Lithium-ion battery cathode materials and their preparation methods, lithium-ion batteries

Abstract

This invention provides a lithium-ion battery cathode material, its preparation method, and a lithium-ion battery. The cathode material comprises a core layer and a surface coating layer, with the surface coating layer covering the surface of the core layer. The core layer provides lithium ions for the charging and discharging process of the lithium-ion battery. The surface coating layer is made of an ion-conducting material coated with an electron-conducting material. The lithium-ion battery cathode material provided by this invention exhibits high discharge specific capacity and cycle stability. Furthermore, the preparation method provided by this invention is simple, low-cost, and easily scaled up for industrialization.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a lithium-ion battery cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics. Taking lithium cobalt oxide (LiCoO2) cathode material as an example, as the earliest commercially available lithium-ion battery cathode material, lithium cobalt oxide (LiCoO2) cathode material has become a widely used lithium-ion battery cathode material due to its mature preparation process, high compaction density, and high volumetric energy density.

[0003] For a long time, the upper limit of charging voltage for lithium-ion batteries based on LiCoO2 cathode material has been limited to 4.25V in practical applications, with a corresponding specific capacity of approximately 140mAh g. -1 Only about 50% of its theoretical capacity is currently available, which is insufficient to meet market demand.

[0004] Increasing the charging cutoff voltage of lithium cobalt oxide is an effective way to improve its energy density. However, with the increase of the charging cutoff voltage, the number of lithium ions undergoing insertion / extraction in the lithium cobalt oxide cathode increases. The repeated insertion / extraction of a large number of lithium ions leads to an increase in the volume change of the lithium cobalt oxide cathode material and a decrease in structural stability. At the same time, under high charge conditions, the oxidizability of the lithium cobalt oxide cathode is enhanced, and the side reactions between it and the electrolyte are intensified, resulting in a sharp increase in interfacial impedance and a serious decrease in battery cycle stability. Summary of the Invention

[0005] The present invention aims to solve at least the problems in the prior art mentioned above, and to provide a lithium-ion battery cathode material and its preparation method.

[0006] The first aspect of the present invention discloses a positive electrode material for a lithium-ion battery, the positive electrode material comprising a core layer and a surface coating layer, the surface coating layer being coated on the surface of the core layer, the core layer being used to provide lithium ions for the charging and discharging process of the lithium-ion battery, and the material of the surface coating layer being an ion-conducting material coated with an electron-conducting material.

[0007] In this invention, the ion-conducting material can simultaneously improve the ion conductivity and electronic conductivity of the core layer material. Therefore, when the core layer material is applied in a lithium-ion battery, it can greatly reduce the interfacial impedance between the core layer material and the electrolyte, stabilize the bulk crystal structure of the core layer, and thus solve the problem of rapid capacity decay caused by the decrease in structural stability and the increase in interfacial impedance of the core layer material under high charging cutoff voltage, thereby obtaining higher discharge specific capacity and cycle stability.

[0008] Furthermore, the material of the core layer is selected from lithium cobalt oxide or NCM (nickel-cobalt-manganese ternary material).

[0009] In this invention, the core layer material is preferably a cathode material that is unstable at high charging cutoff voltages, thus failing to fully realize its theoretical capacity. For example, lithium cobalt oxide, which possesses this characteristic, typically has an upper limit charging voltage of 4.25V in practical applications, corresponding to a specific capacity of 140 mAh g. -1 This only accounts for about 50% of its theoretical capacity. However, directly increasing the charging cutoff voltage of lithium cobalt oxide will reduce the structural stability of the lithium cobalt oxide cathode and worsen the battery cycle performance.

[0010] Furthermore, the electronically conductive material is selected from one or a mixture of at least two of carbon, AZO (aluminum-doped zinc oxide), ITO (indium tin oxide), and conductive polymer materials. Among these, carbon is preferred as the electronically conductive material in this invention because it possesses excellent electronic conductivity, is easy to coat, and has a low cost.

[0011] Furthermore, the carbon is organic carbon. In this invention, the organic carbon is preferably selected from one or more of glucose, sucrose, starch, citric acid, polyethylene glycol, and polymer precursors. The polymer precursor is a precursor used to prepare a polymeric organic carbon source via in-situ polymerization; for example, acrylamide is used to prepare polyacrylamide. The above-mentioned types of organic carbon can be in-situ pyrolyzed on the surface of the ion-conducting material to form a uniform carbon coating layer.

[0012] Furthermore, the ion-conducting material is selected from Li x1 M1 a M2 b A y1 Or Li x2 M3O y2 Wherein, M1 is selected from one of Ti, V, Cr, Mn, Co, Ni, and Zr, and M2 is selected from +2 to +4 valence metal cations. For example, M2 can be Mg. 2+ Zn 2+ Al 3+ Co 3+ Ni 3+ Cr 3+ Mn 4+ The material contains rare earth ions, where A is selected from phosphate, borate, and silicate, and M3 is selected from P, Si, Zr, Ti, B, W, and Nb, with the following properties: 0.5≤x1≤2, 1≤y1≤3, 1≤a≤2, 0≤b≤1, 1≤x1≤4, and 1≤y2≤6. The aforementioned ion-conducting materials are stable under high voltage and exhibit high ionic conductivity, which is beneficial for improving the electrochemical performance of the core layer material. For example, the ion-conducting material can be lithium aluminum titanium phosphate, lithium phosphate, lithium borate, lithium zirconate, etc. Among them, the chemical formula of lithium aluminum titanium phosphate is Li...1+x Al x Ti 2-x (PO4)3, where 0.2≤x≤0.7, for example, x can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc. Lithium titanium aluminum phosphate has good high temperature stability and good lithium ion conductivity.

[0013] In this invention, for lithium cobalt oxide cathode materials with lithium titanium aluminum phosphate-carbon coating, the ionic conductivity and electronic conductivity of the lithium cobalt oxide cathode material can be improved simultaneously, the interfacial impedance can be reduced, the bulk crystal structure of lithium cobalt oxide can be stabilized, and the problem of rapid capacity decay caused by decreased structural stability and increased interfacial impedance of lithium cobalt oxide cathode under high charging cutoff voltage can be solved, thereby obtaining higher discharge specific capacity and cycle stability.

[0014] Further, the particle size range of the core layer is 1–30 μm, the particle size range of the electron-conducting material is 1–50 nm, and the particle size range of the ion-conducting material is 1–200 nm. For example, the particle size of the core layer is 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc.; the particle size of the electron-conducting material is 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, etc.; and the particle size of the ion-conducting material is 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, etc. The electron-conducting material with the above-mentioned particle size range can be well coated on the surface of the ion-conducting material with the above-mentioned particle size range, and then a uniform surface coating layer is formed on the surface of the core layer with the above-mentioned particle size range.

[0015] Further, the mass ratio of the electron-conducting material to the ion-conducting material is (1-100):100, and the mass ratio of the surface coating material to the core layer material is (0.5-5):100. For example, the mass ratio of the electron-conducting material to the ion-conducting material can be 1:100, 5:100, 10:100, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, 80:100, 90:100, 100:100, etc. For example, the mass ratio of the surface coating material to the core layer material is 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, etc. The surface coatings within the above-mentioned mass ratio range have good ion and electronic conductivity, which is beneficial to the electrochemical performance of the core layer material.

[0016] A second aspect of the present invention discloses a method for preparing a lithium-ion battery cathode material, comprising the following steps:

[0017] Preparation of precursors for ion-conducting materials;

[0018] An electron-conducting material is coated onto the surface of the ion-conducting material precursor to prepare a material for the surface coating layer;

[0019] The lithium-ion battery cathode material is obtained by coating the surface of the core layer material with the material of the surface coating layer.

[0020] In this invention, an electron-conducting material is first coated onto the surface of an ion-conducting material to form a surface coating layer. This surface coating layer is then used to coat the core layer. This avoids the problem in existing technologies where reducing substances are generated during the inert atmosphere sintering and carbonization process when directly coating the electron-conducting material onto the core layer surface. These reducing substances cause irreversible damage to the core layer surface. Furthermore, the preparation method of this invention is simple, low-cost, and easily scaled up for industrialization.

[0021] Preferably, the material of the core layer is selected from lithium cobalt oxide or nickel-cobalt-manganese ternary materials;

[0022] Preferably, the electron-conducting material is selected from one or a mixture of at least two of carbon, AZO, ITO, and conductive polymer materials; more preferably, the carbon is organic carbon; and even more preferably, the organic carbon is selected from one or more of glucose, sucrose, starch, citric acid, polyethylene glycol, and polymer precursors.

[0023] Preferably, the ion-conducting material is selected from one or a mixture of at least two of lithium titanium aluminum phosphate, lithium phosphate, lithium borate, and lithium zirconate; more preferably, the ion-conducting material is lithium titanium aluminum phosphate.

[0024] In this invention, for lithium cobalt oxide cathode material with lithium titanium aluminum phosphate-carbon coating, the nano-scale lithium titanium aluminum phosphate with good high-temperature thermal stability is first coated with organic carbon, and then the surface of the lithium cobalt oxide material is coated. This avoids the irreversible effect of reducing substances in the carbonization process on the lithium cobalt oxide cathode, thereby avoiding the formation of products such as Co3O4 and avoiding adverse effects on battery cycle performance.

[0025] Furthermore, the ion-conducting material precursor is a lithium titanium aluminum phosphate precursor, and the preparation method of the lithium titanium aluminum phosphate precursor includes:

[0026] Weigh out lithium source compound, aluminum source compound, titanium source compound and phosphoric acid compound in a preset molar ratio, and disperse them in a mixed solvent to form a precursor solution. Adjust the pH value of the precursor solution to a range of 7 to 10. The preset molar ratio is determined according to the molar ratio of each element in the lithium titanium aluminum phosphate precursor.

[0027] The precursor solution is dried to obtain the first dry material;

[0028] The first dry material is pre-decomposed by heating in air under first conditions to obtain pre-calcined material;

[0029] The pre-calcined material was ground to prepare the lithium titanium aluminum phosphate precursor.

[0030] In this invention, the lithium source compound, aluminum source compound, titanium source compound, and phosphoric acid compound can be selected from any publicly disclosed compound in the prior art. For example, the lithium source compound is selected from lithium nitrate, the aluminum source compound is selected from aluminum nitrate nonahydrate, the titanium source compound is selected from tetrabutyl titanate, and the phosphoric acid compound is selected from diamine hydrogen phosphate. The chemical formula of lithium titanium aluminum phosphate is Li. 1+x Al x Ti 2-x(PO4)3, where 0.2 ≤ x ≤ 0.7, and for example, x can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc. Weigh out the corresponding molar amounts of lithium source compound, aluminum source compound, titanium source compound, and phosphoric acid compound according to the molar amounts of Li, Al, Ti, and P in the chemical formula. The aforementioned mixed solvent is a mixture of ethylene glycol and water, wherein the volume ratio of ethylene glycol to water ranges from (5:95) to (95:5). Exemplary examples include volume ratios of 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, and 95:5. The pH of the precursor solution can be adjusted by adding an appropriate amount of ammonia.

[0031] It is understood that other ion-conducting materials in this invention can be obtained directly using commercially available ion-conducting materials or by using existing preparation processes, which will not be elaborated upon here.

[0032] Preferably, the method for drying the precursor solution includes stirring the precursor solution at 120–220°C at a speed of 300–3000 rpm until it is dried.

[0033] Preferably, the pre-decomposition of the first dry material can be carried out in a muffle furnace. The pre-calcined material is then ground and sieved to obtain a nano-scale lithium aluminum titanium phosphate precursor.

[0034] Further, the first condition is to maintain the temperature at 250–500°C for 2–8 hours. For example, the temperature can be 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, etc., and the holding time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc. Under this first condition, a lithium aluminum titanium phosphate precursor with a uniform particle size distribution of 10–200 nm can be obtained.

[0035] Furthermore, the method for preparing the material of the surface coating layer includes:

[0036] The ion-conducting material precursor is dispersed in water, and the electron-conducting material is added, wherein the mass ratio of the electron-conducting material to the ion-conducting material is (1-100):100, and the mixture is stirred to obtain a mixture. For example, the mass ratio of the electron-conducting material to the ion-conducting material can be 1:100, 5:100, 10:100, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, 80:100, 90:100, 100:100, etc.

[0037] The mixture is dried to obtain a second dry material;

[0038] The second dry material is sintered in an inert atmosphere under second conditions to obtain sintered powder;

[0039] The sintered powder is ground to prepare the material of the surface coating layer.

[0040] Preferably, the dispersion is performed using ultrasonic dispersion; the water is deionized water.

[0041] Preferably, the step of drying the mixture includes stirring the mixture at 50-120°C at a speed of 300-3000 rpm until it is dried.

[0042] Preferably, the sintering of the second dry material can be carried out in a tube furnace. For example, when the electron-conducting material is carbon and the ion-conducting material is lithium titanium aluminum phosphate, carbonization occurs under an inert atmosphere during the sintering process to obtain carbon-coated lithium titanium aluminum phosphate powder.

[0043] Preferably, the step of grinding the sintered powder includes dispersing the sintered powder in ethanol, ball milling it in a planetary ball mill at a ball-to-powder ratio of (10-30):1 and a rotation speed of 350-450 rpm for 10-30 hours, and drying the slurry obtained from the ball milling.

[0044] Further, the second condition is to maintain the temperature at 300–800°C for 4–8 hours. For example, the temperature can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the holding time can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc. Under this second condition, an ion-conducting material with a uniformly coated electron-conducting material can be obtained, that is, a material with a uniformly coated surface coating layer can be obtained.

[0045] Further, the step of coating the surface coating layer onto the surface of the core layer material includes:

[0046] The core layer material is dispersed in water, and the surface coating material is added, wherein the mass ratio of the surface coating material to the core layer material is (0.5-5):100, to obtain a mixture; exemplarily, the mass ratio of the surface coating material to the core layer material is 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, etc.

[0047] The mixture is dried to obtain a third dry material;

[0048] The third dry material is sintered under third conditions to obtain the lithium-ion battery cathode material.

[0049] In this invention, the step of drying the mixture includes stirring the mixture at 50-100°C at a speed of 300-3000 rpm until it is dried.

[0050] Preferably, the sintering of the third dry material can be carried out in a muffle furnace, in air or an inert atmosphere. More preferably, after the third dry material is sintered, it is ground and sieved to obtain the lithium-ion battery cathode material of the present invention; alternatively, the material can be ground and sieved again when preparing a battery using the lithium-ion battery cathode material of the present invention.

[0051] Furthermore, the third condition is to maintain the temperature at 300–700°C for 3–8 hours. For example, the temperature can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, etc., and the holding time can be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc. Under this third condition, a positive electrode material with a uniform ion-electron hybrid conductor coating layer can be obtained.

[0052] A third aspect of the present invention discloses a lithium-ion battery comprising the above-described lithium-ion battery cathode material.

[0053] The lithium-ion battery cathode material provided by this invention has high discharge specific capacity and cycle stability.

[0054] The beneficial effects of this invention are:

[0055] This invention modifies the surface of the core layer with an ion-conducting material coated with an electron-conducting material. This simultaneously improves the ion and electronic conductivity of the core layer material, reduces interfacial impedance, and stabilizes the bulk crystal structure of the core layer. It solves the problem of rapid capacity decay caused by decreased structural stability and increased interfacial impedance of the core layer material at high charge cutoff voltages, resulting in higher discharge specific capacity and cycle stability. Furthermore, the preparation method provided by this invention is simple, low-cost, and easily scaled up for industrialization. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of the present invention.

[0057] Figure 1 This is a scanning electron microscope image of the carbon-coated nano-lithium titanium aluminum phosphate material prepared in Example 1 of this invention;

[0058] Figure 2 This is a scanning electron microscope image of the nano-lithium aluminum titanium phosphate-carbon-coated lithium cobalt oxide cathode material prepared in Example 1 of the present invention;

[0059] Figure 3 This is the XRD pattern of the nano-lithium aluminum titanium phosphate-carbon coated lithium cobalt oxide cathode material prepared in Example 1 of this invention;

[0060] Figure 4 The first charge-discharge curves of lithium-ion batteries prepared from lithium cobalt oxide before coating modification (comparative example of this invention) and lithium cobalt oxide after coating modification with nano-lithium aluminum titanium phosphate-carbon prepared in Example 1 are shown.

[0061] Figure 5 These are the performance curves of lithium-ion batteries prepared from the pre-coated modified lithium cobalt oxide of the comparative example of this invention and the nano-coated modified lithium cobalt oxide cathode material prepared in Example 1, at room temperature, 3.0-4.55V, 1C charge-discharge cycle. Detailed Implementation

[0062] As used in this article:

[0063] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0064] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0065] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0066] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0067] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0068] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0069] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0070] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0071] Example 1

[0072] Dissolve 340 mg of tetrabutyl titanate in a mixed solution formed by 45 ml of ethylene glycol and 5 ml of deionized water. Then add lithium nitrate, aluminum nitrate nonahydrate and diammonium hydrogen phosphate according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3 (x=0.3), stir well, add ammonia water to adjust the pH of the solution to 7.5, and stir thoroughly to form a precursor solution.

[0073] The well-mixed precursor liquid was stirred and dried at 160°C to obtain the first dry material, with a stirring speed of 1000 rpm.

[0074] The first dry material was placed in a muffle furnace and pre-decomposed in air medium. The heating temperature was 300℃ and the temperature was held for 4 hours to obtain the pre-calcined material. The pre-calcined material was ground and sieved to obtain nano-lithium titanium aluminum phosphate precursor with a particle size of about 10nm.

[0075] The nano-lithium titanium aluminum phosphate precursor was ultrasonically dispersed in deionized water, and glucose of about 10% of the mass of the lithium titanium aluminum phosphate precursor was added and stirred to dissolve.

[0076] The mixture was heated and stirred at 80°C until it was evaporated to dryness to obtain the second dry material. The stirring speed was 1200 rpm.

[0077] The second dry material was carbonized and sintered in a tube furnace under an argon atmosphere at a sintering temperature of 650℃ for 6 hours to obtain carbon-coated nano-lithium titanium aluminum phosphate sintered powder, wherein the carbon particles of the coating layer have a particle size of about 50nm.

[0078] The sintered powder was used as a solvent in ethanol and ball-milled in a planetary ball mill at a ball-to-powder ratio of 20:1 and a speed of 400 rpm for 10 hours. The ball-milled slurry was then dried to obtain carbon-coated nano-lithium titanium aluminum phosphate.

[0079] Lithium cobalt oxide powder with a particle size range of 1–10 μm was ultrasonically dispersed in deionized water, and carbon-coated nano-lithium titanium aluminum phosphate (lithium cobalt oxide) of 1.5% by mass was added and mixed evenly to obtain a mixture.

[0080] The mixture was heated and stirred at 70°C until it was evaporated to dryness, yielding the third dry material at a stirring speed of approximately 800 rpm.

[0081] The third dry material was placed in a muffle furnace and sintered in air atmosphere at a temperature of 300℃ for 3 hours to obtain nano-lithium titanium aluminum phosphate-carbon coated lithium cobalt oxide composite cathode material.

[0082] The scanning electron microscope image of the carbon-coated nano-lithium titanium aluminum phosphate material prepared in Example 1 is shown below. Figure 1 As shown, the scanning electron microscope image of the nano-lithium aluminum titanium phosphate-carbon-coated lithium cobalt oxide cathode material is as follows: Figure 2 As shown, the XRD pattern of the nano-lithium aluminum titanium phosphate-carbon-coated lithium cobalt oxide cathode material is as follows: Figure 3 As shown.

[0083] Example 2

[0084] Dissolve 320 mg of tetrabutyl titanate in a mixed solution formed by 30 ml of ethylene glycol and 20 ml of deionized water. Then add lithium nitrate, aluminum nitrate nonahydrate and diammonium hydrogen phosphate according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3 (x=0.4). Stir well, add ammonia water to adjust the pH of the solution to 7.0, and stir thoroughly to form the precursor solution.

[0085] The well-mixed precursor liquid was stirred and dried at 180°C to obtain the first dry material, with a stirring speed of 1100 rpm.

[0086] The first dry material was placed in a muffle furnace and pre-decomposed in air medium. The heating temperature was 350℃ and the temperature was held for 6 hours to obtain the pre-calcined material. The pre-calcined material was ground and sieved to obtain nano-lithium titanium aluminum phosphate precursor with a particle size of about 50nm.

[0087] The nano-lithium titanium aluminum phosphate precursor was ultrasonically dispersed in deionized water, and citric acid, accounting for about 5% of the mass of the lithium titanium aluminum phosphate precursor, was added and stirred to dissolve.

[0088] The mixture was heated and stirred at 85°C until it was evaporated to dryness to obtain the second dry material. The stirring speed was 1300 rpm.

[0089] The second dry material was carbonized and sintered in a tube furnace under an argon atmosphere at a sintering temperature of 600℃ for 4 hours to obtain carbon-coated nano-lithium titanium aluminum phosphate sintered powder, wherein the carbon particles of the coating layer have a particle size of about 10nm.

[0090] The sintered powder was used as a solvent in ethanol and ball-milled in a planetary ball mill at a ball-to-powder ratio of 30:1 and a speed of 300 rpm for 20 hours. The ball-milled slurry was then dried to obtain carbon-coated nano-lithium titanium aluminum phosphate.

[0091] Lithium cobalt oxide powder with a particle size range of about 10-20 μm was ultrasonically dispersed in deionized water, and carbon-coated nano-lithium titanium aluminum phosphate was added at 0.5% of the mass of lithium cobalt oxide. The mixture was then mixed evenly to obtain a mixture.

[0092] The mixture was heated and stirred at 80°C until it was evaporated to dryness, yielding the third dry material at a stirring speed of approximately 1000 rpm.

[0093] The third dry material was placed in a muffle furnace and sintered in air at a temperature of 350℃ for 6 hours to obtain a nano-lithium titanium aluminum phosphate-carbon-coated lithium cobalt oxide composite cathode material.

[0094] Example 3

[0095] Dissolve 300 mg of tetrabutyl titanate in a mixed solution formed by 15 ml of ethylene glycol and 35 ml of deionized water. Then add lithium nitrate, aluminum nitrate nonahydrate and diammonium hydrogen phosphate according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3 (x=0.5), stir well, add ammonia water to adjust the pH of the solution to 8.0, and stir thoroughly to form a precursor solution.

[0096] The well-mixed precursor liquid was stirred and dried at 120°C to obtain the first dry material, with a stirring speed of 1000 rpm.

[0097] The first dry material was placed in a muffle furnace and pre-decomposed in air medium. The heating temperature was 300℃ and the temperature was held for 6 hours to obtain the pre-calcined material. The pre-calcined material was ground and sieved to obtain nano-lithium titanium aluminum phosphate precursor with a particle size of about 20nm.

[0098] The nano-lithium titanium aluminum phosphate precursor was ultrasonically dispersed in deionized water, and polyethylene glycol, accounting for about 1% of the mass of the lithium titanium aluminum phosphate precursor, was added and stirred to dissolve.

[0099] The mixture was heated and stirred at 70°C until it was evaporated to dryness to obtain the second dry material. The stirring speed was 1150 rpm.

[0100] The second dry material was carbonized and sintered in a tube furnace under an argon atmosphere at a sintering temperature of 600℃ for 5 hours to obtain carbon-coated nano-lithium titanium aluminum phosphate sintered powder, wherein the carbon particles of the coating layer have a particle size of about 2nm.

[0101] The sintered powder was used as a solvent in ethanol and ball-milled in a planetary ball mill at a ball-to-powder ratio of 30:1 and a speed of 300 rpm for 10 hours. The ball-milled slurry was then dried to obtain carbon-coated nano-lithium titanium aluminum phosphate.

[0102] Lithium cobalt oxide powder with a particle size range of 1-20 μm was ultrasonically dispersed in deionized water, and carbon-coated nano-lithium titanium aluminum phosphate (lithium cobalt oxide) of 5% by mass was added and mixed evenly to obtain a mixture.

[0103] The mixture was heated and stirred at 60°C until it was evaporated to dryness, yielding the third dry material at a stirring speed of approximately 850 rpm.

[0104] The third dry material was placed in a muffle furnace and sintered in air atmosphere at a temperature of 350℃ for 6 hours to obtain nano-lithium titanium aluminum phosphate-carbon coated lithium cobalt oxide composite cathode material.

[0105] Example 4

[0106] Dissolve 330 mg of tetrabutyl titanate in a mixed solution formed by 5 ml of ethylene glycol and 45 ml of deionized water. Then add lithium nitrate, aluminum nitrate nonahydrate and diammonium hydrogen phosphate according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3 (x=0.35), stir well, add ammonia water to adjust the pH of the solution to 7.0, and stir thoroughly to form a precursor solution.

[0107] The well-mixed precursor liquid was stirred and dried at 120°C to obtain the first dry material, with a stirring speed of 1500 rpm.

[0108] The first dry material was placed in a muffle furnace and pre-decomposed in air medium. The heating temperature was 400℃ and the temperature was held for 4 hours to obtain the pre-calcined material. The pre-calcined material was ground and sieved to obtain nano-lithium titanium aluminum phosphate precursor with a particle size of about 200nm.

[0109] The nano-lithium titanium aluminum phosphate precursor was ultrasonically dispersed in deionized water, and polyacrylamide of approximately 100% of the mass of the lithium titanium aluminum phosphate precursor was added and stirred to dissolve.

[0110] The mixture was heated and stirred at 80°C until it was evaporated to dryness to obtain the second dry material. The stirring speed was 1200 rpm.

[0111] The second dry material was carbonized and sintered in a tube furnace under an argon atmosphere at a sintering temperature of 600℃ for 5 hours to obtain carbon-coated nano-lithium titanium aluminum phosphate sintered powder, wherein the carbon particles of the coating layer have a particle size of about 20nm.

[0112] The sintered powder was used as a solvent in ethanol and ball-milled in a planetary ball mill at a ball-to-powder ratio of 10:1 and a speed of 400 rpm for 30 hours. The ball-milled slurry was then dried to obtain carbon-coated nano-lithium titanium aluminum phosphate.

[0113] Lithium cobalt oxide powder with a particle size range of 10-30 μm was ultrasonically dispersed in deionized water, and carbon-coated nano-lithium titanium aluminum phosphate (2% by mass of lithium cobalt oxide) was added and mixed evenly to obtain a mixture.

[0114] The mixture was heated and stirred at 75°C until it was evaporated to dryness, yielding the third dry material at a stirring speed of approximately 1000 rpm.

[0115] The third dry material was placed in a muffle furnace and sintered in air atmosphere at a temperature of 400℃ for 3 hours to obtain nano-lithium titanium aluminum phosphate-carbon coated lithium cobalt oxide composite cathode material.

[0116] Comparative Example

[0117] Lithium cobalt oxide without nano-carbon coating modification of titanium aluminum phosphate lithium.

[0118] The evaluation method of the present invention for the electrochemical performance of the nano-lithium aluminum titanium phosphate-carbon coated lithium cobalt oxide composite cathode materials in Examples 1-4 and the comparative examples before and after modification is as follows:

[0119] Lithium cobalt oxide (unmodified) or lithium cobalt oxide composite cathode material coated with nano-lithium titanium aluminum phosphate-carbon was mixed with conductive carbon black and polyvinylidene fluoride binder in N,N-dimethylpyrrolidone at a mass ratio of 90:5:5. The mixture was then coated onto aluminum foil, dried in a vacuum oven at 120℃, rolled, and cut into cathode sheets with a diameter of 14mm. Using lithium metal sheets as the anode, a Celgard 2400 membrane as the separator, and a 1mol / L LiPF6 / EC+DMC electrolyte, CR2025 coin cells were assembled in an argon-atmosphere glove box and placed in a constant temperature chamber for charge-discharge cycle testing at a cutoff voltage of 3.0-4.55V and a 1C rate.

[0120] Among them, the lithium cobalt oxide without coating modification in the comparative example and the lithium cobalt oxide composite cathode material with nano-lithium aluminum titanium phosphate-carbon coating modification prepared in Example 1, the first-cycle voltage-specific capacity curves obtained by the first-cycle charge-discharge test of half cell 3.0-4.55V at 0.1C / 0.1C are shown below. Figure 4 As shown, compared with the unmodified lithium cobalt oxide cathode material, the modified lithium cobalt oxide exhibits an increased first-cycle discharge specific capacity from 189 mAh / g to 213 mAh / g, and a coulombic efficiency from 87% to 93%.

[0121] The cycle performance curves of the lithium cobalt oxide cathode material before coating modification and the lithium cobalt oxide cathode material after coating modification prepared in Example 1 are obtained from the 3.0-4.55V, 1C / 1C charge-discharge test, as shown in the figure. Figure 5 As shown, compared with unmodified lithium cobalt oxide, the modified lithium cobalt oxide cathode material has significantly improved cycle stability. After 200 cycles at 3.0-4.55V and 1C / 1C, the capacity retention rate is still as high as 85%, while the unmodified lithium cobalt oxide cathode material has a capacity retention rate of only 45% after 200 cycles.

[0122] Furthermore, the nano-lithium aluminum titanium phosphate-carbon coated modified lithium cobalt oxide composite cathode material prepared in Example 2 has a first-cycle discharge specific capacity of 196 mAh / g and a first-cycle coulombic efficiency of 92% at 3.0-4.55V 0.1C / 0.1C in a half-cell, and a capacity retention rate of 83% after 200 cycles at 1C / 1C.

[0123] The nano-lithium aluminum titanium phosphate-carbon coated modified lithium cobalt oxide composite cathode material prepared in Example 3 has a first-cycle discharge specific capacity of 201 mAh / g and a first-cycle coulombic efficiency of 93% at 3.0-4.55V 0.1C / 0.1C. After 200 cycles at 1C / 1C, the capacity retention rate is 80%.

[0124] The nano-lithium aluminum titanium phosphate-carbon coated modified lithium cobalt oxide composite cathode material prepared in Example 4 has a first-cycle discharge specific capacity of 197 mAh / g and a first-cycle coulombic efficiency of 90% in a half-cell at 3.0-4.55V 0.1C / 0.1C. After 200 cycles at 1C / 1C, the capacity retention rate is 84%.

[0125] The electrochemical performance characterization results of the above examples show that, compared with the modified lithium cobalt oxide composite cathode material in the comparative example, the modified lithium cobalt oxide composite cathode material has significantly improved first-cycle discharge specific capacity, first-cycle coulombic efficiency, and capacity retention.

[0126] As can be seen, the present invention modifies the surface of lithium cobalt oxide cathode with carbon-coated nano-lithium titanium aluminum phosphate, which has the functions of improving the lithium-ion conduction and electronic conduction of lithium cobalt oxide cathode material, reducing interface impedance, and stabilizing the bulk crystal structure of lithium cobalt oxide, thus significantly improving the initial discharge specific capacity, coulombic efficiency and cycle stability of lithium cobalt oxide cathode material under high charging cutoff voltage.

[0127] In the preparation process of this surface coating material, the high-temperature stable nano-lithium titanium aluminum phosphate is first coated with organic carbon, and then the surface of the lithium cobalt oxide cathode is coated. This avoids the irreversible effects of reducing substances during the carbonization process on the lithium cobalt oxide cathode, thereby preventing the formation of products such as Co3O4 and their adverse effects on battery cycle performance. The preparation method provided by this invention is simple, low-cost, and easy to scale up for industrialization.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0129] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A lithium-ion battery cathode material, characterized in that, The positive electrode material includes a core layer and a surface coating layer. The surface coating layer covers the surface of the core layer. The core layer provides lithium ions for the charging and discharging process of the lithium-ion battery. The surface coating layer is made of an ion-conducting material coated with an electron-conducting material. Specifically, the surface coating layer is formed by first coating the surface of the ion-conducting material with the electron-conducting material, and then coating the surface of the core layer with the surface coating layer material. The core layer material is selected from lithium cobalt oxide or nickel-cobalt-manganese ternary materials, and the ion-conducting material is selected from Li... x1 M1 a M2 b A y1 Or Li x2 M3O y2 M1 is selected from one of Ti, V, Cr, Mn, Co, Ni, and Zr; M2 is selected from +2 to +4 valence metal cations; A is selected from one of phosphate, borate, and silicate; M3 is selected from one of P, Si, Zr, Ti, B, W, and Nb; 0.5≤x1≤2, 1≤y1≤3, 1≤a≤2, 0≤b≤1, 1≤x2≤4, and 1≤y2≤6.

2. The lithium-ion battery cathode material as described in claim 1, characterized in that, The electron-conducting material is selected from one or a mixture of at least two of carbon, AZO, ITO, and conductive polymer materials.

3. The lithium-ion battery cathode material as described in claim 2, characterized in that, The carbon mentioned is organic carbon.

4. The lithium-ion battery cathode material as described in claim 1, characterized in that, The particle size range of the core layer is 1–30 μm, the particle size range of the electron-conducting material is 1–50 nm, and the particle size range of the ion-conducting material is 1–200 nm.

5. The lithium-ion battery cathode material as described in claim 1, characterized in that, The mass ratio of the electron-conducting material to the ion-conducting material is (1-100):100, and the mass ratio of the surface coating material to the core layer material is (0.5-5):

100.

6. A method for preparing a lithium-ion battery cathode material, used to prepare the lithium-ion battery cathode material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Preparation of precursors for ion-conducting materials; An electron-conducting material is coated onto the surface of the ion-conducting material precursor and sintered in an inert atmosphere to prepare a material for the surface coating layer. The material on which the surface coating layer is coated is sintered in an air atmosphere to obtain the lithium-ion battery cathode material.

7. The preparation method according to claim 6, characterized in that, The ion-conducting material precursor is a lithium titanium aluminum phosphate precursor, and the preparation method of the lithium titanium aluminum phosphate precursor includes: Weigh out lithium source compound, aluminum source compound, titanium source compound and phosphoric acid compound in a preset molar ratio, and disperse them in a mixed solvent to form a precursor solution. Adjust the pH value of the precursor solution to a range of 7 to 10. The preset molar ratio is determined according to the molar ratio of each element in the lithium titanium aluminum phosphate precursor. The precursor solution is dried to obtain the first dry material; The first dry material is pre-decomposed by heating in air under first conditions to obtain pre-calcined material; The pre-calcined material was ground to prepare the lithium titanium aluminum phosphate precursor.

8. The preparation method according to claim 7, characterized in that, The first condition is to keep warm at 250-500℃ for 2-8 hours.

9. The preparation method according to claim 6, characterized in that, The method for preparing the material of the surface coating layer includes: The ion-conducting material precursor is dispersed in water, and the electron-conducting material is added, wherein the mass ratio of the electron-conducting material to the ion-conducting material is (1-100):100, and the mixture is stirred to obtain a mixture. The mixture is dried to obtain a second dry material; The second dry material is sintered in an inert atmosphere under second conditions to obtain sintered powder; The sintered powder is ground to prepare the material of the surface coating layer.

10. The preparation method according to claim 9, characterized in that, The second condition is to keep warm at 300–800℃ for 4–8 hours.

11. The preparation method according to claim 6, characterized in that, The step of coating the surface of the core layer material with the material of the surface coating layer includes: The core layer material is dispersed in water, and the surface coating material is added, wherein the mass ratio of the surface coating material to the core layer material is (0.5-5):100, to obtain a mixture; The mixture is dried to obtain a third dry material; The third dry material is sintered under third conditions to obtain the lithium-ion battery cathode material.

12. The preparation method according to claim 11, characterized in that, The third condition is to keep warm at 300–700°C for 3–8 hours.

13. A lithium-ion battery, characterized in that, Including the lithium-ion battery cathode material as described in any one of claims 1 to 5.

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