Positive electrode material, preparation method thereof, and lithium ion battery

Abstract

The present invention provides a positive electrode material and a preparation method thereof and a lithium ion battery. The chemical formula of the positive electrode material includes Li a Ni x M y O2, 1≤a≤1.07, 0.8≤x<1, and x+y=1, M includes Co and / or Mn; the half maximum width FWHM of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , and 1.5≤η≤3. By constructing a model of the lattice defects, porosity, and degree of lithium-nickel intermixing of positive electrode materials, the present invention rapidly and efficiently obtains high-nickel, especially ultra-high-nickel, positive electrode materials with high capacity, long cycle life, and high safety performance, thereby shortening the material development cycle and improving battery performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a positive electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] As the market demands for electric vehicle range, fast charging technology, and safety increase, lithium-ion batteries used in electric vehicles are required to have higher energy density, high rate performance, high safety, and long cycle life. Currently, high-nickel ternary cathode materials have become the main cathode materials on the market due to their high specific capacity and long cycle life.

[0003] As the Ni content increases, the battery's cycle performance deteriorates, and the thermal stability and safety performance of the material deteriorate. During storage, LiNi x Co y Mn z O2 materials, especially those with x ≥ 0.8, easily react with CO2 and H2O in the air, generating Li2CO3 and LiOH on the material surface. The residual alkali not only makes it easier to react with PVDF during the electrode homogenization process, increasing the slurry viscosity and causing gelation, but also increases gas production during the electrochemical reaction, posing a safety hazard to the battery.

[0004] Among nickel-cobalt-manganese ternary cathode materials, the high-nickel ternary cathode material NCM811 has been extensively studied and has achieved some results. However, the energy density of NCM811 can only reach 760Wh / kg, which cannot achieve a range of more than 300 miles. If the nickel content is further increased to more than 90% (ultra-high nickel ternary cathode material), the energy density will reach more than 800Wh / kg, which can meet people's demand for more than 300 miles. However, ultra-high nickel ternary cathode materials are currently less studied because ultra-high nickel exacerbates irreversible changes in the crystal phase structure such as cation mixing, lattice collapse, oxygen evolution, and interfacial side reactions, resulting in very poor stability of the material's crystal structure and cycle stability. In other words, the thermal stability and cycle stability problems of ultra-high nickel cathode materials are more obvious.

[0005] Existing technologies modify positive electrode materials by methods such as doping and coating with various additives and changing the sintering temperature. Although this can improve the cycle performance and safety performance of high-nickel materials to a certain extent, it is difficult to fundamentally solve the above problems.

[0006] Therefore, how to improve the cycle stability and safety stability of high-nickel positive electrode materials, especially ultra-high nickel positive electrode materials, and increase their capacity is a technical problem that needs to be solved urgently. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a cathode material, a method for preparing the same, and a lithium-ion battery. By constructing a model of the cathode material's lattice defects, porosity, and degree of lithium-nickel intermixing, the present invention rapidly and efficiently produces high-nickel, particularly ultra-high-nickel, cathode materials with high capacity, long cycle life, and high safety. This shortens the material development cycle and improves battery performance.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a positive electrode material, characterized in that the chemical formula of the positive electrode material includes Li a Ni x M y O2, 1≤a≤1.07, 0.8≤x<1, and x+y=1, M includes Co and / or Mn;

[0010] The half maximum width (FWHM) of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , and 1.5≤η≤3.

[0011] For example, a may be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, or 1.07, x may be 0.8, 0.83, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99, and η may be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0012] It should be noted that the half maximum width FWHM at the (104) crystal plane mentioned in the present invention is 104 The positive electrode material is tested by X-ray diffraction (XRD), and its half-peak width at the (104) crystal plane can be obtained. The specific test method is: the sample to be tested is evenly filled in the glass sample tank, and the sample surface is flattened with a scraper to ensure that the parallelism deviation between the test surface and the instrument reference surface is ≤0.02, the angle range is 10°–90°, the scanning mode is step scanning (step length 0.01°, each step stays for 2 seconds), and the scanning speed is 0.2° / min. The half-peak width is calculated as follows: Jade software reads in the XRD test file.

[0013] Furthermore, the lithium-nickel intermixing degree in cathode materials mentioned in this paper refers to the phenomenon in which some lithium ions (Li⁺) and nickel ions (Ni²⁺) occupy each other's intended positions in the crystal structure of layered cathode materials for lithium-ion batteries (especially high-nickel ternary materials such as NCM and NCA), a state of cationic disorder. The specific calculation process involves acquiring high-resolution XRD spectra, constructing an initial model of the layered structure (e.g., R-3m space group), and refining the Ni and Li site occupancy fractions in the Li / TM layer.

[0014] In high nickel cathode materials, the (104) crystal plane half maximum width (FWHM 104 ) reflects the lattice defects, which will affect the degree of cation mixing, while the porosity will affect the lithium ion transmission process and the material strength. At the same time, the degree of lithium-nickel mixing will cause an irreversible phase change in the crystal structure of the material. Therefore, the present invention realizes multi-faceted regulation of high-nickel positive electrode materials by constructing a model of lattice defects, porosity and lithium-nickel mixing degree values, and limits the result value to 1.5≤η≤3, thereby optimizing the structural stability and ion transmission efficiency of the positive electrode material, obtaining high-nickel, especially ultra-high-nickel, positive electrode materials with high capacity, long cycle and high safety performance, improving battery performance, and shortening the material development cycle.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0016] Preferably, the positive electrode material further includes a doping element.

[0017] Preferably, a coating layer is further provided on the surface of the positive electrode material.

[0018] In the present invention, the positive electrode material may be subjected to conventional doping and coating treatments, and no particular limitation is imposed on the specific doping elements and coating elements. Those skilled in the art may make adaptive selections and adjustments based on actual needs.

[0019] For example, the doping element includes but is not limited to at least one of Ti, Sb, Nb, Ta, W, Mo, Sr, Zr, Al or Y; the coating element of the coating layer includes but is not limited to at least one of Ti, Sr, Nb, B, Al, Li, W or Co, etc., and the coating layer can be various forms of coating such as oxide coating and fluoride coating.

[0020] Preferably, the half-maximum width FWHM 104The range is 0.220 to 0.260, such as 0.220, 0.225, 0.230, 0.235, 0.240, 0.245, 0.250, 0.255 or 0.260, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the porosity P is 3% to 15%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] Preferably, the lithium nickel mixing degree value R Li / Ni The range is 0.99% to 1.25%, such as 0.99%, 1%, 1.03%, 1.05%, 1.08%, 1.1%, 1.13%, 1.15%, 1.18%, 1.2%, 1.23% or 1.25%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In the present invention, the half-maximum width FWHM is further regulated 104 is 0.220-0.260 and / or the porosity P is 3%-15% and / or the lithium nickel mixing degree value R Li / Ni The content of lithium ions in the lithium ion matrix is ​​0.99%~1.25%, which can better construct channels for lithium ion insertion and extraction, enhance structural stability, and improve material capacity and cycle.

[0024] Preferably, the Li a Ni x M y In O2, 0.9≤x<1, for example, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] For the present invention, η = FWHM 104 *P / R Li / Ni , and the relationship of 1.5≤η≤3 is more suitable for ultra-high nickel positive electrode materials, and it is easier to obtain high-porosity, low lithium-nickel mixed positive electrode materials, which has a more obvious effect on improving capacity, cycle performance and safety performance.

[0026] In a second aspect, the present invention provides a method for preparing the positive electrode material according to the first aspect, the preparation method comprising the following steps:

[0027] Mixing a positive electrode precursor material and a lithium source, and performing a first sintering to obtain the positive electrode material;

[0028] During the first sintering process, the method of providing oxygen includes pulse oxygen supply;

[0029] The chemical formula of the positive electrode precursor is Ni x M y A, 0.8≤x<1, and x+y=1, M includes Co and / or Mn, and A includes hydroxide and / or carbonate.

[0030] For example, x may be 0.8, 0.83, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the Ni x M y (OH)2, 0.9≤x<1, for example, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99, etc., but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] The preparation method provided by the present invention adopts a pulsed oxygen supply method to provide oxygen in the first sintering process, which promotes oxygen penetration and avoids the obstruction of oxygen during the internal diffusion process, thereby realizing the regulation of the lattice defects and the degree of lithium-nickel intermixing of the positive electrode material, thereby obtaining a high-nickel, especially ultra-high-nickel, positive electrode material with high capacity, long cycle and high safety performance that conforms to the relationship between lattice defects, porosity and lithium-nickel intermixing values, thereby improving battery performance.

[0033] In the present invention, if continuous oxygen supply is used for oxygen supply, a high-concentration oxygen layer may form on the surface of the material, resulting in obstruction of internal diffusion, affecting the structural stability and lattice defects of the material and the degree of lithium-nickel mixing.

[0034] Preferably, during the mixing process, the mixed raw materials also include a dopant, and the amount of the dopant added is 500ppm~5000ppm of the mass of the positive electrode precursor material, for example, 500ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm or 5000ppm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0035] Preferably, the first sintering includes:

[0036] The temperature is raised to the insulation temperature for insulation treatment, and after the insulation treatment is completed, the temperature is lowered by natural cooling;

[0037] Among them, from the temperature rising stage to the temperature keeping stage, the first stage pulse oxygen supply and the second stage continuous oxygen supply are carried out in sequence, and during the temperature falling stage, the third stage pulse oxygen supply is carried out.

[0038] The present invention realizes dynamic regulation of oxygen through a staged oxygen supply method in the first sintering process, thereby better optimizing the structure of the ultra-high nickel positive electrode material; the first stage pulse oxygen supply process is in the heating stage, during which the material precursor (such as hydroxide or carbonate) begins to decompose, and it is necessary to avoid rapid oxidation leading to densification of the particle surface, and the first stage pulse oxygen supply can promote the discharge of moisture and residual organic matter, while inhibiting the premature formation of an excessively thick oxide layer; the second stage oxygen supply is in the heating section and the heat preservation section, at which time the material gradually forms a layered structure (such as R-3m phase), and this oxygen supply stage can inhibit Ni 2+ Migrate to the Li site (cation mixing), stabilize high-valent transition metals (such as Ni 3+ ), which can accelerate lattice oxygen compensation, ensure that the oxygen vacancies formed after Li2O volatilization are filled in time, and improve structural stability; the third stage pulse oxygen supply is located in the cooling section. This oxygen supply method relieves the cooling stress, promotes the oxidation and decomposition of residual Li impurities (such as Li2CO3), and inhibits the precipitation of secondary phases (such as spinel phase) during the cooling process.

[0039] Preferably, the heating rate in the heating stage is 2°C / min~5°C / min, for example, 2°C / min, 3°C / min, 4°C / min or 5°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the holding temperature is 650°C to 800°C, such as 650°C, 700°C, 750°C or 800°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the insulation time is 3h~12h, for example, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the method of pulse oxygen supply in the first stage includes:

[0043] Oxygen is supplied at a pulse frequency of 1 min / time to 3 min / time. During each oxygen supply process, the volume concentration of oxygen in the gas is 80% to 95%, and the flow rate of the gas is 6 L / min to 8 L / min.

[0044] It is understood that, in addition to oxygen, the gas introduced in the present invention may also include dry air from which carbon dioxide has been removed as an auxiliary carrier gas, or may be a protective gas, nitrogen and / or an inert gas, etc., and it should be noted that the oxygen in the gas introduced in the present invention refers to all the oxygen in the mixed gas.

[0045] For example, during the first stage of pulse oxygen supply, the pulse frequency can be 1 min / time, 2 min / time or 3 min / time, etc.; the volume concentration of the oxygen can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95%, etc.; the flow rate of the introduced gas can be 6 L / min, 6.5 L / min, 7 L / min, 7.5 L / min or 8 L / min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0046] Preferably, the stop temperature of the first stage pulse oxygen supply is 500°C~600°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0047] In the present invention, the first stage of pulse oxygen supply is ensured to be in the temperature rising section of the first sintering, and the stop temperature is further controlled to be 500℃~600℃, which can break the surface oxygen concentration balance and use the pressure difference to drive oxygen to penetrate into the interior of the particles, thereby increasing the oxygen diffusion rate. The instantaneous high oxygen concentration peak of pulse oxygen supply can temporarily increase the local oxygen partial pressure, forcing Ni 2+ It preferentially occupies transition metal sites rather than Li sites, inhibiting lithium-nickel mixing.

[0048] Preferably, the second-stage continuous oxygen supply method includes:

[0049] Oxygen is supplied in a continuous oxygen supply mode. During the oxygen supply process, the volume concentration of oxygen in the introduced gas is 95%~100%, and the flow rate of the introduced gas is greater than 10L / min.

[0050] For example, during the second stage of pulse oxygen supply, the oxygen concentration can be 95%, 96%, 97%, 98%, 99% or 100%, etc.; the flow rate of the introduced gas can be 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min or 20 L / min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0051] Preferably, the third stage pulse oxygen supply method includes:

[0052] Oxygen is supplied at a pulse frequency of 10 min / time to 15 min / time. During the oxygen supply process, the volume concentration of oxygen in the gas is gradually reduced, and the flow rate of the gas is 6 to 8 L / min.

[0053] For example, during the third stage of pulse oxygen supply, the pulse frequency can be 10 min / time, 11 min / time, 12 min / time, 13 min / time, 14 min / time or 15 min / time, etc.; the flow rate of the introduced gas can be 6 L / min, 6.5 L / min, 7 L / min, 7.5 L / min or 8 L / min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0054] Preferably, during the third stage of pulse oxygen supply, the volume concentration of oxygen in the gas is reduced by 3% to 10% each time, such as 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0055] In the third stage of pulse oxygen supply, the present invention performs a gradient reduction of the oxygen volume concentration, which is more conducive to alleviating cooling stress. The pulse oxygen supply promotes the oxidative decomposition of residual Li impurities (such as Li2CO3), while inhibiting the precipitation of secondary phases (such as spinel phase) during the cooling process, reducing oxygen consumption and saving costs.

[0056] In the first sintering process, the present invention realizes dynamic regulation of oxygen through a staged oxygen supply method, thereby better optimizing the structure of the ultra-high nickel positive electrode material; the heating stage is divided into two processes, the initial heating stage adopts the first stage pulse oxygen supply method, in this stage the material precursor (such as hydroxide or carbonate) begins to decompose, and it is necessary to avoid rapid oxidation to cause densification of the particle surface, and the first stage pulse oxygen supply can promote the discharge of moisture and residual organic matter, while inhibiting the premature formation of an excessively thick oxide layer; in the second heating section and the heat preservation section, a continuous oxygen supply (i.e., second stage oxygen supply) is adopted, at this time the material gradually forms a layered structure (such as R-3m phase), and the use of high-concentration oxygen in this oxygen supply stage can inhibit N 2+Migrate to the Li site (cation mixing), stabilize high-valent transition metals (such as Ni 3+ ), and the continuous oxygen supply process can accelerate lattice oxygen compensation, ensure that the oxygen vacancies formed after Li2O volatilization are filled in time, and improve structural stability; the third stage pulse oxygen supply is adopted in the cooling stage. At this time, the oxygen concentration is regulated by pulse oxygen supply. Gradually reducing the oxygen concentration can alleviate the cooling stress, and pulse oxygen supply promotes the oxidation and decomposition of residual Li impurities (such as Li2CO3), while inhibiting the precipitation of secondary phases (such as spinel phase) during the cooling process.

[0057] Furthermore, the present invention also regulates the oxygen supply parameters at each stage, including pulse frequency, oxygen concentration, etc., further improving the stability of the material structure, reducing lithium-nickel mixing, and improving the capacity, cycle and safety performance of the material.

[0058] Preferably, the material after the first sintering is mixed with a coating agent and coated, and then subjected to a second sintering to obtain the positive electrode material.

[0059] It is understandable that, in the present invention, after the first sintering, the corresponding sintered product can be subjected to conventional water washing treatment, which can further reduce the surface residual alkali of the material, avoid the occurrence of side reactions, and improve the cycle performance and safety performance of the positive electrode material.

[0060] Furthermore, the water washing method comprises:

[0061] The product of the first sintering is mixed with water, stirred, and then dried to obtain a material after the first sintering.

[0062] Optionally, the mass ratio of the first sintered product to water is (0.5~4):1, such as 0.5:1, 1:1, 2:1, 3:1 or 4:1, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0063] Optionally, the drying method includes vacuum drying, the drying temperature is 140°C~180°C, for example, 140°C, 150°C, 160°C, 170°C or 180°C, and the drying time is 1h~4h, for example, 1h, 2h, 3h or 4h, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0064] Preferably, the mass of the coating agent is 0.05% to 1% of the mass of the material after the first sintering, for example, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0065] Preferably, oxygen-containing gas is introduced during the second sintering process.

[0066] It should be noted that the oxygen-containing gas in the present invention refers to a gas containing at least oxygen, for example, pure oxygen, air, or a mixed gas of oxygen and protective gas.

[0067] Preferably, the flow rate of the oxygen-containing gas is 6 L / min to 10 L / min, for example, 6 L / min, 7 L / min, 8 L / min, 9 L / min or 10 L / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] Preferably, the volume concentration of oxygen in the oxygen-containing gas is 95% to 100%, for example, 95%, 96%, 97%, 98%, 99% or 100%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] Preferably, the heating rate of the second sintering is 2°C / min to 5°C / min, such as 2°C / min, 3°C / min, 4°C / min or 5°C / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0070] Preferably, the holding temperature of the second sintering is 250°C~680°C, for example, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or 680°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0071] Preferably, the holding time of the second sintering is 3h~8h, for example 3h, 4h, 5h, 6h, 7h or 8h, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] In a third aspect, the present invention further provides a lithium-ion battery, comprising the positive electrode material as described in the first aspect or the positive electrode material prepared by the preparation method as described in the second aspect.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] (1) In high nickel cathode materials, the (104) crystal plane half maximum width (FWHM 104) reflects the lattice defects, which will affect the degree of cation mixing, while the porosity will affect the lithium ion transmission process and the material strength. At the same time, the degree of lithium-nickel mixing will cause an irreversible phase change in the crystal structure of the material. Therefore, the present invention realizes multi-faceted regulation of high-nickel positive electrode materials by constructing a model of lattice defects, porosity and lithium-nickel mixing degree values, and limits the result value to 1.5≤η≤3, thereby optimizing the structural stability and ion transmission efficiency of the positive electrode material, obtaining high-nickel, especially ultra-high-nickel, positive electrode materials with high capacity, long cycle and high safety performance, improving battery performance, and shortening the material development cycle.

[0075] (2) The preparation method provided by the present invention adopts a pulse oxygen supply method to provide oxygen in the first sintering process, which promotes oxygen penetration and avoids the obstruction of oxygen in the internal diffusion process, thereby realizing the regulation of the lattice defects and the degree of lithium-nickel mixing of the positive electrode material, thereby obtaining a high-nickel, especially ultra-high-nickel, positive electrode material with high capacity, long cycle and high safety performance that conforms to the relationship between lattice defects, porosity and lithium-nickel mixing value, thereby improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 and Figure 2 These are SEM images of the positive electrode material provided in Example 1 at different magnifications.

[0077] Figure 3 and Figure 4 SEM images of the positive electrode material provided in Comparative Example 1 at different magnifications.

[0078] Figure 5 and Figure 6 SEM images of the positive electrode material provided in Comparative Example 2 at different magnifications. DETAILED DESCRIPTION

[0079] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions.

[0081] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0082] Example 1

[0083] This embodiment provides a positive electrode material, which includes a material containing a doping element and a coating layer coated on the surface of the material containing the doping element, wherein the doping element includes Nb, Zr and Sr, and the coating layer includes boron oxide. The chemical formula of the undoped and coated positive electrode materials is LiNi 0.93 Co 0.02 Mn 0.05 O2;

[0084] The half maximum width (FWHM) of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , the specific values ​​are shown in Table 1.

[0085] The preparation method of the positive electrode material is as follows:

[0086] (1) Ni 0.93 Co 0.02 Mn 0.05 A (OH)2 precursor, Nb2O5, ZrO2, SrO and lithium hydroxide were mixed, with the total mass of Nb2O5, ZrO2 and SrO (the mass ratio of Nb2O5, ZrO2 and SrO was 7:2:1) being 2000ppm of the mass of the precursor, and the ratio of the molar amount of lithium in the lithium hydroxide to the total molar amount of nickel, cobalt and manganese in the precursor being 1.02:1. The first sintering was performed. During the first sintering process, the temperature was raised to 750°C at 3°C / min, held for 10 hours and then naturally cooled:

[0087] During the heating process, from room temperature (25°C) to 500°C, the first stage of pulse oxygen supply was carried out, with a pulse frequency of 2 minutes per time, and the volume concentration of oxygen in the gas (a mixture of oxygen and dry air without carbon dioxide) was 85% each time, and the gas flow rate was 6L / min;

[0088] During the heating from 500°C to 750°C and the holding stage, the second stage of continuous oxygen supply was carried out. The continuous oxygen supply method was adopted, and the volume concentration of oxygen in the introduced gas (a mixture of oxygen and dry air without carbon dioxide) was 95%, and the gas introduction flow rate was 15L / min.

[0089] During the natural cooling stage, the third stage of pulse oxygen supply was carried out, wherein the pulse frequency was 10 min / time, and each time the gas was introduced, the volume concentration of oxygen was reduced from 100% by 5% step by step, and the gas introduction flow rate was 6 L / min, thereby obtaining the first sintered product;

[0090] (2) mixing the first sintered product with water at a mass ratio of 1:1, stirring and washing, and then vacuum drying at 150° C. to obtain a first sintered material;

[0091] (3) The material after the first sintering is mixed and coated with boric acid as a coating agent, and the amount of boric acid added is 0.1% of the mass of the material after the first sintering. Then, in a gas atmosphere with an oxygen volume concentration of 95%, a mixed gas of oxygen and dry air except carbon dioxide is introduced at a gas flow rate of 6 L / min, and the temperature is raised to 300°C at a heating rate of 5°C / min for a second sintering to obtain the positive electrode material.

[0092] Example 2

[0093] This embodiment provides a positive electrode material, which includes a material containing a doping element and a coating layer coated on the surface of the material containing the doping element, wherein the doping element includes Sb, Zr and Sr, and the coating layer includes boron oxide. The chemical formula of the undoped and coated positive electrode materials is LiNi 0.93 Co 0.02 Mn 0.05 O2;

[0094] The half maximum width (FWHM) of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , the specific values ​​are shown in Table 1.

[0095] The preparation method of the positive electrode material is as follows:

[0096] (1) Ni 0.93 Co 0.02 Mn 0.05A (OH)2 precursor, Sb2O3, ZrO2, SrO and lithium hydroxide were mixed, with the total mass of Sb2O3, ZrO2 and SrO (the mass ratio of Sb2O3, ZrO2 and SrO was 6:3:1) being 5000ppm of the mass of the precursor, and the ratio of the molar amount of lithium in the lithium hydroxide to the total molar amount of nickel, cobalt and manganese in the precursor being 1.01:1. The first sintering was performed. During the first sintering process, the temperature was raised to 800°C at 5°C / min, held for 10 hours and then naturally cooled:

[0097] During the heating process, from room temperature (25°C) to 600°C, the first stage of pulse oxygen supply was carried out, with a pulse frequency of 1 min / time, and the volume concentration of oxygen in the gas (a mixture of oxygen and dry air without carbon dioxide) was 95% each time, and the gas flow rate was 8 L / min;

[0098] During the heating from 600°C to 800°C and the holding stage, the second stage of continuous oxygen supply was carried out. The continuous oxygen supply method was adopted, and the volume concentration of oxygen in the gas (a mixture of oxygen and dry air without carbon dioxide) was 100%, and the gas flow rate was 12L / min.

[0099] During the natural cooling stage, the third stage of pulse oxygen supply was carried out, wherein the pulse frequency was 15 min / time, and each time the gas was introduced, the volume concentration of oxygen was reduced from 100% by 3% step by step, and the gas introduction flow rate was 8 L / min, thereby obtaining the first sintered product;

[0100] (2) mixing the first sintered product with water at a mass ratio of 1.5:1, stirring and washing, and then vacuum drying at 140° C. to obtain a first sintered material;

[0101] (3) The material after the first sintering is mixed and coated with a coating agent, boric acid, in an amount of 0.1% of the mass of the material after the first sintering. Then, in a gas atmosphere with an oxygen volume concentration of 95%, a mixed gas of oxygen and a dry gas except carbon dioxide is introduced at a gas flow rate of 6 L / min, and the temperature is raised to 300°C at a heating rate of 5°C / min for a second sintering to obtain the positive electrode material.

[0102] Example 3

[0103] This embodiment provides a positive electrode material, which includes a material containing a doping element and a coating layer coated on the surface of the material containing the doping element, wherein the doping element includes Sb, Nb, Zr and Sr, and the coating layer includes boron oxide. The chemical formula of the undoped and coated positive electrode materials is LiNi 0.93 Co 0.02 Mn 0.05 O2;

[0104] The half maximum width (FWHM) of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , the specific values ​​are shown in Table 1.

[0105] The preparation method of the positive electrode material is as follows:

[0106] (1) Ni 0.93 Co 0.02 Mn 0.05 A (OH)2 precursor, Sb2O3, Nb2O5, ZrO2, SrO and lithium hydroxide were mixed, with the total mass of Sb2O3, Nb2O5, ZrO2 and SrO (the mass ratio of Sb2O3, Nb2O5, ZrO2 and SrO was 5:3:1:1) being 1000ppm of the mass of the precursor, and the ratio of the molar amount of lithium in the lithium hydroxide to the total molar amount of nickel, cobalt and manganese in the precursor being 1.02:1. The first sintering was performed. During the first sintering process, the temperature was raised to 650°C at 2°C / min, held for 12 hours and then naturally cooled:

[0107] During the heating process, from room temperature (25°C) to 550°C, the first stage of pulse oxygen supply was carried out, with a pulse frequency of 3 minutes per time, an oxygen concentration of 80% by volume in the gas (a mixture of oxygen and dry air without carbon dioxide) each time, and a gas flow rate of 6 L / min;

[0108] During the heating from 550°C to 650°C and the holding stage, the second stage of continuous oxygen supply was carried out. The continuous oxygen supply method was adopted, and the volume concentration of oxygen in the gas (a mixture of oxygen and dry air without carbon dioxide) was 97%, and the gas flow rate was 13L / min.

[0109] During the natural cooling stage, the third stage of pulse oxygen supply was carried out, wherein the pulse frequency was 13 min / time, and each time the gas was introduced, the volume concentration of oxygen was reduced from 100% by 8% step by step, and the gas introduction flow rate was 7 L / min, thereby obtaining the first sintered product;

[0110] (2) mixing the first sintered product with water at a mass ratio of 1:1, stirring and washing, and then vacuum drying at 150° C. to obtain a first sintered material;

[0111] (3) The material after the first sintering is mixed and coated with boric acid as a coating agent, and the amount of boric acid added is 0.1% of the mass of the material after the first sintering. Then, in a gas atmosphere with an oxygen volume concentration of 95%, a mixed gas of oxygen and dry air except carbon dioxide is introduced at a gas flow rate of 6 L / min, and the temperature is raised to 300°C at a heating rate of 5°C / min for a second sintering to obtain the positive electrode material.

[0112] Example 4

[0113] The difference between this embodiment and embodiment 1 is that in this embodiment, the chemical formula of the undoped and coated positive electrode material is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0114] In step (1) of the preparation method, the precursor is Ni 0.95 Co 0.01 Mn 0.04 (OH)2.

[0115] The rest of the preparation methods and parameters were the same as those in Example 1.

[0116] Example 5

[0117] The difference between this embodiment and embodiment 1 is that in this embodiment, the chemical formula of the undoped and coated positive electrode material is LiNi 0.99 Co 0.005 Mn 0.005 O2.

[0118] In step (1) of the preparation method, the precursor is Ni 0.99 Co 0.005 Mn 0.005 (OH)2.

[0119] The rest of the preparation methods and parameters were the same as those in Example 1.

[0120] Example 6

[0121] The difference between this embodiment and embodiment 1 is that the chemical formula of the positive electrode material in this embodiment is LiNi 0.93 Co 0.02 Mn 0.05 O2, that is, not doped and coated.

[0122] In step (1) of the preparation method, Nb2O5, ZrO2, and SrO are not added, and the temperature is raised to 730°C before heat preservation treatment, and step (3) is not performed.

[0123] The rest of the preparation methods and parameters were the same as those in Example 1.

[0124] Example 7

[0125] The difference between this embodiment and embodiment 1 is that in this embodiment, the chemical formula of the undoped and coated positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0126] In step (1) of the preparation method, the precursor is Ni 0.8 Co 0.1 Mn 0.1 (OH)2.

[0127] The rest of the preparation methods and parameters were the same as those in Example 1.

[0128] Example 8

[0129] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, the first-stage pulse oxygen supply method is used for oxygen supply treatment throughout the first sintering stage.

[0130] The rest of the preparation methods and parameters were the same as those in Example 1.

[0131] Example 9

[0132] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, the frequency of pulse oxygen supply in the first stage is 5 minutes per time.

[0133] The rest of the preparation methods and parameters were the same as those in Example 1.

[0134] Example 10

[0135] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, the stop temperature of the first stage pulse oxygen supply process is 650°C.

[0136] The rest of the preparation methods and parameters were the same as those in Example 1.

[0137] Example 11

[0138] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, the stop temperature of the first stage pulse oxygen supply process is 400°C.

[0139] The rest of the preparation methods and parameters were the same as those in Example 1.

[0140] Example 12

[0141] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, oxygen supply treatment is carried out by a first-stage pulse oxygen supply method from room temperature to 750°C to the entire insulation stage, that is, there is no second-stage continuous oxygen supply process.

[0142] The rest of the preparation methods and parameters were the same as those in Example 1.

[0143] Example 13

[0144] The difference between this embodiment and embodiment 1 is that in step (1) of the preparation method of this embodiment, the third stage pulse oxygen supply method is used for oxygen supply treatment throughout the first sintering stage.

[0145] The rest of the preparation methods and parameters were the same as those in Example 1.

[0146] Comparative Example 1

[0147] The difference between this comparative example and Example 1 is that in step (1) of the preparation method of this comparative example, the holding temperature of the first sintering is 600°C.

[0148] The rest of the preparation methods and parameters were the same as those in Example 1.

[0149] Comparative Example 2

[0150] The difference between this comparative example and Example 1 is that in step (1) of the preparation method of this comparative example, the holding temperature of the first sintering is 900°C.

[0151] The rest of the preparation methods and parameters were the same as those in Example 1.

[0152] Comparative Example 3

[0153] The difference between this comparative example and Example 1 is that in step (1) of the preparation method of this comparative example, oxygen is provided in the entire first sintering stage by the second-stage continuous oxygen supply method.

[0154] The rest of the preparation methods and parameters were the same as those in Example 1.

[0155] Figure 1 and Figure 2 SEM images of the cathode material provided in Example 1 at different magnifications are shown.

[0156] Figure 3 and Figure 4 SEM images of the positive electrode material provided in Comparative Example 1 at different magnifications are shown.

[0157] Figure 5 and Figure 6 SEM images of the positive electrode material provided in Comparative Example 2 at different magnifications are shown.

[0158] from Figures 1 to 6 It can be seen that Example 1 and Example 2 achieve the control of primary particles by adjusting the doping elements and proportions, η is within the model range, and has excellent electrical properties; Comparative Example 2 increases the temperature of the first sintering, the primary particle size is significantly increased, η is not within the model range, and the capacity and cycle are reduced.

[0159] Parameter characterization of cathode materials

[0160] (a) Full width at half maximum (FWHM) 104 :The positive electrode materials provided by Examples 1-13 and Comparative Examples 1-3 were subjected to XRD tests. The test conditions were as follows: the sample to be tested was evenly filled in the glass sample tank, the sample surface was flattened with a scraper, and the parallelism deviation between the test surface and the instrument reference surface was ensured to be ≤0.02. The angle range was 10°–90°, the scanning mode was step scanning (step length 0.01°, dwell time 2 seconds per step), and the scanning speed was 0.2° / min. Based on the test results, the half-maximum width FWHM at the (104) crystal plane was obtained. 104 .

[0161] (b) Porosity: The positive electrode materials provided in Examples 1-13 and Comparative Examples 1-3 were tested for porosity using a specific surface area analyzer.

[0162] (c) R Li / Ni : The positive electrode materials provided by Examples 1-13 and Comparative Examples 1-3 were analyzed and read by Jade software to analyze the XRD test data, construct an initial model of the layered structure (such as the R-3m space group), and refine the calculation method of the Ni and Li site occupancy fractions of the Li / TM layer to obtain the lithium-nickel mixing degree value.

[0163] The test results of the above tests are shown in Table 1.

[0164] Table 1

[0165]

[0166] Battery preparation and performance testing

[0167] I. Battery Preparation

[0168] Preparation of the positive electrode plate: The positive electrode materials provided in the embodiment and the comparative example are prepared into a positive electrode slurry in a ratio of positive electrode material: SP: PVDF = 8:1:1 to obtain a single crystal positive electrode slurry for use, wherein the slurry has a solid content of 60%; an aluminum foil is placed on a coating machine, a 150μm applicator is placed on the aluminum foil, the slurry is poured in, the equipment is turned on for coating, and a plate is obtained after coating. The plate is placed in an oven at 110°C for drying and roller pressed to obtain the positive electrode plate.

[0169] The positive electrode sheets provided were cut into discs with a diameter of 15 mm using a punch in a dry environment. In a glove box, a metal lithium sheet was used as the counter electrode, a polypropylene PP diaphragm was selected as the isolation membrane, and an electrolyte was added to assemble a button battery. The electrolyte was an organic solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 30:50:20. The concentration of lithium salt (lithium hexafluorophosphate) in the electrolyte was 1.15 mol / L.

[0170] II Performance Test

[0171] The prepared battery was left to stand for 24 hours before undergoing performance testing.

[0172] (a) Under the conditions of 2.5~4.3V, the discharge capacity and initial efficiency of 0.1C were tested.

[0173] (b) The charge-discharge cycle test was performed at a rate of 1C under the conditions of 3.0~4.4V, and the capacity retention rate after 100 cycles was obtained.

[0174] (c) Thermal stability: Fully charge the battery between 2.5 and 4.3 V, disassemble the battery, scrape off the positive electrode powder, and dry it at 100°C for 6 h. Then perform differential scanning calorimetry (DSC) testing at a heating rate of 4°C / min to a maximum temperature of 400°C. The peak temperature is recorded. The higher the peak temperature, the better the thermal stability of the material.

[0175] The test results of the above tests are shown in Table 2.

[0176] Table 2

[0177]

[0178] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A positive electrode material, characterized in that The chemical formula of the positive electrode material includes Li a Ni x M y O2, 1≤a≤1.07, 0.8≤x<1, and x+y=1, M includes Co and Mn; The half maximum width (FWHM) of the positive electrode material at the (104) crystal plane 104 , porosity P and lithium nickel mixing degree value R Li / Ni Satisfy between: η = FWHM 104 *P / R Li / Ni , and 1.5≤η≤3; The half-peak width FWHM104 is 0.220-0.260; the porosity P is 3%-15%; the lithium nickel mixing degree value R Li / Ni It is 0.99%~1.25%.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material also includes a doping element; And / or, a coating layer is further provided on the surface of the positive electrode material.

3. The positive electrode material according to claim 2, characterized in that The Li a Ni x M y In O2, 0.9≤x<1.

4. A method for preparing the positive electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: Mixing a positive electrode precursor material and a lithium source, and performing a first sintering to obtain the positive electrode material; During the first sintering process, the method of providing oxygen includes pulse oxygen supply; The chemical formula of the positive electrode precursor is Ni x M y (OH)2, 0.8≤x<1, and x+y=1, M includes Co and Mn.

5. The preparation method according to claim 4, characterized in that The Ni x M y (OH)2, 0.9≤x<1; And / or, during the mixing process, the mixed raw materials further include a dopant, and the added amount of the dopant is 500ppm to 5000ppm of the mass of the positive electrode precursor material.

6. The preparation method according to claim 4, characterized in that The first sintering comprises: The temperature is raised to the insulation temperature for insulation treatment, and after the insulation treatment is completed, the temperature is lowered by natural cooling; The first stage of pulse oxygen supply and the second stage of continuous oxygen supply are sequentially performed from the temperature rising stage to the temperature keeping stage, and the third stage of pulse oxygen supply is performed during the temperature falling stage. And / or, the heating rate in the heating stage is 2°C / min~5°C / min, the holding temperature is 650°C~800°C, and the holding time is 3h~12h.

7. The preparation method according to claim 6, characterized in that The first stage pulse oxygen supply method includes: Oxygen is supplied at a pulse frequency of 1 min / time to 3 min / time. During each oxygen supply process, the volume concentration of oxygen in the gas is 80% to 95%, and the flow rate of the gas is 6 L / min to 8 L / min. and / or, the stopping temperature of the pulse oxygen supply in the first stage is 500° C. to 600° C.; And / or, the second-stage continuous oxygen supply method includes: Oxygen is supplied in a continuous oxygen supply mode. During the oxygen supply process, the volume concentration of oxygen in the gas is 95%~100%, and the flow rate of the gas is greater than 10L / min; And / or, the third stage pulse oxygen supply method includes: Oxygen is supplied at a pulse frequency of 10 min / time to 15 min / time. During the oxygen supply process, the volume concentration of oxygen in the gas is gradually reduced, and the flow rate of the gas is 6 L / min to 8 L / min. During the third stage of pulse oxygen supply, the volume concentration of oxygen in the introduced gas is reduced by 3% to 10% each time.

8. The preparation method according to claim 4, characterized in that The material after the first sintering is mixed with a coating agent and coated, and then subjected to a second sintering to obtain the positive electrode material.

9. The preparation method according to claim 8, characterized in that The mass of the coating agent is 0.05% to 1% of the mass of the material after the first sintering; and / or, during the second sintering process, an oxygen-containing gas is introduced, the flow rate of the oxygen-containing gas is 6 L / min to 10 L / min, and the volume concentration of oxygen in the oxygen-containing gas is 95% to 100%; And / or, the heating rate of the second sintering is 2° C. / min-5° C. / min, the holding temperature of the second sintering is 250° C.-680° C., and the holding time of the second sintering is 3 h-8 h.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to any one of claims 1 to 3 or the positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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