the above method, a small amount of E element is also present in the second shell.

[0084] In this embodiment, the reaction chamber is the reaction chamber of an atomic layer deposition apparatus. The dry gas filling the reaction chamber can specifically be dry air.

[0085] In the embodiments of this application, both the first reaction raw material and the second reaction raw material are in a gaseous state.

[0086] In some embodiments of this application, the above preparation method can be further broken down into steps S01-S04:

[0087] Step S01: Place the substrate in a reaction chamber filled with dry gas and heat it to a first preset temperature; in some specific embodiments, the first preset temperature is in the range of 200℃-300℃. Specifically, the first preset temperature can be 200℃, 210℃, 220℃, 250℃, 260℃, 280℃, 300℃, etc.

[0088] Step S02: Introduce the first reaction material into the reaction chamber. After a first preset time, introduce inert gas into the reaction chamber to clean the reaction chamber, so as to remove the first reaction material that failed to be adsorbed on the surface of the substrate.

[0089] Step S03: Introduce the second reaction material into the above reaction chamber. After a second preset time, introduce inert gas to purge the reaction chamber to remove excess second reaction material and byproducts.

[0090] Furthermore, this embodiment also includes step S04: repeating steps S02-S03 several times to obtain the cathode material. The thickness of the second shell can be adjusted by controlling the number of repetitions (deposition cycles), especially achieving atomic-level thickness control. The number of repetitions can be ≥10 times, and in some specific embodiments, it can be ≥15 times, for example, 16-50 times. Specifically, the number of repetitions can be 16, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48 times, etc., and can be selected according to actual application requirements.

[0091] In some embodiments of this application, step S05 is further included: placing the reactants after atomic layer deposition in an oxygen environment for heat preservation treatment. This heat preservation treatment allows the material of the second shell layer to transform entirely or partially from an amorphous phase into a crystalline phase. Furthermore, it can further promote the diffusion and doping of element E towards the center of the substrate, increasing the thickness of the first shell layer and forming gradient doping within it. Specifically, after the heat preservation treatment, the thickness of the first shell layer in the cathode material can be controlled within the range of 1 nm-10 nm, and the content of element E in the first shell layer first increases and then decreases along the direction from the first shell layer to the core. In some specific embodiments, the thickness of the first shell layer is 7 nm-9 nm. In some specific embodiments, the peak position of the element E content in the first shell layer is 50%-80% of the thickness of the first shell layer from the surface of the core.

[0092] In some embodiments of this application, the reactants after atomic layer deposition can be transferred to a tubular reactor and subjected to heat treatment in an oxygen environment. After cooling, the positive electrode material is obtained. In embodiments of this application, the heat treatment temperature can be higher than the aforementioned second preset reaction temperature. In embodiments of this application, the cooling can be natural cooling.

[0093] In some specific embodiments of this application, the conditions for the above-mentioned heat preservation treatment are: heat preservation at 300℃-600℃ for 2h-6h. Specifically, the heat preservation temperature can be 300℃, 325℃, 350℃, 375℃, 400℃, 425℃, 450℃, 475℃, 500℃, 525℃, 550℃, 575℃, etc.; the heat preservation time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, etc. The above-mentioned heat preservation temperature is conducive to the diffusion of element E towards the center of the substrate, and also conducive to the crystallization of the second shell material, without damaging the structure of the core material. In some specific embodiments of this application, the heating rate during the heat preservation treatment is in the range of 1℃ / min-10℃ / min. This is conducive to the further diffusion of element E, as well as the crystallization of the second shell material and the regulation of the crystal structure. Specifically, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, etc.

[0094] In some embodiments of this application, in step S02, when the first reactant is introduced into the reaction chamber, the A element source, the X element source, and the E element source are introduced alternately. Specifically, each time the first reactant is introduced, it can be in the order of A element source / X element source / E element source, or in the order of E element source / X element source / A element source, or X element source / E element source / A element source, but is not limited to this; when steps S02-S03 need to be repeated, the order in which the above-mentioned element sources are introduced can be different when the first reactant is introduced and when the first reactant is introduced for the i-th time (i is a positive integer greater than 1).

[0095] In some specific embodiments of this application, step S02 may include: introducing element A source 3-5 times, element X source 1-3 times, and element E source 3-5 times into the reaction chamber. There is no specific restriction on the order in which these element sources are introduced, as long as the same element source is not introduced twice consecutively. This facilitates sufficient reaction between substances to generate a uniform second shell and also facilitates the doping of element E on the substrate surface. In the embodiments of this application, the introduction time and flow rate of different element sources can be the same or different. The selection can be based on the actual reaction characteristics and material characteristics. In some specific embodiments, the duration of a single introduction of element A source can be 200ms-400ms, the duration of a single introduction of element X source can be 1100ms-1300ms, and the duration of a single introduction of element E source can be 200ms-400ms, but is not limited to these.

[0096] In this application embodiment, the A element source includes at least one of a Li element source and a Na element source. The Li element source includes, but is not limited to, at least one of lithium tert-butoxide and lithium cyclopentadiene. The Na element source includes, but is not limited to, at least one of sodium ethoxide and sodium tert-butoxide. The X element source includes at least one of a P element source, a Si element source, and a B element source. The P element source includes, but is not limited to, at least one of triethyl phosphate, trimethyl phosphate, tris(dimethylamino)phosphine, and diethyl phosphate. The Si element source includes, but is not limited to, at least one of hexamethylsilanediamine, bis(diethylamino)silane, and tris(dimethylamino)silane. The B element source includes, but is not limited to, at least one of triethyl borate and triethylboron. The E element source includes, but is not limited to, at least one of an Al element source, a Mg element source, and a Ti element source. The Al element source includes, but is not limited to, organoaluminum compounds, and organoaluminum compounds include, but are not limited to, at least one of trimethylaluminum, triethylaluminum, and aluminum sec-butoxide. The Mg source includes, but is not limited to, organomagnesia compounds, including, but not limited to, at least one of bis(pentamethylcyclopentene)magnesium, magnesium acetylacetonate octahydrate, bis(n-propylcyclopentadiene)magnesium, and 1,1,1-trifluoroacetylacetonate magnesium. The Ti source includes, but is not limited to, organotitanium compounds, including, but not limited to, at least one of titanium tetrachloride, tetra(ethylmethylamino)titanium, tetra(dimethylamino)titanium, and isopropyl titanate.

[0097] In some embodiments of this application, in step S03, the source of the O element is including but not limited to O3 or H2O.

[0098] In some embodiments of this application, in step S03, the duration of a single introduction of the O element source can be 100ms-300ms, and the number of introductions can be 2-5.

[0099] In this embodiment, the substrate is the same material as the core material in the aforementioned cathode material. In other words, the substrate includes A(Ni) 1-x M x O2, wherein A is Li and / or Na, and M is at least one of Co, Mn, Nb, Ta, V, Mo, W and Zr.

[0100] In some embodiments of this application, taking materials for lithium-ion batteries as an example, the aforementioned substrate includes, but is not limited to, LiNi. 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), etc. Furthermore, in materials for lithium-ion batteries, the molar content of Ni in the substrate is greater than or equal to 80%.

[0101] This application also provides a positive electrode sheet for a battery, including a current collector and a positive active material layer disposed on at least one side of the current collector; the positive active material layer includes the positive electrode material 100 provided in this application. In some embodiments, the positive active material layer includes a positive active material and a binder. In some specific embodiments, the positive active material layer also includes a conductive agent.

[0102] The positive electrode current collector includes, but is not limited to, metal foil or alloy foil. Specifically, when the battery is a lithium secondary battery, the aforementioned metal foil can be aluminum foil or carbon-coated aluminum foil. Specifically, when the battery is a sodium secondary battery, the aforementioned metal foil can be, but is not limited to, aluminum foil or carbon-coated aluminum foil.

[0103] In this application embodiment, there are no special limitations on the binder and conductive agent in the positive electrode active material; they can be any binder and conductive agent known in the art for positive electrode sheets. Exemplarily, the binder includes, but is not limited to, at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylate, polyacrylamide (PAM), and polyimide (PI). The conductive agent can specifically include, but is not limited to, at least one of acetylene black (AB), Ketjen black, Super P conductive carbon black, graphite, graphene, carbon nanotubes, and carbon fibers.

[0104] This application also provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte and a separator located between the positive and negative electrode, and corresponding connecting components and circuits. Specifically, this secondary battery can be a lithium-ion battery or a sodium-ion battery. The negative electrode includes a negative current collector and a layer of negative active material disposed on the negative current collector. The negative electrode, separator, and electrolyte can be any negative electrode, separator, and electrolyte known in the art, and can be selected according to actual needs.

[0105] The secondary battery provided in this application embodiment has both good electrochemical performance and high safety performance, especially high energy density and low risk of thermal runaway. The aforementioned secondary battery can be a lithium secondary battery or a sodium secondary battery.

[0106] This application also provides an electrical device, including the secondary battery provided in this application embodiment. This electrical device includes, but is not limited to, 3C electronic products, such as mobile phones, laptops, tablets, drones, wearable electronic devices, etc. The electrical device may also include powered vehicles, such as new energy vehicles, electric bicycles, etc.

[0107] This application also provides an energy storage system, including the secondary battery provided in the fourth aspect of this application. Because it uses the secondary battery provided in this application, the energy storage system can have better thermal stability and safety performance.

[0108] In some embodiments of this application, the energy storage system includes an energy storage device and a power converter. The energy storage device includes a housing cavity and a secondary battery housed in the housing cavity. The power converter is used to perform power conversion processing on the voltage and / or current, and input the changed voltage and / or current to the energy storage device so that the energy storage device can meet the power requirements of the electrical equipment.

[0109] The technical solution of this application is further described below with reference to several embodiments.

[0110] Example 1

[0111] 1) The substrate (specifically LiNi) 0.836 Co 0.104 Mn 0.06 O2) is placed in the reaction chamber of an atomic layer deposition apparatus filled with dry air and heated to a first preset temperature (specifically 250°C).

[0112] 2) Introduce the first reactant into the reaction chamber. Specifically, introduce element source A (lithium tert-butoxide) four times, 300 ms each time; introduce element source X (trimethyl phosphate) twice, 1200 ms each time; and introduce element source E (trimethylaluminum) four times, 300 ms each time. Different element sources are introduced between adjacent reactions. After the first reaction time, purge the reaction chamber with inert gas.

[0113] 3) Introduce the second reaction material (specifically O3) into the reaction chamber. After the second reaction time, introduce an inert gas into the reaction chamber for washing.

[0114] 4) Steps 2) and 3) above are recorded as one deposition cycle. After 44 deposition cycles, the cathode material is obtained.

[0115] Example 2

[0116] It also includes 5): transferring the reactants obtained in step 4) into a tube furnace and holding them in an oxygen atmosphere, specifically, holding them at 500°C for 5 hours and then cooling them naturally to obtain the cathode material.

[0117] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0118] Comparative Example 1

[0119] 1) The substrate (specifically LiNi) 0.836 Co 0.104 Mn 0.06 O2) is placed in the reaction chamber of an atomic layer deposition apparatus filled with dry air and heated to a first preset temperature (specifically 250°C).

[0120] 2) Introduce the first reactant into the reaction chamber. Specifically, introduce element A (lithium tert-butoxide) four times, each time for 300 ms; introduce element X (trimethyl phosphate) twice, each time for 1200 ms. After the first reaction time, purge the reaction chamber with inert gas.

[0121] 3) Introduce the second reaction material (specifically O3) into the reaction chamber. After the second reaction time, introduce an inert gas into the reaction chamber for washing.

[0122] 4) Steps 2) and 3) above are recorded as one deposition cycle. After 6 cycles of deposition, the cathode material is obtained.

[0123] Comparative Example 2

[0124] Ni substrate 0.836 Co 0.104 Mn 0.06 (OH)₂ and LiOH·H₂O were ground and mixed in an agate mortar at a molar ratio of transition metal to Li of 1:1.05. The resulting mixture was then transferred to a tube furnace and sintered at 730°C for 10 hours in an oxygen atmosphere (oxygen purity above 99.9%, oxygen flow rate 200 mL / min) to obtain the cathode material LiNi. 0.836 Co 0.104 Mn 0.06 O2.

[0125] Performance testing

[0126] (1) The fully charged cathode material was thermally analyzed by differential scanning calorimetry (DSC) and thermogravimetric mass spectrometry (TG / MS).

[0127] 1) Positive electrode sheets were prepared using the positive electrode materials provided in the different embodiments and comparative examples above as the positive electrode active material. Specifically, the positive electrode material, conductive agent (specifically AB), and binder (specifically PVDF) were mixed in a mass ratio of 90:5:5. The resulting mixture was then added to a dispersant (specifically N-methyl-2-pyrrolidone, NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector (specifically aluminum foil) to obtain a positive electrode sheet, which includes a current collector and a layer of positive electrode active material disposed on the surface of the current collector.

[0128] 2) Using lithium metal sheets as the negative electrode, together with the above-mentioned positive electrode, they are assembled into a button cell in a glove box filled with argon gas.

[0129] 3) After charging each coin cell half-cell assembled above to 4.3V using a constant current and constant voltage of 1C (with a constant voltage cutoff current of 0.05C), disassemble it in a glove box, remove the positive electrode sheet, and soak it in a solvent (specifically dimethyl carbonate) for 1 hour. After removing it, rinse it three times with dimethyl carbonate (DMC), and then dry the DMC on the surface of the positive electrode sheet under an inert atmosphere. Scrape 5mg of the positive electrode active material layer from the pretreated positive electrode sheet to obtain each sample.

[0130] 4) The sample and electrolyte (1 mol / L LiPF6 solution, with a volume ratio of 3:7 ethylene carbonate and dimethyl carbonate) were added to a sealed crucible at a ratio of 1 μL:1 mg. DCS tests were performed under Ar atmosphere, with a heating rate of 5 °C / min and a heating range of 30 °C-450 °C. The test results of the cathode materials of Comparative Example 1 and Comparative Example 2 are summarized in Figure 8.

[0131] 5) Place the sample in an open crucible for TG / MS testing. The atmosphere is Ar, the heating rate is 5℃ / min, and the heating range is 30℃-450℃.

[0132] (2) Morphological test

[0133] 1) The positive electrode material (powder) of each embodiment was added to anhydrous ethanol and ultrasonically dispersed to obtain a suspension. A sample was taken with a dropper and dropped onto an electron microscope grid covered with a support film. After drying, its morphology was observed using a FEI F20 field emission transmission electron microscope (TEM). TEM images of the positive electrode materials of Example 1 and Example 2 are shown in Figures 4 and 5, respectively.

[0134] 2) Take the positive electrode material (powder) of each embodiment and place it on carbon conductive adhesive. Observe its morphology using a Zeiss Sigma Scanning Electron Microscope (SEM) in Germany.

[0135] (3) Elemental composition analysis

[0136] 1) Sample preparation: Take the positive electrode materials of each embodiment and mix them with a conductive agent (specifically AB) and a binder (specifically PVDF) in a mass ratio of 90:5:5. Add the resulting mixture to a dispersant (specifically N-methyl-2-pyrrolidone, NMP) to obtain a positive electrode slurry. Coat the positive electrode slurry onto a positive electrode current collector (specifically aluminum foil) to obtain a positive electrode sheet. The positive electrode sheet includes a current collector and a layer of positive electrode active material disposed on the surface of the current collector.

[0137] 2) Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) Testing: The prepared positive electrode sheet was subjected to TOF-SIMS testing. Primary ions excited the sample surface (surface of the positive electrode active material layer), generating minute amounts of secondary ions. Data processing was performed, and the ion mass and elemental composition in the positive electrode material were determined based on the different travel times of the secondary ions to the detector due to their varying masses. The TOF-SIMS results for Examples 1 and 2 are summarized in Figures 9A-9B and 10A-10B, respectively.

[0138] 3) X-ray photoelectron spectroscopy (XPS) analysis: The prepared positive electrode sheet was placed in an X-ray photoelectron spectrometer. The solid surface (surface of the positive electrode active material layer) was excited by X-rays. After data processing, the elements on the surface of the positive electrode material were quantitatively and qualitatively analyzed. The XPS results of Examples 1 and 2 are summarized in Figures 11 and 12, respectively.

[0139] (4) Phase analysis

[0140] The cathode materials of Examples 1, 2 and Comparative Example 2 were tested in an X-ray diffraction (XRD) instrument to obtain their X-ray diffraction (XRD) spectra.

[0141] (5) Electrochemical performance testing

[0142] Using the coin cells prepared in the above thermal analysis test as samples, the cycle performance was tested in a 30℃ constant temperature chamber. Specifically, the cells were charged to 4.3V with a constant current and constant voltage of 1C, and the constant voltage cutoff current was 0.05C. Then, the cells were discharged to 2.5V with a constant current of 1C. The charge / discharge specific energy of the cells in the first cycle and the capacity retention rate after 100 charge / discharge cycles were calculated.

[0143] The results of elemental composition analysis for each sample are summarized in Table 1. The DSC test data and electrochemical performance test results for the closed electrolyte-containing system are summarized in Table 2.

[0144] Table 1

[0145] Table 2

[0146] Combining the data in Tables 1 and 2, it can be seen that the cathode material provided in this application embodiment, through the synergistic effect of the first and second shells, can significantly reduce the heat release of the lithium-nickel composite oxide material in the electrolyte environment. Furthermore, considering the O2 gas generation monitoring curves and thermogravimetric curves during the heating process in Examples 1 and 2, it is fully demonstrated that the cathode material provided in this application embodiment can avoid peak heat release by inducing the core material to release lattice oxygen, thereby greatly improving its thermal stability. In addition, the electrochemical performance test results show that the electrochemical performance of the cathode material provided in this application embodiment is comparable to that of materials in the prior art, and even its capacity retention rate after 100 cycles is significantly better than that of the material in Comparative Example 2. Therefore, this application embodiment provides a cathode material that combines thermal stability and good electrochemical performance.

[0147] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A positive electrode material, characterized in that, It includes a core, a first shell layer and a second shell layer successively coated on the surface of the core; the core includes A(Ni 1-x M x )O2, where 0 < x < 1, and A is Li and / or Na, and M is at least one of Co, Mn, Nb, Ta, V, Mo, W and Zr; The first shell layer includes A(Ni 1-x M x ) 1-a E a O2, where 0 < x < 1, 0 < a < 1, and E is at least one of Al and Mg; The second shell comprises a compound having Li-O and XO bonds, and / or a compound having Na-O and XO bonds; X is at least one of B, P and Si.

2. The cathode material according to claim 1, characterized in that, The thickness of the first shell layer is less than or equal to 10 nm.

3. The cathode material according to claim 1, characterized in that, In the first shell, the content of element E gradually decreases from the first shell toward the core.

4. The cathode material according to claim 3, characterized in that, The thickness of the first shell layer is less than or equal to 1 nm.

5. The positive electrode material according to claim 1, characterized in that, In the first shell, the content of element E first increases and then decreases from the first shell toward the core.

6. The positive electrode material according to claim 5, characterized in that, The thickness of the first shell layer is in the range of 1nm-10nm.

7. The cathode material according to claim 5 or 6, characterized in that, In the first shell, the peak position of the molar content of element E is located at a distance of 50%-80% from the surface of the core.

8. The cathode material according to any one of claims 1-5, characterized in that, 0<a≤0.1。 9. The positive electrode material according to claim 1, characterized in that, Any 1μm of the second shell 2 The thickness difference within the range is less than or equal to 6 nm.

10. The cathode material according to claim 1, characterized in that, Any 1μm 2 In the material of the second shell layer with an area of ​​1 nm to 5 nm and a thickness, the molar content of the X element is in the range of greater than 0 to less than or equal to 13%.

11. The cathode material according to claim 1, characterized in that, The surface of the second shell layer includes a plurality of closely packed nanoparticles, with pores between adjacent nanoparticles, the pore size of which is less than or equal to 1 nm.

12. The cathode material according to any one of claims 1-11, characterized in that, A cross-composite layer is further provided between the first shell and the second shell, the cross-composite layer comprising the compound having Li-O and XO bonds and / or the compound having Na-O and XO bonds, and the E element.

13. The cathode material according to claim 12, characterized in that, The thickness of the cross-composite layer is less than or equal to 2 nm.

14. The cathode material according to any one of claims 1-13, characterized in that, The A(Ni 1-x M x O2 has a layered structure.

15. The method for preparing the cathode material according to any one of claims 1-14, characterized in that, include: The substrate is placed in a reaction chamber filled with dry gas, and a first reaction material and a second reaction material are introduced. After atomic layer deposition, a positive electrode material is prepared. The first reaction material includes an A element source, an X element source, and an E element source. The second reaction material includes an O element source.

16. The preparation method according to claim 15, characterized in that, When the first reaction material is introduced into the reaction chamber, the A element source, the X element source, and the E element source are introduced alternately.

17. The preparation method according to claim 15 or 16, characterized in that, It also includes placing the reactants after atomic layer deposition in an oxygen environment for heat preservation treatment.

18. A positive electrode plate, characterized in that, The positive electrode includes a current collector and a positive active material layer disposed on at least one side of the current collector; the positive active material layer includes the positive electrode material as described in any one of claims 1-14, or the positive electrode material prepared by the preparation method as described in any one of claims 15-17.

19. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and a separator and electrolyte located between the positive electrode and the negative electrode as described in claim 18.

20. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 19.

21. An energy storage system, characterized in that, The energy storage system includes the secondary battery as described in claim 19.

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