Positive electrode material, preparation method thereof, positive electrode sheet, and secondary battery

Abstract

The application relates to the technical field of batteries, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet and a secondary battery. The positive electrode material comprises secondary particle material; the secondary particle material is obtained by stacking primary particle material, the primary particle material comprises nickel-cobalt-aluminum ternary material, the primary particle material is at least partially coated with a Li-Mo-O coating layer; and the secondary particle material is at least partially coated with a Li-Hf-O coating layer. The positive electrode material has strong structural stability and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet and a secondary battery. BACKGROUND

[0002] Lithium ion batteries are attracting more and more attention in the fields of portable electronic products, electric tools and electric vehicles. For electric vehicles, the power battery is naturally the core part of the vehicle, which makes the research results of battery materials emerge in an endless stream. Among them, nickel cobalt manganese (NCM) and nickel cobalt aluminum (NCA) ternary positive electrode materials are considered to be the main positive electrode materials of the next generation of batteries due to their high energy density. At the interface between high-nickel positive electrode materials and sulfide solid-state electrolytes, due to the chemical instability of Ni 4+ and the high voltage platform of the positive electrode material, side reactions occur at the interface. These reactions will convert the surface of the positive electrode material from a layered structure to a rock salt structure, accompanied by the decomposition of the solid-state electrolyte, thereby hindering the transport of lithium ions, leading to capacity decay. With the increase of Ni content, this surface degradation problem becomes more and more serious. In addition, high-nickel positive electrode materials undergo significant anisotropic lattice volume changes during charging and discharging, resulting in micro-cracks in the secondary particles. In liquid electrolyte batteries, these micro-cracks can be maintained by electrolyte penetration, but in all-solid-state batteries, solid electrolyte cannot penetrate into these cracks, resulting in the loss of contact between the internal particles and the electrolyte, thereby becoming electrochemically inert, further exacerbating capacity decay. In addition, due to the dramatic volume change of high-nickel positive electrode materials during charging and discharging, the contact between the positive electrode material particles and the solid electrolyte is lost. This disengagement phenomenon is exacerbated with the increase of Ni content, further hindering the transport of lithium ions, leading to rapid capacity decay.

[0003] In view of the above problems, structure optimization, doping, coating and other methods have certain improvement on the electrochemical performance of high-nickel positive electrode materials. However, the use of only one modification strategy has a single effect, and the combination of multiple modification strategies has a complex process and difficult preparation process, which is not sufficient to support the application of layered oxide positive electrode materials in solid-state batteries. In addition, due to the need for excess lithium during lithiation, the positive electrode material surface usually has high residual lithium, which affects its electrochemical performance.

[0004] Therefore, it is urgent to provide a preparation method of layered positive electrode material with one-step realization of surface coating of primary particles and secondary particles, which can have multiple modification effects and reduce the residual lithium on the surface of the material to improve the electrochemical performance of the material. SUMMARY

[0005] Therefore, the present application aims to at least partially solve one of the problems in the related art. To this end, the present application provides a positive electrode material, a preparation method thereof, a positive electrode sheet, and a secondary battery, which have strong structural stability and excellent electrochemical performance.

[0006] To solve the above technical problems, the present application is implemented as follows:

[0007] According to a first aspect of the present application, embodiments of the present application provide a positive electrode material,

[0008] The positive electrode material comprises a secondary particle material;

[0009] The secondary particle material is obtained by stacking primary particle materials, the primary particle materials comprising nickel-cobalt-aluminum ternary materials, and the primary particle materials being at least partially coated with a Li-Mo-O coating layer;

[0010] The secondary particle material is at least partially coated with a Li-Hf-O coating layer.

[0011] In some embodiments, the particle size of the primary particle material is 10 nm to 300 nm.

[0012] In some embodiments, the thickness of the primary particle material coating layer is 1 nm to 3 nm.

[0013] In some embodiments, the particle size of the secondary particle material is 4 μm to 12 μm.

[0014] In some embodiments, the thickness of the secondary particle material coating layer is 2 nm to 5 nm.

[0015] According to a second aspect of the present application, embodiments of the present application provide a preparation method of a positive electrode material, comprising the following steps:

[0016] After adjusting the pH value of a solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt, and molybdenum salt to alkaline with alkali, performing a co-precipitation reaction, and aging to obtain a precursor material;

[0017] Mixing the precursor material with a lithium salt, and calcining to obtain the positive electrode material.

[0018] In some embodiments, the molar ratio of the nickel salt, the cobalt salt, the aluminum salt, the hafnium salt, and the molybdenum salt is (0.8-1):(0.03-0.08):(0.03-0.08):(0.01-0.03):(0.01-0.03).

[0019] In some embodiments, the solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt and molybdenum salt is prepared by mixing solution I containing nickel salt and cobalt salt, solution II containing aluminum salt, solution III containing hafnium salt and solution IV containing molybdenum salt. Preferably, the total molar concentration of nickel salt and cobalt salt in solution I is 1.5 mol / L to 4 mol / L.

[0020] In some embodiments, the concentration of metal salt in solution II, solution III and solution IV is independently 1.5 mol / L to 4 mol / L.

[0021] In some embodiments, the co-precipitation reaction is performed for 30 h to 48 h.

[0022] In some embodiments, the co-precipitation reaction is performed under heating reflux and stirring.

[0023] In some embodiments, the heating reflux is performed at a temperature of 50°C to 65°C.

[0024] In some embodiments, the stirring is performed at a speed of 450 r / min to 750 r / min.

[0025] In some embodiments, the aging is performed at a temperature of 50°C to 65°C for 8 h to 16 h, and the stirring is performed at a speed of 400 r / min to 600 r / min.

[0026] In some embodiments, the molar ratio of the precursor material to lithium salt is 1: (1 to 1.1).

[0027] In some embodiments, the particle size of the precursor material is 4 μm to 12 μm.

[0028] In some embodiments, the calcination is performed in an oxygen atmosphere, and the calcination is performed at a temperature of 700°C to 900°C for 10 h to 25 h.

[0029] In some embodiments, the pH value is adjusted to 10 to 12.

[0030] In some embodiments, the alkali solution includes sodium hydroxide aqueous solution, ammonia water or hexamethylenetetramine aqueous solution.

[0031] In some embodiments, the concentration of the alkali solution is 10 mol / L to 15 mol / L.

[0032] In some embodiments, the nickel salt includes at least one of NiSO4·6H2O, NiCl2 or NiNO3.

[0033] In some embodiments, the cobalt salt comprises at least one of CoSO4·7H2O, CoCl2, or Co(NO3)2.

[0034] In some embodiments, the aluminum salt comprises at least one of AlCl3, Al2(SO4)3, Al(NO3)3, NaAlO2, Al3(SiO3)3, or Al2S3.

[0035] In some embodiments, the hafnium salt comprises at least one of HfCl4, Hf(NO3)4, or HfO4S.

[0036] In some embodiments, the molybdenum salt comprises at least one of MoO 48 H 90 MoO 12 , (NH4)2MoO4, or Na2MoO4.

[0037] In some embodiments, the lithium salt comprises at least one of LiOH·H2O or Li2CO3.

[0038] According to a third aspect of the present application, the embodiments of the present application provide a positive electrode sheet, comprising a positive electrode material, wherein the positive electrode material is the positive electrode material described above or prepared by the preparation method described above.

[0039] According to a fourth aspect of the present application, the embodiments of the present application provide a secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0040] The technical scheme of the present application has at least the following beneficial effects:

[0041] In the embodiments of the present application, the provided positive electrode material comprises secondary particle material; the secondary particle material is obtained by stacking primary particle material, and the primary particle material comprises lithium nickel cobalt aluminum oxide ternary material doped with molybdenum atoms and hafnium atoms. Through the pinning effect of co-doping of molybdenum atoms and hafnium atoms, the structural stability of the lithium nickel cobalt aluminum oxide ternary material is enhanced. Moreover, due to the large atomic radius of molybdenum and hafnium, not all of them can enter the crystal lattice of the lithium nickel cobalt aluminum oxide ternary material for doping, so part of the molybdenum atoms and hafnium atoms will diffuse to the surface of the material during the preparation process. Due to the difference in diffusion mechanism, the molybdenum element will diffuse from the bulk phase to the surface of the primary particle to form a Li-Mo-O coating layer, while the hafnium atoms will diffuse from the bulk phase to the surface of the secondary particle to form an epitaxial layer, which further reacts with the residual lithium on the surface of the epitaxial layer to form a Li-Hf-O coating layer. In addition, since the residual lithium on the surface of the positive electrode material will be consumed, the side reaction between the positive electrode material and the electrolyte can be inhibited. Therefore, the positive electrode material of the present application has excellent electrochemical performance.

[0042] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0043] Figure 1 The image shown is an X-ray diffraction pattern of the cathode material provided in Embodiment 1 of the present invention.

[0044] Figure 2 This is an elemental distribution diagram of the cross-section of the positive electrode material after polishing, provided in Embodiment 1 of the present invention.

[0045] Figure 3 This is a transmission electron microscope (TEM) image of the primary particulate material in the cathode material provided in Embodiment 1 of the present invention.

[0046] Figure 4 This is a transmission electron microscope (TEM) image of the secondary particulate material in the cathode material provided in Embodiment 1 of the present invention. Detailed Implementation

[0047] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0048] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0053] In existing technologies, the electrochemical performance of high-nickel cathode materials is improved through methods such as structural optimization, doping, and coating. However, using only one modification strategy yields limited results, and combining multiple modification strategies is complex and difficult to implement, insufficient to support the application of layered oxide cathode materials in solid-state batteries. Furthermore, the excessive lithium required during lithiation often results in high residual lithium levels on the cathode material surface, affecting its electrochemical performance.

[0054] [Cathode Material]

[0055] In view of this, embodiments of this application provide a cathode material, which includes secondary particulate material;

[0056] Secondary particulate materials are obtained by stacking primary particulate materials. Primary particulate materials include nickel-cobalt-aluminum ternary materials. At least part of the surface of the primary particulate materials is coated with a Li-Mo-O coating layer.

[0057] The secondary particulate material has at least a partial surface coating of Li-Hf-O.

[0058] The phrase "at least a portion of the surface of the primary particulate material is coated with a Li-Mo-O coating layer" means that the Li-Mo-O coating layer can be disposed on a portion of the surface of the primary particulate material or on the entire surface of the primary particulate material. Similarly, "at least a portion of the surface of the secondary particulate material is coated with a Li-Hf-O coating layer" means that the Li-Hf-O coating layer can be disposed on a portion of the surface of the secondary particulate material or on the entire surface of the secondary particulate material. For example, in this embodiment, the Li-Mo-O coating layer can cover the entire surface of the primary particulate material, and the Li-Hf-O coating layer can cover the entire surface of the secondary particulate material. This application does not impose any particular limitations on this, as long as the purpose of this application is achieved.

[0059] In this application, the primary particulate material includes a ternary lithium nickel cobalt aluminum oxide material doped with molybdenum and hafnium atoms. The pinning effect of the co-doping of molybdenum and hafnium atoms enhances the structural stability of the ternary lithium nickel cobalt aluminum oxide material. Furthermore, due to the large atomic radii of molybdenum and hafnium, not all of them can be incorporated into the crystal lattice of the ternary lithium nickel cobalt aluminum oxide material for doping. Therefore, during the preparation process, some molybdenum and hafnium atoms diffuse to the material surface. Due to differences in diffusion mechanisms, molybdenum diffuses from the bulk phase to the surface of the primary particles, forming a Li-Mo-O coating layer, while hafnium atoms diffuse from the bulk phase to the surface of the secondary particles, forming an epitaxial layer. This epitaxial layer then reacts with residual lithium on its surface, forming a Li-Hf-O coating layer. In addition, the consumption of residual lithium on the surface of the cathode material helps suppress side reactions between the cathode material and the electrolyte.

[0060] In this application, the chemical composition of the cathode material can be represented as Li-Hf-O@Li-Mo-O@Li(Ni 0.9 Co 0.05 Al 0.05 ) 1-x-y Hf x Mo y O2, where 0 <x,y≤0.03。

[0061] In some specific embodiments, the particle size of the primary particulate material is 10 nm to 300 nm. For example, the particle size of the primary particulate material can be 10 nm, 50 nm, 150 nm, 200 nm, 250 nm, 300 nm, etc., or any value within the above range; no specific limitation is made here. If the particle size of the primary particulate material is too large, it will result in a larger secondary particle size, leading to a decrease in capacity; if the particle size of the primary particulate material is too small, it will result in an increased specific surface area and an increased rate of capacity decay.

[0062] In some specific embodiments, the thickness of the primary particulate material coating layer is 1 nm to 3 nm. For example, the thickness of the primary particulate material coating layer can be 1 nm, 2 nm, 3 nm, etc., or it can be any value within the above range; no specific limitation is made here. A primary particulate material coating layer thickness within the above range can provide protection while also preventing excessively thick coating layers from increasing battery polarization.

[0063] In some specific embodiments, the particle size of the secondary particulate material is 4μm to 12μm. For example, the particle size of the secondary particulate material can be 4μm, 6μm, 8μm, 10μm, 12μm, etc., or it can be any value within the above range; no specific limitation is made here. If the secondary particles are too small, the specific surface area will increase, resulting in excessively rapid capacity decay; if the secondary particles are too large, the capacity utilization will be lower.

[0064] In some specific embodiments, the thickness of the secondary particulate material coating layer is 2nm to 5nm. For example, the thickness of the secondary particulate material coating layer can be 2nm, 3nm, 4nm, 5nm, etc., or it can be any value within the above range; no specific limitation is made here. A coating layer thickness within the above range can provide protection while also preventing excessively thick coating layers from increasing battery polarization.

[0065] Therefore, based on the above scheme, a cathode material is provided, comprising secondary particle material. The secondary particle material is obtained by stacking primary particle material, which includes a ternary lithium nickel cobalt aluminum oxide material doped with molybdenum and hafnium atoms. The pinning effect of the co-doping of molybdenum and hafnium atoms enhances the structural stability of the ternary lithium nickel cobalt aluminum oxide material. Furthermore, due to the large atomic radii of molybdenum and hafnium, they cannot all enter the crystal lattice of the ternary lithium nickel cobalt aluminum oxide material for doping. Therefore, during the preparation process, some molybdenum and hafnium atoms diffuse to the material surface. Due to the difference in diffusion mechanisms, molybdenum diffuses from the bulk phase to the surface of the primary particles, forming a Li-Mo-O coating layer, while hafnium atoms diffuse from the bulk phase to the surface of the secondary particles, forming an epitaxial layer. This epitaxial layer then reacts with residual lithium on its surface, forming a Li-Hf-O coating layer. In addition, the consumption of residual lithium on the cathode material surface suppresses side reactions between the cathode material and the electrolyte. Therefore, the cathode material of this application exhibits superior electrochemical performance.

[0066] [Preparation methods for cathode materials]

[0067] Based on the same inventive concept, this application provides a method for preparing a cathode material, including the following steps:

[0068] The solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt and molybdenum salt was adjusted to alkaline with alkali solution, and then subjected to co-precipitation reaction and aging to obtain precursor material;

[0069] The precursor material is mixed with lithium salt and calcined to obtain the cathode material.

[0070] It should be understood that all the characteristics and advantages described above regarding "cathode materials" also apply to the "preparation method of cathode materials," and will not be repeated here.

[0071] In some specific embodiments, the pH value during the co-precipitation reaction and the feed rate can affect the particle size of the cathode material. Those skilled in the art can adjust the pH value and the feed rate of the raw materials as needed to control the particle size of the cathode material. This application does not impose any particular limitation on this.

[0072] In some specific embodiments, the molar ratio of nickel salt, cobalt salt, aluminum salt, hafnium salt, and molybdenum salt is (0.8~1):(0.03~0.08):(0.03~0.08):(0.01~0.03):(0.01~0.03). As an example, the molar ratio of nickel salt, cobalt salt, aluminum salt, hafnium salt, and molybdenum salt can be 0.8:0.03:0.03:0.01:0.01, 0.9:0.05:0.06:0.02:0.02, 1:0.08:0.08:0.03:0.03, etc., or any ratio within the above range, without specific limitation.

[0073] In some specific embodiments, the preparation of a solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt, and molybdenum salt includes: mixing a solution I containing nickel salt and cobalt salt, a solution II containing aluminum salt, a solution III containing hafnium salt, and a solution IV containing molybdenum salt.

[0074] In some specific embodiments, the total molar concentration of nickel and cobalt salts in solution I is 1.5 mol / L to 4 mol / L. As an example, the total molar concentration of nickel and cobalt salts in solution I can be 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, etc., or it can be a value within the above range, without being specifically limited here.

[0075] In some specific embodiments, the concentration of aluminum salt in solution II is 1.5 mol / L to 4 mol / L. As an example, the concentration of aluminum salt in solution II can be 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, etc., or it can be a value within the above range, without being specifically limited here.

[0076] In some specific embodiments, the concentration of hafnium salt in solution III is 1.5 mol / L to 4 mol / L. As an example, the concentration of hafnium salt in solution III can be 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, etc., or it can be a value within the above range, without being specifically limited here.

[0077] In some specific embodiments, the concentration of molybdenum salt in solution IV is 1.5 mol / L to 4 mol / L. As an example, the concentration of molybdenum salt in solution IV can be 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, etc., or it can be a value within the above range, without being specifically limited here.

[0078] In this application, the preparation methods of solutions I, II, III, and IV are not specifically limited, as long as the above solutions can be obtained. As an example, solution I can be obtained by dissolving nickel and manganese salts in deionized water; solution II can be obtained by dissolving aluminum salts in an aqueous sodium hydroxide solution, wherein the concentration of sodium hydroxide in the aqueous sodium hydroxide solution is 3 mol / L; solution III can be obtained by dissolving hafnium salts in deionized water; and solution IV can be obtained by dissolving molybdenum salts in deionized water.

[0079] In some specific embodiments, the alkaline solution includes at least one of an aqueous solution of sodium hydroxide, ammonia, or an aqueous solution of hexamethylenetetramine. As an example, the alkaline solution may be an aqueous solution of sodium hydroxide or ammonia. Preferably, the alkaline solution includes an aqueous solution of sodium hydroxide and ammonia, wherein the aqueous solution of sodium hydroxide acts as a precipitant and the ammonia acts as a complexing agent.

[0080] In some specific embodiments, the concentration of the alkali solution is 10 mol / L to 15 mol / L. As an example, the concentration of the alkali solution can be 10 mol / L, 12 mol / L, 15 mol / L, etc., or it can be a value within the above range, without being specifically limited here.

[0081] In some specific implementations, the pH value is adjusted to 10-12. As an example, the pH value is adjusted to 10, 11, 12, etc., but it can also be any point value within the above range, and no specific limitation is made here.

[0082] In some specific embodiments, solutions I to IV, an alkaline solution, and an ammonia solution are added dropwise into a reaction vessel under the protection of inert gas N2, followed by a coprecipitation reaction.

[0083] In some specific implementations, the thickness of the coating layer can be controlled by adjusting the amounts of solution III and solution IV.

[0084] In some specific embodiments, the coprecipitation reaction time is 30h to 48h. As an example, the coprecipitation reaction time can be 30h, 35h, 40h, 45h, 48h, etc., or it can be any value within the above range, without being specifically limited here.

[0085] In some specific implementations, the conditions for the coprecipitation reaction include heating under reflux and stirring.

[0086] In some specific embodiments, the reflux temperature is 50°C to 65°C. As an example, the reflux temperature can be 50°C, 55°C, 60°C, 65°C, etc., or it can be a value within the above range. No specific limitation is made here.

[0087] In some specific embodiments, the stirring speed is 450 r / min to 750 r / min. As an example, the stirring speed can be 450 r / min, 500 r / min, 600 r / min, 700 r / min, 750 r / min, etc., or it can be a value within the above range. No specific limitation is made here.

[0088] In some specific embodiments, the aging temperature is 50℃~65℃, the time is 8h~16h, and the stirring speed during aging is 400r / min~600r / min. For example, the aging temperature can be 50℃, 55℃, 60℃, 65℃, etc., or any value within the above range; no specific limitation is made here. For example, the aging time can be 8h, 10h, 12h, 14h, 16h, etc., or any value within the above range; no specific limitation is made here. For example, the stirring speed during aging can be 400r / min, 500r / min, 600r / min, etc., or any value within the above range; no specific limitation is made here.

[0089] In this application, the precursor, after aging, has a more uniform particle size distribution, which can cause unreacted ions in the solution to react, making the reaction more complete. At the same time, it can repair the surface morphology of the precursor, making the precursor more spherical, thereby improving the tap density and compaction density of the cathode material.

[0090] In some specific embodiments, the molar ratio of the precursor material to the lithium salt is 1:(1~1.1). As an example, the molar ratio of the precursor material to the lithium salt can be 1:1, 1:1.05, 1:1.1, etc., or any ratio within the above range, without being specifically limited here.

[0091] In some specific embodiments, the particle size of the precursor material is 4μm to 12μm. For example, the particle size of the precursor material can be 4μm, 6μm, 8μm, 10μm, 12μm, etc., or any value within the above range; no specific limitation is made here. If the precursor particle size is too small, the specific surface area of ​​the final cathode material will be too large, resulting in rapid capacity decay and reduced lifespan. If the precursor particle size is too large, the particle size of the final cathode material will be too large, which will prolong the lithium-ion migration path, leading to a decrease in the lithium-ion diffusion rate. This significantly reduces the capacity retention rate of the battery under high-rate charge-discharge conditions and also reduces the content of active material per unit volume, thus lowering the battery's volumetric specific capacity.

[0092] In some specific embodiments, calcination is carried out in an oxygen atmosphere; the calcination temperature is 700℃~900℃, and the calcination time is 10h~25h. For example, the calcination temperature can be 700℃, 800℃, 900℃, etc., or any value within the above range; no specific limitation is made here. For example, the calcination time can be 10h, 15h, 20h, 25h, etc., or any value within the above range; no specific limitation is made here.

[0093] In some specific embodiments, the nickel salt includes at least one of NiSO4·6H2O, NiCl2, or NiNO3. As an example, the nickel salt may be NiSO4·6H2O or NiCl2.

[0094] In some specific embodiments, the cobalt salt includes at least one of CoSO4·7H2O, CoCl2, or Co(NO3)2. As an example, the cobalt salt including CoSO4·7H2O may be CoCl2.

[0095] In some specific embodiments, the aluminum salt includes at least one selected from AlCl3, Al2(SO4)3, Al(NO3)3, NaAlO2, Al3(SiO3)3, or Al2S3. As an example, the aluminum salt may be AlCl3 or Al2(SO4)3.

[0096] In some specific embodiments, the hafnium salt includes at least one of HfCl4, Hf(NO3)4, or HfO4S. As an example, the hafnium salt may be HfCl4 or Hf(NO3)4.

[0097] In some specific embodiments, the molybdenum salt includes C 48 H 90 MoO 12 At least one of (NH4)2MoO4 or Na2MoO4. As an example, the molybdenum salt can be (NH4)2MoO4, or it can be C... 48 H 90 MoO 12 .

[0098] In some specific embodiments, the lithium salt includes at least one of LiOH·H2O or Li2CO3. As an example, the lithium salt can be LiOH·H2O or Li2CO3.

[0099] Therefore, based on the above, this invention first prepares the precursor material by co-precipitation, and then doesigate it with Mo and Hf during the co-precipitation process to prepare a Mo and Hf co-doped precursor. During the high-temperature lithiation stage, due to the large atomic radii of molybdenum and hafnium, they cannot all enter the lattice of the lithium nickel cobalt aluminum oxide ternary material for doping. Therefore, some molybdenum and hafnium atoms diffuse to the material surface. Due to the difference in diffusion mechanisms, molybdenum diffuses from the bulk phase to the surface of the primary particles, forming a Li-Mo-O coating layer, while hafnium atoms diffuse from the bulk phase to the surface of the secondary particles, forming an epitaxial layer. This further reacts with the residual lithium on the surface of the epitaxial layer to form a Li-Hf-O coating layer, consuming the residual lithium on the surface of the cathode material. Thus, a one-step method is used to coat the surfaces of the primary and secondary particles of the polycrystalline material. The cathode material provided in this application enhances the structural stability of lithium nickel cobalt aluminum oxide ternary materials through the pinning effect of co-doping with molybdenum and hafnium atoms, which can suppress the structural collapse of the cathode material; it also hinders the side reactions between the cathode and the solid electrolyte, and reduces the residual lithium on the surface of the high-nickel cathode, thereby enhancing the electrochemical performance of the material.

[0100] Based on the same inventive concept, this application provides a positive electrode sheet, including a positive electrode material, wherein the positive electrode material is the aforementioned positive electrode material or a positive electrode material prepared according to the aforementioned preparation method.

[0101] Since the positive electrode sheet provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0102] Based on the same inventive concept, this application provides a secondary battery including a positive electrode, wherein the positive electrode is the aforementioned positive electrode.

[0103] Since the secondary battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0104] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0105] Example 1

[0106] Weigh appropriate amounts of NiSO4·6H2O and CoSO4·H2O, where the molar ratio of Ni to Co is 9:0.5, and add deionized water to prepare a salt solution I with a total metal ion concentration of 2 mol / L. Dissolve an appropriate amount of NaAlO2 in an aqueous solution of sodium hydroxide (sodium hydroxide concentration is 3 mol / L) to prepare a 1 mol / L Al-containing solution II. Prepare a 0.2 mol / L HfCl4 solution III and a 0.2 mol / L (NH4)2MoO4 solution IV.

[0107] Subsequently, a 10 mol / L sodium hydroxide solution was prepared by mixing deionized water and sodium hydroxide, and a 13.5 mol / L ammonia solution was prepared by mixing deionized water and ammonia water to obtain the alkaline solution and ammonia solution required for the experiment. Sodium hydroxide was used as a precipitant and ammonia water was used as a complexing agent.

[0108] Inside the reactor, under the protection of inert gas N2, solutions I-IV, an alkaline solution, and an ammonia solution were added dropwise. The molar ratio of Ni, Co, and Al was 0.9:0.05:0.05, and the ratio of the total amount of Ni, Co, and Al to the amount of Hf and Mo was 0.98:0.01:0.01. The feed rates were controlled as follows: solution I was fed at 100 mL / h, solution II at 10.4 mL / h, and solutions III and IV at 10.2 mL / h, to ensure simultaneous and complete addition of solutions I-IV. The pH inside the reactor was maintained at a constant 11 (the feed rates of the alkaline solution and ammonia solution were automatically controlled by the reactor apparatus based on real-time pH), the temperature of the circulating reflux water was 55℃, and the stirring speed was 500 rpm / min. These conditions were used to synthesize the hydroxide precursor [Ni...]. 0.9 Co 0.05 Al 0.05 ] 0.98 Hf 0.01 Mo 0.01 (OH) 2 .02 After the reaction, the reactor was kept under an inert atmosphere and stirred at 500 rpm / min for 12 hours to allow the precursor to age. After aging, the precursor was washed several times with deionized water, dried at 120°C, and then sieved through a 400-mesh sieve to obtain the precursor powder.

[0109] The precursor was mixed with lithium hydroxide at a molar ratio of Li:(Ni+Co+Al+Mo+Hf)=1.05. The mixture was sintered at 750℃ for 15 hours in an oxygen atmosphere and then cooled to room temperature to obtain the cathode material.

[0110] Depend on Figure 1 The X-ray diffraction pattern of the cathode material prepared in Example 1 confirms that a ternary cathode material was obtained. Figure 2The image shows the elemental distribution of the cross-section of the cathode material prepared in Example 1 after polishing, proving that Hf and Mo elements are fully doped in the nickel-cobalt-aluminum ternary material. Figure 3 The transmission image of a primary particle selected after FIB (Focused Ion Beam) slicing of the cathode material prepared in Example 1 proves that there is a coating on the surface of the primary particle. Figure 4 Transmission electron microscopy (TEM) images of the secondary particles in the prepared cathode material demonstrate that the secondary particles have a coating layer on their surface. (Summary) Figures 1-4 It can be demonstrated that Hf and Mo elements are doped in the material and form a coating layer on the surface of primary and secondary particles.

[0111] Example 2

[0112] The only difference between Example 2 and Example 1 is that in Example 2, the ratio of the total amount of Ni, Co and Al to the amount of Hf and Mo is 0.97:0.02:0.01 when preparing the precursor material. All other aspects are the same as in Example 1.

[0113] Example 3

[0114] The only difference between Example 3 and Example 1 is that in Example 3, the ratio of the total amount of Ni, Co and Al to the amount of Hf and Mo is 0.96:0.03:0.01 when preparing the precursor material. All other aspects are the same as in Example 1.

[0115] Example 4

[0116] The only difference between Example 4 and Example 1 is that in Example 4, the ratio of the total amount of Ni, Co and Al to the amount of Hf and Mo is 0.97:0.01:0.02 when preparing the precursor material. All other aspects are the same as in Example 1.

[0117] Example 5

[0118] The only difference between Example 5 and Example 1 is that in Example 5, the ratio of the total amount of Ni, Co and Al to the amount of Hf and Mo is 0.96:0.01:0.03 when preparing the precursor material. All other aspects are the same as in Example 1.

[0119] Comparative Example 1

[0120] The only difference between Comparative Example 1 and Example 1 is that, in the preparation of the precursor material in Comparative Example 1, no solutions III and IV were added; otherwise, they were the same as in Example 1.

[0121] Comparative Example 2

[0122] The only difference between Comparative Example 2 and Example 1 is that, in Comparative Example 2, no solution IV was added when preparing the precursor material, and the ratio of the total amount of Ni, Co and Al to the amount of Hf was 0.99:0.01. All other aspects were the same as in Example 1.

[0123] Comparative Example 3

[0124] The only difference between Comparative Example 3 and Example 1 is that, in the preparation of the precursor material in Comparative Example 3, solution III was not added, and the ratio of the total amount of Ni, Co and Al to the amount of Mo was 0.99:0.01. All other aspects were the same as in Example 1.

[0125] Performance testing

[0126] 1. Battery manufacturing

[0127] A mold battery was assembled by mixing positive electrode material, vapor-grown carbon fiber, and sulfide electrolyte (LPSCl) in a mass ratio of 70:3:27, using Li-In alloy as the negative electrode, and sulfide electrolyte (LPSCl) as the electrolyte layer.

[0128] 2. Perform electrochemical performance testing on the battery.

[0129] (1) First Coulombic Efficiency Test: Take the batteries prepared in each example and comparative example, and use the Blue Electric Test System at 25°C. After standing for 5 minutes, charge to 3.65V at 0.1C and record the charging capacity Ccharge. After standing for 5 minutes, discharge to 2.0V at 0.1C and record the discharge capacity Cdischarge. Perform the first Coulombic Efficiency Test. The first Coulombic Efficiency = Cdischarge / Ccharge * 100%.

[0130] (2) Capacity retention test after 300 cycles: Batteries prepared in each example and comparative example were used. The test conditions were as follows: after resting for 5 minutes, charging to 3.65V at 0.1C, resting for 5 minutes, and then discharging to 2.0V at 0.1C. After 2 cycles, charging to 4.0V at 0.3C, resting for 5 minutes, and then discharging to 2.0V at 0.3C. The discharge capacity was recorded as the initial discharge capacity. The cycle was repeated 300 times. The discharge capacity on the 300th cycle was recorded. The capacity retention rate after 300 cycles = discharge capacity on the 300th cycle / initial discharge capacity * 100%. (Note: A higher capacity retention rate indicates a longer electrode lifespan.)

[0131] 3. Surface residual alkali content detection: Quantitative analysis was performed on the XPS spectra and composition of the material at different etching depths. Specifically, surface elemental analysis was conducted using an X-ray photoelectron spectroscopy (XPS, ESCALAB250Xi, UK). The etching parameters were an etching intensity of 5 keV and etching times of 30 s, 60 s, 120 s, 180 s, and 300 s. Avantage was used for peak separation processing of the data.

[0132] The test results for each embodiment and comparative example are shown in Table 1.

[0133] Table 1

[0134]

[0135] As shown in Table 1, the cathode materials prepared in Examples 1-5 have lower surface residual alkali than those in Comparative Example 1 (undoped), Comparative Example 2 (Hf-doped only), and Comparative Example 3 (Mo-doped only). This demonstrates that the cathode material of this application can reduce surface residual alkali and exhibits superior electrochemical performance. The above test results prove that Hf and Mo doping in the material and the formation of coating layers on the surfaces of primary and secondary particles enhance the structural stability of the cathode material and result in superior electrochemical performance.

[0136] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0137] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0138] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0139] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that, The cathode material includes secondary particulate material; The secondary particulate material is obtained by stacking primary particulate material, the primary particulate material including nickel-cobalt-aluminum ternary material, and at least part of the surface of the primary particulate material is coated with a Li-Mo-O coating layer. The secondary particulate material has at least a partial surface coating of Li-Hf-O coating layer; Nickel-cobalt-aluminum ternary materials are lithium nickel-cobalt-aluminum ternary materials doped with molybdenum atoms and hafnium atoms.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics (1) to (4): (1) The particle size of the primary particulate material is 10 nm to 300 nm; (2) The thickness of the primary particulate material coating layer is 1 nm to 3 nm; (3) The particle size of the secondary particulate material is 4μm~12μm; (4) The thickness of the secondary particulate material coating layer is 2nm ~ 5nm.

3. A method for preparing a positive electrode material according to any one of claims 1 to 2, characterized in that, Includes the following steps: The solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt and molybdenum salt was adjusted to alkaline with alkali solution, and then subjected to co-precipitation reaction and aging to obtain precursor material; The precursor material is mixed with lithium salt and calcined to obtain the cathode material. The molar ratio of the nickel salt, cobalt salt, aluminum salt, hafnium salt, and molybdenum salt is (0.8~1):(0.03~0.08):(0.03~0.08):(0.01~0.03):(0.01~0.03). The pH value is adjusted to 10-12.

4. The method for preparing the cathode material according to claim 3, characterized in that, The preparation of the solution containing nickel salt, cobalt salt, aluminum salt, hafnium salt and molybdenum salt includes: mixing solution I containing nickel salt and cobalt salt, solution II containing aluminum salt, solution III containing hafnium salt and solution IV containing molybdenum salt; The total molar concentration of nickel and cobalt salts in solution I is 1.5 mol / L to 4 mol / L; The concentrations of the metal salts in solutions II, III, and IV are each independently between 1.5 mol / L and 4 mol / L.

5. The method for preparing the cathode material according to claim 3, characterized in that, The coprecipitation reaction time is 30h~48h; And / or, the conditions for the coprecipitation reaction include heating under reflux and stirring; The temperature of the heating reflux is 50℃~65℃; The stirring speed is 450 r / min ~ 750 r / min; And / or, the aging temperature is 50℃~65℃, the time is 8h~16h, and the stirring speed during aging is 400r / min~600r / min.

6. The method for preparing the cathode material according to claim 3, characterized in that, The molar ratio of the precursor material to the lithium salt is 1:(1~1.1). And / or, the particle size of the precursor material is 4μm~12μm; And / or, the calcination is carried out in an oxygen atmosphere; the calcination temperature is 700℃~900℃, and the calcination time is 10h~25h.

7. The method for preparing the cathode material according to claim 3, characterized in that, The alkaline solution includes an aqueous solution of sodium hydroxide, ammonia, or an aqueous solution of hexamethylenetetramine. And / or, the concentration of the alkaline solution is 10 mol / L to 15 mol / L.

8. The method for preparing the cathode material according to claim 3, characterized in that, The method for preparing the cathode material satisfies at least one of the following features (1) to (6): (1) The nickel salt includes at least one of NiSO4·6H2O, NiCl2, or NiNO3; (2) The cobalt salt includes at least one of CoSO4·7H2O, CoCl2 or Co(NO3)2; (3) The aluminum salt includes at least one of AlCl3, Al2(SO4)3, Al(NO3)3, NaAlO2, Al3(SiO3)3 or Al2S3; (4) The hafnium salt includes at least one of HfCl4, Hf(NO3)4 or HfO4S; (5) The molybdenum salt includes C 48 H 90 MoO 12 At least one of (NH4)2MoO4 or Na2MoO4; (6) The lithium salt includes at least one of LiOH·H2O or Li2CO3.

9. A positive electrode sheet, comprising a positive electrode material, characterized in that, The cathode material is the cathode material according to any one of claims 1 to 2 or the cathode material prepared by the preparation method according to any one of claims 3 to 8.

10. A secondary battery, comprising a positive electrode, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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