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, and the lithium transition metal oxide comprises an M element, wherein the M element comprises at least one of S, Si and P, and 0.05≤M 50nm / M 0nm ≤0.2, 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] With the rapid development of the new energy industry, rechargeable batteries, with their excellent energy storage characteristics and cycle life, have become the core energy storage component of new energy equipment and are widely used in consumer electronics, new energy vehicles, energy storage power stations, and various portable smart devices. As terminal devices continue to iterate towards higher energy density, higher safety performance, and longer service life, and as new energy vehicles continue to increase their demands for power batteries in terms of range, safety, and adaptability to extreme operating conditions, the performance shortcomings of traditional liquid rechargeable batteries are gradually becoming apparent. The industry urgently needs new energy storage battery systems with better performance to meet the increasingly stringent market application requirements.

[0003] Compared to traditional liquid rechargeable batteries, solid-state batteries use solid electrolytes instead of liquid electrolytes, fundamentally avoiding the safety hazards of leakage, combustion, and explosion associated with liquid electrolytes. They also offer higher energy density, a wider operating temperature window, and longer service life, making them a key development direction for next-generation rechargeable batteries. However, solid-state batteries still face significant technical bottlenecks, particularly in the solid-solid interface system between the cathode and the solid electrolyte. The interface is prone to continuous side reactions, which not only cause active lithium loss and a continuous increase in interface impedance but also lead to degradation of the cathode lattice structure and particle breakage. Ultimately, this results in lower initial coulombic efficiency, faster capacity decay during long cycles, and difficulty in meeting the requirements for large-scale commercialization, severely limiting the industrialization and promotion of solid-state batteries. Summary of the Invention

[0004] This application provides a positive electrode active material comprising a lithium transition metal oxide containing a special element M. By defining the distribution relationship of the special element M in the surface region and a specific internal region of the lithium transition metal oxide, and combining it with the morphology of secondary particles, the material maintains the main performance of the positive electrode active material while also possessing excellent stability and ion insertion / extraction performance. Consequently, the secondary battery using it exhibits both excellent first coulombic efficiency and cycle performance.

[0005] This application also provides a method for preparing the above-mentioned lithium transition metal oxide cathode active material, which is used to prepare the above-mentioned lithium transition metal oxide cathode active material.

[0006] This application also provides a positive electrode sheet comprising the aforementioned lithium transition metal oxide positive electrode active material, which significantly improves the cycle performance of secondary batteries.

[0007] This application also provides a secondary battery that includes the above-mentioned positive electrode, thus having a longer service life.

[0008] 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 S, Si and P, wherein;

[0009] 0.05≤M 50nm / M 0nm ≤0.2 Equation 1

[0010] 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.

[0011] 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.

[0012] 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%.

[0013] The positive electrode active material as described above, wherein N Ni It is 80 mol% - 98 mol%.

[0014] The positive electrode active material as described above, wherein N Ni It is 90 mol% - 98 mol%.

[0015] 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 selected from Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

[0016] 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.

[0017] 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;

[0018] The coating layer includes at least one of N, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

[0019] 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.

[0020] 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:

[0021] 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:(0.003-0.027).

[0022] The temperature of the first sintering treatment is 450℃-550℃, and the holding time is 5h-15h; the temperature of the second sintering treatment is 650℃-800℃, and the holding time is 5h-15h.

[0023] In the preparation method described above, the first raw material system further includes a dopant element source; and / or,

[0024] The heating rate of the first sintering treatment is from 1.0 °C / min to 3.0 °C / min; and / or,

[0025] The heating rate of the second sintering treatment is from 1.0℃ / min to 3.0℃ / min.

[0026] The preparation method described above, wherein the sintering treatment includes a third sintering treatment;

[0027] 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.

[0028] 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.

[0029] This application also provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active layer disposed on at least one surface of the positive current collector;

[0030] 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.

[0031] The positive electrode sheet as described above, wherein the positive electrode active layer further includes a solid electrolyte material.

[0032] This application also provides a battery comprising the positive electrode sheet described in any of the preceding claims.

[0033] The battery as described above, wherein the battery is a solid-state battery or a semi-solid-state battery.

[0034] This application includes a lithium transition metal oxide cathode active material that is a secondary particle. By including at least one element from S, Si, and P 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, the material can have a more reasonable elemental distribution state. This can suppress the occurrence of side reactions in the cathode active material, balance lithium-ion migration efficiency, and improve the first-efficiency and cycle performance of the secondary battery. Attached Figure Description

[0035] Figure 1 This is a SEM image of the positive electrode active material of Example 1-1 of this application;

[0036] Figure 2 The correlation graph between R in Table 3 and discharge capacity (mAh / g, @100 cycles) in Table 4 is shown.

[0037] Figure 3 The correlation plot is shown between R in Table 3 and capacity retention (%, @100 cycles) in Table 4. Detailed Implementation

[0038] 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.

[0039] Currently, the initial efficiency and cycle performance of solid-state batteries still fall short of application expectations. The inventors have investigated this issue and concluded that in solid-state battery systems, an electron transport channel exists between the positive electrode active material and the solid electrolyte layer. Electrons migrate from the positive electrode active material to the interface with the solid electrolyte, triggering redox side reactions in the solid electrolyte. This process not only causes the solid electrolyte itself to decompose and its interfacial impedance to increase sharply, but also damages the surface lattice structure of the positive electrode active material and consumes a large number of active lithium ions, ultimately leading to rapid capacity decay and low initial coulombic efficiency. Therefore, the key issue is how to block the abnormal electron transport from the positive electrode material to the interface without affecting its normal ion conduction function.

[0040] 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 S, Si and P, wherein;

[0041] 0.05≤M 50nm / M 0nm ≤0.2 Equation 1

[0042] 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.

[0043] In this application, the positive electrode active material is a positive electrode active material suitable for lithium secondary batteries, particularly all-solid-state lithium secondary batteries. This lithium positive electrode active material comprises a lithium transition metal oxide, which includes elements M, oxygen, and lithium.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The element M in this application includes at least one of S, Si, and P. This element typically forms compounds with lithium or transition metals (such as Ni, Co, and Mn) in the cathode active material, exhibiting high bond energy, wide band gaps, and dense crystal structures. These crystal structures (e.g., lithium sulfide, lithium silicate, and lithium phosphate) possess extremely high enthalpy of formation, making them extremely stable once formed and resistant to further oxidation and decomposition at high cathode potentials. Simultaneously, these crystal structures effectively block direct solid-solid contact between the cathode active material and the solid electrolyte. More importantly, from an electron blocking perspective, these crystal structures are typical wide band gap insulators. This makes it difficult for electrons excited in the cathode active material to cross the interface layer to reach the solid electrolyte side, while allowing lithium ions to pass through. This selective transport characteristic cuts off the electron supply pathway required for the redox reaction of the solid electrolyte. Therefore, the doping of S, Si, and P achieves physical contact isolation and electronic current interruption without affecting ion transport. The three work together to protect the solid electrolyte from decomposition without affecting ion transport, and also avoids low initial efficiency and cycle degradation caused by side reactions consuming lithium ions in the positive electrode active material.

[0048] In one possible embodiment, element M can be a single element, such as Si, S, or P; in another exemplary embodiment, element M can also be a combination of two or more elements, such as at least two of Si, S, and P, so as to achieve comprehensive optimization of surface stability and ion transport performance through multi-element synergy.

[0049] 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 distribution relationship between M and M is defined to ensure that element M is relatively enriched on the surface while maintaining a low but not completely absent content at the 50nm site. This ratio is limited to 0.05-0.2, and its core purpose is to limit the distribution of M. 0nm It is M 50nm This is achieved by creating a locally enriched chemical environment for the element M at the interface where the lithium transition metal oxide surface directly contacts the solid electrolyte. This relative enrichment allows the lithium transition metal oxide surface to act as a physical barrier, directly blocking solid-solid contact between the positive electrode active material and the solid electrolyte, thus preventing side reactions at the interface. Furthermore, its high electronic insulation properties cut off the migration path of electrons from the positive electrode to the solid electrolyte, fundamentally suppressing the redox decomposition of the solid electrolyte at high potentials. More importantly, M... 50nm Significantly lower than M 0nm This ensures that the 50nm site maintains a crystal structure close to the original composition and high intrinsic capacity characteristics, without diluting the active lithium or damaging the transition metal-oxygen framework due to excessive M element doping. Therefore, the cathode active material of this application can significantly improve the cycle performance of secondary batteries.

[0050] Furthermore, regarding the improvement in first-cycle efficiency, the presence of this crystal structure, which combines physical isolation and electron blocking functions, reduces the consumption of active lithium ions by side reactions, allowing most lithium ions to reversibly migrate back and forth between the positive and negative electrodes, thereby significantly improving the first-cycle coulombic efficiency.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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%.

[0056] 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 regulation and secondary particle structure inhibits particle surface reconstruction.

[0057] 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%.

[0058] 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, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

[0059] Lithium transition metal oxides in maintaining M 50nm / M 0nm Based on a concentration of 0.05-0.2, 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 element M, resulting in a cathode active material surface possessing both low interfacial reactivity and sufficient lithium-ion transport channels, thus improving cycle life.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

[0066] 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 outer surface or only a portion thereof. Specifically, the coating layer first contacts the electrolyte and preferentially undergoes passivation or buffering, 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.

[0067] 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.

[0068] 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.

[0069] It should be noted that all elements in the positive electrode active material mentioned above, excluding lithium and oxygen, refer to all elements other than lithium and oxygen, including lithium transition metal oxides and coating layers.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] In addition, this application also optimizes the particle size distribution of the positive electrode active material.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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:

[0079] A first raw material system comprising a lithium transition metal oxide precursor, an M source, and a lithium source is subjected to sintering treatment. The sintering treatment includes a first sintering treatment and a second sintering treatment in sequence to obtain a positive electrode active material. The molar ratio of M element in the precursor and the M source is 1:(0.003-0.027). The temperature of the first sintering treatment is 450℃-550℃, and the holding time is 5h-15h. The temperature of the second sintering treatment is 650℃-800℃, and the holding time is 5h-15h.

[0080] Specifically, a lithium transition metal oxide precursor refers to a hydroxide of an unlithiated transition metal. Taking the ternary material NCA as an example of a cathode active material, the lithium transition metal oxide precursor is a hydroxide of nickel, cobalt, and manganese. The M source refers to a compound that provides the element M. The M compound is a compound containing the element M and can be at least one of inorganic compounds or organic-inorganic composite compounds. Specific examples of M sources include: sulfur (S), lithium sulfate (Li₂SO₄), aluminum sulfate (Al₂(SO₄)₃), ammonium sulfate ((NH₄)₂SO₄), silicon dioxide (SiO₂), tetraethoxysilane (Si(OCH₂CH₃)₄), lithium phosphate (Li₃PO₄), aluminum phosphate (AlPO₄), and ammonium dihydrogen phosphate (NH₄H₂PO₄), but are not limited to these. A lithium source refers to a compound that provides the element lithium. It can be a lithium-containing compound commonly used in the art. For example, specific examples of lithium sources include lithium hydroxide or its hydrate, lithium carbonate, lithium bicarbonate, lithium oxalate, and other lithium-containing compounds commonly used in the art.

[0081] In this application, the molar ratio of M element in the precursor and the M source is 1:(0.003-0.027), and a two-step sintering process is employed. First, this molar ratio allows the M element to enter the lithium transition metal oxide precursor in a controlled amount, avoiding insufficient doping leading to limited surface stability improvement, and also avoiding excessive doping causing obstruction of lithium-ion diffusion channels. During the sintering process, a first sintering treatment is performed at 450℃-550℃ for 5-15 hours to form an initial enriched layer of M element on the surface. Then, a second sintering treatment is performed at 650℃-800℃ for 5-15 hours to create a controlled diffusion gradient between the surface layer and a depth of 50 nm. Through the synergistic effect of this controlled raw material quantity and the two-step specific sintering method, the M element does not remain entirely on the surface of the lithium transition metal oxide, nor does it uncontrollably penetrate into the interior of the lithium transition metal oxide to form approximately uniform doping, ultimately achieving the M element content distribution difference defined in Equation 1. Furthermore, by selecting secondary particles as the precursor and controlling the temperature of the second sintering treatment, a positive electrode active material including secondary particles can be obtained.

[0082] Specifically, in the process of preparing positive electrode active materials, positive electrode active materials with different Dv50, particle size distribution and Span values ​​can be achieved by selecting precursors with corresponding morphology and size and further adjusting the temperature and time of the first sintering treatment and the second sintering treatment.

[0083] 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 precursor to the dopant element in the dopant element source is 1:(0.003-0.03), which helps to further improve the cycle performance of the battery.

[0084] 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℃-800℃, the structure of the positive electrode active material can be made more stable.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 then uniformly coated onto 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% lithium positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder, and further comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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).

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The positive electrode active material of this application will be further described below through specific embodiments and comparative examples.

[0107] Comparative Example 1-1

[0108] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0109] 1) The Ni composition prepared by co-precipitation method 0.95 Co 0.02 Mn 0.03 The precursor of (OH)2 (secondary particles), lithium hydroxide, S element from M source (ammonium sulfate, (NH4)2SO4), 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.

[0110] 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.

[0111] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0112] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0113] 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.

[0114] Third sintering treatment: oxygen atmosphere, temperature increased from room temperature to 350℃ at a rate of 2℃ / min and held for 7 hours.

[0115] Example 1-1

[0116] 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 the precursor (OH)2, lithium hydroxide, S element in the M source (ammonium sulfate, (NH4)2SO4), and Zr element in the 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.

[0117] Examples 1-2

[0118] 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 the precursor (OH)2, lithium hydroxide, S element in the M source (ammonium sulfate, (NH4)2SO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0119] Examples 1-3

[0120] 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, S element in M ​​source (ammonium sulfate, (NH4)2SO4), and Zr element in dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0121] Comparative Examples 1-2

[0122] 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 the precursor (OH)2, lithium hydroxide, S element in the M source (ammonium sulfate, (NH4)2SO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0123] Comparative Examples 1-3

[0124] 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, S element in M ​​source (ammonium sulfate, (NH4)2SO4), 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.

[0125] Examples 1-4

[0126] 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, S element in M ​​source (ammonium sulfate, (NH4)2SO4), 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.

[0127] Examples 1-5

[0128] 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, S element in M ​​source (ammonium sulfate, (NH4)2SO4), 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.

[0129] Comparative Examples 1-4

[0130] 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, S element in M ​​source (ammonium sulfate, (NH4)2SO4), 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.

[0131] Comparative Example 2-1

[0132] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0133] 1) The Ni composition prepared by co-precipitation method0.95 Co 0.03 Al 0.02 The precursor of (OH)2, lithium hydroxide, Si element from M source (tetraethoxysilane, Si(OCH2CH3)4), 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.

[0134] 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.

[0135] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0136] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0137] 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.

[0138] Third sintering treatment: oxygen atmosphere, temperature increased from room temperature to 350℃ at a rate of 2℃ / min and held for 7 hours.

[0139] Example 2-1

[0140] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.005:0.005.

[0141] Example 2-2

[0142] 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 0.02The molar ratio of the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0143] Example 2-3

[0144] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0145] Comparative Example 2-2

[0146] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0147] Comparative Examples 2-3

[0148] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the 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.

[0149] Examples 2-4

[0150] 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 0.02The molar ratio of the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the 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.

[0151] Examples 2-5

[0152] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the 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.

[0153] Comparative Examples 2-4

[0154] 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 the precursor (OH)2, lithium hydroxide, Si element in the M source (tetraethoxysilane, Si(OCH2CH3)4), and Zr element in the 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.

[0155] Comparative Example 3-1

[0156] The preparation method of the positive electrode active material in this comparative example includes the following steps:

[0157] 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, P element from M source (ammonium dihydrogen phosphate, NH4H2PO4), 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.

[0158] 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.

[0159] First sintering treatment: oxygen atmosphere, temperature increased from room temperature to 520℃ at a rate of 1.5℃ / min and held for 10 hours;

[0160] Second sintering treatment: oxygen atmosphere, heating from 520℃ to 730℃ at a rate of 1.5℃ / min and holding for 10 hours;

[0161] 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.

[0162] 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;

[0163] 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.

[0164] 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.

[0165] Example 3-1

[0166] 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 the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.005:0.005.

[0167] Example 3-2

[0168] 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 the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005.

[0169] Example 3-3

[0170] 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 the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.02:0.005.

[0171] Comparative Example 3-2

[0172] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, the difference being: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.04:0.005.

[0173] Comparative Example 3-3

[0174] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, the difference being: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time for the first sintering treatment is 3h.

[0175] Examples 3-4

[0176] 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 the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time for the first sintering treatment is 7h.

[0177] Examples 3-5

[0178] 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 the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the dopant source (zirconia) is 1.00:1.03:0.01:0.005; in step 2), the holding time for the first sintering treatment is 13h.

[0179] Comparative Examples 3-4

[0180] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Comparative Example 3-1, the difference being: in step 1), Ni... 0.95 Co 0.02 Mn 0.02 Al 0.01 The molar ratio of the precursor (OH)2, lithium hydroxide, P element in the M source (ammonium dihydrogen phosphate, NH4H2PO4), and Zr element in the 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.

[0181] Experimental Example 1

[0182] 1) The composition of the positive electrode active material in the examples and comparative examples was detected.

[0183] 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.

[0184] Table 1A Chemical composition of the positive electrode active materials in the examples and comparative examples

[0185]

[0186] Table 1B Chemical composition of the positive electrode active materials in the examples and comparative examples

[0187]

[0188] 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.

[0189] 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.

[0190] 2) Particle size analysis of positive electrode active materials

[0191] The particle size of the prepared positive electrode active material was analyzed using a particle size analyzer (Master Sizer 3000), and the results are shown in Table 2.

[0192] Table 2. Particle size values ​​of the positive electrode active materials in the examples and comparative examples.

[0193]

[0194] 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.

[0195] 3) M 0nm M 50nm Test

[0196] 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 etching beam was used to etch 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(=M50nm / M 0nm The results are shown in Table 3.

[0197] Table 3. M of the positive electrode active material in the examples and comparative examples 0nm M 50nm Numerical table of R

[0198]

[0199] 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 value of the positive electrode active material in the embodiments is greater than or equal to 0.05 and less than or equal to 0.2, while the R value of the positive electrode active material in the comparative examples is greater than 0.2 or less than 0.05.

[0200] Experimental Example 2

[0201] 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.

[0202] 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. 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.

[0203] The capacity characteristics were evaluated using the various all-solid-state batteries manufactured, as follows.

[0204] 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.

[0205] Table 4. Electrical performance parameters of all-solid-state batteries

[0206]

[0207] 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 2 The 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.

[0208] 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.

[0209] 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.

[0210] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention 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 changes can be made without departing from its scope. The scope of the invention 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 S, Si and P, wherein; 0.05≤M 50nm / M 0nm ≤0.2 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 any one of claims 1-5, characterized in that, The lithium transition metal oxide further includes doping elements, which include at least one of Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

7. The positive electrode active material according to claim 6, 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.

8. The positive electrode active material according to any one of claims 1-5 and 7, 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, V, Cr, Fe, Cu, Zn, B, Al, Sn, Sb, Bi, F, Zr, Mo, Nb, Ta, Hf, Sc, Y, La and Ce.

9. The positive electrode active material according to claim 8, 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.

10. A method for preparing a positive electrode active material according to any one of claims 1-9, 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:(0.003-0.027). The temperature of the first sintering treatment is 450℃-550℃, and the holding time is 5h-15h; the temperature of the second sintering treatment is 650℃-800℃, and the holding time is 5h-15h.

11. The preparation method according to claim 10, 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.

12. The preparation method according to claim 10 or 11, characterized in that, The sintering process 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.

13. The preparation method according to claim 12, characterized in that, The first sintering process, the second sintering process, and the third sintering process are each carried out in an oxygen atmosphere.

14. 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 1-9, or the positive electrode active material prepared by the preparation method according to any one of claims 10-13.

15. The positive electrode sheet according to claim 14, characterized in that, The positive electrode active layer also includes a solid electrolyte material.

16. A battery, characterized in that, The battery includes the positive electrode as described in claim 14 or 15.

17. The battery according to claim 16, characterized in that, The battery is a solid-state battery or a semi-solid-state battery.

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