Positive electrode material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention provides a positive electrode material and a preparation method thereof, an electrochemical device and electronic equipment, and particularly relates to the technical field of batteries. The positive electrode material comprises an inner core and a coating layer, the inner core comprises a first positive electrode active material and a second positive electrode active material adsorbed on the surface of the first positive electrode active material, the chemical formula of the first positive electrode active material is LiNixMnyAeCozO2, in the formula, 0.8 < = x < = 0.94, 0.02 < = y < = 0.2, 0.02 < = z < = 0.1, 0 < = e < = 0.1, and x + y + z + e = 1, A is an inert transition metal element with the same valence state as Mn, and the coating layer is a metal element with the same valence state as Mn. The chemical formula of the second positive electrode active material is LiMnaFebMcPO4, in the formula, a is more than or equal to 0.5 and less than or equal to 0.8, b is more than or equal to 0.1 and less than or equal to 0.4, c is more than or equal to 0 and less than or equal to 0.2, a + b + c is equal to 1, and M is a + 2 valence inert transition metal element; the median particle size of the first positive electrode active material is 3-8 microns; the median diameter of the second positive electrode active material is 0.1-0.7 mu m, and the mass of the first positive electrode active material accounts for 5-35% of the mass of the inner core; the surface of the inner core is coated with the coating layer, and the material of the coating layer comprises solid electrolyte. The discharge gram capacity, the voltage platform and the cycle performance of the battery can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a cathode material and its preparation method, an electrochemical device, and an electronic device. Background Technology

[0002] Lithium-ion batteries, with their advantages of high specific energy, high voltage, long cycle life, and being green and pollution-free, have been widely used in new energy vehicles, energy storage systems, and other fields. With technological advancements, market demands for the range, safety performance, and cost control of lithium-ion batteries continue to rise. As a key component determining the core performance of batteries, the optimization and performance balancing of cathode materials have become a core direction for industry research and development.

[0003] Lithium iron phosphate (LiFePO4, LFP), widely used in energy storage, possesses excellent thermal safety and long-cycle stability. However, its energy density is nearing its theoretical limit, making it insufficient to meet the higher capacity density requirements of energy storage systems. Therefore, a more balanced alternative cathode material is urgently needed. Lithium manganese iron phosphate (LiMn) is another option. x Fe (1-x) O4 (LMFP) material combines the safety characteristics of LFP with the advantages of low cost, and by introducing Mn element to form 4.1V Mn 2+ / Mn 3+ The electrochemical reaction platform effectively improves the voltage output level, making it a highly promising alternative material for LFP. However, the introduction of Mn also brings significant performance defects: on the one hand, the presence of Mn leads to a significant decrease in the lithium-ion conductivity of the material, exacerbating polarization during charge and discharge, resulting in insufficient specific capacity and deteriorated rate performance; on the other hand, Mn... 2+ The battery is prone to dissolution due to the J.T. effect, which damages the solid electrolyte interphase (SEI) membrane at the electrode-electrolyte interface, leading to a decline in battery cycle performance and hindering its large-scale application. Summary of the Invention

[0004] This invention provides a cathode material and its preparation method, an electrochemical device, and an electronic device to improve the poor specific capacity, rate performance, and cycle performance of lithium manganese iron phosphate as a cathode material.

[0005] To achieve the above and other related objectives, the present invention provides a positive electrode material comprising: a core and a coating layer; the core comprising a first positive electrode active material and a second positive electrode active material, the second positive electrode active material being adsorbed on the surface of the first positive electrode active material; the coating layer coating the surface of the core, the material of the coating layer comprising a solid electrolyte; wherein the chemical formula of the first positive electrode active material is LiNi. x Mn y Ae Co z O2, where 0.8≤x≤0.94, 0.02≤y≤0.2, 0.02≤z≤0.1, 0≤e≤0.1, x+y+z+e=1, A is an inert transition metal element with the same valence as Mn, and the chemical formula of the second positive electrode active material is: LiMn a Fe b M c PO4, where 0.5≤a≤0.8, 0.1≤b≤0.4, 0≤c≤0.2, a+b+c=1, and M is an inert transition metal element with a +2 valence; the median particle size of the first positive electrode active material is 3~8μm; the median particle size of the second positive electrode active material is 0.1~0.7μm, and the mass of the first positive electrode active material accounts for 5%~35% of the core mass.

[0006] In one embodiment of the present invention, the mass of the coating layer accounts for 0.5% to 5% of the total mass of the cathode material.

[0007] In one embodiment of the present invention, the particle size of the first positive electrode active material is D, the thickness of the coating layer formed by the adsorption of the second positive electrode active material on the surface of the first positive electrode active material is T, and the core satisfies: 0.1≤D / T≤20.

[0008] In one embodiment of the present invention, 0.36≤D / T≤1.6.

[0009] In one embodiment of the present invention, the first positive electrode active material is a single crystal particle, or a mixture of single crystal particles and polycrystalline particles; if the first positive electrode active material is a mixture of single crystal particles and polycrystalline particles, the mass percentage of polycrystalline particles in the mixture of single crystal particles and polycrystalline particles is less than or equal to 50%.

[0010] In one embodiment of the present invention, the solid electrolyte meets the following requirements: particle size less than or equal to 100 nm, oxidation potential greater than or equal to 4.25 V, and conductivity greater than or equal to 0.1 mS / cm.

[0011] In one embodiment of the present invention, the solid electrolyte includes one or more of oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes.

[0012] The present invention also provides a method for preparing a cathode material, the method comprising the following steps:

[0013] The first positive electrode active material and the second positive electrode active material are added to a solvent, mixed thoroughly, and then spray-dried to obtain a composite powder.

[0014] The solid electrolyte and the composite powder were ball-milled, sieved, and dried to obtain the positive electrode material.

[0015] The present invention also provides an electrochemical device comprising the positive electrode material described in any of the above claims, or the positive electrode material prepared by the above preparation method.

[0016] The present invention also provides an electronic device comprising the above-described electrochemical device.

[0017] The beneficial effects of this invention are as follows: The cathode material proposed in this invention uses a core of first cathode active material (high-nickel NCM) and second cathode active material (LMFP) particles, and achieves performance optimization by precisely controlling the mixing ratio and particle size distribution of the two: The larger-diameter NCM particles serve as a framework support, while the smaller-diameter LMFP particles are adsorbed on the surface of the larger-diameter NCM particles and fill their gaps, which can effectively improve the electrode compaction density; at the same time, the smaller LMFP particles have fewer crystal defects and stronger stability, which can reduce the negative impact that may be caused by the Mn element itself, laying the foundation for the full utilization of the specific capacity. The hybrid core is coated with a solid electrolyte layer, which can significantly improve the ion conduction efficiency of the positive electrode active material, accelerate the migration of lithium ions to the surface of the core active material, promote the efficient insertion and extraction of lithium ions, and thus fully release the specific capacity potential of the active material. In addition, the coating layer can also physically isolate the positive electrode active material from direct contact with the electrolyte, effectively suppress the dissolution of Mn ions, and ensure the long-term stable performance of LMFP capacity. On the other hand, it can reduce the structural deterioration of NCM due to reaction with the electrolyte, and significantly extend the battery cycle life. At the same time, the solid electrolyte itself has excellent high voltage resistance and high thermal stability, which can further improve the safety performance of the battery under high voltage conditions and high temperature environments. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] In the attached diagram:

[0020] Figure 1 This is a schematic diagram of the structure of the positive electrode material provided in one embodiment of the present invention;

[0021] Figure 2 This is a flowchart of a method for preparing a cathode material according to an embodiment of the present invention.

[0022] The attached figures are labeled as follows:

[0023] 100. Positive electrode material; 110. Core; 111. First positive electrode active material; 112. Second positive electrode active material; 1121. Amorphous carbon; 120. Coating layer; 121. Solid electrolyte. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0025] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] The terms or phrases used in this article have the following meanings:

[0028] In this article, the terms "multiple," "various," and "multiple times" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0029] In this document, terms such as “preferred,” “ideal,” “further,” “even more,” and “particularly” are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0030] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0031] In this paper, the median particle size (Dv50) refers to the particle size at which the cumulative volume reaches 50% on the particle size distribution cumulative curve. Dv50 can be measured by, for example, laser diffraction.

[0032] The applicant discovered that the performance of lithium manganese iron phosphate (LMFP) materials is strongly correlated with their Mn content, but the introduction of Mn ions significantly reduces the electronic conductivity and lithium-ion conductivity of the material—electronic transport is hindered, and Li… + The decrease in migration rate deteriorates its rate performance and limits its specific capacity. Furthermore, the Mn element in LMFP introduces a J.T. distortion effect: this structural distortion disrupts the stability of the olivine lattice, leading to Mn... 2+ Dissolution, dissolved Mn 2+ It will migrate to the surface of the negative electrode and deposit, damaging the integrity of the solid electrolyte interface (SEI) film and ultimately leading to a deterioration in battery cycle performance.

[0033] While high-nickel NCM materials offer high capacity advantages, they also present significant interface and safety risks: Firstly, the densely packed active sites on the surface of high-nickel NCM make it prone to interfacial side reactions with the electrolyte, directly shortening battery cycle life; secondly, while high-nickel NCM can achieve high specific capacity in the 4.2V voltage range, theoretically requiring only a small amount of compounding to improve the overall energy of LMFPs, under charged conditions, the large amount of highly oxidized Ni on its surface... 4+ A non-electrochemically active Ni-O rock salt phase surface layer will form at the electrode / electrolyte interface. This layer has weak ion conductivity, which will significantly increase the kinetic barrier for lithium-ion diffusion, leading to a surge in battery impedance and a sharp drop in electrochemical performance; thirdly, Ni in high-nickel NCM 4+ With Co 4+ It has extremely strong catalytic activity and can easily accelerate the oxidative decomposition of organic electrolytes. The generated byproducts (such as lithium carbonate and fluorides) will cover the positive and negative electrode surfaces, further deteriorating the interfacial conduction. At the same time, high-nickel materials have poor thermal stability and are prone to releasing O2 at high temperatures. The reaction of O2 with flammable electrolytes will cause violent exothermic reactions, which will greatly increase the risk of thermal runaway.

[0034] If a direct physical mixture of LMFP and high-nickel NCM is used, on the one hand, this approach requires extremely high precision in the mixing process—the two materials have significant differences in density and particle size, making it difficult to achieve uniform dispersion at the microscale using conventional mechanical mixing, which can easily lead to localized particle segregation and poor battery performance consistency; on the other hand, physical mixing cannot isolate the active material from direct contact with the liquid electrolyte, thus failing to suppress the dissolution of Mn ions in LMFP and also failing to solve the side reaction problem between the highly active surface of high-nickel NCM and the electrolyte, ultimately resulting in the overall performance of the mixed cathode failing to meet expectations.

[0035] Based on this, the present invention provides a cathode material, a method for preparing the cathode material, an electrochemical device comprising the cathode material, and an electronic device comprising the electrochemical device.

[0036] Please see Figure 1 The present invention provides a cathode material 100 comprising a core 110 and a coating layer 120, wherein the core 110 serves as the active host portion of the cathode material 100, reversibly releasing and storing Li. + This directly affects the battery's energy density, specific capacity, cycle life, and safety baseline. The coating layer 120 covers the surface of the core 110, effectively blocking the contact between the electrolyte and the positive electrode active material, and effectively preventing the occurrence of side reactions between the positive electrode active material and the electrolyte.

[0037] Specifically, the core 110 includes a first positive electrode active material 111 and a second positive electrode active material 112, with the second positive electrode active material 112 adsorbed on the surface of the first positive electrode active material 111. The first positive electrode active material 111 is a high-nickel ternary material with the chemical formula LiNi. x Mn y A e Co z O2, where 0.8≤x≤0.94, 0.02≤y≤0.2, 0.02≤z≤0.1, 0≤e≤0.1, x+y+z+e=1, and A is the doping element in the high-nickel ternary material, which can be a transition metal element with the same valence as Mn. For example, x can be 0.8, 0.85, 0.9, or 0.94, etc.; y can be 0.02, 0.1, or 0.2, etc.; z can be 0.02, 0.05, or 0.1, etc.; and e can be 0, 0.05, or 0.1, etc. When e is 0, the first positive electrode active material 111 is an undoped high-nickel ternary material. For example, the first positive electrode active material 111 can be LiNi. 0.8 Mn 0.1 Co 0.1 O2, or LiNi 0.9 Mn 0.05 Co 0.05 O2, or LiNi0.94 Mn 0.02 Co 0.04 O2, etc. When e is not 0, the first positive electrode active material 111 is a doped high-nickel ternary material. The doping element is an inert transition metal element with the same valence as Mn. Here, inert means that the metal will not participate in the valence change process during charging and discharging, but can only play a role in stabilizing the structure and improving conductivity. The inert transition metal element with the same valence as Mn can optimize the function of Mn by atomic-level substitution without destroying the original charge balance and crystal structure. It retains the basic stabilizing effect of Mn on the material, and makes up for the shortcomings of Mn (such as easy dissolution and low MO bond energy) with a more stable +4 valence element. Finally, it achieves a balance between high capacity, long cycle life and high safety of high-nickel material. For example, the doping element A can be Zr. 4+ Ti 4+ Etc., doped high-nickel ternary materials such as LiNi 0.8 Mn 0.05 Zr 0.05 Co 0.1 O2, LiNi 0.8 Mn 0.05 Ti 0.05 Co 0.1 O2, etc.

[0038] The chemical formula of the second positive electrode active material 112 is LiMn. a Fe b M c PO4, where 0.5≤a≤0.8, 0.1≤b≤0.4, 0≤c≤0.2, a+b+c=1, and M is an inert transition metal element with a +2 valence. For example, a can be 0.5, 0.6, 0.7, or 0.8, etc.; b can be 0.1, 0.2, 0.3, or 0.4, etc.; and c can be 0, 0.1, or 0.2, etc. When c is 0, the second positive electrode active material 112 is undoped lithium manganese iron phosphate. In this case, the second positive electrode active material 112 can be LiMn. 0.5 Fe 0.5 PO4, or LiMn 0.6 Fe 0.4 PO4, or LiMn 0.8 Fe 0.2 PO4, etc. When c is not 0, the second positive electrode active material 112 is a doped lithium manganese iron phosphate, and the doping element M can be Mg. 2+ Zn 2+ Ca 2+ Wait a minute. At this point, the second positive electrode active material 112 can be LiMn. 0.5 Fe 0.3 Mg 0.2 PO4, LiMn 0.6 Fe0.3 Ca 0.1 PO4, etc.

[0039] Furthermore, the median particle size (Dv50) of the first positive electrode active material 111 is 3–8 μm, and can be, for example, 3 μm, 5 μm, or 8 μm, etc.; the median particle size (Dv50) of the second positive electrode active material 112 is 0.1–0.7 μm, and can be, for example, 0.1 μm, 0.3 μm, 0.5 μm, or 0.7 μm, etc. By precisely controlling the particle size of the first positive electrode active material 111 and the second positive electrode active material 112, small particles of the second positive electrode active material 112 can be uniformly adsorbed on the surface of large particles of the first positive electrode active material 111 to form a coating layer. Optionally, the thickness difference of the coating layer at each location is less than or equal to 10%, thereby separating the high-nickel NCM active material from the electrolyte and reducing side reactions between the high-nickel NCM active material and the electrolyte. In addition, the small particles of the second positive electrode active material 112 have fewer defects in their crystal structure and are more stable, which can reduce the negative impact of Mn element.

[0040] Furthermore, the mass of the first positive electrode active material 111 accounts for 5% to 35% of the mass of the core 110, that is, the mass of the second positive electrode active material 112 accounts for 65% to 95% of the total mass of the core 110. For example, the mass of the first positive electrode active material 111 accounts for 5% of the mass of the core 110, and the second positive electrode active material 112 accounts for 95% of the mass of the core 110; or the first positive electrode active material 111 accounts for 15% of the mass of the core 110, and the second positive electrode active material 112 accounts for 85% of the mass of the core 110; or the first positive electrode active material 111 accounts for 35% of the mass of the core 110, and the second positive electrode active material 112 accounts for 65% of the mass of the core 110, and so on. Within this ratio range, the high specific capacity of the first positive electrode active material 111 can be used to enhance the specific capacity of the second positive electrode active material 112, while the stability of the second positive electrode active material 112 can be used to isolate the first positive electrode active material 111 from the electrolyte, reducing the occurrence of side reactions. At the same time, the combination of large and small particles can also effectively improve the compaction density of the electrode sheet. If the proportion of the first positive electrode active material 111 is too small and the proportion of the second positive electrode active material 112 is too large, the total specific capacity of the positive electrode material 100 will drop sharply due to the low capacity characteristics of the second positive electrode active material 112, resulting in the battery energy density failing to meet the usage requirements. If the mass proportion of the first positive electrode active material 111 is too large and the mass proportion of the second positive electrode active material 112 is too small, the second positive electrode active material 112 cannot form a continuous and complete coating on the surface of the first positive electrode active material 111, which will lead to the failure of the protective barrier and amplify the inherent defects of high nickel, thereby affecting the cycle performance and rate performance of the battery.

[0041] A coating layer 120 is applied to the surface of the core 110. The coating layer 120 includes a solid electrolyte 121. The presence of the solid electrolyte 121 improves the ionic conductivity of the positive electrode active material, allowing lithium ions to quickly reach the surface of the active material in the core 110. This facilitates lithium ion insertion and extraction, thereby improving the specific capacity of the active material. Furthermore, the solid electrolyte 121 coating of the core 110 reduces direct contact between the active material and the electrolyte. On one hand, it inhibits the dissolution of Mn ions from the second positive electrode active material 112, maintaining the stable capacity of the lithium manganese iron phosphate material. On the other hand, it protects the first positive electrode active material 111, reducing the reaction between the high-nickel NCM material and the electrolyte, thus reducing the deterioration of the high-nickel NCM material and improving cycle life. In addition, the good high-voltage resistance and thermal stability of the solid electrolyte 121 also improve the battery's safety performance.

[0042] In one embodiment, the mass of the coating layer 120 accounts for 0.5% to 5% of the total mass of the cathode material 100. For example, the mass percentage of the coating layer 120 in the cathode material 100 can be 0.5%, 1%, 3%, or 5%, etc. If the mass percentage of the coating layer 120 is insufficient, it is difficult to form a continuous and complete coating layer 120, resulting in partial exposure of the core active material to direct contact with the electrolyte, increased side reactions, discontinuous ion transport channels, high interfacial impedance, large fluctuations in rate performance, and poor electrical performance consistency. If the mass percentage of the coating layer 120 is too large, it indicates excessive coating, which lengthens the lithium ion transport path, significantly reduces migration efficiency, and leads to insufficient capacity utilization and decreased rate performance. Furthermore, the coating layer 120 itself does not possess electrochemical activity (it does not participate in the Li-ion exchange process). + (Intercalation / de-intercalation) Excessive coating layers will directly increase the overall weight of the cathode material, leading to a decrease in the proportion of active material and affecting energy density.

[0043] In one embodiment, the first positive electrode active material 111 is a single crystal particle. The single crystal particle is a complete and single crystal without grain boundary defects. It can avoid intergranular stress and microcracks during charging and discharging to the greatest extent, which significantly extends the life of the composite positive electrode material. At the same time, it greatly reduces the amount of Ni ion dissolution to reduce interfacial side reactions, increases the high-temperature decomposition temperature to build a more reliable thermal safety barrier, and can also optimize ion transport efficiency by having no grain boundary impedance, thereby reducing high-rate polarization.

[0044] In other embodiments, the first positive electrode active material 111 can also be a mixture of single-crystal particles and polycrystalline particles, wherein the mass percentage of polycrystalline particles is less than or equal to 50%, for example, 10%, 30%, etc. Introducing a small amount of lower-cost polycrystalline particles into the single-crystal particles can reduce the overall material cost without significantly sacrificing energy density; furthermore, polycrystalline particles are typically formed by the agglomeration of smaller primary particles, Li...+ The insertion / extraction path is short, allowing for more efficient capacity utilization during the initial charge and discharge phases; polycrystalline particles offer better initial capacity utilization due to their smaller primary particle size, and when combined with the long-term stability of monocrystalline particles, high initial capacity and stable cycling in the middle phase can be achieved.

[0045] In one embodiment, the surface of the second positive electrode active material 112 is coated with amorphous carbon 1121. The main body of the second positive electrode active material 112 is LMFP. The coating of amorphous carbon 1121 not only significantly improves the low electronic conductivity of LMFP and enhances its high-rate charge-discharge capability by constructing a continuous conductive network, but also acts as a physical barrier to prevent direct contact between LMFP and electrolyte, significantly inhibiting Mn dissolution to reduce side reactions and extend cycle life. Simultaneously, it can also suppress particle agglomeration, buffer lattice stress during charge-discharge, and optimize lithium-ion diffusion efficiency and crystal structure stability. The coating amount of amorphous carbon 1121 is less than or equal to 3% of the total mass of the second positive electrode active material 112 and amorphous carbon 1121.

[0046] In the core 110, the second positive electrode active material 112 is uniformly adsorbed on the surface of the first positive electrode active material 111 particles, so that LMFP forms a continuous and dense protective layer, which physically blocks the electrolyte from contacting the surface of the high-nickel material, reduces HF corrosion and interfacial side reactions, and effectively inhibits Ni 2+ Dissolution prevents damage to the negative electrode SEI film and extends cycle life. In addition, thanks to the high thermal decomposition temperature of LMFP, it can delay lattice collapse and oxygen release under high nickel and high temperature, significantly reducing the risk of thermal runaway. Moreover, its good lithium-ion conductor properties can build a continuous Li+ transport channel, which optimizes rate performance while ensuring high nickel and high specific capacity. It can also buffer the volume expansion during high nickel charge and discharge, prevent particle cracking, maintain the integrity of the positive electrode structure, and ultimately achieve a comprehensive improvement in the overall performance of the positive electrode material. The uniform adsorption of the second positive electrode active material 112 on the surface of the first positive electrode active material 111 can be characterized by the following method: First, the positive electrode material particles are observed using a scanning electron microscope (SEM) (Nova NanoSEM450) at a magnification of 10,000 to determine the distribution areas of the first positive electrode active material 111 and the second positive electrode active material 112 in the positive electrode material. Then, elemental mapping analysis of the positive electrode material is performed using an EDS spectrometer. The boundary of the second positive electrode active material 112 is determined based on the distribution of the characteristic element Ni of the first positive electrode active material 111 and the characteristic element Fe of the second positive electrode active material 112. Then, 10 points that equally divide the boundary of the first positive electrode active material 111 are selected (the outer periphery of the first positive electrode active material is divided into 10 equal parts), and the coating thickness of the second positive electrode active material 112 corresponding to the 10 points is tested. If the thickness difference between the measured maximum and minimum values ​​is ≤10%, it is considered that the second positive electrode active material 112 is uniformly adsorbed on the surface of the first positive electrode active material 111.

[0047] In one embodiment, the particle size of the first positive electrode active material 111 is D, and the thickness of the coating layer formed by the second positive electrode active material 112 adsorbed on the surface of the particles of the first positive electrode active material 111 is T. Then, D and T satisfy the relationship: 0.1≤D / T≤20. For example, D / T can be 0.1, 5, 10, 15, or 20, etc. Further, 0.36≤D / T≤1.6. For example, D / T can be 0.36, 0.5, 1.0, or 1.6, etc. In this embodiment, D refers to the size of a single particle of the first positive electrode active material 111. Since the particles of the first positive electrode active material 111 are mostly irregular in shape, the particle size D is the equivalent sphere diameter of the particles of the first positive electrode active material 111, which can be tested by cross-section polishing (CP). The specific testing process is as follows: Cross-section polishing (CP) is performed on the cathode material. Characteristic elements are identified through element mapping: Mn, Fe, and P correspond to the second cathode active material 112, and Co and Ni correspond to the first cathode active material 111, thus clearly marking the spatial distribution of the two types of materials. At least 10 typical second cathode active material 112 coating layers are randomly selected, their thickness is measured, and the average value is recorded as T; similarly, at least 10 first cathode active material 111 particles are randomly selected, their size is measured, and the average value is recorded as D.

[0048] In one embodiment, the solid electrolyte 121 of the coating layer 120 needs to meet the following conditions: particle size less than or equal to 100 nm, oxidation potential greater than or equal to 4.25 V, and conductivity greater than or equal to 0.1 mS / cm. For example, the particle size of the solid electrolyte can be 30 nm, 50 nm, 100 nm, etc. Small-particle-size solid electrolyte 121 has a larger specific surface area, which is more conducive to forming a uniform and dense coating layer 120 on the surface of the core 110. If the particle size of the solid electrolyte 121 is too large, the coating area of ​​the solid electrolyte 121 per unit mass is significantly limited, making it difficult to achieve full coverage of the active material particles and easily resulting in local exposed areas. Meanwhile, the oxidation potential and conductivity of the solid electrolyte 121 are key performance indicators to ensure the effectiveness of the coating layer: the oxidation potential needs to be compatible with the battery's operating voltage range to ensure that the solid electrolyte 121 will not undergo oxidation and decomposition during charging and discharging, thereby maintaining its own and the interface's chemical stability; the conductivity needs to reach a certain level to ensure that lithium ions can be smoothly transported within the coating layer 120, avoiding the aggravation of battery polarization and insufficient capacity due to obstructed ion conduction, and ultimately ensuring that the coating layer plays a protective role without affecting the overall electrochemical performance of the battery.

[0049] In some embodiments, the solid electrolyte 121 includes one or more of oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes. That is, the solid electrolyte 121 can be a single material or a combination of two or more materials. For example, the solid electrolyte 121 can be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination of a halide-based solid electrolyte and an oxide-based solid electrolyte, etc. Further, the solid electrolyte 121 can be LLZO (Li7La3Zr2O). 12 LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3), LLTO(Li7La3Ti2O) 12 One or more of the following, for example, the solid electrolyte is LLZO, or LATP, or LLTO, etc.

[0050] In this invention, the solid electrolyte 121 of the coating layer 120 is uniformly coated on the surface of the active material of the core 110. Optionally, the thickness difference at various locations of the coating layer 120 is less than or equal to 10%. The core function of the solid electrolyte 121 is to achieve efficient ion transport. Uniform coating ensures that the surface of the active material particles is better covered by the electrolyte, reducing vacant and broken ion pathways. Furthermore, the consistent thickness of the coating layer avoids differences in local conduction resistance, thereby reducing overall ion transport polarization, ensuring the ion supply efficiency of the battery under high-rate charge and discharge, and avoiding capacity decay or heat generation caused by local ion transport lag. The method for determining the uniform coating of solid electrolyte is as follows: First, the cathode material particles are observed at 10,000x magnification using a scanning electron microscope (SEM) (Nova NanoSEM450) to determine the distribution areas of the core 110 and coating layer 120 in the cathode material. Then, elemental mapping analysis of the cathode material is performed using an EDS spectrometer. The boundary of the solid electrolyte coating is determined based on the characteristic elements of the solid electrolyte (which need to be determined according to the specific solid electrolyte composition, such as La and Zr in LLZO, Al and Ti in LATP). Then, 10 points that equally divide the core boundary are selected (the outer periphery of the core 110 is divided into 10 equal parts), and the thickness of the solid electrolyte coating layer corresponding to the 10 points is tested. If the difference between the maximum and minimum thickness values ​​is ≤10%, the solid electrolyte coating layer is considered to be uniformly coated on the surface of the core 110.

[0051] Please see Figure 1 and Figure 2 The present invention also provides a method for preparing the above-mentioned positive electrode material 100, comprising the following steps:

[0052] S1. Add the first positive electrode active material 111 and the second positive electrode active material 112 to the solvent, mix thoroughly, and then spray dry to obtain composite powder.

[0053] S2. The solid electrolyte 121 and the composite powder are ball-milled, sieved and dried to obtain the positive electrode material 100.

[0054] Specifically, the first positive electrode active material 111 in step S1 has the chemical formula LiNi. x Mn y A e Co z O2, where 0.8≤x≤0.94, 0.02≤y≤0.2, 0.02≤z≤0.1, 0≤e≤0.1, x+y+z+e=1, and A is the doping element in the high-nickel ternary material, which can be an inert transition metal element with the same valence as Mn. The chemical formula of the second positive electrode active material 112 is LiMn. a Fe b M c PO4, where 0.5≤a≤0.8, 0.1≤b≤0.4, 0≤c≤0.2, a+b+c=1, and M is an inert transition metal element with a +2 valence. The Dv50 of the first positive electrode active material 111 is 3~8μm, and the Dv50 of the second positive electrode active material 112 is 0.1~0.7μm. The first positive electrode active material 111 and the second positive electrode active material 112, which meet the above particle size requirements, are added to a solvent in a certain proportion, thoroughly mixed, and then spray-dried. The small particles of the second positive electrode active material 112 are adsorbed on the surface of the large particles of the first positive electrode active material 111, forming a composite powder.

[0055] The solvent in step S1 can be any solvent that can uniformly disperse the first positive electrode active material 111 and the second positive electrode active material 112 without chemically reacting with them. For example, the solvent can be deionized water, methanol, ethanol, etc. The amount of solvent used is not limited, as long as it can disperse the first positive electrode active material 111 and the second positive electrode active material 112. The mass ratio of the first positive electrode active material 111 to the second positive electrode active material 112 is (5%–35%) : (65%–95%). The methods for fully mixing the two materials include, but are not limited to, mixing using a mixer, stirring with a stirrer, and ultrasonic dispersion. After the two are mixed evenly, the dispersion is spray-dried: First, the dispersion is atomized into micron-sized droplets. The droplets contain both the first positive electrode active material 111 and the second positive electrode active material 112 particles. Then, the droplets rapidly evaporate moisture in the hot airflow and continue to shrink. The surface tension generated by the shrinkage will push the second positive electrode active material 112 particles in the droplets to gather on the surface of the first positive electrode active material 111 particles. At the same time, after the distance between the particles is shortened, the van der Waals forces, electrostatic attraction and other effects are significantly enhanced, which further promotes the adsorption of the second positive electrode active material 112 particles on the surface of the first positive electrode active material 111 particles. The rapid drying characteristics of spray drying will fix this adsorption state in time and avoid secondary dispersion of particles.

[0056] Step S2 involves ball milling the solid electrolyte 121 and the composite powder obtained in step S1 for 8–48 hours. During ball milling, the impact, compression, and shearing of the grinding media break down the initial agglomerates of the solid electrolyte and composite powder. Simultaneously, localized instantaneous high temperature and pressure activate the particle surface and remove the adsorption layer. Because the surface energy of the solid electrolyte 121 is lower than that of the composite powder, based on the principle of minimum surface energy, the solid electrolyte 121 spontaneously covers the surface of the composite powder. Furthermore, mechanical force promotes plastic deformation or local diffusion of the surface atoms of both, forming physicochemical adsorption, thereby ensuring that small-diameter solid electrolyte 121 particles uniformly coat the surface of the composite powder particles. The ball milling time in this step can be, for example, 8 hours, 16 hours, 24 hours, 36 hours, or 48 hours, etc. Insufficient ball milling time results in uneven or loose solid electrolyte coating, while excessive processing time affects both product quality and production efficiency. After ball milling, the cathode material is obtained after sieving and drying.

[0057] The present invention also provides an electrochemical device comprising the positive electrode material described above or the positive electrode material prepared by the above preparation method.

[0058] In one embodiment, the electrochemical device is a lithium-ion battery, which can be a liquid lithium-ion battery (with a non-aqueous electrolyte) or a solid lithium-ion battery (with a solid electrolyte), and there is no limitation herein.

[0059] The following is a detailed description of the structure of a liquid lithium-ion battery, taking it as an example: A lithium-ion battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator.

[0060] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive current collector is, for example, aluminum foil or carbon-coated aluminum foil, and the positive active material layer can be disposed on one surface of the positive current collector or on both surfaces. The positive active material layer includes a positive active material, a positive conductive agent, a positive binder, and a positive dispersant, wherein the positive active material is the positive material described above in this invention. The positive binder includes any one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber. Exemplarily, the positive binder can be polyvinylidene fluoride, polytetrafluoroethylene, or a combination of sodium carboxymethyl cellulose and styrene-butadiene rubber. The positive conductive agent includes, but is not limited to, one or more of conductive carbon black (SP), acetylene black, nano-metal powder, carbon nanotubes, and graphene. Exemplarily, the conductive agent is conductive carbon black; or a combination of carbon fiber and conductive carbon black; or a combination of carbon nanotubes and graphene, etc. The positive electrode dispersant includes one or more of polyvinylpyrrolidone, polyether comb-like polyurethane, trialkyl phosphate, stearate phosphate, etc., for example, it can be polyvinylpyrrolidone or trialkyl phosphate, etc.

[0061] The preparation process of the positive electrode sheet is illustrated below: First, the positive electrode active material, positive electrode conductive agent, positive electrode binder, and positive electrode dispersant are placed into a mixing tank in a mass ratio of (90%–98%):(1%–4%):(1%–4%):(0.01%–2%). Then, N-methylpyrrolidone is added at a solid content of 45%–70%, and the mixture is stirred and mixed evenly to prepare a positive electrode slurry. Finally, the positive electrode slurry is prepared at a ratio of (0.2g–0.4g) / 1540.25mm. 2 The areal density is uniformly coated onto the positive electrode current collector, and after drying, rolling, and cutting, the positive electrode sheet is obtained. The ratio of the positive electrode active material, positive electrode conductive agent, positive electrode binder, and positive electrode dispersant can be selected within the above range according to actual needs, for example, 90%:4%:4%:2%; or 95%:2%:2%:1%; or 97.5%:1%:1%:0.5%, etc. The solid content of the positive electrode slurry can be 45%, 60%, or 70%, etc., and the coating areal density of the positive electrode slurry can be 0.2g / 1540.25mm. 2 0.3g / 1540.25mm 2 Or 0.4g / 1540.25mm 2 ,etc.

[0062] The thickness of the positive electrode sheet on one side is 40–300 μm, for example, it can be 40 μm, 100 μm, 200 μm or 300 μm, etc.; the compaction density is 2.1–2.85 g / cm³. 3 For example, it can be 2.1 g / cm³. 3 2.3g / cm 3 2.5g / cm 3 Or 2.85g / cm 3 .

[0063] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative current collector is selected, for example, from copper foil or carbon-coated copper foil. The negative active material layer can be disposed on one surface or both surfaces of the negative current collector. The negative active material layer includes a negative active material, a negative conductive agent, a negative binder, and a negative dispersant. The specific types of the negative active material, negative conductive agent, negative binder, and negative dispersant are not specifically limited here; materials known in the art for use in lithium-ion batteries can be used, and those skilled in the art can select them according to actual needs.

[0064] For example, the negative electrode active material includes, but is not limited to, artificial graphite, natural graphite, etc. The negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black (Super P), carbon fiber (VGCF), carbon nanotubes (CNT), Ketjen black, nano silver powder, and graphene. For example, it can be acetylene black, conductive carbon black, or a combination of carbon fiber and carbon nanotubes, etc. The negative electrode binder is selected from one or more of vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, and styrene-butadiene rubber. For example, it can be vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or styrene-butadiene rubber, etc. The negative electrode dispersant is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0065] The preparation process of the negative electrode sheet is exemplified as follows: First, the negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are placed in a mixing tank at a mass ratio of (93%–98%):(0.2%–1.5%):(1%–3%):(0.01–1.5%), and stirred thoroughly. Then, N-methylpyrrolidone or deionized water is added at a solid content of 45%–70%, and the mixture is stirred and stirred evenly to prepare the negative electrode slurry. Finally, the negative electrode slurry is prepared at a ratio of (0.1g–0.2g) / 1540.25mm. 2The areal density of the coating is uniformly applied to the negative electrode current collector, and after drying and rolling processes, the negative electrode sheet is obtained. The ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode dispersant can be selected within the above range according to actual needs. For example, it can be 93%:1.5%:3%:1.5%; or 95%:1%:3%:1%; or 98%:0.2%:1%:0.8%, etc. The solid content of the negative electrode slurry can be 45%, 60%, or 70%, etc., and the coating areal density of the negative electrode slurry can be 0.1g / 1540.25mm. 2 0.2g / 1540.25mm 2 Or 0.15g / 1540.25mm 2 ,etc.

[0066] The thickness of the negative electrode sheet on one side is 30–150 μm, for example, 30 μm, 80 μm, 120 μm, or 150 μm, etc.; the compaction density is 1.45–1.8 g / cm³. 3 Between, for example, it could be 1.45 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 Or 1.8g / cm 3 .

[0067] A separator is placed between the positive and negative electrodes to separate them, preventing short circuits inside the battery. It also allows lithium ions to move between the positive and negative electrodes, facilitating the charging and discharging process. The separator can be made of porous materials such as polyethylene (PE), polypropylene (PP), glass fiber, or composite membranes.

[0068] Non-aqueous electrolytes play a role in conducting lithium ions during battery charging and discharging. Non-aqueous electrolytes include organic solvents and lithium salts. The lithium salt can be selected from one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Further, lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts, such as a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, is selected as the lithium salt with superior overall performance. The organic solvent may be selected from one or more of the following: fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0069] Non-aqueous electrolytes may also include functional additives, such as fluoroethylene carbonate (FEC), propylene-1,3-sulfonyl lactone (PST), tetravinylsilane (TVSI), vinylene carbonate (VC), ethylene sulfate (DTD), etc., which can be added according to the actual needs of production.

[0070] Battery assembly: The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cells are obtained by winding or stacking. The bare cells are then installed into the battery casing and thoroughly baked until the water content is below 450 ppm. After liquid injection, formation, sealing, and inspection, a lithium-ion battery is obtained.

[0071] In other embodiments, the lithium-ion battery is a solid-state lithium-ion battery. The electrolyte of the solid-state lithium-ion battery is solid. Common solid electrolytes include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc., which will not be elaborated here. Those skilled in the art can choose according to actual production needs.

[0072] It should be noted that the structures not described in detail in the above lithium-ion batteries can all be set up with reference to existing technologies, and will not be elaborated here.

[0073] This application also provides an electronic device that includes the aforementioned lithium-ion battery, which can be used in the form of a single cell, a battery module, or a battery pack to power the electronic device.

[0074] In some embodiments, electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0075] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0076] Example 1

[0077] This embodiment provides a cathode material, which includes a core and a coating layer. The core includes a first cathode active material, LiNi. 0.8 Mn 0.1 Co 0.1 O2 (Dv50: 3.3μm single crystal); Second cathode active material LiMn 0.6 Fe 0.4 PO4 (carbon content: 1.6%; Dv50: 0.4μm), of which LiNi 0.8 n 0.1 Co 0.1 O2 accounts for 10% of the core mass, and small-particle-size LiMn 06 Fe 04 PO4 adsorbed on large-particle-size LiNi 0.8 Mn 0.1 Co 0.1 The surface of O2 particles; the coating layer is coated on the core surface, and the coating layer is composed of solid electrolyte LLZO.

[0078] The cathode material is prepared by the following method:

[0079] 900g of LiMn 0.6 Fe 0.4 PO4 material and 100g LiNi 0.8 Mn 0.1 Co 0.1 O2 material was added to 20L of deionized water and stirred thoroughly at 60℃ for 5h. The resulting slurry was then transferred to a spray dryer for spray drying and granulation, and dried at 250℃ to obtain a composite powder. The composite powder was then ball-milled with 45g of LLZO with a particle size of 50nm for 24h, and the mixture was sieved to obtain the cathode material.

[0080] This embodiment also provides a lithium-ion battery containing the positive electrode material. The specific composition of the lithium-ion battery is as follows:

[0081] (1) Preparation of positive electrode sheet

[0082] The above-mentioned positive electrode material, positive electrode conductive agent acetylene black, positive electrode binder polyvinylidene fluoride (PVDF), and positive electrode dispersant polyvinylpyrrolidone (PVP) were added to a mixing tank in a weight ratio of 96:2:1:1. Then, N-methylpyrrolidone (NMP) was added at a solid content of 60% and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. The thickness of the single-sided positive electrode active material layer of the positive electrode sheet was 200 μm, and the compaction density was 2.58 g / cm³. 3 .

[0083] (2) Preparation of negative electrode sheet

[0084] Artificial graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (adhesive), and sodium carboxymethyl cellulose (CMC-Na) were thoroughly mixed in a mixer at a weight ratio of 97:1:1:1. Then, deionized water with a solid content of 60% was added and mixed evenly to obtain a negative electrode slurry. This slurry was then uniformly coated onto a copper foil (negative electrode current collector). After drying and cold pressing, a negative electrode sheet was obtained. The thickness of the single-sided negative electrode active material layer of the negative electrode sheet was 100 μm, and the compaction density was 1.65 g / cm³. 3 .

[0085] (3) Separator: Polypropylene membrane.

[0086] (4) Electrolyte preparation

[0087] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DEC are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1mol / L.

[0088] (5) Battery assembly

[0089] The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to obtain a bare cell. The bare cell is packaged in an aluminum-plastic film, and the prepared electrolyte is injected into the dried cell. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained; the nominal capacity of this lithium-ion battery is 1 Ah.

[0090] Example 2

[0091] The difference between this embodiment and Embodiment 1 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 20% of the core mass, and the solid electrolyte coating accounts for 5% of the total mass of the cathode material.

[0092] Example 3

[0093] The difference between this embodiment and Embodiment 1 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 30% of the core mass, while the solid electrolyte coating accounts for 2.8% of the mass.

[0094] Example 4

[0095] The difference between this embodiment and Embodiment 1 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 35% of the core mass, while the solid electrolyte coating accounts for 1% of the mass.

[0096] Example 5

[0097] The difference between this embodiment and Embodiment 1 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 5% of the core mass, and the solid electrolyte coating accounts for 5% of the mass.

[0098] Example 6

[0099] The difference between this embodiment and Embodiment 3 is that: LiMn 0.6 Fe 0.4 The Dv50 of PO4 is 0.1 μm, and the mass percentage of the solid electrolyte coating is 3.7%.

[0100] Example 7

[0101] The difference between this embodiment and Embodiment 3 is that: LiMn 0.6 Fe 0.4 The Dv50 of PO4 is 0.7 μm, and the mass percentage of the solid electrolyte coating is 2.2%.

[0102] Example 8

[0103] The difference between this embodiment and Embodiment 3 is that the second positive electrode active material is LiMn. 0.5 Fe 0.5 PO4.

[0104] Example 9

[0105] The difference between this embodiment and Embodiment 3 is that the second positive electrode active material is LiMn. 0.7 Fe 0.3 PO4.

[0106] Example 10

[0107] The difference between this embodiment and Embodiment 3 is that the second positive electrode active material is LiMn. 0.8 Fe 0.2 PO4.

[0108] Example 11

[0109] The difference between this embodiment and Embodiment 3 is that the second positive electrode active material is LiMn. 0.6 Fe 0.3 Zn 0.1 PO4.

[0110] Example 12

[0111] The difference between this embodiment and Embodiment 3 is that the second positive electrode active material is LiMn. 0.6 Fe 0.3 The surface of PO4 is not coated with amorphous carbon.

[0112] Example 13

[0113] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.9 Mn 0.05 Co 0.05 O2.

[0114] Example 14

[0115] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.94 Mn 0.04 Co 0.02 O2.

[0116] Example 15

[0117] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.8 Mn 0.1 Zr 0.05 Co 0.05 O2.

[0118] Example 16

[0119] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.8 Mn 0.1 Co 0.1O2 is a mixture of monocrystalline and polycrystalline materials, with polycrystalline materials accounting for 50% of the total mass.

[0120] Example 17

[0121] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.8 Mn 0.1 Co 0.1 O2 is a mixture of monocrystalline and polycrystalline materials, with polycrystalline materials accounting for 30% of the total mass.

[0122] Example 18

[0123] The difference between this embodiment and Embodiment 3 is that the first positive electrode active material is LiNi. 0.8 Mn 0.1 Co 0.1 O2 is a mixture of monocrystalline and polycrystalline materials, with polycrystalline materials accounting for 60% of the total mass.

[0124] Example 19

[0125] The difference between this embodiment and Embodiment 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 The Dv50 of O2 is 5 μm, and the mass percentage of the solid electrolyte coating layer is 4%.

[0126] Example 20

[0127] The difference between this embodiment and Embodiment 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 The Dv50 of O2 is 8 μm, and the mass percentage of the solid electrolyte coating layer is 0.5%.

[0128] Example 21

[0129] The difference between this embodiment and Embodiment 3 is that the solid electrolyte used in the coating layer is LLTO, and the mass percentage of the solid electrolyte coating layer is 4.3%.

[0130] Example 22

[0131] The difference between this embodiment and Embodiment 3 is that the solid electrolyte used in the coating layer is LATP, and the mass percentage of the solid electrolyte coating layer is 2.1%.

[0132] Example 23

[0133] The difference between this embodiment and Embodiment 3 is that the solid electrolyte used in the coating layer is LZG(Li) 14Zn(GeO4)4 (conductivity does not meet requirements), the mass percentage of the solid electrolyte coating layer is 2.1%.

[0134] Example 24

[0135] The difference between this embodiment and Embodiment 3 is that the mass of the coating layer accounts for 0.5% of the total mass of the cathode material.

[0136] Example 25

[0137] The difference between this embodiment and Embodiment 3 is that the mass of the coating layer accounts for 5% of the total mass of the cathode material.

[0138] Example 26

[0139] The difference between this embodiment and Embodiment 3 is that the mass of the coating layer accounts for 10% of the total mass of the cathode material.

[0140] Example 27

[0141] The difference between this embodiment and Embodiment 3 is that the particle size of the solid electrolyte LLZO is 100 nm, and the mass percentage of the solid electrolyte coating layer is 1%.

[0142] Example 28

[0143] The difference between this embodiment and Embodiment 3 is that the particle size of the solid electrolyte LLZO is 150 nm, and the mass percentage of the solid electrolyte coating layer is 0.3%.

[0144] Example 29

[0145] The difference between this comparative example and Example 1 is that the first positive electrode active material and the second positive electrode active material are evenly dispersed in deionized water and then dried in an oven at 80°C.

[0146] Example 30

[0147] The difference between this comparative example and Example 1 is that the composite powder and the solid electrolyte LLZO were ball-milled and mixed for 6 hours.

[0148] Comparative Example 1

[0149] The difference between this comparative example and Example 3 is that: LiMn 0.6 Fe 0.4 The Dv50 of PO4 is 0.8 μm, and the mass percentage of the solid electrolyte coating is 1.9%.

[0150] Comparative Example 2

[0151] The difference between this comparative example and Example 3 is that: LiMn 0.6 Fe 0.4The Dv50 of PO4 is 0.05 μm, and the mass percentage of the solid electrolyte coating is 8.8%.

[0152] Comparative Example 3

[0153] The difference between this comparative example and Example 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 The Dv50 of O2 is 9 μm, and the mass percentage of the solid electrolyte coating layer is 0.2%.

[0154] Comparative Example 4

[0155] The difference between this comparative example and Example 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 The Dv50 of O2 is 1 μm, and the mass percentage of the solid electrolyte coating layer is 4.2%.

[0156] Comparative Example 5

[0157] The difference between this comparative example and Example 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 40% of the total mass of the core, while the solid electrolyte coating accounts for 0.4%.

[0158] Comparative Example 6

[0159] The difference between this comparative example and Example 3 is that: LiNi 0.8 Mn 0.1 Co 0.1 O2 accounts for 1% of the total mass of the core, and the solid electrolyte coating accounts for 10%.

[0160] Comparative Example 7

[0161] The difference between this comparative example and Example 1 is that no coating layer is provided on the surface of the core.

[0162] Comparative Example 8

[0163] The difference between this comparative example and Example 1 is that the cathode material is LiMn. 0.6 Fe 0.4 PO4.

[0164] Comparative Example 9

[0165] The difference between this comparative example and Example 1 is that the first positive electrode active material and the second positive electrode active material are directly physically mixed.

[0166] Comparative Example 10

[0167] The difference between this comparative example and Example 1 is that the cathode material is LiMn. 0.6 Fe 0.4 A PO4 coating layer containing 5% solid electrolyte is used.

[0168] Table 1: Parameters of Examples 1-30 and Comparative Examples 1-10

[0169]

[0170]

[0171]

[0172]

[0173] The Dv50 of the first positive electrode active material, the Dv50 of the second positive electrode active material, the proportion of the first positive electrode active material, the D / T ratio, and the particle size and proportion of the solid electrolyte in Table 1 can also be measured by the following methods:

[0174] Particle size detection: After cleaning the fully loaded positive electrode sheet (i.e., the positive electrode sheet with SOH (State of Health) ≥ 90%), cross-sectional CP is performed. The second positive electrode active material (LFMP) and the first positive electrode active material (NCM) are identified by the characteristic elements Mn, Fe, P, Co, and Ni, respectively. Particle size is statistically analyzed by sampling.

[0175] D / T testing: After cleaning the fully loaded positive electrode sheet (cell SOH≥90%), cross-sectional CP is performed. The second positive electrode active material (LFMP) and the first positive electrode active material (NCM) are identified by the characteristic elements Mn, Fe, P, Co, and Ni, respectively. The thickness of multiple second positive electrode active materials is measured, and the average value is taken as T. The particle size of 10 first positive electrode active materials is measured, and the average value is taken as D.

[0176] Solid electrolyte particle size detection: The solid electrolyte is observed by SEM and the size of the particles in the field of view is measured. To reduce measurement error, more than 10 particles can be randomly selected and their average value is calculated.

[0177] Solid electrolyte type and mass percentage detection: After cleaning the fully loaded positive electrode (cell SOH≥90%), a certain amount of active material (≥500g) is scraped off and subjected to ICP (Inductively Coupled Plasma) test. The type of solid electrolyte used is confirmed by the measured elements. The solid electrolyte content can be determined by TGA (Thermogravimetric Analysis), and its mass percentage can be calculated.

[0178] The conductivity testing method for solid electrolytes is as follows: The composition of the solid electrolyte is determined by ICP results, and its particle size can be determined by SEM and particle size measurement software. Then, according to the test results, a certain amount of solid electrolyte that meets the requirements is pressed into a small disc with a diameter of 1.4 cm under a pressure of 50 MPa. The disc and a stainless steel sheet are used as working electrodes to assemble a symmetrical battery. The resistance is tested by an electrochemical workstation at a frequency of 0.1 to 100 MHz. The conductivity is calculated by the following formula: Conductivity = 1.4 / (R * S); where R is the resistance, 1.4 is the diameter of the disc, and S is the area of ​​the disc.

[0179] The ratio of the first positive electrode active material to the second positive electrode active material was tested: After cleaning the fully loaded positive electrode sheet (cell SOH≥90%), a certain amount of active material (≥500g) was scraped off and subjected to ICP test. The ratio of the two materials was confirmed by measuring the ratio of elements such as Mn, Fe, P, Co, and Ni.

[0180] Detection of uniform adsorption of the second positive electrode active material by the first positive electrode active material particles in the core: After cleaning the full positive electrode sheet (cell SOH≥90%), a certain amount of positive electrode powder (>1g) was scraped off and placed in 50ml of ethanol. After ultrasonic treatment for at least 30min, a sample was prepared for testing: First, the positive electrode material particles were observed at 10000x magnification using a scanning electron microscope (SEM) (equipment model Nova NanoSEM450) to determine the distribution areas of the first and second positive electrode active materials in the positive electrode material. Then, elemental mapping analysis of the positive electrode material was performed using an EDS spectrometer. The boundary of the second positive electrode active material was determined based on the distribution of the characteristic element Ni of the first positive electrode active material and the characteristic element Fe of the second positive electrode active material. Then, 10 points that equally divide the boundary of the first positive electrode material were selected (the outer periphery of the first positive electrode active material was divided into 10 equal parts), and the coating thickness of the second positive electrode active material corresponding to the 10 points was tested. If the thickness difference between the maximum and minimum measured values ​​is ≤10%, it is considered that the second positive electrode active material is uniformly adsorbed on the surface of the first positive electrode active material. Solid electrolyte coating uniformity test: After cleaning the full positive electrode sheet (cell SOH≥90%), scrape off a certain amount of positive electrode powder (>1g), place it in 50ml ethanol, and sonicate for at least 30min to prepare a sample for testing: First, use a scanning electron microscope (SEM) (equipment model NovaNanoSEM450) at 10000x magnification to observe the positive electrode material particles and determine the distribution area of ​​the core 110 and coating layer 120 in the positive electrode material. Then, use an EDS energy dispersive spectroscopy to perform elemental mapping analysis on the positive electrode material. According to the characteristic elements of the solid electrolyte (which need to be determined according to the specific solid electrolyte composition, such as La and Zr in LLZO, Al and Ti in LATP, etc.), determine the boundary of the solid electrolyte coating. Then, select 10 points that equally divide the core boundary (divide the outer periphery of the core 110 into 10 parts) and test the thickness of the solid electrolyte coating layer corresponding to the 10 points. If the difference between the maximum and minimum thickness values ​​is ≤10%, it is considered that the solid electrolyte coating layer is uniformly coated on the surface of the core 110.

[0181] In addition, to verify the performance of the cathode material of this application, the lithium-ion batteries assembled in each embodiment and comparative example were activated (activation process: constant current charging to 4.2V at 0.33C, then constant voltage charging to 0.05C; standing for 30 min; then constant current discharging to 2.8V at 0.33C; standing for 30 min; repeating the above steps 3 times) and then performance tests were performed. The test results are shown in Table 2, and the test methods are as follows:

[0182] (1) DCR change test:

[0183] The battery was charged to 4.2V at a constant current and constant voltage of 0.33C, then allowed to stand for 30 minutes, followed by discharge at 0.33C to 2.8V. This process was repeated three times, and the average discharge capacity of the three discharges was recorded as C0. The battery was then charged to Vmax at a constant current and constant voltage of 0.33C0, allowed to stand for 30 minutes, and then discharged at a constant current of 0.33C0, with the cutoff capacity set at 0.5C0. At this point, the cell was considered to be at 50% SOC. After standing for 1 hour, the voltage at the end of the standing period was recorded as V0. The battery was then discharged at a constant current of 1C0 for 30 seconds, and the voltage at the end of the discharge period was recorded as V... 30 Then DCR = (V0 - V 30 The change in DCR is: (DCR - baseline) / baseline × 100%, where the baseline is comparative example 8 (pure LiMn). 0.6 Fe 0.4 PO4).

[0184] (2) Capacity retention test

[0185] The activated battery was placed in a constant-temperature testing device set to 45℃, charged at 1C constant current and constant voltage to 4.2V, allowed to stand for 30 minutes, and then discharged at 1C constant current to 2.8V. This process was repeated 500 times. 1C capacity retention = C n / C1, where C1 is the discharge capacity of the first cycle, C n Let be the discharge capacity of the nth cycle.

[0186] (3) Discharge capacity test at 0.33C under 2.8~4.2V

[0187] The activated battery is placed in a constant temperature testing device with the device temperature set to 25℃. It is charged to 4.2V at a constant current and constant voltage of 0.33C (1C = nominal battery capacity). After standing for 30 minutes, it is discharged to 2.8V at a constant current of 0.33C to obtain the discharge capacity C0. The discharge capacity is then C0 / m, where m is the mass of the positive electrode active material.

[0188] (4) 0.33C discharge plateau test at 2.8~4.2V

[0189] The activated battery was placed in a constant temperature testing device, with the device temperature set to 25°C and 0.33°C.

[0190] (1C = nominal battery capacity) Charge to 4.2V with constant current and constant voltage, let stand for 30 minutes, then discharge to 2.8V with constant current at 0.33C. The discharge capacity C0 and discharge energy E0 are obtained. Then the 0.33C discharge plateau = E0 / C0.

[0191] Table 2: Performance of Examples 1-30 and Comparative Examples 1-10

[0192]

[0193]

[0194]

[0195]

[0196] As shown in Tables 1 and 2, the mass percentage of the first positive electrode active material in the core of the positive electrode materials in Examples 1-5 and Comparative Examples 5-6 differs. Simultaneously, the proportion of solid electrolyte varies to achieve a better coating effect. Test results show that the positive electrode material formed by combining high-nickel ternary materials and lithium manganese iron phosphate in a certain proportion exhibits significantly lower battery impedance, improved cycle performance, discharge capacity, and discharge platform compared to pure lithium manganese iron phosphate (Comparative Example 8). The performance improvement is optimal when the mass percentage of high-nickel ternary materials is between 5% and 35%. A high mass percentage of high-nickel ternary materials indicates a low mass percentage of lithium manganese iron phosphate, preventing the formation of a continuous protective barrier from the small particles of second positive electrode active material. This exacerbates the side reactions between the high-nickel ternary materials and the electrolyte, affecting battery performance. Conversely, if the proportion of high-nickel ternary materials is too low and the proportion of lithium manganese iron phosphate is too high, the total specific capacity of the positive electrode material will decrease sharply due to the low capacity characteristics of the second positive electrode active material, resulting in a battery capacity and discharge platform approaching that of lithium manganese iron phosphate.

[0197] In Examples 3, 6-7, 19-20 and Comparative Examples 1-4, the Dv50 of the first and second positive electrode active materials are different. The test results show that the Dv50 of the first positive electrode active material is controlled in the range of 3 to 8 μm, and the Dv50 of the second positive electrode active material is controlled in the range of 0.1 to 0.7 μm. The small particles of the second positive electrode active material are uniformly adsorbed on the surface of the large particles of the first positive electrode active material, thereby optimizing the overall performance of the battery.

[0198] In Examples 3 and 8-12, the types of second positive electrode active materials are different. The test results show that different types of lithium manganese iron phosphate can effectively improve the insufficient specific capacity by compounding a certain proportion of high nickel ternary materials and solid electrolyte coating, thereby improving the discharge specific capacity and discharge platform of the cell.

[0199] In Examples 3 and 13-18, the types of the first positive electrode active materials differ. Using high-nickel ternary materials with different proportions of nickel, cobalt, and manganese, doped high-nickel ternary materials, and high-nickel ternary materials that combine single-crystal and polycrystalline materials can effectively improve the insufficient specific capacity of lithium manganese iron phosphate, thereby enhancing the battery's discharge capacity and discharge platform. Among these, single-crystal materials show better improvement than polycrystalline materials. If the polycrystalline content is high, stress concentration at grain boundaries can lead to cycle cracking, thus affecting the battery's cycle performance.

[0200] In Examples 3 and 21-23, the solid electrolytes used in the coating layer of the positive electrode materials are different. Solid electrolytes that meet the following conditions can play a protective role without affecting the overall electrochemical performance of the battery: particle size less than or equal to 100 nm, oxidation potential greater than or equal to 4.25 V, and conductivity greater than or equal to 0.1 mS / cm.

[0201] In Examples 3 and 24-26, the mass percentage of the coating layer in the cathode materials differed. Test results showed that when the coating layer accounted for 0.5% to 5% of the total mass of the cathode material, the improvement effect on the cathode material was better. Excessive coating would lead to insufficient specific capacity due to the extended lithium-ion transport path. Insufficient coating would make it difficult to form a continuous and complete coating layer, resulting in some of the core active material being exposed to direct contact with the electrolyte, increasing side reactions, causing discontinuous ion transport channels, high interfacial impedance, and poor rate performance.

[0202] In Examples 3, 27, and 28, the solid electrolytes used in the coating layers of the cathode materials have different particle sizes. When the particle size of the solid electrolyte is less than or equal to 100 nm, it is more conducive to forming a uniform and dense coating layer on the core surface. If the particle size of the solid electrolyte is too large, it is difficult to achieve complete coverage of the active material particles, and local exposed areas are likely to appear, thus losing the core function of protecting the active material.

[0203] Compared to Example 1, Example 29 did not employ spray drying; instead, it directly used an oven-drying method to dry the first and second positive electrode active materials. This drying method lacks the extrusion drive of droplet contraction and the reinforcement of surface forces at close range. The second and first positive electrode active materials are mixed only by mechanical force, resulting in weak adsorption effects and easy stratification due to differences in density and particle size, making it impossible to form a stable adsorption structure. Therefore, the improvement effect on the materials is slightly worse.

[0204] Compared to Example 1, Example 30, with a ball milling time of 6 hours (when the ball milling time is insufficient), resulted in an uneven or loosely coated solid electrolyte layer, leading to a slightly worse improvement effect on the material.

[0205] Compared to Example 1, Comparative Example 7 did not have a solid electrolyte coating layer on the positive electrode material. As the positive electrode active material lost the protective effect of the coating layer, it could not avoid contact between the electrolyte and the positive electrode active material, resulting in an increase in side reactions between the positive electrode active material and the electrolyte, which affected the electrochemical performance of the battery.

[0206] Compared to Example 1, Comparative Example 9 directly mixes the powders of the first positive electrode active material, the second positive electrode active material, and the solid electrolyte. The three materials are mixed by mechanical force, which cannot form the core-shell structure of this application, and the effect on improving the performance of the material is not good.

[0207] Compared to Example 1, Comparative Example 10's cathode material core does not contain high-nickel ternary materials. Instead, a solid electrolyte coating layer is directly formed on the surface of pure lithium manganese iron phosphate. The test results show that, compared to pure lithium manganese iron phosphate (Comparative Example 8), only coating with a solid electrolyte can improve the interfacial impedance, but it cannot solve the problem of insufficient specific capacity of lithium manganese iron phosphate. Therefore, the discharge specific capacity and discharge plateau of Comparative Example 10 are close to those of Comparative Example 8.

[0208] The cathode material provided by this invention employs a core composed of a first cathode active material (high-nickel NCM) and a second cathode active material (LMFP) particles, with performance optimized through precise control of their mixing ratio and particle size distribution. This hybrid core is coated with a solid electrolyte layer, which significantly improves the ion conduction efficiency of the cathode active material, accelerates lithium ion migration to the surface of the core active material, promotes efficient lithium ion insertion and extraction, and thus fully releases the specific capacity potential of the active material. Furthermore, the coating layer physically isolates the cathode active material from direct contact with the electrolyte, effectively suppressing the dissolution of Mn ions and ensuring the long-term stable performance of the LMFP capacity. On the other hand, it reduces structural deterioration of NCM due to reaction with the electrolyte, significantly extending battery cycle life. Simultaneously, the solid electrolyte itself possesses excellent high-voltage resistance and high thermal stability, further enhancing battery safety performance under high-voltage and high-temperature conditions. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0209] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A positive electrode material, characterized in that, include: The core comprises a first positive electrode active material and a second positive electrode active material, wherein the second positive electrode active material is adsorbed on the surface of the first positive electrode active material; A coating layer is applied to the surface of the core, and the material of the coating layer includes a solid electrolyte. The chemical formula of the first positive electrode active material is LiNi. x Mn y A e Co z O2, where 0.8≤x≤0.94, 0.02≤y≤0.2, 0.02≤z≤0.1, 0≤e≤0.1, x+y+z+e=1, and A is an inert transition metal element with the same valence as Mn; The chemical formula of the second positive electrode active material is: LiMn a Fe b M c PO4, where 0.5≤a≤0.8, 0.1≤b≤0.4, 0≤c≤0.2, a+b+c=1, and M is an inert transition metal element with a +2 valence; The median particle size of the first positive electrode active material is 3–8 μm; the median particle size of the second positive electrode active material is 0.1–0.7 μm, and the mass of the first positive electrode active material accounts for 5%–35% of the mass of the core.

2. The cathode material according to claim 1, characterized in that, The coating layer accounts for 0.5% to 5% of the total mass of the cathode material.

3. The cathode material according to claim 1, characterized in that, The particle size of the first positive electrode active material is D, the thickness of the coating layer formed by the adsorption of the second positive electrode active material on the surface of the first positive electrode active material is T, and the core satisfies: 0.1≤D / T≤20.

4. The cathode material according to claim 3, characterized in that, 0.36≤D / T≤1.

6.

5. The positive electrode material according to claim 1, characterized in that, The first positive electrode active material is a single crystal particle, or a mixture of single crystal particles and polycrystalline particles; if the first positive electrode active material is a mixture of single crystal particles and polycrystalline particles, the mass percentage of polycrystalline particles in the mixture of single crystal particles and polycrystalline particles is less than or equal to 50%.

6. The cathode material according to claim 1, characterized in that, The solid electrolyte meets the following requirements: particle size less than or equal to 100 nm, oxidation potential greater than or equal to 4.25 V, and conductivity greater than or equal to 0.1 mS / cm.

7. The cathode material according to claim 5, characterized in that, The solid electrolyte includes one or more of oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes.

8. A method for preparing the positive electrode material according to any one of claims 1 to 7, characterized in that, Includes the following steps: The first positive electrode active material and the second positive electrode active material are added to a solvent, mixed thoroughly, and then spray-dried to obtain a composite powder. The solid electrolyte and the composite powder were ball-milled, sieved, and dried to obtain the positive electrode material.

9. An electrochemical device, characterized in that, Includes the cathode material according to any one of claims 1 to 7, or the cathode material prepared by the preparation method according to claim 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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