Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery materials, and discloses a positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material comprises a bulk phase and a coating layer, the bulk phase comprises a nickel-rich layered oxide matrix containing lithium, zirconium, boron and aluminum, a doping element A, an optional doping element D and a doping element E; the weighted average valences of the doping element A, the doping element D and the doping element E meet the condition that [sigma (nA * dA) + sigma (nD * dD) + sigma (nE * dE)] / (sigma nA + sigma nD + sigma nE) is greater than or equal to 2.5 and less than or equal to 4.5; the coating layer comprises a low-temperature coating layer and a high-temperature coating layer which are sequentially arranged from inside to outside; and the positive electrode material meets the condition that e-strain * IA104 / IA0122 is greater than or equal to 0.2. The positive electrode material has excellent structural stability and mechanical stability under harsh conditions of high temperature and high voltage, and further has excellent cycle performance and safety performance.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles and the energy storage industry, lithium-ion batteries with high energy density and long cycle life have become a research focus. Layered transition metal oxides are considered ideal cathode materials due to their high specific capacity (>200mAh / g); however, their large-scale application still faces severe challenges. ① Poor structural stability: Nickel-rich ternary materials are prone to lattice oxygen precipitation and phase transformation (transformation from layered to spinel / rock salt phase) under deep delithiation (high voltage > 4.3V) or high temperature (> 45℃) conditions, leading to capacity decay and safety hazards.

[0003] ② Increased interfacial side reactions: Side reactions occur between the material surface and the electrolyte, resulting in a thicker CEI film and increased impedance. At the same time, the dissolution of transition metal ions leads to a decline in battery performance.

[0004] ③ Insufficient mechanical stability: The lattice volume change during the charging and discharging process can easily cause microcracks in the particles, accelerating electrolyte penetration and bulk structure destruction.

[0005] Current modification technologies are mainly divided into two categories, but both have limitations: Bulk doping: Single valence state elements (such as Al) 3+ Mg 2+ While doping can partially stabilize the crystal lattice, it is difficult to synergistically control electronic conductivity and structural strength. Surface coating: Traditional single-layer coatings (such as Al2O3 and Li3PO4) can only provide a physical barrier and cannot simultaneously solve the problems of near-surface structural degradation and low interfacial ion / electron transport efficiency. In addition, high-temperature coatings are prone to porosity, and low-temperature coatings have weak bonding forces, making it difficult to form a continuous and dense protective layer.

[0006] Therefore, there is an urgent need to develop a multi-element cathode material to overcome the performance bottleneck of nickel-rich ternary cathode materials under high voltage and high temperature conditions. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of poor structural and mechanical stability and numerous interfacial side reactions in existing layered metal oxide cathode materials, and to provide a cathode material, its preparation method, and a lithium-ion battery. This cathode material exhibits excellent structural and mechanical stability under harsh conditions of high temperature and high voltage, thereby resulting in excellent cycle performance and safety performance.

[0008] To achieve the above objectives, the present invention provides a cathode material comprising a bulk phase and a coating layer; The bulk phase comprises a nickel-rich layered oxide matrix containing lithium zirconium boron aluminum and doping element A, optional doping element D, and doping element E; The doping element A is selected from at least one of Sr, Cr, Na, Mg, K, Zn, and Ba; The doping element D is selected from at least one of Y, Sb, Sc, and Bi; The doping element E is selected from at least one of Nb, W, Ti, Mo, Ce, Si, Te, and Ta; The weighted average valence of dopant elements A, D, and E satisfies: 2.5 ≤ [Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤4.5; where nA, nD, and nE are the amounts of dopant elements A, D, and E in the bulk phase, respectively, in mol; and dA, dD, and dE are the valences of dopant elements A, D, and E in the bulk phase, respectively. The coating layer includes a low-temperature coating layer and a high-temperature coating layer arranged sequentially from the inside to the outside; The high-temperature coating layer contains Co, Al and element G; element G is selected from at least one of Zr, Nb, W, Ti, Mo, Ce, Sb, Si, Te, and Ta. The low-temperature coating layer contains B and element Z; element Z is selected from at least one of W, Al, and Ti. The positive electrode material satisfies e -strain ×IA 104 / IA 012 2 ≥0.2, where strain is the micro-strain of the cathode material, in units of % IA 104 IA 012 The percentages (%) of the relative diffraction peak areas of the (104) and (012) crystal planes of the cathode material as measured in XRD tests are respectively.

[0009] A second aspect of the present invention provides a method for preparing the cathode material described in the first aspect, comprising: (1) A nickel-rich precursor containing zirconium, boron and aluminum, a lithium source, a compound containing doped element A, a compound containing doped element D and a compound containing doped element E are mixed and then subjected to a first sintering to obtain a bulk material. (2) The bulk material, a first coating agent containing Co, Al and element G, and an optional lithium source are mixed and then subjected to a second sintering to obtain an intermediate material; (3) The intermediate material is mixed with a second coating agent containing B and element N and then subjected to a third sintering to obtain a positive electrode material; Among them, the temperature of the third roasting is less than or equal to the temperature of the second roasting and less than or equal to the temperature of the first roasting.

[0010] A third aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the first aspect of the present invention.

[0011] The multi-level synergistically enhanced lithium zirconium boron aluminum nickel-rich cathode material provided by this invention has a specific structural composition, including a multi-element nickel-rich layered oxide bulk phase, a high-temperature co-coating layer, and a low-temperature boron-containing coating layer. It can solve the problems of structural degradation, interfacial side reactions, and mechanical failure of nickel-rich ternary cathode materials under high voltage (>4.3V) and / or high temperature (>45℃) conditions. While maintaining high specific capacity, it improves cycle life by more than 10% and thermal stability by 30% compared with nickel-rich ternary cathode materials, making it particularly suitable for high-energy-density power batteries. Attached Figure Description

[0012] Figure 1 The image shows a cross-sectional scanning electron microscope (SEM) image of the cathode particles after the battery using the cathode material prepared in Example 1 of the present invention has been cycled at 25°C for 100 cycles.

[0013] Figure 2 The image shows a cross-sectional scanning electron microscope (SEM) image of the cathode particles of a battery prepared using the cathode material prepared in Comparative Example 1 of the present invention after cycling at 25°C for 100 cycles. Detailed Implementation

[0014] 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 and 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.

[0015] The first aspect of the present invention provides a cathode material, the cathode material comprising a bulk phase and a coating layer; The bulk phase comprises a nickel-rich layered oxide matrix containing lithium zirconium boron aluminum and doping elements A, D, and E. The doping element A is selected from at least one of Sr, Cr, Na, Mg, K, Zn, and Ba; The doping element D is selected from at least one of Y, Sb, Sc, and Bi; The doping element E is selected from at least one of Nb, W, Ti, Mo, Ce, Si, Te, and Ta; The weighted average valence of dopant elements A, D, and E satisfies: 2.5 ≤ [Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤4.5; where nA, nD, and nE are the amounts of dopant elements A, D, and E in the bulk phase, respectively, in mol; and dA, dD, and dE are the valences of dopant elements A, D, and E in the bulk phase, respectively. The coating layer includes a high-temperature coating layer and a low-temperature coating layer arranged sequentially from the inside to the outside; The high-temperature coating layer contains Co, Al and element G; element G is selected from at least one of Zr, Nb, W, Ti, Mo, Ce, Sb, Si, Te, and Ta. The low-temperature coating layer contains B and element Z; element Z is selected from at least one of W, Al, and Ti. The positive electrode material satisfies e -strain ×IA 104 / IA 012 2 ≥0.2, where strain is the micro-strain of the cathode material, in units of % IA 104 IA 012 The percentages (%) of the relative diffraction peak areas of the (104) and (012) crystal planes of the cathode material as measured in XRD tests are respectively.

[0016] In this invention, the types and contents of elements in the bulk phase and coating layer of the cathode material are determined by energy-dispersive X-ray spectroscopy (EDS).

[0017] In this invention, "from inside to outside" refers to the material's interior to its surface.

[0018] In this invention, the micro-strain of the cathode material refers to the relative change in the local interatomic spacing caused by lattice distortion within the cathode material relative to its ideal state (stress-free state), which is obtained by processing the XRD data of the cathode material using the "Size & Strain" analysis function of Jade software.

[0019] In this invention, the unit of the relative diffraction peak area percentage of the (104) crystal plane and the (012) crystal plane is %, and the relative diffraction peak area percentage refers to the area percentage of each diffraction peak relative to the strongest peak in this spectrum.

[0020] According to the present invention, the dopant element A is selected from at least one of Sr, Cr, Na, Mg, K, Zn, and Ba. According to some preferred embodiments of the present invention, the dopant element A is selected from at least one of Sr, Na, Mg, and Ba.

[0021] According to the present invention, the doping element E is selected from at least one of Nb, W, Ti, Mo, Ce, -Si, Te, and Ta. According to some preferred embodiments of the present invention, the doping element E is selected from at least one of Nb, W, Ti, Mo, and Ce.

[0022] In this invention, the high-temperature coating layer contains Co, Al, and element G; element G is selected from at least one of Zr, Nb, W, Ti, Mo, Ce, Sb, Si, Te, and Ta. According to some preferred embodiments of this invention, in the high-temperature coating layer, element G is selected from at least one of Zr, Nb, W, Ti, Mo, and Ce, which facilitates the comprehensive optimization of interfacial chemistry, structural mechanics, and transport dynamics under high-temperature driving.

[0023] According to the present invention, in the cathode material, the lithium-containing nickel-zirconium-boron layered oxide matrix includes multi-valence synergistic doping elements A, D, and E. The defects of single-valence doping are solved through the valence complementarity of doping elements A / D / E. Element A is a low-valence element, which alleviates lattice stress and suppresses phase transitions; element D is a medium-valence element, which stabilizes the oxygen lattice and reduces oxygen precipitation; and element E is a high-valence element, which provides strong lattice anchoring and anchors the transition metal. The synergistic effect of the above-mentioned preferred doping elements is beneficial for systematically solving multiple inherent problems of high-nickel materials at the atomic scale through charge compensation, radius matching, and functional complementarity.

[0024] According to the present invention, the weighted average valence of the dopant elements A, D, and E satisfies: 2.5 ≤ [Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤3.6; wherein nA, nD, and nE are the amounts of dopant elements A, D, and E in the bulk phase, respectively, in mol; and dA, dD, and dE are the valences of dopant elements A, D, and E in the bulk phase, respectively.

[0025] According to some preferred embodiments of the present invention, the weighted average valence of the dopant element A, dopant element D, and dopant element E satisfies 2.6≤[Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤3.5.

[0026] In this invention, controlling the average valence state of the doping element group helps to avoid local lattice distortion. If the weighted average valence is too low, low valence states dominate, lattice expansion intensifies, and structural stability is insufficient. If the weighted average valence is too high, there are too many high valence states, lithium sites are occupied, leading to a decrease in capacity and ionic conductivity. The weighted average valence can reach an equilibrium state within the above-mentioned preferred range, giving the material optimal structural support and a high lithium-ion diffusion rate.

[0027] According to the present invention, the positive electrode material satisfies e -strain ×IA 104 / IA 012 2 ≥0.2, where strain is the micro-strain of the cathode material, in units of % IA 104 IA 012 These represent the relative diffraction peak area percentages of the (104) and (012) crystal planes of the cathode material as measured in XRD tests. According to some preferred embodiments of the present invention, the cathode material satisfies 0.25 ≤ e -strain ×IA 104 / IA 012 2 ≤0.55.

[0028] In this invention, the cathode material satisfies the above formula—it exhibits smaller lattice distortion caused by point defects, dislocations, atomic shifts, etc.; it promotes preferential growth of the low surface energy (104) plane, resulting in a more ordered structure, a more stable surface, and Li… + The diffusion channels are more unobstructed; the appearance of high surface energy (012) surfaces is suppressed, reducing side reactions with electrolyte, oxygen release and cation mixing; this structural feature is conducive to achieving better high voltage and high temperature performance.

[0029] According to the present invention, preferably, based on the total mass of the cathode material, the total content of dopant element A, dopant element D and dopant element E in the cathode material is 0.1-1%, more preferably 0.2-0.7%.

[0030] In this invention, the content of the doping element within the above-mentioned preferred range is beneficial to improve the structural stability and cycle life of the cathode material while ensuring capacity.

[0031] According to the present invention, preferably, based on the total mass of the cathode material, the content of the high-temperature coating layer in the cathode material is 0.05-3%, more preferably 0.3-2%, which is beneficial to forming a thin, continuous, defect-free protective layer.

[0032] Preferably, in the high-temperature coating layer, the mass ratio of Al to element G is (0.1-10):1, more preferably (0.5-5):1, which is conducive to achieving a combined optimization of "conduction optimization" and "structural reinforcement".

[0033] Preferably, in the high-temperature coating layer, the total content of Al and element G, by elemental mass, is not higher than the content of element Co, which is beneficial for forming a composite interface layer with both high ionic conductivity and excellent chemical stability.

[0034] Preferably, based on the total mass of the cathode material, the Co content in the high-temperature coating layer is 0.05-2%.

[0035] According to some preferred embodiments of the present invention, based on the total mass of the cathode material, the content of the low-temperature coating layer in the cathode material is 0.05-1%, preferably 0.05-0.3%, which is beneficial for balancing protection and ion conductivity.

[0036] According to the present invention, preferably, in the low-temperature coating layer, the mass ratio of B to element Z is (0.1-10):1; more preferably, it is (0.5-3):1.

[0037] According to the present invention, preferably, based on the total mass of the positive electrode material, the total content of the high-temperature coating layer and the low-temperature coating layer in the positive electrode material is 0.15-3.5%, and more preferably, based on the total mass of the positive electrode material, the total content of the high-temperature coating layer and the low-temperature coating layer is 0.35-2%.

[0038] In this invention, the total content of the high-temperature coating layer and the low-temperature coating layer being within the above-mentioned preferred range is beneficial to achieving interface coupling between the conductive network in the high-temperature coating layer and the borosilicate glass state in the low-temperature coating layer.

[0039] According to some preferred embodiments of the present invention, when the dopant element E and element G are the same element, the total content of the dopant element E and dopant element G in the bulk phase and the high-temperature coating layer is 0.1-1.5% based on the total mass of the cathode material.

[0040] In this invention, the preferred method described above is beneficial for controlling the spatial distribution of elements in the "bulk phase" and "interface" of the material.

[0041] The lithium zirconium boron aluminum nickel-rich cathode material provided by this invention comprises a three-layer structure from the inside out: a nickel-rich layered oxide, a high-temperature co-coating layer, and a low-temperature boron-containing coating layer. The zirconium boron aluminum multi-element nickel-rich material optimizes crystal orientation and significantly reduces microstrain by adjusting the relative exposure of the (104) and (012) crystal planes through surface energy adjustment. The nickel-rich layered oxide exhibits multi-valence synergistic doping, enhancing the bulk structure while providing high capacity. The high-temperature co-coating layer constructs a near-surface conductive network and structural support layer, exhibiting excellent conductivity and near-surface stability. The low-temperature coating layer densifies the interface, providing interfacial mechanical protection, preventing side reactions between the cathode material and the electrolyte, and further improving the interfacial stability of the material. Under the above multi-level synergistic effect, the structural and chemical stability of this cathode material is significantly enhanced, possessing high capacity, good cycle stability, and good thermal stability.

[0042] The second aspect of the present invention provides a method for preparing the cathode material described in the first aspect of the present invention, comprising: (1) A nickel-rich precursor containing zirconium, boron and aluminum, a lithium source, a compound containing doped element A, a compound containing doped element D and a compound containing doped element E are mixed and then subjected to a first sintering to obtain a bulk material. (2) The bulk material, a first coating agent containing Co, Al and element G, and an optional lithium source are mixed and then subjected to a second sintering to obtain an intermediate material; (3) The intermediate material is mixed with a second coating agent containing B and element Z and then subjected to a third sintering to obtain a cathode material; Among them, the temperature of the third roasting is less than or equal to the temperature of the second roasting and less than or equal to the temperature of the first roasting.

[0043] In this invention, step (1) further includes pulverizing the first sintered material to obtain the bulk material. This invention does not impose any particular limitation on the pulverization conditions, as long as the technical objective of this invention is achieved.

[0044] In this invention, step (2) further includes pulverizing the second sintered material to obtain the intermediate material. This invention does not impose any particular limitations on the pulverization conditions, as long as the technical objective of this invention is achieved.

[0045] The present invention does not have any particular limitation on the mixing conditions described in steps (1) and (2), but the mixing is sufficient.

[0046] In this invention, there is no particular limitation on the type of lithium source, and lithium sources conventionally used in the art for preparing layered oxide cathode materials can be used. According to some preferred embodiments of the invention, the lithium source is selected from LiOH and / or Li₂CO₃.

[0047] According to some preferred embodiments of the present invention, in step (2), the molar ratio of the Co content in the first coating agent to (the total free Li content in the bulk material + the lithium content of the lithium source in step (2)) is 0.1-2.5.

[0048] This invention does not particularly limit the source of the compounds containing dopant element A, dopant element D, and dopant element E, and can use dopant element feeding methods conventionally used in the art for preparing layered oxide cathode materials. According to some preferred embodiments of this invention, each of the above compounds is independently selected from at least one of the oxides, hydroxides, lithium salts, phosphates, and sulfates of the corresponding element.

[0049] In this invention, in the first coating agent, elements Al and G are each independently selected from at least one of the oxides, hydroxides, lithium salts, phosphates, and sulfates of the corresponding elements; in the first coating agent, the source of Co is selected from at least one of the oxides, hydroxides, hydroxyoxides, and phosphates of Co. This invention does not particularly limit the source of the first coating agent; it can be obtained using known methods or commercially available products.

[0050] In this invention, the doping elements A, D, E, G, and Z are all within the same element range as described in the first aspect above, and will not be repeated here.

[0051] According to the present invention, in the preparation method of the cathode material, in step (1), during the sintering, lattice reconstruction is completed by high-temperature solid solution of multivalent elements to achieve atomic-level doping of bulk elements.

[0052] According to the present invention, in step (2), a continuous high-temperature coating layer is formed by medium-temperature diffusion during the sintering process.

[0053] According to the present invention, in step (3), during the sintering process, a flowing glass phase is formed by low-temperature vitrification, which fills the pores of the high-temperature layer, completes the encapsulation of the low-temperature coating layer, and blocks the electrolyte penetration.

[0054] According to the present invention, the temperature of step (2) is less than or equal to the temperature of step (1), and the temperature of step (3) is less than or equal to the temperature of step (2). The three-step temperature gradient sintering process is beneficial for high-temperature skeleton → low-temperature interface fine repair.

[0055] In this invention, a nickel-rich precursor of zirconium boron aluminum is selected and combined with multiple valence elements for synergistic doping to form a preferentially grown, low-defect, and stable crystal structure, reducing lattice distortion and inhomogeneity within the material. Simultaneously, high- and low-temperature double coating is used to further promote the reconstruction of the low-energy (104) crystal plane and passivate the high-energy (102) plane, preventing side reactions and buffering stress. Ultimately, a cathode material structure satisfying ei is obtained. -strain ×IA 104 / IA 012 2 ≥0.2. According to some preferred embodiments of the present invention, the conditions for the first calcination include: a temperature of 600-1000℃, preferably 650-850℃; and a time of 7-20h, preferably 10-17h.

[0056] According to some preferred embodiments of the present invention, the conditions for the second calcination include: a temperature of 400-800°C, preferably 400-700°C; and a time of 5-20 hours, preferably 8-16 hours. According to some preferred embodiments of the present invention, the conditions for the third calcination include: a temperature of 200-600°C, preferably 200-450°C; and a time of 5-20 hours, preferably 8-16 hours.

[0057] In this invention, the above-mentioned preferred calcination conditions are beneficial for constructing a stable bulk crystal structure, a strongly bonded interface layer, and an ultimate barrier.

[0058] In this invention, a nickel-rich precursor of zirconium boron aluminum is selected and combined with multiple valence elements for synergistic doping to form a preferentially grown, low-defect, and stable crystal structure, reducing lattice distortion and inhomogeneity within the material. Simultaneously, high- and low-temperature double coating is used to further promote the reconstruction of the low-energy (104) crystal plane and passivate the high-energy (102) plane, preventing side reactions and buffering stress. Ultimately, a cathode material structure satisfying ei is obtained. -strain ×IA 104 / IA 012 2 ≥0.2. A third aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the first aspect of the present invention.

[0059] The lithium-ion battery provided by this invention contains the positive electrode material provided by this invention, which improves the operating voltage and temperature window, and takes into account both high capacity and long cycle life. It can be used as the first choice for high-end electric vehicles, low-altitude aircraft, humanoid robots and other fields.

[0060] The present invention will be described in detail below through embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0061] Example 1 (1) Ni 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005 (OH)2, LiOH, Sr2CO3, and Nb2O5 are added to a high-speed mixer for high-speed mixing. In the mixture formulation, Ni... 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005The mass ratio of (OH)2, LiOH, Sr, and Nb is 1:47wt%:0.1wt%:0.1wt%. The mixing speed is 800 rpm / min. After mixing for 30 min, the first mixture is obtained and placed in a box furnace. It is sintered at 890℃ for 12 h in an oxygen atmosphere. After naturally cooling to room temperature, the material is taken out and crushed to obtain matrix powder (the weighted average valence of the doped elements in the matrix is ​​3.5). The content of Li2CO3 in the matrix is ​​3100 ppm and the content of LiOH is 5400 ppm.

[0062] (2) Mix the matrix powder, CoOOH, Al(OH)3, ZrO2 and LiOH. In the mixture formula, the mass ratio of matrix, Co, Al, Zr and Li is 1:0.8wt%:0.2wt%:0.1wt%. Sinter at 700℃ for 10h in an oxygen atmosphere and then pulverize to obtain the intermediate. (3) The intermediate is mixed with H3BO3 and Al2O3, wherein the amount of B and Al added is 0.1wt% and 0.1wt% respectively, and sintered at 300℃ for 8h in air atmosphere to obtain the final material (denoted as P1).

[0063] Microstrain testing was performed on the prepared material P1. The measured microstrain was 0.033% (denoted as strain). XRD testing was performed on the prepared material P1, and the relative diffraction peak area percentage of the 104 crystal plane was measured to be 81.2% (denoted as IA). 104 The relative diffraction peak area percentage of the 012 crystal plane is 13.3% (denoted as IA). 012 The calculated structural parameters e of the lithium zirconium boron aluminum nickel-rich cathode material -strain ×IA 104 / IA 012 2 It is 0.44.

[0064] Example 2 (1) Ni 0.90 Co 0.05 Al 0.05 Zr 0.00003 B 0.00005 (OH)2, LiOH, MgO, Y2O3, and WO3 are added to a high-speed mixer for high-speed mixing. In the mixture formulation, Ni... 0.90 Co 0.05 Al 0.05 Zr 0.00003 B 0.00005The mass ratio of (OH)2, LiOH, Mg, Y, and W is 1:47wt%:0.1wt%:0.2wt%:0.1wt%. The mixing speed is 800 rpm / min. After mixing for 30 min, the first mixture is obtained and placed in a box furnace. It is sintered at 840℃ for 14 h in an oxygen atmosphere. After naturally cooling to room temperature, the material is taken out and crushed to obtain matrix powder (the weighted average valence of the doped elements in the matrix is ​​2.6). The content of Li2CO3 in the matrix is ​​3300 ppm and the content of LiOH is 6200 ppm.

[0065] (2) Mix the matrix powder, Co(OH)2, Al2O3 and Nb2O5. In the mixture formula, the mass ratio of matrix, Co, Al and Nb is 1:0.3wt%:0.1wt%:0.2wt%. Sinter at 680℃ for 10h in an oxygen atmosphere and then pulverize to obtain the intermediate. (3) The intermediate is mixed with H3BO3 and Li2WO4, wherein the amount of B and W added is 0.1wt% and 0.15wt% respectively, and sintered at 350℃ for 8h under an oxygen atmosphere to obtain the final material (denoted as P2).

[0066] The obtained structural parameters e of the lithium zirconium boron aluminum nickel-rich cathode material -strain ×IA 104 / IA 012 2 It is 0.38.

[0067] Example 3 (1) Ni 0.69 Co 0.15 Mn 0.15 Al 0.01 Zr 0.00003 B 0.00005 (OH)2, Li2CO3, Ba(OH)2, Sb2O3, and Nb2O5 are added to a high-speed mixer for high-speed mixing. In the mixture formulation, Ni... 0.69 Co 0.15 Mn 0.15 Al 0.01 Zr 0.00003 B 0.00005 The mass ratio of (OH)2, Li2CO3, Ba, Sb, and Nb is 1:47wt%:0.3wt%:0.1wt%:0.1wt%. The mixing speed is 800 rpm / min, and the mixture is mixed for 30 min to obtain the first mixture. The mixture is placed in a box furnace and sintered at 950℃ for 15 h in air atmosphere. After naturally cooling to room temperature, the material is taken out and crushed to obtain the matrix powder (the weighted average valence of the doped elements in the matrix is ​​3.0). The content of Li2CO3 in the matrix is ​​1200 ppm, and the content of LiOH is 2100 ppm.

[0068] (2) Mix the matrix powder, Co3O4, Al2O3, TiO2 and Li2CO3. In the mixture formula, the mass ratio of matrix, Co, Al, Ti and Li is 1:1.5wt%:0.3wt%:0.2wt%:0.1wt%. Sinter at 700℃ for 10h in air atmosphere and then pulverize to obtain the intermediate. (3) The intermediate is mixed with H3BO3 and TiO2, wherein the amount of B and Ti added is 0.1wt% and 0.1wt% respectively, and sintered at 300℃ for 8h in air atmosphere to obtain the final material (denoted as P3).

[0069] The obtained structural parameters e of the lithium zirconium boron aluminum nickel-rich cathode material -strain ×IA 104 / IA 012 2 It is 0.49.

[0070] Example 4 The method is the same as in Example 1, except that Ni is used. 0.90 Co 0.05 Al 0.05 Zr 0.00003 B 0.00005 (OH)2, LiOH, Na2SO4, Sb2O3, and MoO3 are added to a high-speed mixer for high-speed mixing. In the mixture formulation, Ni... 0.90 Co 0.05 Al 0.05 Zr 0.0000 3B 0.00005 The mass ratio of (OH)₂, LiOH, Na, Sb, and Mo is 1:47wt%:0.05wt%:0.1wt%:0.35wt%. The matrix contains 4200ppm Li₂CO₃ and 5800ppm LiOH. The resulting material is designated as P3. The structural parameters e of the lithium zirconium boron aluminum nickel-rich cathode material obtained are... -strain ×IA 104 / IA 012 2 The value is 0.59, and the weighted average valence of the dopant element is 4.0.

[0071] Comparative Example 1 Ni 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005 (OH)2 and LiOH are added to a high-speed mixer for high-speed mixing. In the mixture formulation, Ni... 0.8 Co 0.1 Mn 0.1The mass ratio of (OH)₂ to LiOH is 1:47wt%, the mixing speed is 800 rpm / min, and the mixing time is 30 min to obtain the first mixture. This mixture is then placed in a box furnace and sintered at 890℃ for 12 h under an oxygen atmosphere. After naturally cooling to room temperature, the material is removed, pulverized, and the resulting cathode material is denoted as D1. The structural parameters of the obtained cathode material are e. -strain ×IA 104 / IA 012 2 It is 0.12.

[0072] Comparative Example 2 The method is the same as in Example 1, except that Ni is selected as the precursor. 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005 (OH)2, without performing steps (2) and (3), yields the positive electrode material, denoted as D2. The obtained positive electrode material structural parameters e... -strain ×IA 104 / IA 012 2 It is 0.14.

[0073] Comparative Example 3 The method is the same as in Example 1, except that Ni is selected as the precursor. 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005 (OH)2, without proceeding to step (3), yields the positive electrode material, denoted as D3. The obtained positive electrode material structural parameters e -strain ×IA 104 / IA 012 2 It is 0.18.

[0074] Comparative Example 4 The method is the same as in Example 1, except that Ni is selected as the precursor. 0.79 Co 0.10 Mn 0.10 Al 0.01 Zr 0.00003 B 0.00005 (OH)2, without proceeding to step (2), yields the positive electrode material, denoted as D4. The obtained positive electrode material structural parameters e -strain ×IA 104 / IA 012 2 It is 0.16.

[0075] Comparative Example 5 The method is the same as in Example 1, except that the precursor is Ni. 0.8 Co 0.1 Mn 0.1 (OH)₂. The resulting cathode material is denoted as D5. The structural parameters e of the obtained cathode material are... -strain ×IA 104 / IA 012 2 It is 0.10.

[0076] Comparative Example 6 The method is the same as in Example 3, except that Ba doping is not performed (i.e., Ba(OH)2 is not added).

[0077] The obtained cathode material is denoted as D6. The structural parameters e of the obtained cathode material are... -strain ×IA 104 / IA 012 2 It is 0.17.

[0078] Comparative Example 7 The method is the same as in Example 4, except that Nb doping is not performed (i.e., Nb2O5 is not added).

[0079] The obtained cathode material is denoted as D7. The structural parameters e of the obtained cathode material are... -strain ×IA 104 / IA 012 2 It is 0.15.

[0080] Test case CR2032 button cells were fabricated using the cathode materials prepared in the above embodiments and comparative examples. The fabrication process is as follows: The positive electrode material, conductive agent carbon black SP, and solvent NMP were mixed at a weight ratio of 1:0.02:0.54 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a clean aluminum foil and dried to obtain a positive electrode sheet. Using a CR2032 battery casing, the above-mentioned electrode was used as the positive electrode, a lithium metal sheet as the negative electrode, an 18mm 2325 separator, and Jinniu JN908-6 electrolyte. The cells were assembled sequentially to obtain button cells (denoted as B1-B4 and DB1-DB7, respectively). The assembled cells were left to stand for 24 hours, and then their electrical performance was tested.

[0081] The prepared batteries were subjected to capacity performance testing, high-voltage cycle performance testing, and high-temperature storage performance testing.

[0082] Capacity performance test conditions: set the charge and discharge voltage to 3.0-4.3V, the charge rate to 0.2C, and the discharge rate to 0.5C.

[0083] High-voltage cycle performance test conditions: set the charge and discharge voltage to 2.8-4.45V, the charge rate to 0.5C, and the discharge rate to 0.5C.

[0084] High-temperature storage performance test conditions: 4.45V fully charged state, stored at 60℃ for 7 days, and then its impedance growth rate is tested. Specifically, the battery before and after storage is tested at room temperature to obtain R0 (initial interface impedance before high-temperature storage) and R1 (interface impedance measured after high-temperature storage and recovery to room temperature). The impedance growth rate is calculated as [(R1-R0) / R0]×100%.

[0085] Crack rate calculation method: number of cracked particles / total number of particles × 100%. The statistical object is the primary particles of the cathode material after high voltage cycling (100 cycles). Cracked particles are defined as particles whose crack length is ≥ 1 / 3 of the particle diameter or whose cracks penetrate the particle.

[0086] Table 1

[0087] As shown in Table 1, under the aforementioned test conditions, the three-level synergistic modification strategy provided by this invention can maintain the high-voltage cycle retention rate of the nickel-rich cathode material above 93%, significantly reduce the crack rate after cycling to below 3%, and achieve an impedance increase of no more than 15% after high-temperature storage. While maintaining high capacity, it significantly improves cycle life, thermal stability, and mechanical strength, thereby enhancing the long lifespan and high safety of the battery system. In contrast, the cathode material prepared in the comparative experiment cannot achieve the aforementioned comprehensive effects. Figure 1 This is a cross-sectional scanning electron microscope (SEM) image of the positive electrode particles of a battery prepared with the positive electrode material described in Example 1 of this invention after 100 cycles at 25°C. Figure 1 As can be seen from this, the material prepared by this invention can still maintain particle integrity after cycling. Figure 2 This is a cross-sectional scanning electron microscope image of the positive electrode particles of the battery prepared by the positive electrode material described in Comparative Example 1 of the present invention after 100 cycles at 25°C. As can be seen from the image, cracks were generated in the positive electrode material after cycling.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that, The cathode material includes a bulk phase and a coating layer; The bulk phase comprises a nickel-rich layered oxide matrix containing lithium zirconium boron aluminum and doping element A, optional doping element D, and doping element E; The doping element A is selected from at least one of Sr, Cr, Na, Mg, K, Zn, and Ba; The doping element D is selected from at least one of Y, Sb, Sc, and Bi; The doping element E is selected from at least one of Nb, W, Ti, Mo, Ce, Si, Te, and Ta; The weighted average valence of dopant elements A, D, and E satisfies: 2.5 ≤ [Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤4.5; where nA, nD, and nE are the amounts of dopant elements A, D, and E in the bulk phase, respectively, in mol; and dA, dD, and dE are the valences of dopant elements A, D, and E in the bulk phase, respectively. The coating layer includes a low-temperature coating layer and a high-temperature coating layer arranged sequentially from the inside to the outside; The high-temperature coating layer contains Co, Al and element G; element G is selected from at least one of Zr, Nb, W, Ti, Mo, Ce, Sb, Si, Te, and Ta. The low-temperature coating layer contains B and element Z; element Z is selected from at least one of W, Al, and Ti. The positive electrode material satisfies e -strain ×IA 104 / IA 012 2 ≥0.2, where strain is the micro-strain of the cathode material, in units of % IA 104 IA 012 These represent the percentage of the relative diffraction peak areas of the (104) and (012) crystal planes of the cathode material as measured in XRD tests.

2. The cathode material according to claim 1, wherein, In the bulk phase, the doping element A is selected from at least one of Sr, Na, Mg, and Ba; And / or, the doping element E is selected from at least one of Nb, W, Ti, Mo, and Ce; And / or, in the high-temperature coating layer, the element G is selected from at least one of Zr, Nb, W, Ti, Mo, and Ce.

3. The cathode material according to claim 1 or 2, wherein, The weighted average valence of dopant A, dopant D, and dopant E satisfies 2.6 ≤ [Σ(nA×dA)+Σ(nD×dD)+Σ(nE×dE)] / (ΣnA+ΣnD+ΣnE)≤3.

5.

4. The cathode material according to any one of claims 1-3, wherein, The positive electrode material satisfies 0.25 ≤ e -strain ×IA 104 / IA 012 2 ≤0.

55.

5. The cathode material according to any one of claims 1-4, wherein, Based on the total mass of the cathode material, the total content of dopant element A, dopant element D and dopant element E in the cathode material is 0.1-1%, preferably 0.2-0.7%.

6. The cathode material according to any one of claims 1-5, wherein, Based on the total mass of the cathode material, the content of the high-temperature coating layer in the cathode material is 0.05-3%, preferably 0.3-2%; Preferably, in the high-temperature coating layer, the mass ratio of Al to element G is (0.1-10):1, more preferably (0.5-5):1; Preferably, in the high-temperature coating layer, the total content of Al and element G, by elemental mass, is not higher than the content of element Co; Preferably, based on the total mass of the cathode material, the Co content in the high-temperature coating layer is 0.05-2%.

7. The cathode material according to any one of claims 1-6, wherein, Based on the total mass of the cathode material, the content of the low-temperature coating layer in the cathode material is 0.05-1%, preferably 0.05-0.3%; Preferably, in the low-temperature coating layer, the mass ratio of B to element Z is (0.1-10):1; more preferably, it is (0.5-3):

1.

8. The cathode material according to any one of claims 1-7, wherein, Based on the total mass of the cathode material, the total content of the high-temperature coating layer and the low-temperature coating layer in the cathode material is 0.15-3.5%; Preferably, the total content of the high-temperature coating layer and the low-temperature coating layer is 0.35-2% based on the total mass of the cathode material.

9. The cathode material according to any one of claims 1-8, wherein, When the dopant element E and element G are the same element, based on the total mass of the cathode material, the total content of the dopant element E and dopant element G in the bulk phase and the high-temperature coating layer is 0.1-1.5%.

10. A method for preparing the cathode material according to any one of claims 1-9, comprising: (1) A nickel-rich precursor containing zirconium, boron and aluminum, a lithium source, a compound containing doped element A, a compound containing doped element D and a compound containing doped element E are mixed and then subjected to a first sintering to obtain a bulk material. (2) The bulk material, a first coating agent containing Co, Al and element G, and an optional lithium source are mixed and then subjected to a second sintering to obtain an intermediate material; (3) The intermediate material is mixed with a second coating agent containing B and element Z and then subjected to a third sintering to obtain a cathode material; Among them, the temperature of the third roasting is less than or equal to the temperature of the second roasting and less than or equal to the temperature of the first roasting.

11. The method according to claim 10, wherein, The conditions for the first roasting include: a temperature of 600-1000℃, preferably 650-850℃; and a time of 7-20h, preferably 10-17h. And / or, the conditions for the second calcination include: a temperature of 400-800℃, preferably 400-700℃; and a time of 5-20h, preferably 8-16h. And / or, the conditions for the third calcination include: a temperature of 200-600℃, preferably 200-450℃; and a time of 5-20h, preferably 8-16h.

12. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the positive electrode material according to any one of claims 1-9.

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