Modified lithium nickelate material and preparation method and application thereof

Abstract

According to the modified lithium nickelate positive electrode material and the preparation method and application thereof, the nickel element in the modified lithium nickelate positive electrode material accounts for 98% or above of the total molar weight of the nickel element, and the modified lithium nickelate positive electrode material is co-doped with three functional elements A, B and C, so that a synergistic interaction effect is achieved for improving the performance of the material; the expansion and shrinkage degree of a material crystal structure in the charging and discharging process can be effectively inhibited, the electronic conductivity of the material is improved, the phenomena of positive ion mixing aggravation and oxygen escape under high voltage are inhibited, the mechanical strength of the material is synergistically improved, and the phenomena of particle cracking and pulverization caused by cyclic stress of the material are reduced; the structural stability and the electrochemical stability of the lithium nickelate matrix material are enhanced, the structural stability and the charge-discharge efficiency of the lithium nickelate positive electrode material are obviously improved, and the reversible capacity is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-ion batteries, and particularly relates to the modification of lithium nickelate. Background Art

[0002] The rapid development of the new energy vehicle industry has put forward higher requirements for its core component, the power battery, which requires high energy density, long cycle life, high safety, and high charge and discharge efficiency. Currently, lithium iron phosphate power batteries and ternary lithium power batteries are widely used in new energy vehicles. Lithium iron phosphate batteries are lithium-ion batteries with LiFePO4 as the cathode material, while ternary lithium power batteries are lithium-ion batteries with lithium nickel cobalt manganese oxide (NCM) or lithium nickel cobalt aluminate (NCA) as the cathode material. Among them, ternary lithium power batteries dominate the high-end passenger vehicle market with their ultra-high nickelization and solid-state technologies. For ternary power batteries with nickel-based layered transition metal oxides as the cathode material, their energy density increases with the increase of Ni content, but at the same time, there are problems of poor cycle performance.

[0003] Lithium nickelate (LiNiO2) is a nickel-based layered cathode material with the highest specific capacity, but its cycling rate performance is also the worst. During the charging process, the LiNiO2 crystal material will go through three phase transition stages: hexagonal H1 → monoclinic M, monoclinic M → hexagonal H2, hexagonal H2 → hexagonal H3. During this period, the lattice parameter a slowly decreases, and the lattice parameter c first slowly increases and then rapidly decreases; the phase transition proceeds reversely during the discharging process. Due to the anisotropic change of the unit cell, with the increase of the number of cycles, the LiNiO2 cathode material particles are crushed, and the battery capacity decays. In addition, at high voltages, the LiNiO2 material is prone to the phenomena of increased cation mixing and oxygen release, which will not only cause structural damage to the material, but also may trigger thermal runaway and increase the safety risk. Cation mixing will make the diffusion path of lithium ions irregular, interfere with the insertion and extraction of lithium ions, and reduce the rate performance and charge and discharge efficiency of the battery. The release of oxygen will not only damage the structure of the battery, but also may exacerbate the heat accumulation inside the battery, trigger thermal runaway, and increase the risk of combustion and explosion.

[0004] By engineering the microstructure of the crystal, such as delaying the H2→H3 phase transition, suppressing Li / Ni disordered mixing, and suppressing oxygen escape, the intrinsic structural defects of the material can be specifically improved, optimizing the stability of the layered structure and the lithium-ion transport kinetics at the atomic level, and achieving an improvement in the structural stability and cycling performance of the lithium nickelate cathode material. Among them, element doping is the most effective strategy, which can break through the limitations of the intrinsic defects of LiNiO2 while maintaining a high energy density. Currently, the common doping elements are Co and Mn, where Co is expensive and toxic; when the Ni content > 90%, the stabilizing effect of Mn on the material weakens. In response, the prior art improves the above problems through other element doping, coating modification and other means.

[0005] The patent document with the publication number CN115974176A discloses a method for modifying a lithium nickelate cathode material in which aluminum and titanium jointly replace nickel elements, obtaining a cobalt-free and manganese-free lithium nickelate-based cathode material, which is environmentally friendly, but the initial efficiency of this material is low, and the LiNi 0.95 Al 0.025 Ti 0.025 O2 cathode material has an initial efficiency of only about 82%, and the preparation process involves two high-temperature treatments, increasing energy consumption and production costs, which is not conducive to large-scale industrial production. The patent document with the announcement number CN108807983B discloses a method for preparing a porous lithium nickelate cathode material doped with magnesium and tin. The obtained lithium nickelate material has a porous structure that provides more channels for the insertion and extraction of lithium ions, significantly improving the cycling performance. However, its porous structure results in a low tap density, unable to exert the advantage of the high specific capacity of the lithium nickelate material, and the preparation process is relatively complex. Summary of the Invention

[0006] Aiming at the above technical problems, the purpose of the present invention is to provide a modified lithium nickelate cathode material, its preparation method and application.

[0007] To achieve the above purpose, the present invention proposes the following solutions: In the first aspect, a modified lithium nickelate cathode material is provided. In the modified lithium nickelate cathode material, nickel element accounts for more than 98% of the total molar amount of nickel-site elements. In the modified lithium nickelate, three functional elements A, B, and C are co-doped. Among them, element A is selected from one or more of Na, Mg, K, Ca, Sr, Ba, La, Pr, Nd; element B is selected from one or more of Y, Cd, Ce, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, B, Cr; element C is selected from one or more of Sc, Ti, V, Fe, Nb, Mo, Hf, Ta, W, Re, Si, Ga, Ge, As, Sb.

[0008] Furthermore, the modified lithium nickelate cathode material has a secondary particle morphology formed by aggregation of nanoscale primary particles; the modified lithium nickelate cathode material has a layered α-NaFeO2 structure.

[0009] Furthermore, the doping amounts of elements A, B, and C are each independently 0.001 to 1% of the molar amount of the modified lithium nickelate cathode material.

[0010] Furthermore, element A tends to occupy the lithium site of lithium nickelate, and elements B and C tend to occupy the nickel site of lithium nickelate. Furthermore, the chemical formula of the modified lithium nickelate cathode material is Li 1-x Ni 1-y-z A x B y C z O2, where 0.99 ≤ 1 - x ≤ 1.01, and 0.00001 ≤ x, y, z ≤ 0.01.

[0011] In a second aspect, a method for preparing a modified lithium nickelate cathode material is provided, including: Mixing a nickel hydroxide precursor uniformly with a lithium source and metal compounds of elements A, B, and C to obtain a mixture; Performing heat treatment on the mixture under a protective atmosphere and then cooling it under an oxygen atmosphere to obtain the modified lithium nickelate cathode material.

[0012] Furthermore, the metal compounds of elements A, B, and C are each independently selected from one or more of oxides, hydroxides, carbonates, acetates, and nitrates.

[0013] Furthermore, the metal compounds of elements A, B, and C are nanoscale compounds.

[0014] Furthermore, the molar ratio of the amount of a single element of A, B, or C in the metal compounds of elements A, B, and C to the molar amount of the nickel hydroxide precursor is each independently 0.00001 to 0.01:1.

[0015] Furthermore, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium oxalate, and preferably lithium hydroxide.

[0016] Furthermore, the molar ratio of lithium contained in the nickel hydroxide precursor to the lithium source is 1:1.04 to 1.08.

[0017] Furthermore, the protective atmosphere is an oxygen atmosphere; the oxygen partial pressure in the oxygen atmosphere is not less than 98%.

[0018] Further, the heat treatment is two-stage sintering; in the two-stage sintering, the holding temperature of the first-stage sintering is 400-600°C; the holding time of the first-stage sintering is 4-6 h; the heating rate of the first-stage sintering is 3-8°C / min; the holding temperature of the second-stage sintering is 600-800°C; the holding time of the second-stage sintering is 10-20 h; the heating rate from the holding temperature of the first stage to the holding temperature of the second-stage sintering during the second-stage sintering is 3-5°C / min.

[0019] Further, the cooling is natural cooling; the natural cooling includes cooling in an oxygen atmosphere to below 200°C and then taking out.

[0020] The third invention provides a positive electrode, including the modified lithium nickelate positive electrode material described above or the modified lithium nickelate positive electrode material prepared by the preparation method described above.

[0021] In the fourth aspect, a lithium-ion battery is provided, including the positive electrode described above.

[0022] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: In the provided modified lithium nickelate positive electrode material, the nickel content is 98% or more. By using co-doping of elements of types A, B, and C inside and on the surface of the particles, a synergistic effect is achieved in improving the material performance, which can effectively inhibit the degree of expansion and contraction of the material crystal structure during charge and discharge, improve the electronic conductivity of the material, inhibit the aggravation of cation mixing and oxygen escape under high voltage, synergistically enhance the mechanical strength of the material, reduce the particle cracking and pulverization phenomena caused by cyclic stress, enhance the structural stability and electrochemical stability of the lithium nickelate matrix material, significantly improve the structural stability and charge-discharge efficiency of the lithium nickelate positive electrode material, and have a high reversible capacity.

[0023] By adopting multi-element co-doping, the synergistic effect can enable the material to maintain good performance under high-rate conditions, improve problems such as structural collapse, cation mixing, and oxygen escape that easily occur in the charge and discharge process of the ultra-high nickel positive electrode material, and it is expected to improve the material stability under high voltage.

[0024] The provided material preparation process flow is simple, the price is low, the raw materials are widely sourced, it is suitable for large-scale industrial production, and the synthesized product can meet the battery requirements of high energy density and long cycle life. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 XRD patterns of the multi-element co-doped ultra-high nickel cathode materials prepared in Example 1 and Comparative Examples 1, 2, 3, and 4.

[0027] Figure 2 SEM image of the multi-element co-doped material prepared in Example 1.

[0028] Figure 3 SEM image of the original lithium nickelate prepared in Comparative Example 1. Detailed implementation manners

[0029] Some embodiments of the present invention provide a modified lithium nickelate cathode material. In the modified lithium nickelate cathode material, nickel element accounts for more than 98% of the total molar amount of nickel-site elements. The modified lithium nickelate is co-doped with three functional elements A, B, and C. Element A is selected from one or more of Na, Mg, K, Ca, Sr, Ba, La, Pr, and Nd; Element B is selected from one or more of Y, Cd, Ce, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, B, and Cr; Element C is selected from one or more of Sc, Ti, V, Fe, Nb, Mo, Hf, Ta, W, Re, Si, Ga, Ge, As, and Sb.

[0030] In the modified lithium nickelate cathode material, nickel element accounts for more than 98% of the total molar amount of nickel-site elements, such as 98%, 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99.0%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, etc.

[0031] In view of the problems existing in the lithium nickelate cathode material, the applicant has carried out DFT calculations and carried out co-doping using three types of functional elements A, B, and C. The functional element A occupies the Li site of the matrix material, acts as a pillar ion, maintains the Li layer spacing, and inhibits the structural collapse of the material during charge and discharge. The functional element B occupies the Ni site of the matrix material and inhibits the Li / Ni mixing under high voltage through steric hindrance effects. The functional element C occupies the Ni site of the matrix material and inhibits the oxygen escape under high voltage by virtue of strong metal-oxygen bonds. Moreover, it has been verified that the co-doping of the three types of elements A, B, and C can play a synergistic effect (1 + 1 + 1 > 3), effectively inhibiting the degree of expansion and contraction of the material crystal structure during charge and discharge, improving the electronic conductivity of the material, inhibiting the aggravation of cation mixing and oxygen escape under high voltage, synergistically enhancing the mechanical strength of the material, reducing the particle cracking and pulverization phenomena caused by cyclic stress, enhancing the structural stability and electrochemical stability of the lithium nickelate matrix material, significantly improving the structural stability and charge-discharge efficiency of the lithium nickelate cathode material, and having a high reversible capacity.

[0032] In some preferred embodiments, the element A is selected from one or more of Mg, Sr, and La.

[0033] In some preferred embodiments, the element B is selected from one or more of Y, Yb, Lu, and B.

[0034] In some preferred embodiments, the element C is selected from one or more of Ti, V, Nb, Mo, and Re.

[0035] In some preferred embodiments, the modified lithium nickelate cathode material has a secondary particle morphology formed by the aggregation of nanoscale primary particles; the modified lithium nickelate cathode material has a layered α-NaFeO2 structure.

[0036] In some preferred embodiments, the element A tends to occupy the lithium site of lithium nickelate, and the elements B and C tend to occupy the nickel site of lithium nickelate.

[0037] In some preferred embodiments, the doping amounts of the elements A, B, and C are each independently 0.001% to 1% of the molar amount of the modified lithium nickelate cathode material, such as 0.001%, 0.002%, 0.005%, 0.008%, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, etc.

[0038] In some preferred embodiments, the chemical formula of the modified lithium nickelate cathode material is Li1-x Ni 1-y- z A x B y C z O2, where 0.99 ≤ 1 - x ≤ 1.01, 0.00001 ≤ x ≤ 0.01, 0.00001 ≤ y ≤ 0.01, 0.00001 ≤ z ≤ 0.01.

[0039] Some embodiments of the present invention also provide a method for preparing a modified lithium nickelate cathode material, comprising: Mixing a nickel hydroxide precursor with a lithium source and metal compounds of elements A, B, and C uniformly to obtain a mixture; Performing heat treatment on the mixture under a protective atmosphere and then cooling it under an oxygen atmosphere to obtain the modified lithium nickelate cathode material.

[0040] In some preferred embodiments, the metal compounds of elements A, B, and C are each independently selected from one or more of oxides, hydroxides, carbonates, acetates, and nitrates.

[0041] In some preferred embodiments, the molar ratio of the metal amount of a single type of element A, B, or C in the metal compounds of elements A, B, and C to the molar amount of the nickel hydroxide precursor is each independently 0.00001 - 0.01:1, such as 0.00001:1, 0.00005:1, 0.0001:1, 0.0002:1, 0.0003:1, 0.0004:1, 0.0005:1, 0.0006:1, 0.0007:1, 0.0008:1, 0.0009:1, 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, etc.

[0042] In some preferred embodiments, the metal compounds of elements A, B, and C are nanoscale compounds.

[0043] In some preferred embodiments, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium oxalate, preferably lithium hydroxide.

[0044] In some preferred embodiments, the molar ratio of the nickel hydroxide precursor to the lithium contained in the lithium source is 1:1.04 - 1.08, such as 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, etc.

[0045] The modified lithium nickelate cathode material is sintered with high-purity oxygen as the protective atmosphere to fully oxidize Ni 2+ to Ni3+ , reduce the Li / Ni mixing and promote the integrity of the crystal structure to improve the performance of the lithium nickelate cathode material. In some preferred embodiments, the protective atmosphere is an oxygen atmosphere; the oxygen partial pressure in the oxygen atmosphere is not less than 98%.

[0046] In some preferred embodiments, the heat treatment is two-stage sintering; in the two-stage sintering, the holding temperature of the first-stage sintering is 400 - 600 °C (such as 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, etc.); the holding time of the first-stage sintering is 4 - 6 h (such as 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc.); the heating rate of the first-stage sintering is 3 - 8 °C / min (such as 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, etc.); the holding temperature of the second-stage sintering is 600 - 800 °C (such as 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, etc.); the holding time of the second-stage sintering is 10 - 20 h (such as 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, etc.); the heating rate from the holding temperature of the first stage to the holding temperature of the second-stage sintering during the second-stage sintering is 3 - 5 °C / min (such as 3 °C / min, 4 °C / min, 5 °C / min, etc.).

[0047] In some preferred embodiments, the cooling is natural cooling; the natural cooling includes cooling in an oxygen atmosphere to below 200 °C and then taking out.

[0048] Some embodiments of the present invention provide a cathode, including the modified lithium nickelate cathode material described above or the modified lithium nickelate cathode material prepared by any of the preparation methods described above.

[0049] Some embodiments of the present invention provide a lithium-ion battery, including the cathode described above.

[0050] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and in detail with reference to the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0051] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0052] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0053] The chemical reagents or raw materials used in the following steps and processes are all of analytical grade or battery grade.

[0054] Example 1 A preparation method of Sr, B, V multi - element co - doped ultra - high nickel cathode material, comprising the following steps: (1) Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0052 g of nano - scale SrO (purity 99.9%), 0.0031 g of nano - scale H3BO3 (purity 99.9%), and 0.0046 g of nano - scale V2O5 (purity 99.9%) respectively. First, place LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder without obvious particles, then put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material has a uniform color without variegation; (2) Put the ground material into a calcination furnace, introduce high - purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it at a heating rate of 5 °C / min to 500 °C and keep it warm for 5 h, then heat it at a heating rate of 3 °C / min to 620 °C and keep it warm for 15 h, and then naturally cool it to below 200 °C to obtain the Sr, B, V multi - element co - doped ultra - high nickel cathode material.

[0055] According to the DFT calculation results and XRD refinement, it can be known that there are simultaneously Sr 2+ lithium - site doping and B 3+ and V 5+ nickel - site doping in the bulk phase of the ultra - high nickel cathode material. Combining the raw material ratio, the chemical formula of the obtained ultra - high nickel cathode material is Li 0.999 Sr 0.001 Ni 0.998 B 0.001 V 0.001 O2 (marked as LNO - SrBV). The XRD pattern of the obtained ultra - high nickel cathode material is as shown in Figure 1 shown. It can be seen from Figure 1 that the prepared modified lithium nickelate cathode material is a pure - phase layered α - NaFeO2 structure without impurity phases; the SEM image is as shown in Figure 2 shown. It can be seen from Figure 2 that the prepared cathode material has a good structure, and the morphology is secondary particles aggregated by nano - scale primary particles with an average particle size of about 9 μm; using Fullpro to refine the XRD data, both R p and R wp are less than 5%, and the Li + / Ni 2+ mixing ratio is 2.1%.

[0056] Button cell assembly: In an argon glove box, a total of 0.3 g of materials were weighed according to the mass ratio of active material: conductive agent: binder of 8:1:1 and ground for 15 min until evenly mixed. An appropriate amount of organic solvent N-methylpyrrolidone (NMP) was added and grinding was continued for 10 min to form a slurry with fluidity, which was uniformly coated on a flat aluminum foil current collector with a thickness of 200 μm and dried in a vacuum drying oven at 90 °C for 8 h. The dried electrode was cut into circular pieces with a diameter of 12 mm. Using the prepared electrode as the positive electrode and a lithium sheet as the counter electrode, the battery case model used was CR2025, and the battery was assembled in the glove box (Ar atmosphere, H2O and O2 content less than 0.01 ppm). After the assembled button cell was left standing at 25 °C for 12 h, a series of electrochemical performance tests were carried out.

[0057] Electrochemical performance test: The charge and discharge of the button cell were carried out in a LAND battery test system, and the voltage range was 2.8~4.3 V. Before the cycle test, it was first activated twice with a small current density of 0.1C (1C = 200 mAh·g -1 ), and then the charge and discharge cycle test was carried out at a current density of 1C.

[0058] Disassembly of button cell: The button cell charged to 4.3 V was transferred to the glove box for disassembly. The electrode was soaked in an organic solvent dimethyl carbonate (DMC) or diethyl carbonate (DEC) for half an hour and then rinsed clean, and naturally dried in the glove box for subsequent structural defect characterization tests.

[0059] The obtained ultra-high nickel cathode material was tested for electrochemical performance. Its discharge specific capacity at a current density of 0.1C was 234.5 mAh·g -1 , and the first efficiency was 92.4%; the discharge specific capacity after 100 cycles at a current density of 1C was 193.9 mAh·g -1 , and the capacity retention rate was 92%. The button cell that was cycled 100 times and charged to 4.3 V was transferred to the glove box for disassembly and cleaning, and naturally dried in the glove box. Then, the oxygen vacancy concentration was measured quantitatively by positron annihilation spectroscopy (PAS) to be 3.5%.

[0060] Example 2 A preparation method of a Mg, Ce, Ti multi-element co-doped ultra-high nickel cathode material, comprising the following steps: (1)Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0020 g of nano-MgO (purity 99.9%), 0.0086 g of nano-CeO2 (purity 99.9%), and 0.0040 g of nano-TiO2 (purity 99.9%) respectively. First, place LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder without obvious particles. Then, put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material color is uniform without variegation; (2)Put the ground material into a calcination furnace, introduce high-purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it at a heating rate of 5 °C / min to 500 °C and hold for 5 h, then heat it at a heating rate of 3 °C / min to 620 °C and hold for 15 h, and then cool it naturally to below 200 °C to obtain a super-high nickel cathode material Li 0.999 Mg 0.001 Ni 0.998 Ce 0.001 Ti 0.001 O2 (marked as LNO-MCT).

[0061] Perform XRD detection and Fullpro refinement on the obtained lithium nickelate cathode material to obtain a Li + / Ni 2+ mixed arrangement rate of 2.3%; perform electrochemical performance tests on the obtained lithium nickelate cathode material. Its discharge specific capacity at a current density of 0.1C is 231.4 mAh·g -1 , and the initial efficiency is 90.3%; the discharge specific capacity after cycling 100 times at a current density of 1C is 189.3 mAh·g -1 , and the capacity retention rate is 90.3%. Disassemble and clean the coin cell that has been cycled 100 times and charged to 4.3V in a glove box, let it dry naturally in the glove box, and then quantitatively measure its oxygen vacancy concentration to be 3.4% through positron annihilation spectroscopy (PAS).

[0062] Example 3 A preparation method of an Sr, Y, Mo multi-element co-doped super-high nickel cathode material, comprising the following steps: (1)Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0052 g of nanoscale SrO (purity 99.9%), 0.0056 g of nanoscale Y2O3 (purity 99.5%), and 0.0072 g of nanoscale MoO3 (purity 99.9%) respectively. First, place LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder without obvious particles. Then, put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material has a uniform color without variegation; (2)Put the ground material into a calcination furnace, introduce high-purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it at a heating rate of 5 °C / min to 500 °C and hold for 5 h, then heat it at a heating rate of 3 °C / min to 620 °C and hold for 15 h, and then cool it naturally to below 200 °C to obtain a Sr, Y, Mo multi-element co-doped ultra-high nickel cathode material Li 0.999 Sr 0.001 Ni 0.99 8Y 0.001 Mo 0.001 O2 (labeled as LNO - SYM).

[0063] Perform XRD detection and Fullpro refinement on the obtained lithium nickelate cathode material to obtain a Li + / Ni 2+ mixing ratio of 2.5%; perform electrochemical performance tests on the obtained lithium nickelate cathode material. Its discharge specific capacity at a current density of 0.1C is 231.0 mAh·g -1 , and the initial efficiency is 91.5%; the discharge specific capacity after cycling 100 times at a current density of 1C is 190.8 mAh·g -1 , and the capacity retention rate is 91.5%. Disassemble and clean the coin cell that has been cycled 100 times and charged to 4.3V in a glove box, let it dry naturally in the glove box, and then quantitatively measure its oxygen vacancy concentration to be 3.6% through positron annihilation spectroscopy (PAS).

[0064] Comparative Example 1 Preparation of the original lithium nickelate cathode material, including the following steps: (1)Weigh 4.6357 g of Ni(OH)2 (purity 99.9%) and 2.2887 g of LiOH·H2O (purity 97%) respectively. First, place LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder without obvious particles. Then, put the nanoscale Ni(OH)2 into the mortar and mix them evenly, and continue to grind for 20 min until the material has a uniform color without variegation; Among them, the lithium source used is lithium hydroxide monohydrate, and the molar ratio of it to the nickel hydroxide precursor used is 1.06:1; (2) Put the ground material into a calcination furnace, introduce high-purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it to 500 °C at a heating rate of 5 °C / min and hold for 5 h, then heat it to 620 °C at a heating rate of 3 °C / min and hold for 15 h, and then naturally cool it to below 200 °C to obtain the lithium nickelate cathode material (marked as LNO).

[0065] The XRD pattern of the obtained lithium nickelate cathode material is as Figure 1 shown, and the SEM image is as Figure 3 shown. By comparing Figure 2 and Figure 3 it is found that the macroscopic structure has changed significantly.

[0066] The obtained lithium nickelate cathode material was subjected to XRD detection and Fullpro refinement to obtain a Li + / Ni 2+ mixing ratio of 3.3%; the obtained lithium nickelate cathode material was subjected to electrochemical performance testing, and its discharge specific capacity at a current density of 0.1C was 231.3 mAh·g -1 , and the initial efficiency was 90.1%; the discharge specific capacity after cycling 100 times at a current density of 1C was 173.7 mAh·g -1 , and the capacity retention rate was 84.9%. The button battery that had been cycled 100 times and charged to 4.3V was disassembled and cleaned in a glove box, left to dry naturally in the glove box, and then the oxygen vacancy concentration was quantitatively measured by positron annihilation spectroscopy (PAS) to be 5.0%, indicating that the electrochemical performance of the un-doped and modified matrix material was poor and there were many bulk defects.

[0067] Comparative Example 2 A preparation method of a B and V element co-doped ultra-high nickel cathode material, comprising the following steps: (1) Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0031 g of nano-scale H3BO3 (purity 99.9%) and 0.0046 g of nano-scale V2O5 (purity 99.9%) respectively. First, put LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder state without obvious particles, then put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material color is uniform and there is no variegation; among them, the lithium source used is lithium hydroxide monohydrate, and its molar ratio to the nickel hydroxide precursor used is 1.06:1; the added H3BO3 and the nickel hydroxide precursor used have a molar ratio of 0.001:1; the added V2O5 and the nickel hydroxide precursor used have a molar ratio of 0.001:1; (2) Put the ground material into a calcination furnace, introduce high-purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it to 500 °C at a heating rate of 5 °C / min and hold for 5 h, then heat it to 620 °C at a heating rate of 3 °C / min and hold for 15 h, and then naturally cool it to below 200 °C to obtain a LiNi ultra-high nickel cathode material co-doped with 0.2% molar content of B and V elements 0.998 B 0.001 V 0.001 O2 (marked as LNO-BV). The XRD pattern of the obtained modified lithium nickelate cathode material is as Figure 1 shown.

[0068] Perform XRD detection and Fullpro refinement on the obtained lithium nickelate cathode material to obtain a Li + / Ni 2+ mixing ratio of 3.3%; perform electrochemical performance tests on the obtained ultra-high nickel cathode material, and its discharge specific capacity at a current density of 0.1C is 231.7 mAh·g -1 , and the initial efficiency is 93.5%; the discharge specific capacity after cycling 100 times at a current density of 1C is 175.9 mAh·g -1 , and the capacity retention rate is 85.5%. Disassemble and clean the coin cell that has been cycled 100 times and charged to 4.3V in a glove box, let it dry naturally in the glove box, and then quantitatively measure its oxygen vacancy concentration to be 3.8% by positron annihilation spectroscopy (PAS).

[0069] Comparative Example 3 A preparation method of an Sr, V element co-doped ultra-high nickel cathode material, comprising the following steps: (1) Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0052 g of nano-scale SrO (purity 99.9%) and 0.0046 g of nano-scale V2O5 (purity 99.9%) respectively. First, put LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder state without obvious particles, then put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material color is uniform without variegation; among them, the lithium source used is lithium hydroxide monohydrate, and its molar ratio to the nickel hydroxide precursor used is 1.06:1; the added SrO and the nickel hydroxide precursor used The molar ratio is 0.001:1; the added V2O5 and the nickel hydroxide precursor used have a molar ratio of 0.001:1; (2) Put the ground material into a calcination furnace, introduce high-purity oxygen, adjust the flow rate to 0.8 - 1.0 L / min, heat it at a heating rate of 5 °C / min to 500 °C and hold for 5 h, then heat it at a heating rate of 3 °C / min to 620 °C and hold for 15 h, and then cool it naturally to below 200 °C to obtain a Li-based ultra-high nickel cathode material co-doped with 0.2% molar content of Sr and V elements 0.999 Ni 0.999 Sr 0.001 V 0.001 O2 (labeled as LNO-SrV). The XRD pattern of the obtained modified lithium nickelate cathode material is as Figure 1 shown.

[0070] Perform XRD detection and Fullpro refinement on the obtained lithium nickelate cathode material to obtain a Li + / Ni 2+ mixing ratio of 3.6%; perform electrochemical performance testing on the obtained ultra-high nickel cathode material, and its discharge specific capacity at a current density of 0.1C is 230.2 mAh·g -1 , and the initial efficiency is 91.5%; the discharge specific capacity after 100 cycles at a current density of 1C is 179.4 mAh·g -1 , and the capacity retention rate is 86.4%. Disassemble and clean the coin cell that has been cycled 100 times and charged to 4.3V in a glove box, let it dry naturally in the glove box, and then quantitatively measure its oxygen vacancy concentration by positron annihilation spectroscopy (PAS) to be 4.8%.

[0071] Comparative Example 4 A preparation method of an Sr and B co-doped ultra-high nickel cathode material, comprising the following steps: (1) Weigh 4.6357 g of Ni(OH)2 (purity 99.9%), 2.2887 g of LiOH·H2O (purity 97%), 0.0052 g of nanoscale SrO (purity 99.9%) and 0.0031 g of nanoscale H3BO3 (purity 99.9%) respectively. First, place LiOH·H2O in a mortar and grind it for 15 min until it becomes a powder state without obvious particles, then put the remaining compounds into the mortar and mix them evenly, and continue to grind for 20 min until the material color is uniform and without impurities; among them, the lithium source used is lithium hydroxide monohydrate, and its molar ratio to the nickel hydroxide precursor used is 1.06:1; the added SrO and the nickel hydroxide precursor used have a molar ratio of 0.001:1; the added H3BO3 and the nickel hydroxide precursor used have a molar ratio of 0.001:1; (2) The heat treatment process is the same as that in Example 1 to obtain a Li-based ultra-high nickel cathode material co-doped with 0.2% molar content of Sr and B elements 0.999 Ni 0.999 Sr0.001 B 0.001 O2 (labeled as LNO-SrB). The XRD pattern of the obtained modified lithium nickelate cathode material is as Figure 1 shown.

[0072] The obtained lithium nickelate cathode material was subjected to XRD detection and Fullpro refinement to obtain a Li + / Ni 2+ mixing ratio of 2.8%; the obtained ultra-high nickel cathode material was tested for its electrochemical performance, and its discharge specific capacity at a current density of 0.1C was 232.0 mAh·g -1 , and the initial efficiency was 93.2%; the discharge specific capacity after 100 cycles at a current density of 1C was 178.9 mAh·g -1 , and the capacity retention rate was 86.7%. The button cell that was cycled 100 times and charged to 4.3V was removed from the glove box for disassembly and cleaning, and then naturally dried in the glove box. Then, its oxygen vacancy concentration was quantitatively measured by positron annihilation spectroscopy (PAS) to be 4.6%.

[0073] The lithium-nickel mixing data of the lithium nickelate cathode materials prepared in each example and comparative example, the battery performance of the obtained cathode materials assembled, and the oxygen vacancy concentration data in the cathode materials of the battery after 100 cycles at a current density of 1C are shown in Table 1.

[0074] Table 1 From the lithium-nickel mixing data of the cathode materials obtained in Example 1 and Comparative Examples 1-4, it can be seen that compared with the undoped lithium nickelate cathode material, the lithium-nickel mixing degree of the doped lithium nickelate obtained in Comparative Example 3 with co-doping of Sr and V increased, and the lithium-nickel mixing of the co-doped lithium nickelate obtained in Comparative Example 4 with co-doping of Sr and B and Example 1 with co-doping of Sr, B and V decreased, and the latter decreased more significantly, indicating that the co-doping of Sr, B and V in Example 1 played a synergistic effect on reducing lithium-nickel mixing. At the same time, the lithium-nickel mixing of the co-doped lithium nickelate in Examples 2-3 also decreased significantly.

[0075] Regarding the battery performance of the cathode materials assembled in Example 1 and Comparative Examples 1-4, compared with the battery assembled with the cathode material prepared in Comparative Example 1, the initial Coulombic efficiency of the batteries assembled with the cathode materials prepared in Example 1 and Comparative Examples 2-4 increased at 0.1C, indicating that the structural stability of the matrix material was improved; comparing the batteries assembled with the cathode materials prepared in Example 1 and Comparative Examples 1-4 after activation at 0.1C and then cycled at 1C, the initial capacity was Example 1 > Comparative Example 3 > Comparative Example 4 > Comparative Example 2 > Comparative Example 1. It can be seen that the rate performance of the battery became better after doping; it can also be seen from Table 1 that the cycle performance of the batteries assembled with the cathode materials prepared in Examples 1-3 was better than that of each comparative example.

[0076] The oxygen vacancy concentrations of the cathode materials prepared in each of the examples and comparative examples were compared after the batteries assembled with them were cycled 100 times. The oxygen vacancy concentrations of the cathode materials in Examples 1 to 3 and Comparative Examples 2 to 4 all decreased.

[0077] In summary, compared with the batteries assembled with the pure lithium nickelate cathode material prepared in Comparative Example 1, the cycling performance of the batteries assembled with the cathode materials prepared in Comparative Examples 2 to 4 and Example 1 was improved, the oxygen vacancy concentration after cycling decreased, and the lithium-nickel mixing, cycling performance, and oxygen vacancy of the modified lithium nickelate cathode material obtained in Example 1 showed a synergistic effect in the improvement of the above properties compared with Comparative Examples 2 to 4. Moreover, compared with the initial discharge specific capacity of the modified lithium nickelate cathode materials prepared in Comparative Examples 2 to 4, the initial discharge specific capacity of the modified lithium nickelate cathode material prepared in Example 1 increased significantly. The above performance comparison shows that the co-doping of elements of types A, B, and C inside and on the surface of the particles can inhibit the degree of expansion and contraction of the material crystal structure during charge and discharge through a synergistic effect, improve the electronic conductivity of the material, inhibit the aggravation of cation mixing and oxygen escape at high voltages, synergistically improve the mechanical strength of the material, reduce the particle cracking and pulverization phenomena caused by cyclic stress, enhance the structural stability and electrochemical stability of the lithium nickelate matrix material, significantly improve the structural stability and charge-discharge efficiency of the lithium nickelate cathode material at high voltages, and have a high reversible capacity. By comparing Examples 1 to 3, it was found that excellent material properties can be obtained by changing the doping element combination, indicating that the doping combination strategy proposed in the present invention is effective.

[0078] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Modified lithium nickelate cathode material, characterized in that, In the modified lithium nickelate cathode material, the nickel element accounts for more than 98% of the total molar amount of nickel-site elements. In the modified lithium nickelate, three functional elements A, B, and C are co-doped. Element A is selected from one or more of Na, Mg, K, Ca, Sr, Ba, La, Pr, and Nd; Element B is selected from one or more of Y, Cd, Ce, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, B, and Cr; Element C is selected from one or more of Sc, Ti, V, Fe, Nb, Mo, Hf, Ta, W, Re, Si, Ga, Ge, As, and Sb.

2. The modified lithium nickelate cathode material according to claim 1, wherein, The modified lithium nickelate cathode material has a secondary particle morphology formed by the aggregation of nano-scale primary particles; the modified lithium nickelate cathode material has a layered α-NaFeO2 structure.

3. The modified lithium nickelate cathode material according to claim 1, characterized in that, At least part of Element A occupies the lithium site of lithium nickelate, and at least part of Elements B and C occupy the nickel site of lithium nickelate; the doping amounts of Elements A, B, and C are each independently 0.001 to 1% of the molar amount of the modified lithium nickelate cathode material.

4. The modified lithium nickelate cathode material according to claim 1, characterized in that, The chemical formula of the modified lithium nickelate cathode material is Li 1-x Ni 1-y-z A x B y C z O2, where 0.99 ≤ 1 - x ≤ 1.01 and 0.00001 ≤ x, y, z ≤ 0.

01.

5. Preparation method of modified lithium nickelate cathode material, characterized in that, Including: Mixing a nickel hydroxide precursor with a lithium source and metal compounds of Elements A, B, and C evenly to obtain a mixture; Performing heat treatment on the mixture under a protective atmosphere and then cooling it under an oxygen atmosphere to obtain the modified lithium nickelate cathode material.

6. The preparation method of the modified lithium nickelate cathode material according to claim 5, wherein, The metal compounds of Elements A, B, and C are each independently selected from one or more of oxides, hydroxides, carbonates, acetates, and nitrates; The metal compounds of Elements A, B, and C are nano-scale compounds; The molar ratio of a single type of element A, B, or C in the metal compounds of Elements A, B, and C to the molar amount of the nickel hydroxide precursor is each independently 0.00001 to 0.01:

1.

7. The preparation method of the modified lithium nickelate cathode material according to claim 5, characterized in that, The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium oxalate, and preferably lithium hydroxide; The molar ratio of lithium contained in the nickel hydroxide precursor to the lithium source is 1:1.04 to 1.

08.

8. The preparation method of the modified lithium nickelate cathode material according to claim 5, characterized in that, The protective atmosphere is an oxygen atmosphere; the oxygen partial pressure in the oxygen atmosphere is not less than 98%; The heat treatment is two-stage sintering; In the two-stage sintering, the holding temperature of the first-stage sintering is 400 to 600 °C; the holding time of the first-stage sintering is 4 to 6 h; the heating rate of the first-stage sintering is 3 to 8 °C / min; the holding temperature of the second-stage sintering is 600 to 800 °C; the holding time of the second-stage sintering is 10 to 20 h; the heating rate from the holding temperature of the first stage to the holding temperature of the second-stage sintering during the second-stage sintering is 3 to 5 °C / min; The cooling is natural cooling; The natural cooling includes cooling to below 200 °C in an oxygen atmosphere and then taking out.

9. The positive electrode, characterized in that, Including the modified lithium nickelate cathode material described in any one of claims 1 to 4 or the modified lithium nickelate cathode material prepared by the preparation method described in any one of claims 5 to 8.

10. A lithium-ion battery, characterized in that, Including the cathode described in claim 9.

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