A positive electrode active material, a method for preparing the same, and an application thereof

Abstract

The application provides a positive electrode active material and a preparation method and application thereof. The positive electrode active material comprises secondary particles; the positive electrode active material comprises a lithium transition metal oxide, the lithium transition metal oxide comprises an M element, the M element comprises at least one of Nb, V, Ta, W and Mo; 0.07≤M 50nm / M 0nm ≤ 0.22, M 0nm is the M element on the surface of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen; M 50nm is the M element at a 50 nm site of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen. The positive electrode active material helps to make the secondary battery have excellent initial coulomb efficiency and cycle performance.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] As the core of modern electrochemical energy storage systems, secondary batteries have been widely used in key areas such as electric vehicles, large-scale energy storage power stations, portable electronic devices, and aerospace. With the accelerated global energy structure transformation towards cleaner and smarter energy sources, the market is placing higher demands on battery energy density, safety, and lifespan. Against this backdrop, solid-state batteries have attracted significant attention due to their substantial safety advantages. Compared to traditional liquid electrolyte batteries, solid-state electrolytes are non-flammable, have no leakage risk, and can effectively suppress lithium dendrite growth, thus significantly improving the intrinsic safety of the battery. Simultaneously, solid-state batteries possess a wide electrochemical window, allowing for the matching of high-voltage cathode materials, making it possible to achieve higher energy densities.

[0003] However, solid-state batteries still face prominent problems in practical applications, such as insufficient cycle performance and first-time coulombic efficiency (first-efficiency), which seriously restricts their further development and commercial application.

[0004] How to effectively improve the cycle stability and first coulombic efficiency of solid-state batteries while maintaining their high safety advantage has become a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides a positive electrode active material comprising a lithium transition metal oxide containing a special element M. By specifically defining the distribution relationship of element M on the surface and in a specific region inside the lithium transition metal oxide, and combining it with the particle morphology of secondary particles, the stability of the positive electrode active material is significantly improved, thereby enabling secondary batteries using it to have both excellent first coulombic efficiency and cycle performance.

[0006] This application also provides a method for preparing the above-mentioned positive electrode active material, which is used to prepare the above-mentioned positive electrode active material.

[0007] This application also provides a positive electrode sheet comprising the above-mentioned positive electrode active material, which significantly improves the cycle performance of secondary batteries.

[0008] This application also provides a secondary battery that includes the above-mentioned positive electrode, thus having a longer service life.

[0009] This application provides a positive electrode active material, the positive electrode active material comprising secondary particles; the positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising an element M, wherein the element M comprises at least one selected from Nb, V, Ta, W and Mo;

[0010] 0.07≤M 50nm / M 0nm ≤0.22 Equation 1

[0011] In Equation 1, M 0nm M represents the element M on the surface of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen; M 50nm The M element is located at the 50 nm site of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen.

[0012] The positive electrode active material as described above, wherein the lithium transition metal oxide comprises a main metal element and a secondary metal element, wherein the main metal element comprises nickel, and the secondary metal element comprises at least one of cobalt, manganese and aluminum.

[0013] The positive electrode active material as described above, wherein, based on all metal elements except lithium and oxygen, the molar percentage N of nickel is... Ni It ranges from 70 mol% to 98 mol%.

[0014] The positive electrode active material as described above, wherein N Ni It is 80 mol% - 98 mol%.

[0015] The positive electrode active material as described above, wherein N Ni It is 90 mol% - 98 mol%.

[0016] The positive electrode active material as described above, wherein the M element includes at least one of Nb, W and Mo.

[0017] The positive electrode active material as described above, wherein the lithium transition metal oxide further includes a doping element, the doping element including at least one of Mg, Ca, Sr, Ba, Ti, Cr, Fe, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

[0018] In the positive electrode active material as described above, the molar ratio of the doping element to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):1.

[0019] The positive electrode active material as described above further includes a coating layer disposed on at least a portion of the surface of the lithium transition metal oxide;

[0020] The coating layer includes at least one of N, Mg, Ca, Sr, Ba, Ti, Cr, Mn, Fe, Co, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

[0021] In the positive electrode active material described above, the molar ratio of all elements in the coating layer except lithium and oxygen to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):1.

[0022] This application also provides a method for preparing the positive electrode active material according to any one of the above claims, comprising the following steps:

[0023] A first raw material system comprising a lithium transition metal oxide precursor, an M source, and a lithium source is subjected to sintering treatment, wherein the sintering treatment includes a first sintering treatment and a second sintering treatment performed sequentially to obtain the positive electrode active material; wherein the molar ratio of the M element in the precursor and the M source is 1:(0.003-0.03).

[0024] The temperature of the first sintering treatment is 450℃-540℃, and the holding time is 5h-15h; the temperature of the second sintering treatment is 650℃-790℃, and the holding time is 5h-15h.

[0025] In the preparation method described above, the first raw material system further includes a dopant element source; and / or,

[0026] The heating rate of the first sintering treatment is from 1.0 °C / min to 3.0 °C / min; and / or,

[0027] The heating rate of the second sintering treatment is from 1.0℃ / min to 3.0℃ / min.

[0028] The preparation method described above, wherein the sintering treatment further includes a third sintering treatment;

[0029] The third sintering process includes: heat-preserving the second raw material system, which includes the product of the second sintering process and the coating source, at 250℃-450℃ for 5h-15h to obtain the positive electrode active material.

[0030] In the preparation method described above, the first sintering treatment, the second sintering treatment, and the third sintering treatment are each carried out in an oxygen atmosphere.

[0031] This application provides a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active layer disposed on at least one surface of the positive current collector;

[0032] The positive electrode active layer comprises the positive electrode active material described in any one of the above claims, or the positive electrode active material prepared by any one of the above claims.

[0033] The positive electrode sheet as described above, wherein the positive electrode active layer further includes a solid electrolyte material.

[0034] This application also provides a battery comprising the positive electrode sheet described in any of the preceding claims.

[0035] The battery as described above, wherein the battery is a solid-state battery or a semi-solid-state battery.

[0036] This application includes a lithium transition metal oxide cathode active material that is a secondary particle. By including at least one element from Nb, V, Ta, W, and Mo in the lithium transition metal oxide, and controlling the atomic percentage of the element at the 50nm site on the surface of the lithium transition metal oxide to meet a specific ratio based on the atomic percentage of all elements except lithium and oxygen, the material can have a more reasonable element distribution state, thereby suppressing the occurrence of side reactions in the cathode active material, taking into account lithium ion migration efficiency, and improving the first efficiency and cycle performance of the secondary battery. Attached Figure Description

[0037] Figure 1 This is a SEM image of the positive electrode active material of Example 1-1 of this application;

[0038] Figure 2 The correlation graph between R in Table 3 and discharge capacity (mAh / g, @100 cycles) in Table 4 is shown.

[0039] Figure 3 The correlation plot is shown between R in Table 3 and capacity retention (%, @100 cycles) in Table 4. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Currently, the initial efficiency and cycle performance of solid-state batteries still fall short of application expectations. The inventors have investigated this issue and believe that the reason for this deficiency lies in two main obstacles encountered when conventional cathode active materials are directly applied to solid-state systems. Firstly, lattice oxygen on the surface of the cathode active material easily escapes during electrochemical cycling. This escaped active oxygen undergoes severe interfacial side reactions with sulfide or oxide solid electrolytes, leading to a continuous increase in interfacial impedance. Secondly, to improve structural stability, certain metal dopants are currently introduced. While these dopants can stabilize the lattice in the bulk phase, they also form a barrier to ion migration, hindering the rapid exchange of lithium ions at the interface between the cathode and the solid electrolyte. These two problems together lead to rapid capacity decay and low initial coulombic efficiency. Therefore, the key to overcoming this technological bottleneck lies in optimizing the lithium-ion transport path while ensuring efficient confinement of lattice oxygen.

[0042] Based on this, the first aspect of this application provides a positive electrode active material, the positive electrode active material comprising secondary particles; the positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising an element M, the element M comprising at least one of Nb, V, Ta, W and Mo, wherein;

[0043] 0.07≤M 50nm / M 0nm ≤0.22 Equation 1

[0044] In Equation 1, M 0nm M represents the element M on the surface of a lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen; M 50nm The M element is located at a 50 nm site in lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen.

[0045] In this application, the positive electrode active material is suitable for lithium secondary batteries, especially all-solid-state lithium secondary batteries. This positive electrode active material includes a lithium transition metal oxide, which comprises M, oxygen, and lithium.

[0046] It should be clarified that the atomic percentage based on all elements other than lithium and oxygen referred to in this application means calculating the proportion of element M at specific sites (0nm and 50nm) using the total number of atoms of elements other than lithium and oxygen in lithium transition metal oxides as a normalization benchmark. Since lithium has a weak signal in conventional surface analysis and oxygen is easily affected by surface adsorption states, using all elements other than lithium and oxygen as a statistical benchmark can more accurately reflect the true distribution of element M in lithium transition metal oxides, thus providing better repeatability of the ratio. Specifically, XPS (X-ray Photoelectron Spectroscopy) can be used to analyze M.0nm and M 50nm Quantitative detection was performed.

[0047] It should be noted that the information depth of XPS analysis is typically a few nanometers. Therefore, the M in this application... 0nm This refers to the average atomic percentage of element M, based on the total number of atoms of elements other than lithium and oxygen, detected within a depth of XPS information (0 nm-10 nm) extending from the surface of a lithium transition metal oxide (LiMeO) oxide into its interior. Accordingly, M... 50nm This refers to the use of argon ions (Ar) + The sample surface was sputtered and etched at a speed of 5 nm / min (standard sample - Ta2O5). When the physical removal thickness reached 50 nm, the M element detected within an XPS information depth (0 nm - 10 nm) was based on the average atomic percentage of the total number of atoms of elements other than lithium and oxygen, using the fresh surface formed after etching as a reference.

[0048] Furthermore, the detection spot area of ​​XPS analysis is typically much larger than the particle size of a single secondary particle of the positive electrode active material. Therefore, M in this application 0nm and M 50nm These values ​​refer to the statistical average of multiple positive electrode active materials (usually at least 100) contained within the XPS detection spot irradiation range (spot size 200μm×200μm), rather than measurements for a single particle.

[0049] The element M in this application includes at least one of Nb, V, Ta, W, and Mo. This element typically has a high valence state and strong MO bond bonding ability, which can introduce a more stable local chemical environment on the surface of lithium transition metal oxides. In one possible embodiment, the element M can be a single element, such as Nb, W, or Mo; in another exemplary embodiment, the element M can also be a combination of two or more elements, such as at least two of Nb, W, and Mo, so as to achieve comprehensive optimization of surface stability, structural stability, and transport performance through multi-element synergy.

[0050] It is worth noting that the doping of element M in this application does not employ a simple, uniform doping approach, but rather a more nuanced approach to M. 50nm and M 0nm The relationship between M and M is defined to allow M to form a relatively enriched state on the surface of lithium transition metal oxides, while maintaining a low but not completely absent content at the 50 nm site. This is achieved by... 50nm / M 0nmBy controlling the concentration between 0.07 and 0.22, the surface of lithium transition metal oxide can have a strong chemical stabilizing effect, while preventing the excessive diffusion of M element into the interior and continuous occupation of too many lithium ion migration-related sites. This achieves a balance between interface protection and lithium ion diffusion, thereby improving the battery's initial efficiency and cycle performance.

[0051] Specifically, the relative enrichment of element M on the surface of lithium transition metal oxides can preferentially regulate the electronic structure and local chemical bond state of the contact region between the lithium transition metal oxides and the external electrolyte, making the surface less susceptible to oxygen release, transition metal reduction migration, and side reactions with the electrolyte; simultaneously, M 50nm Significantly lower than M 0nm This avoids the formation of a high-resistance region at the 50nm site that is detrimental to lithium-ion diffusion. Therefore, this application essentially performs functional partitioning of lithium transition metal oxides, that is, endowing the surface with stronger protective properties while retaining more of the main structural features at the 50nm site that are conducive to lithium-ion migration and capacity utilization.

[0052] Furthermore, due to M 0nm Relatively higher than M 50nm The surface reactivity of lithium transition metal oxides is significantly reduced, thereby decreasing the irreversible lithium consumed during the first charge to form interfacial byproducts, allowing more lithium to be reversibly extracted and returned to the positive electrode during subsequent discharge. Furthermore, M... 0nm and M 50nm The differentiated design avoids the bottleneck of surface lithium extraction kinetics, allowing lithium ions to diffuse smoothly from the bulk phase of the lithium transition metal oxide to the surface and enter the electrolyte without being trapped by surface defects or disordered structures, thus ensuring efficient lithium extraction during the first charge. Therefore, the positive electrode active material of this application also exhibits excellent first-charge performance.

[0053] In addition to the aforementioned differentiated restrictions on the content of element M, this application also specifies the morphology of the positive electrode active material. Specifically, the positive electrode active material of this application is a secondary particle formed by the agglomeration of primary particles. Compared to primary particles, after agglomeration into secondary particles, the gaps between the primary particles can act as stress buffer spaces, absorbing volumetric deformation stress. This significantly reduces the probability of overall pulverization and cracking of the secondary particles during long-term cycling, thereby enabling long-term control of the rate of new side reactions and stabilizing cycle life. At the same time, it avoids the adsorption of active lithium by ultrafine powder generated from particle breakage, reducing irreversible lithium loss and improving initial efficiency.

[0054] This application does not specifically limit the shape of the primary particles that agglomerate to form secondary particles. For example, primary particles can be spherical, elliptical, rhomboid, cuboid, cube, irregular, or a mixture thereof.

[0055] Furthermore, the lithium transition metal oxide includes a main metal element and a secondary metal element. The main metal element includes nickel, and the secondary metal element includes at least one of cobalt, manganese, and aluminum. For example, the lithium transition metal oxide can be at least one of nickel-cobalt-manganese-based ternary cathode active materials, nickel-cobalt-aluminum-based ternary cathode active materials, and nickel-cobalt-manganese-aluminum-based quaternary cathode active materials.

[0056] Among them, the nickel-cobalt-manganese-based ternary cathode active material is the NCM system in this field, the nickel-cobalt-aluminum-based ternary cathode active material is the NCA system in this field, and the nickel-cobalt-manganese-aluminum-based quaternary cathode active material is the NCMA system in this field. Limiting the cathode active material of this application to the above-mentioned composition helps to further improve the energy density and cycle performance of secondary batteries.

[0057] In one possible implementation, the positive electrode active material contains, based on all metal elements except lithium and oxygen, a molar percentage N of nickel. Ni It ranges from 70 mol% to 98 mol%.

[0058] By N Ni By controlling the content within this range, the positive electrode active material can maintain a high reversible specific capacity while also ensuring structural stability and processing controllability. This is because increasing the nickel content enhances redox activity and improves energy density, while limiting it to below 98 mol% avoids lattice instability, oxygen release, and exacerbated interfacial side reactions caused by excessive nickel content. On the other hand, when N... Ni At a content of not less than 70 mol%, the material still possesses the high capacity characteristics required for high-nickel cathodes and can be used with M 50nm / M 0nm The synergistic effect of secondary particle structure inhibits particle surface reconstruction.

[0059] Among them, N is based on the molar percentage of all metal elements except lithium and oxygen. Ni , is the proportion of nickel in the positive electrode active material after normalization using all metal elements except lithium and oxygen as a reference. This definition more accurately reflects the proportion of nickel in the transition metal sublattice and facilitates the design of its proportion with element M and other doping elements. Furthermore, N Ni For 80 mol%-98 mol%, and further, N Ni It is 90 mol% - 98 mol%.

[0060] The inventors discovered that when the M element includes at least one selected from Nb, W, and Mo, its improvement on the cycle performance and initial coulombic efficiency of the battery is more significant.

[0061] In one possible implementation, the lithium transition metal oxide further includes a dopant element, which includes at least one of Mg, Ca, Sr, Ba, Ti, Cr, Fe, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

[0062] Lithium transition metal oxides in maintaining M 50nm / M 0nm Based on a concentration of 0.07-0.22, the aforementioned doping elements are further introduced, allowing them to exist through lattice substitution, near-surface enrichment, or grain boundary segregation, thereby enabling localized stabilization of the cathode active material. Simultaneously, the doping elements can synergistically interact with the differentiated distribution control of M element content, resulting in a cathode active material surface possessing both low interfacial reactivity and sufficient lithium-ion transport channels, thus improving cycle life.

[0063] Furthermore, the molar ratio of the doping element to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):1. Specifically, "all elements except lithium and oxygen" can be understood as the total amount of all elements in the positive electrode active material except lithium and oxygen.

[0064] By limiting the molar ratio of the dopant element to all elements in the positive electrode active material except lithium and oxygen to (0.003-0.03):1, it is equivalent to controlling the total doping amount at a low level, such as 0.003:1, 0.004:1, 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.003:1. This appropriate amount of doping can introduce a stabilizing effect in the local lattice, which can suppress the phase transition and structural collapse of the positive electrode active material during charging and discharging, without significantly increasing the ion migration barrier. This balances structural stability and transport efficiency, and avoids excessive doping that weakens the continuity of the main lattice, occupies the lithium-ion diffusion channels, and causes stress accumulation inside the particles.

[0065] Furthermore, this ratio constraint is particularly applicable when the positive electrode active material is a ternary or quaternary system as described above, because these materials typically have a high nickel content, making them more prone to side reactions and lattice distortion on the surface. By controlling the above molar ratio of dopant elements and all elements except lithium and oxygen, a moderate stabilization effect can be formed on the surface of the lithium transition metal oxide and at the 50nm site, while maintaining the reversible insertion / extraction capability of the internal host phase, thereby improving the capacity retention during cycling.

[0066] When batteries are used as the testing object, the mass percentage of doped elements in lithium transition metal oxides and the mass percentage of all elements other than lithium and oxygen in positive electrode active materials can be detected by the following methods.

[0067] Specifically, the battery is fully discharged to 0% SOC, the positive electrode sheet is removed, and calcined at 500-600℃ to remove the conductive agent and binder. The aluminum foil is then removed to obtain powder, which is the positive electrode active material of the battery. 0.5g of the positive electrode active material is soaked in 10ml of 0.1M HCl at room temperature (25-30℃) for 10 minutes, filtered, and the filtrate is tested using ICP to determine the mass percentage of dopant elements in the filtrate. Another 0.5g of the positive electrode active material is completely dissolved in aqua regia and tested using ICP to obtain the mass content of each element in the positive electrode active material. Subsequently, the molar mass of the corresponding elements is converted to obtain the molar amount of the dopant elements and the molar amount of all elements in the positive electrode active material except lithium and oxygen.

[0068] In one specific embodiment, the positive electrode active material further includes a coating layer disposed on at least a portion of the surface of the lithium transition metal oxide; the coating layer includes at least one of N, Mg, Ca, Sr, Ba, Ti, Cr, Mn, Fe, Co, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

[0069] The coating layer is disposed on at least a portion of the surface of the lithium transition metal oxide to create an interface buffer between the lithium transition metal oxide and the external medium. It may cover the entire or a portion of the outer surface. Specifically, the coating layer first contacts the electrolyte and preferentially passivates or buffers it, thereby inhibiting the continuous erosion of the lithium transition metal oxide surface. This allows the positive electrode active material to maintain a high capacity retention rate during cycling, thus improving the long-term cycle stability of the secondary battery.

[0070] Based on the need to further improve the cycle performance of secondary batteries, in one possible implementation, the molar ratio of all elements in the coating layer except lithium and oxygen to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):1.

[0071] By limiting the molar ratios of all elements except lithium and oxygen in the coating layer and all elements except lithium and oxygen in the positive electrode active material to the above range, the total amount of coating layer can be kept at a low level, for example, close to the upper limit of 0.03:1 to enhance surface passivation, or further reduced to 0.003:1, 0.02:1 or lower, to adapt to scenarios with higher ion transport requirements.

[0072] It should be noted that all elements other than lithium and oxygen in the above molar ratio of the positive electrode active material refer to all elements other than lithium and oxygen, including lithium transition metal oxides and coating layers.

[0073] When the battery is the object of testing, the following methods can be used to detect the mass percentage of all elements except lithium and oxygen in the coating layer, as well as the mass percentage of all elements except lithium and oxygen in the positive electrode active material.

[0074] Specifically, the battery is fully discharged to 0% SOC, the positive electrode is removed, and calcined at 500-600℃ to remove the conductive agent and binder. The aluminum foil is then removed to obtain powder, which is the positive electrode active material of the battery. 0.5g of the positive electrode active material is soaked in 10ml of 0.1M HCl at room temperature (25-30℃) for 10 minutes, filtered, and the filtrate is tested using ICP to determine the mass percentage of the coated elements. Another 0.5g of the positive electrode active material is completely dissolved in aqua regia and tested using ICP to obtain the mass percentage of each element (including the coated elements) in the positive electrode active material. Subsequently, the molar mass of each element is converted to obtain the molar amounts of all elements in the coating layer except lithium and oxygen, and the molar amounts of all elements in the positive electrode active material except lithium and oxygen.

[0075] In one specific embodiment, the Dv50 of the positive electrode active material is 2-15 μm. Within this range, the specific surface area and structural stability can be effectively balanced, thereby improving cycle performance. Here, Dv50 represents the median particle size of the secondary particle volume distribution, i.e., the particle size corresponding to 50% of the particle volume is smaller than this value.

[0076] In addition, this application also optimizes the particle size distribution of the positive electrode active material.

[0077] In one specific embodiment, the particle size distribution curve of the positive electrode active material of this application includes three particle size distribution peaks. That is, after testing the positive electrode active material with a laser particle size analyzer, its volume particle size distribution curve exhibits a distinct three-peak characteristic. In order of increasing peak particle size, the peak particle size of the first particle size distribution peak is D1, the peak particle size of the second particle size distribution peak is D2, and the peak particle size of the third particle size distribution peak is D3; wherein, 1μm≤D1<7μm, 7μm≤D2≤13μm, and 13μm<D3≤20μm.

[0078] In detail, when the positive electrode active material includes the D1 particle size distribution peak, it can shorten the diffusion path of lithium ions inside the particles and increase the specific surface area, thereby improving the reaction activity and rate response; when the positive electrode active material includes the D2 particle size distribution peak, it can achieve a balance between particle flowability, compaction density and electrolyte contact uniformity, which is suitable for balancing energy density and cycle stability; when the positive electrode active material includes the D3 particle size distribution peak, it is beneficial to improve the electrode compaction density and volumetric energy density, and also helps to improve the particle filling structure after slurry film formation.

[0079] In one specific embodiment, the Span value of the positive electrode active material is S; 0.1≤S<0.8, or 0.8≤S≤1.5, or 1.5<S≤3.

[0080] The Span value (S) is used to characterize the width of the particle size distribution of the positive electrode active material. It is usually calculated from Dv90, Dv50, and Dv10, where Span = (Dv90 - Dv10) / Dv50. Dv90, Dv50, and Dv10 represent the particle sizes corresponding to 90%, 50%, and 10% of the cumulative particle size volume distribution, respectively. When 0.1 ≤ S < 0.8, it is beneficial to further enhance the size concentration of the positive electrode active material, reduce batch-to-batch fluctuations, and improve the uniformity of slurry dispersion, suitable for scenarios requiring high-consistency electrode sheets. When S is between 0.8 and 1.5, the particle size distribution is moderate, achieving a balance between particle packing density, pore connectivity, and compaction molding properties, thus considering both processing stability and electrochemical utilization. When 1.5 < S ≤ 3, the particle size distribution is relatively wide, and the synergistic packing of large and small particles can improve the densification degree, thereby improving the electrode sheet compaction density.

[0081] The second aspect of this application also provides a method for preparing the positive electrode active material of the first aspect, comprising the following steps:

[0082] A first raw material system comprising a lithium transition metal oxide precursor, an M source, and a lithium source is subjected to sintering treatment, which includes a first sintering treatment and a second sintering treatment performed sequentially to obtain a positive electrode active material. The molar ratio of M element in the precursor and the M source is 1:(0.003-0.03). The temperature of the first sintering treatment is 450℃-540℃, and the holding time is 5h-15h. The temperature of the second sintering treatment is 650℃-790℃, and the holding time is 5h-15h.

[0083] Specifically, a lithium transition metal oxide precursor refers to a hydroxide of an unlithiated transition metal. Taking the ternary material NCA as an example, the lithium transition metal oxide precursor is a nickel-cobalt-manganese hydroxide. The M source refers to a compound that provides the element M, which can be at least one of inorganic compounds or organic-inorganic composite compounds. Examples of specific M sources include oxides of inorganic compounds, such as niobium pentoxide (Nb₂O₅), vanadium pentoxide (V₂O₅), tantalum pentoxide (Ta₂O₅), tungsten trioxide (WO₃), and molybdenum trioxide (MoO₃), but these are not limited to these. A lithium source refers to a compound that provides the element lithium, which can be a lithium-containing compound commonly used in the art. Examples of specific lithium sources include lithium hydroxide or its hydrate, lithium carbonate, lithium bicarbonate, lithium oxalate, and other lithium-containing compounds commonly used in the art.

[0084] The molar ratio of element M in the precursor and the M source in this application is 1:(0.003-0.03), and a two-step sintering process is employed. First, the above molar ratio allows element M to enter the lithium transition metal oxide precursor in a controlled amount, avoiding insufficient doping leading to limited improvement in surface stability, and also avoiding excessive doping leading to obstruction of lithium-ion diffusion channels. During the sintering process, a first sintering treatment is performed at 450℃-540℃ for 5-15 hours to form an initial enrichment layer of element M on the surface, followed by a second sintering treatment at 650℃-790℃ for 5-15 hours to form a controlled diffusion gradient between the surface layer and a depth of 50 nm. Through the synergistic effect of this raw material quantity control and the two-step specific sintering method, element M will not completely remain on the surface of the lithium transition metal oxide, nor will it penetrate uncontrollably into the interior of the lithium transition metal oxide to form an approximately uniform doping, ultimately achieving the content distribution difference of element M defined by Equation 1. Furthermore, by selecting secondary particles as the precursor and controlling the temperature of the above-mentioned second sintering treatment, it is possible to ensure that a positive electrode active material including secondary particles is obtained.

[0085] Specifically, in the process of preparing positive electrode active materials, positive electrode active materials with different Dv50 particle size distributions and Span values ​​can be achieved by selecting precursors with corresponding morphology and size and further adjusting the temperature and time of the first and second sintering treatments.

[0086] In one specific embodiment, to achieve the doping of the aforementioned dopant element in lithium transition metal oxide, the first raw material system further includes a dopant element source. The dopant element source refers to a compound containing the dopant element. Furthermore, the molar ratio of the dopant element in the precursor to the dopant source is 1:(0.003-0.03), which helps to further improve the cycle performance of the battery.

[0087] The inventors discovered that when the heating rate of the first sintering treatment is controlled at 1.0℃ / min to 3.0℃ / min, organic residues, volatiles, and some lattice rearrangement stress can be released slowly during the first sintering treatment; when the heating rate of the second sintering treatment is also controlled at 1.0℃ / min to 3.0℃ / min, in conjunction with a sintering temperature of 650℃-790℃, the structure of the positive electrode active material can be made more stable.

[0088] It is understandable that after the second sintering process is completed, there may be post-processing steps such as crushing, grading, washing, filtering, drying and iron removal.

[0089] Furthermore, the sintering process also includes a third sintering process. Specifically, after the second sintering process, a third sintering process is performed; the third sintering process includes: holding the second raw material system, comprising the product from the second sintering process and the coating source, at 250℃-450℃ for 5h-15h to obtain the positive electrode active material. It can be understood that the purpose of the third sintering process is to apply a coating layer to the surface of the product after the second sintering process.

[0090] Specifically, the product after the second sintering treatment is a lithium transition metal oxide. By holding the second raw material system, comprising the lithium transition metal oxide and the coating source, at 250℃-450℃ for 5h-15h, the coating source forms a coating layer on at least a portion of the surface of the lithium transition metal oxide. The coating source can be selected according to the composition of the target coating layer, and can be a compound containing at least one of N, Mg, Ca, Sr, Ba, Ti, Cr, Mn, Fe, Co, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La, and Ce, such as oxides, carbonates, hydroxides, nitrates, sulfates, fluorides, phosphates, or organometallic salts.

[0091] Furthermore, the molar ratio of the coating elements in the precursor and the coating source is 1:(0.003-0.03), which helps to further improve the cycle performance of the battery. The coating elements include at least one of N, Mg, Ca, Sr, Ba, Ti, Cr, Mn, Fe, Co, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La, and Ce.

[0092] It should be noted that the third sintering process in this application can be performed once or multiple times. The specific number of times can be selected according to the target number of coating layers. For example, when the target number of coating layers for the positive electrode active material is one layer, the second raw material system includes lithium transition metal oxide and at least one coating source, and the preparation of the positive electrode active material can be completed after one third sintering process. When the target number of coating layers for the positive electrode active material is multiple layers, such as two layers, the second raw material system includes lithium transition metal oxide and part of the coating source, and a single-layer coated positive electrode active material is obtained after one third sintering process. Subsequently, the single-layer coated positive electrode active material is mixed with the remaining coating source, and a double-layer coated positive electrode active material is obtained after a second third sintering process.

[0093] It is understandable that after the third sintering process is completed, post-processing steps such as crushing, grading and iron removal may also be included.

[0094] In one specific embodiment, the first sintering treatment, the second sintering treatment, and the third sintering treatment are all carried out in an oxygen atmosphere.

[0095] A third aspect of this application provides a positive electrode sheet comprising the positive electrode active material of the first aspect or the positive electrode active material prepared in the second aspect. Therefore, this positive electrode sheet has the advantage of effectively improving the first-efficiency and cycle performance of a secondary battery.

[0096] In one specific embodiment, the positive electrode sheet of this application includes a positive current collector and a positive active layer comprising a positive active material disposed on the surface of the positive current collector.

[0097] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material of this application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and more specifically, 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0098] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0099] Furthermore, the positive electrode active layer of this application also includes a solid electrolyte material. This solid electrolyte material is used to reduce the ion transport impedance inside the positive electrode active layer, weaken the polarization caused by insufficient interparticle contact, and suppress side reactions between the positive electrode active material and adjacent interfaces, thereby improving the cycle stability of the positive electrode sheet in solid-state lithium secondary batteries.

[0100] This application does not limit the form in which the solid electrolyte material exists. For example, the solid electrolyte material can be dispersed between the positive electrode active materials to fill the pores between the positive electrode active materials and promote ion conduction across particles; it can also be coated on the surface of the positive electrode active materials to form a transition layer on the surface that allows ions to pass through and is chemically more stable. Furthermore, the mass percentage of the solid electrolyte material in the positive electrode active layer can be limited according to requirements.

[0101] This application does not limit the chemical composition of the solid electrolyte material. It can be any one of sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, or a compound system of the above materials. Exemplary examples include Li6PS5Cl (Lithium Argyrodite Chloride), Li3PS4 (Lithium Thiophosphate), LATP (Lithium Aluminum Titanium Phosphate), and LLZO (Lithium Lanthanum Zirconium Oxide).

[0102] This application provides a secondary battery in a fourth aspect, which includes the positive electrode plate of the third aspect. Therefore, the secondary battery of this application exhibits excellent initial coulombic efficiency and cycle performance.

[0103] It is conceivable that, in addition to the aforementioned positive electrode, the secondary battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0104] This application does not strictly limit the negative electrode active material in the negative electrode sheet, and can be at least one of commonly used negative electrode active materials, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys). This application does not strictly limit the choice of electrolyte, and can include one or more of the solvents commonly used in electrolytes, as well as the electrolyte lithium salts commonly used in electrolytes. For example, the solvent can be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt can be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0105] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0106] In the preparation of secondary batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain bare cells, which are then packaged into pre-stamped aluminum-plastic film bags. After the packaged batteries are dried at 85°C, electrolyte is injected into the dried batteries. The batteries undergo resting, formation, and secondary sealing to complete the preparation of the secondary batteries.

[0107] In one possible embodiment, the battery is a solid-state battery or a semi-solid-state battery, which belongs to the secondary battery structure using a non-liquid or low-liquid electrolyte system. For the purposes of this application, the battery typically includes a positive electrode, a negative electrode, an electrolyte layer, and a casing, with the electrolyte layer disposed between the positive and negative electrodes. Because the positive electrode in this application includes the aforementioned positive electrode active material from the first aspect, this battery is particularly suitable for using a solid electrolyte or a battery with a predominantly solid component structure, in order to suppress interfacial side reactions and maintain high cycle stability under high voltage and high temperature conditions.

[0108] In this application, a solid-state battery refers to a secondary battery whose electrolyte layer is mainly composed of a solid electrolyte. The solid electrolyte can be any one or more combinations of sulfide-based, oxide-based, polymer-based, or composite solid electrolytes. A semi-solid-state battery refers to a secondary battery with a mixed electrolyte system containing solid components and may further contain a small amount of liquid components. The mixed electrolyte can be a gel electrolyte, a quasi-solid electrolyte, or a solid-liquid composite electrolyte.

[0109] The positive electrode active material of this application will be further described below through specific embodiments and comparative examples.

[0110] Comparative Example 1-1

[0111] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0112] 1) The Ni composition prepared by co-precipitation method 0.95 Co 0.02 Mn 0.03 The precursor (secondary particles) of (OH)2, lithium hydroxide, Nb element from M source (niobium pentoxide, Nb2O5), and Zr element from dopant source (zirconia) are added to a mixing container in a molar ratio of 1.00:1.03:0.002:0.005 and mixed uniformly to obtain a mixed powder.

[0113] 2) After the mixed powder is subjected to the first sintering treatment and the second sintering treatment in a box furnace under the following conditions, it is cooled, crushed, graded, washed, filtered, dried and iron removed to obtain lithium transition metal oxide.

[0114] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0115] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0116] 3) Lithium transition metal oxide and boric acid as the coating source were added to a mixing container at a molar ratio of lithium transition metal oxide to element B of 1.00:0.005 and mixed evenly. The mixture was then subjected to a third sintering treatment in a box furnace under the following conditions: cooling, crushing, grading and iron removal, to obtain the positive electrode active material of this comparative example.

[0117] Third sintering treatment: oxygen atmosphere, temperature increased from room temperature to 350℃ at a rate of 2℃ / min and held for 7 hours.

[0118] Example 1-1

[0119] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 1-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.005:0.005. Figure 1 This is a SEM image of the positive electrode active material of Example 1-1 of this application. Figure 1 As shown, the positive electrode active material is a secondary particle.

[0120] Examples 1-2

[0121] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 1-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0122] Examples 1-3

[0123] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 1-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0124] Comparative Examples 1-2

[0125] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 1-1, except that in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0126] Comparative Examples 1-3

[0127] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 1-1, except that in step 1), Ni... 0.95Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 3h.

[0128] Examples 1-4

[0129] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 1-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 7h.

[0130] Examples 1-5

[0131] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 1-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 13h.

[0132] Comparative Examples 1-4

[0133] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 1-1, except that in step 1), Ni... 0.95 Co 0.02 Mn 0.03 The molar ratio of (OH)2 precursor, lithium hydroxide, Nb element in M ​​source (niobium pentoxide, Nb2O5), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 18h.

[0134] Comparative Example 2-1

[0135] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0136] 1) The Ni composition prepared by co-precipitation method 0.95 Co0.03 Al 0.02 The precursor of (OH)2, lithium hydroxide, W element from the M source (tungsten trioxide, WO3), and Zr element from the dopant source (zirconia) are added to a mixing container in a molar ratio of 1.00:1.03:0.002:0.005 and mixed uniformly to obtain a mixed powder.

[0137] 2) After the mixed powder is subjected to the first sintering treatment and the second sintering treatment in a box furnace under the following conditions, it is cooled, crushed, graded, washed, filtered, dried and iron removed to obtain lithium transition metal oxide.

[0138] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0139] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0140] 3) Lithium transition metal oxide and boric acid as the coating source were added to a mixing container at a molar ratio of lithium transition metal oxide to element B of 1.00:0.005 and mixed evenly. The mixture was then subjected to a third sintering treatment in a box furnace under the following conditions: cooling, crushing, grading and iron removal, to obtain the positive electrode active material of this comparative example.

[0141] Third sintering treatment: oxygen atmosphere, temperature increased from room temperature to 350℃ at a rate of 2℃ / min and held for 7 hours.

[0142] Example 2-1

[0143] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 2-1, except that: in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.005:0.005.

[0144] Example 2-2

[0145] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 2-1, except that: in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0146] Example 2-3

[0147] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 2-1, except that: in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0148] Comparative Example 2-2

[0149] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 2-1, except that in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0150] Comparative Examples 2-3

[0151] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 2-1, except that in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 3h.

[0152] Examples 2-4

[0153] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 2-1, except that: in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 7h.

[0154] Examples 2-5

[0155] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 2-1, except that: in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 13h.

[0156] Comparative Examples 2-4

[0157] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 2-1, except that in step 1), Ni... 0.95 Co 0.03 Al 0.02 The molar ratio of (OH)2 precursor, lithium hydroxide, W element in M ​​source (tungsten trioxide, WO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 18h.

[0158] Comparative Example 3-1

[0159] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0160] 1) The Ni composition prepared by co-precipitation method 0.95 Co 0.02 Mn 0.02 Al 0.01 The precursor of (OH)2, lithium hydroxide, Mo element from the M source (molybdenum trioxide, MoO3), and Zr element from the dopant source (zirconia) are added to a mixing container in a molar ratio of 1.00:1.03:0.002:0.005 and mixed uniformly to obtain a mixed powder.

[0161] 2) After the mixed powder is subjected to the first sintering treatment and the second sintering treatment in a box furnace under the following conditions, it is cooled, crushed, graded, washed, filtered, dried and iron removed to obtain lithium transition metal oxide.

[0162] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0163] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0164] 3) Lithium transition metal oxide and boric acid as coating source are added to a mixing container at a molar ratio of lithium transition metal oxide to element B of 1.00:0.005 and mixed evenly. The first and third sintering treatments are carried out in a box furnace under the following conditions: cooling, crushing, grading and iron removal, to obtain the third sintering product.

[0165] First and third sintering treatment: oxygen atmosphere, temperature is increased from room temperature to 350℃ at a rate of 2℃ / min and then held for 7h;

[0166] 4) The third sintering product and alumina as the coating source were added to a mixing container at a molar ratio of lithium transition metal oxide to Al element of 1.00:0.005 and mixed evenly. The second and third sintering treatments were carried out in a box furnace under the following conditions: cooling, crushing, grading and iron removal, to obtain the positive electrode active material of this comparative example.

[0167] Second and third sintering treatment: oxygen atmosphere, temperature increased from room temperature to 350℃ at a rate of 2℃ / min and held for 7 hours.

[0168] Example 3-1

[0169] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 3-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.005:0.005.

[0170] Example 3-2

[0171] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 3-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0172] Example 3-3

[0173] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 3-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0174] Comparative Example 3-2

[0175] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, except that in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0176] Comparative Example 3-3

[0177] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, except that in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 3h.

[0178] Examples 3-4

[0179] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 3-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 7h.

[0180] Examples 3-5

[0181] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Comparative Example 3-1, except that: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 13h.

[0182] Comparative Examples 3-4

[0183] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, except that in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of (OH)2 precursor, lithium hydroxide, Mo element in M ​​source (molybdenum trioxide, MoO3), and Zr element in dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time of the first sintering treatment is 18h.

[0184] Experimental Example 1

[0185] 1) The composition of the positive electrode active material in the examples and comparative examples was detected.

[0186] Elemental analysis of the prepared positive electrode active material was performed using an ICP-OES analyzer. For the ICP-OES analysis, the major components were analyzed using an Agilent 5800 (RF power 1200W) analyzer, while trace elements such as dopants and coating elements were analyzed using a Perkin Elmer Avio550 (RF power 1300W). The results are shown in Tables 1A and 1B. Tables 1A and 1B include both experimental and analytical chemical formulas.

[0187] Table 1A Chemical composition of the positive electrode active materials in the examples and comparative examples

[0188]

[0189] Table 1B Chemical composition of the positive electrode active materials in the examples and comparative examples

[0190]

[0191] In Tables 1A and 1B, the experimental chemical formulas directly represent the molar ratios used in the preparation methods, while the analytical chemical formulas are expressed using a 1.0 molar basis for all components except lithium and oxygen. However, Tables 1A and 1B do not include trace amounts of impurities.

[0192] Referring to Tables 1A and 1B, it can be confirmed that the experimental and analytical values ​​for all components except lithium are in good agreement. This is presumably due to the removal of lithium during the washing process in the preparation of the positive electrode active material.

[0193] 2) Particle size analysis of positive electrode active materials

[0194] The particle size analysis of the prepared lithium cathode active material was performed using a particle size analyzer (Master Sizer 3000), and the results are shown in Table 2.

[0195] Table 2. Particle size values ​​of the positive electrode active materials in the examples and comparative examples.

[0196]

[0197] As shown in Table 2, there is no significant difference in average particle size and particle size distribution between the positive electrode active materials prepared by the first sintering treatment and the second sintering treatment. Therefore, it can be confirmed that the sintering treatment conditions during the preparation of the positive electrode active material do not have a significant impact on the average particle size and particle size distribution of the positive electrode active material.

[0198] 3) M 0nm M 50nm Test

[0199] M was analyzed using the XPS analysis equipment (Shimadzu AXIS Supra+). 0nm M 50nm Testing was conducted. Specifically, after XPS analysis of the surface of the positive electrode active material, M was calculated. 0nm Reusing argon ions (Ar) + The laser beam etched the positive electrode active material at a speed of 5 nm / min (standard sample - Ta2O5), starting from the surface. After etching to a thickness of 50 nm, the etched surface was analyzed by XPS to calculate M. 50nm In XPS analysis, the content of M was calculated based on the elements other than lithium and oxygen in the analytical formulas in Table 1. 0nm M 50nm and R(=M 50nm / M 0nm The results are shown in Table 3.

[0200] Table 3. M of the positive electrode active material in the examples and comparative examples 0nm M 50nm Numerical table of R

[0201]

[0202] As shown in Table 3, the preparation method of this application can obtain a positive electrode active material that satisfies Formula 1. Specifically, the R of the lithium positive electrode active material in the examples is greater than or equal to 0.07 and less than or equal to 0.22, while the R of the positive electrode active material in the comparative examples is greater than 0.22 or less than 0.07.

[0203] Experimental Example 2

[0204] To evaluate the battery performance of the positive electrode active materials in the examples and comparative examples, all-solid-state batteries were manufactured using the following method.

[0205] A positive electrode slurry was prepared by uniformly mixing 84.0 wt% of positive electrode active material, 14.0 wt% of sulfide electrolyte Li6PS5Cl, and 1.0 wt% of vapor-grown carbon fiber (VGCF) as a conductive material in a first mixing process. Then, 1.0 wt% of PTFE as a binder was added, and the mixture was uniformly mixed a second time to obtain a positive electrode slurry. A positive electrode sheet (comprising an aluminum foil and a positive electrode active layer on the surface of the aluminum foil, the positive electrode active layer being obtained by drying the positive electrode slurry) was then prepared using a high-temperature press. The negative electrode sheet comprised a copper foil and a negative electrode active layer on the surface of the copper foil. The negative electrode active layer, by mass percentage, consisted of 70.0 wt% graphite, 28.0 wt% sulfide electrolyte Li6PS5Cl, 1.0 wt% conductive agent VGCF, and 1.0 wt% binder PTFE. The sulfide electrolyte Li6PS5Cl was pressurized at 200 MPa to form a solid electrolyte layer. A solid electrolyte layer was placed between the positive and negative electrodes, and the battery was compressed at 400 MPa to create an all-solid-state battery.

[0206] The capacity characteristics were evaluated using the various all-solid-state batteries manufactured, as follows.

[0207] The all-solid-state battery was initially charged at 45°C with a constant current of 0.1C to 4.30V (cutoff at 0.02C), and then initially discharged at a constant current of 0.2C to 2.5V. Next, the all-solid-state battery was charged at 45°C with a constant current of 0.5C to 4.30V (cutoff at 0.05C), and then discharged at a constant current of 1.0C to 2.5V. This constituted one cycle, which was repeated 100 times. The results are shown in Table 4.

[0208] Table 4. Electrical performance parameters of all-solid-state batteries

[0209]

[0210] The correlation between R in Table 3 and the discharge capacity (mAh / g, @100 cycles) at 100 cycles in Table 4 is shown in the figure. Figure 2The correlation between R in Table 3 and the capacity retention rate (%, @ 100 cycles) at 100 cycles in Table 4 is shown in the figure. Figure 3 middle. Figure 2 The correlation graph between R in Table 3 and discharge capacity (mAh / g, @100 cycles) in Table 4 is shown. Figure 3 The correlation plot is shown between R in Table 3 and capacity retention (%, @100 cycles) in Table 4.

[0211] Reference Figure 2 and Figure 3 It can be seen that, compared with the positive electrode active material that does not satisfy Formula 1, the positive electrode active material of this application that satisfies Formula 1 has a better discharge capacity and capacity retention rate after 100 cycles.

[0212] In summary, by controlling the content of a specific component M at the surface and 50nm site of the lithium transition metal oxide using the method for preparing the positive electrode active material proposed in this application, it is possible to prepare a positive electrode active material for lithium secondary batteries with improved battery capacity characteristics, and by using a positive electrode active material with these characteristics, it is possible to prepare a lithium secondary battery with improved capacity characteristics.

[0213] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes secondary particles; the positive electrode active material includes a lithium transition metal oxide, the lithium transition metal oxide includes an element M, and the element M includes at least one of Nb, V, Ta, W and Mo, wherein; 0.07≤M 50nm / M 0nm ≤0.22 Equation 1 In Equation 1, M 0nm M represents the element M on the surface of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen; M 50nm The M element is located at the 50 nm site of the lithium transition metal oxide, based on the atomic percentage of all elements except lithium and oxygen.

2. The positive electrode active material according to claim 1, characterized in that, The lithium transition metal oxide comprises a main metal element and a secondary metal element, wherein the main metal element comprises nickel and the secondary metal element comprises at least one of cobalt, manganese and aluminum.

3. The positive electrode active material according to claim 2, characterized in that, In the aforementioned positive electrode active material, based on all metal elements except lithium and oxygen, the molar percentage of nickel is N. Ni It ranges from 70 mol% to 98 mol%.

4. The positive electrode active material according to claim 3, characterized in that, N Ni It is 80 mol% - 98 mol%.

5. The positive electrode active material according to claim 4, characterized in that, N Ni It is 90 mol% - 98 mol%.

6. The positive electrode active material according to claim 1, characterized in that, The M element includes at least one of Nb, W, and Mo.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The lithium transition metal oxide further includes doping elements, which include at least one of Mg, Ca, Sr, Ba, Ti, Cr, Fe, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

8. The positive electrode active material according to claim 7, characterized in that, The molar ratio of the doping element to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):

1.

9. The positive electrode active material according to any one of claims 1-6 and 8, characterized in that, The positive electrode active material further includes a coating layer, which is disposed on at least a portion of the surface of the lithium transition metal oxide; The coating layer includes at least one of N, Mg, Ca, Sr, Ba, Ti, Cr, Mn, Fe, Co, Cu, Zn, B, Al, Si, Sn, P, Sb, Bi, S, F, Zr, Hf, Sc, Y, La and Ce.

10. The positive electrode active material according to claim 9, characterized in that, The molar ratio of all elements in the coating layer except lithium and oxygen to all elements in the positive electrode active material except lithium and oxygen is (0.003-0.03):

1.

11. A method for preparing the positive electrode active material according to any one of claims 1-10, characterized in that, Includes the following steps: A first raw material system comprising a lithium transition metal oxide precursor, an M source, and a lithium source is subjected to sintering treatment, wherein the sintering treatment includes a first sintering treatment and a second sintering treatment performed sequentially to obtain the positive electrode active material; wherein the molar ratio of the M element in the precursor and the M source is 1:(0.003-0.03). The temperature of the first sintering treatment is 450℃-540℃, and the holding time is 5h-15h; the temperature of the second sintering treatment is 650℃-790℃, and the holding time is 5h-15h.

12. The preparation method according to claim 11, characterized in that, The first raw material system further includes a dopant element source; and / or, The heating rate of the first sintering treatment is from 1.0 °C / min to 3.0 °C / min; and / or, The heating rate of the second sintering treatment is from 1.0℃ / min to 3.0℃ / min.

13. The preparation method according to claim 11 or 12, characterized in that, The sintering process also includes a third sintering process; The third sintering process includes: heat-preserving the second raw material system, which includes the product of the second sintering process and the coating source, at 250℃-450℃ for 5h-15h to obtain the positive electrode active material.

14. The preparation method according to claim 13, characterized in that, The first sintering process, the second sintering process, and the third sintering process are each carried out in an oxygen atmosphere.

15. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; The positive electrode active layer comprises the positive electrode active material according to any one of claims 1-10, or the positive electrode active material prepared by the preparation method according to any one of claims 11-14.

16. The positive electrode sheet according to claim 15, characterized in that, The positive electrode active layer also includes a solid electrolyte material.

17. A battery, characterized in that, The battery includes the positive electrode as described in claim 15 or 16.

18. The battery according to claim 17, characterized in that, The battery is a solid-state battery or a semi-solid-state battery.

Images