Modified lithium-rich cathode material, and preparation method and application thereof

Abstract

This invention relates to a modified lithium-rich cathode material, its preparation method, and its application. The modified lithium-rich cathode material comprises a core and a coating layer covering the surface of the core. The core comprises a first cathode substrate material, and the coating layer comprises a second cathode substrate material doped with a dopant element, which includes a lanthanide metal. The chemical formula of the modified lithium-rich cathode material is Li. a [Ni x Co y Mn 1‑x‑y ] 2‑a‑b M b O2, where M is a lanthanide metal, 1.2≤a≤1.6, 0

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a modified lithium-rich cathode material, its preparation method, and its application. Background Technology

[0002] The future development direction of lithium-ion batteries lies in electrode materials that offer low cost, high capacity, and high safety. Lithium-rich cathode materials have attracted widespread attention from researchers due to their advantages such as low cost, environmental friendliness, and ultra-high discharge specific capacity (>250mAh / g). The high specific capacity of lithium-rich materials stems from the simultaneous participation of cations and anions in the redox reaction, where O... 2- Oxidized to O - Or O2 2- When charged to a high voltage, oxygen on the surface is released as O2. While the anionic oxygen participates in charge compensation, triggering more redox couples to participate in the redox reaction, it also brings a series of side reactions. For example, the release of oxygen leads to the reduction of surface transition metal (TM) ions, and the highly oxidized O2... - Reactions with the electrolyte lead to electrolyte decomposition, dissolution of TM ions, and irreversible phase transitions in the surface structure. Furthermore, at high potentials, side reactions occur between the cathode material and the electrolyte, resulting in the dissolution of TM ions, electrolyte decomposition, and thickening of the electrode-electrolyte interface (CEI), hindering Li... + Ion diffusion. This leads to drawbacks in lithium-rich cathode materials, such as low initial coulombic efficiency and poor capacity and voltage cycling performance, hindering their commercial application.

[0003] Existing studies have confirmed that during battery operation, oxygen release mainly occurs on the surface of lithium-rich cathode materials, while bulk oxygen participates in reversible redox reactions. Therefore, to suppress surface O2 release, reduce interfacial side reactions, and improve the structural stability of materials, researchers employ surface coating methods to enhance interfacial stability, and bulk doping to improve structural stability. For example, existing technology CN109888214A discloses a modified nickel-cobalt-manganese ternary material and its preparation method, using a mixture of soluble hydroxide, ammonia, and ammonium salt as a mixed precipitant. The addition of ammonium salt acts as a buffer, resulting in a milder reaction during nucleation. The final ternary material has a smaller particle size and better performance, yielding an aluminum-doped nickel-cobalt-manganese ternary material with a carbon coating layer. By optimizing the Al doping amount and the carbon coating layer thickness, the material capacity is further improved. However, while the surface coating layer suppresses O2 release, it has little impact on the stability of the bulk structure, and bulk doping with elements such as Al cannot simultaneously address surface issues.

[0004] Therefore, in order to achieve the synergy and unity of surface coating and doping, the development of a lithium-rich cathode material with excellent structural stability on both the surface and the bulk has become an urgent problem to be solved at present. Summary of the Invention

[0005] To solve the above technical problems, the purpose of the present invention is to provide a modified lithium-rich cathode material, its preparation method and application. The modified lithium-rich cathode material provided by the present invention introduces lanthanide metal doping elements into the coating layer to stabilize the surface and bulk structures of the cathode material, thereby significantly improving the capacity performance and cycling performance of the lithium-rich cathode material.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a modified lithium-rich cathode material, which includes a core and a coating layer coated on the surface of the core. The core includes a first cathode base material, and the coating layer includes a second cathode base material doped with doping elements;

[0008] The doping elements include lanthanide metal elements; the first cathode base material and the second cathode base material are independently selected from any one of lithium nickel cobalt manganese oxide or lithium nickel manganese oxide;

[0009] The chemical formula of the modified lithium-rich cathode material is Li a [Ni x Co y Mn 1-x-y 2-a-b M b O2, where M is a lanthanide metal element, 1.2 ≤ a ≤ 1.6, such as 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.6, etc., 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.39, etc., 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc., 0 < b < 0.15, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 or 0.14, etc.

[0010] ​The modified lithium-rich cathode material provided by this invention comprises a lanthanide metal doping layer on the surface of the cathode substrate. The presence of the lanthanide metal dopant acts as a support in the bulk structure of the lithium-rich cathode material, stabilizing its layered structure and suppressing irreversible phase transitions or even structural collapse during deep delithiation. Furthermore, the lanthanide metal doping layer contains numerous oxygen vacancies, which can accommodate O2 and reduce irreversible O2 release. The modified lithium-rich cathode material provided by this invention exhibits excellent bulk and surface structural stability, and significantly improves the capacity and cycle performance of lithium-rich cathode materials.

[0011] Preferably, in the modified lithium-rich cathode material, the concentration of the dopant element increases in a gradient from the surface of the core to the surface of the coating layer.

[0012] The present invention further designs dopant elements with concentration gradient doping on the coating layer, which can further enhance the supporting role of surface dopant elements in the bulk structure and optimize the layered structure stability of the cathode material.

[0013] Preferably, the composition of the first positive electrode substrate material is exactly the same as that of the second positive electrode substrate material.

[0014] In this invention, "the composition of the first positive electrode substrate material and the composition of the second positive electrode substrate material are completely the same" means that both the first positive electrode substrate material and the second positive electrode substrate material are lithium nickel cobalt manganese oxide or lithium nickel manganese oxide, wherein the types of metal elements and the molar ratio of each metal element in the first positive electrode substrate material and the second positive electrode substrate material are equal.

[0015] Preferably, the doping element includes any one or a combination of at least two of cerium, lanthanum, praseodymium, samarium, or ytterbium, and is preferably cerium and / or lanthanum.

[0016] Preferably, the doping elements include cerium and lanthanum.

[0017] Preferably, when the doping elements include cerium and lanthanum, the chemical formula of the modified lithium-rich cathode material is Li. a [Ni x Co y Mn 1-x-y ] 2-a-mz-z Ce mz La zO2, where 1.2 ≤ a ≤ 1.6, such as 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.6, etc.; 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.39, etc.; 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc.; 1 ≤ m ≤ 5, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, etc.; 0 < z < 0.03, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.015, 0.02, 0.025 or 0.029, etc.; mz + z = b, 0 < b < 0.15, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 or 0.14, etc. <![CDATA[ ]] <![CDATA[

[0018] ]] In the present invention, the "mz" refers to m × z, that is, the product of m and z. <![CDATA[ ]] <![CDATA[

[0019] ]] In a second aspect, the present invention provides a method for preparing a modified lithium-rich cathode material according to the first aspect, and the preparation method includes the following steps: <![CDATA[ ]] <![CDATA[

[0020] ]] (1) A first mixed solution, a first precipitant and a first complexing agent are added to a bottom solution in a co-current manner to carry out a first co-precipitation reaction to obtain a first precursor material with a target particle thickness; the metal elements in the first mixed solution include nickel element and manganese element, or include nickel element, cobalt element and manganese element; <![CDATA[ ]] <![CDATA[

[0021] ]] (2) A second mixed solution, a second precipitant, a second complexing agent and a metered amount of a lanthanide metal source are continuously added to the reaction solution containing the first precursor material obtained in step (1) in a co-current manner to carry out a second co-precipitation reaction to obtain a second precursor material; the metal elements in the second mixed solution include nickel element and manganese element, or include nickel element, cobalt element and manganese element; <![CDATA[ ]] <![CDATA[

[0022] ]] (3) The second precursor material is mixed with a lithium source and calcined to obtain the modified lithium-rich cathode material. <![CDATA[ ]] <![CDATA[

[0023] ]]The preparation method provided by the present invention first prepares a first precursor material with a target particle thickness through a primary co-precipitation reaction, and then continues a secondary co-precipitation reaction to form a lanthanide element-doped coating layer on the surface of the first precursor material, obtaining a second precursor material. Then, the second precursor material is mixed with a lithium source and formed into a cathode material with a core-shell structure under calcination conditions. The coating layer on the surface of the cathode material has doping of lanthanide metal elements. The doping elements play a supporting role in the bulk structure of the cathode material, reducing the irreversible phase transformation and collapse of the layered structure during deep de-lithiation. On the other hand, the secondary co-precipitation reaction combined with the calcination process can form a solid electrolyte coated with lanthanide elements on the surface of the cathode material, which has a large number of oxygen defects and can accommodate the oxygen released on the surface, reducing the irreversible oxygen release during the first cycle of the lithium-rich material. The preparation method of the present invention realizes the doping and coating on the surface of the lithium-rich cathode material through continuously performing two specific process co-precipitation reactions combined with the calcination process with the lithium source. The prepared modified lithium-rich cathode material has excellent capacity performance and cycle performance. The adopted preparation method is simple in operation and good in repeatability, which helps to realize the large-scale commercial production of the modified lithium-rich cathode material.

[0024] Preferably, the molar ratio of nickel element, cobalt element and manganese element in the first mixed solution added in step (1) is x:y:(1 - x - y), where 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.4, etc., and 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc. <000W174>

[0025] Preferably, the total concentration of metal elements in the first mixed solution in step (1) is 80 - 120 g / L, such as 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L or 120 g / L, etc.

[0026] Preferably, the first precipitating agent in step (1) includes sodium hydroxide solution and / or potassium hydroxide solution.

[0027] Preferably, the concentration of the first precipitating agent in step (1) is 20 - 45 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt% or 45 wt%, etc.

[0028] Preferably, the first complexing agent in step (1) includes any one or a combination of at least two of ammonia water, ammonium oxalate, oxalic acid, ammonium sulfate, EDTA (ethylenediaminetetraacetic acid) or citric acid.

[0029] Preferably, the concentration of the first complexing agent added in step (1) is 5 - 40 g / L, such as 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L or 40 g / L, etc.

[0030] Preferably, during the co - current process in step (1), the concentration of the first complexing agent in the reaction system is maintained at 1 - 5 g / L, such as 1 g / L, 2 g / L, 3 g / L, 4 g / L or 5 g / L, etc.

[0031] In the present invention, the addition amount of the complexing agent is regulated by limiting the concentration of the complexing agent in the reaction system during the co - current process.

[0032] Preferably, the bottom liquid in step (1) comprises water, a precipitating agent and a complexing agent.

[0033] Preferably, in the bottom liquid of step (1), the concentration of the complexing agent is 1 - 10 g / L, such as 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, etc., and the pH of the bottom liquid is 11 - 13, such as 11, 12 or 13, etc.

[0034] Preferably, the pH of the first coprecipitation reaction in step (1) is 9 - 11, such as 9, 10 or 11, etc.

[0035] Preferably, the target particle thickness of the first precursor material in step (1) is 70 - 97% of the target particle size thickness of the second precursor material in step (2), such as 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96% or 97%, etc., preferably 80 - 97%.

[0036] Preferably, the molar ratio of nickel element, cobalt element and manganese element in the second mixed solution added in step (2) is x:y:(1 - x - y), where 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.39, etc., and 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc.

[0037] Preferably, the total concentration of metal elements in the second mixed solution added in step (2) is 80-120 g / L, such as 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L or 120 g / L, etc.

[0038] Preferably, the nickel element in the first mixed solution and the second mixed solution is provided by a nickel source.

[0039] Preferably, the nickel source includes nickel sulfate.

[0040] Preferably, the cobalt element in the first mixed solution and the second mixed solution is provided by a cobalt source.

[0041] Preferably, the cobalt source includes cobalt sulfate.

[0042] Preferably, the manganese element in the first mixed solution and the second mixed solution is provided by a manganese source.

[0043] Preferably, the manganese source includes manganese sulfate.

[0044] Preferably, the addition amount of the lanthanide metal element in the lanthanide metal source in step (2) satisfies that the chemical formula of the obtained second precursor material is [Ni x Co y Mn 1-x-y 2-a-b M b (OH)2, where M includes lanthanide metal elements, 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.39, etc., 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc., 0 < b < 0.15, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 or 0.14, etc., 1.2 ≤ a ≤ 1.6, such as 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.6, etc.

[0045] In the present invention, in the second precursor material, the addition amount of the lanthanide metal element needs to satisfy the mass ratio of each element in the prepared modified lithium-rich cathode material, and thus needs to satisfy the ratio of each element in the above chemical formula of the prepared second precursor material.

[0046] ​Preferably, the lanthanide metal element in the lanthanide metal source in step (2) includes any one or a combination of at least two of cerium element, lanthanum element, praseodymium element, samarium element or ytterbium element, preferably cerium element and / or lanthanum element.

[0047] Preferably, the lanthanide metal element in the lanthanide metal source in step (2) is cerium element and lanthanum element.

[0048] Preferably, when the lanthanide metal element in the lanthanide metal source in step (2) is cerium element and lanthanum element, the chemical formula of the obtained second precursor material is [Ni x Co y Mn 1-x-y 2-a-mz-z Ce mz La z (OH)2, where 0 < x < 0.4, such as 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.39, etc., 0 ≤ y ≤ 0.2, such as 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc., 1 ≤ m ≤ 5, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, etc., 0 < z < 0.03, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.015, 0.02, 0.025 or 0.029, etc., 1.2 ≤ a ≤ 1.6, such as 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.6, etc., mz + z = b, 0 < b < 0.15, such as 0.0001, 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 or 0.14, etc.

[0049] Preferably, the total concentration of the lanthanide metal element in the lanthanide metal source in step (2) is 0.1 - 2 g / L, such as 0.1 g / L, 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L or 2.0 g / L, etc.

[0050] Preferably, the lanthanide metal source in step (2) includes sulfates of lanthanide metal elements.

[0051] Preferably, the second precipitant in step (2) includes sodium hydroxide solution and / or potassium hydroxide solution.

[0052] ​Preferably, in step (2), the concentration of the second precipitant is 20-45 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or 45 wt%.

[0053] Preferably, in step (2), the second complexing agent comprises any one or a combination of at least two of oxalic acid, ammonia, ammonium oxalate, ammonium sulfate, or EDTA (ethylenediaminetetraacetic acid).

[0054] Preferably, the concentration of the second complexing agent added in step (2) is 5-40 g / L, such as 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L or 40 g / L.

[0055] Preferably, during the co-current process in step (2), the concentration of the second complexing agent in the reaction system is maintained at 1-5 g / L, such as 1 g / L, 2 g / L, 3 g / L, 4 g / L or 5 g / L.

[0056] Preferably, the pH of the second coprecipitation reaction in step (2) is 9-11, such as 9, 10 or 11.

[0057] Preferably, the particle size of the second precursor material obtained in step (2) is 6-15 μm, such as 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, and more preferably 8-10 μm.

[0058] Preferably, after the second coprecipitation reaction is completed, the obtained product is further separated to obtain a solid product, and the solid product is dried.

[0059] Preferably, in step (3), the total molar amount of metal elements in the second precursor material and the molar ratio of lithium elements in the lithium source are (0.4-0.8):(1.2-1.6), for example, 0.4:1.6, 0.5:1.5, 0.6:1.4, 0.7:1.3 or 0.8:1.2, etc.

[0060] Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium acetate.

[0061] Preferably, the calcination in step (3) includes a first calcination stage and a second calcination stage performed sequentially.

[0062] This invention employs a two-stage calcination process involving a second precursor material and a lithium salt. The calcination temperature, combined with the dopant metal elements in the coating layer of the second precursor material, allows diffusion of these dopant metal elements into the first precursor obtained from the first co-precipitation reaction. This enables the dopant metal elements to be doped onto the surface of the resulting lithium-rich cathode material in a concentration gradient manner. Ultimately, this results in a modified lithium-rich cathode material with a progressively increasing dopant concentration from the core surface to the coating layer. This further enhances the stability of the bulk and surface structures of the cathode material, effectively suppressing irreversible phase transitions and even structural collapse during deep delithiation. Simultaneously, the specific calcination process design, combined with the reactions between the dopant metal elements, facilitates the formation of numerous oxygen defects on the coating layer, thereby reducing oxygen release.

[0063] Preferably, the temperature of the first calcination stage is 400-600℃, such as 400℃, 425℃, 450℃, 475℃, 500℃, 525℃, 550℃, 575℃ or 600℃, and more preferably 450-550℃.

[0064] Preferably, the first calcination time is 4-12 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, and more preferably 6-8 hours.

[0065] Preferably, the temperature of the second calcination stage is 800-1000℃, such as 800℃, 825℃, 850℃, 875℃, 900℃, 925℃, 950℃, 975℃ or 1000℃, and more preferably 850-950℃.

[0066] Preferably, the second calcination time is 6-24h, such as 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, and more preferably 10-24h.

[0067] Thirdly, the present invention provides a positive electrode sheet comprising the modified lithium-rich positive electrode material as described in the first aspect.

[0068] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the third aspect.

[0069] Compared with the prior art, the present invention has at least the following beneficial effects:

[0070] (1) The modified lithium-rich cathode material provided by this invention has a coating layer containing lanthanide metal dopant on the surface of the cathode substrate material. The presence of the lanthanide metal dopant acts as a support in the bulk structure of the lithium-rich cathode material, stabilizing its layered structure and suppressing irreversible structural phase transitions or even structural collapse during deep delithiation. Furthermore, the lanthanide metal dopant coating layer contains a large number of oxygen vacancies, which can accommodate O2 and reduce irreversible O2 release. The modified lithium-rich cathode material provided by this invention exhibits excellent bulk and surface structural stability, and significantly improves the capacity and cycle performance of the lithium-rich cathode material.

[0071] (2) The preparation method of the present invention achieves the doping and coating of the surface of lithium-rich cathode material by continuously carrying out a co-precipitation reaction of two specific processes combined with the calcination process of lithium source. The modified lithium-rich cathode material prepared has excellent bulk structure and surface structure stability, as well as high capacity performance and cycle performance. The preparation method is simple to operate and has good repeatability, which helps to realize the large-scale commercial production of modified lithium-rich cathode material. Attached Figure Description

[0072] Figure 1 These are the X-ray diffraction patterns of the modified lithium-rich cathode materials prepared in Examples 1, 4-5, and Comparative Example 1.

[0073] Figure 2 This is a capacity-voltage curve of the modified lithium-rich cathode materials prepared in Examples 1, 2-3 and Comparative Example 1 when applied to lithium-ion batteries for the first charge and discharge.

[0074] Figure 3 The diagram shows the cycling process of the modified lithium-rich cathode materials prepared in Examples 1, 2-3 and Comparative Example 1 in lithium-ion batteries. Detailed Implementation

[0075] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0076] Example 1

[0077] This embodiment provides a modified lithium-rich cathode material, comprising a core and a coating layer covering the surface of the core. The core comprises lithium nickel manganese oxide, and the coating layer comprises lithium nickel manganese oxide doped with doped elements, including cerium and lanthanum. The molar ratio of nickel to manganese within the lithium nickel manganese oxide in both the core and the coating layer is equal. The chemical formula of the modified lithium-rich cathode material is Li. 1.2[Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004 The doping concentrations of O2, cerium, and lanthanum increase in a gradient from the surface of the core to the surface of the coating layer.

[0078] This embodiment provides a method for preparing the above-mentioned modified lithium-rich cathode material, including the following steps:

[0079] (1) Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a first mixed solution, wherein the molar ratio of nickel to manganese in the first mixed solution is 0.34:0.66 and the total concentration of metal elements in the first mixed solution is 100 g / L; the first mixed solution, a 30 wt% sodium hydroxide solution, and a 30 g / L oxalic acid solution are added to the bottom liquid in a co-current flow. The bottom liquid includes deionized water, oxalic acid, and sodium hydroxide solution. The concentration of oxalic acid in the bottom liquid is 5 g / L and the pH of the bottom liquid is 11. During the co-current flow, the concentration of oxalic acid in the reaction system is maintained at 3 g / L to carry out a first coprecipitation reaction. The pH of the first coprecipitation reaction is 10 to obtain a first precursor material with a particle thickness of 9 μm.

[0080] (2) Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a second mixed solution, wherein the molar ratio of nickel to manganese in the second mixed solution is 0.34:0.66 and the total concentration of metal elements in the second mixed solution is 100 g / L; cerium sulfate and lanthanum sulfate are mixed to prepare a third mixed solution, wherein the molar ratio of cerium to lanthanum in the third mixed solution is 4:1 and the total concentration of metal elements in the third mixed solution is 0.1 g / L.

[0081] Continuing with the reaction solution of the first precursor material obtained in step (1), a second mixed solution, a third mixed solution, a 30 wt% sodium hydroxide solution, and 30 g / L oxalic acid are added concurrently to the reaction solution. During the concurrent addition, the concentration of oxalic acid in the reaction system is maintained at 3 g / L to carry out the second coprecipitation reaction. The pH of the second coprecipitation reaction is 10. After centrifugation, the solid product is dried to obtain the second precursor material. The elements in the second precursor material must satisfy the chemical formula [Ni...]. 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004 The proportions of each element in (OH)2, and the particle size of the second precursor material is 10 μm.

[0082] (3) The second precursor material obtained in step (2) is mixed with lithium carbonate at a ratio of 0.8:1.2 of the total molar amount of metal elements in the second precursor material to the molar amount of lithium elements in lithium carbonate. The mixed product is then calcined at 500°C for 6 hours and then calcined at 930°C for 10 hours to obtain the modified lithium-rich cathode material.

[0083] Example 2

[0084] This embodiment provides a modified lithium-rich cathode material, comprising a core and a coating layer covering the surface of the core. The core comprises lithium nickel manganese oxide, and the coating layer comprises lithium nickel manganese oxide doped with doped elements, including cerium and lanthanum. The molar ratio of nickel and manganese in the lithium nickel manganese oxide within the core and the coating layer is equal. The chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.35 Mn 0.65 ] 0.7992 (Ce 0.5 La 0.5 ) 0.0008 The doping concentrations of O2, cerium, and lanthanum increase in a gradient from the surface of the core to the surface of the coating layer.

[0085] This embodiment provides a method for preparing the above-mentioned modified lithium-rich cathode material, including the following steps:

[0086] (1) Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a first mixed solution, wherein the molar ratio of nickel to manganese in the first mixed solution is 0.35:0.65 and the total concentration of metal elements in the first mixed solution is 80 g / L; the first mixed solution, a 20 wt% sodium hydroxide solution, and 40 g / L oxalic acid are added to the bottom solution in a co-current flow. The bottom solution includes deionized water, oxalic acid, and sodium hydroxide solution. The concentration of oxalic acid in the bottom solution is 6 g / L and the pH of the bottom solution is 11. During the co-current flow, the concentration of oxalic acid in the reaction system is maintained at 5 g / L to carry out a first coprecipitation reaction. The pH of the first coprecipitation reaction is 9 to obtain a first precursor material with a particle thickness of 6.8 μm.

[0087] (2) Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a second mixed solution, wherein the molar ratio of nickel to manganese in the second mixed solution is 0.35:0.65 and the total concentration of metal elements in the second mixed solution is 80 g / L; cerium sulfate and lanthanum sulfate are mixed to prepare a third mixed solution, wherein the molar ratio of cerium to lanthanum in the third mixed solution is 1:1 and the total concentration of metal elements in the third mixed solution is 0.4 g / L.

[0088] Continuing with the reaction solution of the first precursor material obtained in step (1), a second mixed solution, a third mixed solution, a 20 wt% sodium hydroxide solution, and 40 g / L oxalic acid are added concurrently to the reaction solution. During the concurrent addition, the concentration of oxalic acid in the reaction system is maintained at 5 g / L to carry out the second coprecipitation reaction. The pH of the second coprecipitation reaction is 9. After centrifugation, the solid product is dried to obtain the second precursor material. Each element in the second precursor material must satisfy the chemical formula [Ni...]. 0.35 Mn 0.65 ] 0.7992 (Ce 0.5 La 0.5 ) 0.0008 The proportions of each element in (OH)2, and the particle size of the second precursor material is 8 μm.

[0089] (3) The second precursor material obtained in step (2) is mixed with lithium hydroxide at a ratio of 0.8:1.2 of the total molar amount of metal elements in the second precursor material to the molar amount of lithium elements in lithium carbonate. The mixed product is calcined at 450°C for 8 hours and then calcined at 850°C for 16 hours to obtain the modified lithium-rich cathode material.

[0090] Example 3

[0091] This embodiment provides a modified lithium-rich cathode material, comprising a core and a coating layer covering the surface of the core. The core comprises lithium nickel manganese oxide, and the coating layer comprises lithium nickel manganese oxide doped with doped elements, including cerium and lanthanum. The molar ratio of nickel to manganese within the lithium nickel manganese oxide in both the core and the coating layer is equal. The chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.2 Mn 0.8 ] 0.7997 (Ce 0.7 La 0.3 ) 0.0003 The doping concentrations of O2, cerium, and lanthanum increase in a gradient from the surface of the core to the surface of the coating layer.

[0092] This embodiment provides a method for preparing the above-mentioned modified lithium-rich cathode material, including the following steps:

[0093] (1) Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a first mixed solution, wherein the molar ratio of nickel to manganese in the first mixed solution is 0.2:0.8 and the total concentration of metal elements in the first mixed solution is 120 g / L; the first mixed solution, a 45 wt% sodium hydroxide solution, and 5 g / L oxalic acid are added to the bottom liquid in parallel flow, the bottom liquid includes deionized water, oxalic acid and sodium hydroxide solution, the concentration of oxalic acid in the bottom liquid is 2 g / L, the pH of the bottom liquid is 12, and the concentration of oxalic acid in the reaction system is kept at 1 g / L during the parallel flow process to carry out the first coprecipitation reaction, the pH of the first coprecipitation reaction is 11, and the first precursor material is obtained, the particle thickness of the first precursor is 9.5 μm.

[0094] (2) Cerium sulfate and lanthanum sulfate are mixed to prepare a third mixed solution. The molar ratio of cerium to lanthanum in the third mixed solution is 7:3, and the total concentration of metal elements in the third mixed solution is 0.5 g / L. Nickel sulfate and manganese sulfate are mixed with deionized water to prepare a second mixed solution. The molar ratio of nickel to manganese in the second mixed solution is 0.2:0.8, and the total concentration of metal elements in the second mixed solution is 120 g / L.

[0095] In step (1), a second mixed solution, a third mixed solution, a 45 wt% sodium hydroxide solution, and 5 g / L oxalic acid are added concurrently to the reaction solution of the first precursor material. During the concurrent addition, the concentration of oxalic acid in the reaction system is maintained at 1 g / L to carry out the second coprecipitation reaction. The pH of the second coprecipitation reaction is 11. After centrifugation, the solid product is dried to obtain the second precursor material. The elements in the second precursor material must satisfy the chemical formula [Ni...]. 0.2 Mn 0.8 ] 0.7997 (Ce 0.7 La 0.3 ) 0.0003 The proportions of each element in (OH)2, and the particle size of the second precursor material is 10 μm.

[0096] (3) The second precursor material obtained in step (2) is mixed with lithium carbonate at a ratio of 0.8:1.2 of the total molar amount of metal elements in the second precursor material to the molar amount of lithium elements in lithium acetate. The mixed product is calcined at 550°C for 6 hours and then calcined at 850°C for 10 hours to obtain the modified lithium-rich cathode material.

[0097] Example 4

[0098] The only difference between this embodiment and Embodiment 1 is that the lanthanum element in the modified lithium-rich cathode material provided in this embodiment is omitted, and the chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.7996 Ce 0.0004 O2. All other contents are the same as in Example 1.

[0099] Example 5

[0100] The only difference between this embodiment and Embodiment 1 is that the cerium element in the modified lithium-rich cathode material provided in this embodiment is omitted, and the chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.7996 La 0.0004 O2. All other contents are the same as in Example 1.

[0101] Example 6

[0102] The only difference between this embodiment and Embodiment 1 is that in the modified lithium-rich cathode material provided in this embodiment, the doping elements cerium and lanthanum are replaced with praseodymium and ytterbium, and the chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.7996 (Pu 0.8 Yb 0.2 ) 0.0004 O2. All other contents are the same as in Example 1.

[0103] Example 7

[0104] The only difference between this embodiment and Embodiment 1 is that the modified lithium-rich cathode material provided in this embodiment has a molar ratio of cerium to lanthanum in the dopant elements of 2:3, and the chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.4 La 0.6 ) 0.0004 O2. All other contents are the same as in Example 1.

[0105] Example 8

[0106] The only difference between this embodiment and Embodiment 1 is that the modified lithium-rich cathode material provided in this embodiment has a molar ratio of cerium to lanthanum in the dopant elements of 7:1, and the chemical formula of the modified lithium-rich cathode material is Li. 1.2 [Ni0.34 Mn 0.66 ] 0.7996 (Ce 0.875 La 0.125 ) 0.0004 O2. All other contents are the same as in Example 1.

[0107] Example 9

[0108] The only difference between this embodiment and Embodiment 1 is that in the preparation method of the modified lithium-rich cathode material provided in this embodiment, the target particle thickness of the first precursor material obtained in step (1) is 7 μm, that is, the target particle thickness of the first precursor material obtained in step (1) is 70% of the target particle size thickness of the second precursor obtained in step (2). All other contents are the same as in Embodiment 1.

[0109] Comparative Example 1

[0110] The only difference between this comparative example and Example 1 is that the modified lithium-rich cathode material provided in this comparative example omits the doping element, and the chemical formula of the cathode material is Li. 1.2 (Ni 0.34 Mn 0.66 ) 0.8 O2. All other contents are the same as in Example 1.

[0111] Comparative Example 2

[0112] The only difference between this embodiment and Example 1 is that the chemical formula of the modified lithium-rich cathode material provided in this comparative example is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.6 (Ce 0.8 La 0.2 ) 0.2 O2. All other contents are the same as in Example 1.

[0113] Comparative Example 3

[0114] The only difference between this comparative example and Example 1 is that in the modified lithium-rich cathode material provided in this comparative example, the doping element is uniformly doped in the cathode material, and its chemical formula is Li. 1.2 [Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004O2; Correspondingly, in the preparation method provided in this comparative example, steps (1) and (2) are replaced by: mixing nickel sulfate, manganese sulfate, cerium sulfate, lanthanum sulfate and solvent together to obtain a mixed solution; adding a 30wt% sodium hydroxide solution and a 30g / L oxalic acid solution to the bottom solution in a co-current manner; the bottom solution includes deionized water, oxalic acid and sodium hydroxide solution; the concentration of oxalic acid in the bottom solution is 5g / L; the pH of the bottom solution is 11; the concentration of oxalic acid in the co-current system is maintained at 3g / L during the co-current process; the first coprecipitation reaction is carried out; the pH of the first coprecipitation reaction is 10; a precursor material with a particle thickness of 10μm is obtained; the elements in the second precursor material need to satisfy the chemical formula [Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004 The proportions of each element in (OH)2. Everything else is the same as in Example 1.

[0115] Performance testing:

[0116] The modified lithium-rich cathode materials provided in Examples 1-9 and Comparative Examples 1-3 were mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 8:1:1. This mixture was then added dropwise to a slurry prepared in N-methylpyrrolidone. The resulting slurry was uniformly coated onto aluminum foil, dried, and then a supporting sheet was stamped to obtain the cathode electrode. The cathode electrode, lithium metal sheet, separator (Celgard-2400), electrolyte solution (LBC3021C11), gasket, spring, and battery casing were assembled into a coin cell. The electrochemical performance of the battery was tested under 0.1C / 0.1C conditions within a voltage range of 2-4.8V. The test results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] The test results show that:

[0121] (1) As can be seen from Examples 1 to 5, the modified lithium-rich cathode material provided by the present invention introduces lanthanide metal doping elements into the coating layer, which stabilizes the surface and bulk structure of the cathode material, thereby significantly improving the capacity performance and cycle performance of the lithium-rich cathode material.

[0122] (2) By comparing Example 1 and Example 6, it can be seen that if the doped cerium and lanthanum elements are replaced with other lanthanide elements, the cost will increase significantly and the performance will decrease.

[0123] (3) By comparing Examples 1 and Examples 7-8, it can be seen that if the molar ratio of cerium to lanthanum is too low or too high, a solid electrolyte rich in oxygen defects cannot be formed on the surface of the material, thereby reducing the release of O2 and thus reducing the discharge capacity.

[0124] (4) By comparing Example 1 and Example 9, it can be seen that if the target particle thickness of the first precursor material in the process of preparing the cathode material is too low, the content of doped transition metal ions in the bulk phase will be too high, which will hinder the migration of lithium ions and reduce the electrochemical performance.

[0125] (5) By comparing Example 1 and Comparative Example 1, it can be seen that if the doping elements in the coating layer are omitted in the cathode material provided by the present invention, the surface structure and bulk structure stability of the obtained cathode material will be poor, and irreversible O2 will be released from the surface of the cathode material during battery operation, resulting in a significant deterioration in battery capacity performance and cycle performance.

[0126] Figure 1 X-ray diffraction patterns of the modified lithium-rich cathode materials prepared in Examples 1, 4-5 and Comparative Example 1 are given. As can be seen from the figure, the doping of cerium and / or lanthanum elements and the coating of the surface layer constructed on the surface of the lithium-rich cathode material by the present invention through a one-step two-stage co-precipitation reaction combined with calcination process do not change the bulk structure of the lithium-rich cathode material.

[0127] Figure 2 and Figure 3 Performance graphs of the modified lithium-rich cathode materials prepared in Examples 1, 2-3 and Comparative Example 1 when applied to lithium-ion batteries are given. Compared with undoped lithium-rich cathode materials, the modified lithium-rich cathode materials prepared by the preparation method provided in this invention have higher initial discharge specific capacity and better cycle performance.

[0128] (6) By comparing Example 1 and Comparative Example 2, it can be seen that if the content of doped elements is too high, the active metal ions participating in the charge transfer reaction will be less, which will reduce the capacity.

[0129] (7) By comparing Example 1 and Comparative Example 3, it can be seen that if the doping elements are uniformly doped in the cathode material and the lanthanide metal source is directly co-precipitated with the nickel source, cobalt source and manganese source, the bulk structure stability of the cathode material cannot be effectively achieved, which leads to irreversible structural phase transition or even structural collapse during battery charging and discharging, and thus the electrochemical performance of the battery is greatly reduced.

[0130] In summary, the modified lithium-rich cathode material provided by this invention comprises a lanthanide metal doping layer on the surface of the cathode substrate. The presence of the lanthanide metal dopant acts as a support in the bulk structure of the lithium-rich cathode material, stabilizing its layered structure and suppressing irreversible phase transitions or even structural collapse during deep delithiation. Furthermore, the lanthanide metal doping layer contains numerous oxygen vacancies, which can accommodate O2 and reduce irreversible O2 release. The modified lithium-rich cathode material provided by this invention exhibits excellent bulk and surface structural stability, and significantly improves the capacity and cycle performance of lithium-rich cathode materials.

[0131] 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 method for preparing a modified lithium-rich cathode material, characterized in that, The preparation method includes the following steps: (1) The first mixed solution, the first precipitant and the first complexing agent are added to the bottom liquid in parallel to carry out the first coprecipitation reaction to obtain the first precursor material with the target particle thickness; the metal elements in the first mixed solution include nickel and manganese, or, include nickel, cobalt and manganese. The molar ratio of nickel, cobalt, and manganese in the first mixed solution is x:y:(1-xy), where 0 <x<0.4,0≤y≤0.2; (2) In the reaction solution containing the first precursor material obtained in step (1), the second mixed solution, the second precipitant, the second complexing agent and the formulated amount of lanthanide metal source are added in parallel to carry out the second coprecipitation reaction to obtain the second precursor material; the metal elements in the second mixed solution include nickel and manganese, or include nickel, cobalt and manganese. The molar ratio of nickel, cobalt, and manganese in the second mixed solution is x:y:(1-xy), where 0 <x<0.4,0≤y≤0.2; (3) The second precursor material is mixed with a lithium source and calcined to obtain the modified lithium-rich cathode material; The modified lithium-rich cathode material includes a core and a coating layer covering the surface of the core. The core includes a first cathode substrate material, and the coating layer includes a second cathode substrate material doped with doping elements. The doping element includes lanthanide metals; the first cathode substrate material and the second cathode substrate material are independently selected from either lithium nickel cobalt manganese oxide or lithium nickel manganese oxide. The modified lithium-rich cathode material has a chemical formula of Li a [Ni x Co y Mn 1-x-y ] 2-a-b M b O2, wherein M is a lanthanide metal element, 1.2≤a≤1.6, 0 2. The preparation method according to claim 1, characterized in that, In the modified lithium-rich cathode material, the concentration of the dopant element increases in a gradient from the surface of the core to the surface of the coating layer.

3. The preparation method according to claim 1, characterized in that, The composition of the first positive electrode substrate material is exactly the same as that of the second positive electrode substrate material.

4. The preparation method according to claim 1, characterized in that, The doping element includes any one or a combination of at least two of cerium, lanthanum, praseodymium, samarium, or ytterbium.

5. The preparation method according to claim 4, characterized in that, The doping element is cerium and / or lanthanum.

6. The preparation method according to claim 5, characterized in that, The doping elements include cerium and lanthanum.

7. The preparation method according to claim 6, characterized in that, When the doping elements include cerium and lanthanum, the chemical formula of the modified lithium-rich cathode material is Li. a [Ni x Co y Mn 1-x-y ] 2-a-mz-z Ce mz La z O2, where 1.2≤a≤1.6, 0 <x<0.4,0≤y≤0.2,1≤m≤5,0<z<0.03,mz+z=b,0<b<0.15。 8. The preparation method according to claim 1, characterized in that, Step (1) The total concentration of metal elements in the first mixed solution is 80-120 g / L.

9. The preparation method according to claim 1, characterized in that, Step (1) The concentration of the first precipitant is 20-45 wt%.

10. The preparation method according to claim 1, characterized in that, The concentration of the first complexing agent added in step (1) is 5-40 g / L.

11. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the first complexing agent in the reaction system is maintained at 1-5 g / L during the co-current process.

12. The preparation method according to claim 1, characterized in that, The base liquid in step (1) includes water, a precipitant, and a complexing agent.

13. The preparation method according to claim 1, characterized in that, In step (1), the pH of the first coprecipitation reaction is 9-11.

14. The preparation method according to claim 1, characterized in that, In step (1), the target particle thickness of the first precursor material is 70-97% of the target particle size thickness of the second precursor material in step (2).

15. The preparation method according to claim 14, characterized in that, In step (1), the target particle thickness of the first precursor material is 80-97% of the target particle size thickness of the second precursor material in step (2).

16. The preparation method according to claim 1, characterized in that, The total concentration of metal elements in the second mixed solution added in step (2) is 80-120 g / L.

17. The preparation method according to claim 1, characterized in that, The amount of lanthanide metal elements added to the lanthanide metal source in step (2) satisfies the requirement that the chemical formula of the second precursor material obtained is [Ni x Co y Mn 1-x-y ] 2-a-b M b (OH)₂, where M includes lanthanide metals, 0 <x<0.4,0≤y≤0.2,0<b<0.15,1.2≤a≤1.6。 18. The preparation method according to claim 1, characterized in that, The lanthanide metal elements in the lanthanide metal source mentioned in step (2) include any one or at least two of the following elements: cerium, lanthanum, praseodymium, samarium, or ytterbium.

19. The preparation method according to claim 18, characterized in that, The lanthanide metal elements in the lanthanide metal source in step (2) are cerium and / or lanthanum.

20. The preparation method according to claim 19, characterized in that, The lanthanide metal elements in the lanthanide metal source mentioned in step (2) are cerium and lanthanum.

21. The preparation method according to claim 20, characterized in that, When the lanthanide metal element in the lanthanide metal source described in step (2) is cerium and lanthanum, the chemical formula of the resulting second precursor material is [Ni x Co y Mn 1-x-y ] 2-a-mz-z Ce mz La z (OH)2, where 0 <x<0.4,0≤y≤0.2,1≤m≤5,0<z<0.03,1.2≤a≤1.6,mz+z=b,0<b<0.15。 22. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the second precipitant is 20-45 wt%.

23. The preparation method according to claim 1, characterized in that, The concentration of the second complexing agent added in step (2) is 5-40 g / L.

24. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the second complexing agent in the reaction system is maintained at 1-5 g / L during the co-current process.

25. The preparation method according to claim 1, characterized in that, In step (2), the pH of the second coprecipitation reaction is 9-11.

26. The preparation method according to claim 1, characterized in that, The particle size of the second precursor material obtained in step (2) is 6-15 μm.

27. The preparation method according to claim 26, characterized in that, The particle size of the second precursor material obtained in step (2) is 8-10 μm.

28. The preparation method according to claim 1, characterized in that, Step (3) The total molar amount of metal elements in the second precursor material and the molar ratio of lithium elements in the lithium source are (0.4-0.8):(1.2-1.6).

29. The preparation method according to claim 1, characterized in that, The calcination in step (3) includes a first calcination stage and a second calcination stage that are carried out sequentially.

30. The preparation method according to claim 29, characterized in that, The temperature of the first calcination stage is 400-600℃.

31. The preparation method according to claim 30, characterized in that, The temperature of the first calcination stage is 450-550℃.

32. The preparation method according to claim 29, characterized in that, The first calcination time is 4-12 hours.

33. The preparation method according to claim 32, characterized in that, The first calcination time is 6-8 hours.

34. The preparation method according to claim 29, characterized in that, The temperature of the second calcination stage is 800-1000℃.

35. The preparation method according to claim 34, characterized in that, The temperature of the second calcination stage is 850-950℃.

36. The preparation method according to claim 29, characterized in that, The second calcination time is 6-24 hours.

37. The preparation method according to claim 36, characterized in that, The second calcination time is 10-24 hours.

38. A positive electrode plate, characterized in that, The positive electrode sheet comprises a modified lithium-rich positive electrode material prepared by the preparation method according to any one of claims 1-37.

39. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 38.

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