A positive electrode active material, a method for manufacturing the same, a positive electrode sheet, a secondary battery, and an electric device

Abstract

The application relates to the technical field of battery positive electrode materials, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The positive electrode active material comprises a lithium nickel manganese oxide, a first coating layer comprising a phosphorus-containing compound arranged on a first crystal surface of the lithium nickel manganese oxide, and a second coating layer comprising a lithium metal oxyphosphate arranged on a second crystal surface of the lithium nickel manganese oxide. The positive electrode active material provided by the application can improve the cycle performance of a secondary battery.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, and particularly to a cathode active material and its preparation method, a cathode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-nickel-manganese cathode active materials have become a key research focus in the field of lithium-ion battery cathode materials due to their significant advantages such as excellent rate performance, high operating voltage, and low cost. Their theoretical performance aligns with the high power output and economic efficiency requirements of electric vehicles and energy storage systems, making them highly commercially viable. However, this material suffers from several undeniable drawbacks: firstly, its surface structure stability is poor; during charge-discharge cycles, metallic manganese easily dissolves from the crystal lattice, causing the material structure to gradually collapse and resulting in rapid capacity decay; secondly, continuous side reactions occur between the electrolyte and the surface of the active material, accelerating the chemical degradation of the material and severely hindering the large-scale application of lithium-nickel-manganese cathode active materials.

[0003] To improve material performance, surface coating technology is widely used in the modification of lithium nickel manganese cathode active materials. Existing technologies typically use oxides or other single components to coat the materials, but this method has significant limitations. Coating temperature is a key factor affecting the modification effect: when the temperature is too high, the material's crystal faces tend to become inert, leading to a decrease in specific capacity and weakening the material's electrochemical performance; while when the temperature is too low, the adhesion between the coating layer and the crystal faces is insufficient, causing the coating layer to easily detach, failing to effectively prevent electrolyte corrosion, and making it difficult to guarantee the material's cycle performance. Therefore, optimizing the coating process, precisely controlling the coating temperature, improving the adhesion between the coating layer and the active material's crystal faces, and simultaneously avoiding material performance degradation are key to solving the bottleneck in the application of lithium nickel manganese cathode active materials. Summary of the Invention

[0004] To address the impact of the surface coating of the positive electrode active material on the crystal activity in the prior art, this invention provides a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device.

[0005] To achieve the above objectives, a first aspect of the present invention provides a positive electrode active material, comprising: Lithium nickel manganese oxide; and A first coating comprising a phosphorus-containing compound is disposed on the first crystal surface of the lithium nickel manganese oxide; A second coating comprising lithium oxyphosphate is disposed on the second crystal plane of the lithium nickel manganese oxide.

[0006] In one embodiment of the present invention, the first crystal plane includes at least one of (011), (101), or (010) crystal planes; and / or The second crystal plane includes at least one of (111), (001), (100) or (110) crystal planes.

[0007] In one embodiment of the present invention, the phosphorus content in the phosphorus-containing compound is between 200 ppm and 5000 ppm; and / or The lithium phosphate metal compound contains a metal element selected from at least one of titanium, magnesium, lanthanum, tungsten, and chromium; and / or The first coating has a thickness of 1 nm to 100 nm; and / or The second coating has a thickness of 1 nm to 100 nm.

[0008] A second aspect of the present invention also provides a method for preparing a positive electrode active material, comprising the following steps: Step (1): Obtain lithium nickel manganese oxide; Step (2): A first coating layer comprising a phosphorus-containing compound is formed on the first and second crystal planes of the lithium nickel manganese oxide in step (1); Step (3) involves an induced reaction on the second crystal surface of the lithium nickel manganese oxide obtained in step (2) to generate a second coating comprising lithium oxyphosphate metal lithium.

[0009] In one embodiment of the present invention, the method for obtaining the lithium nickel manganese oxide includes: A lithium, nickel, and manganese source solution is mixed with a blending agent and reacted under heating conditions to form a gel; The gel was calcined to obtain lithium nickel manganese oxide; Preferably, the lithium source is selected from at least one of lithium acetate, lithium oxalate, or lithium carbonate; the nickel source is selected from at least one of nickel acetate, nickel oxalate, or nickel carbonate; and the manganese source is selected from at least one of manganese acetate, manganese oxalate, or manganese carbonate. Preferably, the blending agent is selected from at least one of aminotriacetic acid or glycolic acid.

[0010] In one embodiment of the present invention, the method for generating the first coating comprising the phosphorus-containing compound includes: The lithium nickel manganese oxide obtained in step (1) is added to a salt solution containing metal ions with stable valence states that can form phosphate precipitates; A solution containing a phosphate compound is then added to react with the lithium nickel manganese oxide to form a first coating containing a phosphorus compound on the first and second crystal faces of the lithium nickel manganese oxide. Preferably, the salt containing metal ions with stable valence states that can form phosphate precipitates is selected from at least one of niobium ethanol, magnesium acetate, and zinc acetate; Preferably, the phosphate-containing compound is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and tris(2,2,2-trifluoroethyl) phosphite.

[0011] In one embodiment of the present invention, a method for generating a second coating comprising lithium oxyphosphate metal oxide includes: The lithium nickel manganese oxide obtained in step (2) is reacted with a second crystal plane-directed metal hydroxide to generate a second coating including lithium oxyphosphate metal hydroxide on the second crystal plane of the lithium nickel manganese oxide. Preferably, the method for obtaining the second crystal plane-guided metal hydroxide includes: Additives are added to the second crystal plane-guided metal salt solution and a solvothermal reaction is carried out; Preferably, the second crystal plane-directed metal salt is selected from at least one of titanium sulfate, magnesium sulfate, lanthanum chloride, sodium tungstate, and chromium chloride; the auxiliary agent is selected from at least one of urea, methylamine, trimethylamine, and tetramethylethylenediamine.

[0012] A third aspect of the present invention provides a positive electrode sheet comprising a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode active material of the first aspect of the present invention or the positive electrode active material obtained by the method of the second aspect of the present invention.

[0013] A fourth aspect of the present invention provides a secondary battery comprising a positive electrode sheet according to a third aspect of the present invention.

[0014] A fifth aspect of the present invention provides an electrical device comprising a secondary battery according to a fourth aspect of the present invention.

[0015] Other features and beneficial effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other beneficial effects of the invention can be realized and obtained by means of the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Unless otherwise specified, the positional relationships shown in the drawings in the following description are based on the direction in which the components are drawn in the figure.

[0017] Figure 1 This is a schematic diagram of the structure of the positive electrode active material provided in Embodiment 1 of the present invention; Figure 2This is an SEM image of the positive electrode active material provided in Example 1 of the present invention; Figure 3 This is the X-ray diffraction pattern of lithium nickel manganese oxide provided in Example 1 of the present invention; Figure 4 This is another SEM image of the positive electrode active material provided in Example 1 of the present invention; Figure 5 for Figure 4 Elemental (EDS) analysis of the (011) crystal plane at point A in the middle; Figure 6 for Figure 4 Elemental (EDS) analysis of the (111) crystal plane at point B in the middle; Figure 7 This is a cross-sectional transmission electron microscope image of the crystal plane of the positive electrode active material (101) provided in Example 1 of the present invention; Figure 8 This is a cross-sectional transmission electron microscope image of the (111) crystal plane of the positive electrode active material provided in Example 1 of the present invention; Figure 9 This is a comparison chart of the cycle performance of the positive electrode active materials obtained in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that all terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0020] Currently, lithium nickel manganese cathode active materials typically have a spinel structure, and existing synthesis methods result in significant differences in activity across different crystal facets. Lithium-nickel-manganese (LiNM) cathode active materials have always been a research hotspot for lithium-ion batteries due to their excellent rate performance, high operating voltage, and low cost. However, the large differences in activity across different crystal faces of LiNM cathode active materials synthesized by existing methods, as well as the severe drawbacks such as manganese dissolution during cycling, have significantly inhibited the large-scale application of LiNM cathode active materials. Current research shows that by coating the surface of LiNM cathode active materials with a stable protective layer, direct contact between the cathode active material and the electrolyte can be avoided or reduced, thereby reducing manganese dissolution and particle-electrolyte reaction and effectively improving the chemical stability of the material. However, current methods mainly use metal oxides (such as Al2O3, ZrO2, TiO2, MgO, etc.) or other single components for coating, which can only slightly enhance the electrochemical performance.

[0021] To address the aforementioned technical problems, this invention proposes a positive electrode active material. By selectively coating the material with phosphorus-containing compounds and lithium oxide phosphate, a uniform and robust protective layer (containing phosphorus compounds) can be formed on the surface of the lithium nickel manganese positive electrode active material. Simultaneously, the lithium oxide phosphate coating effectively enhances the activity of the inert crystal facets and improves lithium-ion conductivity, resulting in a significant improvement in the capacity and cycle performance of the coated lithium nickel manganese positive electrode active material. The following will describe this positive electrode active material in more detail.

[0022] In a first aspect, the present invention provides a positive electrode active material comprising: lithium nickel manganese oxide; a first coating layer comprising a phosphorus-containing compound disposed on a first crystal surface of the lithium nickel manganese oxide; and a second coating layer comprising a lithium oxyphosphate metal lithium compound disposed on a second crystal surface of the lithium nickel manganese oxide.

[0023] It is understandable that the aforementioned "active material" refers to a substance that can provide activity to the positive electrode active material and realize the energy conversion of the battery.

[0024] In this invention, the surface of the positive electrode active material is provided with a first coating layer containing phosphorus compound and a lithium oxide phosphate coating layer on the first and second crystal planes of the lithium nickel manganese oxide, respectively. The two surface effects work together to isolate excessive contact with the electrolyte, suppress side reactions, inhibit the degradation of the internal structure of the material, and effectively reduce the influence of the coating layer on the crystal plane activity.

[0025] In one embodiment of the present invention, the chemical formula of the phosphorus-containing compound is N. a (PO4) b Where a and b ≠ 0, and N is a first metallic element; preferably, the first metallic element is selected from at least one of niobium, magnesium, and zinc; In one embodiment of the present invention, the chemical formula of the lithium phosphate metal compound is Li. c M d Oe (PO4) f Wherein, c, d, e, f≠0, and M is a second metallic element; preferably, the second metallic element is selected from at least one of titanium, magnesium, lanthanum, tungsten, and chromium.

[0026] In a preferred embodiment of the present invention, the phosphorus content in the phosphorus-containing compound is between 200 ppm and 5000 ppm. For example, the phosphorus content in the phosphorus-containing compound can be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or within any range of the above values. By controlling the phosphorus content within this range, a phosphorus-containing compound coating of suitable thickness can be formed on the crystal plane. If the phosphorus content is too low, the coating will be insufficient and unable to provide protection; if it is too high, the coating will be too thick, which will significantly reduce the activity of the positive electrode active material.

[0027] In a preferred embodiment of the present invention, the first coating has a thickness of 1 nm to 100 nm.

[0028] In a preferred embodiment of the present invention, the second coating has a thickness of 1 nm to 100 nm.

[0029] In some embodiments of the present invention, the positive electrode active material contains lithium nickel manganese oxide crystals that belong to the cubic crystal system with space group Fd3m or P4332, and the lithium nickel manganese oxide contains seven crystal planes (111), (001), (100), (110), (011), (101) and (010).

[0030] Lithium-nickel-manganese (LiNM) cathode active materials have long been a research hotspot in lithium-ion battery cathode active materials due to their excellent rate performance, high operating voltage, and low cost. However, the unstable surface structure and manganese dissolution during cycling severely hinder their large-scale application. Research shows that by coating the surface of LiNM cathode active materials with a stable protective layer, direct contact between the active material and the electrolyte can be avoided or reduced, manganese dissolution and particle-electrolyte reaction can be minimized, effectively improving the chemical stability of the material. However, the reactivity of different crystal faces of LiNM cathode active materials varies. Blindly coating all crystal faces with the same compound will inevitably affect the reactivity of weakly reactive crystal faces, increasing the interfacial impedance of the material. Therefore, the controllable construction of the coating has great value in both scientific research and practical applications.

[0031] The positive electrode active material provided in a preferred embodiment of the present invention includes: Lithium nickel manganese oxide, wherein the lithium nickel manganese oxide comprises seven crystal planes: (111), (001), (100), (110), (011), (101), and (010); A first coating comprising a phosphorus-containing compound is disposed on a first crystal plane of the lithium nickel manganese oxide, the first crystal plane comprising at least one of (011), (101) and (010) crystal planes; A second coating comprising lithium oxyphosphate is disposed on the second crystal plane of the lithium nickel manganese oxide, the second crystal plane comprising at least one of (111), (001), (100), and (110) crystal planes; In this embodiment, lithium phosphate oxide coatings are selectively induced to form on inert crystal planes such as (111), (001), (100), and (110). This selective coating forms a phosphorus-containing compound protective layer on the material surface, effectively eliminating residual lithium on the material surface and inhibiting electrolyte erosion, thereby suppressing phase transformation, stabilizing the crystal structure, and improving the cycle performance of lithium-ion batteries. On the other hand, by inducing the reaction between metal hydroxide and phosphorus-containing compound coatings, the decrease in ion conductivity and increase in interfacial impedance caused by the coating of phosphorus oxides on inert crystal planes such as (111), (001), (100), and (110) are optimized.

[0032] In a preferred embodiment of the present invention, the metal element contained in the phosphate lithium metal is selected from at least one of titanium, magnesium, lanthanum, tungsten and chromium. The inventors have found that the phosphate lithium formed by the metal salts of the above metal elements through induced reaction is more compatible with the (111), (001), (100) and (110) crystal planes, which is beneficial to the controllable construction of the coating.

[0033] This invention provides a positive electrode active material, which contains seven crystal facets coated with two different materials: a first coating containing a phosphorus compound and a second coating containing a lithium oxide phosphate. First, a phosphorus compound coating is generated on all crystal facets by reacting a phosphorus source with a salt containing metal ions with stable valence states capable of forming phosphate precipitates. Then, a lithium oxide phosphate coating is selectively induced to form on the (111), (001), (100), or (110) inert crystal facets. This selective coating, on the one hand, forms a phosphorus compound protective coating on the material surface, effectively eliminating residual lithium and inhibiting electrolyte erosion, thereby suppressing phase transitions, stabilizing the crystal structure, and improving the cycle performance of lithium-ion batteries; on the other hand, by inducing the reaction between the metal hydroxide and the phosphorus compound coating, the decrease in ion conductivity and increase in interfacial impedance caused by the coating of phosphorus oxides on the (111), (001), (100), or (110) inert crystal facets are optimized.

[0034] Secondly, the present invention provides a method for preparing a positive electrode active material, comprising the following steps: Step (1): Obtain lithium nickel manganese oxide; The method for obtaining the lithium nickel manganese oxide includes: A lithium, nickel, and manganese source solution is mixed with a blending agent and reacted under heating conditions to form a gel; The gel was calcined to obtain lithium nickel manganese oxide; In a preferred embodiment of the present invention, the heating temperature for forming the gel can be 50-90°C, for example, the heating temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any range of the above values. The reaction time of the lithium, nickel, and manganese source solutions with the blending agent under heating conditions can be 6-12 hours, for example, the reaction time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any range of the above values. In some preferred embodiments of the present invention, the lithium source is selected from at least one of lithium acetate, lithium oxalate, or lithium carbonate; the nickel source is selected from at least one of nickel acetate, nickel oxalate, or nickel carbonate; and the manganese source is selected from at least one of manganese acetate, manganese oxalate, or manganese carbonate. Preferably, the gel is subjected to stepwise calcination at 300-990°C, which includes two high-temperature plateaus. This temperature is intended to decompose the gel to remove water and carbon. The main component of this gel is an organic carbon chain containing various metal ions. Acetates, oxalates, and carbonates are not pure compounds after forming a gel, but rather organic carbon chains formed under the action of a blending agent. For example, the first plateau temperature can be 300-350°C, such as 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or any range of the above values. The second plateau temperature can be 550-990°C, such as 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 990°C, or any range of the above values.

[0035] In a preferred embodiment of the present invention, the mass ratio of the lithium source, nickel source and manganese source is (1-5):(0.5-1.5):(1-10); In a preferred embodiment of the present invention, the blending agent is selected from at least one of aminotriacetic acid or glycolic acid. The selected blending agent not only plays the role of crosslinking ions, but also plays the role of dispersing, inducing transition metal ions to grow along specific crystal planes to form three-dimensional channels.

[0036] Step (2): A first coating comprising a phosphorus-containing compound is formed on the first and second crystal planes of the lithium nickel manganese oxide in step (1); preferably, the first crystal plane comprises at least one of (011), (101) or (010) crystal planes; and the second crystal plane comprises at least one of (111), (001), (100) or (110) crystal planes.

[0037] The method for generating the first coating comprising the phosphorus-containing compound includes: The lithium nickel manganese oxide obtained in step (1) is added to a salt solution containing metal ions with stable valence states that can form phosphate precipitates; A solution containing a phosphate compound is then added to react with the lithium nickel manganese oxide to form a first coating containing a phosphorus compound on the first and second crystal faces of the lithium nickel manganese oxide. In a preferred embodiment of the present invention, after adding the lithium nickel manganese oxide obtained in step (1) to a salt solution containing metal ions with stable valence states that can generate phosphate precipitates, the mixture is heated and stirred. The heating temperature is 35-80°C, for example, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or within any range of the above values.

[0038] In a preferred embodiment of the present invention, after adding the lithium nickel manganese oxide obtained in step (1) to a salt solution containing metal ions with stable valence states that can generate phosphate precipitates, the pH of the solution is adjusted by a pH adjuster, and the pH of the system is maintained unchanged after adding a solution containing a phosphate compound; preferably, the pH adjuster is at least one of ammonia, ammonium acetate, and ammonium citrate. More preferably, the pH is controlled to be 5-9, for example 5, 6, 7, 8, 9 or any of the above values; controlling the solution within this pH range can improve the coating effect of the first coating including the phosphorus-containing compound, thereby improving the coating effect of the second coating including the lithium oxide phosphate.

[0039] In a preferred embodiment of the present invention, the salt containing metal ions with stable valence states and capable of generating phosphate precipitates is selected from at least one of niobium ethanol, magnesium acetate, and zinc acetate. Such metal ions can not only optimize the crystal lattice of material particles, but more importantly, they can induce the crystal planes to undergo preferred orientation, providing crystal plane adsorption for the subsequent selective second coating. In a preferred embodiment of the present invention, the phosphate-containing compound is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and tris(2,2,2-trifluoroethyl) phosphite. Preferably, the flow rate of the solution of the phosphate-containing compound added is 0.001 to 0.5 mol / h, for example, 0.001 mol / h, 0.01 mol / h, 0.02 mol / h, 0.04 mol / h, 0.08 mol / h, 0.1 mol / h, 0.2 mol / h, 0.3 mol / h, 0.4 mol / h, 0.5 mol / h, or within any range of the above values. Step (3) involves an induced reaction on the second crystal surface of the lithium nickel manganese oxide obtained in step (2) to generate a second coating comprising lithium oxyphosphate metal lithium.

[0040] Methods for generating a second coating including lithium oxyphosphate metal oxide include: The lithium nickel manganese oxide obtained in step (2) is reacted with a second crystal plane-directed metal hydroxide to generate a second coating including lithium oxyphosphate metal hydroxide on the second crystal plane of the lithium nickel manganese oxide. In a preferred embodiment of the present invention, the method for obtaining the second crystal plane-guided metal hydroxide includes: Add an additive to the second crystal plane-oriented metal salt solution and carry out a solvothermal reaction; preferably, the solvothermal reaction in step (3) is to slowly add the additive to the lithium nickel manganese oxide and the second crystal plane-oriented metal salt solid-liquid mixture obtained in step (2) under stirring and then place it in a high temperature and high pressure reactor and react at 180-260℃ for 4-10 hours. The reaction of the lithium nickel manganese oxide obtained in step (2) with the second crystal plane-directed metal hydroxide includes: calcining at 350-700°C for 4-12 hours in an oxygen atmosphere, and by further controlling the sintering conditions, the lithium phosphate oxide metal hydroxide coatings of the (111), (001), (100), and (110) crystal planes can be uniformly formed without enrichment.

[0041] In a preferred embodiment of the present invention, the second crystal plane-directed metal salt is selected from at least one of titanium sulfate, magnesium sulfate, lanthanum chloride, sodium tungstate, and chromium chloride; the second crystal plane-directed metal and metal ions with stable valence states that can form phosphate precipitates will form a bidirectional adsorption effect, promoting N to fall on inert crystal planes such as (111), (001), (100), and (110); the auxiliary agent is selected from at least one of urea, methylamine, trimethylamine, and tetramethylethylenediamine.

[0042] Based on the above, the embodiments of the present invention firstly generate a first coating layer containing a phosphorus compound on the surface of the material body through self-reaction, and secondly selectively induce the generation of a second coating layer containing lithium oxide phosphate on the inert crystal plane. On the one hand, this self-reacting coating layer can be more deeply integrated with the lithium nickel manganese cathode active material, thereby solving the problem of easy coating peeling off. On the other hand, the generation of a second coating layer containing lithium oxide phosphate on the inert crystal plane can effectively enhance the activity of the inert crystal plane, reduce the interfacial impedance, and effectively reduce the influence of the coating layer on the crystal plane activity.

[0043] The above method, by selectively inducing reactions on certain crystal planes to generate a coating, effectively reduces the low energy density caused by excessively thick coatings, and is economical and practical, reducing the overuse of coating materials.

[0044] Furthermore, the surface of the positive electrode active material provided in this embodiment of the invention is divided into a first coating layer containing a phosphorus compound and a second coating layer containing a lithium metal oxide phosphate. The two surfaces work together to isolate excessive contact with the electrolyte, suppress side reactions, inhibit the degradation of the internal structure of the material, and effectively reduce the influence of the coating layer on the crystal surface activity.

[0045] Furthermore, the secondary battery and power-consuming device of the present invention will be described appropriately below.

[0046] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0047] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes the positive active material of the first aspect of the present invention or the positive active material obtained by the method of the second aspect of the present invention.

[0048] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0049] In some embodiments of the present invention, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0050] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0051] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0052] In some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0053] In some embodiments of the present invention, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present invention is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0054] Electrolytes function to conduct ions between the positive and negative electrode plates. This invention does not impose particular limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0055] In some embodiments of the present invention, the secondary battery further includes a separator. The present invention does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0056] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0057] In this invention, unless otherwise specified, a "cell battery" refers to a basic unit capable of converting chemical energy into electrical energy, and typically includes at least a positive electrode, a negative electrode, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor for the active ions between the positive and negative electrodes.

[0058] The present invention does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0059] Secondary batteries can be battery modules or battery packs.

[0060] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0061] In addition, the present invention also provides an electrical device, which includes the secondary battery provided in the fourth aspect of the present invention. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0062] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0063] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0064] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0065] The following describes embodiments of the present invention. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0066] Example 1 Lithium, nickel and manganese acetates were dissolved in water in a ratio of 2:1:3, and then mixed with 1M aminotriacetic acid solution. The mixture was heated at 80°C for 6 hours to form a gel. The gel was then calcined at 300°C for 4 hours and 900°C for 8 hours. The calcined powder was then ground to obtain the primary positive electrode active material. The primary positive electrode active material was added to a 1M magnesium acetate solution at a solid-liquid ratio of 200 g / L. The solution was heated and stirred at 60°C, and the pH was adjusted to 8 using ammonia. Finally, a tris(2,2,2-trifluoroethyl) phosphite solution was added at a flow rate of 0.02 mol / L to maintain the pH of the system at 8 until the reaction was completed. The reaction system was then separated into solid and liquid phases, washed, and dried to obtain the secondary positive electrode active material. The secondary positive electrode active material was mixed with 0.1M sodium tungstate solution at a solid-liquid ratio of 500 g / L to form a solid-liquid mixture. 0.2 mol of tetramethylethylenediamine was slowly added under stirring and then transferred to a high-temperature and high-pressure reactor. The mixture was subjected to a solvothermal reaction at 220°C for 4 h. After the reaction was completed, the mixture was washed and dried, and then calcined at 350°C for 4 h under an oxygen atmosphere to obtain the positive electrode active material.

[0067] Depend on Figures 1 to 3 It can be seen that the positive electrode active material obtained in this application includes lithium nickel manganese oxide containing the XXXX phase, further combined with Figures 4 to 8 It can be observed that a first coating layer containing phosphorus compounds is formed on the (011), (101) and (010) crystal planes, while a second coating layer containing lithium oxyphosphate is formed on the (111), (001), (100) or (110) crystal planes.

[0068] Example 2 Lithium, nickel and manganese acetates were dissolved in water in a ratio of 5:1:9, and then mixed with 2M glycolic acid solution. The mixture was heated at 70°C for 7 hours to form a gel. The gel was then calcined at 330°C for 4 hours and 880°C for 8 hours. The calcined powder was then ground to obtain the primary positive electrode active material. The primary positive electrode active material was added to a 1M zinc acetate solution at a solid-liquid ratio of 250 g / L. The solution was heated and stirred at 60°C, and the pH was adjusted to 7 using ammonium citrate. Finally, ammonium dihydrogen phosphate solution was added at a flow rate of 0.04 mol / L to maintain the pH of the system at 7 until the reaction was completed. The reaction system was then separated into solid and liquid phases, washed, and dried to obtain the secondary positive electrode active material. The secondary positive electrode active material was mixed with 0.1M chromium chloride solution at a solid-liquid ratio of 550 g / L to form a solid-liquid mixture. 0.1 mol of methylamine was slowly added under stirring and then transferred to a high-temperature and high-pressure reactor. The mixture was subjected to a solvothermal reaction at 220°C for 4 h. After the reaction was completed, the mixture was washed and dried, and then calcined at 350°C for 4 h under an oxygen atmosphere to obtain the positive electrode active material.

[0069] Example 3 Lithium, nickel and manganese acetates were dissolved in water in a ratio of 1:1:1, and then mixed with a 1.5M aminotriacetic acid solution. The mixture was heated at 80°C for 6 hours to form a gel. The gel was then calcined at 300°C for 4 hours and at 600°C for 8 hours. The calcined powder was then ground to obtain the primary positive electrode active material. The primary positive electrode active material was added to a 0.5M niobium ethanol solution at a solid-liquid ratio of 230 g / L. The solution was heated and stirred at 60°C, and the pH was adjusted to 7.5 using ammonium acetate. Finally, a tris(2,2,2-trifluoroethyl) phosphite solution was added at a flow rate of 0.02 mol / L to maintain the pH of the system at 7.5 until the reaction was completed. The reaction system was then separated into solid and liquid phases, washed, and dried to obtain the secondary positive electrode active material. The secondary positive electrode active material was mixed with 0.1M titanium sulfate solution at a solid-liquid ratio of 450 g / L to form a solid-liquid mixture. 0.05 mol of trimethylamine was slowly added under stirring and then transferred to a high-temperature and high-pressure reactor. The mixture was subjected to a solvothermal reaction at 280°C for 4 h. After the reaction was completed, the mixture was washed and dried, and then calcined at 450°C for 4 h under an oxygen atmosphere to obtain the positive electrode active material.

[0070] Comparative Example 1 This comparative example only formed a phosphorus-containing compound coating, and did not induce the formation of a lithium phosphate oxide coating; Similar to Example 1, only the secondary positive electrode active material was obtained, and then sintering was performed: Lithium, nickel and manganese acetates were dissolved in water in a ratio of 2:1:3, and then mixed with 1M aminotriacetic acid solution. The mixture was heated at 80°C for 6 hours to form a gel. The gel was then calcined at 300°C for 4 hours and 900°C for 8 hours. The calcined powder was then ground to obtain the primary positive electrode active material. The primary positive electrode active material was added to a 1M magnesium acetate solution at a solid-liquid ratio of 200 g / L. The solution was heated and stirred at 60°C, and the pH was adjusted to 8 using ammonia. Finally, a tris(2,2,2-trifluoroethyl) phosphite solution was added at a flow rate of 0.02 mol / L to maintain the pH of the system at 8 until the reaction was completed. The reaction system was then separated into solid and liquid phases, washed, and dried to obtain the secondary positive electrode active material. The secondary positive electrode active material was calcined at 350°C for 4 hours in an oxygen atmosphere to obtain the positive electrode active material.

[0071] Test case 1) X-ray diffraction analysis and testing Following the general rules of X-ray diffraction analysis in JIS K0131-1996, X-ray diffraction patterns of positive electrode active materials were determined using X-ray diffraction. A Bruker D8 Advance XRD instrument was used, and the XRD analysis conditions were: Cu target, scanning voltage 40 kV, current 40 mA, and scanning range 15°–71°.

[0072] 2) Morphological testing The morphology of the positive electrode active material was tested using a scanning electron microscope (Hitachi brand, SU8230) and a transmission electron microscope (Hitachi brand, HT7800).

[0073] 3) Loop testing A coin cell battery was constructed by combining lithium nickel manganese oxide cathode material and graphite anode material. Under 25°C conditions, it was charged at a constant current rate of 0.5C to 4.85V, and then charged at a constant voltage rate of 4.85V until the current equals 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 0.5C to 3.5V. This cycle test was repeated 100 times, and the capacity retention rate after 100 cycles was calculated.

[0074] See Figure 9 Comparing Example 1 with Comparative Example 1, it can be seen that the capacity retention rate (93.6%) of the positive electrode active material provided in this application after 100 cycles is much higher than that of the comparative example (89.5%).

[0075] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of the present invention can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or the background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that, include: Lithium nickel manganese oxide; as well as A first coating comprising a phosphorus-containing compound is disposed on the first crystal surface of the lithium nickel manganese oxide; A second coating comprising lithium oxide phosphate is disposed on the second crystal plane of the lithium nickel manganese oxide; The first crystal plane includes at least one of (011), (101), or (010) crystal planes; The second crystal plane includes at least one of (111), (001), (100) or (110) crystal planes.

2. The positive electrode active material according to claim 1, characterized in that, The phosphorus content in the phosphorus-containing compound is between 200 ppm and 5000 ppm; and / or The lithium phosphate metal compound contains a metal element selected from at least one of titanium, magnesium, lanthanum, tungsten, and chromium; and / or The first coating has a thickness of 1 nm to 100 nm; and / or The second coating has a thickness of 1 nm to 100 nm.

3. A method for preparing the positive electrode active material according to claim 1 or 2, characterized in that, Includes the following steps: Step (1): Obtain lithium nickel manganese oxide; Step (2): A first coating layer comprising a phosphorus-containing compound is formed on the first and second crystal planes of the lithium nickel manganese oxide in step (1); Step (3) involves an induced reaction on the second crystal surface of the lithium nickel manganese oxide obtained in step (2) to generate a second coating comprising lithium oxyphosphate metal lithium.

4. The method for preparing the positive electrode active material according to claim 3, characterized in that, The method for obtaining the lithium nickel manganese oxide includes: Lithium, nickel, and manganese source solutions are mixed with a kneading agent and reacted under heating conditions to form a gel. The gel was calcined to obtain lithium nickel manganese oxide.

5. The method for preparing the positive electrode active material according to claim 4, characterized in that, The lithium source is selected from at least one of lithium acetate, lithium oxalate, or lithium carbonate; the nickel source is selected from at least one of nickel acetate, nickel oxalate, or nickel carbonate; and the manganese source is selected from at least one of manganese acetate, manganese oxalate, or manganese carbonate.

6. The method for preparing the positive electrode active material according to claim 4, characterized in that, The blending agent is selected from at least one of aminotriacetic acid or glycolic acid.

7. The method for preparing the positive electrode active material according to claim 3, characterized in that, The method for generating the first coating comprising the phosphorus-containing compound includes: The lithium nickel manganese oxide obtained in step (1) is added to a salt solution containing metal ions with stable valence states that can form phosphate precipitates; A solution containing a phosphate compound is then added to react with the lithium nickel manganese oxide to form a first coating containing a phosphorus compound on the first and second crystal faces.

8. The method for preparing the positive electrode active material according to claim 7, characterized in that, The salt containing metal ions with stable valence states that can form phosphate precipitates is selected from at least one of niobium ethanol, magnesium acetate, and zinc acetate.

9. The method for preparing the positive electrode active material according to claim 7, characterized in that, The phosphate-containing compound is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and tris(2,2,2-trifluoroethyl) phosphite.

10. The method for preparing the positive electrode active material according to claim 3, characterized in that, Methods for generating a second coating including lithium oxyphosphate metal oxide include: The lithium nickel manganese oxide obtained in step (2) is reacted with a second crystal plane-directed metal hydroxide to generate a second coating including lithium oxyphosphate on the second crystal plane of the lithium nickel manganese oxide.

11. The method for preparing the positive electrode active material according to claim 10, characterized in that, The method for obtaining the second crystal plane-guided metal hydroxide includes: Additives are added to a second crystal plane-oriented metal salt solution and a solvothermal reaction is carried out.

12. The method for preparing the positive electrode active material according to claim 11, characterized in that, The second crystal plane-directed metal salt is selected from at least one of titanium sulfate, magnesium sulfate, lanthanum chloride, sodium tungstate, and chromium chloride; the auxiliary agent is selected from at least one of urea, methylamine, trimethylamine, and tetramethylethylenediamine.

13. A positive electrode plate, characterized in that, It includes a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1-2 or the positive electrode active material prepared by any one of claims 3-12.

14. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 13.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 14.

Images