Composite positive electrode material, preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The invention provides a composite positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery. The composite positive electrode material comprises porous particles and a metal oxide layer coating the surfaces of the porous particles, the chemical formula of the porous particles is Li < x > Ni < y > Co < z > Mn < n > Nb < m > La < q > O < 2 >, wherein x is 1.1 to 1.3, y is 0.12 to 0.14, z is 0.12 to 0.14, n is 0.5 to 0.54, m is 0.005 to 0.015, and q is 0.001 to 0.008; the chemical formula of the metal oxide layer is MaOb, M is a metal element, a is 1-4, and b is 1-6. Based on the co-doping and metal oxide surface coating technology, by constructing the porous structure, the purposes of remarkably improving the cycling stability of the lithium-manganese-rich positive electrode material and inhibiting transition metal dissolution and voltage attenuation are achieved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a composite cathode material, its preparation method, cathode sheet, and lithium-ion battery. Background Technology

[0002] Lithium-rich manganese cathode materials possess a specific capacity exceeding 250 mAh / g, significantly higher than the 220 mAh / g of high-nickel ternary materials, making them a next-generation high-energy-density cathode material. However, this high specific capacity comes at the cost of material stability. Currently, they suffer from issues such as oxygen evolution, low initial coulombic efficiency, transition metal dissolution, and voltage decay. Furthermore, the high upper limit cutoff voltage of 4.8 V in lithium-rich manganese materials easily leads to electrolyte decomposition. These factors hinder the industrialization of lithium-rich manganese materials, thus necessitating modification.

[0003] Currently, researchers and companies have explored various strategies to improve the performance of lithium-rich manganese materials. Among these, elemental doping and surface coating are the two most common methods. Elemental doping enhances the bonding strength of MO bonds by replacing some transition metal or oxygen sites, which helps stabilize the material structure and reduce voltage decay. Surface coating aims to form a protective film on the material surface, reducing direct contact with the electrolyte, inhibiting the dissolution of transition metals, and simultaneously improving the thermal and electrochemical stability of the material.

[0004] While the aforementioned methods have alleviated some of the problems associated with lithium-rich manganese materials to a certain extent, they have also introduced new challenges. For example, while atomic layer deposition (ALD) surface coating can achieve uniform coating, its high cost and difficulty in large-scale production make it unsuitable for industrial applications. Although sol-gel methods can effectively reduce transition metal leaching, the cost of raw materials and their potential hazards also limit their application in large-scale production. These technical challenges necessitate the development of more economical, efficient, and environmentally friendly methods for modifying lithium-rich manganese cathode materials to overcome existing limitations and drive continued progress and technological innovation in the lithium-ion battery industry.

[0005] In summary, while existing methods for modifying lithium-rich manganese cathode materials each have their advantages, they still have significant shortcomings in practical applications. Therefore, providing a method for preparing composite cathode materials that can effectively suppress voltage decay and improve material stability, thereby obtaining cathode active materials with higher cycle stability, is one of the technical problems that needs to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a composite cathode material, its preparation method, cathode sheet, and lithium-ion battery, so as to solve the problem that it is difficult to prepare cathode materials with excellent electrochemical cycle stability in the prior art.

[0007] To achieve the above objectives, a first aspect of the present invention provides a composite cathode material comprising porous particles and a metal oxide layer coating the surface of the porous particles; the porous particles have the chemical formula Li. x Ni y Co z Mn n Nb m La q O2, where x is 1.1~1.3, y is 0.12~0.14, z is 0.12~0.14, n is 0.5~0.54, m is 0.005~0.015, and q is 0.001~0.008; the chemical formula of the metal oxide layer is M. a O b , where M is a metallic element, a is 1~4, and b is 1~6.

[0008] Furthermore, the porosity of the porous particles is 35% to 45%; and / or, the D50 of the porous particles is 3 μm to 10 μm; and / or, the thickness of the metal oxide layer is 0.1 nm to 8 nm.

[0009] A second aspect of the present invention provides a method for preparing a composite cathode material, comprising: step S1, mixing a lithium source, a dopant source, a lithium-rich manganese precursor, and a pore-forming agent, followed by a first calcination to obtain an intermediate product; step S2, sequentially mixing the intermediate product and a metal oxide, followed by a second calcination to obtain the composite cathode material; the chemical formula of the metal oxide is M a O b , where M is a metallic element, a is 1~4, and b is 1~6.

[0010] Further, in step S1, the doping element source includes a niobium source and a lanthanum source, and with the molar amount of the lithium-rich manganese precursor as 1, the molar amount of the niobium source is 0.005~0.015; the molar amount of the lanthanum source is 0.001~0.008; and the molar ratio of the lithium source, the lithium-rich manganese precursor and the pore-forming agent is (1~1.6):1:(0.05~0.15).

[0011] Further, in step S1, the first calcination includes the following steps performed sequentially: holding at 300℃~600℃ for 2h~6h, then heating to 600℃~900℃ at a heating rate of 3℃ / min~5℃ / min, and holding at that temperature for 10h~24h.

[0012] Furthermore, in step S1, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; and / or, the niobium source is selected from one or more of niobium oxide, niobium chloride, niobium fluoride, and niobium oxalate; and / or, the lanthanum source is selected from one or more of lanthanum oxide, lanthanum fluoride, lanthanum acetate, and lanthanum carbonate; and / or, the pore-forming agent is selected from one or more of urea, ammonium bicarbonate, SP, and starch, preferably ammonium bicarbonate; and / or, the lithium-rich manganese precursor is added in the form of lithium-rich manganese hydroxide, and the chemical formula of the lithium-rich manganese hydroxide is Ni 0.13 Co 0.13 Mn 0.54-x (OH)2, where x = 0.006~0.023.

[0013] Furthermore, M a O b In the intermediate product, M is selected from one or more of Mg, Zn, Ti, Zr, Co, Sr, Ce, Y and Al, a is 1 to 3, b is 1 to 4; and / or the weight ratio of the intermediate product to the metal oxide is 1:(0.0005 to 0.05); preferably, the metal oxide is selected from one or more of magnesium oxide, zinc oxide, titanium dioxide, zirconium oxide, cobalt tetroxide, strontium oxide, cerium oxide, yttrium oxide and aluminum oxide.

[0014] Further, the metal oxide is titanium dioxide, and the weight ratio of the intermediate product to titanium dioxide is 1:(0.008~0.012); preferably, the D50 of titanium dioxide is 1nm~100nm.

[0015] Furthermore, the mixing process is ball milling, with a milling speed of 200 r / min to 800 r / min and a time of 0.5 h to 5 h; and / or, the second calcination is held at a temperature of 200 ℃ to 700 ℃ for a time of 2 h to 8 h.

[0016] A third aspect of the present invention provides a positive electrode sheet comprising an active material layer, wherein the active material layer comprises the aforementioned composite positive electrode material; or, the active material layer comprises a composite positive electrode material prepared by the aforementioned method for preparing the composite positive electrode material.

[0017] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned positive electrode.

[0018] By applying the technical solution of this invention, the original technical problems of lithium-rich manganese materials, such as severe voltage decay, transition metal dissolution, and lithium-nickel mixing, are addressed. Based on co-doping combined with metal oxide surface coating technology and by constructing a porous structure, the cycle stability of lithium-rich manganese cathode materials is significantly improved, transition metal dissolution and voltage decay are suppressed, thereby achieving the technical effect of improving battery energy density and enhancing its safety and reliability. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 The results of scanning electron microscopy (SEM) characterization of the composite cathode material obtained in Example 1 of this invention are shown below.

[0021] Figure 2 The above are the SEM characterization results of the composite cathode material obtained in Comparative Example 1 of this invention. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0023] As described in the background section, existing technologies suffer from the difficulty in preparing cathode materials with excellent electrochemical cycle stability. To address this problem, a first aspect of the present invention provides a composite cathode material comprising porous particles and a metal oxide layer coating the surface of the porous particles; the porous particles have the chemical formula Li. x Ni y Co z Mn n Nb m La q O2, where x is 1.1~1.3, y is 0.12~0.14, z is 0.12~0.14, n is 0.5~0.54, m is 0.005~0.015, and q is 0.001~0.008; the chemical formula of the metal oxide layer is M. a O bWhere M is a metallic element, a is 1-4, and b is 1-6. Based on co-doping combined with metal oxide surface coating technology, and by constructing a porous structure, the cycle stability of lithium-rich manganese cathode materials is significantly improved, transition metal dissolution and voltage decay are suppressed. Furthermore, thanks to the synergistic effect of doping and metal oxide coating, the porosity, electrochemical activity, and structural stability of the resulting composite cathode material are significantly optimized, making it a preferred cathode material for high-performance batteries.

[0024] In the chemical formula of the porous particles mentioned above, x can be 1.1, 1.2, 1.3, or any two values ​​within a range; y can be 0.12, 0.13, 0.14, or any two values ​​within a range; z can be 0.12, 0.13, 0.14, or any two values ​​within a range; n can be 0.5, 0.51, 0.52, 0.525, 0.53, 0.54, or any two values ​​within a range; m can be 0.005, 0.008, 0.010, 0.015, or any two values ​​within a range; and q can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, or any two values ​​within a range. In the chemical formula of the metal oxide layer, a can be 1, 2, 3, 4, or any range of two values, and b can be 1, 2, 3, 4, 5, 6, or any range of two values.

[0025] To further optimize the electrochemical performance and mechanical stability of the obtained composite cathode material, in several preferred embodiments, the porosity of the porous particles is preferably 35%~45% (specifically 36.58%, 37.14%, 37.49%, 38.47%, 39.26%, 40.55%, 41.23%, 42.69%, 43.26%, 44.37%); and / or, the D50 of the porous particles is 3μm~10μm (more preferably 3μm~7μm, specifically 3.88μm, 4.02μm, 4.52μm, 4.98μm, 5.34μm, 6.19μm, 6.87μm, 7μm); and / or, the thickness of the metal oxide layer is 0.1nm~8nm (more preferably 1nm~5nm, specifically 1nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 5nm).

[0026] A second aspect of the present invention provides a method for preparing a composite cathode material, comprising: step S1, mixing a lithium source, a dopant source, a lithium-rich manganese precursor, and a pore-forming agent, followed by a first calcination to obtain an intermediate product; step S2, sequentially mixing the intermediate product and a metal oxide, followed by a second calcination to obtain the composite cathode material; the chemical formula of the metal oxide is Ma O b , where M is a metallic element, a is 1~4, and b is 1~6.

[0027] This invention is based on co-doping combined with metal oxide surface coating technology, and by constructing a porous structure, it achieves a significant improvement in the cycle stability of lithium-rich manganese cathode materials, as well as the suppression of transition metal dissolution and voltage decay. In the above preparation process, a mixture of lithium source, dopant source, lithium-rich manganese precursor, and pore-forming agent is calcined at high temperature within a set temperature range. During calcination, the niobium and lanthanum sources decompose, and the ion diffusion rate accelerates at high temperatures. A solid-state reaction occurs, in which Nb... 5+ Selective substitution of Mn and La sites in lithium-rich manganese bulk phase 3+ Segregating on the surface / grain boundaries, the pore-forming agent synergistically enhances the structural stability and interfacial compatibility of the material, thereby improving cycle stability and forming co-doped lithium-rich manganese materials. During this process, the pore-forming agent undergoes thermal decomposition, generating gas. These gases create an "erosion" effect within and between the material particles, promoting pore formation and increasing the material's porosity. The presence of pores not only increases the diffusion rate of lithium ions but also improves the material's rate performance and cycle stability. This is because pores shorten the lithium-ion transport path, promote electrolyte penetration, and provide more insertion and extraction sites for lithium ions during charging, reducing resistance to lithium-ion transport.

[0028] Subsequently, in the second stage, the intermediate product (i.e., the co-doped porous lithium-rich manganese material) is mixed with metal oxide and subjected to a second calcination. During this process, the metal oxide reacts with the O on the surface of the lithium-rich manganese cathode material. 2- The formation of Ti-OM (M stands for metal) bonds enhances the MO bond energy, further stabilizing the material structure. The metal oxide coating inhibits transition metal dissolution, reduces lattice distortion, and effectively suppresses voltage decay. Simultaneously, the inert nature of the metal oxide reduces its reactivity with the electrolyte, minimizing electrolyte decomposition and thus improving the overall safety and lifespan of the battery.

[0029] In summary, the synergistic effect of co-doping and metal oxide coating has solved several key problems of lithium-rich manganese materials. It has not only significantly reduced voltage decay and reduced transition metal dissolution during cycling, but also improved the rate performance and cycle stability of the material. As a result, the modified composite cathode material has reached a new level in terms of the balance between electrochemical performance and structural stability.

[0030] In step S1, the preferred doping element sources include niobium and lanthanum sources, because the ionic radius of Nb is greater than that of Mn. 4+The ionic radius of Li is greater than that of Mn-O, and the bond energy of Nb-O is higher than that of Mn-O. This enhanced bond energy helps to more effectively suppress the formation of oxygen vacancies and reduce lattice distortion. The addition of Nb can also expand the Li-O bond radius. + The diffusion channels effectively suppress lattice oxygen evolution and voltage decay, thereby further improving the structural stability and cycling performance of the material. La 3+ The ionic radius is larger than that of Li + Large lanthanum doping preferentially forms a stable La-O protective layer on the material surface, effectively suppressing oxygen evolution on the surface of lithium-rich manganese materials under high voltage (>4.5V), reducing electrolyte oxidation and decomposition, and more effectively preventing internal short circuits. Simultaneously, La doping promotes uniform particle growth during calcination, reducing agglomeration and significantly enhancing the ion transport efficiency of the resulting composite cathode material. Furthermore, to further optimize the material structure and suppress poor performance due to insufficient doping, while also reducing non-electrochemical activity inhibition due to excessive doping, it is preferable that, with a molar amount of lithium-rich manganese precursor of 1, the molar amount of niobium source added is 0.005~0.015 (more preferably 0.01±0.002), and the molar amount of lanthanum source added is 0.001~0.008 (more preferably 0.005±0.0002). By optimizing the types and amounts of the aforementioned doped metals, the electronic structure and thermodynamic stability of the resulting composite cathode material can be further improved. It can also better cooperate with the subsequent metal oxide coating layer, thereby significantly improving the overall electrochemical performance and cycle stability of the composite cathode material.

[0031] Furthermore, in the above process, insufficient addition of pore-forming agent may result in inadequate porosity, failing to effectively improve the Li + Diffusion can occur, but excessive addition of pore-forming agents can easily cause material structure collapse, particle breakage, and poor cycle stability. Therefore, based on this, the preferred molar ratio of lithium source, lithium-rich manganese precursor, and pore-forming agent is (1~1.6):1:(0.05~0.15), more preferably (1~1.6):1:0.1, so as to improve lithium-ion intercalation efficiency while promoting the formation of pores with more suitable quantity and morphology, thereby comprehensively improving the lithium-ion transport capacity and structural stability of the final composite cathode material.

[0032] Furthermore, in the first calcination process of step S1, in order to promote the smooth reorganization of the internal structure of the material and maximize the effectiveness of the pore-forming agent, reduce the material structure damage caused by excessive high temperature, and better suppress the uneven distribution of doped elements caused by low temperature calcination, it is preferable to include the following steps in sequence: holding at 300℃~600℃ for 2h~6h, then raising the temperature to 600℃~900℃ at a heating rate of 3℃ / min~5℃ / min, and holding at that temperature for 10h~24h.

[0033] In the first calcination process described above, the initial holding temperature can be 300℃, 400℃, 450℃, 500℃, 550℃, 600℃, or any range formed by any two of the above values. The initial holding temperature can be 600℃, 700℃, 750℃, 800℃, 850℃, 900℃, or any range formed by any two of the above values.

[0034] In practical applications, the lithium source can be selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; the niobium source can be selected from one or more of niobium oxides (specifically niobium pentoxide, niobium dioxide, and niobium monoxide), niobium chlorides (specifically niobium pentachloride and niobium tetrachloride), niobium fluorides (specifically niobium pentafluoride and niobium tetrafluoride), and niobium oxalates (specifically niobium oxalate); the lanthanum source can be selected from one or more of lanthanum oxides (specifically lanthanum trioxide), lanthanum fluorides (specifically lanthanum trifluoride), lanthanum acetates (specifically lanthanum acetate), and lanthanum carbonates (specifically lanthanum carbonate); the lithium-rich manganese precursor is lithium-rich manganese hydroxide, and the chemical formula of the lithium-rich manganese hydroxide is Ni 0.13 Co 0.13 Mn 0.54-x (OH)2, where x = 0.006~0.023, specifically 0.006, 0.008, 0.010, 0.012, 0.014, 0.015, 0.018, 0.019, 0.022, 0.023, and any two of the above values ​​forming a range.

[0035] Furthermore, the pore-forming agent can be selected from one or more of urea, ammonium bicarbonate, SP, and starch. Among them, ammonium bicarbonate is used as a pore-forming agent based on its decomposition characteristics, thereby better protecting the composition and structure of the material while promoting pore formation, ultimately resulting in a composite cathode material with higher electrochemical activity and cycle stability.

[0036] In several preferred embodiments, the chemical formula of the above intermediate product is Li. x Ni y Co z Mn n Nb m La q O2, where x is 1.1~1.3, y is 0.12~0.14, z is 0.12~0.14, n is 0.5~0.54, m is 0.005~0.015, and q is 0.001~0.008. Based on the above chemical formula, a slight excess of Li can provide additional lithium ions, which is beneficial to improving the specific capacity of the material, and also better reduces the excess Li. +The potential for lithium-nickel mixing maintains the material's structural stability and electrochemical performance. The balanced ratio of nickel to cobalt and manganese further promotes a better balance between electrochemical performance, structural stability, and safety. In particular, appropriate doping amounts of niobium and lanthanum are crucial; the incorporation of niobium ions enhances the MO bond energy in the material, suppresses oxygen vacancy formation, and expands the Li bond space. + The diffusion channels of ions effectively reduce voltage decay and lattice oxygen evolution. Due to their larger ionic radius, lanthanum ions preferentially form a stable La-O protective layer on the material surface, inhibiting surface oxygen evolution and electrolyte oxidative decomposition, thus improving the material's thermal and electrochemical stability. Based on this, subsequent coating with metal oxides can create a synergistic effect, more effectively addressing the voltage decay, transition metal dissolution, and lithium-nickel mixing problems inherent in lithium-rich manganese materials, thereby improving the structural stability and electrochemical activity of the resulting composite cathode material.

[0037] To further optimize the properties and thickness of the formed metal oxide coating, thereby providing more effective protection on the surface of the doped porous core that does not hinder ion transport, in M a O b In this chemical formula, M is preferably selected from one or more of Mg, Zn, Ti, Zr, Co, Sr, Ce, Y, and Al, a is 1-3, b is 1-4; and / or, the weight ratio of the intermediate product to the metal oxide is 1:(0.0005-0.05). Specifically, the metal oxide used in this invention can be selected from one or more of magnesium oxide, zinc oxide, titanium dioxide, zirconium oxide, cobalt tetroxide, strontium oxide, cerium oxide, yttrium oxide, and aluminum oxide. The weight ratio of the intermediate product to the metal oxide can specifically be 1:0.0005, 1:0.001, 1:0.005, 1:0.01, 1:0.03, or 1:0.05.

[0038] In several typical embodiments, titanium dioxide is preferred as the metal oxide, and the weight ratio of the intermediate product to titanium dioxide is 1:(0.008~0.012), specifically 1:0.008, 1:0.01, or 1:0.012. Based on this mass ratio, TiO2 can form a more uniform thin coating layer. Compared with other metal oxides, it does not lead to a decrease in ion transport efficiency and can more effectively protect the material surface, thereby more significantly inhibiting the dissolution of transition metals, reducing side reactions on the material surface, and enhancing its overall structural stability and cycle life. In order to promote more sufficient contact with the intermediate product, i.e., the doped porous lithium-rich manganese-based core, to form a tighter Ti-O bond, promote a more uniform distribution of electrons, and thus more significantly improve the conductivity and cycle stability of the resulting composite cathode material, the D50 of titanium dioxide is further preferred to be 1nm~100nm, preferably 50±5nm.

[0039] To further improve the uniformity and stability of the formed metal oxide coating layer, thereby more effectively improving the cycle performance and electrochemical stability of the obtained composite cathode material, in step S4, preferably: the mixing treatment is ball milling, and the ball milling speed is 200 r / min to 800 r / min (specifically, it can be 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800, and any two of the above values), and the time is 0.5 h to 5 h; and / or, preferably, the second calcination holding temperature is 200℃ to 700℃ (specifically, it can be 200℃, 300℃, 40℃, 500℃, 600℃, 700℃, and any two of the above values), and the holding time is 2 h to 8 h.

[0040] In several more typical embodiments, preferably: the ball milling speed is 200 r / min to 250 r / min, and the time is 2 ± 0.5 h; and / or, the holding temperature of the second calcination is 500 ± 50 °C, and the holding time is 3 ± 0.5 h. In the above preferred embodiments, the preferred ball milling conditions can refine the particles, uniformly disperse the coating material, and improve the reactivity, promote the exposure of active sites on the surface of the intermediate product, enhance the more thorough and uniform mixing and bonding of the metal oxide with it, thereby forming a more uniform coating layer in the second calcination stage, and significantly improving the structural stability and electrochemical performance of the material. The preferred second calcination conditions can promote the O2O2 reaction between the metal oxide and the surface of the lithium-rich manganese material. 2- The formation of stable MO bonds further enhances the structural and electrochemical stability of the resulting composite material, ultimately reducing lattice distortion and transition metal dissolution more effectively during application and suppressing voltage decay.

[0041] A third aspect of the present invention provides a positive electrode sheet comprising an active material layer, wherein the active material layer comprises the aforementioned composite positive electrode material; or, the active material layer comprises a composite positive electrode material prepared by the aforementioned method for preparing the composite positive electrode material. By integrating the aforementioned high-performance composite positive electrode material into the electrode sheet, the overall performance of the resulting battery can be significantly improved, including cycle stability, rate performance, and safety.

[0042] A fourth aspect of the present invention provides a lithium-ion battery comprising the aforementioned positive electrode sheet. Due to the optimized structure and composition of the composite positive electrode material in the positive electrode sheet, the resulting lithium-ion battery exhibits longer cycle life, better rate performance, and higher safety.

[0043] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0044] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0045] Example 1

[0046] A method for preparing a composite cathode material:

[0047] (1) The lithium source LiOH, the niobium source niobium pentoxide, the lanthanum source lanthanum trioxide, and the lithium-rich manganese hydroxide precursor (whose chemical formula is Ni) are used. 0.13 Co 0.13 Mn 0.54-x (OH)₂ (x=0.006~0.023) and pore-forming agent sodium bicarbonate were mixed evenly in a molar ratio of 1.2:0.01:0.005:1:0.1. The mixture was then heated to 500℃ for 5 hours in a high-temperature tube furnace or muffle furnace, followed by a heating rate of 3℃ / min to 850℃ and a holding time of 12 hours. After pulverization and grinding, the mixture was passed through a 300-mesh sieve to obtain the intermediate product, namely the niobium- and lanthanum co-doped porous lithium-rich manganese cathode material LMR, with the chemical formula Li. 1.2 Ni 0.13 Co 0.13 Mn 0.525 Nb 0.01 La 0.005 O2.

[0048] (2) The intermediate product obtained above was mixed with TiO2 (with a D50 of 50 nm) at a weight ratio of 1:0.01, and then placed in a ball mill jar and ball-milled for 2 h at a speed of 200 r / min using a planetary ball mill. The ball-milled mixture was placed in a ceramic boat and calcined in a muffle furnace at 500 °C for 3 h to obtain a composite cathode material. The structure of the obtained composite cathode material includes porous particles with a porosity of 40.55% and a D50 of 4.52 μm, and a metal oxide layer with a thickness of 2 nm coated on them.

[0049] The SEM characterization results of the obtained composite cathode material are shown in the figure. Figure 1 .

[0050] Example 2

[0051] A method for preparing a composite cathode material:

[0052] The only difference between this embodiment and Embodiment 1 is that in step (1), with the molar amount of lithium-rich manganese precursor being 1, the molar amount of niobium source is changed to 0.005, and the molar amount of lanthanum source is changed to 0.001.

[0053] Example 3

[0054] A method for preparing a composite cathode material:

[0055] The only difference between this embodiment and Embodiment 1 is that in step (1), with the molar amount of lithium-rich manganese precursor being 1, the molar amount of niobium source is changed to 0.015, and the molar amount of lanthanum source is changed to 0.008.

[0056] Example 4

[0057] A method for preparing a composite cathode material:

[0058] The only difference between this embodiment and embodiment 1 is that in step (1), the conditions for the first calcination are changed to: holding at 200°C for 8 hours, and then raising the temperature to 950°C at a rate of 6°C / min and holding for 8 hours.

[0059] Example 5

[0060] A method for preparing a composite cathode material:

[0061] The only difference between this embodiment and embodiment 1 is that in step (1), the conditions for the first calcination are changed to: heating to 800°C at a heating rate of 2°C / min and holding for 20 hours, and only one calcination is performed.

[0062] Example 6

[0063] A method for preparing a composite cathode material:

[0064] The only difference between this embodiment and embodiment 1 is that in step (2), aluminum oxide of equal weight is used instead of titanium dioxide.

[0065] Example 7

[0066] A method for preparing a composite cathode material:

[0067] The only difference between this embodiment and embodiment 1 is that in step (2), the weight ratio of the intermediate product to titanium dioxide is changed to 1:0.0005.

[0068] Example 8

[0069] A method for preparing a composite cathode material:

[0070] The only difference between this embodiment and embodiment 1 is that in step (2), the weight ratio of the intermediate product to titanium dioxide is changed to 1:0.05.

[0071] Example 9

[0072] A method for preparing a composite cathode material:

[0073] The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed of the ball mill is changed to 200 r / min and the time is changed to 5 h.

[0074] Example 10

[0075] A method for preparing a composite cathode material:

[0076] The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed of the ball mill is changed to 800 r / min and the time is changed to 0.5 h.

[0077] Example 11

[0078] A method for preparing a composite cathode material:

[0079] The only difference between this embodiment and embodiment 1 is that in step (2), the holding temperature of the second calcination is changed to 200°C and the holding time is changed to 8h.

[0080] Example 12

[0081] A method for preparing a composite cathode material:

[0082] The only difference between this embodiment and embodiment 1 is that in step (2), the holding temperature of the second calcination is changed to 700°C and the holding time is changed to 2h.

[0083] Comparative Example 1

[0084] A method for preparing a cathode material:

[0085] The only difference between this comparative example and Example 1 is that: no niobium source, lanthanum source and pore-forming agent were added in step (1), and step (2) was not performed. The lithium-rich manganese-based product obtained in step (1) was directly used as the cathode material sample.

[0086] The SEM characterization results of the obtained lithium-rich manganese-based products are shown in the figure. Figure 2 .

[0087] Comparative Example 2

[0088] A method for preparing a cathode material:

[0089] The only difference between this comparative example and Example 1 is that no pore-forming agent was added in step (1), and step (2) was not performed. The lithium-rich manganese-based product obtained in step (1) was directly used as the positive electrode material sample.

[0090] Comparative Example 3

[0091] A method for preparing a cathode material:

[0092] The only difference between this comparative example and Example 1 is that: no niobium source and lanthanum source were added in step (1), and step (2) was not performed. The lithium-rich manganese-based product obtained in step (1) was directly used as the cathode material sample.

[0093] Material structural parameter testing:

[0094] Porosity of porous particles: The porosity of the lithium-rich manganese material is calculated using the formula: Porosity = 100% - (compacted density / true density) × 100%.

[0095] D50 of porous particles: obtained by laser particle size analyzer.

[0096] Thickness of the metal oxide layer: obtained from transmission electron microscopy (TEM) measurements.

[0097] The test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] Lithium-ion battery sample assembly and performance testing:

[0101] 1. Method for manufacturing the positive electrode sheet: A positive electrode slurry is obtained by mixing 90-96.5 wt.% (95 wt.% in this test method), 2-4 wt.% (3 wt.% in this test method), and 1-3 wt.% (2 wt.% in this test method) of the positive active material with a solvent and stirring until homogeneous. This slurry is then uniformly coated onto the positive current collector aluminum foil, and the desired positive electrode sheet is obtained through drying, rolling, and slitting. The electronic conductive agent can be selected from conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotubes, etc. (SP is used in this test method), the binder is polyvinylidene fluoride (PVDF) and its derivatives (PVDF is used in this test method), and the solvent is N-methylpyrrolidone.

[0102] 2. Preparation of the negative electrode sheet: A negative electrode slurry is obtained by mixing 90-97 wt.% (95 wt.% in this test method) of the negative electrode active material, 0.5-3 wt.% (2 wt.% in this test method) of the electronic conductive agent, and 1.5-4 wt.% (3 wt.% in this test method) of the binder with a solvent. This slurry is then uniformly coated onto the negative electrode current collector copper foil, and the desired negative electrode sheet is obtained through drying and rolling. The negative electrode active material can be selected from graphite, silicon oxide, silicon carbon, and other negative electrode materials and their derivatives (graphite is used in this test method). The electronic conductive agent can be selected from conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, etc. (SP is used in this test method). The binder can be selected from polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber (SBR), or sodium carboxymethyl cellulose (CMC), etc. (1.5 wt.% CMC and 1.5 wt.% SBR are used in this test method).

[0103] 3. Assembly of Single-Cell Soft-Pack Batteries: Assemble single-cell soft-pack batteries in an environment with a dew point < -40℃, stacking them into single-cell soft-pack cells in the order of negative electrode-positive electrode-negative electrode; inject electrolyte, with the positive electrode surface density being 135g / m³. 2 The negative electrode surface density is 120 g / m³. 2 .

[0104] 4. Electrochemical performance testing method of the battery: In a constant temperature test room at 25℃, each lithium-ion battery sample was placed for 12 hours, then charged to 4.7V at a constant current and constant voltage rate of 0.1C, discharged to 2.0V at a constant current rate, and cycled twice for activation. Then, it was cycled at 2.0-4.5V, and the average voltage decay after 100 cycles was calculated. At the same time, the capacity retention rate after 100 cycles at 1C was calculated, and the amount of manganese dissolved after 100 cycles was obtained.

[0105] The positive electrode material samples obtained from each embodiment and comparative example were used as positive electrode active materials. Positive electrode sheets were prepared according to the above method, and then assembled into lithium-ion battery samples. The above performance tests were performed, and the results are shown in Table 2.

[0106] Table 2

[0107]

[0108] As can be seen from the above description, the embodiments of the present invention have achieved the preparation of a high-performance cathode material, and the resulting composite cathode material possesses superior porosity, electrochemical activity, and structural stability. After being prepared as an electrode sheet and assembled into a battery, the corresponding battery sample exhibits lower voltage decay, less transition metal spillage, and superior cycle life.

[0109] Specifically, in each embodiment:

[0110] Comparing Examples 2 and 3 with Example 1, it can be seen that by optimizing the amount of niobium source and lanthanum source added, the electronic structure and thermodynamic stability of the obtained composite cathode material can be further optimized, and it can also better cooperate with the subsequent metal oxide coating layer, thereby significantly improving the overall electrochemical performance and cycle stability of the composite cathode material.

[0111] Comparing Examples 4 and 5 with Example 1, it can be seen that by optimizing the condition parameters of the first calcination treatment, the internal structure of the material can be reorganized smoothly and the pore-forming agent can play a greater role, reducing the material structure damage caused by excessive high temperature, and better suppressing the uneven distribution of doped elements caused by low temperature calcination, ultimately obtaining a composite cathode material with better performance.

[0112] Comparing Example 6 with Example 1, it can be seen that by preferably using titanium dioxide as the metal oxide, the dissolution of transition metals can be more significantly suppressed, side reactions on the material surface can be reduced, and the overall structural stability and cycle life can be enhanced.

[0113] Comparing Examples 7 and 8 with Example 1, it can be seen that in step S2, by optimizing the weight ratio of the intermediate product to the metal oxide, the properties and thickness of the formed metal oxide coating layer can be further optimized, thereby providing more effective protection on the surface of the doped porous core that does not hinder ion transport. In particular, for titanium dioxide, the preferred amount promotes the formation of a more uniform thin coating layer, which neither leads to a decrease in ion transport efficiency nor hinders the protection of the material surface.

[0114] Comparing Examples 9 and 10 with Example 1, it can be seen that in step S2, by optimizing the conditions and parameters of the ball milling process, the uniformity and stability of the formed metal oxide coating layer can be further improved, thereby more effectively enhancing the cycle performance and electrochemical stability of the obtained composite cathode material.

[0115] Comparing Examples 11 and 12 with Example 1, it can be seen that by optimizing the conditions and parameters of the second calcination treatment, the oxidation of metal oxides and the surface of lithium-rich manganese materials is promoted. 2- The formation of stable MO bonds further enhances the structural and electrochemical stability of the resulting composite material, ultimately reducing lattice distortion and transition metal dissolution more effectively during application and suppressing voltage decay.

[0116] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cathode material, characterized in that, It includes porous particles and a metal oxide layer covering the surface of the porous particles; The chemical formula of the porous particles is Li x Ni y Co z Mn n Nb m La q O2, where x is 1.1~1.3, y is 0.12~0.14, z is 0.12~0.14, n is 0.5~0.54, m is 0.005~0.015, and q is 0.001~0.008; The chemical formula of the metal oxide layer is M a O b , where M is a metallic element, a is 1~4, and b is 1~6.

2. The composite cathode material according to claim 1, characterized in that, The porosity of the porous particles is 35%~45%; and / or, The porous particles have a D50 of 3 μm to 10 μm; and / or, The thickness of the metal oxide layer is 0.1 nm to 8 nm.

3. A method for preparing a composite cathode material, characterized in that, include: Step S1: The lithium source, doping element source, lithium-rich manganese precursor and pore-forming agent are mixed and then calcined for the first time to obtain the intermediate product. In step S2, the intermediate product and the metal oxide are sequentially mixed and calcined to obtain the composite cathode material. The chemical formula of the metal oxide is M a O b , where M is a metallic element, a is 1~4, and b is 1~6.

4. The method for preparing the composite cathode material according to claim 3, characterized in that, In step S1 The doping element source includes a niobium source and a lanthanum source, and with the molar amount of the lithium-rich manganese precursor being 1, the molar amount of the niobium source is 0.005~0.015; the molar amount of the lanthanum source is 0.001~0.

008. The molar ratio of the lithium source, the lithium-rich manganese precursor, and the pore-forming agent is (1~1.6):1:(0.05~0.15).

5. The method for preparing the composite cathode material according to claim 3 or 4, characterized in that, In step S1, the first calcination includes the following steps performed sequentially: holding at 300℃~600℃ for 2h~6h, then heating to 600℃~900℃ at a heating rate of 3℃ / min~5℃ / min, and holding at that temperature for 10h~24h.

6. The method for preparing the composite cathode material according to claim 4, characterized in that, In step S1 The lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; and / or, The niobium source is selected from one or more of niobium oxides, niobium chlorides, niobium fluorides, and niobium oxalates; and / or, The lanthanum source is selected from one or more of lanthanum oxides, lanthanum fluorides, lanthanum acetates, and lanthanum carbonates; and / or, The pore-forming agent is selected from one or more of urea, ammonium bicarbonate, SP, and starch, preferably ammonium bicarbonate; and / or, The lithium-rich manganese precursor is a lithium-rich manganese hydroxide, and the chemical formula of the lithium-rich manganese hydroxide is Ni. 0.13 Co 0.13 Mn 0.54-x (OH)2, where x = 0.006~0.

023.

7. The method for preparing the composite cathode material according to any one of claims 3 to 6, characterized in that, The M a O b In this context, M is selected from one or more of Mg, Zn, Ti, Zr, Co, Sr, Ce, Y, and Al; a is 1 to 3; and b is 1 to 4; and / or, The mass ratio of the intermediate product to the metal oxide is 1:(0.0005~0.05). Preferably, the metal oxide is selected from one or more of magnesium oxide, zinc oxide, titanium dioxide, zirconium oxide, cobalt tetroxide, strontium oxide, cerium oxide, yttrium oxide, and aluminum oxide.

8. The method for preparing the composite cathode material according to claim 7, characterized in that, The metal oxide is titanium dioxide, and the mass ratio of the intermediate product to the titanium dioxide is 1:(0.008~0.012). Preferably, the D50 of the titanium dioxide is 1nm~100nm.

9. The method for preparing the composite cathode material according to any one of claims 3 to 8, characterized in that, In step S2 The mixing process is ball milling, with a milling speed of 200 r / min to 800 r / min and a time of 0.5 h to 5 h; and / or, The second calcination is held at a temperature of 200℃ to 700℃ for 2 hours to 8 hours.

10. A positive electrode sheet, comprising an active material layer, characterized in that, The active material layer includes the composite cathode material as described in claim 1 or 2; or, the active material layer includes the composite cathode material prepared by the method for preparing the composite cathode material as described in any one of claims 3 to 9.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 10.

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