A positive electrode material, a preparation method and application thereof

Abstract

The application provides a positive electrode material and a preparation method and application thereof. The positive electrode material comprises a positive electrode base and a coating layer on at least part of the surface of the positive electrode base; the positive electrode base comprises a compound shown in formula 1; Li a1 Ni b1 Co c1 Mn d1 A e1 O s1 Formula 1; A comprises at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, Ba, P, S, F; the coating layer comprises a compound shown in formula 2; Li a2 Al b2 W c2 Ti d2 (PO4) 3 Formula 2.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a cathode material, its preparation method, and its application. Background Technology

[0002] High-nickel layered cathode materials are widely used in high-energy-density lithium-ion batteries due to their high specific capacity (>200 mAh / g) and excellent rate performance, especially in electric vehicles (EVs) and energy storage systems (ESS). With the increasing demands of the new energy industry for battery energy density, cycle life, and fast-charging performance, the market penetration rate of high-nickel layered cathode materials continues to grow. However, high-nickel layered cathode materials face significant challenges in practical applications:

[0003] Poor structural stability: High nickel content (Ni>0.8) makes the material prone to phase transitions during charging and discharging (such as the transformation from layered structure to rock salt phase), forming oxygen vacancies and lattice distortion, which in turn leads to capacity decay and deterioration of cycle performance; Interfacial side reactions: Side reactions between the surface of high nickel layered cathode materials and electrolyte, air and water (such as the release of CO2 / H2O and Li2CO3 deposition) will accelerate interface degradation, resulting in increased polarization and internal resistance, which limits low-temperature and fast-charging performance.

[0004] Therefore, there is an urgent need to develop a cathode material that combines excellent structural stability and interfacial properties. Summary of the Invention

[0005] In view of this, the present invention provides a cathode material with excellent structural stability and excellent interfacial performance between the cathode sheet comprising the cathode material and the electrolyte. In practical applications, it can improve the cycle performance and rate performance of the battery. The preparation method of the cathode material is simple to operate and suitable for widespread application.

[0006] The present invention provides a positive electrode material, wherein the positive electrode material includes a positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate;

[0007] The positive electrode substrate includes the compound shown in Formula 1;

[0008] Li a1 Ni b1 Co c1 Mn d1 A e1 O2 Formula 1;

[0009] In Equation 1, 0.9≤a1≤1.1, 0.65≤b1≤0.95, 0≤c1≤0.3, 0≤d1≤0.3, and 0≤e1≤0.1;

[0010] A includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, Ba, P, S, and F;

[0011] The coating layer comprises the compound shown in Formula 2;

[0012] Li a2 Al b2 W c2 Ti d2 (PO4)3 Equation 2;

[0013] In Equation 2, 1≤a2≤1.5, 0.05≤b2≤0.3, 0.1≤c2≤0.3, and 1.5≤d2≤2.

[0014] The cathode material as described above, wherein, in the X-ray diffraction pattern of the cathode material, it has a (003) surface intensity with a 2θ of 18.8-19°; and / or,

[0015] In the coating layer, the average particle size of the compound represented by Formula 2 is 50-150 nm.

[0016] In the cathode material described above, the thickness of the coating layer is 100-200 nm.

[0017] The cathode material as described above, wherein the mass percentage of the compound represented by Formula 2 in the cathode material is 0.1-0.5%.

[0018] The positive electrode material as described above, wherein, in a fully charged state, the thermogravimetric curve of the positive electrode material satisfies Equation 3;

[0019] |T max -X∣ / (60 100 |TG max -TG x |)≥1 Equation 3;

[0020] In Equation 3, X is the temperature at which free water and water of crystallization completely evaporate;

[0021] T max This is the temperature corresponding to the maximum rate of weightlessness.

[0022] TG max This is the TG value corresponding to the maximum rate of weightlessness;

[0023] TG x This represents the TG value corresponding to X℃.

[0024] Furthermore, X is 120-170℃.

[0025] A second aspect of the present invention provides a method for preparing the cathode material as described above, comprising:

[0026] A first raw material system comprising the compound shown in Formula 1 and the compound shown in Formula 2 is subjected to a first calcination treatment to obtain the positive electrode material comprising a positive electrode matrix and a coating layer.

[0027] The preparation method described above, wherein the first calcination treatment sequentially includes a first-stage calcination treatment and a second-stage calcination treatment;

[0028] In the aforementioned calcination process, the temperature is 750-850℃ and the time is 6-10 hours.

[0029] In the two-stage roasting process, the temperature is 650-750℃ and the time is 1-2 hours.

[0030] The preparation method described above, wherein the compound represented by Formula 2 is a nanoscale material; and / or,

[0031] The compound shown in Formula 2 is prepared by a method comprising the following steps:

[0032] The second raw material system, including Li source, Al source, W source, Ti source and P source, was subjected to hydrothermal reaction and second calcination treatment in sequence to obtain the compound shown in Formula 2.

[0033] In the preparation method described above, the hydrothermal reaction is carried out at a temperature of 150-200°C for a time of 8-12 hours; and / or,

[0034] In the second calcination treatment, the temperature is 700-800℃ and the time is 1-3 hours; and / or,

[0035] The second raw material system also includes polyvinylpyrrolidone.

[0036] A third aspect of the present invention provides a positive electrode sheet, wherein the positive electrode material is as described above.

[0037] A fourth aspect of the present invention provides a battery comprising a positive electrode as described above.

[0038] In the cathode material of the present invention, the coating layer including the compound (LAWTP) shown in Formula 2 can achieve multi-dimensional optimization of the interface protection, bulk stability and thermal safety of the cathode material.

[0039] The method for preparing the cathode material of the present invention can produce the above-mentioned cathode material. The preparation method is simple to operate and suitable for widespread application.

[0040] The positive electrode sheet of the present invention includes the above-mentioned positive electrode material. When applied to a battery, the positive electrode sheet can improve the cycle performance and rate performance of the battery.

[0041] The battery of the present invention, including the above-mentioned positive electrode, has excellent cycle performance and rate performance, can extend the service life of electronic devices, and has excellent market application prospects. Attached Figure Description

[0042] Figure 1 The XRD patterns are of the cathode materials of Example 1 and Comparative Example 3;

[0043] Figure 2 Here is a SEM image of the cathode material from Example 1;

[0044] Figure 3 The EPMA diagram shows the P element distribution of the cathode material in Example 1.

[0045] Figure 4 Thermogravimetric curve of the cathode material in Example 1;

[0046] Figure 5 The thermogravimetric curves of the cathode materials in Example 1 and Comparative Example 2 are shown. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Currently, the modification of high-nickel layered cathode materials mainly involves the following technical approaches:

[0049] (1) Surface coating technology

[0050] Inert material coating: such as Al2O3, LiPO4, LATP (Li 1.3 Al 0.3 Ti 1.7 Solid electrolyte coatings such as (PO4)3 can suppress direct contact between the material and the electrolyte, reducing side reactions; however, the coating is prone to local defects or inhomogeneities, leading to Li + Transport kinetics are limited; some coating materials (such as LATP) exhibit side reactions with the electrolyte (such as Ti). 4+ (Reduction), lack of long-term stability.

[0051] (2) Element doping

[0052] Bulk doping: Introduction of Al3+ Mg 2+ Zr 4+ Elements such as these suppress Li by occupying sites in the transition metal layer or lithium layer. + / Ni 2+ Mixing elements can enhance the strength of the TM-O bond; however, doping elements may disrupt the layered structure of the material, leading to capacity loss; and it is difficult to solve the problems of interface and bulk stability at the same time.

[0053] (3) Single crystal structure design

[0054] Single crystallization process: Single crystal particles are prepared by controlling synthesis conditions to reduce grain boundary defects and delay structural degradation. However, the synthesis cost of single crystal particles is high, and surface side reactions cannot be completely avoided.

[0055] (4) Concentration gradient design

[0056] Gradient doping / coating: This method optimizes interface stability and bulk lithium conductivity by controlling the compositional differences between the material surface and the bulk phase. However, it is complex, difficult to control the gradient, and prone to performance fluctuations.

[0057] In existing technologies, the coating layer and bulk phase modification lack synergistic effects, making it difficult to simultaneously address issues of interfacial ion transport kinetics, bulk structural stability, and thermal safety. For example, while LATP coating can improve interfacial stability, its side reactions with the electrolyte and Ti... 4+ The reduction problem has not yet been effectively solved; while elemental doping can enhance the bulk structure, its effect on interface protection is limited. Therefore, a multi-mechanism synergistic modification scheme that combines interface protection, bulk stability, and improved thermal safety is urgently needed. This invention achieves multi-dimensional optimization of the interface protection, bulk stability, and thermal safety of the cathode material by including a LAWTP-containing coating layer.

[0058] The present invention provides a positive electrode material, comprising a positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate;

[0059] The positive electrode substrate includes the compound shown in Formula 1;

[0060] Li a1 Ni b1 Co c1 Mn d1 A e1 O2 Formula 1;

[0061] In Equation 1, 0.9≤a1≤1.1, 0.65≤b1≤0.95, 0≤c1≤0.3, 0≤d1≤0.3, and 0≤e1≤0.1;

[0062] A includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, Ba, P, S, and F;

[0063] The coating layer includes the compound shown in Formula 2;

[0064] Li a2 Al b2 W c2 Ti d2 (PO4)3 Equation 2;

[0065] In Equation 2, 1≤a2≤1.5, 0.05≤b2≤0.3, 0.1≤c2≤0.3, and 1.5≤d2≤2.

[0066] The positive electrode material of the present invention is a composite structure comprising a positive electrode substrate and a coating layer.

[0067] In the cathode material, the cathode substrate uses high-nickel ternary layered cathode material as the main body. By adjusting the molar ratio of Li to transition metal elements and introducing doping elements into the high-nickel ternary layered cathode material, the lattice stability of the cathode material is optimized and lithium-nickel mixing is suppressed.

[0068] The coating layer includes the compound shown in Formula 2 (LAWTP). The doping of W can reduce the possibility of side reactions between the compound shown in Formula 2 and the electrolyte, especially suppressing the Ti in the compound shown in Formula 2. 4+ The reduction of W improves the long-term stability of the cathode material; furthermore, W can stabilize the NASICON structure of LATP and reduce the formation of impurity phases. In the coating layer, Al... 3 + W 6+ Ti 4+ At least one of them can enter the near-surface lattice of the cathode matrix, causing lattice contraction. Relative to the matrix material, the (003) diffraction peak is slightly shifted to a higher angle (0.1-0.3°). Lattice contraction can suppress oxygen vacancy formation, delay the transformation of the layered structure to the rock salt phase, and improve the lattice stability of the cathode material; Al 3+ W 6+ Ti 4+ Doping with at least one of these components can reduce cation mixing and improve lithium-ion transport pathways, thereby enhancing the cycle life and rate performance of the cathode material; and Al 3+ W 6+ Ti 4+At least one of them can enter the near-surface lattice of the cathode matrix, enhance the strength of the metal-oxygen (TM-O) bond, reduce lattice oxygen loss, and improve the thermal safety of the cathode material; the coating layer can also reduce the charge transfer resistance, form an ultra-thin protective barrier, prevent electrolyte corrosion and microcrack propagation, provide interface protection, and enable the cathode material to exhibit high initial capacity, good cycle stability and excellent rate performance.

[0069] Therefore, the present invention includes a positive electrode substrate as shown in Formula 1 and a coating layer as shown in Formula 2, which has both excellent structural stability and interfacial performance, and can improve the cycle performance and rate performance of the battery.

[0070] In some embodiments of the present invention, the X-ray diffraction pattern of the cathode material exhibits a (003) surface intensity with a 2θ of 18.8-19.0°. This indicates lattice contraction in the cathode material, with the (003) diffraction peak slightly shifted to a higher angle (2θ is 18.4-18.7° when the (003) surface intensity does not shift), which can suppress oxygen vacancy formation, delay the transformation of the layered structure to the rock salt phase, and improve the lattice stability of the cathode material.

[0071] In some embodiments of the present invention, when the average particle size of the compound shown in Formula 2 in the coating layer is 50-150 nm, the nanoscale LAWTP particles can effectively fill the microcracks on the surface of the positive electrode substrate, block the penetration path of the electrolyte, further reduce the side reaction rate between the positive electrode material and the electrolyte, and improve the cycle performance of the battery. Furthermore, the nanoscale LAWTP can form a dense and uniform coating layer, which can provide more adequate protection for the positive electrode substrate while ensuring the capacity of the positive electrode material, thereby improving the cycle performance of the battery. At the same time, the nanoscale LAWTP has a higher specific surface area and more surface active sites, which can accelerate the migration of lithium ions at the interface and improve the rate performance of the battery.

[0072] For example, the average particle size can be any one of 50 nm, 60 nm, 70 nm, 100 nm, 110 nm, 130 nm, 150 nm, or a range of any two of them.

[0073] Typically, the primary particle size of polycrystalline cathode materials is in the micrometer range, while the average particle size of the compound shown in Equation 2 is in the nanometer range. In some embodiments, SEM testing can be performed on the cathode material to obtain an SEM image of the cathode material. The nano-sized particles in the SEM image can be statistically analyzed to calculate the average particle size, thus obtaining the average particle size of the compound shown in Equation 2. For example, a Nano Measurer can be used for statistical analysis and calculation.

[0074] In some embodiments of the present invention, when the thickness of the coating layer is 100-200 nm, on the one hand, the capacity of the cathode material can be guaranteed, and on the other hand, the cathode substrate can be more fully protected, thereby improving the interfacial performance, bulk stability and thermal safety of the cathode material.

[0075] For example, the thickness of the coating layer can be any of 100nm, 120nm, 150nm, 170nm, 180nm, 190nm, 200nm, or any combination thereof.

[0076] In some implementations, the cathode material can be subjected to EPMA testing to obtain an EPMA map of the cathode material, and the thickness of the coating layer can be determined based on the distribution of Al, Ti, W and P in the EPMA map.

[0077] The inventors discovered in their research that when the mass percentage of the compound represented by Formula 2 in the cathode material is 0.1-0.5% (i.e., the mass percentage of the compound represented by Formula 2 in the mass of the cathode material), the compound represented by Formula 2 and the compound represented by Formula 1 can be more fully matched, enabling the cathode material to possess excellent capacity, interfacial properties, bulk stability, and thermal safety. Since the doping amount of the compound represented by Formula 2 is extremely low compared to the cathode substrate, differing by three orders of magnitude, the mass of the cathode substrate can be considered equivalent to the mass of the cathode material.

[0078] For example, in the cathode material, the mass percentage of the compound shown in Formula 2 can be any one of 0.1%, 0.2%, 0.3%, 0.45%, 0.5%, or any combination thereof.

[0079] LAWTP, as an inorganic material with good thermal stability, enables the cathode material to have excellent structural stability at high temperatures, reducing the damage of by-products to the cathode material structure. Ti, W, and Al can enter the near-surface of the cathode matrix, causing a slight shift of the (003) diffraction peak to a higher angle, inhibiting oxygen vacancy formation, and delaying the transformation of the layered structure to the spinel and rock salt phases. Macroscopically, this manifests as an increase in the oxygen release temperature of the cathode material (the mass of the cathode material only changes at higher temperatures), resulting in excellent thermal stability. In the fully delithiated state (fully charged state), the decomposition temperature of the cathode material increases, reducing oxygen release. The inventors discovered in their research that the decomposition temperature and weight loss of the cathode material can be matched, while eliminating interference from changes in non-cathode materials (mass reduction occurs in the range from room temperature to X℃, mainly due to the volatilization of free water and water of crystallization, which can be completely volatilized at X℃), thus enabling the cathode material to have better thermal stability. In some embodiments of this invention, in the fully charged state, the thermogravimetric curve of the cathode material satisfies Equation 3; |T max-X∣ / (60 100 |TG max -TG x |)≥1 Equation 3;

[0080] In Equation 3, X is the temperature at which free water and water of crystallization completely evaporate;

[0081] T max This is the temperature corresponding to the maximum rate of weightlessness.

[0082] TG max This is the TG value corresponding to the maximum rate of weightlessness;

[0083] TG x This represents the TG value corresponding to X℃.

[0084] In this application, |T max -X∣ refers to the absolute value of the difference between the maximum weight loss peak temperature and X℃, that is, the temperature range (℃) from X℃ to the maximum weight loss peak temperature; ∣TG max -TG x | refers to TG max With TG x The absolute value of the difference is used to represent the temperature difference from X℃ to T℃. max The total magnitude of weight loss between [amount]. |T max -X∣ / (60 100 |TG max -TG x | is denoted as K, where K is related to the material temperature from X℃ to T. max The average weight loss rate of cathode materials is inversely proportional to the temperature range (X℃ to T℃). K≥1 refers to the change from X℃ to T℃. max The average weight loss rate of the cathode material is ≤0.00017 / ℃. When K≥1, it can ensure that the outgassing or weight loss is slow between X℃ (120–170 ℃) and the maximum weight loss peak temperature. This indicates that the entry of W and Ti elements into the lattice of the cathode matrix can stabilize the oxygen in the lattice, slow down the release of oxygen, and stabilize the structure of the cathode material.

[0085] Furthermore, when X is 120-170℃, it is possible to completely evaporate the free water and crystal water in the cathode material while saving energy, thus eliminating the interference of changes in the non-cathode material itself.

[0086] Free water typically evaporates completely at 120°C, and water of crystallization evaporates completely at 150°C. In some implementations, to avoid weight loss effects caused by non-material structural changes, X can be set to 150°C.

[0087] A second aspect of the present invention provides a method for preparing a cathode material according to the first aspect, comprising:

[0088] A first raw material system comprising the compound shown in Formula 1 and the compound shown in Formula 2 is subjected to a first calcination treatment to obtain a positive electrode material comprising a positive electrode matrix and a coating layer.

[0089] Specifically, a first raw material system comprising the compound shown in Formula 1 and the compound shown in Formula 2 is subjected to a first calcination treatment. In the first calcination treatment, the compound shown in Formula 2 forms a coating layer that coats at least a portion of the surface of the compound shown in Formula 1 (as the positive electrode substrate), thereby obtaining the positive electrode material of the present invention.

[0090] The preparation method of the present invention can prepare the above-mentioned cathode material. The preparation method is simple to operate and suitable for widespread application.

[0091] In this invention, |T can be adjusted by adjusting the amount of LAWTP added and the temperature and time of the first calcination treatment. max -X∣ / (60 100 |TG max -TG x |). For example, by adjusting the dosage of LAWTP, |T can be made max -X∣ / (60 100 |TG max -TG x |) Within a suitable threshold, the capacity and thermal stability of the cathode material are guaranteed.

[0092] Furthermore, the first roasting process sequentially includes a first-stage roasting process and a second-stage roasting process;

[0093] In the first stage of roasting, the temperature is 300-350℃ and the time is 6-10h;

[0094] In the two-stage roasting process, the temperature is 650-750℃ and the time is 1-2 hours.

[0095] The first calcination process of this invention may sequentially include a first-stage calcination process and a second-stage calcination process, wherein the temperature of the second-stage calcination process is higher than that of the first-stage calcination process. This invention achieves the coating of the compound shown in Formula 2 through two-step heating. In the lower-temperature first-stage calcination process, LAWTP can form a uniform and thin coating layer on the surface of the positive electrode substrate. In the higher-temperature second-stage calcination process, Al³⁺ and W⁻ can be coated. 6 ⁺、Ti 4+ At least one of the components enters the near-surface of the cathode substrate to improve the structure of the cathode substrate, thereby obtaining a cathode material with both excellent interfacial properties and stability.

[0096] In this invention, the compound represented by Formula 1 can be obtained commercially or prepared in a laboratory. In some embodiments, the compound represented by Formula 1 can be obtained by calcining a nickel-cobalt-manganese precursor (nickel-cobalt-manganese hydroxide precursor and / or nickel-cobalt-manganese carbonate precursor) with a lithium source.

[0097] In this invention, LAWTP can be obtained commercially or synthesized in a laboratory.

[0098] In some embodiments of the present invention, when the compound shown in Formula 2 is a nanoscale material, the coating layer of the obtained cathode material includes the compound with nanoscale particle size, and the thickness of the obtained coating layer can be nanoscale, effectively improving the cycle performance and rate performance of the battery.

[0099] In some embodiments of the present invention, the compound represented by Formula 2 can be prepared by a method comprising the following steps:

[0100] The second raw material system, including Li source, Al source, W source, Ti source and P source, was subjected to hydrothermal reaction and second calcination treatment in sequence to obtain the compound shown in Formula 2.

[0101] The LAWTP obtained by the present invention through hydrothermal reaction and second calcination treatment is nanoscale in size. When applied to the coating of positive electrode substrate, it helps to form a more uniform, dense and thin coating layer, thereby improving the interfacial performance and stability of the positive electrode material.

[0102] In some embodiments, the second raw material system also includes polyvinylpyrrolidone (PVP), which, as a surfactant and structure directing agent, can optimize the morphology, size, and dispersibility of LAWTP.

[0103] In this invention, the lithium source can be a compound containing lithium commonly used in the art, for example, the lithium source can be LiOH; the Al source can be a compound containing aluminum commonly used in the art, for example, the aluminum source can be Al(NO3)3; the W source can be a compound containing W commonly used in the art, for example, the tungsten source can be WO3; the Ti source can be a compound containing titanium commonly used in the art, for example, the titanium source can be TiO2; and the P source can be a compound containing phosphorus commonly used in the art, for example, the phosphorus source can be NH4H2PO4.

[0104] In this invention, the temperature and time of the hydrothermal reaction can be selected to control the particle size of LAWTP. In some embodiments of this invention, when the temperature of the hydrothermal reaction is 150-200°C and the time is 8-12 hours, LAWTP with a size of 50-150 nm can be obtained, thereby forming a more uniform, dense, and thin coating layer.

[0105] In some embodiments of the present invention, when the temperature is 700-800°C and the time is 1-3 hours in the second calcination process, nano-sized LAWTP can be formed more efficiently while saving energy.

[0106] A third aspect of the present invention provides a positive electrode sheet comprising the above-described positive electrode material.

[0107] The positive electrode of the present invention, having included the above-mentioned positive electrode material, has excellent cycle performance and rate performance.

[0108] A fourth aspect of the present invention provides a battery comprising the above-described positive electrode.

[0109] It is understood that a battery also includes a negative electrode, a separator, an electrolyte, and an outer packaging. In this invention, the positive electrode, separator, and negative electrode can be stacked to form a stacked electrode assembly, which is then placed in an outer packaging. Electrolyte is injected into the outer packaging, and after sealing and formation, a battery is formed. Alternatively, the positive electrode, separator, and negative electrode can be stacked and then wound to obtain a wound electrode assembly. The electrode assembly is then placed in an outer packaging, electrolyte is injected into the outer packaging, and after sealing and formation, a battery is formed.

[0110] The battery of the present invention, due to the inclusion of a positive electrode sheet in the third aspect, has excellent cycle performance and rate performance.

[0111] The present invention also provides an electronic device, including a battery according to a fourth aspect.

[0112] It should be noted that the aforementioned electronic device can be any conventional device that requires electricity, such as, but not limited to, computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc. Because the electronic device includes a battery, it has superior battery life and extended lifespan.

[0113] The present invention will be further described below with reference to specific embodiments:

[0114] Example 1

[0115] The battery in this embodiment is prepared by a method including the following steps:

[0116] 1) Preparation of cathode materials

[0117] Step 1: Follow Li 1.3 Al 0.1 W 0.1 Ti 1.7The proportion of (PO4)3 molecular formula is used to dissolve LiOH, Al(NO3)3, WO3, TiO2, NH4H2PO4, and PVP in water to obtain a second raw material system. The second raw material system is transferred to a high-pressure reactor and subjected to hydrothermal reaction at 160℃ for 10h. After centrifugation and washing, it is dried at 120℃ and subjected to a second calcination treatment at 750℃ for 2h under oxygen-containing conditions to obtain nano-LAWTP.

[0118] Step 2: Mix NCM90 / 8 / 2 type hydroxide precursor with LiOH·H2O in a certain proportion, wherein the molar content of Li element to the total molar content of transition metal elements (Ni, Co, and Mn) is 1.05:1; sinter at 800℃ in an oxygen atmosphere and hold for 8 hours to obtain primary sintered material. After cooling, mechanically crush the primary sintered material, wash it with water at a material-to-water mass ratio of 1:1, and dry it to obtain LiNi. 0.9 Co 0.08 Mn 0.02 O2 cathode substrate; LiNi 0.9 Co 0.08 Mn 0.02 O2 and LAWTP are mixed at a mass ratio of 1:0.003 to form a first raw material system. The first raw material system is subjected to a first-stage roasting treatment and a second-stage roasting treatment. In the first-stage roasting treatment, the temperature is 300℃ and the time is 10h. In the second-stage roasting treatment, the temperature is 700℃ and the time is 1h. After cooling and crushing, a positive electrode material including a positive electrode matrix and a coating layer is obtained.

[0119] 2) Preparation of positive electrode sheet

[0120] The positive electrode material, conductive agent (Super P), and binder (PVDF) are added to NMP at a mass ratio of 92:3:5, and mixed and homogenized using a degassing machine to obtain a positive electrode slurry. The mixed positive electrode slurry is coated onto one or both sides of an aluminum foil, dried, cold-pressed, and slit to obtain a positive electrode sheet. The areal density of the positive electrode sheet on one side is 8 mg / cm³. 2 .

[0121] 3) Preparation of negative electrode sheet

[0122] Graphite, conductive agent (Super P), styrene-butadiene rubber, and carboxymethyl cellulose were added to deionized water in a mass ratio of 95.5:1:2:1.5 and mixed and homogenized using a degassing machine to obtain a negative electrode slurry. The mixed negative electrode slurry was coated on both sides of copper foil, dried, cold-pressed, and slit to obtain a negative electrode sheet.

[0123] 4) Assembly of the full battery

[0124] The double-sided coated positive electrode, separator, and negative electrode obtained above are sequentially stacked, with an NP ratio of 1.12, to obtain an electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film package, dried, and then electrolyte is injected into the aluminum-plastic film to obtain a full cell. The electrolyte used for the full cell test is the TC-E5VA electrolyte produced by Guangzhou Tinci Advanced Materials Co., Ltd.

[0125] Other battery parameters are shown in Table 1.

[0126] Example 2

[0127] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0128] 1) Preparation of cathode materials

[0129] In step two, LiNi 0.9 Co 0.08 Mn 0.02 The mass ratio of O2 to LAWTP is 1:0.002.

[0130] Example 3

[0131] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0132] 1) Preparation of cathode materials

[0133] In step two, NCM90 / 8 / 2 type hydroxide precursor and LiOH·H2O are mixed in a certain proportion to obtain a mixture, wherein the molar content of Li element to the total molar content of transition metal elements (Ni, Co and Mn) is 1.05:1; aluminum source (Al2O3), magnesium source (MgO), zirconium source (ZrO), and titanium source (TiO2) are added and uniformly mixed in a high-speed mixer to obtain the calcination material, wherein the amount of aluminum source added is 1000 ppm of the precursor mass, the amount of magnesium source added is 1000 ppm of the precursor mass, the amount of zirconium source added is 2000 ppm of the precursor mass, and the amount of titanium source added is 1000 ppm of the precursor mass; the calcination material is placed in a sagger and sintered at 800℃ in an oxygen atmosphere for 8 hours to obtain the primary sintered material. The cooled primary sintered material is mechanically crushed, washed with water at a material-to-water mass ratio of 1:1, and dried to obtain LiNi. 0.899 Co 0.0798 Mn 0.020 Al 0.003 Mg 0.004 Zr 0.002 Ti 0.002 O2 positive electrode substrate;

[0134] The positive electrode substrate prepared in this embodiment is used to replace the positive electrode substrate in Example 1.

[0135] Example 4

[0136] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0137] 1) Preparation of cathode materials

[0138] In step one, according to Li 1.4 Al 0.1 W 0.15 Ti 1.6 The second raw material system was obtained by dissolving LiOH, Al(NO3)3, WO3, TiO2, NH4H2PO4, and PVP in water according to the (PO4)3 molecular formula. The second raw material system was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 160℃ for 10h. After centrifugation and washing, it was dried at 120℃ and subjected to a second calcination treatment at 750℃ for 2h under oxygen-containing conditions to obtain nano-LAWTP.

[0139] Example 5

[0140] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0141] 1) Preparation of cathode materials

[0142] Step 1: Follow Li 1.3 Al 0.1 W 0.1 Ti 1.7 The second raw material system was obtained by dissolving LiOH, Al(NO3)3, WO3, TiO2, NH4H2PO4, and PVP in water according to the (PO4)3 molecular formula. The second raw material system was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 200℃ for 10h. After centrifugation and washing, it was dried at 120℃ and subjected to a second calcination treatment at 750℃ for 2h under oxygen-containing conditions to obtain nano-LAWTP.

[0143] Example 6

[0144] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0145] 1) Preparation of cathode materials

[0146] In step two, LiNi 0.9 Co 0.08 Mn 0.02 The mass ratio of O2 to LAWTP is 1:0.005.

[0147] Example 7

[0148] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0149] 1) Preparation of cathode materials

[0150] In step two, LiNi 0.9 Co 0.08 Mn 0.02 The mass ratio of O2 to LAWTP is 1:0.01.

[0151] Comparative Example 1

[0152] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0153] 1) Preparation of cathode materials

[0154] In step one, the second raw material system does not include WO3, and the second raw material system is prepared according to Li 1.3 Al 0.3 Ti 1.7 The LATP nanoparticles were obtained by dissolving LiOH, Al(NO3)3, TiO2, NH4H2PO4, and PVP in water according to the molecular formula of (PO4)3.

[0155] In step two, LATP is used instead of LAWTP.

[0156] Comparative Example 2

[0157] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0158] 1) Preparation of cathode materials (cathode materials do not include the coating layer)

[0159] A mixture was prepared by mixing NCM90 / 8 / 2 type hydroxide precursor with LiOH·H2O in a certain proportion, wherein the molar content of Li element to the total molar content of transition metal elements (Ni, Co and Mn) was 1.05:1; aluminum source (Al2O3), magnesium source (MgO), zirconium source (ZrO) and titanium source (TiO2) were added and uniformly mixed in a high-speed mixer to obtain the calcination material, wherein the amount of aluminum added was 1000 ppm of the precursor mass, the amount of magnesium added was 1000 ppm of the precursor mass, the amount of zirconium added was 2000 ppm of the precursor mass, and the amount of titanium added was 1000 ppm of the precursor mass.

[0160] The material to be calcined was placed in a sagger and sintered at 800℃ under an oxygen atmosphere for 8 hours to obtain a primary sintered material. The cooled primary sintered material was mechanically crushed, washed with water at a material-to-water mass ratio of 1:1, and then dried to obtain LiNi. 0.89 Co0.079 Mn 0.020 Al 0.003 Mg 0.004 Zr 0.002 Ti 0.002 O2 cathode material.

[0161] Comparative Example 3

[0162] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0163] 1) Preparation of cathode materials (cathode materials do not include the coating layer)

[0164] An NCM90 / 8 / 2 type hydroxide precursor was mixed with LiOH·H2O in a certain proportion, wherein the molar content of Li was 1.05:1 compared with the total molar content of transition metal elements (Ni, Co, and Mn). The mixture was sintered at 800℃ in an oxygen atmosphere for 8 hours to obtain a primary sintered material. The cooled primary sintered material was mechanically crushed, washed with water at a material-to-water mass ratio of 1:1, and dried to obtain LiNi. 0.9 Co 0.08 Mn 0.02 O2 cathode material.

[0165] Performance testing

[0166] The following performance tests were performed on the cathode materials and batteries in the examples and comparative examples, and the results are shown in Table 1.

[0167] 1) XRD test

[0168] Bruker D8 ADVANCE, scan range (2θ): 10-80°; 0.02° step size, 1s per step.

[0169] Figure 1 The XRD patterns of the cathode materials of Example 1 and Comparative Example 3 are shown below. Figure 1 It can be seen that, compared with Comparative Example 3, the characteristic peak of the (003) surface intensity of the cathode material in Example 1 shifted to a higher angle by 0.15°, indicating that the Al in the compound shown in Formula 2 in the coating layer... 3+ W 6+ Ti 4+ At least one of them enters the near-surface lattice of the cathode substrate (unlike direct doping of at least one of Al, W, and Ti into the cathode substrate, direct doping of at least one of Al, W, and Ti into the cathode substrate will cause the characteristic peak of the (003) surface intensity to shift to a lower angle).

[0170] 2) The content of each element in the cathode material and the content of LAWTP.

[0171] For ICP testing of cathode materials, the content of each element in the cathode material is obtained, including: weighing 0.4g of cathode material, performing plate digestion with 10ml of aqua regia to obtain the test solution, and testing the test solution. The quantitative method adopts the standard curve method. When testing the main elements Li, Ni, Co, and Mn, the test solution is diluted 100 times with a 2% (w / w) HNO3 aqueous solution before testing. When testing other elements (such as element A and the elements in LAWTP), no dilution is required, and the test solution is tested directly.

[0172] EPMA was used to test the cathode material to obtain the content of main elements (such as Li, Ni, Co, Mn) and dopant elements (A element) in the cathode matrix;

[0173] The LAWTP content can be calculated by combining the ICP test results and the EPMA results.

[0174] 3) SEM testing

[0175] The cathode material in the examples was subjected to SEM testing. Figure 2 This is a SEM image of the cathode material in Example 1. Figure 2 This is a magnified view of a single secondary particle of the cathode material. Figure 2 As can be seen, the secondary particles of the cathode material in this embodiment are micrometer-sized. The cathode material includes a coating layer, and the coating layer contains nanometer-sized particles with an average particle size of 100 nm.

[0176] 4) Thickness of the coating layer

[0177] EPMA testing was performed on the cathode material in the embodiment, and the coating thickness of the cathode material was obtained from the EPMA diagram. Figure 3 The EPMA plot of the P element distribution of the cathode material in Example 1 is shown below. Figure 3 It can be seen that the thickness of the LAWTP coating layer is 160nm.

[0178] 5) Initial capacity at 0.1C

[0179] The testing equipment was the Xinwei CT-4008 test cabinet, with the voltage window set to 3.0-4.25V. The first charge and discharge was performed using a small current of 0.1C, and the discharge capacity was recorded.

[0180] 6) Capacity retention rate over 100 cycles (C)

[0181] The testing equipment was the Xinwei CT-4008 test cabinet, with the voltage window set to 3.0-4.25V. Cyclic charge and discharge were performed using a 1C current. The discharge capacity of the first cycle and the discharge capacity of the 100th cycle were recorded. The capacity retention rate was calculated as the discharge capacity of the 100th cycle divided by the discharge capacity of the first cycle.

[0182] 7) 3C capacity

[0183] The testing equipment was the Xinwei CT-4008 test cabinet, with the voltage window set to 3.0-4.25V. Cyclic charging and discharging were performed using a 3C current, and the discharge capacity was recorded.

[0184] 8) Thermogravimetric test

[0185] A fully charged fresh battery is disassembled to obtain the positive electrode sheet. After cleaning and drying the positive electrode sheet with NMP, the positive active layer on the positive electrode sheet is scraped off to obtain positive electrode powder.

[0186] The TG test was performed on the cathode powder under a nitrogen atmosphere, a temperature rise rate of 5℃ / min, and a temperature range of room temperature to 300℃.

[0187] Figure 4 Thermogravimetric curve of the cathode material in Example 1; Figure 5 The thermogravimetric curves of the cathode materials in Example 1 and Comparative Example 2 are shown. Figure 4 The calculated K value of the cathode material in Example 1 is 1.48. Figure 5 It can be seen that the cathode material in the embodiments has better thermal stability.

[0188] Table 1

[0189]

[0190] According to Table 1, the 2θ of the (003) surface intensity characteristic peak of the cathode material in the embodiment of the present invention is larger, indicating that the (003) surface intensity is shifted to a higher angle, the lattice of the cathode material shrinks, and it has better structural stability.

[0191] The battery of the present invention has better 0.1C initial capacity, 100-cycle capacity retention rate and 3C capacity, indicating that the present invention can improve the cycle performance and rate performance of the battery by forming a coating layer including the compound shown in Formula 2 on at least a portion of the surface of the positive electrode substrate including the compound shown in Formula 1.

[0192] As can be seen from Examples 1 and 3, when Al and Ti are also included in the cathode matrix, the (003) surface intensity characteristic peak of the cathode material shifts to a lower angle, which can increase the K value and further improve the cycle performance of the cathode material.

[0193] As can be seen from Examples 1 and 5, by selecting the particle size of LAWTP in the coating layer of the cathode material, the cycle performance and rate performance of the battery can be improved.

[0194] As can be seen from Examples 1 and 6 and 7, by selecting the content of LAWTP in the cathode material, the thickness of the coating layer can be affected, thereby affecting the cycle performance and rate performance of the battery.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate; The positive electrode substrate includes the compound shown in Formula 1; Li a1 Ni b1 Co c1 Mn d1 A e1 O₂ formula 1; In Equation 1, 0.9≤a1≤1.1, 0.65≤b1≤0.95, 0≤c1≤0.3, 0≤d1≤0.3, and 0≤e1≤0.1; A includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, Ba, P, S, and F; The coating layer comprises the compound shown in Formula 2; Li a2 Al b2 W c2 Ti d2 (PO4)3 formula 2; In Equation 2, 1≤a2≤1.5, 0.05≤b2≤0.3, 0.1≤c2≤0.3, and 1.5≤d2≤2.

2. The cathode material according to claim 1, characterized in that, In the X-ray diffraction pattern of the cathode material, it has a (003) surface intensity with a 2θ of 18.8-19.0°; and / or, In the coating layer, the average particle size of the compound represented by Formula 2 is 50-150 nm.

3. The cathode material according to claim 1 or 2, characterized in that, The thickness of the coating layer is 100-200 nm.

4. The cathode material according to any one of claims 1-3, characterized in that, In the cathode material, the mass percentage of the compound represented by Formula 2 is 0.1-0.5%.

5. The cathode material according to any one of claims 1-4, characterized in that, In a fully charged state, the thermogravimetric curve of the positive electrode material satisfies Equation 3; |T max -X∣ / (60 100 |TG max -TG x |)≥1 Equation 3; In Equation 3, X is the temperature at which free water and water of crystallization completely evaporate; T max This is the temperature corresponding to the maximum rate of weightlessness. TG max This is the TG value corresponding to the maximum rate of weightlessness; TG x This represents the TG value corresponding to X℃. Preferably, X is 120-170℃.

6. A method for preparing the cathode material according to any one of claims 1-5, characterized in that, include: A first raw material system comprising the compound shown in Formula 1 and the compound shown in Formula 2 is subjected to a first calcination treatment to obtain the positive electrode material comprising a positive electrode matrix and a coating layer.

7. The preparation method according to claim 6, characterized in that, The first roasting process includes a first-stage roasting process and a second-stage roasting process. In the aforementioned calcination process, the temperature is 300-350℃ and the time is 6-10 hours. In the two-stage roasting process, the temperature is 650-750℃ and the time is 1-2 hours.

8. The preparation method according to claim 6 or 7, characterized in that, The compound shown in Formula 2 is a nanoscale material; and / or, The compound shown in Formula 2 is prepared by a method comprising the following steps: The second raw material system, including Li source, Al source, W source, Ti source and P source, was subjected to hydrothermal reaction and second calcination treatment in sequence to obtain the compound shown in Formula 2.

9. The preparation method according to claim 8, characterized in that, In the hydrothermal reaction, the temperature is 150-200℃ and the time is 8-12 hours; and / or, In the second calcination treatment, the temperature is 700-800℃ and the time is 1-3 hours; and / or, The second raw material system also includes polyvinylpyrrolidone.

10. A positive electrode plate, characterized in that, Includes the cathode material as described in any one of claims 1-5.

11. A battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

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