Modified lithium-rich positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to a modified lithium-rich positive electrode material and a preparation method and application thereof.The modified lithium-rich positive electrode material comprises an inner core and a coating layer coating the surface of the inner core, the inner core comprises a first positive electrode substrate material, and the coating layer comprises a second positive electrode substrate material doped with doping elements; the doping elements comprise lanthanide series metal elements; the chemical formula of the modified lithium-rich positive electrode material is Lia [Ni < x > Co < y > Mn < 1-x-y >] < 2-a-b > M O < 2 >, M is a lanthanide metal element, a is greater than or equal to 1.2 and less than or equal to 1.6, 0 lt; xlt; 0 < = y < = 0.2, 0 lt; blt; and 0.15%. According to the modified lithium-rich positive electrode material provided by the invention, lanthanide metal doping elements are introduced into the coating layer, and the surface and bulk phase structure of the positive electrode material is stabilized, so that the capacity performance and the cycle performance of the lithium-rich positive electrode material are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a modified lithium-rich positive electrode material and a preparation method and application thereof. Background Art

[0002] The future development direction of lithium-ion batteries is low-cost, high-capacity, and high-safety electrode materials. Lithium-rich cathode materials have attracted widespread attention from researchers due to their advantages such as low cost, environmental friendliness, and ultra-high discharge capacity (>250mAh / g). The high specific capacity of lithium-rich materials comes from the simultaneous participation of cations and anions in the redox reaction, where O 2- Oxidation to O - or O2 2- When charged to a high voltage, the oxygen on the surface is released in the form of O2. The anionic oxygen participates in charge compensation, triggering more electron pairs to participate in the redox reaction, and also brings about a series of side reactions. For example, the release of oxygen leads to the reduction of transition metal (TM) ions on the surface, and the high oxidation state of O - Reacts with the electrolyte, leading to the decomposition of the electrolyte, the dissolution of TM ions, and irreversible phase change of the surface structure. In addition, at high potential, the positive electrode material reacts with the electrolyte, leading to the dissolution of TM ions, the decomposition of the electrolyte, and the thickening of the electrode-electrolyte interface (CEI), which hinders the Li + This causes lithium-rich cathode materials to face defects such as low initial coulombic efficiency, poor capacity and voltage cycling performance, hindering the commercial application of lithium-rich cathode materials.

[0003] Existing studies have confirmed that during battery operation, the release of oxygen mainly occurs on the surface of the lithium-rich positive electrode material, while the oxygen in the bulk phase participates in the reversible redox reaction. Therefore, in order to suppress the release of surface O2, reduce interface side reactions, and improve the structural stability of the material, researchers have adopted a surface coating method to improve the interface stability, and to adopt bulk doping to improve the stability of the structure. For example, prior art 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 plays the role of a buffer, and the system reacts relatively mildly during the nucleation process. The ternary material finally formed has a smaller particle size and better performance, and a nickel-cobalt-manganese ternary material with an aluminum-doped core and a carbon coating layer as the outer shell is obtained. By optimizing the Al doping amount and the thickness of the carbon coating layer, the material capacity is further improved. However, the setting of the surface coating layer will suppress the release of O2, but has little effect on the stability of the bulk structure, and the bulk doping of elements such as Al cannot take into account the surface.

[0004] Therefore, in order to achieve the coordinated unity of surface coating and doping, developing 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, the modified lithium-rich cathode material 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 a doping element;

[0008] The doping element includes a lanthanide metal element; 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 positive electrode material provided by the present invention has a coating layer containing a positive electrode base material doped with a lanthanide metal element on the surface of the positive electrode base material. The presence of the lanthanide metal doping element, on the one hand, can play a supporting role in the bulk structure of the lithium-rich positive electrode material, stabilize the layered structure of the positive electrode material, and inhibit irreversible structural phase change or even structural collapse during deep delithiation. On the other hand, the coating layer doped with the lanthanide metal doping element also has a large number of oxygen defects, which can accommodate O2 and reduce the irreversible release of O2. The modified lithium-rich positive electrode material provided by the present invention has excellent bulk structure and surface structure stability, and can significantly improve the capacity performance and cycle performance of the lithium-rich positive electrode material.

[0011] Preferably, in the modified lithium-rich positive electrode material, the concentration of the doping element increases gradually from the surface of the core to the surface of the coating layer.

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

[0013] Preferably, the composition of the first positive electrode base material and the composition of the second positive electrode base material are completely the same.

[0014] In the present invention, "the composition of the first positive electrode base material and the composition of the second positive electrode base material are exactly the same" means that the first positive electrode base material and the second positive electrode base material are both lithium nickel cobalt manganese oxide, or both are lithium nickel manganese oxide, wherein the types of metal elements and the molar ratios of the metal elements in the first positive electrode base material and the second positive electrode base 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, preferably cerium and / or lanthanum.

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

[0017] Preferably, when the doping element includes 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.

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

[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:

[0020] (1) The first mixed solution, the first precipitating agent and the first complexing agent are added to the bottom liquid 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;

[0021] (2) In the reaction solution containing the first precursor material obtained in step (1), a second mixed solution, a second precipitating agent, a second complexing agent and a metered amount of lanthanide metal source are continuously added 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;

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

[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 with 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, and the doping elements play a strut role in the bulk phase structure of the cathode material, reducing the irreversible phase change and collapse of the layered structure during deep de - lithiumation. 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 the co - precipitation reaction of two specific processes and combining with the calcination process of the lithium source. The prepared modified lithium - rich cathode material has excellent capacity performance and cycling 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.

[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) includes 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, for example, 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 co-precipitation 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, and is 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, 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, the concentration of the second precipitant in step (2) is 20-45 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt% or 45 wt%.

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

[0054] Preferably, the concentration of the second complexing agent added in step (2) is 5-40 g / L, for example, 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 parallel flow 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, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc., preferably 8-10 μm.

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

[0059] Preferably, in step (3), the molar ratio of the total molar amount of the metal element in the second precursor material to the lithium element in the lithium source is (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 of lithium carbonate, lithium hydroxide or lithium acetate, or a combination of at least two of them.

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

[0062] The present invention performs two consecutive calcination processes on a mixture of a second precursor material and a lithium salt. Combined with the calcination temperature, the doped metal elements in the surface coating layer of the second precursor material can diffuse into the interior of the first precursor obtained by the first coprecipitation reaction, thereby achieving doping of the doped metal elements on the surface of the obtained lithium-rich positive electrode material in the form of a concentration gradient change, and finally obtaining a modified lithium-rich positive electrode material in which the concentration of the doped elements increases gradually from the surface of the positive electrode material core to the surface of the coating layer, thereby further improving the stability of the bulk structure and surface structure of the positive electrode material, and effectively suppressing irreversible structural phase change or even structural collapse during deep delithiation; at the same time, the design of the specific calcination process combined with the reaction between the doped metal elements is conducive to the formation of a large number of oxygen defects on the coating layer, thereby reducing the release of oxygen.

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

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

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

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

[0067] In a third aspect, the present invention provides a positive electrode plate, which includes the modified lithium-rich positive electrode material as described in the first aspect.

[0068] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet 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 positive electrode material provided by the present invention has a coating layer containing a positive electrode base material doped with a lanthanide metal element on the surface of the positive electrode base material. The presence of the lanthanide metal doping element, on the one hand, can play a supporting role in the bulk structure of the lithium-rich positive electrode material, stabilize the layered structure of the positive electrode material, and inhibit irreversible structural phase change or even structural collapse during deep delithiation. On the other hand, the coating layer doped with the lanthanide metal doping element also has a large number of oxygen defects, which can accommodate O2 and reduce the irreversible release of O2. The modified lithium-rich positive electrode material provided by the present invention has excellent bulk structure and surface structure stability, and can significantly improve the capacity performance and cycle performance of the lithium-rich positive electrode material.

[0071] (2) The preparation method of the present invention realizes the doping and coating of the surface of the lithium-rich positive electrode material by continuously carrying out a co-precipitation reaction of a secondary specific process in combination with a calcination process of a lithium source. The prepared modified lithium-rich positive electrode material has excellent bulk structure and surface structure stability, as well as high capacity performance and cycle performance. The preparation method adopted is simple to operate and has good repeatability, which is conducive to the large-scale commercial production of the modified lithium-rich positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 1 is the X-ray diffraction pattern of the modified lithium-rich positive electrode material prepared in Example 1, Examples 4-5 and Comparative Example 1.

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

[0074] Figure 3 This is a cycle diagram of the application of the modified lithium-rich positive electrode materials prepared in Example 1, Examples 2-3 and Comparative Example 1 to lithium-ion batteries. DETAILED DESCRIPTION

[0075] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through 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 shall be subject to the claims.

[0076] Example 1

[0077] This embodiment provides a modified lithium-rich positive electrode material, including a core and a coating layer coated on the surface of the core, wherein the core includes lithium nickel manganese oxide, the coating layer includes lithium nickel manganese oxide doped with doping elements, the doping elements include cerium and lanthanum, the molar ratio of nickel and manganese in the lithium nickel manganese oxide in the core and the coating layer is equal, and the chemical formula of the modified lithium-rich positive electrode 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 gradually from the surface of the core to the surface of the coating layer.

[0078] This embodiment provides a method for preparing the modified lithium-rich positive electrode material, comprising 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 element to manganese element 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 sodium hydroxide solution with a concentration of 30 wt%, and oxalic acid with a concentration of 30 g / L are added to a bottom liquid in parallel, the bottom liquid includes deionized water, oxalic acid and sodium hydroxide solution, the oxalic acid concentration in the bottom liquid is 5 g / L, and the pH of the bottom liquid is 11. During the parallel flow process, the oxalic acid concentration in the reaction system is maintained at 3 g / L, and a first coprecipitation reaction is performed. The pH of the first coprecipitation reaction is 10, and a first precursor material is obtained. The particle thickness of the first precursor is 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 element to manganese element 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 element to lanthanum element 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] Continue to add the second mixed solution, the third mixed solution, a sodium hydroxide solution with a concentration of 30wt% and oxalic acid with a concentration of 30g / L to the reaction solution of the first precursor material obtained in step (1) in parallel, and maintain the concentration of oxalic acid in the reaction system at 3g / L during the parallel flow process, and perform a second coprecipitation reaction. The pH of the second coprecipitation reaction is 10. Then, after centrifugation, the solid product is dried to obtain a second precursor material. Each element in the second precursor material needs to satisfy the chemical formula [Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004 The ratio of each element in (OH)2, the particle size of the second precursor material is 10μm.

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

[0083] Example 2

[0084] This embodiment provides a modified lithium-rich positive electrode material, including a core and a coating layer coated on the surface of the core, wherein the core includes lithium nickel manganese oxide, the coating layer includes lithium nickel manganese oxide doped with doping elements, the doping elements include cerium and lanthanum, the molar ratio of nickel and manganese in the lithium nickel manganese oxide in the core and the coating layer is equal, and the chemical formula of the modified lithium-rich positive electrode 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 gradually from the surface of the core to the surface of the coating layer.

[0085] This embodiment provides a method for preparing the modified lithium-rich positive electrode material, comprising 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 element to manganese element 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 sodium hydroxide solution with a concentration of 20 wt%, and oxalic acid with a concentration of 40 g / L are added to a bottom liquid in parallel, the bottom liquid includes deionized water, oxalic acid and sodium hydroxide solution, the oxalic acid concentration in the bottom liquid is 6 g / L, and the pH of the bottom liquid is 11. During the parallel flow process, the oxalic acid concentration in the reaction system is maintained at 5 g / L, and a first coprecipitation reaction is performed. The pH of the first coprecipitation reaction is 9, and a first precursor material is obtained. The particle thickness of the first precursor is 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 element to manganese element 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 element to lanthanum element 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] Continue to add the second mixed solution, the third mixed solution, a sodium hydroxide solution with a concentration of 20wt%, and oxalic acid with a concentration of 40g / L to the reaction solution of the first precursor material obtained in step (1) in parallel, and maintain the concentration of oxalic acid in the reaction system at 5g / L during the parallel flow process, and perform a second coprecipitation reaction. The pH of the second coprecipitation reaction is 9. Then, after centrifugation, the solid product is dried to obtain a second precursor material. Each element in the second precursor material needs to satisfy the chemical formula [Ni 0.35 Mn 0.65 ] 0.7992 (Ce 0.5 La 0.5 ) 0.0008 The ratio of each element in (OH)2, the particle size of the second precursor material is 8μm.

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

[0090] Example 3

[0091] This embodiment provides a modified lithium-rich positive electrode material, including a core and a coating layer coated on the surface of the core, wherein the core includes lithium nickel manganese oxide, the coating layer includes lithium nickel manganese oxide doped with doping elements, the doping elements include cerium and lanthanum, the molar ratio of nickel and manganese in the lithium nickel manganese oxide in the core and the coating layer is equal, and the chemical formula of the modified lithium-rich positive electrode 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 gradually from the surface of the core to the surface of the coating layer.

[0092] This embodiment provides a method for preparing the modified lithium-rich positive electrode material, comprising 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 element to manganese element 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 is added to a bottom liquid in parallel with a sodium hydroxide solution with a concentration of 45 wt% and oxalic acid with a concentration of 5 g / L, wherein the bottom liquid comprises deionized water, oxalic acid and sodium hydroxide solution, the oxalic acid concentration in the bottom liquid is 2 g / L, and the pH of the bottom liquid is 12. During the parallel flow process, the oxalic acid concentration in the reaction system is maintained at 1 g / L, and a first coprecipitation reaction is performed. The pH of the first coprecipitation reaction is 11, and a 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, wherein the molar ratio of cerium element to lanthanum element 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, wherein the molar ratio of nickel element to manganese element 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] The second mixed solution, the third mixed solution, a sodium hydroxide solution with a concentration of 45 wt% and oxalic acid with a concentration of 5 g / L are added to the reaction solution of the first precursor material obtained in step (1) in parallel, and the concentration of oxalic acid in the reaction system is maintained at 1 g / L during the parallel flow process. A second coprecipitation reaction is performed, and the pH of the second coprecipitation reaction is 11. After centrifugation, the solid product is dried to obtain a second precursor material. Each element in the second precursor material needs to satisfy the chemical formula [Ni 0.2 Mn 0.8 ] 0.7997 (Ce 0.7 La 0.3 ) 0.0003 The ratio of each element in (OH)2, the particle size of the second precursor material is 10μm.

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

[0097] Example 4

[0098] The only difference between this embodiment and embodiment 1 is that the modified lithium-rich cathode material provided in this embodiment omits the lanthanum element in the doping element, 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. The rest of the contents are the same as those in Example 1.

[0099] Example 5

[0100] The only difference between this embodiment and embodiment 1 is that the modified lithium-rich cathode material provided in this embodiment omits the cerium element in the doping element, 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. The rest of the contents are the same as those 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 by 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. The rest of the contents are the same as those 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 doping 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. The rest of the contents are the same as those 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 doping 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. The rest of the contents are the same as those in Example 1.

[0107] Example 9

[0108] The only difference between this embodiment and Example 1 is that in the method for preparing the modified lithium-rich positive electrode 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 thickness of the second precursor obtained in step (2). The remaining contents are the same as in Example 1.

[0109] Comparative Example 1

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

[0111] Comparative Example 2

[0112] The difference between this embodiment and embodiment 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. The rest of the contents are the same as those in Example 1.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 1 is that in the modified lithium-rich positive electrode material provided in this comparative example, the doping element is uniformly doped in the positive electrode 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; Accordingly, in the preparation method provided in this comparative example, step (1) and step (2) are replaced by: nickel sulfate, manganese sulfate, cerium sulfate, lanthanum sulfate are mixed together with a solvent to obtain a mixed solution, and the obtained mixed solution is a sodium hydroxide solution with a concentration of 30wt%, and oxalic acid with a concentration of 30g / L is added to the bottom liquid in parallel, the bottom liquid includes deionized water, oxalic acid and sodium hydroxide solution, the oxalic acid concentration in the bottom liquid is 5g / L, the pH of the bottom liquid is 11, and the concentration of oxalic acid in the parallel flow system is maintained at 3g / L during the parallel flow process, and a first coprecipitation reaction is carried out, the pH of the first coprecipitation reaction is 10, and a precursor material with a particle thickness of 10μm is obtained. Each element in the second precursor material needs to satisfy the chemical formula [Ni 0.34 Mn 0.66 ] 0.7996 (Ce 0.8 La 0.2 ) 0.0004 The ratio of each element in (OH) 2. The rest of the contents are the same as in Example 1.

[0115] Performance testing:

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

[0117] Table 1

[0118]

[0119]

[0120] The test results show that:

[0121] (1) It can be seen from Examples 1 to 5 that the modified lithium-rich positive electrode material provided by the present invention introduces lanthanide metal doping elements into the coating layer to stabilize the surface and bulk structure of the positive electrode material, thereby significantly improving the capacity performance and cycle performance of the lithium-rich positive electrode 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 in the present invention, the cost will be greatly increased and the performance will be reduced.

[0123] (3) By comparing Example 1 with 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, resulting in a decrease in 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 positive electrode material of the present invention is too low, the content of the 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 with Comparative Example 1, it can be seen that if the doping element in the coating layer is omitted in the positive electrode material provided by the present invention, the surface structure and bulk structure stability of the obtained positive electrode material will be poor, and irreversible O2 release will occur on the surface of the positive electrode material during battery operation, and the capacity performance and cycle performance of the battery will be significantly deteriorated.

[0126] Figure 1 The X-ray diffraction patterns of the modified lithium-rich positive electrode materials prepared in Example 1, Examples 4-5 and Comparative Example 1 are given. It can be seen from the figure that the present invention constructs the doping of cerium and / or lanthanum elements on the surface of the lithium-rich positive electrode material and the coating of the surface coating layer through a one-step two-step co-precipitation reaction combined with a calcination process, without changing the bulk structure of the lithium-rich positive electrode material.

[0127] Figure 2 and Figure 3 Performance diagrams of the modified lithium-rich positive electrode materials prepared in Example 1, Examples 2-3 and Comparative Example 1 and applied to lithium-ion batteries are given. Compared with the undoped lithium-rich positive electrode material, the modified lithium-rich positive electrode material prepared by the preparation method provided by the present invention has a higher first discharge specific capacity and relatively excellent cycle performance.

[0128] (6) By comparing Example 1 with Comparative Example 2, it can be seen that if the content of the doping element in the present invention is too high, it will result in fewer active metal ions participating in the charge transfer reaction, which will reduce the capacity.

[0129] (7) By comparing Example 1 with Comparative Example 3, it can be seen that if the doping elements are uniformly doped in the positive electrode material of the present invention and the lanthanide metal source is directly subjected to a co-precipitation reaction with the nickel source, cobalt source and manganese source, the bulk structural stability of the positive electrode material cannot be effectively achieved, resulting in irreversible structural phase change or even structural collapse during the battery charging and discharging process, thereby significantly reducing the electrochemical performance of the battery.

[0130] In summary, the modified lithium-rich positive electrode material provided by the present invention has a coating layer of a positive electrode base material doped with a lanthanide metal element on the surface of the positive electrode base material. The presence of the lanthanide metal doping element, on the one hand, can play a supporting role in the bulk structure of the lithium-rich positive electrode material, stabilize the layered structure of the positive electrode material, and inhibit the irreversible structural phase change or even structural collapse during deep delithiation. On the other hand, the coating layer doped with the lanthanide metal doping element also has a large number of oxygen defects, which can accommodate O2 and reduce the irreversible release of O2. The modified lithium-rich positive electrode material provided by the present invention has excellent bulk structure and surface structure stability, and can significantly improve the capacity performance and cycle performance of the lithium-rich positive electrode material.

[0131] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A modified lithium-rich cathode material, characterized in that: The modified lithium-rich positive electrode material comprises a core and a coating layer coated on the surface of the core, wherein the core comprises a first positive electrode base material, and the coating layer comprises a second positive electrode base material doped with a doping element; The doping element includes a lanthanide metal element; the first positive electrode base material and the second positive electrode base material are independently selected from any one of lithium nickel cobalt manganese oxide or lithium nickel manganese oxide; 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, 0 <x<0.4,0≤y≤0.2,0<b<0.15。 2. The modified lithium-rich cathode material according to claim 1, characterized in that In the modified lithium-rich positive electrode material, the concentration of the doping element increases gradually from the surface of the core to the surface of the coating layer; Preferably, the composition of the first positive electrode base material and the composition of the second positive electrode base material are exactly the same; Preferably, the doping element includes any one or a combination of at least two of cerium, lanthanum, praseodymium, samarium or ytterbium, preferably cerium and / or lanthanum; Preferably, the doping elements include cerium and lanthanum; Preferably, when the doping element includes 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。 3. A method for preparing the modified lithium-rich cathode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) adding a first mixed solution, a first precipitant, and a first complexing agent to a bottom solution in parallel to perform a first coprecipitation reaction to obtain a first precursor material having a target particle thickness; the metal elements in the first mixed solution include nickel and manganese, or nickel, cobalt, and manganese; (2) adding a second mixed solution, a second precipitant, a second complexing agent, and a formulated amount of a lanthanide metal source to the reaction solution containing the first precursor material obtained in step (1) to perform a second coprecipitation reaction to obtain a second precursor material; The metal elements in the second mixed solution include nickel and manganese, or nickel, cobalt and manganese; (3) Mixing the second precursor material with a lithium source and calcining the mixture to obtain the modified lithium-rich positive electrode material.

4. The preparation method according to claim 3, characterized in that The molar ratio of nickel, cobalt and manganese in the first mixed solution added in step (1) is x:y:(1-xy), wherein 0 <x<0.4,0≤y≤0.2; Preferably, the total concentration of the metal elements in the first mixed solution in step (1) is 80-120 g / L; Preferably, the concentration of the first precipitant in step (1) is 20-45 wt%; Preferably, the concentration of the first complexing agent added in step (1) is 5-40 g / L; Preferably, during the parallel flow process in step (1), the concentration of the first complexing agent in the reaction system is maintained at 1-5 g / L.

5. The preparation method according to claim 3 or 4, characterized in that The base liquid in step (1) comprises water, a precipitant and a complexing agent; Preferably, the pH of the first coprecipitation reaction in step (1) is 9-11; Preferably, the target particle thickness of the first precursor material in step (1) is 70-97%, preferably 80-97%, of the target particle thickness of the second precursor material in step (2).

6. The preparation method according to any one of claims 3 to 5, characterized in that The molar ratio of nickel, cobalt and manganese in the second mixed solution added in step (2) is x:y:(1-xy), wherein 0 <x<0.4,0≤y≤0.2; Preferably, the total concentration of the metal elements in the second mixed solution added in step (2) is 80-120 g / L; Preferably, the amount of the lanthanide metal element added to the lanthanide metal source in step (2) satisfies the chemical formula of the second precursor material obtained: [Ni x Co y Mn 1-x-y ] 2-a-b M b (OH)2, wherein M includes lanthanide metal elements, 0 <x<0.4,0≤y≤0.2,0<b<0.15,1.2≤a≤1.6; 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, lanthanum, praseodymium, samarium or ytterbium, preferably cerium and / or lanthanum; Preferably, the lanthanide metal elements in the lanthanide metal source in step (2) are cerium and lanthanum; Preferably, when the lanthanide metal elements in the lanthanide metal source in step (2) are cerium and lanthanum, 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<0.4,0≤y≤0.2,1≤m≤5,0<z<0.03,1.2≤a≤1.6,mz+z=b,0<b<0.15。 7. The preparation method according to any one of claims 3 to 6, characterized in that Step (2) the concentration of the second precipitant is 20-45 wt%; Preferably, the concentration of the second complexing agent added in step (2) is 5-40 g / L; Preferably, during the parallel flow process in step (2), the concentration of the second complexing agent in the reaction system is maintained at 1-5 g / L; Preferably, the pH of the second coprecipitation reaction in step (2) is 9-11; Preferably, the particle size of the second precursor material obtained in step (2) is 6-15 μm, preferably 8-10 μm.

8. The preparation method according to any one of claims 3 to 7, characterized in that In step (3), the molar ratio of the total molar amount of the metal element in the second precursor material to the lithium element in the lithium source is (0.4-0.8):(1.2-1.6); Preferably, the calcination in step (3) includes a first calcination stage and a second calcination stage which are carried out successively; Preferably, the temperature of the first calcination stage is 400-600°C, preferably 450-550°C; Preferably, the first calcination time is 4-12 hours, preferably 6-8 hours; Preferably, the temperature of the second calcination stage is 800-1000°C, preferably 850-950°C; Preferably, the second calcination time is 6-24 hours, preferably 10-24 hours.

9. A positive electrode plate, characterized in that: The positive electrode plate includes the modified lithium-rich positive electrode material according to claim 1 or 2.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 9.

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