Positive electrode material and lithium ion battery

Abstract

The invention provides a positive electrode material and a lithium ion battery. The positive electrode material provided by the invention is a lithium transition metal composite oxide, the positive electrode material comprises an Al element, the section of the positive electrode material is represented by a scanning electron microscope and an element energy spectrum instrument, the enrichment degree x of Al is greater than or equal to 20% and less than or equal to 40%, and the depletion degree y of Al is greater than or equal to 20% and less than or equal to 50%. According to the invention, the enrichment degree x of Al is controlled to be 20-40%, and the depletion degree y of Al is controlled to be 20-50%, so that the cycle stability of the positive electrode material is remarkably improved, the applicant speculates that in the positive electrode material, the local super-coordination tendency of an Al-O bond is inhibited through the cooperation of an Al depletion region and an Al enrichment region in the range, and the cycle stability of the positive electrode material is improved. And anisotropic stress caused by lattice distortion is reduced, so that Li layer slippage and oxygen layer mismatching in the charging and discharging process can be inhibited, and generation of intragranular cracks is relieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive electrode materials, in particular to a positive electrode material and a lithium ion battery. BACKGROUND

[0002] With the rapid development of new energy vehicles and energy storage technology, as the core power source, the energy density and cycle life of lithium ion batteries become key indicators. In the positive electrode material, with the increase of the content of the positive electrode material, the structural stability of the positive electrode material in the cycle process will also decrease. In order to improve the cycle stability of the positive electrode material, the cycle performance of the positive electrode material is usually improved by introducing a doping element into the positive electrode material. However, in the process of introducing the doping element, on the one hand, the regional distribution of the doping element is not balanced, which leads to the decrease of the rate performance of the positive electrode material; on the other hand, the doping element is usually selected from the metal with electrochemical inertness and stable ionic radius, but the high doping amount (>1.5 wt%) will block the lithium layer channel, which leads to the decrease of the initial coulombic efficiency and limits the performance optimization of the positive electrode material.

[0003] Therefore, the present application is provided. SUMMARY

[0004] The main purpose of the present application is to provide a positive electrode material and a lithium ion battery, so as to solve the technical problem in the prior art that it is difficult to realize the uniform distribution of the doping element in the positive electrode material by using the traditional mechanical method, and the local concentration gradient is easy to appear, which leads to the limitation of the modification effect.

[0005] In order to achieve the above purpose, according to one aspect of the present application, a positive electrode material is provided, the positive electrode material is a lithium transition metal composite oxide, the positive electrode material comprises an Al element, the section of the positive electrode material is characterized by a scanning electron microscope and an energy dispersive spectrometer, the EDS element distribution map of the positive electrode material is divided into a grid with z squares, z≥300, the enrichment degree x of Al satisfies: 20%≤x≤40%, the barren degree y of Al satisfies: 20%≤y≤50%; wherein, based on the total atom number of the positive electrode material, the square with the atomic percentage of Al element greater than 40at% is an Al enrichment square, the square with the atomic percentage of Al element less than 20at% is an Al barren square, the number of the Al enrichment square is m, the number of the Al barren square is n, the enrichment degree x of Al is m / z, and the barren degree y of Al is n / z.

[0006] Further, in the positive electrode material, the unevenness S of the distribution of the Al element satisfies: 150≤S 2 ≤220, and 2 ; ;

[0007] wherein, the EDS element distribution map is divided into four quadrants, Let A be the number of Al-rich squares in the i-th quadrant of the four quadrants. The average number of enriched squares in quadrant A1.

[0008] Furthermore, in the XRD spectrum of the cathode material, the 104 peak 2θ satisfies: 44.38°≤2θ≤44.42°.

[0009] Furthermore, 0.6 ≤ x / y ≤ 1.20;

[0010] Furthermore, 0.7 ≤ x / y ≤ 1.14;

[0011] Furthermore, the median particle size D50 of the cathode material is 4.5-5.5 μm.

[0012] Furthermore, the span value of the cathode material is 0.40-0.60.

[0013] Furthermore, the chemical formula of the cathode material is LiNi. 1-a-b Co a Mn b M c O2, where 0.04≤a≤0.10, 0.05≤b≤0.10, 0.001≤c≤0.0015, and M includes Al.

[0014] Furthermore, the content of Al in the cathode material is 3500-5500 ppm.

[0015] Furthermore, the impedance of the positive electrode material is 15-25Ω.

[0016] Furthermore, the compaction density of the cathode material is 2.8-3.1 g / cm³. 3 .

[0017] Furthermore, the tap density of the cathode material is 2.4-2.8 g / cm³. 3 .

[0018] Furthermore, the pH of the cathode material surface is 11.4-11.7.

[0019] According to another aspect of this application, a lithium-ion battery is provided, which includes the positive electrode material provided in the first aspect above.

[0020] By applying the technical solution of this application, the cathode material provided in this application, by controlling the Al enrichment x to be between 20% and 40% and the Al depletion y to be between 20% and 50%, is beneficial to significantly improve the cycle stability of the cathode material. The applicant speculates that in the cathode material, the cooperation between the Al depletion region and the Al enrichment region within the above range is beneficial to suppress the local overcoordination tendency of Al-O bonds, reduce the anisotropic stress caused by lattice distortion, thereby suppressing Li layer slip and oxygen layer mismatch during charging and discharging, and alleviating the generation of intracrystalline and intercrystalline cracks. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0022] Figure 1 A statistical graph showing the enrichment x and depletion y of Al, the cathode material provided in Example 1, determined using scanning electron microscopy and elemental energy dispersive spectroscopy.

[0023] Figure 2 The distribution of peak 104 in the XRD spectra of the cathode materials provided in Examples 1-2 and Comparative Example 1 is shown;

[0024] Figure 3 This is a schematic diagram of the structure of a secondary battery during charging according to an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the structure of a secondary battery during discharge, according to an embodiment of the present invention. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0027] In a first typical embodiment of this application, a cathode material is provided, which includes Al element. The cross-section of the cathode material is characterized by scanning electron microscopy and elemental energy dispersive spectroscopy. The EDS elemental distribution map of the cathode material is divided into a grid with z squares, z≥300. The enrichment degree x of Al satisfies: 20%≤x≤40%, and the depletion degree y of Al satisfies: 20%≤y≤50%. Based on the total number of atoms in the cathode material, squares with the percentage of Al atoms greater than 40at% are Al-enriched squares, and squares with the percentage of Al atoms less than 20at% are Al-depleted squares. The number of Al-enriched squares is m, and the number of Al-depleted squares is n. The enrichment degree x of Al = m / z; the depletion degree y of Al = n / z.

[0028] In the present application, the test method of the enrichment degree x and the barren degree y of Al is as follows: the section of the positive electrode material is characterized by a scanning electron microscope and an energy dispersive spectrometer at a magnification of 5K, and the EDS element area distribution map of the section of the positive electrode material is divided into z square grids, z≥300, the side length of the grid is 0.4-0.6 μm, wherein, based on the total atomic number of the positive electrode material, the grid of the region with an atomic percentage of Al element greater than 40 at% is an Al enrichment grid, the number of Al enrichment grids is m, the grid with an atomic percentage of Al element less than 20 at% is an Al barren grid, the number of Al barren grids is n, then the enrichment degree x of Al is defined as m / z, and the barren degree y of Al is defined as n / z.

[0029] In the positive electrode material provided in the present application, the enrichment degree x of Al can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40% or a range value composed of any two numerical values; in some embodiments, the enrichment degree of Al is 20%≤x≤25%, or, 25%≤x≤30%, or 30%≤x≤35%, or 35%≤x≤40%.

[0030] The barren degree y of Al can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50% or a range value composed of any two numerical values. In some embodiments, the barren degree of Al is 20%≤y≤30%, or, 30%≤y≤40%, or 40%≤y≤50%.

[0031] Applicants have found through extensive research that, in the positive electrode material provided in the present application, by controlling the enrichment degree x of Al to be between 20%-40% and the barren degree y of Al to be between 20%-50%, it is beneficial to have good rate performance and first coulomb efficiency on the basis of ensuring the cycle stability of the positive electrode material. Specifically, the cooperation of the Al barren region and the Al enrichment region within the above range is beneficial to inhibit the local over-coordination tendency of Al-O bonds in the positive electrode material, reduce the anisotropic stress caused by lattice distortion, so as to inhibit Li layer slip and oxygen layer mismatch in the charging and discharging process, relieve the generation of intracrystalline and intercrystalline cracks, and further inhibit the collapse of the layered structure caused by the aggregation of oxygen vacancies at high temperature, thereby ensuring the cycle stability of the positive electrode material while having good rate performance and first coulomb efficiency.

[0032] The above local over-coordination tendency refers to the excessive aggregation of Al elements in a local region, resulting in the proportion of Al atoms in the lattice exceeding the original lattice ratio.

[0033] In the cathode material provided in this application, the enrichment region of Al element in the cathode material satisfies (20% ≤ x ≤ 40%), which can effectively increase the bonding force between metal and oxygen atoms, thereby stabilizing the layered structure of the ternary material, suppressing the harmful phase transition caused by active oxygen overflow during cycling, thus ensuring the smoothness of the lithium-ion transport channel and reducing the impedance of the cathode material. In some embodiments of this application, the non-uniformity of Al element distribution S 2 Satisfy: 150≤S 2 ≤220, and

[0034] ;

[0035] The EDS elemental distribution map of the above-mentioned gridded cathode material is divided into four quadrants. This refers to the number of Al-rich squares in the i-th quadrant of the four quadrants. This refers to the average number of Al-enriched squares in the four quadrants.

[0036] In this application, the distribution non-uniformity S of Al element 2 The testing method is as follows: In the EDS elemental distribution map of the above-mentioned gridded cathode material, the circumcircle of the cross-section of the cathode material particle (the cross-section of any particle in the cathode material cross-section) is taken as the center. Based on the center of the circumcircle, the circumcircle is divided into four equal parts to divide the EDS elemental distribution map into four regions, resulting in four quadrants: I, II, III, and IV. The number of Al-enriched squares in quadrant I is m1, the number of Al-enriched squares in quadrant II is m2, the number of Al-enriched squares in quadrant III is m3, and the number of Al-enriched squares in quadrant IV is m4.

[0037] The distribution non-uniformity of Al is s², where,

[0038] , This refers to the number of Al-rich squares in the i-th quadrant of the four quadrants. The average number of enriched squares in quadrant A1.

[0039] The applicant discovered through extensive research that by controlling the non-uniformity S of Al distribution in the cathode material... 2 A value between 150 and 220 is beneficial for further improving the cycle stability of the cathode material; specifically, the Al distribution non-uniformity S 2 When Al is between 150 and 220, 3+ A symmetrical charge-compensating lattice can be formed within the four quadrants, and the symmetrical charge-compensating lattice makes Al 3+ In Li + During extraction, the transition metal (such as Ni) is buffered by dynamic charge rearrangement. 3+ / Ni 4+The oxidation stress of the material is reduced, the redox activity of the lattice oxygen is limited in a reversible range, the bond energy tolerance window of the lattice oxygen is widened, and the surface layer structure can still maintain the integrity of the layered framework in the high pressure range, thereby ensuring the cycle stability of the positive electrode material while having good rate performance and first coulomb efficiency.

[0040] Specifically, the position distribution unevenness S of the positive electrode material provided in the present application is less than or equal to 200. 2 may be 150, 153, 155, 160, 161, 163, 165, 167, 168, 170, 175, 179, 180, 188, 190, 199, 200, 210, 213, 214, 219, 220 or a range value composed of any two numerical values. In some specific embodiments, 150≤S 2 ≤160, or 160≤S 2 ≤170, or 170≤S 2 ≤200, or 200≤S 2 ≤220.

[0041] In some embodiments of the present application, the peak position 2θ value of the 104 peak in the XRD spectrum of the positive electrode material satisfies: 44.38°≤2θ≤44.42°. Compared with the Al element doping in the prior art, the 2θ value is shifted from 44.5° to 44.38°-44.42°, indicating that the interlayer distance in the layered structure of the positive electrode material is increased, the lithium ion transmission channel is widened, the lithium ion transmission rate is accelerated, and the polarization phenomenon of the positive electrode material is reduced.

[0042] Specifically, the 104 peak position 2θ value of the positive electrode material can be 44.38°, 44.39°, 44.40°, 44.41°, 44.42° or a range value composed of any two numerical values.

[0043] In some embodiments of the present application, 0.6≤x / y≤1.20. Specifically, it can be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.67, 0.69, 0.70, 0.71, 0.74, 0.76, 0.77, 0.79, 0.80, 0.83, 0.85, 0.86, 0.88, 0.90, 0.93, 0.95, 0.98, 1.02, 1.05, 1.08, 1.09, 1.12, 1.13, 1.17, 1.19, 1.20 or a range value composed of any two numerical values. Preferably, 0.7≤x / y≤1.14.

[0044] In some embodiments of the present application, based on the volume particle size distribution of the positive electrode material, the particle size median D50 of the positive electrode material is 4.5-5.5 μm. By controlling the particle size median D50 of the positive electrode material to be within the above range, it indicates that the particle size of the positive electrode material is small, which is beneficial to shorten the diffusion path of lithium ions and increase the diffusion rate of lithium ions. Specifically, the particle size median D50 of the positive electrode material can be 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm or a range value composed of any two of the above values.

[0045] In some embodiments of the present application, based on the volume particle size distribution of the positive electrode material, the span value of the positive electrode material is 0.40-0.60. By controlling the particle size distribution width of the positive electrode material to be within the above range, the compaction density and energy density of the positive electrode material can be effectively improved. Specifically, the span value of the positive electrode material can be 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60 or a range value composed of any two of the above values.

[0046] In some embodiments of the present application, the chemical formula of the positive electrode material is LiNi 1-a-b-c Co a Mn b M c O2, wherein 0.04≤a≤0.10, 0.05≤b≤0.10, 0.001≤c≤0.0015, 0.7≤1-a-b-c≤0.9, M includes Al, and M can further include at least one element of Zr, Y, W, thereby more favorably improving the cycle stability and specific capacity of the positive electrode material. Specifically, a can be 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or a range value composed of any two of the above values; b can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or a range value composed of any two of the above values; c can be 0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015 or a range value composed of any two of the above values. 1-a-b-c can be 0.7, 0.72, 0.73, 0.74, 0.75, 0.78, 0.79, 0.80, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90 or a range value composed of any two of the above values.

[0047] In some embodiments of this application, the Al content in the cathode material is 3500ppm-5500ppm. An appropriate atomic percentage of Al doping helps reduce the blockage of lithium-ion channels by Al doping, thus improving both the structural stability and coulombic efficiency of the cathode material. Specifically, the Al content in the cathode material can be 3500ppm, 3600ppm, 3800ppm, 4000ppm, 4200ppm, 4500ppm, 4800ppm, 5000ppm, 5200ppm, 5500ppm, or any range of two such values.

[0048] In some embodiments of this application, the impedance of the cathode material is 15Ω-25Ω, which is more conducive to improving the lithium-ion transport efficiency and thus improving the first coulombic efficiency. Specifically, the impedance of the cathode material is 15Ω, 18Ω, 20Ω, 22Ω, 25Ω, or any combination of two values.

[0049] In some embodiments of this application, the compaction density of the cathode material is 2.8 g / cm³. 3 -3.1 g / cm 3 This further facilitates the improvement of its specific capacity. Specifically, the compaction density of the cathode material can be 2.8 g / cm³. 3 2.9 g / cm 3 3.0 g / cm 3 3.1 g / cm 3 Or a range of values ​​consisting of any two numerical values.

[0050] In some embodiments of this application, the tap density of the positive electrode material is 2.4 g / cm³. 3 -2.8 g / cm 3 This further improves the cycle stability of the positive electrode. Specifically, the tap density of the positive electrode material can be 2.4 g / cm³. 3 2.5 g / cm 3 2.6 g / cm 3 2.7 g / cm 3 2.8 g / cm 3 Or a range of values ​​consisting of any two numerical values.

[0051] In some embodiments of this application, the pH of the cathode material surface is 11.4-11.7, which is more conducive to improving the dispersion stability of the cathode slurry prepared from the cathode material. Specifically, the pH of the cathode material surface can be 11.4, 11.5, 11.6, 11.7 or any range of two values.

[0052] This application addresses the problems associated with the mechanical mixing and doping of traditional cathode materials and proposes the following solutions:

[0053] In a second typical embodiment of this application, a method for preparing a cathode material is also provided. The method includes the following steps: Step S1, providing an aluminum salt solution, mixing the aluminum salt and a transition metal salt in a liquid phase to obtain a mixed solution; Step S2, subjecting the mixed solution to spray pyrolysis to obtain an Al-doped transition metal oxide; Step S3, mixing the Al-doped transition metal oxide with a lithium salt and calcining to obtain the cathode material.

[0054] The method for preparing the cathode material provided in this application involves mixing aluminum salt and transition metal salt in a liquid phase, utilizing solvation effect and complexation reaction to achieve Al 3+ It exhibits atomic-level uniform dispersion with transition metals. Compared to traditional mechanical mixing, the intermolecular interactions in the liquid phase enable Al... 3+ Forming stable chelates with transition metal ions can eliminate physical dispersion inhomogeneity and avoid localized concentration gradients caused by mechanical grinding. The mixed solution is then atomized into micron-sized droplets, which are then sprayed into a high-temperature reactor. In the reactor, the micron-sized droplets are instantly dried and pyrolyzed, forming Al-doped transition metal oxide powder. Thus, during the rapid pyrolysis of the micron-sized droplets, Al elemental segregation is suppressed, avoiding the component stratification caused by solute migration in traditional drying processes, and ensuring Al... 3+ The Al is uniformly distributed within the cathode material. Furthermore, the Al content is controlled by a low-temperature platform during the calcination stage. 3+ Diffusion kinetics are employed to achieve deep and uniform doping within the crystal lattice. Furthermore, the cathode material prepared using the aforementioned method, with uniform Al doping, not only optimizes the structural stability and electrochemical performance of the cathode material but also suppresses lattice distortion and irreversible phase transitions during charge and discharge by stabilizing the layered structure, reducing microcrack formation and thus improving cycle stability. Simultaneously, the continuous lithium-ion diffusion channels formed within the cathode material reduce polarization, improve rate performance, and avoid capacity decay caused by local concentration gradients. Moreover, uniform Al doping significantly suppresses oxygen release and electrolyte decomposition at high temperatures by anchoring lattice oxygen and transition metal sites, enhancing thermal safety. In addition, uniform Al doping also reduces transition metal dissolution and interfacial side reactions, extending cycle life.

[0055] Step S1: Provide an aluminum salt solution, and mix the aluminum salt and transition metal salt in the liquid phase to obtain a mixed solution.

[0056] In some embodiments of this application, in step S1 above, liquid phase mixing is carried out by mechanical stirring at a speed of 200-400 rpm for a mixing time of 10-20 min, which is more conducive to achieving uniform mixing of aluminum ions and transition metal ions at the atomic scale.

[0057] In the step S1, the liquid phase blending of the aluminum salt solution and the transition metal salt is adopted, under the stirring action, Al 3+ The transition metal ions are atomically pre-assembled in the solvation layer. Compared with the traditional mechanical mixing of solid particles, the liquid phase environment eliminates the diffusion barrier between elements, and the [Al-O-M] (M=Ni / Co / Mn) coordination structure is formed through the bridging of solvent molecules. This molecular-level pre-dispersion breaks the heterogeneous interface between Al2O3 and the main phase particles in mechanical mixing, and the distribution accuracy of Al-O bond is improved from microns to nanometers, which lays a chemical foundation for subsequent uniform doping.

[0058] Specifically, the stirring speed can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, or a range value composed of any two numerical values; the stirring and mixing time can be 10 min, 12 min, 15 min, 18 min, 20 min, or a range value composed of any two numerical values.

[0059] In some embodiments of the present application, in the step S1, the aluminum content in the mixed solution is 3500 ppm-6000 ppm, so as to make the aluminum content in the prepared positive electrode material be 3500 ppm-5500 ppm, thereby improving the structural stability of the positive electrode material while taking into account excellent capacity performance. Specifically, the aluminum content in the mixed solution can be 3500 ppm, 3800 ppm, 4000 ppm, 4200 ppm, 4500 ppm, 4800 ppm, 5000 ppm, 5200 ppm, 5500 ppm, 5800 ppm, 6000 ppm, or a range value composed of any two numerical values.

[0060] In some embodiments of the present application, in the step S1, the molar ratio of nickel, manganese and cobalt is 80-90:4-10:5-10. Specifically, it can be 88:5:7, 83:10:7, etc. In step S2, the mixed solution is subjected to spray pyrolysis to obtain a transition metal oxide doped with Al.

[0061] In some embodiments of the present application, in the step S2, the spray pyrolysis of the mixed solution includes: atomizing the mixed solution and spraying it into a pyrolysis tower for pyrolysis to obtain a transition metal oxide doped with Al.

[0062] In some embodiments of the present application, in the step S2, atomizing the mixed solution includes: spraying the mixed solution through a centrifugal atomizing nozzle to form micron-sized droplets.

[0063] In some embodiments of the present application, in the step S2, the feeding speed is 1 L / min-3 L / min, and the temperature of the pyrolysis tower is 400-600℃, so as to facilitate the realization of the instantaneous drying of the droplets, the solvent evaporation and the salt decomposition are completed within milliseconds, and the migration segregation of Al 3+ is more effectively inhibited, and the uniformity of the pre-mixed liquid phase is "frozen" at the sub-micron scale. Specifically, the temperature of the spray pyrolysis can be 400℃, 420℃, 450℃, 480℃, 500℃, 520℃, 550℃, 580℃, 600℃, or a range value formed by any two of the above values; the feeding speed during the spray pyrolysis can be 1.0 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min, 2.0 L / min, 2.2 L / min, 2.5 L / min, 2.8 L / min, 3.0 L / min, or a range value formed by any two of the above values. It should be noted that the feeding speed refers to the flow rate of the mixed solution sprayed into the pyrolysis tower.

[0064] In the step S2, the mixed solution is subjected to spray pyrolysis to realize the instantaneous drying of the micro-droplets, and the solvent evaporation and the salt decomposition are completed within milliseconds. The rapid non-equilibrium thermodynamic process inhibits the migration segregation of Al 3+ , and the uniformity of the pre-mixed liquid phase is "frozen" at the sub-micron scale. Compared with the traditional mechanical mixing-roller kiln drying process (drying time > 2h), this technology reduces the distribution variation coefficient of Al in the primary particles from 35% to 8%, forms an in-situ crosslinking structure of the Al-O-M (M refers to a transition metal) network inside each pyrolysis particle, improves the micro-area distribution uniformity of Al, and completely avoids the thermodynamic segregation tendency of Al at the grain boundaries in the mechanical mixing.

[0065] In step S3, the transition metal oxide doped with Al is mixed with a lithium salt and calcined to obtain a positive electrode material.

[0066] In some embodiments of the present application, the molar ratio of the lithium salt to the transition metal oxide is 1.04 or 1.03.

[0067] In some embodiments of the present application, in the step S3, the calcination includes low-temperature calcination and high-temperature calcination performed in sequence, the temperature of the low-temperature calcination is 400℃-600℃, and the holding time is 1-3h, the temperature of the high-temperature calcination is 650℃-850℃, and the holding time is 6-12h. By controlling the temperature of the low-temperature calcination to be 400℃-600℃ and the holding time to be 1-3h, the slow-release lattice embedding of Al 3+ is more facilitated, in this stage, Al 3+ preferentially occupies the octahedral sites of the transition metal layer to form a solid solution precursor structure with the main phase; and in this way, in the high-temperature calcination stage, Al 3+The possibility of segregation is reduced. Compared to traditional high-temperature sintering (>700℃), low-temperature calcination first reduces the segregation of Al. 3+ By controlling the diffusion distance within a low range to avoid concentration gradients caused by long-distance migration, and then calcining at high temperature, the staged sintering strategy improves the uniformity of Al lattice substitution compared to mechanical mixing processes. The range of lattice parameter fluctuations is compressed, which is more conducive to improving the doping uniformity of Al.

[0068] In step S3 above, Al is achieved through calcination. 3+ Slow-release lattice embedding. Al at this stage 3+ It preferentially occupies octahedral sites in the transition metal layer, forming a solid solution precursor structure with the main phase. Al 3+ The diffusion distance is controlled within a low range to avoid concentration gradients caused by long-range migration. A strategy of first low-temperature calcination and then high-temperature calcination is employed to promote Al diffusion during the low-temperature calcination stage. 3+ Bulk diffusion, extending Al 3+ Migration time, making Al 3+ The process allows for full penetration into the transition metal or lithium layer, avoiding surface segregation caused by subsequent high-temperature sintering. This improves the uniformity of Al lattice substitution compared to mechanical mixing processes and compresses the range of lattice parameter fluctuations.

[0069] Specifically, the low-temperature roasting temperature can be 400℃, 420℃, 450℃, 480℃, 500℃, 520℃, 550℃, 580℃, 600℃, or any range of two values; the holding time can be 1h, 1.2h, 1.5h, 1.8h, 2.0h, 2.2h, 2.5h, 2.8h, 3.0h, or any range of two values. The high-temperature roasting temperature can be 650℃, 680℃, 700℃, 720℃, 750℃, 780℃, 800℃, or any range of two values; the holding time can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any range of two values.

[0070] In some embodiments of this application, step S3 of the method for preparing the cathode material further includes mixing the matrix particles obtained by sintering in S3 with one or both of a Zr-containing compound and a W-containing compound to obtain a mixed coating material. Specifically, the Zr-containing compound can be nano-zirconia, and the W-containing compound can be tungsten trioxide. The mixed coating material is sintered to obtain the cathode material, with a holding temperature of 800°C and a holding time of 10 hours.

[0071] In some specific embodiments, the above-mentioned primary coating includes one or both of a Zr-containing compound or a W-containing compound, wherein the Zr-containing compound can be nano-zirconia, and the W-containing compound can be tungsten trioxide.

[0072] In some embodiments, the secondary sintering comprises: feeding the sintered substrate material in S3 into a primary coating machine, and adding zirconium oxide and / or tungsten trioxide auxiliary materials, at a mixing speed of 250 rpm, to obtain uniformly mixed coated materials. The content of the auxiliary materials is 3000 ppm to 5000 ppm based on the total mass of the substrate material.

[0073] In some embodiments of the present application, the aluminum salt in the aluminum salt solution in S1 is a soluble aluminum salt, including but not limited to aluminum chloride, aluminum sulfate, or aluminum nitrate, etc.; the manganese salt is a soluble manganese salt, including but not limited to manganese nitrate, manganese sulfate, or manganese chloride, etc. The nickel salt is a soluble nickel salt, including but not limited to nickel nitrate, nickel sulfate, or nickel chloride, etc.; the cobalt salt is a soluble cobalt salt, including but not limited to cobalt nitrate, cobalt sulfate, or cobalt chloride, etc.

[0074] In some embodiments of the present application, the lithium salt in S3 is a lithium salt commonly used in the art, including but not limited to lithium carbonate, lithium hydroxide, etc.

[0075] In some embodiments of the present application, when the doping element contains other doping elements (such as Zr, Y, W, etc.) in addition to Al, then in S3, a compound containing the other doping elements is mixed with the aluminum-doped transition metal oxide and the lithium salt to be calcined, so as to dope the other doping elements into the positive electrode material.

[0076] In a second typical embodiment of the present application, a positive electrode sheet is provided, which comprises the positive electrode material provided in the first aspect.

[0077] The positive electrode sheet of the present application comprises a positive electrode current collector and a positive electrode material active layer provided on at least one surface of the positive electrode current collector. The positive electrode current collector can be an aluminum foil or a nickel foil, etc., or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode material active layer comprises the positive electrode material of the first aspect.

[0078] The positive electrode material active layer further comprises a binder for binding the positive electrode active material particles to facilitate the formation of a film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the binder can include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0079] The positive electrode material active layer can further include a conductive material, which includes but is not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material can include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material can include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0080] In particular, when the positive electrode sheet is prepared, the positive electrode material, the conductive material, and the binder can be dispersed in an appropriate amount of solvent, and mixed by sufficient stirring to form a uniform positive electrode slurry. The positive electrode slurry can be uniformly coated on the positive electrode current collector, and then dried, rolled, and cut to obtain the positive electrode sheet. In one particular embodiment, the positive electrode active layer includes, by mass percentage, 70% to 99% of the positive electrode material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder.

[0081] In a fourth typical embodiment of the present application, a secondary battery is provided, which includes the positive electrode sheet provided in the second aspect.

[0082] Due to the inclusion of the positive electrode sheet with excellent performance as described above, the secondary battery has the advantages of high capacity, excellent rate performance, and cycle stability. The secondary battery can be a lithium ion battery, a sodium ion battery, a solid electrolyte battery, etc., without limitation.

[0083] In particular, the secondary battery includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located in the housing.

[0084] The housing can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), for example, a soft package battery. In other embodiments, it can also be a steel shell battery, an aluminum shell battery, etc.

[0085] Please refer to Figure 3 and Figure 4 , the electrode assembly 100 includes a positive electrode sheet 101, a negative electrode sheet 102, and a separator film 103, which is arranged between the positive electrode sheet 101 and the negative electrode sheet 102. When charging, please refer to Figure 3 , the active ions (such as lithium ions) are deintercalated from the crystal lattice of the positive electrode material (such as the intercalated compound) of the positive electrode sheet 101, pass through the separator film 103 through the electrolyte, reach the negative electrode sheet 102, and are inserted into the crystal lattice of the negative electrode material. When discharging, please refer to Figure 4, active ions (e.g., lithium ions) are deintercalated from the crystal lattice of the negative electrode material of the negative electrode sheet 102, pass through the separator 103 via the electrolyte, reach the positive electrode sheet 101, and are intercalated into the crystal lattice of the positive electrode material (e.g., a lithiated intercalation compound), and electrons move from the negative electrode sheet 102 to the positive electrode sheet 101 via an external circuit, and the reverse movement of the electrons forms an electric current, which can be used by an electrical device.

[0086] In some embodiments, the electrode assembly 100 can be a stacked structure formed by alternately stacking the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102. In other embodiments, the electrode assembly 100 can also be a wound structure formed by winding the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102 after being alternately stacked.

[0087] The positive electrode sheet 101 includes a positive electrode current collector and a positive electrode material active layer provided on at least one surface of the positive electrode current collector. The positive electrode current collector can be an aluminum foil or a nickel foil, or any composite current collector known in the art, such as, but not limited to, a current collector formed by combining a conductive foil and a polymer substrate.

[0088] The negative electrode sheet 102 includes a negative electrode current collector and a negative electrode material active layer provided on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, or any composite current collector known in the art, such as, but not limited to, a current collector formed by combining a conductive foil and a polymer substrate.

[0089] The negative electrode active material layer includes a negative electrode material, which can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material can also be used. The negative electrode active material can be used alone or in combination with two or more types.

[0090] The negative electrode material active layer also includes a binder for binding the negative electrode active material particles to facilitate the formation of a film layer and to improve the adhesion between the negative electrode material active layer and the negative electrode current collector. In some embodiments, the binder can include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon, among others.

[0091] The negative material active layer can also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material can include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material can include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative, such as polyaniline, polythiophene, or polypyrrole.

[0092] The separator film 103 includes a film layer having a porous structure, and the material thereof includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator film 103 can be a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film, etc.

[0093] The electrolyte has a role of conducting ions between the positive electrode sheet 101 and the negative electrode sheet 102. The state of the electrolyte can be one or more of a gel state, a solid state, and a liquid state. In some embodiments, the electrolyte employs an electrolytic solution. The electrolytic solution has a role of conducting active ions between the positive electrode sheet 101 and the negative electrode sheet 102. In some embodiments, the electrolytic solution includes a lithium salt and an organic solvent. The lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethylsulfonyl)methide (LiC(SO2CF3)3), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPO2F2), but is not limited thereto. For example, the lithium salt is selected as LiPF6 because it can give a high ionic conductivity and improve cycle characteristics. The organic solvent can be a carbonate compound, a carboxylic ester compound, an ether compound, a nitrile compound, other organic solvents, or a combination thereof. Examples of the carbonate compound include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.

[0094] In the preparation of the secondary battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain an electrode core, the electrode core is packaged into an aluminum-plastic film that is pre-stamped and molded, the battery after packaging is dried to remove moisture, the electrolytic solution is injected into the dried battery, and the battery after aging, formation, and secondary sealing is completed to prepare the secondary battery.

[0095] The application will be further described in detail with reference to specific examples, which are not to be understood as limiting the scope of the application as claimed.

[0096] The advantageous effects of the application will be further illustrated below with reference to examples and comparative examples.

[0097] Example 1

[0098] The embodiment provides an Al-doped positive electrode material, which is prepared according to the following steps.

[0099] (1) Dissolving aluminum chloride (AlCl3) in deionized water to prepare an aluminum chloride solution with a molar concentration of 0.1 mol / L; preparing a transition metal salt solution by using nickel sulfate, cobalt sulfate and manganese sulfate, and controlling the total metal concentration to be 1.5 mol / L. Mixing the transition metal salt solution and the aluminum chloride solution according to [n(Ni+Co+Mn)]:[n(Al)]=1:0.0045, adjusting the mixed solution to pH=11.0±0.5, and stirring the mixed solution at a speed of 200 rpm for 20 minutes; and obtaining a mixed solution by ultrasonic treatment at 50 kHz during the mixing process.

[0100] (2) Pumping the mixed solution into a pyrolysis tower at a rate of 2 L / min by using a centrifugal atomizing nozzle, using nitrogen as a carrier gas, controlling the inlet section temperature of the pyrolysis tower to be 200 ℃, the middle section temperature to be 400 ℃, and the outlet section temperature to be 150 ℃, and controlling the residence time of the material to be 10 seconds, so that the mixed solution is completely dehydrated and forms a transition metal oxide, namely a powder material A.

[0101] (3) Adding the powder material A and a lithium salt (lithium carbonate) into a high-speed mixer to obtain a high-mixing material, wherein n(Li):n(n(Ni)+n(Co)+n(Mn))=1.04:1. Putting the obtained high-mixing material into a roller kiln to perform calcination, performing low-temperature calcination at 500 ℃ for 2 h and high-temperature calcination at 740 ℃ for 8 h of solid-phase reaction to obtain a base material B.

[0102] (4) Mixing the base material B with nano-zirconium oxide and then sintering to obtain a positive electrode material C, wherein the content of the nano-zirconium oxide is 4000 ppm based on the total mass of the base material B, and the sintering temperature is 800 ℃ and the holding time is 10 h.

[0103] Example 2-16

[0104] Example 2-16 adopts the same process flow as that of Example 1, and the difference lies in the molar ratio of nickel, cobalt and manganese in the front transition metal salt solution, the liquid mixing time and speed, the aluminum content in the mixed solution, the spray pyrolysis temperature and the liquid pumping rate, the low-temperature calcination temperature and the holding time in step (1). The specific related parameters are shown in Table 1. The ratio of Li refers to the ratio of the number of moles of Li element to the total number of moles of Ni+Co+Mn three elements. S1-S16 in Table 1 represent Examples 1-16 respectively.

[0105] Example 17

[0106] Example 17 differs from Example 1 in that in step (4), the base material B is mixed with tungsten trioxide and then sintered to obtain the positive electrode material C, wherein the content of tungsten trioxide is 3000 ppm based on the total mass of the base material B, the sintering temperature is 800 DEG C, and the holding time is 10 h.

[0107] Example 18

[0108] Example 18 differs from Example 1 in that in step (4), the base material B is mixed with nano-zirconium oxide and tungsten trioxide and then sintered to obtain the positive electrode material C, wherein the total content of nano-zirconium oxide and tungsten trioxide is 4000 ppm based on the total mass of the base material B, the sintering temperature is 800 DEG C, and the holding time is 10 h.

[0109] Comparative Examples 1-3

[0110] Comparative Examples 1-3 are prepared by using a conventional mechanical mixing process, and the specific parameters are shown in Table 2. D1-D3 in Table 1 represent Comparative Examples 1-3, respectively.

[0111] The step of preparing the positive electrode material by the mechanical mixing process comprises:

[0112] (1) The lithium carbonate, the nickel-cobalt-manganese co-precipitation ternary material precursor, and the hydroxyl aluminum oxide are put into the high-speed mixer through the feeding port, the high-speed mixer is started, and pre-mixing is first performed at a speed of 100 r / min for 2 min, and then high-speed mixing is performed at a speed of 250 r / min for 30 min. After mixing, the high-mixing material is obtained.

[0113] (2) The high-mixing material is calcined to obtain the positive electrode material.

[0114] Table 1

[0115]

[0116] Note: The above Al content refers to the Al content in the mixed solution.

[0117] Table 2

[0118]

[0119] Test Example 1

[0120] The positive electrode materials provided by the above examples and comparative examples are respectively detected in terms of chemical formula composition, atomic percentage of Al element, enrichment degree x of Al, barren degree y of Al, unevenness S of Al distribution, 104 peak value 2θ in XRD spectrum, median particle size D50, span value, tap density, vibration density, and surface pH, and the results are shown in Tables 3 and 4. 2 , XRD spectrum, median particle size D50, span value, tap density, vibration density, and surface pH, and the results are shown in Tables 3 and 4.

[0121] Among them, (1) the method for testing the elemental composition in the cathode material is as follows: take 0.3g~0.35g of the sample to be tested, dissolve it in aqua regia, cool and make up to a volume of 100ml to prepare the test stock solution; take 1mL of the test stock solution, dilute it 100 times, and test the content of the main elements Li, Ni, Co, Mn, Al and other elements by using the American Agilent 5110 ICP-OES.

[0122] (4) The test methods for Al enrichment x and depletion y are as follows: The cathode material particles are cut using an ion mill (IM5000) to obtain a cross-section. The cross-section is placed under a scanning electron microscope (SEM). After magnification of 5K, the cross-section of the cathode material particles is scanned using an EDS (energy scattering spectrometer product of OXFORD Instruments) to obtain the cross-section EDS image. The cross-section EDS image is divided into square grids by gridding, so that the side length of the grid is 0.4-0.6μm and the total number of grids in the cross-section is z. In the grid, the grids containing the percentage of Al atoms greater than 40 at% are identified as Al aggregate grids, and the number of Al aggregate grids is m. The number of Al aggregate grids is m. The squares in the at% region are identified as element-poor squares, and their number is n. Then, the enrichment degree of Al is defined as x=m / z, and the depletion degree of Al is defined as y=n / z. The enrichment degree of Al and the depletion degree of Al in the cross-sections of at least 20 cathode material particles are statistically analyzed to obtain the average enrichment degree of Al and the average depletion degree of Al.

[0123] (5) The non-uniformity of Al distribution S 2 The testing method is as follows: In the EDS elemental distribution map of the above-mentioned gridded cathode material, the EDS elemental distribution map is divided into four regions with the circumcircle as the center, resulting in four quadrants: I, II, III, and IV. The number of Al-enriched squares in quadrant I is m1, the number of Al-enriched squares in quadrant II is m2, the number of Al-enriched squares in quadrant III is m3, and the number of Al-enriched squares in quadrant IV is m4. ,in, Let A be the number of Al-rich squares in the i-th quadrant of the four quadrants. The average number of enriched squares in quadrant A1.

[0124] (6) The test method for the 104 peak 2θ in the XRD spectrum is as follows: The sample is characterized by XRD using an XRD diffractometer (RIGAICU UITIMAIV), with a scanning range of 10~90° and a scanning step of 0.05°. The incident angle (2θ) of the 104 peak of the characterized sample is read according to the Jade software.

[0125] (7) The particle size distribution test method is as follows: an appropriate amount of sample is poured into pure water, ultrasonic dispersion is performed, an appropriate amount of surfactant (such as sodium hexametaphosphate) is added, and then a British Malvern Mastersizer 3000 model laser particle size analyzer is used for analysis to obtain the volume distribution particle size D10, D50, D90 and Span value of the positive electrode material particles, Span = (D10+D90) / (2*D50).

[0126] (8) The test method for the compaction density is as follows: a compaction density instrument of the American Micron 4350 model is used to test the compaction performance of the positive electrode material. After 1 g of the positive electrode material is treated and compacted for 30 s under a pressure of 3T, the compaction density of the material is obtained.

[0127] (9) The test method for the tap density is as follows: a Kona Dual Autotap device is used to test the tap density of the positive electrode material. 100 mL of the positive electrode material sample is placed in a measuring cylinder, and after mechanical vibration for 1000 times, the tap density of the positive electrode material is calculated through the sample mass and the volume after vibration.

[0128] (10) The test method for the surface pH is as follows: a Mettler pH meter is used to measure the pH value of the material. 5 g of the powder sample is dissolved in 45 ml of pure water, stirred at a certain speed for 30 min, and then tested with the pH meter.

[0129] Table 3

[0130]

[0131] Figure 1 The data statistical graph of the enrichment degree x and the barren degree y of the positive electrode material Al provided in Example 1 is determined based on the SEM-EDS mapping method, from which Figure 1 It can be seen that the Al element in the positive electrode material provided in Example 1 is uniformly diffused, and the enrichment degree x of the Al element is 26%, and the barren degree of Al is 36%.

[0132] Figure 2 The distribution graph of the 104 peak in the XRD spectrum of the positive electrode material provided in Examples 1-2 and Comparative Example 1, from which Figure 2 It can be seen that the 2θ of the positive electrode material provided in Example 1-2 is obviously shifted to the left relative to the positive electrode material provided in Comparative Example 1.

[0133] Table 4

[0134]

[0135] Test Example 2

[0136] The positive electrode materials provided by the above examples and comparative examples were respectively assembled into button cells. The cells were assembled according to the following steps: 0.8 g of the positive electrode material, 0.1 g of conductive carbon black, and 0.1 g of polyvinylidene fluoride were put into a ball mill tank, 15 mL of N-methyl pyrrolidone was added, and a uniform slurry was formed by ball milling, followed by uniform coating on an aluminum foil, vacuum drying at 110°C for 12 h to obtain a positive electrode sheet. The dried electrode sheet was cut into a round sheet with a diameter of 15 mm, and assembled in a glove box according to the positive electrode shell, electrode sheet, electrolyte (EC / DMC / EMC volume ratio 1:1:1, LiPF6 concentration is 1 mol / L), separator (Celgard PP / PE / PP three-layer composite film), lithium sheet, electrolyte, foam nickel, negative electrode shell, and sealed. After standing for 24 h, a button cell was obtained.

[0137] The first discharge gram capacity, the first cycle coulombic efficiency, the 50 cycle capacity retention rate, and the 50 week cycle battery volume expansion rate of the corresponding batteries were tested, and the results are shown in Table 5 below.

[0138] Among them, (1) the test method of the first discharge gram capacity and the first coulombic efficiency: using a LAND battery test system, the first discharge gram capacity (0.1C) and the first charge specific capacity (0.1C) were tested at 25°C, 3.0 V-4.3 V, the reference capacity was set to 200 mA / g, 1C corresponding to the current density was 200 mA / g, and the first coulombic efficiency was calculated, the first coulombic efficiency = the first cycle discharge capacity / the first cycle charge capacity.

[0139] (2) The test method of the 50 cycle capacity retention rate is: the discharge gram capacity of the above battery after 50 cycles is tested, and the 50 week cycle retention rate is calculated, the 50 week cycle retention rate = the discharge gram capacity after 50 cycles / the first cycle discharge gram capacity.

[0140] (3) The test method of the direct current resistance (DCR) is: the assembled button cell is placed for 10 h, and the first charge and discharge (0.1C / 0.1C) is carried out at 25°C, 3.0 V-4.3 V. After completion, it is charged to 100% SOC at 0.1C, and then constant voltage charged to the current less than 0.05C, the battery at this time corresponds to 100% SOC state, standing for 10 min, recording the voltage V0 at this time, using 3C discharge current (I 3C ) pulse discharge for 30 s, recording the voltage V1 at this time, according to (V0-V1) / I 3C , the direct current resistance DCR at this time is calculated.

[0141] The positive electrode materials provided by the above examples and comparative examples were respectively assembled into soft package batteries: 80 g of the positive electrode material, 10 g of conductive carbon black, and 10 g of polyvinylidene fluoride were put into a ball milling tank, N-methyl pyrrolidone was added, and the slurry was uniformly formed by ball milling, then the slurry was uniformly coated on an aluminum foil, and the coated aluminum foil was vacuum dried at 110°C for 12 h to obtain a positive electrode sheet. The positive electrode sheet was cut into a square shape by using a mold, and the positive electrode sheet, a separator (Celgard PP / PE / PP three-layer composite film), and a lithium sheet were laminated in a glove box, and the side of the aluminum plastic film was heat sealed, liquid injection was performed, and finally the top was heat sealed and sealed. After standing for 24 h, a soft package battery was obtained.

[0142] The test method for the 50-week electrode sheet expansion rate was as follows: the prepared soft package battery was immersed in a beaker containing deionized water, and the scale V0 at this time was recorded. The soft package battery after 50 weeks of cycle test was immersed in the beaker, and the scale V1 at this time was recorded. The test method for the 50-week electrode sheet expansion rate of the soft package battery was calculated according to (V1-V0) / V0*100, which could reflect the gas production performance of the material.

[0143] Table 5

[0144]

[0145] As can be seen from Table 5, the positive electrode materials provided by Examples 1-18 have Al enrichment degree x between 20%-40%, Al barren degree y between 20%-50%, and 150 2 ≤220, which indicates that atomic-level uniform doping is achieved inside the positive electrode material. This optimized microstructure enables the material of the examples to exhibit higher initial discharge capacity, lower interface impedance, and more excellent cycle performance.

[0146] In contrast, the positive electrode materials provided by Comparative Examples 1-3 have Al enrichment degree x>40%, Al barren degree>50%, and S 2 >220, which indicates that the Al element is unevenly distributed inside the positive electrode material, causing local concentration gradient and structural defects, and thus leading to higher charge transfer impedance and faster capacity decay.

[0147] As can be seen from Table 5, the positive electrode materials provided by Examples 1-18 have Al enrichment degree x between 20%-40%, Al barren degree y between 20%-50%, and 150

[0148] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A positive electrode material, characterized in that, The cathode material is a lithium transition metal composite oxide, which includes Al. The cross-section of the cathode material is characterized by scanning electron microscopy and elemental energy dispersive spectroscopy. A cathode material particle is randomly selected, and its EDS elemental distribution map is divided into a grid with z squares, where z ≥ 300. The enrichment degree x of Al satisfies: 20% ≤ x ≤ 40%, and the depletion degree y of Al satisfies: 20% ≤ y ≤ 50%. Based on the total number of atoms in the cathode material, squares with an Al atomic percentage greater than 40 at% are Al-enriched squares, and squares with an Al atomic percentage less than 20 at% are Al-depleted squares. The number of Al-enriched squares is m, and the number of Al-depleted squares is n. The enrichment degree x of Al = m / z, and the depletion degree y of Al = n / z.

2. The cathode material according to claim 1, characterized in that, In the cathode material, the non-uniformity of Al element distribution S 2 Satisfy: 150≤S 2 ≤220, and ， The EDS element distribution map is divided into four quadrants. Let A be the number of Al-rich squares in the i-th quadrant of the four quadrants. The average number of enriched squares in quadrant A1.

3. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: 1) The 2θ value corresponding to the 104 peak in the XRD spectrum of the cathode material satisfies: 44.38°≤2θ≤44.42°; 2) 0.6 ≤ x / y ≤ 1.20; 3) 0.7≤x / y≤1.

14.

4. The cathode material according to claim 1, characterized in that, The median particle size D50 of the positive electrode material is 4.5-5.5 μm; And / or, the span value of the positive electrode material is 0.40-0.

60.

5. The positive electrode material according to claim 1, characterized in that, The chemical formula of the cathode material is LiNi. 1-a- b Co a Mn b M c O2, wherein 0.04≤a≤0.10, 0.05≤b≤0.10, 0.001≤c≤0.0015, 0.7≤1-abc≤0.9, and M includes at least one element from Al and Zr, Y, and W.

6. The cathode material according to claim 1, characterized in that, The cathode material contains 3500-5500 ppm of Al.

7. The cathode material according to claim 1, characterized in that, The impedance of the positive electrode material is 15-25Ω.

8. The cathode material according to any one of claims 1 to 7, characterized in that, The compaction density of the positive electrode material is 2.8-3.1 g / cm³. 3 .

9. The cathode material according to any one of claims 1 to 7, characterized in that, The tap density of the positive electrode material is 2.4-2.8 g / cm³. 3 ; And / or, the pH of the surface of the positive electrode material is 11.4-11.

7.

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

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