A positive electrode material, a preparation method and application thereof

Abstract

The application provides a positive electrode material and a preparation method and application thereof. The positive electrode material comprises secondary particles and a coating layer, the coating layer covers at least part of the surface of the secondary particles; the coating layer comprises a cobalt compound and an A element, the A element is selected from at least one of Ba, Sr and B, wherein the average particle size of the particles in the coating layer is greater than or equal to 150 nm. By introducing the A element, the grain size and crystallinity of the cobalt compound in the coating layer are improved, and when the positive electrode material is applied to a lithium ion battery, the cycle performance and capacity retention rate of the battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a cathode material, its preparation method, and its application. Background Technology

[0002] Ternary cathode materials are considered the most promising cathode materials for energy storage batteries due to their high capacity, low delithiation potential, and low cost. During the synthesis of ternary materials, some Ni... 2+ Easy to occupy Li + The presence of lithium at specific sites leads to cation mixing, requiring the addition of an excessive Li source. Simultaneously, the nickel element in the ternary material is alkaline, readily absorbing moisture and CO2 upon exposure to air. This reacts with residual lithium on the surface to form residual alkalis such as LiOH and Li₂CO₃, severely impacting the electrochemical and storage performance of the ternary material. Furthermore, LiOH readily reacts with LiPF₆ in the electrolyte to generate HF. At 100% SOC, HF dissolves transition metal ions in the cathode material, causing the collapse of the layered structure of the cathode material.

[0003] Currently, to overcome the impact of residual alkali on the layered structure of cathode materials, surface coating of ternary cathode materials is often used. For example, patent documents CN113707851A, CN114094093A, and CN110247031A all employ dry coating to coat cobalt compounds onto the surface of the cathode material to address the issues of high residual alkali content and unstable surface structure. However, due to the uneven distribution of residual alkali and the cathode material's poor high-temperature resistance, the cobalt-containing compounds in the surface coating layer have small grains and low crystallinity. These low-crystallinity, small-particle-size cobalt-containing compounds (lithium cobalt oxide or cobalt oxide) are prone to corrosion and dissolution during long-term cycling, leading to deterioration in cycle performance. Although increasing the sintering temperature is one method to improve crystallinity, the barrier for cobalt ions to embed in the layered structure is relatively small. Increasing the sintering temperature can cause cobalt at the interface to migrate into the primary particles, resulting in the loss of the protective coating effect. Summary of the Invention

[0004] This invention provides a cathode material in which cobalt compounds and element A are introduced into the coating layer. Applying this cathode material to lithium-ion batteries can improve the cycle performance and capacity retention of the batteries.

[0005] The present invention also provides a method for preparing a cathode material, and the cathode material prepared by the method is applied to a lithium-ion battery, which has excellent cycle performance and capacity retention.

[0006] The present invention also provides a positive electrode sheet and a lithium-ion battery including the positive electrode sheet. The positive electrode sheet includes the above-mentioned positive electrode material, so the lithium-ion battery assembled from the positive electrode sheet has both excellent cycle performance and capacity retention.

[0007] In a first aspect, the present invention provides a positive electrode material comprising secondary particles and a coating layer, the coating layer covering at least a portion of the surface of the secondary particles;

[0008] The coating layer comprises a cobalt compound and element A, wherein element A is selected from at least one of Ba, Sr, and B, and the average particle size of the particles in the coating layer is ≥150 nm.

[0009] In the cathode material described above, the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the X-ray diffraction pattern of the coating layer is LCO. FWHM Satisfy: 0 < LCO FWHM ≤0.190.

[0010] The cathode material described above, wherein the molecular formula of the cathode material is: Li a Ni 1-x-y-z Co x M y A z O 2+e This indicates that 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0 < z ≤ 0.050, and 0.95 are all valid values. <a<1.30、0≤e≤0.2;

[0011] Wherein, M is selected from Mn and / or Al, and A is selected from at least one of Ba, Sr, and B.

[0012] The cathode material as described above, wherein 45% ≤ (C A2 -C A1 ) / C A2 , where C A1 The percentage of element A (A) in all metallic elements except Li, obtained by X-ray photoelectron spectroscopy (XPS) analysis of the cathode material after etching. A2 The atomic proportion of element A in all metal elements except Li was obtained by using an inductively coupled plasma spectrometer to measure the positive electrode material.

[0013] In the cathode material described above, the mass ratio of the secondary particles to the coating layer is 1:(0.0003~0.0332); and / or,

[0014] The average particle size of the cathode material is 9–12 μm.

[0015] A second aspect of the present invention provides a method for preparing the cathode material as described above, comprising the following steps:

[0016] (1) The precursor and lithium source are mixed to obtain a first mixture; the first mixture is subjected to a first sintering treatment to obtain an intermediate;

[0017] (2) The intermediate, the compound providing cobalt, and the compound providing A are mixed to obtain a second mixture, and the second mixture is subjected to a second sintering treatment to obtain the cathode material.

[0018] In the preparation method described above, the mass ratio of cobalt to the intermediate in the compound providing cobalt is 0.02–2.00%; and / or,

[0019] The mass ratio of element A to the intermediate in the compound providing element A is 0.02 to 1.10%.

[0020] In the preparation method described above, the first sintering treatment includes a first-stage sintering and a second-stage sintering. The temperature of the first-stage sintering is 400–600°C and the time is 2–8 h. The temperature of the second-stage sintering is 650–1000°C and the time is 10–14 h.

[0021] In the preparation method described above, the temperature of the second sintering treatment is 50–200°C lower than the highest temperature of the first sintering treatment, and the time is 2–20 hours.

[0022] A third aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material as described in the first aspect above or the positive electrode material prepared by the preparation method as described in the second aspect above.

[0023] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode sheet as described in the third aspect above.

[0024] The implementation of this invention has at least the following beneficial effects:

[0025] The cathode material provided by this invention introduces a coating layer containing cobalt compounds and element A on the surface of secondary particles. Element A can depolymerize the ionic clusters composed of metal and oxygen (in the form of Metal-O), reduce the melt viscosity, and facilitate the synthesis of cobalt-containing compounds with large grain size and high crystallinity. This improves the corrosion resistance and coating area of ​​the coating layer, ensuring that the cathode material maintains a stable layered structure, thereby improving the cycle performance and capacity retention of the battery under long-term operation. Attached Figure Description

[0026] Figure 1 This is a SEM image of the cathode material in Embodiment 1 of the present invention;

[0027] Figure 2 This is a SEM image of the simulated coating layer in Embodiment 1 of the present invention;

[0028] Figure 3 This is the XRD pattern of the simulated coating layer in Embodiment 1 of the present invention;

[0029] Figure 4 This is a SEM image of the cathode material in Embodiment 2 of the present invention;

[0030] Figure 5 This is a SEM image of the simulated coating layer in Embodiment 2 of the present invention;

[0031] Figure 6 This is the XRD pattern of the simulated coating layer in Embodiment 2 of the present invention;

[0032] Figure 7 This is a SEM image of the cathode material in Embodiment 3 of the present invention;

[0033] Figure 8 This is a SEM image of the simulated coating layer in Embodiment 3 of the present invention;

[0034] Figure 9 This is the XRD pattern of the simulated coating layer in Embodiment 3 of the present invention;

[0035] Figure 10 This is a SEM image of the cathode material in Embodiment 4 of the present invention;

[0036] Figure 11 This is a SEM image of the simulated coating layer in Embodiment 4 of the present invention;

[0037] Figure 12 This is the XRD pattern of the simulated coating layer in Embodiment 4 of the present invention;

[0038] Figure 13 This is a SEM image of the cathode material in Comparative Example 1 of this invention;

[0039] Figure 14 This is a SEM image of the simulated coating layer in Comparative Example 1 of this invention;

[0040] Figure 15 This is the XRD pattern of the simulated coating layer in Comparative Example 1 of this invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] In a first aspect, the present invention provides a cathode material comprising secondary particles and a coating layer, the coating layer covering at least a portion of the surface of the secondary particles; the coating layer comprising a cobalt compound and element A, wherein element A is selected from at least one of Ba, Sr, and B, and wherein the average particle size of the particles in the coating layer is ≥150 nm.

[0043] In this invention, secondary particles refer to particles composed of aggregated primary particles. The structure of secondary particles not only expands the transport path of lithium ions in the active material, but also possesses a through-hole structure that facilitates electrolyte penetration, thereby enriching the lithium ion transport path and increasing the ion migration rate. Secondary particles have a spherical or near-spherical shape, such as an ellipsoid.

[0044] The coating layer covers at least part of the surface of the secondary particles, forming a uniform and dense protective layer on the surface of the secondary particles. The coating layer not only ensures that the electrolyte continuously wets the secondary particles, but also protects the secondary particles, prevents direct contact between the electrolyte and the secondary particles, effectively prevents the electrolyte from corroding the secondary particles, and inhibits the dissolution of transition metals, thereby improving the stability of the cathode material structure and lithium ion migration, and thus improving the electrochemical performance of the battery.

[0045] The inventors believe that the particle size of the coating layer directly affects the coating area and stability, thus impacting the battery's cycle performance. By limiting the average particle size of the coating layer to ≥150 nm, the electrochemical performance of the battery can be improved by increasing the area coverage and enhancing interfacial stability. Specifically, the average particle size of the coating layer can be obtained by performing scanning electron microscopy (SEM) on the cathode material, counting at least 50 particles, and calculating the average particle size.

[0046] According to the research of this invention, applying the cathode material provided by this invention to lithium-ion batteries is beneficial to improving the cycle performance and capacity retention of the battery. This is because, on the one hand, introducing a cobalt compound coating layer on the surface of the secondary particles effectively avoids the problems of high residual alkali and poor cycle performance caused by the surface instability of the secondary particles; on the other hand, under the temperature conditions of sintering treatment, element A can depolymerize Metal-O ion clusters and reduce the viscosity of the melt. By introducing element A into the coating layer, it is beneficial to synthesize cobalt compounds with larger particle size and higher crystallinity, improve the corrosion resistance and coating area of ​​the coating layer, and ensure that the cathode material maintains a stable layered structure, thereby improving the long-term cycle performance and capacity retention of the battery.

[0047] Furthermore, the cathode material of the present invention, by introducing element A, can form secondary particles with the above-mentioned coating layer at a sintering temperature not exceeding 750°C, thus avoiding cobalt migration caused by high sintering temperature and ensuring the integrity of the coating layer.

[0048] The present invention does not limit the specific type of the cobalt compound, as long as it contains cobalt element. In some embodiments, the cobalt compound is layered lithium cobalt oxide, which facilitates the migration of lithium ions. This is because, on one hand, the coating layer containing layered lithium cobalt oxide has high structural strength, which improves the stability of lithium ion migration in the electrolyte; on the other hand, the coating layer has good wettability to the electrolyte, which increases the contact area between the electrolyte and secondary particles, facilitates expanding the migration path of lithium ions, improves the lithium ion migration performance, and enhances the electrochemical performance of the battery.

[0049] In the X-ray diffraction pattern (XRD pattern) of layered lithium cobalt oxide, the 104 crystal plane can be observed, and the full width at half maximum of the diffraction peak corresponding to the 104 crystal plane is LCO FWHM A smaller value indicates a larger particle size and higher crystallinity of the layered lithium cobalt oxide. When the cobalt compound is layered lithium cobalt oxide, in some embodiments, the full width at half maximum LCO of the diffraction peak corresponding to the 104 crystal plane in the X-ray diffraction pattern of the coating layer FWHM satisfies: 0<LCO FWHM ≤0.190. By limiting LCO FWHM , it ensures that the layered lithium cobalt oxide has sufficiently large particle size and sufficiently high crystallinity, solves the problems of high residual alkali content on the surface of the positive electrode material and unstable surface structure, and improves the electrochemical performance of the battery.

[0050] The present invention does not limit the molecular formula of the positive electrode material. For example, in some embodiments, the molecular formula of the positive electrode material of the present invention is: Li a Ni 1-x-y-z Co x M y A z O 2+e , wherein 0≤x≤0.35, 0≤y≤0.35, 0<z≤0.050, 0.95<a<1.30, 0≤e≤0.2; M is selected from Mn and / or Al, and A is selected from at least one of Ba, Sr and B. The increased addition ratio of nickel is beneficial to improving the energy density of the battery; the addition ratio of cobalt includes the total amount of cobalt in the secondary particles and cobalt in the coating layer, and the addition ratio of cobalt can stabilize the layered structure of the positive electrode material, which is beneficial to improving the cycle performance and rate performance of the battery; the addition ratio of element M not only improves the structural stability of the positive electrode material and the safety of the battery, but also reduces the material cost of the lithium ion battery.

[0051] In the present invention, 45%≤(C A2 -C A1 ) / C A2 , wherein C A1The percentage of element A (A) in all metallic elements except Li, obtained by X-ray photoelectron spectroscopy (XPS) analysis of the cathode material after etching. A2 The atomic proportion of element A in all metal elements except Li was obtained by using an inductively coupled plasma spectrometer to measure the positive electrode material.

[0052] The ions used in ion etching are Ar. + Ions; the ion etching energy is 4-8 keV; the ion etching time is preferably 20-40 min; the ion etching angle is preferably 2 degrees; the ion etching rotation speed is 1-2 rpm.

[0053] The present invention does not impose excessive limitations on the mass ratio of secondary particles to the coating layer. In some embodiments, the mass ratio of secondary particles to the coating layer is 1:(0.0003 to 0.0332), for example, 1:0.0003, 1:0.0004, 1:0.0005, 1:0.001, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.0332, or any combination thereof.

[0054] The present invention does not impose too much limitation on the average particle size of the cathode material. In some embodiments, the average particle size of the cathode material is 9 to 12 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm or any combination thereof.

[0055] A second aspect of the present invention provides a method for preparing the cathode material described in the first aspect, comprising the following steps:

[0056] (1) The precursor and lithium source are mixed to obtain a first mixture; the first mixture is subjected to a first sintering treatment to obtain an intermediate;

[0057] (2) The intermediate, the compound providing cobalt, and the compound providing A are mixed to obtain a second mixture. The second mixture is subjected to a second sintering treatment to obtain a positive electrode material.

[0058] In this invention, the selection of materials and the order of addition have a significant impact on the structure of the cathode material. By incorporating a first sintering treatment and a second sintering treatment, it is beneficial to form the aforementioned coating layer on the surface of the secondary particles.

[0059] In some embodiments, the mass ratio of cobalt to the intermediate in the compound providing cobalt is 0.02 to 2.00%, for example, a range consisting of 0.02%, 0.05%, 0.1%, 0.5%, 1.00%, 1.50%, 2.00%, or any two thereof; and / or, the mass ratio of element A to the intermediate in the compound providing element A is 0.02 to 1.10%, for example, a range consisting of 0.02%, 0.05%, 0.1%, 0.5%, 1.00%, 1.10%, or any two thereof.

[0060] This invention does not impose excessive limitations on the specific type of precursor or the specific preparation process; it can be prepared using conventional co-precipitation methods in the art. For example, the precursor is Ni. 1-x-y-z Co x M y The specific preparation process of (OH)2 includes: introducing a precipitant and a complexing agent into a metal salt solution to carry out a co-precipitation reaction, thereby obtaining the precursor. The metal salt solution includes Ni salt, Co salt, and M salt; the precipitant can be sodium hydroxide; and the complexing agent can be ammonia.

[0061] The precursor and lithium source are mixed to obtain a first mixture. In the first mixture, the molar ratio of lithium element in the lithium source to the sum of Ni, Co, and M elements in the precursor is (0.95–1.3):1, preferably (1.01–1.2):1. The lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium nitrate, preferably lithium hydroxide.

[0062] The present invention does not limit the parameters of the first sintering treatment, and conventional methods in the art can be used for preparation. For example, in some embodiments, the first sintering treatment includes a first stage sintering and a second stage sintering, wherein the temperature of the first stage sintering is 400-600°C and the time is 2-8 hours, and the temperature of the second stage sintering is 650-1000°C and the time is 10-14 hours.

[0063] Following the first sintering process, the first sintering product is further crushed to obtain an intermediate, thus preventing agglomeration. The intermediate can be directly mixed with a compound providing cobalt and a compound providing aluminum (A) for a second sintering process. Compared to existing methods that involve adding a water washing and drying step after the first sintering to remove residual alkali from the surface of the cathode material, the preparation method provided by this invention is simple to operate and avoids the negative effects of water washing.

[0064] The present invention does not limit the specific types of compounds providing cobalt or compounds providing element A. For example, the compounds providing cobalt are at least one of cobalt oxide, cobalt carbonate, cobalt sulfate, cobalt hydroxy oxide, and cobalt hydroxide; the compounds providing element A are at least one of element A oxide, element A carbonate, element A sulfate, element A hydroxide, and element A oxide hydrate.

[0065] This invention does not limit the parameters of the second sintering treatment. For example, in some embodiments, the temperature of the second sintering treatment is 50–200°C lower than the highest temperature of the first sintering treatment, and the time is 2–20 hours. The atmosphere for the second sintering treatment is air, oxygen, nitrogen, or vacuum. For example, a second sintering treatment temperature of 150°C–750°C is not only beneficial for the formation of secondary particles but also for the formation of a stable coating layer on the surface of the secondary particles. If the temperature is higher than the highest sintering temperature of the first sintering treatment, the prepared cathode particles will undergo secondary growth, which is not conducive to cyclic stress relief.

[0066] A third aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material provided in the first aspect or the positive electrode material prepared by the preparation method provided in the second aspect.

[0067] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode provided in the third aspect.

[0068] The cathode material and lithium-ion battery of the present invention are described in detail below through specific embodiments. The preparation method of the precursor in the following embodiments and comparative examples includes the following steps: Nickel source, cobalt source, M source, and water are mixed, wherein nickel, cobalt, and manganese are mixed in a molar ratio of 88:6:6 to obtain a salt solution. The salt solution is placed in a reactor, and a precipitant and a complexing agent are added to the salt solution to carry out a co-precipitation reaction. The ammonia value in the system is controlled at 4 g / L. The pH value of the system is adjusted to 10.66 using a sodium hydroxide solution as a precipitant. Uniform stirring is used during precipitation to ensure uniform growth of the material particles, resulting in the Ni precursor. 0.88 Co 0.06 Mn 0.06 (OH)2. Among them, the nickel source is nickel sulfate, the M source is manganese sulfate, the cobalt source is cobalt sulfate, the complexing agent is ammonia water, and the precipitant is sodium hydroxide.

[0069] Example 1

[0070] (1) The lithium source and the precursor were mixed at a molar ratio of 1.03:1 to obtain the first mixture. The mixture was heated to 500℃ at 2℃ / min and held at that temperature for 2 hours under an oxygen atmosphere, and then heated to 760℃ at 2℃ / min and held at that temperature for 11 hours. After crushing and sieving, the intermediate Li was obtained. 1.03Ni 0.88 Co 0.06 Mn 0.06 O2 (average particle size 10.5 μm);

[0071] (2) SrO and Co(OH)2 (average particle size of 200 nm) were mixed with the intermediate using a high-speed mixer to obtain a second mixture. The addition ratio was 0.12 wt% SrO and 0.79 wt% Co(OH)2. The second mixture was then sintered at a target temperature of 660 °C for 10 h under an oxygen atmosphere to obtain the cathode material Li. 1.02 Ni 0.872 Co 0.068 Mn 0.059 Sr 0.001 O2.

[0072] Simulated coating layer: The residual alkali, SrO, and Co(OH)2 were mixed according to the proportions of this embodiment and sintered at the temperature of the second sintering treatment in this embodiment. The crystallization status of the synthesized lithium cobalt oxide was analyzed by XRD and SEM. The residual alkali was simulated by weighing out an equal amount of lithium carbonate and lithium hydroxide as the intermediate in this embodiment.

[0073] The SEM images of the cathode material and simulated coating layer in this embodiment are as follows: Figure 1 and Figure 2 As shown, the XRD pattern of the simulated coating layer is as follows: Figure 3 As shown.

[0074] Example 2

[0075] The preparation method is basically the same as that in Example 1, except that the compound for element A is selected differently in step (2). Specifically, 0.12 wt% SrO is replaced with 0.14 wt% BaCO3, while other conditions remain unchanged, to obtain the cathode material Li. 1.02 Ni 0.872 Co 0.068 Mn 0.059 Ba 0.001 O2.

[0076] Simulated coating layer: The residual alkali, BaCO3, and Co(OH)2 were mixed according to the proportions of this embodiment and sintered at the temperature of the second sintering treatment in this embodiment. The crystallization status of the synthesized lithium cobalt oxide was analyzed by XRD and SEM. The residual alkali was simulated by weighing out an equal amount of lithium carbonate and lithium hydroxide as the intermediate in this embodiment.

[0077] The SEM images of the cathode material and simulated coating layer in this embodiment are as follows: Figure 4 and Figure 5 As shown, the XRD pattern of the simulated coating layer is as follows: Figure 6 As shown.

[0078] Example 3

[0079] The preparation method is basically the same as that in Example 1, except that the compound for element A is selected differently in step (2). Specifically, 0.12 wt% SrO is replaced with 0.14 wt% H3BO3, while other conditions remain unchanged, to obtain the cathode material Li. 1.012 Ni 0.865 Co 0.067 Mn 0.059 B 0.009 O2.

[0080] Simulated coating layer: The residual alkali, H3BO3, and Co(OH)2 were mixed according to the proportions of this embodiment and sintered at the temperature of the second sintering treatment in this embodiment. The crystallization status of the synthesized lithium cobalt oxide was analyzed by XRD and SEM. The residual alkali was simulated by weighing out an equal amount of lithium carbonate and lithium hydroxide as the intermediate in this embodiment.

[0081] The SEM images of the cathode material and simulated coating layer in this embodiment are as follows: Figure 7 and Figure 8 As shown, the XRD pattern of the simulated coating layer is as follows: Figure 9 As shown.

[0082] Example 4

[0083] The preparation method is basically the same as that in Example 1, except that the compound of element A is selected differently in step (2). Specifically, 0.12wt% SrO is replaced with 0.14wt% H3BO3 and 0.12wt% SrO, while other conditions remain unchanged, to obtain the cathode material Li. 1.012 Ni 0.864 Co 0.067 Mn 0.059 Sr 0.001 B 0.009 O2.

[0084] Simulated coating layer: The residual alkali, H3BO3, SrO and Co(OH)2 were mixed according to the proportions of this embodiment and sintered at the temperature of the second sintering treatment in this embodiment. The crystallization status of the synthesized lithium cobalt oxide was analyzed by XRD and SEM. The residual alkali was simulated by weighing out an equal amount of lithium carbonate and lithium hydroxide as the intermediate in this embodiment.

[0085] The SEM images of the cathode material and simulated coating layer in this embodiment are as follows: Figure 10 and Figure 11 As shown, the XRD pattern of the simulated coating layer is as follows: Figure 12 As shown.

[0086] Comparative Example 1

[0087] The preparation method is basically the same as in Example 1, except that in step (2), no compound containing element A is added (i.e., no SrO or Co(OH)2 is added), and other conditions remain unchanged, to obtain Li. 1.02 Ni 0.872 Co 0.068 Mn 0.06 O2.

[0088] Simulating the outer surface of the positive electrode material: The residual alkali and Co(OH)2 were mixed in the proportion of this comparative example and sintered at the temperature of the second sintering treatment of this comparative example. The crystallization status of the synthesized lithium cobalt oxide was analyzed by XRD and SEM. The residual alkali was simulated by weighing out an equal amount of lithium carbonate and lithium hydroxide as the intermediate of Example 1.

[0089] SEM images of the cathode material and simulated coating in this comparative example are shown below. Figure 13 and Figure 14 As shown, the XRD pattern of the simulated coating layer is as follows: Figure 15 As shown.

[0090] Comparative Example 2

[0091] The preparation method is basically the same as that in Example 1, except that the sintering temperature in the second stage of step (1) is different. Specifically, the sintering temperature in step (1) is changed from 2℃ / min to 760℃ and held for 11 hours to 2℃ / min to 860℃ and held for 11 hours. Other conditions remain unchanged, and the intermediate Li of this example is obtained. 1.03 Ni 0.83 Co 0.06 Mn 0.11 O2; Replace the intermediate of Example 1 with the intermediate Li of this example. 1.03 Ni 0.83 Co 0.06 Mn 0.11 O2, a compound without the addition of element A in step (2), with other conditions unchanged, yields Li 1.02 Ni 0.823 Co 0.068 Mn 0.109 O2.

[0092] Comparative Example 3

[0093] The preparation method is basically the same as in Example 1, except that in step (2) no compound of element A is added, and the temperature of the second sintering treatment is different. Specifically, the second sintering treatment, which was performed at a target temperature of 660°C for 10 hours, is replaced with the second sintering treatment performed at a target temperature of 770°C for 10 hours, while other conditions remain unchanged, to obtain Li 1.012 Ni 0.873 Co 0.068 Mn0.06 O2.

[0094] Comparative Example 4

[0095] (1) The precursor, lithium hydroxide, and SrO were mixed and heated to 500℃ at 2℃ / min for 2 hours under an oxygen atmosphere, and then heated to 760℃ at 2℃ / min for 11 hours to calcine. After crushing and sieving, the intermediate Li was obtained. 1.03 Ni 0.879 Co 0.06 Mn 0.06 Sr 0.001 O2 (average particle size 10.5 μm), wherein the ratio of precursor, lithium hydroxide and SrO is 1.03:0.999:0.001 according to the molar ratio of Li / (Ni+Co+M) / Sr.

[0096] (2) Co(OH)₂ (average particle size of 200 nm) was mixed with the intermediate using a high-speed mixer to obtain a second mixture. The addition ratio was 0.79 wt% Co(OH)₂. The second mixture was then sintered at a target temperature of 660 °C for 10 h under an oxygen atmosphere to obtain the cathode material Li. 1.02 Ni 0.872 Co 0.068 Mn 0.059 Sr 0.001 O2.

[0097] Comparative Example 5

[0098] The preparation method is basically the same as that in Example 1, except that the sintering temperature in the second stage of step (1) is different. Instead of heating to 760°C at 2°C / min and holding for 11 hours, the temperature is increased to 860°C at 2°C / min and held for 11 hours. Other conditions remain unchanged, and the intermediate Li of this example is obtained. 1.03 Ni 0.83 Co 0.06 Mn 0.11 O2; Replace the intermediate of Example 1 with the intermediate Li of this example. 1.03 Ni 0.83 Co 0.06 Mn 0.11 O2, other conditions unchanged, yield Li 1.02 Ni 0.823 Co 0.067 Mn 0.109 Sr 0.001 O2.

[0099] Experimental example:

[0100] 1. Semi-electrical test: The positive electrode material, conductive carbon black SP, and polyvinylidene fluoride PVDF were mixed and slurried in a ratio of 90%:5%:5%, with the areal density controlled at 17 mg / cm³. 2 After being rolled, the compaction was controlled at 3.4 mg / cm³. 3 The cells were assembled into 2430 button cells. The cells were tested for specific capacity by charging and discharging at 0.2C, with a test voltage range of 2.5V-4.25V.

[0101] 2. Full Electrical Testing: A positive electrode slurry was prepared by mixing SP, conductive graphite KS-6, and PVDF in a ratio of 94.5%, 2%, 1%, and 2.5%. The slurry was then coated and rolled to form positive electrode sheets, with the sheet areal density controlled at 16 mg / cm³. 2 The negative electrode uses artificial graphite, which is homogenized in a ratio of graphite:SP:carboxymethyl cellulose (CMC):styrene-butadiene rubber (SBR) of 95.5%:1%:1.5%:2%, and the coating density is controlled at 10 mg / cm². 2 The separator used is a 20μm dry-process PP / PE / PP membrane, and the electrolyte is a conventional electrolyte with the main components being ethylene ester (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), containing additives such as vinylene carbonate (VC) and 1,3-propanesulfonic acid lactone (PS). The lithium salt is 1mol / L LiPF6. The battery is assembled into a 503048 model with a capacity of about 800mAh. It was tested with a voltage range of 3.0-4.25V and its capacity retention was compared after 300 cycles of 1C charge-discharge at 45℃.

[0102] 3. Profile Etching: The etching equipment used was the Gatan 697Ilion II, employing Ar... + Ion etching of powder materials was performed under the following conditions: 6 keV, 30 min, 2-degree angle, and 1 rpm stage rotation. X-ray photoelectron spectroscopy (XPS) analysis of the cathode material after ion etching revealed that the atomic ratio of a to all metals except Li was C. A1 The high-capacity, high-nickel ternary cathode material, as measured using inductively coupled plasma technology, showed that the atomic ratio of alumina (A) to all metals except lithium (C) was [missing information]. A2 Calculation formula (C) A2 -C A1 ) / C A2 The XPS test utilizes a scanning X-ray photoelectron spectroscopy (XPS) instrument, model: Thermo ESCALAB 250XI, to test the cathode material.

[0103] 4. ICP Test: Weigh 0.4g of the cathode material sample into a 250ml beaker, add 7.5mL of analytical grade hydrochloric acid and 2.5mL of analytical grade nitric acid, and heat at 195℃ for 30min to dissolve. Transfer the heated liquid to a volumetric flask and dilute to the final volume with pure water, then dilute to the measurable range. Use an ICP instrument to measure the molecular formula of the cathode material.

[0104] 5. XRD test: A Bruker D8AA25 X-ray diffractometer was used, with Cu as the target material, voltage of 40kV, current of 40mA, Soller value of 2.5, and JADE and TOPAS software for data processing.

[0105] 6. SEM test: SE mode, the magnification of the cathode material is 30K, the simulation magnification of the coating layer is 50K, and the average particle size in the coating layer is obtained by statistical analysis of at least 50 points.

[0106] The above-described examples and comparative examples were subjected to physicochemical and electrochemical tests under the same test conditions. The test results are shown in Table 1 below.

[0107] Table 1 Performance characterization of cathode materials and lithium-ion batteries

[0108]

[0109] As shown in Table 1, applying the cathode material provided by this invention to batteries can improve both the cycle performance and capacity retention of the batteries.

[0110] As shown in Examples 1-4 and Comparative Examples 1-2, by introducing element A, the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the X-ray diffraction pattern of the coating layer in Examples 1-4 increases. FWHM The relatively small size of the lithium cobalt oxide crystals synthesized in this invention, combined with the size of the particles in the coating layer, indicates that the lithium cobalt oxide crystals are large and highly crystallized. This is beneficial for improving the corrosion resistance and coating area of ​​the coating layer, ensuring that the cathode material maintains a stable layered structure, and thus improving the long-term cycle performance and capacity retention of the battery.

[0111] As shown in Examples 1-4 and Comparative Examples 2 and 5, compared to introducing element A into single-crystal particles, the formation of an element A-containing coating layer on the surface of secondary particles in this invention is more beneficial to the electrochemical performance of the battery. As shown in Comparative Examples 2 and 5, introducing element A is beneficial for obtaining a smaller LCO content. FWHM This results in large-sized and highly crystallized lithium cobalt oxide crystals.

[0112] According to Comparative Examples 1 and 3, without introducing element A, increasing the sintering temperature helps to reduce the LCO content. FWHMThis process resulted in large and highly crystallized lithium cobalt oxide crystals. However, as the sintering temperature increased, the battery's cycle performance deteriorated. The inventors concluded that as the sintering temperature increased, cobalt ions migrated into the interior of the particles and no longer provided protective coating, leading to a deterioration in the battery's cycle performance.

[0113] As can be seen from Comparative Examples 1 and 4, compared to introducing element A into the interior of the secondary particles, introducing element A into the coating layer located on the surface of the secondary particles in this invention is more beneficial to improving the cycle performance and capacity retention of the battery.

[0114] The cathode material of this invention has a layered structure. This invention identifies the influence of fluxing element A on the size of lithium cobalt oxide particles in the coating layer by using a simulated coating layer method. It determines that the aforementioned fluxing ions (i.e., ions formed by element A) can increase the primary particle size of lithium cobalt oxide (LCO) in the coating layer, thereby significantly improving the electrochemical performance of the cathode material, such as DCR, capacity, and cycle life, by increasing area coverage and improving interfacial stability.

[0115] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A positive electrode material, characterized in that, The cathode material includes secondary particles and a coating layer, wherein the coating layer covers at least a portion of the surface of the secondary particles; The coating layer comprises a cobalt compound and element A, wherein element A is selected from at least one of Ba, Sr, and B, and the average particle size of the particles in the coating layer is ≥150 nm, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the 104 crystal plane in the X-ray diffraction pattern of the coating layer is LCO. FWHM Satisfy: 0 < LCO FWHM ≤0.190; 45%≤(C) A2 -C A1 ) / C A2 , where C A1 The percentage of element A (A) in all metallic elements except Li, obtained by X-ray photoelectron spectroscopy (XPS) analysis of the cathode material after etching. A2 The atomic proportion of element A in all metal elements except Li, as measured using an inductively coupled plasma spectrometer for the cathode material; The molecular formula of the positive electrode material is: Li a Ni 1-x-y-z Co x M y A z O 2+e , wherein 0<x≤0.35, 0<y≤0.35, 0<z≤0.050, 0.95<a<1.30, 0≤e≤0.2; M is selected from Mn and / or Al, and A is selected from at least one of Ba, Sr and B.

2. The cathode material according to claim 1, characterized in that, The mass ratio of the secondary particles to the coating layer is 1:(0.0003~0.0332); and / or, The average particle size of the cathode material is 9~12μm.

3. A method for preparing the cathode material according to claim 1 or 2, characterized in that, Includes the following steps: (1) The precursor and lithium source are mixed to obtain the first mixture; The first mixture is subjected to a first sintering treatment to obtain an intermediate; (2) The intermediate, the compound providing cobalt, and the compound providing A are mixed to obtain a second mixture, and the second mixture is subjected to a second sintering treatment to obtain the cathode material.

4. The preparation method according to claim 3, characterized in that, The mass ratio of cobalt to the intermediate in the compound providing cobalt is 0.02~2.00%; and / or, The mass ratio of element A to the intermediate in the compound providing element A is 0.02 to 1.10%.

5. The preparation method according to claim 3, characterized in that, The first sintering process includes a first sintering stage and a second sintering stage. The temperature of the first sintering stage is 400~600℃ and the time is 2~8h. The temperature of the second sintering stage is 650~1000℃ and the time is 10~14h.

6. The preparation method according to claim 3 or 4, characterized in that, The temperature of the second sintering treatment is 50-200°C lower than the highest temperature of the first sintering treatment, and the time is 2-20 hours.

7. A positive electrode plate, characterized in that, The positive electrode sheet includes the positive electrode material according to claim 1 or 2, or the positive electrode material prepared by the preparation method according to any one of claims 3-6.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 7.

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