Positive electrode material, preparation method thereof, secondary battery and electric device

Abstract

The invention provides a positive electrode material, a preparation method of the positive electrode material, a secondary battery and an electric device. The positive electrode material comprises an inner core and a coating material, the inner core comprises a nickel-containing lithium transition metal oxide, and the coating material comprises a ferroelectric ceramic material and a fast ion conductor material. The preparation method of the positive electrode material comprises the steps that nickel-containing lithium transition metal oxide and a coating material are mixed and then calcined in the oxygen atmosphere, the positive electrode material is obtained, and the coating material comprises a ferroelectric ceramic material and a fast ion conductor material. The two coating materials construct a double-coating structure on the surface of the inner core, the active ion kinetics at the positive electrode is improved through a synergistic effect, the discharge rate of the secondary battery is improved, and the positive electrode material is effectively protected, so that the cycle performance is optimized.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode material, its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] With the continuous expansion and popularization of electric aircraft applications, related technologies are developing rapidly. Achieving high-power discharge at low SOC to meet landing requirements is one of the current key technological challenges.

[0003] High-nickel ternary lithium battery systems possess high energy density, but the severely compressed Co content leads to a significant degradation in power performance. Current technologies utilize low-boiling-point solvents to enhance lithium-ion conductivity, thereby improving power performance. However, high-rate discharge is a heat accumulation process; the temperature rise causes the low-boiling-point solvents to volatilize, resulting in battery gas production and failure, thus reducing overall battery reliability. Improving the power performance of high-nickel battery systems requires more effective and safer solutions. Summary of the Invention

[0004] This application provides a cathode material, a method for preparing the same, a secondary battery, and an electrical device to improve the power performance of the secondary battery.

[0005] The first aspect of this application provides a cathode material, including a core and a coating material, wherein the core includes a nickel-containing lithium transition metal oxide, and the coating material includes a ferroelectric ceramic material and a fast ion conductor material.

[0006] In the aforementioned cathode materials, the coating material constructs a dual-material coating on the core surface of a nickel-containing lithium transition metal oxide. The two materials work synergistically to achieve rapid lithium-ion transport, thereby improving the discharge rate of the cathode material at low SOC. Specifically, the ferroelectric ceramic material utilizes its spontaneous polarization to alleviate the formation of the electric double layer on the cathode material surface, thus improving the uniformity of lithium-ion distribution and lithium-ion conductivity. The fast-ion conductor material exhibits properties similar to a liquid electrolyte, possessing extremely high alkali metal cation conductivity, which can lower the desolvation barrier of lithium-ions and accelerate the interfacial transport speed. Furthermore, the ferroelectric ceramic material improves the uniformity of lithium-ion distribution on the cathode material surface, providing a better ion dispersion basis for lithium-ion conduction, and further facilitating the role of the fast-ion conductor material in lowering the lithium-ion desolvation barrier. The synergistic effect of these two materials significantly improves the lithium-ion conductivity on the cathode material surface, thereby contributing to improved discharge rate of the secondary battery. The coating material can also play a role in physical isolation, reducing the erosion of the nickel-containing lithium transition metal oxide surface by the electrolyte, which is beneficial to improving the cycle performance of the cathode material.

[0007] In any embodiment of the first aspect, the characteristic element A of the ferroelectric ceramic material has a mass content of 2.3% to 6.5% in the cathode material, and the characteristic element A is different from the metal element in the core and the metal element in the fast ion conductor material; and / or, the characteristic element B of the fast ion conductor material has a mass content of 0.2% to 1.8% in the cathode material, and the characteristic element B is different from the metal element in the core and the metal element in the ferroelectric ceramic material.

[0008] In any embodiment of the first aspect, the mass ratio of feature element A to feature element B is (2 to 30):1, preferably (2.4 to 8.2):1.

[0009] In any embodiment of the first aspect, the average particle size of the coating material is 50 nm to 150 nm.

[0010] In any embodiment of the first aspect, the ferroelectric ceramic material has the general formula XYO3, where X is selected from Li. + Na + K + Mg 2 + Ca 2+ 、Sr 2+ Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5+ 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ .

[0011] In any embodiment of the first aspect, the fast ion conductor material is selected from one or more of LATP, LAGP, LLZO, LLTO, LiBO2, LiAlO2, and LiPO3.

[0012] In any embodiment of the first aspect, the molar content of nickel in the transition metal element of the nickel-containing lithium transition metal oxide is greater than or equal to 80%, optionally greater than or equal to 90%, and further optionally greater than or equal to 95%.

[0013] In any embodiment of the first aspect, the nickel-containing lithium transition metal oxide comprises lithium having the chemical formula Li x Ni y M1-y Oxides of O2, 1.01≤x≤1.06, 0.8≤y≤0.995, M is selected from one or more of Co, Mn, Al, Zr, Ba, Ti, Y, Sr, Sb, Mg, Nb, B, and W.

[0014] In any embodiment of the first aspect, the lithium-ion diffusion coefficient of the cathode material is 10. -8 ~10 -4 S / cm, selectable as 10 -6 ~10 -5 S / cm.

[0015] In any embodiment of the first aspect, the cathode material has one or more of the following characteristics: (1) a BET specific surface area of ​​0.1 m². 2 / g~1.0m 2 / g, can be selected as 0.1m 2 / g~0.5m 2 / g; (2) The particle size of Dv50 is 8μm~15μm, and can be selected as 10μm~12μm.

[0016] In any embodiment of the first aspect, the cathode material further includes aluminum oxide coated on the surface of a nickel-containing lithium transition metal oxide; optionally, the mass content of aluminum oxide in the cathode material is 1000 ppm to 4000 ppm.

[0017] The second aspect of this application provides a method for preparing a cathode material, comprising: mixing a nickel-containing lithium transition metal oxide with a coating material and then calcining it in an oxygen atmosphere to obtain a cathode material, wherein the coating material includes ferroelectric ceramic materials and fast ion conductor materials.

[0018] In any embodiment of the second aspect, the above preparation method includes: mixing a nickel-containing lithium transition metal oxide with a ferroelectric ceramic material and then calcining it for the first time in an oxygen atmosphere to obtain a nickel-containing lithium transition metal oxide coated with ferroelectric ceramic material; mixing the nickel-containing lithium transition metal oxide coated with ferroelectric ceramic material with a fast ion conductor material and then calcining it for the second time in an oxygen atmosphere to obtain a cathode material.

[0019] In any embodiment of the second aspect, the temperature of the first calcination is 300°C to 350°C, and the duration is 6 to 12 hours.

[0020] In any embodiment of the second aspect, the temperature of the second calcination is 300°C to 350°C, and the duration is 6 to 12 hours.

[0021] In any embodiment of the second aspect, the ferroelectric ceramic material has one or more of the following characteristics: (1) the mass of the ferroelectric ceramic material is 4% to 11% of the mass of the nickel-containing lithium transition metal oxide; (2) the ferroelectric ceramic material has the general formula XYO3, where X is selected from Li + Na + K + Mg 2+ Ca 2+ 、Sr 2+ Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5+ 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ (3) The Dv50 particle size of the ferroelectric ceramic material is 50nm~150nm.

[0022] In any embodiment of the second aspect, the fast ion conductor material has one or more of the following characteristics: (1) the mass of the fast ion conductor material is 1% to 4.5% of the mass of the nickel-containing lithium transition metal oxide; (2) the fast ion conductor material is selected from one or more of LATP, LAGP, LLZO, LLTO, LiBO2, LiAlO2, and LiPO3.

[0023] In any embodiment of the second aspect, before mixing the nickel-containing lithium transition metal oxide with the coating material, the preparation method further includes a process of washing the nickel-containing lithium transition metal oxide with water, and washing the nickel-containing lithium transition metal oxide until free Li in the washing water is obtained. + The content is less than 2500 ppm.

[0024] A third aspect of this application provides a secondary battery, including a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including any positive electrode material in the first aspect or a positive electrode material prepared by any preparation method in the second aspect.

[0025] In any embodiment of the third aspect, the charge transfer impedance Rct of the positive electrode of the secondary battery is 0.5Ω to 5Ω, and can be selected as 0.5Ω to 1Ω.

[0026] In any embodiment of the third aspect, after the positive electrode of the secondary battery is immersed in an equal volume of electrolyte for 6 to 10 hours, the electrolyte retention of the positive electrode is 1.3 g / Ah to 2.0 g / Ah, optionally 1.5 g / Ah to 1.65 g / Ah. The electrolyte retention is calculated as (weight of the positive electrode after immersion - weight of the positive electrode) / weight of the positive electrode. The electrolyte includes a solvent and a lithium salt. The solvent includes ethylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and ethyl acrylate in a volume ratio of 2:2:1:2:3. The lithium salt includes LiPF6 and LiFSI in a molar ratio of 4:6. The concentration of the lithium salt in the electrolyte is 1.1 mol / L.

[0027] The fourth aspect of this application provides an electrical device including a secondary battery, which includes any of the secondary batteries described in the third aspect. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0029] Figure 1 This is a scanning electron microscope image of the cathode material according to one embodiment of this application.

[0030] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0031] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0032] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0033] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0034] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0035] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0036] The accompanying drawings are not drawn to scale.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0039] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0040] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode material, its preparation method, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0046] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] [Cathode Material]

[0048] State of Charge (SOC) is an important parameter for measuring the state of a battery's charge, representing the ratio of the battery's remaining charge to its rated capacity, usually expressed as a percentage. Typically, under low SOC conditions, lithium ions in a secondary battery rapidly accumulate on the surface of the positive electrode material to form an electrical double layer, significantly reducing the rate of charge transfer at the interface. This causes the battery to discharge rapidly to the cutoff potential, resulting in a significant decrease in rate performance.

[0049] To effectively improve the high-rate discharge capability of secondary batteries at low SOC, the first embodiment of this application provides a positive electrode material, which includes a core and a coating material. The core includes a nickel-containing lithium transition metal oxide, and the coating material includes a ferroelectric ceramic material and a fast ion conductor material.

[0050] In the aforementioned cathode materials, the coating material constructs a double-coating structure on the core surface of a nickel-containing lithium transition metal oxide. The two coating materials work synergistically to achieve rapid lithium-ion transport, thereby improving the discharge rate of the cathode material at low SOC. Specifically, the ferroelectric ceramic material utilizes its inherent spontaneous polarization to alleviate the formation of the electric double layer on the cathode material surface, thus improving the uniformity of lithium-ion distribution and lithium-ion conductivity. The fast-ion conductor material exhibits properties similar to a liquid electrolyte, with extremely high conductivity of alkali metal cations, which can lower the desolvation barrier of lithium-ions and accelerate the interfacial transport speed. Furthermore, the ferroelectric ceramic material improves the uniformity of lithium-ion distribution on the cathode material surface, providing a better ion dispersion basis for lithium-ion conduction, which is more conducive to the fast-ion conductor material's role in lowering the lithium-ion desolvation barrier. The synergistic effect of these two materials significantly improves the lithium-ion conductivity on the cathode material surface, thus contributing to improved discharge rate of the secondary battery.

[0051] In addition, the coating material can play a physical isolation role, reducing the erosion of the nickel-containing lithium transition metal oxide surface by the electrolyte, which is beneficial to improving the cycle performance of the cathode material.

[0052] In some embodiments, the coating material is distributed in an island-like or dot-like pattern on the surface of the nickel-containing transition metal oxide. There is no specific restriction on the inner and outer layer order of the ferroelectric ceramic material and the fast ion conductor material. In some embodiments, the ferroelectric ceramic material coats the surface of the nickel-containing lithium transition metal oxide, and part of the fast ion conductor material coats the exposed surface of the ferroelectric ceramic material, forming a double-coating structure with the ferroelectric ceramic material as the inner layer and the fast ion conductor material as the outer layer. In this case, the ferroelectric ceramic material in the inner layer helps to eliminate space charge accumulation, while the fast ion conductor material in the outer layer helps to improve the lithium-ion transport speed, thereby improving the lithium-ion conductivity on the surface of the cathode material. For example... Figure 1 A scanning electron microscope image of the positive electrode material in one embodiment of this application is shown.

[0053] The morphology of the aforementioned double-coated structure can be determined by field emission scanning electron microscopy (FESEM). Sample preparation can be performed as follows: When the above-mentioned cathode material needs to be obtained from a secondary battery, after disassembling the secondary battery to obtain the cathode sheet, use ceramic scissors to cut the cathode sheet into samples of 6mm*6mm size, attach them to a sample stage coated with paraffin wax, and ensure that the samples slightly protrude from the edge of the sample stage; set the voltage and time for ion grinding and polishing, and polish the 150μm thick cathode sheet sample at 7.5kV for 50 minutes; after obtaining the cross-section through ion grinding, perform EDS energy dispersive spectroscopy micro-area composition analysis using a surface scanning method, selecting 3 single particles for surface scanning, with specific parameters set as follows: In-lens mode, 20kV voltage, aperture diameter of 60μm, and working distance of 8.5mm, which can intuitively obtain the distribution of elements in different regions.

[0054] To improve coating uniformity, in some embodiments, the average particle size of the coating material is 50 nm to 150 nm. Furthermore, coating materials with nanoscale particle sizes exhibit high adhesion to the core surface. The aforementioned average particle size can be determined through further statistical analysis following transmission electron microscopy imaging.

[0055] In the coating material of the cathode material, the contents of ferroelectric ceramic material and fast ion conductor material can be adjusted by the amount of raw materials added.

[0056] When determining the ferroelectric ceramic material in the prepared cathode material, a unique element in the ferroelectric ceramic material can be selected as characteristic element A. The mass content of characteristic element A in the cathode material is used to indirectly characterize the content of the ferroelectric ceramic material. In some embodiments, the mass content of characteristic element A in the cathode material is 2.3% to 6.5%, and characteristic element A is different from the metal elements in the core and the metal elements in the fast ion conductor material. Using ferroelectric ceramic material within the above-mentioned content range can significantly improve the ionic conductivity of the cathode material while avoiding the reduction in the effective specific capacity of the cathode material due to excessive use of ferroelectric ceramic material.

[0057] The mass content of characteristic element A in the cathode material of the aforementioned ferroelectric ceramic material can be tested using methods and equipment known in the art, such as referring to the EPA 6010D-2014 standard. Specifically, ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) can be used. The sample to be tested is first digested into a liquid with a strong acid, and then the liquid is introduced into the ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then recover from the excited state to the ground state. During the above process, energy is released and recorded as different characteristic spectral lines for trace element quantitative analysis.

[0058] In some embodiments, the ferroelectric ceramic material has the general formula XYO3, where X is selected from Li. + Na + K + Mg 2+ Ca 2+ 、Sr 2 + Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5+ 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ The aforementioned ferroelectric ceramic materials are all known in this field, exhibiting good ion conduction and chemical stability. Any element from element X or element Y can be used as characteristic element A, provided it meets the criteria for being characteristic element A.

[0059] When X is Ba 2+ During the coating process, some Ba elements diffuse into the core, achieving high-entropy doping of the core. Furthermore, Ba's relatively large atomic radius helps stabilize the material's structure to some extent, suppressing c-axis expansion of the core material during cycling. This improves the material's cycling stability and reduces dissolution losses in the cathode material.

[0060] Similarly, when determining the fast ion conductor material in the prepared cathode material, an element unique to the fast ion conductor material can be selected as characteristic element B. The mass content of the fast ion conductor in the cathode material can be used to indirectly characterize the content of the fast ion conductor in the cathode material. In some embodiments, the mass content of characteristic element B of the fast ion conductor material in the cathode material is 0.2% to 1.8%, and characteristic element B is different from the metal element in the core and the metal element in the ferroelectric ceramic material.

[0061] The test method for the mass content of the characteristic element B in the above-mentioned fast ion conductor in the positive electrode material can be tested by methods and equipment known in the art. For example, it can be determined according to the EPA 6010D-2014 standard. Specifically, ICP-OES (element analysis - inductively coupled plasma emission spectrometry) can be used for testing. First, the sample to be tested is digested into a liquid with strong acid, and then the liquid is introduced into the ICP light source by atomization. Further, after the gaseous atoms to be tested are ionized and excited in a strong magnetic field, they return from the excited state to the ground state. During the above process, energy is released and recorded as different characteristic spectral lines for trace element quantitative analysis.

[0062] In some embodiments, the above-mentioned fast ion conductor material is selected from LATP (Li 1+n Al n Ti 2-n (PO4)3, 0 ≤ n ≤ 0.5), LAGP (Li 1+n Al n Ge 2-n (PO4)3, 0 ≤ n ≤ 0.5), LLZO (Li7La3Zr2O 12 ), LLTO (Li 3n La 2 / 3-n TiO3, 0 < n < 0.16, and there are also 1 / 3 - 2n holes), LiBO2, LiAlO2, LiPO3, or one or more of them. In the positive electrode material, the fast ion conductor material may be one of the above-mentioned fast ion conductors, such as LLZO, or may exist in the form of a composite of two or more of the above-mentioned fast ion conductors, such as a composite of LATP and LAGP in a certain mass ratio. The properties of the above-mentioned fast ion conductor materials are stable, which can reduce the side reaction between the positive electrode material and the electrolyte under high potential conditions, reduce gas generation, and improve the cycle performance of the positive electrode material.

[0063] Any metal element or non-metal element other than Li element and O element in the above-mentioned fast ion conductor material can be used as the characteristic element B, as long as it can meet the conditions for being the characteristic element B.

[0064] For example, the characteristic element A can be Pb 2+ 、Ba 2+ or La 2+ , and the characteristic element B can be Ti 4+ 、Ge 4+ or Zr 4+ .

[0065] The lattice compatibility between the above-mentioned fast ion conductor material and the ferroelectric ceramic material is better, which can further exert the synergistic effect of the two and effectively improve the lithium ion conductivity at the interface of the positive electrode material.

[0066] In some embodiments, the mass ratio of characteristic element A to characteristic element B is (2-30):1. When the mass ratios of elements A and B are within the above range, the synergistic effect of the fast ion conductor material and the ferroelectric ceramic material is enhanced; preferably, the mass ratio of characteristic element A to characteristic element B is (2.4-8.2):1, which makes the improvement in ionic conductivity and cycle stability more prominent.

[0067] In some embodiments, the molar content of nickel in the aforementioned nickel-containing lithium transition metal oxide is greater than or equal to 80%, optionally greater than or equal to 90%, and further optionally greater than or equal to 95%. For example, the molar content of nickel in the transition metal can be 85%, 88%, 90%, 95%, or 99%. In nickel-containing lithium transition metal oxide materials, nickel is the main redox reaction element. High-nickel-content cathode materials often have higher energy densities. However, while achieving high energy density performance, the cobalt content in the cathode material is greatly reduced, resulting in a decline in the power performance of the secondary battery. Moreover, during cycling, the high-nickel ternary system is prone to Jahn-Teller distortion, leading to structural degradation, which correspondingly affects capacity retention and cycle stability. Therefore, the coating material settings in the above embodiments of this application are particularly important for improving the ion conduction performance and cycle stability of high-nickel lithium transition metal oxides.

[0068] In some embodiments, nickel-containing lithium transition metal oxides include those having the chemical formula Li x Ni y M 1-y O2 oxides, 1.01≤x≤1.06, 0.8≤y≤0.995, for example, y is 0.8, 0.82, 0.85, 0.87, 0.9, 0.92, 0.95, or 0.99, and M is selected from one or more of Co, Mn, Al, Zr, Ba, Ti, Y, Sr, Sb, Mg, Nb, B, and W. The above-mentioned nickel-containing lithium transition metal oxides can be typical nickel-cobalt-manganese or nickel-cobalt-aluminum ternary materials and corresponding doped and modified materials.

[0069] In some embodiments, the lithium-ion diffusion coefficient of the above-mentioned cathode material is 10. -8 ~10 -4 S / cm, selectable as 10 -6 ~10 -5 S / cm. The cathode material formed by coating ferroelectric ceramic materials and fast ion conductor materials with a nickel-containing lithium transition metal oxide core exhibits a significant decrease in impedance at the interface, effectively improving the lithium-ion diffusion coefficient and thus enhancing the rate performance of the secondary battery.

[0070] The lithium-ion diffusion coefficient can be determined using either galvanostatic intermittent titration (GITT) or electrochemical impedance spectroscopy. For electrochemical impedance spectroscopy, the following method can be used: A CHI604D impedance analyzer is employed, with the amplitude voltage set to 5mV and the frequency range to 10... 2 ~10 5 Hz, charge transfer impedance R after 300 cycles at room temperature. ct The lithium-ion diffusion coefficient is calculated using the following formula: D (Li+) =RT / nFR ct , where R ct It is the charge transfer impedance, F is the Faraday resistance constant, T is the absolute temperature, n is the number of electrons gained or lost, and R is the gas constant.

[0071] The GITT method for determining the lithium-ion diffusion coefficient can be referenced as follows: A 1.2mAh coin cell is used, with the positive electrode being the test electrode and metallic lithium as the negative electrode. The coin cell is first charged to 100% SOC, then allowed to rest for 1 hour before testing. A 0.1C pulse discharge is applied, with each pulse lasting 15 minutes, followed by a 30-minute rest period. Each pulse discharge reduces the battery's SOC by 2.5%. Forty pulse discharges are performed, and the relationship between SOC and open-circuit voltage is recorded for each discharge. The lithium-ion diffusion coefficient is then calculated using the following formula: D (Li+) =A(△E) s / △E t ) 2 , where △E s The change in equilibrium voltage during pulse discharge, ΔE t The total voltage change during the pulse discharge period is the result of subtracting the ohmic voltage drop, with coefficient A = 4r. 2 / π·t, where r is the particle size of the positive electrode material and t is the duration of the pulse discharge.

[0072] In some embodiments, the cathode material has one or more of the following characteristics: (1) a BET specific surface area of ​​0.1 m². 2 / g~1m 2 / g, can be selected as 0.1m 2 / g~0.5m 2 / g; (2) The Dv50 particle size is 8μm to 15μm, and can be selected as 10μm to 12μm. The cathode material with the above BET specific surface area and / or Dv50 particle size range has a higher volumetric energy density.

[0073] Specific surface area is a well-known term in the art and can be tested using methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET method. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0074] The Dv50 particle size is a well-known concept in the art, referring to the particle size at which the cumulative volume of a powder particle reaches 50% from the smallest particle size side in its volume-based particle size distribution. The Dv50 particle size of the cathode material can be determined using a Malvern 3000 laser particle size analyzer according to the standard procedure and requirements of GB / T 19077.1-2016 / ISO 13320:2009 Particle size distribution laser diffraction method.

[0075] In some embodiments, the cathode material further includes alumina, which is coated on the surface of a nickel-containing lithium transition metal oxide. The main functions of the alumina coating include: consuming hydrofluoric acid generated during the operation of the secondary battery, inhibiting the dissolution of the transition metal from the cathode material, and improving the electrochemical performance of the cathode material. To reduce the negative impact of the alumina coating on the power performance of the secondary battery, the alumina content should not be too high. Therefore, in some embodiments, the alumina content in the cathode material is preferably 1000 ppm to 4000 ppm. The alumina can be exposed on the surface of the cathode material or coated by the coating material; there is no particular limitation on this.

[0076] [Preparation methods for cathode materials]

[0077] The second embodiment of this application provides a method for preparing a cathode material, which includes: mixing a nickel-containing lithium transition metal oxide with a coating material and then calcining it in an oxygen atmosphere to obtain a cathode material, wherein the coating material includes ferroelectric ceramic materials and fast ion conductor materials.

[0078] This preparation method is simple and easy to apply industrially. In the cathode material obtained by this method, the coating material constructs a double-coating structure on the core surface of a nickel-containing lithium transition metal oxide. The two coating materials work synergistically to achieve rapid lithium-ion transport, thereby improving the discharge rate of the cathode material at low SOC. Specifically, the ferroelectric ceramic material can utilize its inherent spontaneous polarization to slow down the formation of the electric double layer on the cathode material surface, thus improving the uniformity of lithium-ion distribution and lithium-ion conductivity. The fast-ion conductor material exhibits properties similar to a liquid electrolyte, with extremely high conductivity of alkali metal cations, which can lower the desolvation barrier of lithium-ions and accelerate the interfacial transport speed. Furthermore, the ferroelectric ceramic material improves the uniformity of lithium-ion distribution on the cathode material surface, providing a better ion dispersion basis for lithium-ion conduction, and further facilitating the fast-ion conductor material's role in lowering the lithium-ion desolvation barrier. The synergistic effect of these two materials significantly improves the lithium-ion conductivity on the cathode material surface, thus contributing to improved discharge rate of the secondary battery.

[0079] In the above preparation method, there is no particular restriction on the coating order of the ferroelectric ceramic material and the fast ion conductor material; they can be coated sequentially or simultaneously. In some embodiments, the preparation method includes: mixing a nickel-containing lithium transition metal oxide with the ferroelectric ceramic material, and then performing a first calcination under an oxygen atmosphere to obtain a cathode material coated with the ferroelectric ceramic material; mixing the cathode material coated with the ferroelectric ceramic material with the fast ion conductor material, and then performing a second calcination under an oxygen atmosphere to obtain the cathode material. In this case, the cathode material has a double-coated structure with the ferroelectric ceramic material coating the inner layer and the fast ion conductor material coating the outer layer. The ferroelectric ceramic material in the inner layer helps to eliminate space charge accumulation, while the fast ion conductor in the outer layer helps to improve the lithium-ion transport speed.

[0080] In addition, in some embodiments, nickel-containing lithium transition metal oxide can be mixed with fast ion conductor material first, and after the first calcination, it can be mixed with ferroelectric ceramic material and calcined a second time to obtain the cathode material provided in this application.

[0081] In some embodiments, the first calcination temperature is 300℃~350℃, and the duration is 6~12 hours; the second calcination temperature is 300℃~350℃, and the duration is 6~12 hours. Based on extensive experimental research, the inventors have found that controlling the temperature and duration of the two calcinations in the solid-state method for preparing cathode materials within the above-mentioned preferred range can, on the one hand, significantly suppress the agglomeration of solid particles and further improve the dispersibility of the coating material; on the other hand, it can better control the grain size and specific surface area of ​​the calcined product, which is beneficial for the cathode material to obtain better processing performance and electrochemical performance.

[0082] In some embodiments, the ferroelectric ceramic material in the above preparation method has one or more of the following characteristics: 1) the mass of the ferroelectric ceramic material is 4% to 11% of the mass of the nickel-containing lithium transition metal oxide; 2) the ferroelectric ceramic material has the general formula XYO3, where X is selected from Li + Na + K + Mg 2+ Ca 2+ 、Sr 2+ Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5+ 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ ;3) The Dv50 particle size of the ferroelectric ceramic material is 50nm~150nm.

[0083] In the process of coating nickel-containing lithium transition metal oxides with ferroelectric ceramic materials, the ferroelectric ceramic materials include, but are not limited to, Ba. 2+ Pb 2+ Large-radius cations, including nickel-containing lithium transition metal oxides, can diffuse into the bulk phase of the lithium transition metal oxide. By doping with high-entropy elements, the cathode material structure can be stabilized, and the expansion along the c-axis and the corresponding changes in lattice parameters can be suppressed during cycling. This can effectively delay the structural degradation of the cathode material and improve its cycling stability.

[0084] In addition, ferroelectric ceramic materials with high lattice compatibility with nickel-containing lithium transition metal oxides are selected during calcination, and the ferroelectric ceramic particles are controlled at the nanoscale, which is conducive to the adhesion and uniform coating of ferroelectric ceramic materials on the surface of the cathode material, so as to give full play to their effects.

[0085] In some embodiments, the fast ion conductor material in the above preparation method has one or more of the following characteristics: 1) the mass of the fast ion conductor material is 1% to 4.5% of the mass of the nickel-containing lithium transition metal oxide; 2) the fast ion conductor material is selected from one or more of LATP, LAGP, LLZO, LLTO, LiBO2, LiAlO2, and LiPO3. The fast ion conductor nanoparticles in the above-mentioned amounts appear as islands or dots on the surface of the cathode material, exhibiting a relatively uniform distribution. This forms channels on the surface that facilitate lithium-ion diffusion, which is beneficial for further improving the first coulombic efficiency and rate performance of the cathode material.

[0086] In some embodiments, the preparation method further includes washing the nickel-containing lithium transition metal oxide with water before mixing it with the coating material, and washing the nickel-containing lithium transition metal oxide until free Li in the washing water is obtained. + The content is below 2500 ppm. Deionized water is used for washing, and the specific operation can be carried out in accordance with conventional methods in this field, which will not be elaborated here. The main purpose is to remove residual alkaline substances in nickel-containing lithium transition metal oxides.

[0087] The nickel-containing lithium transition metal oxide used in this application can be a conventional nickel-containing lithium transition metal oxide in the art, or a nickel-containing lithium transition metal oxide prepared by conventional methods. Examples are given below.

[0088] In some embodiments, nickel-containing lithium transition metal oxides can be prepared as follows: a nickel-containing transition metal precursor, a lithium source, and an optional dopant are mixed and calcined to obtain a first intermediate product; the first intermediate product is washed with water and dried to obtain a nickel-containing lithium transition metal oxide.

[0089] In some embodiments, the lithium source includes lithium hydroxide, and the dopant may be ZrO2 or Zr(OH)4. The nickel-containing lithium transition metal oxide is processed through Zr... 4+ Doping can increase the carrier concentration, improve the stability of the layered structure to a certain extent, reduce the charge transfer impedance Rct, and help improve the cycle performance of the cathode material.

[0090] Before coating ferroelectric ceramic materials and fast ion conductor materials, other materials can also be coated on the surface of nickel-containing lithium transition metal oxides. In some embodiments, the process of preparing nickel-containing lithium transition metal oxides further includes: washing and drying the first intermediate product with water and then mixing it with a coating agent to obtain a second intermediate product; sintering the second intermediate product in an oxygen atmosphere to obtain nickel-containing lithium transition metal oxides; optionally, the coating agent is alumina, and its mass content in the nickel-containing lithium transition metal oxides is between 1000 ppm and 4000 ppm. If alumina coating is performed, the nickel-containing lithium transition metal oxides do not need to be washed with water before coating the ferroelectric ceramic materials and fast ion conductor materials.

[0091] In some embodiments, the oxygen flow rate is 0.5 L / min to 2 L / min, the heating rate is 1 °C / min to 5 °C / min, the sintering temperature is 680 °C to 730 °C, and the sintering time is 6 hours to 12 hours. This facilitates complete oxidation, improves the valence state of the metal elements, and optimizes the uniformity and firmness of the coating material.

[0092] The cathode material provided in the first embodiment of this application can be prepared using the preparation method provided in the second embodiment described above.

[0093] [Rechargeable Battery]

[0094] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0095] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0096] A third embodiment of this application also provides a secondary battery, including a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes any of the positive electrode materials provided in the first embodiment or any of the positive electrode materials prepared by any of the preparation methods provided in the second embodiment.

[0097] In the cathode material provided in this application, the coating material constructs a double-coating structure on the surface of a nickel-containing lithium transition metal oxide core. The two coating materials work synergistically to achieve rapid lithium-ion transport, thereby improving the discharge rate of the cathode material at low SOC. Specifically, the ferroelectric ceramic material utilizes its inherent spontaneous polarization to slow down the formation of the electric double layer on the cathode material surface, thus improving the uniformity of lithium-ion distribution and lithium-ion conductivity. The fast-ion conductor material exhibits properties similar to a liquid electrolyte, with extremely high conductivity of alkali metal cations, which can lower the desolvation barrier of lithium-ions and accelerate the interfacial transport speed. Furthermore, the ferroelectric ceramic material improves the uniformity of lithium-ion distribution on the cathode material surface, providing a better ion dispersion basis for lithium-ion conduction and further facilitating the fast-ion conductor material's role in lowering the lithium-ion desolvation barrier. The synergistic effect of these two materials significantly improves the lithium-ion conductivity on the cathode material surface, thereby improving the discharge rate of the secondary battery.

[0098] [Positive electrode plate]

[0099] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes the positive electrode material provided in the above embodiments of this application or the positive electrode material obtained by the preparation method provided in the above embodiments.

[0100] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In some embodiments, the charge transfer impedance Rct of the positive electrode is 0.5Ω to 5Ω, and can be selected as 0.5Ω to 1Ω. Charge transfer impedance reflects the migration ability of lithium ions; a smaller charge transfer impedance Rct indicates that the positive electrode material has high Li-ion transfer resistance. + Diffusion migration rate.

[0102] Charge transfer impedance Rct can be determined by electrochemical impedance spectroscopy (EIS). The method is as follows: When testing the charge transfer impedance Rct of the positive electrode in a secondary battery, the secondary battery is charged to 100% SOC and then disassembled to obtain the positive electrode. The positive electrode is cut and cleaned, and then the positive electrode is assembled, the tabs are welded, and the aluminum-plastic film is sealed. The side is sealed to prevent leakage. After liquid injection, it is left to stand at 45°C for 10 hours to form a symmetrical battery. The symmetrical battery is tested under the conditions of 5V voltage and 400mA current. The test frequency range is 500kHz to 30MHz. 73 frequency points are selected within this range, and each frequency point is tested twice to obtain the Nyquist spectrum. The charge transfer impedance Rct is obtained by fitting the equivalent circuit model. The electrolyte used in this test included solvents and lithium salts. The solvents included ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and ethyl acrylate (EA) in a volume ratio of 2:2:1:2:3. The lithium salts included LiPF6 and LiFSI in a molar ratio of 4:6. The concentration of lithium salts in the electrolyte was 1.1 mol / L.

[0103] The liquid retention capacity of the positive electrode refers to the ratio of the mass increase of the positive electrode after immersion relative to its mass before immersion to the mass of the positive electrode before immersion. In some embodiments, after immersing the positive electrode in an equal volume of electrolyte for 6 to 10 hours, the liquid retention capacity of the positive electrode is 1.3 g / Ah to 2.0 g / Ah, optionally 1.5 g / Ah to 1.65 g / Ah. The electrolyte includes a solvent and a lithium salt. The solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and ethyl acrylate (EA) in a volume ratio of 2:2:1:2:3. The lithium salt includes LiPF6 and LiFSI in a molar ratio of 4:6, and the concentration of the lithium salt in the electrolyte is 1.1 mol / L. Ferroelectric ceramic coating materials located on the surface of nickel-containing lithium transition metal oxide cores are beneficial to improving the interfacial performance between cathode materials and electrolytes, enabling cathode materials to have higher liquid retention capacity, which can further improve the cycle life of secondary batteries and reduce safety risks.

[0104] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0106] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0108] [Negative electrode plate]

[0109] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0110] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0113] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0114] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0117] [Electrolytes]

[0118] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0119] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0120] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0121] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0122] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0123] [Isolation membrane]

[0124] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0125] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0126] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0127] In some implementations, the secondary battery includes a single secondary battery cell, or a battery module and a battery pack.

[0128] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0129] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0130] This application does not impose any particular limitation on the shape of the secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 The example shown is a square-structured secondary battery cell 5.

[0131] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0132] In some implementations, the secondary battery cells can be assembled into a battery module. The number of secondary battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0133] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0134] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0135] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0136] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0137] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0138] For the aforementioned electrical devices, secondary battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0139] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0140] [Example]

[0141] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0142] Preparation of nickel-containing lithium transition metal oxides:

[0143] Nickel hydroxide, lithium hydroxide, manganese sulfate, and dopant Zr(OH)4 were mixed in a molar ratio of Li, Ni, Co, and Mn of 1.05:0.99:0.009:0.001 and then calcined at 750°C for 13 hours to obtain the high-nickel ternary material Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2, wherein the Zr doping amount is 2000ppm;

[0144] The above-mentioned high-nickel ternary material was washed with water at a solid-liquid ratio of 0.5:1 and a washing time of 5 minutes. After filtration and vacuum drying, high-nickel ternary material powder was obtained.

[0145] High-nickel ternary material powder was mixed with coating agent Al2O3 to obtain a mixture containing 1500 ppm of coating agent. The mixture was placed in a sintering crucible and then sent to an atmosphere furnace for sintering under an oxygen atmosphere. The oxygen flow rate was 5 L / min, the heating rate was 2 °C / min, the holding temperature was 600 °C, and the time was 5 hours. After furnace cooling under an oxygen atmosphere, alumina-coated high-nickel ternary material Li was obtained. 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2, as a nickel-containing lithium transition metal oxide core.

[0146] Example 1

[0147] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0148] The first coated positive electrode material is combined with the fast ion conductor LLZO (Li7La3Zr2O) 12 The Dv50 particle size is around 75 nm (the Dv50 particle size of LLZO used in the following examples or comparative examples is the same). The LLZO and Li... 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 1.

[0149] The morphology of the cathode material before and after double coating in Example 1 was characterized by SEM, and the results are as follows: Figure 1 As shown.

[0150] Example 2

[0151] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn0.001 The mixture of O2 at a mass ratio of 0.04:1 was heated to 325°C and calcined for 6 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0152] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.01:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 2.

[0153] Example 3

[0154] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.11:1 was heated to 345°C and calcined for 11 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0155] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.045:1 was heated to 330°C and calcined for 2 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 3.

[0156] Example 4

[0157] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.08:1 was heated to 340℃ and calcined for 10 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0158] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001The mixture of O2 at a mass ratio of 0.08:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 4.

[0159] Example 5

[0160] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 332℃ and calcined for 9 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0161] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 333°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 5.

[0162] Example 6

[0163] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0164] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.01:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 6.

[0165] Example 7

[0166] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0167] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.045:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 7.

[0168] Example 8

[0169] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.04:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0170] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.045:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 8.

[0171] Example 9

[0172] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 was mixed evenly at a mass ratio of 0.11:1, heated to 330℃, and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0173] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.01:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 9.

[0174] Example 10

[0175] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with strontium titanate according to the reaction of strontium titanate and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 310℃ and calcined for 9 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0176] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 10.

[0177] Example 11

[0178] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0179] The first coated cathode material is combined with the fast ion conductor LLTO (Li 0.35 La 0.55 TiO3 (Dv50 particle size around 70nm) is based on LLTO and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 11.

[0180] Example 12

[0181] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 was mixed evenly at a mass ratio of 0.06:1, heated to 330°C, and calcined for 8 hours under an oxygen atmosphere to obtain the first coated positive electrode material. In this embodiment, the Dv50 particle size of the alumina-coated high-nickel ternary material is smaller than that of other embodiments and comparative examples.

[0182] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 12.

[0183] Example 13

[0184] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 was mixed evenly at a mass ratio of 0.06:1, heated to 330°C, and calcined for 8 hours under an oxygen atmosphere to obtain the first coated positive electrode material. In this embodiment, the Dv50 particle size of the alumina-coated high-nickel ternary material is larger than that of other embodiments and comparative examples.

[0185] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 13.

[0186] Example 14

[0187] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 was replaced with commercially available high-nickel ternary material NCM811 (LiNi). 0.8 Co 0.1 Mn 0.1 O2), commercial high-nickel ternary material NCM811 and barium titanate according to barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330℃ and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0188] The first coated cathode material and the fast ion conductor LLZO were combined according to the relationship between LLZO and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.02:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 14.

[0189] Example 15

[0190] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 and fast ion conductor LLZO are reacted according to the reaction of LLZO and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 was mixed evenly at a mass ratio of 0.02:1, heated to 330℃, and calcined for 8 hours under an oxygen atmosphere to obtain the first coated cathode material.

[0191] The aforementioned first coated cathode material and barium titanate were mixed in a manner corresponding to barium titanate and Li. 1.05 Ni 0.99 Co 0.009 Mn 0.001 The mixture of O2 at a mass ratio of 0.06:1 was heated to 330°C and calcined for 8 hours in an oxygen atmosphere to obtain the positive electrode active material of Example 15.

[0192] Example 16

[0193] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001O2, barium titanate, and the fast ion conductor LLZO are reacted in a mass ratio of BaTiO3:LLZO:Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The positive electrode active material of Example 16 was obtained by mixing O2 in a ratio of 0.06:0.02:1 until homogeneous, heating to 330°C, and calcining for 8 hours under an oxygen atmosphere.

[0194] Comparative Example 1

[0195] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 reacts with barium titanate according to the reaction of barium titanate and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The positive electrode active material of Comparative Example 1 was obtained by mixing O2 at a mass ratio of 0.06:1, heating to 330℃, and calcining for 8 hours under an oxygen atmosphere.

[0196] Comparative Example 2

[0197] The above-mentioned alumina-coated high-nickel ternary material Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 and fast ion conductor LLZO are reacted according to the reaction of LLZO and Li 1.05 Ni 0.99 Co 0.009 Mn 0.001 The positive electrode active material of Comparative Example 2 was obtained by mixing O2 at a mass ratio of 0.02:1, heating to 330℃, and calcining for 8 hours in an oxygen atmosphere.

[0198] Comparative Example 3

[0199] In this comparative example, the high-nickel ternary material Li coated with the above-mentioned alumina is used. 1.05 Ni 0.99 Co 0.009 Mn 0.001 O2 is used directly as the positive electrode active material without any coating or calcination.

[0200] [Characteristics and Testing Methods]

[0201] The physicochemical properties of the positive electrode active materials in the above embodiments and comparative examples were tested and characterized according to the following methods.

[0202] Characterization of elements and their content in the positive electrode active material: ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) was used. The sample to be tested was first digested into a liquid with a strong acid, and then the liquid was introduced into the ICP light source by atomization. The gaseous atoms to be tested were further ionized and excited in a strong magnetic field, and then recovered from the excited state to the ground state. During the above process, energy was released and recorded as different characteristic spectral lines for trace element quantitative analysis.

[0203] BET specific surface area determination of positive electrode active material: The specific surface area was determined by nitrogen adsorption analysis and calculated using the BET method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0204] Dv50 particle size determination of positive electrode active material: The particle size was determined by a Malvern 3000 laser particle size analyzer according to the standard procedure and requirements of GB / T 19077.1-2016 / ISO 13320:2009 Particle size distribution laser diffraction method.

[0205] The Dv50 particle size (using data rounded to the nearest ten), characteristic element types, and mass content of the ferroelectric ceramic material used for coating are detailed in Table 1. Characteristic element A is a characteristic element of the ferroelectric ceramic material, and characteristic element B is a characteristic element of the fast ion conductor; both can be determined using elemental analysis-inductively coupled plasma optical emission spectrometry (ICP-OES). The mass content of a characteristic element refers to its mass content in the cathode material.

[0206] Table 1

[0207] Using the cathode materials from the above embodiments or comparative examples, secondary battery samples were prepared according to the following methods, and the performance of each battery sample was tested.

[0208] [Preparation of the positive electrode sheet]

[0209] The positive electrode active material from the above examples or comparative examples was mixed with conductive agent carbon black and binder polyvinylidene fluoride (PVDF) at a mass ratio of 97:1:2. N-methylpyrrolidone was added, and the mixture was stirred for 3 hours to obtain a positive electrode slurry. This slurry was then uniformly coated onto the positive electrode current collector at a coating mass of 26.5 mg / cm³. 2 After drying, cold pressing, and slitting, positive electrode sheets are obtained.

[0210] [Preparation of the negative electrode sheet]

[0211] Artificial graphite (active material), carbon black (conductive agent), carbon nanotubes (CNTs), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were added to deionized water in a weight ratio of 94.5:1:0.375:2.8:1.325 and mixed for 3 hours to obtain a negative electrode active material slurry. The negative electrode active material slurry was then uniformly coated onto a negative electrode current collector with a coating mass of 7.5 mg / cm³. 2 The positive electrode sheet is obtained by drying, cold pressing, and slitting.

[0212] [Isolation membrane]

[0213] A 1-micron-thick ceramic insulation layer and a 1-micron-thick adhesive layer are coated with a polypropylene film as the base film.

[0214] Electrolyte

[0215] An electrolyte with a concentration of 1.1 mol / L was prepared by dissolving LiPF6 / LIFSI in a solvent containing ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and ethyl acrylate (EA) in a volume ratio of 2:2:1:2:3, with a LiPF6 to LIFSI molar ratio of 4:6. By adding a solvent with low viscosity, high conductivity, and low boiling point, and increasing the amount of film-forming agent added, the above electrolyte system exhibited improved kinetics.

[0216] [The Manufacturing Process of Lithium-ion Batteries]

[0217] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, a lithium-ion battery is obtained.

[0218] Subsequently, the performance of the lithium-ion battery was tested, and the testing methods can be referred to as follows:

[0219] [Determination of liquid retention capacity of positive electrode]

[0220] The liquid retention capacity refers to the ratio of the mass increase of the positive electrode sheet after immersion to the mass before immersion, to the mass of the positive electrode sheet before immersion. The positive electrode sheet is weighed and calculated before immersion and after immersion in an equal volume of electrolyte for 6 to 10 hours. The electrolyte used for the measurement includes solvent and lithium salt. The solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and ethyl acrylate (EA) in a volume ratio of 2:2:1:2:3. The lithium salt includes LiPF6 and LiFSI in a molar ratio of 4:6. The concentration of lithium salt in the electrolyte is 1.1 mol / L.

[0221] [Measurement of charge transfer resistance Rct]

[0222] Electrochemical impedance spectroscopy (EIS) was used to determine the positive electrode sheet after the secondary battery was charged to 100% SOC. The positive electrode sheet was then cut and cleaned, followed by assembly, tab welding, and aluminum-plastic film encapsulation. Side sealing was used to prevent leakage. After liquid injection, the battery was left to stand at 45°C for 10 hours to form a symmetrical battery. This symmetrical battery was tested at 5V and 400mA, with a test frequency range of 500kHz to 30MHz. 73 frequency points were selected within this range, and each frequency point was tested twice to obtain the Nyquist plot. The charge transfer impedance Rct was obtained by fitting the Nyquist plot using an equivalent circuit model.

[0223] [Lithium-ion diffusion coefficient determination]

[0224] The lithium-ion diffusion coefficient was determined by intermittent galvanostatic titration (GITT). A 1.2 mAh coin cell was used, with the positive electrode of the coin cell obtained in the above examples or comparative examples, and metallic lithium as the negative electrode. The coin cell was first charged to 100% SOC, and after resting for 1 hour, the test was started. A pulse discharge at a rate of 0.1C was applied, with each pulse lasting 15 minutes, followed by a 30-minute rest period. Each pulse discharge reduced the battery SOC by 2.5%. Forty pulse discharges were performed, and the relationship between SOC and open-circuit voltage was recorded for each discharge. The lithium-ion diffusion coefficient was calculated using the following formula: D (Li+) =A(△E) s / △E t ) 2 , where △E s The change in equilibrium voltage during pulse discharge, ΔE t The total voltage change during the pulse discharge period is the result of subtracting the ohmic voltage drop, with coefficient A = 4r. 2 / π·t, where r is the particle size of the positive electrode material and t is the duration of the pulse discharge.

[0225] [Method for determining discharge retention rate]

[0226] The secondary battery is charged to 4.25V at a rate of 0.33C, and then discharged to 2.5V at a rate of 0.33C. The discharge capacity is recorded as C0. The secondary battery is charged to 4.25V at a rate of 0.33C, and then discharged to 2.5V at a rate of 4C. The discharge capacity is recorded as C1. The discharge retention rate is C1 / C0.

[0227] The results of the physicochemical properties of the above-mentioned cathode material and cathode sheet, as well as the test results of the performance indicators of the secondary battery, are recorded in Table 2.

[0228] Table 2

[0229] Since the particle size of the coating material is only at the nanometer level and the coating amount is limited, the Dv50 particle size of the cathode material is mainly determined by the core size before coating. The change in the BET specific surface area is related to the density of the mixed powder aggregation during calcination. If the mixed powder is relatively loosely arranged during calcination, the BET specific surface area of ​​the resulting cathode material particles will be larger.

[0230] According to the results in Table 2, the larger the lithium-ion diffusion coefficient of the positive electrode, the smaller the charge transfer impedance, which is more conducive to the secondary battery having higher energy density and better power performance.

[0231] The two coating materials have a synergistic effect on improving the secondary battery. Under the same preparation conditions and process parameters, the discharge capacity retention rate of the secondary battery is not as good as that of the dual-material coating scheme in Example 1, whether the fast ion conductor material is coated alone or the ferroelectric ceramic material is coated alone.

[0232] The coating method has a significant impact on the performance indicators of lithium-ion batteries. Under the premise that other preparation conditions and process parameters are the same, Example 1 first coats the ferroelectric ceramic material and then coats the fast ion conductor material, while Example 15 first coats the fast ion conductor material and then coats the ferroelectric ceramic material. Comparing Examples 1 and 15, although the physical properties of the positive electrode active materials are relatively similar, the discharge retention rate of the secondary battery in Example 15 is much lower than that in Example 1.

[0233] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A cathode material comprising a core and a coating material, wherein the core comprises a nickel-containing lithium transition metal oxide, and the coating material comprises a ferroelectric ceramic material and a fast ion conductor material.

2. The cathode material according to claim 1, wherein, The characteristic element A of the ferroelectric ceramic material has a mass content of 2.3% to 6.5% in the cathode material, and the characteristic element A is different from the metal element in the core and the metal element in the fast ion conductor material; and / or, the characteristic element B of the fast ion conductor material has a mass content of 0.2% to 1.8% in the cathode material, and the characteristic element B is different from the metal element in the core and the metal element in the ferroelectric ceramic material.

3. The cathode material according to claim 1, wherein, The mass ratio of the characteristic element A to the characteristic element B is (2-30):1, preferably (2.4-8.2):

1.

4. The cathode material according to any one of claims 1 to 3, wherein, The average particle size of the coating material is 50 nm to 150 nm.

5. The cathode material according to any one of claims 1 to 4, wherein, The ferroelectric ceramic material has the general formula XYO3, where X is selected from Li. + Na + K + Mg 2+ Ca 2+ 、Sr 2+ Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5 + 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ .

6. The cathode material according to any one of claims 1 to 5, wherein, The fast ion conductor material is selected from one or more of LATP, LAGP, LLZO, LLTO, LiBO2, LiAlO2, and LiPO3.

7. The cathode material according to any one of claims 1 to 6, wherein, In the nickel-containing lithium transition metal oxide, the molar content of nickel in the transition metal element is greater than or equal to 80%, optionally greater than or equal to 90%, and further optionally greater than or equal to 95%.

8. The cathode material according to any one of claims 1 to 7, wherein, The nickel-containing lithium transition metal oxide includes those having the chemical formula Li x Ni y M 1-y Oxides of O2, 1.01≤x≤1.06, 0.8≤y≤0.995, M is selected from one or more of Co, Mn, Al, Zr, Ba, Ti, Y, Sr, Sb, Mg, Nb, B, and W.

9. The cathode material according to any one of claims 1 to 8, wherein, The lithium-ion diffusion coefficient of the cathode material is 10. -8 ~10 -4 S / cm, selectable as 10 -6 ~10 -5 S / cm.

10. The cathode material according to any one of claims 1 to 9, wherein, The cathode material has one or more of the following characteristics: (1) The specific surface area of ​​BET is 0.1 m². 2 / g~1.0m 2 / g, can be selected as 0.1m 2 / g~0.5m 2 / g; (2) The particle size of Dv50 is 8μm to 15μm, and can be selected as 10μm to 12μm.

11. The cathode material according to any one of claims 1 to 10, wherein, The cathode material further includes aluminum oxide, which coats the surface of the nickel-containing lithium transition metal oxide; optionally, the mass content of aluminum oxide in the cathode material is 1000ppm to 4000ppm.

12. A method for preparing a cathode material, comprising: A cathode material is obtained by mixing a nickel-containing lithium transition metal oxide with a coating material and then calcining it in an oxygen atmosphere. The coating material includes ferroelectric ceramic materials and fast ion conductor materials.

13. The preparation method according to claim 12, wherein, The preparation method includes: Nickel-containing lithium transition metal oxides were mixed with ferroelectric ceramic materials and then calcined for the first time in an oxygen atmosphere to obtain nickel-containing lithium transition metal oxides coated with ferroelectric ceramic materials. The nickel-containing lithium transition metal oxide coated with the ferroelectric ceramic material is mixed with a fast ion conductor material and then calcined a second time in an oxygen atmosphere to obtain the cathode material. Optionally, the temperature of the first calcination is 300℃~350℃, and the duration is 6~12 hours; Optionally, the second calcination temperature is 300℃~350℃, and the duration is 6~12 hours.

14. The preparation method according to claim 12 or 13, wherein, The ferroelectric ceramic material has one or more of the following characteristics: 1) The mass of the ferroelectric ceramic material is 4% to 11% of the mass of the nickel-containing lithium transition metal oxide; 2) The ferroelectric ceramic material has the general formula XYO3, where X is selected from Li. + Na + K + Mg 2+ Ca 2+ 、Sr 2+ Pb 2+ Ba 2+ and La 2+ One or more of them, Y is selected from Ti 4+ Zr 4+ V 5+ 、Nb 5+ and Ta 2+ One or more of them; optionally, X is selected from Li + Pb 2+ 、Sr 2+ and Ba 2+ One or more of them, where Y is Ti 4+ and / or Nb 5+ ; 3) The Dv50 particle size of the ferroelectric ceramic material is 50nm to 150nm.

15. The preparation method according to any one of claims 12 to 14, wherein, The fast ion conductor material has one or more of the following characteristics: 1) The mass of the fast ion conductor material is 1% to 4.5% of the mass of the nickel-containing lithium transition metal oxide; 2) The fast ion conductor material is selected from one or more of LATP, LAGP, LLZO, LLTO, LiBO2, LiAlO2, and LiPO3.

16. The preparation method according to any one of claims 12 to 15, wherein, Before mixing the nickel-containing lithium transition metal oxide with the coating material, the preparation method further includes a water washing process for the nickel-containing lithium transition metal oxide, and the nickel-containing lithium transition metal oxide is washed until free Li in the washing water is obtained. + The content is less than 2500 ppm.

17. A secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising the positive electrode material according to any one of claims 1 to 11 or the positive electrode material prepared by the preparation method according to any one of claims 12 to 16.

18. The secondary battery according to claim 17, wherein, The charge transfer impedance Rct of the positive electrode is 0.5Ω to 5Ω, and can be selected as 0.5Ω to 1Ω.

19. The secondary battery according to claim 17 or 18, wherein, After the positive electrode sheet is immersed in an equal volume of electrolyte for 6 to 10 hours, the liquid retention of the positive electrode sheet is 1.3 g / Ah to 2.0 g / Ah, optionally 1.5 g / Ah to 1.65 g / Ah. The liquid retention is calculated as (weight of the positive electrode sheet after immersion - weight of the positive electrode sheet) / weight of the positive electrode sheet. The electrolyte includes a solvent and a lithium salt. The solvent includes ethylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and ethyl acrylate in a volume ratio of 2:2:1:2:

3. The lithium salt includes LiPF6 and LiFSI in a molar ratio of 4:

6. The concentration of the lithium salt in the electrolyte is 1.1 mol / L.

20. An electrical device comprising a secondary battery, wherein, The secondary battery includes the secondary battery as described in any one of claims 17 to 19.

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