Composite positive active material and preparation method thereof, composite positive plate, solid-state battery and electric equipment

Abstract

The invention provides a composite positive active material and a preparation method thereof, a composite positive plate, a solid-state battery and electric equipment, and relates to the technical field of batteries. According to the composite positive electrode active material, the core of the active material is modified by adopting the lithium phosphate nanoparticles doped with the rare earth elements, so that the problems of structural stability and interface ion transmission of the core of the active material can be solved at the same time; the modified composite positive electrode active material can synchronously realize structural stability, interface optimization and interface side reaction inhibition, so that triple functions of inhibiting the volume expansion of an active material core, improving the interface ion conductivity and blocking transition metal ion diffusion are achieved; furthermore, the energy density, the cycling stability and the safety of the solid-state battery applying the composite positive electrode active material can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite positive electrode active material and its preparation method, a composite positive electrode sheet, a solid-state battery and an electrical device thereof. Background Technology

[0002] Solid-state batteries, by using solid electrolytes instead of traditional liquid electrolytes, effectively solve safety issues such as leakage, flammability, and thermal runaway associated with liquid lithium batteries. They can also be matched with metallic lithium (Li) anodes, significantly improving battery energy density and becoming a core development direction for next-generation power batteries. However, the industrialization of all-solid-state batteries still faces key technological bottlenecks in the cathode process. On the one hand, cathode active materials (such as lithium nickel cobalt manganese oxide (NCM) and lithium cobalt oxide (LCO)) are prone to volume expansion during charging and discharging (expansion rates can reach 5%-10%), leading to cracking of the internal structure of the cathode sheet and disrupting ion transport channels. On the other hand, there is a severe interfacial impedance (typically >1000 Ω·cm²) between the cathode active material and the solid electrolyte, and both are prone to interfacial side reactions during cycling (such as...). (interdiffusion with transition metal ions), forming a high-resistivity interface phase (such as...) , This leads to a rapid decline in the capacity of solid-state batteries.

[0003] In related technologies, solutions to the aforementioned problems with positive electrode sheets often focus on optimizing a single function. Specifically, this could involve coating the surface of the positive electrode active material... , Coatings can be used to suppress interfacial side reactions, but coatings can easily increase ion transport resistance; or the interfacial impedance can be reduced by increasing the content of solid electrolyte, but this will lead to a decrease in the proportion of positive electrode active material, sacrificing the energy density of solid-state batteries.

[0004] Therefore, developing a multifunctional composite cathode active material that can simultaneously achieve "suppressing volume expansion, reducing interfacial impedance, and reducing side reactions" is the key to breaking through the performance bottleneck of solid-state batteries. Summary of the Invention

[0005] This application provides a composite positive electrode active material and its preparation method, a composite positive electrode sheet, a solid-state battery, and an electrical device. The composite positive electrode active material has high ion transport efficiency and structural stability, which can improve the cycle performance, energy density, and safety of solid-state batteries.

[0006] In a first aspect, this application provides a composite positive electrode active material, comprising: an active material core and a first coating layer covering at least a portion of the surface of the active material core, the first coating layer comprising lithium phosphate nanoparticles doped with rare earth elements; the rare earth elements include one or more of Y, Nd, and La.

[0007] In one specific implementation, the molar amount of rare earth element doping is 0.5%-2% of the molar amount of lithium phosphate nanoparticles.

[0008] In one specific embodiment, the particle size D50 of the lithium phosphate nanoparticles is 50nm-100nm.

[0009] In one specific embodiment, the composite positive electrode active material further includes: a second coating layer covering at least a portion of the surface of the active material core, wherein a first coating layer covers at least a portion of the surface of the second coating layer; the second coating layer includes alumina and / or zirconium oxide.

[0010] In one specific embodiment, the active material core includes lithium nickel cobalt manganese oxide, or a composite core formed by combining lithium cobalt oxide and lithium manganese oxide.

[0011] In a second aspect, this application provides a method for preparing a composite positive electrode active material as provided in the first aspect. The method includes: dispersing rare earth element-doped lithium phosphate nanoparticles and an active material core coated with a second coating layer in a solvent at a certain mass percentage, performing ultrasonic dispersion treatment, and then sequentially performing vacuum drying and molding sintering to obtain the composite positive electrode active material.

[0012] In one specific implementation, the mass percentage of rare earth element-doped lithium phosphate nanoparticles and active material cores coated with a second coating layer is 1%:99%-10%:90%.

[0013] Thirdly, this application provides a composite positive electrode sheet, comprising: a positive current collector and a composite positive active material layer, wherein the composite positive active material layer comprises the composite positive active material provided in the first aspect above, or comprises the composite positive active material prepared by the preparation method provided in the second aspect above.

[0014] Fourthly, this application provides a solid-state battery, comprising: a negative electrode, a solid electrolyte layer, and a composite positive electrode as provided in the third aspect above, wherein the solid electrolyte layer is disposed between the negative electrode and the composite positive electrode.

[0015] In one specific implementation, the solid-state battery can be an all-solid-state battery.

[0016] Fifthly, this application provides a battery assembly comprising at least two solid-state batteries as described in the fourth aspect above.

[0017] In a sixth aspect, this application provides an electrical device, including: a solid-state battery as provided in the fourth aspect above, or a battery assembly as provided in the fifth aspect above.

[0018] The composite positive electrode active material, its preparation method, composite positive electrode sheet, solid-state battery, and electrical device provided in this application include an active material core and a first coating layer covering at least a portion of the surface of the active material core. The first coating layer includes rare earth element-doped lithium phosphate. The nanoparticles include rare earth elements such as Y, Nd, and La. This application modifies the core of the active material using lithium phosphate nanoparticles doped with rare earth elements, simultaneously addressing the structural stability of the core and the interfacial ion transport issues. This allows the modified composite cathode active material to simultaneously achieve structural stability, interface optimization, and suppression of interfacial side reactions, achieving a triple function of suppressing core volume expansion, improving interfacial ion conductivity, and blocking transition metal ion diffusion. This, in turn, improves the energy density, cycle stability, and safety of solid-state batteries using this composite cathode active material. Detailed Implementation

[0019] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0020] Based on the problems existing in related technologies, this application embodiment introduces lithium phosphate nanoparticles doped with rare earth elements as a multifunctional modifier, which can simultaneously solve the problems of structural stability of the active material core and interfacial ion transport. This allows the modified composite positive electrode active material to simultaneously achieve structural stability, interface optimization, and suppression of interfacial side reactions, thereby achieving the triple function of suppressing the volume expansion of the active material core, improving the interfacial ion conductivity, and blocking the diffusion of transition metal ions.

[0021] The application scenarios of the embodiments of this application will be described below first.

[0022] The composite positive electrode active material provided in this application embodiment can be applied to high energy density lithium-ion batteries, especially electric vehicles, large-scale energy storage systems and high-end consumer electronic devices that require high safety and long cycle life.

[0023] This application provides a composite positive electrode active material, comprising: an active material core and a first coating layer covering at least a portion of the surface of the active material core, wherein the first coating layer comprises lithium phosphate nanoparticles doped with rare earth elements; the rare earth elements include one or more of Y, Nd, and La.

[0024] For example, the active material core can be lithium nickel cobalt manganese oxide (NCM), or a composite core formed by lithium cobalt oxide (LCO) and lithium manganese oxide (LMO). Among them, lithium nickel cobalt manganese oxide can be NCM811.

[0025] For example, in the first coating layer, the doped rare earth elements are used to regulate the lattice structure of the lithium phosphate nanoparticles.

[0026] In the composite positive electrode active material provided in this application embodiment, by modifying the core of the active material with lithium phosphate nanoparticles including rare earth elements, the following beneficial effects can be achieved:

[0027] 1) By filling the composite positive electrode active material with the rigid crystal structure of lithium phosphate nanoparticles or coating at least part of the surface of the core of the positive electrode active material, it can serve as a structural support point to suppress the volume expansion of the active material core, avoid cracking of the composite positive electrode active material, and improve the structural stability of the composite positive electrode active material.

[0028] 2) Rare earth elements can be used to adjust the interfacial charge distribution of composite cathode active materials, thereby reducing lithium ion concentration. This reduces the migration barrier, thereby lowering the interfacial impedance between the composite cathode active material and the solid electrolyte, and improving the interfacial ionic conductivity and ion transport efficiency of the composite cathode active material.

[0029] 3) Lithium phosphate nanoparticles exhibit good chemical compatibility with both positive electrode active materials and solid electrolytes, and can block transition metal ions (such as...). , The diffusion of the composite positive electrode active material into the solid electrolyte reduces the interfacial side reactions between the composite positive electrode active material and the solid electrolyte, thereby reducing the formation of a high-resistivity interfacial phase between the composite positive electrode active material and the solid electrolyte.

[0030] It is understood that the composite cathode active material provided in this application embodiment can simultaneously achieve multiple functions such as suppressing volume expansion, reducing interface impedance, and reducing interface side reactions, avoiding performance trade-offs caused by single improvements (such as sacrificing energy density for impedance reduction), thereby improving the energy density, cycle stability, and safety of solid-state batteries using this composite cathode active material.

[0031] For example, in one possible implementation, the first coating layer provided in this application embodiment can be a combination of bulk doping and surface coating, that is, the first coating layer can be a core-shell structure modifier to further enhance the functional synergy of the composite positive electrode active material.

[0032] For example, the first coating layer includes a lithium phosphate nanoparticle core doped with rare earth elements, and a rare earth element coating layer covering at least a portion of the surface of the lithium phosphate nanoparticle core doped with rare earth elements.

[0033] It is understood that the first coating layer provided in this application embodiment adopts a core-shell structure modification strategy that combines bulk doping and surface coating. Its core is lithium phosphate nanoparticles doped with rare earth elements, and the shell is a rare earth element coating layer that coats at least part of the surface of the core of the lithium phosphate nanoparticles doped with rare earth elements. This can synergistically improve the ion conduction performance or electronic conduction performance of the composite positive electrode active material, as well as the cycle stability, while taking into account high capacity and high rate characteristics.

[0034] Optionally, in one specific embodiment, the molar amount of rare earth element doping is 0.5%-2% of the molar amount of lithium phosphate nanoparticles.

[0035] It is understandable that the doping mode of rare earth elements in the first coating layer of lithium phosphate nanoparticles can be lattice substitution doping, i.e., rare earth element ions (such as...) , , Uniform doping can be achieved by replacing lithium ions in the lithium phosphate lattice without destroying the crystal structure of lithium phosphate, thus realizing the lattice control of lithium phosphate through rare earth elements.

[0036] For example, the molar amount of rare earth element doping can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% of the molar amount of lithium phosphate nanoparticles, or any combination thereof.

[0037] Optionally, in one possible implementation, the particle size D50 of the lithium phosphate nanoparticles is 50 nm-100 nm.

[0038] For example, the particle size D50 of lithium phosphate nanoparticles can be a range of 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or any combination thereof.

[0039] Optionally, in one possible implementation, the composite cathode material provided in this application embodiment further includes: a second coating layer covering at least a portion of the surface of the active material core, wherein the first coating layer covers at least a portion of the surface of the second coating layer; the second coating layer includes alumina and / or zirconium oxide.

[0040] For example, in the composite positive electrode active material provided in the embodiments of this application, a second coating layer can be coated on at least a portion of the surface of the active material core by atomic layer deposition (ALD) technology, and a first coating layer can be further coated on at least a portion of the surface of the second coating layer to obtain a composite positive electrode active material with dual coating layers.

[0041] For example, in some embodiments, the second coating layer may include aluminum oxide ( In some embodiments, the second cladding layer may include zirconium oxide (ZrO2). In some embodiments, the second coating layer may include alumina and zirconium oxide.

[0042] Optionally, in one specific embodiment, the thickness of the second coating layer can be 0.5nm-10nm.

[0043] For example, the thickness of the second coating layer can be a range of 0.5nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, or any combination thereof.

[0044] It is understood that in the composite positive electrode active material provided in the embodiments of this application, by coating at least part of the surface of the active material core with a second coating layer, the direct contact between the active material core and the solid electrolyte can be initially blocked, thereby reducing the interfacial side reactions between the active material core and the solid electrolyte.

[0045] Optionally, in one possible implementation, the active material core comprises lithium nickel cobalt manganese oxide, or a composite core formed by combining lithium cobalt oxide and lithium manganese oxide.

[0046] For example, lithium nickel cobalt manganese oxide can be used as the core of lithium nickel cobalt manganese oxide positive electrode active material. Its specific composition includes, but is not limited to, the molar ratio of nickel, cobalt and manganese, element doping modification scheme and crystal morphology. The embodiments of this application do not limit the above composition, and can be determined according to the actual application requirements.

[0047] For example, lithium nickel cobalt manganese oxide can be NCM111, NCM523, NCM622, NCM811, etc.

[0048] For example, in a composite core formed by lithium cobalt oxide and lithium manganese oxide, lithium cobalt oxide can be used as the active host, and lithium manganese oxide can be compounded to form the core.

[0049] For example, in the composite core formed by lithium cobalt oxide and lithium manganese oxide, the mass percentage of lithium cobalt oxide and lithium manganese oxide is 65%-95%: 5%-35%.

[0050] For example, the mass percentages of lithium cobalt oxide and lithium manganese oxide in the composite core formed by the combination of lithium cobalt oxide and lithium manganese oxide can be 65%:35%, 70%:30%, 75%:25%, 80%:20%, 85%:15%, 90%:10%, 95%:5%, or any combination thereof.

[0051] It is understandable that by compounding lithium manganese oxide with lithium cobalt oxide, the stability of the spinel structure of lithium manganese oxide (volume expansion rate <2%) can be utilized to alleviate the volume fluctuation of lithium cobalt oxide.

[0052] Optionally, this application embodiment also provides a method for preparing the composite positive electrode active material provided in the above embodiment. The preparation method includes: dispersing rare earth element-doped lithium phosphate nanoparticles and an active material core coated with a second coating layer in a solvent at a certain mass percentage, performing ultrasonic dispersion treatment, and then performing vacuum drying and molding sintering in sequence to obtain the composite positive electrode active material.

[0053] The second coating layer is similar to that described above, and will not be repeated here.

[0054] For example, in one possible implementation, rare earth element-doped lithium phosphate nanoparticles can be prepared by: , , Dissolved in deionized water at a molar ratio of 3:1:0.01, stirred at 70°C for 3 hours to generate a precursor; heated to 700°C at 8°C / min under an Ar atmosphere and held for 4 hours, the precursor was obtained. Doped lithium phosphate nanoparticles.

[0055] The preparation methods for lithium phosphate nanoparticles doped with rare earth elements such as Nd and La are similar to those described above, and will not be repeated here.

[0056] For example, the solvent used to disperse rare earth element-doped lithium phosphate nanoparticles and the active material core coated with a second coating layer can be an organic solvent, such as anhydrous ethanol.

[0057] Optionally, in one possible implementation, the ultrasonic power in the ultrasonic dispersion process can be 200W-300W.

[0058] Preferably, in one possible implementation, the ultrasonic power can be 250 W.

[0059] Optionally, in one possible implementation, the ultrasonic time in the ultrasonic dispersion process can be 30 min to 60 min.

[0060] Preferably, in one possible implementation, the ultrasound time can be 45 minutes.

[0061] Understandably, the ultrasonic treatment conditions described above are intended to ensure that rare earth element-doped lithium phosphate nanoparticles can be uniformly coated on at least a portion of the surface of the active material core, thereby preventing the aggregation of rare earth element-doped lithium phosphate nanoparticles.

[0062] Optionally, in one specific embodiment, the vacuum drying temperature is 60℃-80℃, the vacuum degree is -0.09MPa-0.1MPa, and the vacuum drying time is 8h-12h.

[0063] For example, the temperature for vacuum drying can be 60°C, 65°C, 70°C, 75°C, 80°C, or any combination thereof.

[0064] For example, the vacuum level can be a range of -0.09 MPa, -0.08 MPa, -0.07 MPa, -0.06 MPa, -0.05 MPa, -0.04 MPa, -0.03 MPa, -0.02 MPa, -0.01 MPa, 0.01 MPa, 0.02 MPa, 0.03 MPa, 0.04 MPa, 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.1 MPa, or any combination thereof.

[0065] For example, the drying time can be a range of 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, or any combination thereof.

[0066] Understandably, the above-mentioned vacuum drying conditions can ensure the complete removal of solvents, preventing the generation of bubbles during subsequent sintering and thus avoiding damage to the structure of the composite positive electrode active material.

[0067] Optionally, in one specific embodiment, the specific implementation of molding and sintering the mixed powder of vacuum-dried rare-earth element-doped lithium phosphate nanoparticles and an active material core coated with a second coating layer can be as follows: the mixed powder is pre-pressed and then sintered under an inert atmosphere to obtain a composite positive electrode active material.

[0068] Optionally, in one specific embodiment, the pre-compression pressure is 10MPa-20MPa.

[0069] For example, the pre-compression pressure can be a range of 10 MPa, 12 MPa, 14 MPa, 16 MPa, 18 MPa, 20 MPa, or any combination thereof.

[0070] For example, the inert atmosphere can be an argon atmosphere.

[0071] Optionally, in one specific embodiment, the purity of the inert gas in the inert atmosphere is ≥99.999%, and the oxygen content in the inert atmosphere is <0.1ppm.

[0072] Optionally, in one specific embodiment, the sintering temperature of the sintering reaction is 300℃-400℃.

[0073] For example, the sintering temperature can be a range of 300°C, 350°C, 400°C, or any combination thereof.

[0074] Understandably, the above-mentioned molding and sintering conditions can prevent the structure of the active material core from being destroyed by high temperatures.

[0075] In this embodiment, rare earth element-doped lithium phosphate nanoparticles and an active material core coated with a second coating layer are dispersed in a solvent at a certain mass percentage. After ultrasonic dispersion treatment, they are sequentially vacuum dried and sintered to obtain a composite positive electrode active material that can simultaneously achieve structural stability, interface optimization, and suppression of interface side reactions. This material achieves the triple functions of suppressing the volume expansion of the active material core, improving the interfacial ionic conductivity, and blocking the diffusion of transition metal ions. As a result, the energy density, cycle stability, and safety of solid-state batteries using this composite positive electrode active material can be improved.

[0076] Optionally, in one specific embodiment, the mass percentage of rare earth element-doped lithium phosphate nanoparticles and active material cores coated with a second coating layer is 1%:99%-10%:90%.

[0077] For example, the mass percentage of rare earth element-doped lithium phosphate nanoparticles and active material cores coated with a second coating layer can be 1%:99%, 2%:98%, 3%:97%, 4%:96%, 5%:95%, 6%:94%, 7%:93%, 8%:92%, 9%:91%, 10%:90%, or any combination thereof.

[0078] The method for preparing composite positive electrode active materials provided in this application is suitable for large-scale industrial production and can accelerate the application of high-energy-density and high-safety solid-state batteries.

[0079] Optionally, embodiments of this application provide a composite positive electrode sheet, comprising: a positive current collector and a composite positive active material layer, wherein the composite positive active material layer comprises the composite positive active material provided in the above embodiments, or comprises the composite positive active material prepared by the preparation method provided in the above embodiments.

[0080] For example, in one possible implementation, the composite positive electrode active material layer can be prepared by using a "ultrasonic dispersion-vacuum drying-low temperature sintering" process, and the specific preparation method may include the following steps:

[0081] 1) Weigh the composite positive electrode active material, solid electrolyte, conductive agent and binder according to a certain mass percentage ratio, add solvent and mix, then ultrasonically disperse the mixture for 30 min - 60 min (preferably ultrasonic dispersion time can be 45 min) with an ultrasonic power of 200W-300W (preferably ultrasonic power can be 250W) to obtain composite positive electrode slurry;

[0082] 2) The composite cathode slurry is vacuum dried for 8-12 hours (preferably 10 hours) at a vacuum temperature of 60℃-80℃ (preferably 75℃) and a vacuum degree of -0.09MPa-0.1MPa (preferably -0.085MPa) to completely remove the solvent from the composite cathode slurry, thereby obtaining the dried composite cathode mixed powder;

[0083] 3) The composite cathode mixed powder obtained in step 2) is pre-pressed under a pressure of 10 MPa - 20 MPa (preferably 15 MPa), and then sintered for 3 hours in an inert atmosphere (purity ≥ 99.999%, oxygen content < 0.1 ppm) at a sintering temperature of 300℃-400℃ (preferably 350℃) to obtain the composite cathode active material layer.

[0084] For example, the solid electrolyte in the composite positive electrode active material layer can be a composite system of lithium lanthanum zirconate (LLZO) oxide and lithium phosphorus sulfur compound (LPS).

[0085] Experiments show that in the composite positive electrode active material layer provided in this application embodiment, the interfacial impedance between the composite positive electrode active material and the solid electrolyte can be reduced to 200Ω·cm²-500Ω·cm², taking into account both high energy density and ion transport efficiency.

[0086] For example, the thickness of the composite cathode sheet in a solid-state battery can be 100 μm. This application does not limit the thickness of the composite cathode sheet in a solid-state battery; the specific thickness can be determined according to actual application requirements.

[0087] It is understood that the embodiments of this application prepare the composite positive electrode active material layer by using the "ultrasonic dispersion-vacuum drying-low temperature sintering" process. Ultrasonic dispersion is used to ensure that the rare earth element-doped lithium phosphate nanoparticles in the composite positive electrode active material can be uniformly coated on the surface of the solid electrolyte, avoiding particle agglomeration. Vacuum drying is used to completely remove the solvent and prevent the generation of bubbles during the subsequent sintering process, which would damage the structure of the composite positive electrode active material layer. Low temperature sintering is used to avoid the destruction of the structure of the composite positive electrode active material by high temperature. At the same time, it can make the solid electrolyte and the composite positive electrode active material form a close contact, reducing the interfacial resistance.

[0088] It is understood that the composite positive electrode active material layer provided in this application embodiment is prepared by low-temperature sintering (300℃-400℃) and conventional ultrasonic dispersion equipment, which does not require special high-end equipment, is easy to scale up and mass-produce, and has process feasibility.

[0089] Optionally, embodiments of this application also provide a solid-state battery, including: a negative electrode, a solid electrolyte layer, and a composite positive electrode as provided in the above embodiments, wherein the solid electrolyte layer is disposed between the negative electrode and the composite positive electrode.

[0090] For example, the negative electrode can be a lithium metal (Li) sheet with high energy density, a lithium-carbon (Li-C) composite negative electrode with better cycle stability, or a silicon (Si) based negative electrode with lower cost.

[0091] For example, the solid electrolyte in the solid electrolyte layer can be the same as the solid electrolyte in the composite positive electrode active material layer, which can be a composite system of lithium lanthanum zirconate (LLZO) oxide and lithium phosphorus sulfur compound (LPS).

[0092] Understandably, lithium lanthanum zirconate has high ionic conductivity (ionic conductivity > 100% at room temperature). With high stability and a conductivity of S / cm, lithium phosphorus-sulfur can fill the gaps between lithium lanthanum zirconate particles, forming a continuous ion transport network, thus increasing the ionic conductivity of the composite solid electrolyte to [value missing] at room temperature. S / cm - S / cm can balance ion transport efficiency and stability.

[0093] Optionally, in one specific embodiment, the thickness of the solid electrolyte layer is 10μm-30μm.

[0094] For example, the thickness of the solid electrolyte layer can be 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm or any combination thereof.

[0095] It is understood that in the solid-state battery provided in this application embodiment, by setting the solid electrolyte in the solid electrolyte layer to be consistent with the solid electrolyte in the composite positive electrode, and the thickness of the solid electrolyte layer to be 10μm-30μm, the efficient transport of lithium ions between the composite positive electrode and the negative electrode is ensured, while avoiding the superposition of interlayer interface impedance.

[0096] In one specific implementation, the assembly process of the solid-state battery can be: in an inert glove box ( , The negative electrode, solid electrolyte layer and composite positive electrode are hot-pressed and encapsulated in a solution with a content of <0.1ppm. A pressure of 5MPa-10MPa is applied at 60℃-100℃ to make the layers of the negative electrode, solid electrolyte layer and composite positive electrode tightly bonded together, reducing the interfacial gaps, and thus obtaining a solid-state battery.

[0097] In one specific implementation, the solid-state battery can be an all-solid-state battery.

[0098] It is understood that solid-state batteries incorporating the composite cathode provided in the embodiments of this application can achieve a synergistic improvement in high energy density, long cycle life, and high safety.

[0099] Experiments show that solid-state batteries using the composite positive electrode active material provided in the embodiments of this application have the following core performance advantages:

[0100] 1) High energy density: With a composite positive electrode active material accounting for 60-80% and a matching lithium metal negative electrode, the energy density of solid-state batteries can reach 400Wh / kg-450Wh / kg, which is more than 50% higher than the energy density of traditional liquid lithium batteries (such as 250Wh / kg-300Wh / kg);

[0101] 2) High cycle stability: The solid-state battery retains ≥78% capacity after 500 cycles at 25℃ and 1C rate. Its cycle stability is far superior to that of solid-state batteries without rare earth element doping lithium phosphate nanoparticles (such as capacity retention <60% after 500 cycles).

[0102] 3) High safety: The solid electrolyte is non-flammable, and the rare earth element-doped lithium phosphate nanoparticles improve the thermal stability of the composite positive electrode active material. The thermal runaway temperature of the solid battery is ≥200℃ (the thermal runaway temperature of the traditional liquid lithium battery is about 170℃-180℃). After 100 hours of storage at 150℃, the capacity decay is ≤5%, which meets the high temperature safety requirements of power batteries.

[0103] This application also provides a battery assembly, including at least two solid-state batteries as described in the above embodiments.

[0104] For example, the battery assembly can be a battery pack or a battery module, etc.

[0105] This application also provides an electrical device, including: a solid-state battery as provided in the above embodiments, or a battery assembly as provided in the embodiments.

[0106] This application does not specifically limit the electronic device, which can be any electrical device including the battery, including but not limited to mobile phones, portable devices, laptops, electric bicycles, electric cars, electric toys, and energy storage devices.

[0107] The following detailed description, through specific embodiments, illustrates the composite positive electrode active material, its preparation method, and its application provided in this application.

[0108] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0109] Example 1

[0110] This embodiment provides a composite positive electrode active material, the preparation method of which includes the following steps:

[0111] 1) Y-doped lithium phosphate nanoparticles ( ) and at least part of the surface is covered with The NCM layer was dispersed in anhydrous ethanol at a mass percentage of 5%:95% and mixed to obtain a mixture, wherein the molar amount of Y element was 1% of the molar amount of lithium phosphate nanoparticles, and the particle size D50 of lithium phosphate nanoparticles was 60 nm. The layer thickness is 1 nm;

[0112] 2) The mixture was ultrasonically dispersed for 45 minutes using an ultrasonic power of 250W to obtain the ultrasonically dispersed mixture.

[0113] 3) The mixture obtained in step 2) was vacuum dried for 10 h at a vacuum temperature of 75℃ and a vacuum degree of -0.085MPa to obtain a dried mixed powder;

[0114] 4) The mixed powder was pre-pressed under a pressure of 15 MPa and then sintered at 350°C for 3 hours under an inert atmosphere to obtain the composite positive electrode active material.

[0115] Example 2

[0116] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the molar amount of Y element is 0.5% of the molar amount of lithium phosphate nanoparticles.

[0117] Example 3

[0118] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the molar amount of Y element is 1.5% of the molar amount of lithium phosphate nanoparticles.

[0119] Example 4

[0120] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the molar amount of Y element is 2% of the molar amount of lithium phosphate nanoparticles.

[0121] Example 5

[0122] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the particle size D50 of the lithium phosphate nanoparticles is 50 nm.

[0123] Example 6

[0124] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the particle size D50 of the lithium phosphate nanoparticles is 80 nm.

[0125] Example 7

[0126] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the particle size D50 of the lithium phosphate nanoparticles is 100 nm.

[0127] Example 8

[0128] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the Y-doped lithium phosphate nanoparticles are replaced with Nd-doped lithium phosphate nanoparticles. ).

[0129] Example 9

[0130] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that the Y-doped lithium phosphate nanoparticles are replaced with La-doped lithium phosphate nanoparticles. ).

[0131] Example 10

[0132] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that of Example 1. The difference is that the core of the active material is replaced by a complex of LCO and LMO, wherein the mass ratio of LCO to LMO is 80%:20%.

[0133] Comparative Example 1

[0134] This embodiment provides a positive electrode active material, the preparation method of which is basically the same as that in Example 1, except that at least part of the surface is coated with a The NCM layer was dispersed in anhydrous ethanol and mixed to obtain a mixture, wherein, The thickness of the layer is 1 nm.

[0135] Comparative Example 2

[0136] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that of Example 1, except that the Y-doped lithium phosphate nanoparticles are replaced with lithium phosphate nanoparticles.

[0137] Comparative Example 3

[0138] This embodiment provides a composite positive electrode active material, the preparation method of which is basically the same as that in Example 10, except that at least part of the surface is coated with... The LCO and LMO complex layer was dispersed in anhydrous ethanol and mixed to obtain a mixture, wherein... The thickness of the layer is 1 nm.

[0139] Test case

[0140] For the composite positive electrode active materials prepared in the above embodiments and comparative examples, the electrochemical performance, impedance, thermal runaway temperature, and capacity decay rate of solid-state batteries containing the composite positive electrode active materials were tested using the following test methods.

[0141] First, the preparation method of solid-state batteries will be explained.

[0142] The composite positive electrode active materials prepared in the above embodiments and comparative examples are mixed with a solid electrolyte and added to the composite positive electrode to obtain a composite positive electrode sheet. The solid electrolyte serves as the solid electrolyte layer, and lithium metal is used as the negative electrode sheet to assemble a solid-state battery. The preparation of this solid-state battery specifically includes the following steps:

[0143] 1) Preparation of composite positive electrode:

[0144] A composite positive electrode active material, a composite electrolyte of lithium lanthanum zirconate oxide and lithium phosphorus sulfur compound, a conductive agent (vapor-grown carbon fiber (VGCF)), and a binder (polytetrafluoroethylene (PTFE)) are mixed in a mass ratio of 80:17.5:2:0.5 to prepare a composite positive electrode active material layer. The composite positive electrode active material layer is then combined with stainless steel to form a composite positive electrode sheet.

[0145] 2) Lithium metal is used as the negative electrode;

[0146] 3) Preparation of the solid electrolyte layer:

[0147] A solid electrolyte layer was prepared by thoroughly mixing a composite electrolyte of lithium lanthanum zirconate oxide and lithium phosphorus sulfur compound with a binder (PTFE) at a mass ratio of 99.5:0.5.

[0148] 4) In a glove box, the composite positive electrode, solid electrolyte layer and negative electrode are stacked in sequence and hot-pressed into an aluminum-plastic film at a temperature of 80℃ and a pressure of 550Mpa to obtain a solid battery.

[0149] The following describes the testing methods for the electrochemical performance, impedance, thermal runaway temperature, and capacity decay rate of solid-state batteries after 100 hours of storage at 150°C.

[0150] 1. The electrochemical performance testing of solid-state batteries specifically includes the following steps:

[0151] 1) First charge-discharge test: The solid-state battery was tested at 25℃ with a constant current of 0.1C for 1 cycle, with a voltage range of 2.7 V - 4.5 V;

[0152] 2) Cyclic test: The solid-state battery is subjected to 500 cycles of 1C constant current charge and discharge at 25℃, with a voltage range of 2.7 V - 4.5 V.

[0153] 2. Impedance testing of solid-state batteries:

[0154] A multi-channel electrochemical workstation was used, at a frequency of Impedance tests were performed on solid-state batteries under a voltage amplitude of 5mV.

[0155] 3. The thermal runaway temperature test for solid-state batteries specifically includes the following steps:

[0156] 1) Sample pretreatment

[0157] Select ≥3 fully charged solid-state battery samples to ensure repeatability, and let them stand for 24 hours at room temperature 25℃±2℃ and humidity 45%±5%. Record the initial voltage, mass, size and other parameters of the solid-state battery.

[0158] 2) Build a test system

[0159] Place the solid-state battery in an adiabatic accelerating rate calorimeter (ARC) or a differential scanning calorimeter (DSC). Fix the solid-state battery according to the test requirements. For example, for cell-level testing, ensure that the solid-state battery is in close contact with the thermocouple (one temperature measurement point is arranged on the positive electrode, one on the negative electrode, and one on the casing).

[0160] 3) Heating program settings

[0161] The stepped heating-constant temperature-waiting mode is adopted: the initial heating rate is 5℃ / min - 10℃ / min, and after reaching the set temperature (e.g., 50℃), the temperature is held for 10 minutes to monitor the temperature change of the solid-state battery; if there is no obvious heat release, the temperature continues to rise, with each step increasing by 5℃-10℃, until the solid-state battery exhibits self-heating (temperature deviates from the set value by ≥2℃).

[0162] 4) Data monitoring and recording

[0163] The system collects data on solid-state battery temperature, voltage, heat release rate, and gas generation in real time throughout the process. It focuses on recording the initial heat release temperature (Tonset) (the critical temperature at which the battery begins to release heat), the temperature corresponding to the maximum temperature rise rate (Tmax), and the final thermal runaway temperature. At the same time, it observes whether the solid-state battery exhibits phenomena such as swelling, smoke, fire, or explosion.

[0164] 5) Post-test processing

[0165] After the test, the system was allowed to cool to room temperature. The solid-state battery sample was then removed, and its appearance and morphology were observed. The thermal runaway characteristic curve was plotted in combination with the test data, and the thermal stability and thermal runaway mechanism of the solid-state battery were analyzed.

[0166] 6) Repeatability verification

[0167] Repeat the above test more than 3 times for the same batch of solid-state batteries, remove abnormal data, and take the average value as the final test result to ensure the reliability of the data.

[0168] 4. The capacity decay rate test of solid-state batteries at 150℃ for 100 hours specifically includes the following steps:

[0169] 1) Sample pretreatment

[0170] Select at least three solid-state battery samples from the same batch, fully charged, to ensure repeatability; allow them to stand for 24 hours at room temperature (25℃±2℃) and humidity (45%±5%), and record the initial parameters of the solid-state batteries, such as the initial discharge capacity (…). ), voltage, mass, and size.

[0171] 2) High-temperature storage test

[0172] The pretreated solid-state battery was placed in a high-temperature chamber, and the internal temperature was set to 150℃±2℃. The timer was started and the temperature was maintained for 100 hours. During storage, the solid-state battery was protected from external short circuits and compression. The temperature stability of the high-temperature chamber and the appearance of the solid-state battery were checked every 24 hours (whether it was bulging, leaking, or smoking).

[0173] 3) Sample post-processing

[0174] After 100 hours of storage, close the high-temperature chamber and allow the solid-state battery to cool naturally to room temperature of 25℃±2℃. Then, let it stand for another 24 hours. After cooling, observe and record the changes in the appearance of the solid-state battery (such as whether there is deformation or cracks).

[0175] 4) Capacity retest

[0176] The solid-state battery was discharged under the same discharge regime (discharge rate and cutoff voltage) as the initial capacity test, and the discharge capacity of the solid-state battery after storage was recorded. ).

[0177] 5) Data calculation and repeatability verification

[0178] The capacity decay rate of a single solid-state battery is calculated according to the formula. The average value of the test data of all samples in the same batch is taken, outliers are removed, and the capacity decay rate of the batch of batteries after 100 hours of storage at 150°C is finally determined.

[0179] in, .

[0180] Table 1 shows the parameters corresponding to the various embodiments and comparative examples provided in this application.

[0181] Table 1

[0182]

[0183] Table 2 shows the test results of the electrochemical performance, impedance, thermal runaway temperature, and capacity decay rate of the solid-state battery after 100 hours of storage at 150°C.

[0184] Table 2

[0185]

[0186] The following conclusions can be drawn from Tables 1 and 2:

[0187] 1) As can be seen from the results of Examples 1 to 7, and Comparative Examples 1 and 2, compared with NCM as the positive electrode active material and the positive electrode active material obtained by combining NCM with lithium phosphate nanoparticles, the composite positive electrode active material provided in this application can achieve the triple functions of inhibiting the volume expansion of the active material core, improving the interfacial ionic conductivity, and blocking the diffusion of transition metal ions. Accordingly, the first discharge specific capacity, 500-cycle capacity retention rate, and thermal runaway temperature of the solid-state battery using the composite positive electrode active material provided in this application are significantly improved, and the capacity decay rate and impedance after 100h storage at 150°C are significantly reduced, thereby improving the energy density, cycle stability, and safety of the solid-state battery using the composite positive electrode active material.

[0188] 2) As can be seen from the results of Examples 1 to 4, as the percentage of rare earth element doping molar amount to lithium phosphate molar amount increases, the overall performance of the solid-state battery first increases and then decreases, and the overall performance of the solid-state battery is best when the rare earth element doping molar amount is 1% of the lithium phosphate nanoparticle molar amount.

[0189] 3) As can be seen from the results of Examples 1, 5 to 7, as the particle size D50 of lithium phosphate nanoparticles increases, the overall performance of the corresponding solid-state battery first increases and then decreases, and the overall performance of the corresponding solid-state battery is best when the particle size D50 of lithium phosphate nanoparticles is 60nm.

[0190] 4) The results of Examples 1, 8 and 9 show that different rare earth elements Y, Nd and La can all modify the core of the active material, and the energy density, cycle stability and safety of the corresponding solid-state battery are significantly improved.

[0191] 5) As can be seen from the results of Examples 1 and 10, lithium sulfate nanoparticles doped with rare earth elements can modify the core of different active materials such as NCM and LCO-LMO, and the energy density, cycle stability and safety of the corresponding solid-state battery are significantly improved.

[0192] 6) As can be seen from the results of Example 10 and Comparative Example 3, compared with the positive electrode active material being LCO-LMO, the composite positive electrode active material provided in this application embodiment can achieve the triple functions of suppressing the core volume expansion of the active material, improving the interfacial ionic conductivity, and blocking the diffusion of transition metal ions. Accordingly, the energy density, cycle stability, and safety of solid-state batteries using the composite positive electrode active material provided in this application embodiment are significantly improved.

[0193] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A composite positive electrode active material, characterized in that, include: An active material core and a first coating layer covering at least a portion of the surface of the active material core, the first coating layer comprising lithium phosphate nanoparticles doped with rare earth elements; The rare earth elements include one or more of Y, Nd, and La.

2. The composite positive electrode active material according to claim 1, characterized in that, The molar amount of rare earth element doping is 0.5%-2% of the molar amount of lithium phosphate nanoparticles.

3. The composite positive electrode active material according to claim 1, characterized in that, The particle size D50 of the lithium phosphate nanoparticles is 50nm-100nm.

4. The composite positive electrode active material according to any one of claims 1 to 3, characterized in that, Also includes: A second coating layer covering at least a portion of the surface of the core of the active material, wherein the first coating layer covers at least a portion of the surface of the second coating layer; The second coating layer comprises alumina and / or zirconium oxide.

5. The composite positive electrode active material according to any one of claims 1 to 3, characterized in that, The active material core includes lithium nickel cobalt manganese oxide, or a composite core formed by lithium cobalt oxide and lithium manganese oxide.

6. A method for preparing a composite positive electrode active material as described in any one of claims 1 to 5, characterized in that, The preparation method includes: Rare earth element-doped lithium phosphate nanoparticles and an active material core coated with a second coating layer are dispersed in a solvent at a certain mass percentage. After ultrasonic dispersion treatment, they are successively vacuum dried and sintered to obtain the composite positive electrode active material.

7. The preparation method according to claim 6, characterized in that, The mass percentage of the rare earth element-doped lithium phosphate nanoparticles and the active material core coated with the second coating layer is 1%:99%-10%:90%.

8. A composite positive electrode, characterized in that, include: A positive current collector and a composite positive active material layer, wherein the composite positive active material layer comprises the composite positive active material as described in any one of claims 1 to 5, or comprises the composite positive active material prepared by the preparation method described in claim 6 or 7.

9. A solid-state battery, characterized in that, include: The negative electrode, the solid electrolyte layer, and the composite positive electrode as described in claim 8, wherein the solid electrolyte layer is disposed between the negative electrode and the composite positive electrode.

10. An electrical appliance, characterized in that, include: The solid-state battery as described in claim 9.

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