Single-crystal positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a single-crystal positive electrode material, a preparation method thereof and a lithium ion battery. The single-crystal positive electrode material comprises a positive electrode base material and a tungsten-containing coating layer coating the surface of the positive electrode base material, the tungsten-containing coating layer comprises a water-soluble tungsten-containing material and an acid-soluble tungsten-containing material; the positive electrode base material comprises a nickel-based layered oxide positive electrode material; the single-crystal positive electrode material meets the condition that C1 / C2 is greater than or equal to 80%, C1 is the mass ratio of the W element in the water-soluble tungsten-containing material in the single-crystal positive electrode material, which is tested by an ICP (Inductively Coupled Plasma) water-soluble method, to all metal elements except the Li element, and C2 is the mass ratio of the W element in the acid-soluble tungsten-containing material in the single-crystal positive electrode material, which is tested by an ICP acid-soluble method, to all metal elements except the Li element. Through the tungsten-containing coating layer for regulating and controlling the lithium-tungsten ratio, the structure of the coating layer is stable, the coating effect is excellent, the capacity and the cycle performance under high voltage are improved, and the gas production rate in the cycle process is effectively reduced.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and relates to a single-crystal cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] A high charging cutoff voltage (≥4.5V) can economically and effectively increase the energy density of nickel-rich cathode lithium-ion batteries, but it will impair their mechanical and electrochemical stability. For nickel-cobalt-manganese materials, when charged to 4.1V, due to Ni... 3+ Rapid oxidation, O 2- Electron loss begins in the 2p orbitals; when the voltage increases to >4.3V, additional oxygen anions participate in charge compensation to balance the Ni formed due to >80% Li+ extraction. 4+ This weakens the electrostatic repulsion between oxygen layers, resulting in a significant contraction of the lattice parameters. Furthermore, the continuous charge loss from lattice oxygen accelerates the escape of oxygen anions, and the resulting oxygen free radicals readily cause electrolyte decomposition and generate undesirable side reactions. These drawbacks can lead to problems during long-term cycling at high operating voltages.

[0003] Current common modification methods for high-voltage single-crystal cathode materials include bulk doping and surface coating. Coating technology primarily uses oxides such as Al2O3 and TiO2 to prevent side reactions between the electrolyte and the active material. While this has achieved some success, the following problems remain: 1. The coating layer reduces the capacity of the cathode material; 2. The coating layer has low ionic conductivity, which inhibits lithium-ion insertion and release during subsequent electrochemical reactions, leading to reduced capacity and rate performance; 3. During repeated charge-discharge cycles, the active material structure changes after multiple contractions and expansions, causing the single-crystal cathode and coating layer to loosen and detach, affecting cycle performance and increasing internal resistance; 4. Uneven coating layer distribution and incomplete coverage of the cathode material surface affect the coating layer's ability to improve electrochemical performance.

[0004] Therefore, how to achieve high capacity, low gas production, and long cycle performance of single-crystal cathode materials under high voltage is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a single-crystal cathode material, its preparation method, and a lithium-ion battery. The single-crystal cathode material provided in this application, by controlling the lithium-tungsten ratio in the tungsten-containing coating layer, achieves a stable structure and excellent coating effect in the tungsten-containing coating layer, thereby improving the capacity and cycle performance of the cathode material at high voltage and effectively reducing gas generation during cycling.

[0006] To achieve the purpose of this application, the following technical solution is adopted:

[0007] In a first aspect, the present application provides a single-crystal cathode material, which includes a cathode matrix material and a tungsten-containing coating layer coated on the surface of the cathode matrix material;

[0008] The cathode matrix material includes a nickel-based layered oxide cathode material, and the tungsten-containing coating layer includes a water-soluble tungsten-containing material and an acid-soluble tungsten-containing material;

[0009] Among them, the single-crystal cathode material satisfies C1 / C2≥80%, where C1 is the mass ratio of the W element in the water-soluble tungsten-containing material in the single-crystal cathode material tested by the ICP water-soluble method to all metal elements except the Li element, and C2 is the mass ratio of the W element in the acid-soluble tungsten-containing material in the single-crystal cathode material tested by the ICP acid-soluble method to all metal elements except the Li element.

[0010] The following are the preferred technical solutions of the present application, but do not limit the technical solutions provided by the present application. Through the following preferred technical solutions, the technical purposes and beneficial effects of the present application can be better achieved.

[0011] Preferably, the chemical general formula of the nickel-based layered oxide cathode material is Li a Ni 1-x-y Co x Mn y M z O 2+e , where 0.95 < a < 1.30, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.10, 0 ≤ e ≤ 0.2, and M includes doping elements.

[0012] Preferably, the tungsten-containing coating layer includes at least one tungsten-containing compound, and the tungsten-containing compound includes lithium tungstate.

[0013] Preferably, the lithium tungstate includes Li2W5O 16 、Li2W4O 13 、Li2W2O7、Li2WO4、Li6W2O9、Li4WO5 or Li6WO6, or any combination of at least two of them.

[0014] Preferably, the working voltage of the single-crystal cathode material is ≥4.4V, preferably ≥4.45V, and further preferably ≥4.5V.

[0015] In a second aspect, the present application provides a preparation method of the single-crystal cathode material as described in the first aspect, and the preparation method includes the following steps:

[0016] (1) Mix the cathode precursor material and the lithium source, and perform a first sintering to obtain a first-sintered material;

[0017] (2) The surface residual alkali of the calcined material was tested to obtain the molar amount of lithium in the surface residual alkali. Based on the test results, the tungsten coating source of the coating material was simulated and selected, and the simulation results were obtained.

[0018] (3) Based on the simulation results in step (2), the sintering material in step (1) is mixed with the tungsten coating source corresponding to the simulation results, and then sintered for the second time to obtain the single crystal cathode material.

[0019] The second sintering in step (3) is completely consistent with the sintering process in step (2).

[0020] Preferably, the general chemical formula of the positive electrode precursor in step (1) is Ni 1-x-y-z Co x Mn y M z A, where 0≤x≤0.1, 0≤y≤0.3, 0≤z≤0.10, M includes dopant elements, and A includes hydroxide ions and / or carbonate ions.

[0021] Understandable

[0022] Preferably, the lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium nitrate or lithium acetate, with lithium carbonate being the most preferred.

[0023] Preferably, step (1) the first sintering includes performing a first stage sintering and a second stage sintering in sequence.

[0024] Preferably, the sintering temperature in the first stage is 600–800°C, and the sintering time in the first stage is 2–8 hours.

[0025] Preferably, the sintering temperature in the second stage is 650–1000°C, and the sintering time in the second stage is 10–14 h.

[0026] Preferably, the simulation selection method in step (2) includes: taking an amount of lithium-containing compound equal to the residual alkali on the surface of a calcined material and mixing it with tungsten coating sources of different contents, sintering it to obtain tungsten-containing compounds of corresponding groups, characterizing the structure and stability of each group of tungsten-containing compounds, and obtaining the required coating material based on the characterization results, which is counted as the simulation result.

[0027] Preferably, the tungsten coating source in step (2) includes any one or a combination of at least two of tungsten oxides and / or tungsten oxyacids.

[0028] Preferably, in step (2), the tungsten coating sources with different contents are selected from tungsten coating sources with different lithium-tungsten molar ratios.

[0029] Preferably, in step (2), the sintering temperature is 400-800℃, and more preferably 500-750℃.

[0030] Preferably, in step (2), the sintering time is 2–20 h, more preferably 5–15 h. Preferably, the simulation results include: selecting a tungsten-containing compound with acceptable stability as the coating material.

[0031] Preferably, the criterion for determining the stability of the tungsten-containing compound is: the peak drop in each cycle of the cyclic voltammetry test is ≤10%.

[0032] Preferably, the mass of the tungsten coating source in step (3) is 0.02 to 2 wt% of the mass of the calcined material, and more preferably 0.05 to 1.5 wt%.

[0033] Thirdly, this application also provides a lithium-ion battery, the lithium-ion battery comprising the single-crystal cathode material as described in the first aspect or the single-crystal cathode material prepared by the preparation method described in the second aspect.

[0034] Compared with the prior art, this application has the following advantages:

[0035] This application, based on the different solubility characteristics of tungsten-containing coatings in water and acid systems, determines the form of the surface coating material by measuring the ratio using water-soluble / acid-soluble methods. This reflects the distribution gradient of tungsten inside and on the surface of the cathode substrate material, thereby regulating the structural stability of the tungsten-containing coating. When C1 / C2 ≥ 80%, the tungsten-containing coating exhibits high structural stability, uniform coating, and excellent coating effect, improving the stability of the coating and preventing its detachment. It also provides lithium-ion channels, resulting in high capacity and high rate performance. Furthermore, it enables the single-crystal cathode material to have advantages such as good cycle stability under high voltage conditions and low gas generation during high-temperature storage cycles. This solves the problem in existing technologies where the coating has low ionic conductivity and is prone to loosening and detachment, leading to insufficient prevention of side reactions between the electrolyte and the active material. Attached Figure Description

[0036] Figure 1 The image shows the XRD pattern of lithium tungstate-1 obtained in step (2) of Example 1.

[0037] Figure 2 The image shows the SEM image of lithium tungstate-1 obtained in step (2) of Example 1.

[0038] Figure 3 The image shows the XRD pattern of lithium tungstate-2 obtained in step (2) of Example 1.

[0039] Figure 4The image shows the SEM image of lithium tungstate-2 obtained in step (2) of Example 1.

[0040] Figure 5 The image shows the XRD pattern of lithium tungstate-3 obtained in step (2) of Example 1.

[0041] Figure 6 The image shows the SEM image of lithium tungstate-3 obtained in step (2) of Example 1.

[0042] Figure 7 The CV curve of lithium tungstate-1 obtained in step (2) of Example 1 is shown.

[0043] Figure 8 The CV curve of lithium tungstate-2 obtained in step (2) of Example 1 is shown.

[0044] Figure 9 The CV curve of lithium tungstate-3 obtained in step (2) of Example 1 is shown. Detailed Implementation

[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0047] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0048] In one specific embodiment, the present invention provides a single-crystal cathode material, the single-crystal cathode material comprising a cathode substrate material and a tungsten-containing coating layer covering the surface of the cathode substrate material;

[0049] The cathode substrate material includes a nickel-based layered oxide cathode material; the tungsten-containing coating layer includes a water-soluble tungsten-containing material and an acid-soluble tungsten-containing material;

[0050] Wherein, the single-crystal cathode material satisfies C1 / C2≥80%, where C1 is the mass ratio of W element in the water-soluble tungsten-containing material of the single-crystal cathode material to all metal elements except Li element, as determined by the ICP water dissolution method, and C2 is the mass ratio of W element in the acid-soluble tungsten-containing material of the single-crystal cathode material to all metal elements except Li element, as determined by the ICP acid dissolution method.

[0051] For example, C1 / C2 can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] It should be noted that the ICP water dissolution method in this application specifically refers to weighing 1g of positive electrode material into a beaker, adding deionized water, shaking well, dissolving at a constant temperature for a certain time, filtering, and using ICP to test the W content of the filtrate; the ICP acid dissolution method specifically refers to weighing 1g of positive electrode material into a beaker, adding aqua regia solution (36% hydrochloric acid and 68% nitric acid, volume ratio 3:1), shaking well, digesting at a constant temperature for a certain time, filtering, and using ICP to test the W content of the filtrate.

[0053] Furthermore, the nickel-based layered oxide cathode material described in this application refers to a lithium-ion layered oxide material in a lithium-ion battery system that uses nickel as the main metal element; and it is a single-crystal material.

[0054] The water-soluble tungsten-containing materials mentioned in this application refer to Li2WO4 and / or Li4WO5, and the acid-soluble tungsten-containing materials refer to Li2WO4, Li4WO5, Li6WO6, Li6W2O9, Li2W2O7 and / or Li2W4O 13 Any one or at least two of them.

[0055] It is also understood that the water-soluble tungsten-containing materials in this application are soluble in both water and acid; the acid-soluble tungsten-containing materials are soluble in acid but not in water.

[0056] At high charging cutoff voltages (≥4.4V), additional oxygen anions in the single-crystal cathode material participate in charge compensation to balance the Ni formed due to Li+ extraction >80%. 4+ This weakens the electrostatic repulsion between oxygen layers, resulting in a significant contraction of the lattice parameters. Furthermore, the continuous charge loss from lattice oxygen accelerates the escape of oxygen anions, and the resulting oxygen free radicals readily cause electrolyte decomposition and generate undesirable side reactions. These drawbacks can lead to problems during long-term cycling at high operating voltages.

[0057] The tungsten-containing coating layer of this application contains both water-soluble tungsten-containing materials and acid-soluble tungsten-containing materials. Furthermore, the morphological form of the surface coating substance is confirmed based on the proportion of tungsten elements in different tungsten-containing materials measured by the water-soluble method / acid-soluble method, reflecting the distribution gradient of tungsten inside and on the surface of the cathode matrix material, thereby regulating the structural stability of the tungsten-containing coating layer. When C1 / C2 ≥ 80%, it indicates that the water-soluble tungsten-containing material in the tungsten-containing coating layer plays a dominant role, which shows that the tungsten-containing coating layer has high structural stability, uniform coating, and excellent coating effect, improving the stability of the coating layer and preventing the shedding of the coating layer. At the same time, the high water-soluble tungsten-containing material also provides a channel for lithium ions, thus having high capacity and high rate performance. At the same time, it also enables the single-crystal cathode material to have the advantages of good cycle stability under high voltage conditions and less gas generation during high-temperature storage cycling; it solves the problem that the ion conductivity of the coating layer in the prior art is low, and it is prone to looseness and shedding, resulting in the inability to fully prevent the side reaction between the electrolyte and the active substance.

[0058] As a preferred embodiment, the chemical general formula of the nickel-based layered oxide cathode material is Li a Ni 1-x- y Co x Mn y M z O 2+e , where 0.95 < a < 1.30, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.10, 0 ≤ e ≤ 0.2, and M includes doping elements.

[0059] For example, a can be 0.96, 0.97, 0.98, 0.99, 1, 1.05, 1.1, 1.15, 1.2, 1.25, or 1.3, etc.; x can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc.; z can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc.; e can be 0, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, or 0.2, etc., but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0060] In this application, regulating the chemical general formula of the nickel-based layered oxide cathode material to be Li a Ni 1-x-y- z Co x Mn y M z O 2+e is more conducive to the exertion of the effect of the tungsten-containing coating layer.

[0061] It is understood that this application does not further limit the doping element M in the nickel-based oxide cathode material. Without departing from the inventive concept of this application, any known conventional doping element is applicable in principle. For example, the doping element M includes, but is not limited to, any one or at least two combinations of Zr, Sr, Al, Y, Ti, Nb, Ta, Mo, La or Ce.

[0062] In a preferred embodiment, the water-soluble tungsten-containing material in the tungsten-containing coating layer includes at least one tungsten-containing compound, which includes a lithium tungstate compound.

[0063] Furthermore, the lithium tungstate compound includes Li2W5O. 16 Li2W4O 13 Any one or at least two of Li2W2O7, Li2WO4, Li6W2O9, Li4WO5 or Li6WO6.

[0064] Lithium tungstates with different structures have different structural stability and different solubility in water and acid. This application uses lithium tungstates with different structures as the material in the tungsten-containing coating layer, which can better improve the coating effect by controlling the stability of the coating layer.

[0065] In a preferred embodiment, the operating voltage of the single-crystal cathode material is ≥4.4V, such as 4.4V, 4.43V, 4.45V, 4.46V, 4.48V, 4.5V, 4.55V, 4.6V or 4.65V, preferably ≥4.45V, and more preferably ≥4.5V, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0066] In another specific embodiment, this application provides a method for preparing a single-crystal cathode material as described in the above specific embodiments, the preparation method comprising the following steps:

[0067] (1) Mix the positive electrode precursor material and the lithium source, and perform the first sintering to obtain the first sintered material;

[0068] (2) The surface residual alkali of the calcined material was tested to obtain the molar amount of lithium in the surface residual alkali. Based on the test results, the tungsten coating source of the coating material was simulated and selected, and the simulation results were obtained.

[0069] (3) Based on the simulation results in step (2), the sintering material in step (1) is mixed with the tungsten coating source corresponding to the simulation results, and then sintered for the second time to obtain the single crystal cathode material.

[0070] The second sintering in step (3) is completely consistent with the sintering process in step (2).

[0071] Before the actual coating of the tungsten-containing coating layer, this application simulates the selection of the coating layer material in step (2) based on the residual alkali content on the surface of the first-burned material. The tungsten-containing coating layer on the surface of the actual cathode substrate material can be obtained separately. The structure and stability of the tungsten-containing coating layer are characterized, thereby obtaining the tungsten coating source with excellent stability. Based on the above simulation results, the tungsten-containing coating layer with good stability and excellent coating effect can be synthesized in situ after consuming the residual alkali on the surface of the first-burned material and omitting the water washing step. It also avoids obtaining a finished product of single-crystal cathode material with substandard performance and generating unnecessary cost losses.

[0072] In this application, if the tungsten-containing coating is prepared directly without simulation, the stability of the W-containing coating will be uncertain and the material performance will not meet the standards. At the same time, if the sintering conditions of steps (2) and (3) are different, the simulated coating results and the actual coating results will be biased, which will lead to the cathode material performance not meeting the standards. In addition, the tungsten-containing coating needs to be formed in situ to obtain the corresponding high-performance single-crystal cathode material that meets the C1 / C2≥80%.

[0073] In a preferred embodiment, the general chemical formula of the positive electrode precursor in step (1) is Ni. 1-x-y-z Co x Mn y M z A, where 0≤x≤0.1, 0≤y≤0.3, 0≤z≤0.10, and A is a hydroxide ion.

[0074] For example, x can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc.; z can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0075] In a preferred embodiment, the lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium nitrate or lithium acetate, preferably lithium carbonate.

[0076] It should be noted that this application does not impose any special restrictions on the amount of lithium used in the specific lithium preparation process in step (1). Depending on actual needs, those skilled in the art may provide lithium sources in insufficient, equal, or excessive amounts.

[0077] For example, in step (1), the ratio of the molar amount of lithium in the lithium source to the total molar amount of the main metal elements (such as Ni, Co and Mn) in the cathode precursor material is (0.95 to 1.3):1, such as 0.95:1, 1:1, 1.03:1, 1.05:1, 1.08:1, 1.13:1, 1.15:1, 1.18:1, 1.2:1, 1.23:1, 1.25:1, 1.28:1 or 1.3:1, etc.

[0078] In a preferred embodiment, step (1) the first sintering includes performing a first stage sintering and a second stage sintering in sequence.

[0079] As a preferred embodiment, the sintering temperature of the first stage is 600 to 800°C, such as 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C, 775°C or 800°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] As a preferred embodiment, the sintering time of the first stage is 2 to 8 hours, such as 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] As a preferred embodiment, the sintering temperature of the second stage is 650 to 1000°C, such as 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] As a preferred embodiment, the sintering time of the second stage is 10 to 14 hours, such as 10 hours, 11 hours, 12 hours, 13 hours or 14 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0083] As a preferred embodiment, the simulation selection method includes: taking an equal amount of lithium-containing compound and tungsten coating source with different contents as the residual alkali on the surface of the calcined material, mixing them, sintering them to obtain tungsten-containing compounds of corresponding groups, characterizing the structure and stability of each group of tungsten-containing compounds, and obtaining the required coating material based on the characterization results, which are counted as simulation results.

[0084] Before the actual coating of the tungsten-containing coating layer, this application prepares the simulated coating layer material in step (2) based on the amount of residual alkali on the surface of the calcined material. An equal amount of lithium-containing compound with the residual alkali on the surface is sintered with the tungsten coating source to obtain the tungsten-containing coating layer on the surface of the actual cathode substrate material. The structure and stability of the tungsten-containing coating layer are characterized, and a coating layer material with excellent stability can be obtained. Based on the above simulation results, a tungsten-containing coating layer with good stability and excellent coating effect can be synthesized in situ after consuming the residual alkali on the surface of the calcined material and omitting the water washing step. This also avoids obtaining a finished product of a single crystal cathode material with substandard performance and unnecessary cost loss.

[0085] In a preferred embodiment, the tungsten coating source in step (2) includes tungsten oxide and / or tungsten oxyacid.

[0086] For example, the tungsten-containing oxides include WO3 and / or WO2, and the tungsten oxyacids include H2WO4.

[0087] In a preferred embodiment, the tungsten coating sources with different contents are selected from tungsten coating sources with different lithium-tungsten molar ratios.

[0088] In the simulated coating process, given that the amount of lithium compound is known, this application selects different lithium-tungsten ratios as tungsten coating sources with different contents; for example, tungsten coating sources with lithium-tungsten ratios of 1:2.5, 1:2, 1:1, 2:1, 2.5:1, 3:1, 4:1, 5:1 or 6:1 can be selected respectively.

[0089] Furthermore, it should be noted that the lithium-containing compound in this application, which is in equal amounts to the residual alkali on the surface, is preferably a substance of the same type as the residual alkali on the surface, such as lithium hydroxide and lithium carbonate.

[0090] In a preferred embodiment, the sintering temperature in step (2) is 400 to 800°C, such as 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, preferably 500 to 750°C, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0091] In a preferred embodiment, the sintering time in step (2) is 2 to 20 hours, such as 2 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 18 hours or 20 hours, preferably 5 to 15 hours, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0092] As a preferred embodiment, in step (2), the present application can use XRD testing to characterize the specific structure of each group of tungsten-containing compounds, which is the X-ray diffraction test method. The specific test process includes: grinding the actual sintering product of lithium-containing compounds and tungsten-coated source into powder, loading it into the sample stage for testing, comparing the processed diffraction pattern with the standard card, and determining the phase composition in the sample.

[0093] XRD testing can directly yield the actual sintering product of lithium-containing compounds and tungsten coating source, thus revealing the specific structure of the coating material.

[0094] As a preferred embodiment, the simulation results include: selecting a tungsten-containing compound with acceptable stability as the coating material.

[0095] As a preferred embodiment, the criterion for determining the stability of the tungsten-containing compound is: the peak drop in each cycle of the cyclic voltammetry test is ≤10%.

[0096] It is understood that the cyclic voltammetry test described in this application is the CV test method, and the peak drop of the second cycle refers to the rate of change of the peak height of the CV curve at 4.2V obtained by the CV test in the second cycle.

[0097] In this application, the stability of the obtained tungsten-containing compound is determined by CV testing. CV can directly determine the stability of the simulated coating, thereby screening stable coating layers; and it is more applicable to the coating process of single-crystal cathode materials.

[0098] In a preferred embodiment, the mass of the tungsten coating source in step (3) is 0.02 to 2 wt% of the mass of the calcined material, for example, 0.02 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, or 2 wt%, preferably 0.05 to 1.5 wt%, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0099] In this application, step (3) is further defined to ensure that the amount of tungsten coating source added in the actual coating process is uniform, thereby better exerting the coating effect. On this basis, if the lithium content in the residual alkali on the surface is too low and the determined tungsten compound cannot be obtained with the addition of the actual coating source, an additional lithium source can be added.

[0100] Furthermore, this application does not impose any specific limitations on the test method for the residual alkali content on the surface of the calcined material; all conventional methods for measuring the residual alkali content on the surface are applicable to this application.

[0101] For example, this application provides a method for testing the molar amount of lithium in residual alkali on the surface: the positive electrode material is dissolved in hydrochloric acid of a certain concentration, and after the reaction is complete, it is filtered, the ion concentration in the filtrate is tested, and the molar amount of lithium on the surface and the amount of lithium hydroxide and lithium carbonate are determined by an electric titrator.

[0102] In one application embodiment, this application also provides a lithium-ion battery, the lithium-ion battery comprising a single-crystal cathode material as described in one specific embodiment above or a single-crystal cathode material prepared by the preparation method described in another specific embodiment above.

[0103] Example 1

[0104] This embodiment discloses a single-crystal cathode material, which includes a cathode substrate material having a single-crystal structure and a tungsten-containing coating layer covering the surface of the cathode substrate material.

[0105] The chemical formula of the positive electrode substrate material is Li 1.05 Ni 0.6 Co 0.1 Mn 0.3 O2.

[0106] The mass ratio of W element to all metal elements except Li element obtained by ICP water dissolution method for the single crystal cathode material is denoted as C1; the mass ratio of W element to all metal elements except Li element obtained by ICP acid dissolution method for the single crystal cathode material is denoted as C2, and the ratio of C1 / C2 is calculated and recorded in Table 1.

[0107] The preparation method of the single-crystal cathode material is as follows:

[0108] (1) Ni cobalt manganese composite hydroxide Ni 0.6 Co 0.1 Mn 0.3 (OH)₂ and lithium carbonate were mixed, with the molar ratio of Li to the sum of the molar ratios of Ni, Co, and Mn being 1.05:1. The mixture was then sintered in an oxygen atmosphere at a heating rate of 2℃ / min to 800℃ for a first stage of sintering for 2 hours, followed by a second stage of sintering at 2℃ / min to 950℃ for 11 hours. The resulting sintered product was crushed and passed through a 250-mesh sieve to obtain a single-crystal powder (with the chemical formula Li) with a D50 of 3.8 μm. 1.05 Ni 0.6 Co 0.1 Mn 0.3 O2;

[0109] (2) Without water washing, the surface residual alkali of the calcined material is directly tested to obtain the molar amount of lithium in the surface residual alkali. Based on the molar amount of lithium in the surface residual alkali, equal amounts of lithium hydroxide and lithium carbonate are taken, and the corresponding WO3 is weighed in the Li / W molar ratio of 3:1, 6:1 and 9:1 respectively. The lithium hydroxide and lithium carbonate with different molar ratios are mixed with WO3 respectively. Then the mixture is placed under an oxygen atmosphere and heated to 500℃ at a heating rate of 3℃ / min. It is sintered at 500℃ for 8h to obtain lithium tungstate-1, lithium tungstate-2 and lithium tungstate-3. Then the material structure is confirmed by XRD test.

[0110] The XRD and SEM images of lithium tungstate-1 are shown below. Figure 1 and Figure 2 As shown in the figure, the structure of lithium tungstate-1 is (Li2WO4)7(H2O)4.

[0111] The XRD and SEM images of lithium tungstate-2 are as follows: Figure 3 and Figure 4 As shown in the figure, the structure of lithium tungstate-2 is Li4WO5+(Li2WO4)7(H2O)4.

[0112] The XRD and SEM images of lithium tungstate-3 are as follows: Figure 5 and Figure 6 As shown in the figure, it can be concluded that the structure of lithium tungstate-3 is Li4WO5+Li6W2O9;

[0113] The stability of coin cells prepared from lithium tungstate-1, lithium tungstate-2, and lithium tungstate-3 was verified by CV testing.

[0114] The CV curve of lithium tungstate-1 is as follows: Figure 7 As shown, from Figure 7 It can be determined that the peak height at 4.2V changes by 6.8% in the second cycle;

[0115] The CV curve of lithium tungstate-2 is as follows: Figure 8 As shown, from Figure 8 It can be determined that the peak height at 4.2V changes by 17.7% in the second cycle;

[0116] The CV curve of lithium tungstate-3 is as follows: Figure 9 As shown, from Figure 9 It can be determined that the peak height at 4.2V changes by 68.8% in the second cycle;

[0117] Based on the XRD and CV curve results, it can be concluded that lithium tungstate-1 has better stability, so lithium tungstate-1 was selected as the material for the actual tungsten coating layer.

[0118] (3) Based on the simulation results of step (2), WO3 of the same amount as the obtained lithium tungstate-1 is selected as the tungsten coating source. The calcined material and WO3 are thoroughly mixed for 10 min using a high-speed mixer. The mass of WO3 is 0.25 wt% of the mass of the calcined material. The mixture is placed under an oxygen atmosphere and heated to 500°C at a heating rate of 3°C / min. It is sintered at 500°C for 8 h to perform coating treatment and obtain single crystal cathode material-1 (its chemical formula is shown in Table 1).

[0119] Meanwhile, to verify the accuracy of the simulation results, the same amount of WO3 obtained from the calcined material and lithium tungstate-2 and lithium tungstate-3 were used as tungsten coating sources. The calcined material and WO3 were thoroughly mixed for 10 minutes using a high-speed mixer. The mixture was placed under an oxygen atmosphere and heated to 500°C at a heating rate of 3°C / min. It was then sintered at 500°C for 8 hours to perform the coating treatment, resulting in single-crystal cathode material-2 corresponding to lithium tungstate-2 and single-crystal cathode material-3 corresponding to lithium tungstate-3 (their chemical formulas are shown in Table 1).

[0120] Example 2

[0121] The difference between this embodiment and embodiment 1 is that WO3 in steps (2) and (3) is replaced with H2WO4, and the ratio of lithium tungstate-1 is used.

[0122] The remaining preparation method parameters are consistent with those in Example 1.

[0123] Example 3

[0124] The difference between this embodiment and embodiment 1 is that the sintering temperature in steps (2) and (3) is 600°C.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Example 4

[0127] The difference between this embodiment and Embodiment 1 is that in this embodiment, the nickel-cobalt-manganese composite hydroxide is Ni 0.68 Co 0.10 Mn 0.12 O2, the chemical formula of the positive electrode active material matrix is ​​Li 1.05 Ni 0.68 Co 0.10 Mn 0.12 O2.

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Example 5

[0130] The difference between this embodiment and Embodiment 1 is that in this embodiment, the nickel-cobalt-manganese composite hydroxide is Ni0.84 Co 0.06 Mn 0.1 O2, the chemical formula of the positive electrode active material matrix is ​​Li 1.02 Ni 0.84 Co 0.06 Mn 0.1 O2 was ultimately coated with lithium tungstate-1 to form WO3.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Comparative Example 1

[0133] The difference between this comparative example and Example 1 is that the single-crystal cathode material provided in this comparative example does not contain a tungsten-containing coating layer.

[0134] In the preparation method, step (2) is skipped and step (3) is performed directly, without adding any coating material.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Comparative Example 2

[0137] The difference between this comparative example and Example 1 is that this comparative example does not perform the simulation process of step (2), but directly mixes lithium tungstate-1 with a certain material in step (3).

[0138] The remaining preparation methods and parameters are consistent with those in Example 1.

[0139] Comparative Example 3

[0140] The difference between this comparative example and Example 1 is that the sintering temperature in steps (2) and (3) is 300°C, while the rest of the preparation methods and parameters are the same as in Example 1.

[0141] Table 1 shows the chemical formulas, C1 values, C2 values, and C1 / C2 values ​​of the single-crystal cathode materials provided in Examples 1-5 and Comparative Examples 1-3.

[0142] Table 1

[0143]

[0144] [Battery Fabrication and Performance Testing]

[0145] I. Battery Manufacturing

[0146] The single-crystal cathode materials-1,-2, and-3 provided in Example 1 were respectively mixed with the cathode materials provided in Example 2 and Comparative Examples 1-2 according to the following ratios: active material: conductive agent SP: conductive agent KS-6: PVDF = 94.5%: 2%: 1%: 2.5%. N-methylpyrrolidone (NMP) was used as a solvent to prepare the cathode slurry. The cathode sheets were then fabricated through coating and rolling processes, with the sheet areal density controlled at 16 mg / cm². 2 .

[0147] The negative electrode uses artificial graphite, prepared by homogenizing a slurry with a graphite:SP:CMC:SBR ratio of 95.5%:1%:1.5%:2% using deionized water as a solvent. The slurry is then coated and rolled to form the negative electrode sheet. The surface density of the coated electrode sheet is controlled at 10 mg / cm². 2 .

[0148] The separator uses a 20μm dry-process PP / PE / PP separator, the electrolyte is a conventional electrolyte, the main components are EC, DMC and DEC in a volume ratio of 1:1:1, containing VC and PS additives, the lithium salt is 1mol / L LiPF6, and it is assembled into a 503048 model battery with a battery capacity of about 800mAh.

[0149] II. Performance tests were conducted on the batteries provided in Examples 1-2 and Comparative Examples 1-2:

[0150] (a) Discharge capacity: The voltage range is 3.0-4.45V, and the discharge capacity is tested at a charge-discharge rate of 1C.

[0151] (b) Cycling performance: At 60°C, with a voltage range of 3.0-4.45V, the capacity retention rate was compared after 300 charge-discharge cycles at a rate of 1C, and the amount of W dissolved after the cycle was calculated.

[0152] (c) Gas production test: Test the gas production growth rate over a 28-day cycle.

[0153] The test results are shown in Table 2.

[0154] Table 2

[0155]

[0156]

[0157] In summary, this application, based on the different solubilities of the tungsten-containing coating in water and acid systems, and by determining the form of the surface coating material according to the ratio measured by the water-soluble / acid-soluble method, reflects the distribution gradient of tungsten inside and on the surface of the cathode substrate material, thereby regulating the structural stability of the tungsten-containing coating. When C1 / C2 ≥ 80%, the tungsten-containing coating exhibits high structural stability, uniform coating, and excellent coating effect, improving the stability of the coating and preventing its detachment. It also provides lithium-ion channels, resulting in high capacity and high rate performance. Furthermore, it enables the single-crystal cathode material to have advantages such as good cycle stability under high voltage conditions and low gas generation during high-temperature storage cycles. This solves the problem in existing technologies where the coating layer has low ionic conductivity and is prone to loosening and detachment, leading to insufficient prevention of side reactions between the electrolyte and the active material.

[0158] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A single-crystal cathode material, characterized in that, The single-crystal cathode material includes a cathode substrate material and a tungsten-containing coating layer covering the surface of the cathode substrate material; The cathode substrate material includes a nickel-based layered oxide cathode material; the tungsten-containing coating layer includes a water-soluble tungsten-containing material and an acid-soluble tungsten-containing material; Wherein, the single-crystal cathode material satisfies C1 / C2≥80%, where C1 is the mass ratio of W element in the water-soluble tungsten-containing material of the single-crystal cathode material to all metal elements except Li element, as determined by the ICP water dissolution method, and C2 is the mass ratio of W element in the acid-soluble tungsten-containing material of the single-crystal cathode material to all metal elements except Li element, as determined by the ICP acid dissolution method.

2. The single-crystal cathode material according to claim 1, characterized in that, The chemical general formula of the nickel-based layered oxide cathode material is Li a Ni 1-x-y-z Co x Mn y M z O 2+e , where 0.95 < a < 1.30, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.10, 0 ≤ e ≤ 0.2, and M includes doping elements.

3. The single-crystal cathode material according to claim 1, characterized in that, The water-soluble tungsten-containing material in the tungsten-containing coating includes at least one tungsten-containing compound.

4. The single-crystal cathode material according to claim 3, characterized in that, The tungsten-containing compounds include lithium tungstate salt compounds.

5. The single-crystal cathode material according to claim 4, characterized in that, The lithium tungstate compound includes Li2W5O 16 Li2W4O 13 Any one or at least two of Li2W2O7, Li2WO4, Li6W2O9, Li4WO5 or Li6WO6.

6. The single-crystal cathode material according to claim 1, characterized in that, The operating voltage of the single-crystal cathode material is ≥4.4V, preferably ≥4.45V, and even more preferably ≥4.5V.

7. A method for preparing a single-crystal cathode material as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) Mix the positive electrode precursor material and the lithium source, and perform the first sintering to obtain the first sintered material; (2) The surface residual alkali of the calcined material was tested to obtain the molar amount of lithium in the surface residual alkali. Based on the test results, the tungsten coating source of the coating material was simulated and selected, and the simulation results were obtained. (3) Based on the simulation results in step (2), the sintering material in step (1) is mixed with the tungsten coating source corresponding to the simulation results, and then sintered for the second time to obtain the single crystal cathode material. The second sintering in step (3) is completely consistent with the sintering process in step (2).

8. The preparation method according to claim 7, characterized in that, The general chemical formula of the positive electrode precursor in step (1) is Ni 1-x-y-z Co x Mn y M z A, where 0≤x≤0.1, 0≤y≤0.3, 0≤z≤0.10, M includes dopant elements, and A includes hydroxide ions and / or carbonate ions; Preferably, the lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium nitrate or lithium acetate, preferably lithium carbonate; Preferably, step (1) the first sintering includes performing a first stage sintering and a second stage sintering in sequence; Preferably, the sintering temperature in the first stage is 600–800°C, and the sintering time in the first stage is 2–8 hours. Preferably, the sintering temperature in the second stage is 650–1000°C, and the sintering time in the second stage is 10–14 h.

9. The preparation method according to claim 7, characterized in that, The simulation selection method in step (2) includes: taking an equal amount of lithium-containing compound with the residual alkali on the surface of a calcined material and mixing it with tungsten coating source of different contents, sintering it to obtain tungsten-containing compounds of corresponding groups, performing structural characterization and stability characterization on each group of tungsten-containing compounds, and obtaining the required coating material based on the characterization results, which is counted as the simulation result.

10. The preparation method according to claim 9, characterized in that, The tungsten coating source in step (2) includes tungsten oxide and / or tungsten oxyacid; Preferably, in step (2), the tungsten coating sources with different contents are selected from tungsten coating sources with different lithium-tungsten molar ratios; Preferably, in step (2), the sintering temperature is 400–800°C, more preferably 500–750°C; Preferably, in step (2), the sintering time is 2 to 20 hours, and more preferably 5 to 15 hours.

11. The preparation method according to claim 9 or 10, characterized in that, The simulation results include: selecting a tungsten-containing compound with acceptable stability as the coating material.

12. The preparation method according to claim 11, characterized in that, The criteria for determining whether a tungsten-containing compound meets stability requirements are: when performing cyclic voltammetry on the tungsten-containing compound, the peak drop in each cycle of the cyclic voltammetry test is ≤10%.

13. The preparation method according to claim 7, characterized in that, The mass of the tungsten coating source in step (3) is 0.02 to 2 wt% of the mass of the calcined material, preferably 0.05 to 1.5 wt%.

14. A lithium-ion battery, characterized in that, The lithium-ion battery includes the single-crystal cathode material as described in any one of claims 1-6 or the single-crystal cathode material prepared by the preparation method as described in any one of claims 7-13.

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