Positive electrode active material and preparation method and application thereof

Abstract

The invention provides a positive active material as well as a preparation method and application thereof. The positive active material comprises a positive base material, a transition layer and a coating layer, the transition layer is coated on the surface of the positive electrode base material, and the coating layer is coated on the surface of the transition layer; the surface smoothness of the positive electrode active material is greater than 95%; the positive electrode base material comprises a manganese element; the chemical formula of the coating layer is Li < 1 > Al < 1 > (P < O < 4-delta > F < 2 delta >) < c > F < d > < 1 >; the transition layer has the chemical composition of Li < 2 > Ni < x > < 1 > Co < y > < 1 > Mn < z > < 1 > MeFe < f > Al < 2 > P < c > < 2 > F < d > < 2 > O < g >. The positive electrode active material provided by the invention comprises the positive electrode base material, the transition layer and the coating layer, the surface smoothness of the positive electrode active material is limited, and when the positive electrode active material is applied to the lithium ion battery, the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a positive electrode active material, its preparation method and application. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic products, and artificial intelligence machines, the lithium battery market is placing higher demands on the development of energy storage devices with high energy density. Typically, the energy density of lithium-ion batteries is determined by high specific capacity and high voltage cathode active materials, such as 5V-level spinel LiNi. 0.5 Mn 1.5 O4 (LNMO) can provide a specific capacity of 650 Wh / kg, thus improving the energy density of lithium-ion batteries. However, during cycling, LNMO has poor stability and is prone to interfacial side reactions with the electrolyte. In addition, electrolyte decomposition products can form a CEI film on the positive electrode surface, increasing the battery impedance.

[0003] To address these issues, surface coating is commonly used to modify LNMO cathode active materials. Conventional coating agents include metal oxides (such as Al₂O₃, ZrO₂, TiO₂, etc.), fluorides (such as LiF, AlF₃, NH₄F, etc.), phosphates (such as FePO₄, Li₃PO₄, etc.), polymers, and fast ion conductors. However, traditional coating methods often suffer from uneven and non-dense coating, failing to completely cover the surface of the cathode active material. This leads to rapid damage to the coating layer during cycling, further exacerbating the degradation of the transition metal Mn. 2+ Dissolution causes continuous capacity decay, leading to poorer cycle stability of the battery. Summary of the Invention

[0004] The main objective of this invention is to provide a positive electrode active material that, when applied to lithium-ion batteries, can improve the cycle performance of lithium-ion batteries.

[0005] The present invention also provides a method for preparing a positive electrode active material, which can prepare the above-mentioned positive electrode active material, and the process is simple and low in cost.

[0006] The present invention also provides a positive electrode sheet, which, since it includes the above-mentioned positive electrode active material, can improve the cycle performance of lithium-ion batteries when used in lithium-ion batteries.

[0007] The present invention also provides a lithium-ion battery, which has excellent cycle performance because it includes the above-mentioned positive electrode plate.

[0008] In a first aspect, the present invention provides a positive electrode active material, comprising a positive electrode substrate material, a transition layer, and a coating layer; wherein the transition layer coats the surface of the positive electrode substrate material, and the coating layer coats the surface of the transition layer;

[0009] The surface smoothness of the positive electrode active material is >95%;

[0010] The positive electrode substrate material includes manganese.

[0011] The chemical formula of the coating layer is Li. a1 Al b1 (PO 4-δ F 2δ ) c1 F d1 Where, 0≤a1≤1.0, 0.001≤b1≤0.2, 0.01≤c1≤0.5, 0.01≤d1≤0.5, 0.01≤δ≤0.2, d1=a1+3b1-3c1;

[0012] The chemical formula of the transition layer is Li. a2 Ni x1 Co y1 Mn z1 M e Fe f Al b2 P c2 F d2 O g , 0.95≤a2≤1.20, 0≤x1≤0.95, 0≤y1≤0.25, 0.05≤z1≤1.60, 0.001≤e≤0.02, 0≤f≤0.65, 1.5≤g≤4.5, 0.001≤b2≤0.1, 0.01≤c2≤1.2, 0.005≤d2≤0.1, M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

[0013] For the positive electrode active material as described above, b2≤b1, d2≤d1;

[0014] c2>1, c2-1≤c1; c2<1, c2≤c1.

[0015] In the positive electrode active material described above, the coating layer accounts for 0.5-3.0% of the mass fraction of the positive electrode active material;

[0016] The transition layer accounts for 0.05-1.0% of the mass fraction of the positive electrode active material.

[0017] In the positive electrode active material described above, the thickness ratio of the coating layer to the transition layer is 1:0.01-0.5;

[0018] And / or, the thickness of the coating layer is 5-30 nm; the thickness of the transition layer is 0.5-10 nm.

[0019] The positive electrode active material as described above, wherein the positive electrode substrate material is a single crystal material, and the average particle size of the positive electrode substrate material is 0.2-20 μm;

[0020] Alternatively, the positive electrode substrate material is a polycrystalline material, and the average particle size of the positive electrode substrate material is 3-50 μm.

[0021] The positive electrode active material as described above, wherein the positive electrode matrix material includes LiNi 0.5 Mn 1.5-x M x O4, LiMn 2-x M x O4, LiMn 0.6-x Fe 0.4 M x PO4, Li(Ni) y Co z Mn 1-y-z ) 1-x M x At least one of O2; wherein 0.001≤x≤0.050, 0.50≤y≤0.095, 0.001≤z≤0.02, and M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

[0022] Secondly, the present invention provides a method for preparing the positive electrode active material as described above, comprising the following steps:

[0023] After nano-sizing of aluminum, phosphorus, and fluorine sources, they are mixed with the positive electrode matrix material to obtain a mixed system. The mixed system is then sintered at 700-1000℃ for 5-10 hours to obtain the positive electrode active material.

[0024] In the preparation method described above, the mass ratio of the positive electrode substrate material to the total mass of the aluminum source, phosphorus source, and fluorine source is 1:0.01-0.5;

[0025] And / or, the mass ratio of the aluminum source, phosphorus source, and fluorine source is 1:0.3-15:0.2-5.

[0026] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material as described above or the positive electrode active material prepared by the preparation method described above.

[0027] Fourthly, the present invention provides a lithium-ion battery, comprising the positive electrode sheet as described above.

[0028] The positive electrode active material provided by this invention includes a positive electrode substrate material, a transition layer, and a coating layer. The surface smoothness of the positive electrode active material is limited to achieve complete and uniform coating of the positive electrode substrate material by the coating layer, suppressing direct contact between the positive electrode substrate material and the electrolyte, reducing the occurrence of interfacial side reactions, and enhancing the structural and interfacial stability of the material. When applied to lithium-ion batteries, it can improve the cycle performance of lithium-ion batteries. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 Here is a SEM image of the positive electrode active material prepared in Example 1;

[0031] Figure 2 Here is a SEM image of the positive electrode active material prepared in Example 3;

[0032] Figure 3 Here is a SEM image of the positive electrode active material prepared in Example 9;

[0033] Figure 4 SEM image of the positive electrode active material prepared in Example 11;

[0034] Figure 5 Here is a SEM image of the positive electrode active material prepared in Comparative Example 1;

[0035] Figure 6 Here is a SEM image of the positive electrode active material prepared in Comparative Example 2;

[0036] Figure 7 Here is a SEM image of the positive electrode active material prepared in Comparative Example 3;

[0037] Figure 8 Here is a SEM image of the positive electrode active material prepared in Comparative Example 4;

[0038] Figure 9 Here is a SEM image of the positive electrode active material prepared in Comparative Example 5;

[0039] Figure 10Here is a SEM image of the positive electrode active material prepared in Comparative Example 11;

[0040] Figure 11 The image shows the SEM image of the positive electrode active material prepared in Comparative Example 12. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] In a first aspect, the present invention provides a positive electrode active material, comprising a positive electrode substrate material, a transition layer, and a coating layer; wherein the transition layer coats the surface of the positive electrode substrate material, and the coating layer coats the surface of the transition layer;

[0043] The surface smoothness of the positive electrode active material is >95%;

[0044] The positive electrode substrate material includes manganese.

[0045] The chemical formula of the coating layer is Li. a1 Al b1 (PO 4-δ F 2δ ) c1 F d1 Where, 0≤a1≤1.0, 0.001≤b1≤0.2, 0.01≤c1≤0.5, 0.01≤d1≤0.5, 0.01≤δ≤0.2, d1=a1+3b1-3c1;

[0046] The chemical formula of the transition layer is Li. a2 Ni x1 Co y1 Mn z1 M e Fe f Al b2 P c2 F d2 O g, 0.95≤a2≤1.20, 0≤x1≤0.95, 0≤y1≤0.25, 0.05≤z1≤1.60, 0.001≤e≤0.02, 0≤f≤0.65, 1.5≤g≤4.5, 0.001≤b2≤0.1, 0.01≤c2≤1.2, 0.005≤d2≤0.1, M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

[0047] The positive electrode active material provided by this invention includes a positive electrode substrate material, a transition layer, and a coating layer. The transition layer is formed by the mutual diffusion and infiltration of the positive electrode substrate material and the coating layer. Therefore, the transition layer coats the surface of the positive electrode substrate material, and the coating layer coats the surface of the transition layer, achieving a high degree of surface coating on the positive electrode substrate material. In this invention, the surface smoothness of the positive electrode active material is >95%, indicating a high degree of interfacial bonding between the coating layer and the positive electrode substrate material, which can completely encapsulate the surface of the positive electrode substrate material, thereby achieving a uniform and dense coating effect.

[0048] As can be seen from the chemical formulas of the coating layer and transition layer of the positive electrode active material of the present invention, the coating layer and transition layer simultaneously include three elements: aluminum, phosphorus, and fluorine. Therefore, the positive electrode active material simultaneously combines the protective ability of the alumina inert layer, the conductivity of phosphate, and the HF corrosion resistance of fluoride. It can not only inhibit the contact between the positive electrode substrate material and the electrolyte, but also reduce the surface Mn content. 3+ The formation of fluorine reduces the occurrence of interfacial side reactions and promotes the diffusion of lithium ions. In addition, fluorine can combine with oxygen in phosphate at high temperatures, and will not cause a decrease in capacity due to the consumption of oxygen in the positive electrode matrix material. Therefore, it can enhance the structural stability and interfacial stability of the positive electrode active material and effectively improve the cycle performance of the positive electrode active material.

[0049] The present invention does not limit the test method for surface smoothness. For example, a scanning electron microscope can be used to test it at an accelerating voltage of 5kV, a magnification of 50K, and a working distance of 8.1mm. The surface smoothness is the area of ​​non-point-like coatings on the surface of the positive electrode active material divided by the field of view area at this magnification.

[0050] The positive electrode active material provided by this invention includes a positive electrode substrate material, a transition layer, and a coating layer. The surface smoothness of the positive electrode active material is limited to achieve complete and uniform coating of the positive electrode substrate material by the coating layer. This suppresses direct contact between the positive electrode substrate material and the electrolyte, avoids agglomeration and segregation of the coating layer, reduces the specific surface area of ​​the positive electrode active material, thereby reducing the contact area between the positive electrode active material and the electrolyte, reducing the occurrence of interfacial side reactions, and enhancing the structural and interfacial stability of the material. When applied to lithium-ion batteries, it can improve the cycle performance of lithium-ion batteries.

[0051] In some embodiments of the present invention, b2≤b1, d2≤d1;

[0052] c2>1, c2-1≤c1; c2<1, c2≤c1.

[0053] Where c2>1 represents the case where the cathode substrate material includes phosphorus (P), for example, if the cathode substrate material is lithium manganese iron phosphate, the remaining P content in the transition layer after removing the P from the cathode substrate material is less than or equal to the P content in the coating layer, i.e., c2-1≤c1. Where c2<1 represents the case where the cathode substrate material does not include P, the P content in the transition layer is less than or equal to the P content in the coating layer, i.e., c2≤c1.

[0054] As defined above, aluminum, phosphorus, and fluorine are incorporated into the surface of the cathode substrate material in decreasing concentration order, from the coating layer to the transition layer. The high concentration of doped elements on the surface forms a dense and uniform coating layer, improving the interfacial stability of the cathode active material, effectively inhibiting HF corrosion in the electrolyte, and reducing the oxidative decomposition of the electrolyte and the degradation of the transition metal Mn. 2+ The leaching of [something] can improve the cycle performance of the battery.

[0055] In some embodiments of the present invention, the coating layer accounts for 0.5-3.0% of the mass fraction of the positive electrode active material;

[0056] The transition layer accounts for 0.05-1.0% of the mass fraction of the positive electrode active material.

[0057] In this invention, the mass fraction of the coating layer and the mass fraction of the transition layer in the positive electrode active material are within a suitable range. This allows the transition layer and the coating layer to completely coat the positive electrode substrate material, suppressing the contact between the positive electrode substrate material and the electrolyte, reducing the occurrence of interfacial side reactions, improving the structural and interfacial stability of the positive electrode active material, and thus improving the cycle stability of the lithium-ion battery. It also allows the positive electrode active material to fully utilize its capacity performance, thereby increasing the energy density of the lithium-ion battery.

[0058] In some embodiments of the present invention, the thickness ratio of the covering layer to the transition layer is 1:0.01-0.5;

[0059] And / or, the thickness of the coating layer is 5-30 nm; the thickness of the transition layer is 0.5-10 nm.

[0060] It is understood that the thickness ratio of the coating layer to the transition layer, as well as the thickness of the coating layer and the transition layer, will affect the electronic conductivity of the positive electrode active material to a certain extent, thereby affecting the cycle performance of the lithium-ion battery. The coating layer and the transition layer in this invention have suitable thicknesses and thickness ratios, which can balance the conduction of electrons and ions.

[0061] In one embodiment, the thickness ratio of the coating layer to the transition layer is controlled to be 1:0.01-0.5, the thickness of the coating layer is 5-30 nm, and the thickness of the transition layer is 0.5-10 nm, within a suitable range. Suitable thickness and thickness ratio can suppress particle growth and reduce the diffusion distance of lithium ions. Furthermore, suitable thickness and thickness ratio provide excellent conductivity, which is beneficial for electron transport and improves the electronic conductivity of the positive electrode active material, thereby improving the cycle performance of the battery.

[0062] The present invention does not limit the testing method for the coating layer and transition layer thickness. For example, the thickness of the coating layer and transition layer of the positive electrode active material can be obtained by measuring the thickness of the coating layer and transition layer in a transmission electron microscope.

[0063] In some embodiments of the present invention, the positive electrode substrate material is a single crystal material, and the average particle size of the positive electrode substrate material is 0.2-20 μm;

[0064] Alternatively, the positive electrode substrate material is a polycrystalline material, and the average particle size of the positive electrode substrate material is 3-50 μm.

[0065] When the cathode substrate material in this invention is a single-crystal material, the average particle size of the cathode substrate material is controlled to be 0.2-20 μm; when the cathode substrate material in this invention is a polycrystalline material, the average particle size of the cathode substrate material is controlled to be 3-50 μm. This can shorten the diffusion path of lithium ions inside the cathode active material, thereby increasing the diffusion rate of lithium ions and improving the rate performance of the battery. In addition, an appropriate average particle size can reduce the volume change of the cathode active material during charging and discharging, thereby improving the cycle stability of the lithium-ion battery.

[0066] In some embodiments of the present invention, the positive electrode substrate material includes LiNi. 0.5 Mn 1.5-x M x O4, LiMn 2- x M x O4, LiMn0.6-x Fe 0.4 M x PO4, Li(Ni) y Co z Mn 1-y-z ) 1-x M x At least one of O2; wherein 0.001≤x≤0.050, 0.50≤y≤0.095, 0.001≤z≤0.02, and M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

[0067] The cathode matrix materials of the present invention all include a dopant element M in lithium nickel manganese oxide, lithium manganese oxide, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide. The dopant element M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S. These transition metal elements have a strong dispersing effect on the cathode matrix material, which can reduce the adhesion of primary grains and facilitate subsequent coating treatment of the dispersed material particles. This allows the coated cathode active material to be used in lithium-ion batteries, thereby improving the cycle performance of lithium-ion batteries.

[0068] Secondly, the present invention provides a method for preparing the positive electrode active material as described above, comprising the following steps:

[0069] After nano-sizing of aluminum, phosphorus, and fluorine sources, they are mixed with the positive electrode matrix material to obtain a mixed system. The mixed system is then sintered at 700-1000℃ for 5-10 hours to obtain the positive electrode active material.

[0070] In the preparation method of the positive electrode active material of the present invention, aluminum source, phosphorus source, and fluorine source can be nano-sized by air jet milling or sand milling, and then mixed with positive electrode matrix material to obtain a mixed system. The mixed system is then sintered at a temperature of 700-1000℃, preferably 750-950℃, for a sintering time of 1-15h, preferably 5-10h. Nano-sized aluminum, phosphorus, and fluorine sources result in more uniform coating and are less prone to agglomeration or segregation. If sintering is performed at a low temperature, such as below 700℃, the aluminum, phosphorus, and fluorine sources will not completely melt, resulting in a large number of fine particles distributed on the surface of the positive electrode matrix material. This leads to low surface smoothness of the positive electrode active material, increasing its specific surface area and the contact area between the positive electrode active material and the electrolyte, thereby reducing the surface stability of the positive electrode active material. In this invention, high-temperature sintering is used, with a sintering temperature of 700-1000℃. The aluminum source, phosphorus source, and fluorine source can be completely melted, and the surface smoothness of the positive electrode active material is greater than 95%, thereby reducing the specific surface area of ​​the positive electrode active material.

[0071] Aluminum and phosphorus are both low-melting-point elements. During high-temperature sintering, they can form low-melting-point substances together with fluorine, coating the surface of the cathode substrate material. Some of the coating material is incorporated into the material surface, thus forming a complete and uniform coating layer. At high temperatures, the aluminum, phosphorus, and fluorine sources completely melt and spread across the entire surface of the cathode substrate material. They do not form agglomerates or exist as dot-like coatings on the cathode substrate material, but rather are incorporated into the surface interface of the cathode substrate material in a concentration gradient, achieving a dense and uniform coating effect. This may be because the ionic radii of aluminum and fluorine are similar to those of nickel and manganese, and the phosphate ions in phosphate can form strong covalent bonds with nickel and manganese ions. Therefore, at high temperatures, aluminum, phosphorus, and fluorine elements penetrate into the surface of the cathode substrate material in a decreasing concentration gradient manner. The high concentration of doped elements on the surface is sufficient to form a dense and uniform coating layer, improving the interfacial stability of the cathode active material, effectively hindering the corrosion of HF in the electrolyte, and reducing the oxidative decomposition of the electrolyte and the transition metal Mn. 2+ The dissolution of [something] improves the cycle performance of the battery.

[0072] The aluminum source is mainly an aluminum-containing compound, such as at least one of aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum silicate, aluminum sulfide, sodium aluminate, aluminum titanate, aluminum stearate, and alum, preferably at least one of aluminum oxide and aluminum hydroxide.

[0073] The phosphorus source is mainly a phosphorus-containing compound, such as at least one of phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, magnesium phosphate, calcium phosphate, iron phosphate, copper phosphate, zinc phosphate, titanium phosphate, zirconium phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, pyrophosphate, lithium pyrophosphate, sodium pyrophosphate, magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, copper pyrophosphate, zinc pyrophosphate, titanium pyrophosphate, zirconium pyrophosphate, nickel pyrophosphate, cobalt pyrophosphate, manganese pyrophosphate, elemental phosphorus, phosphorus pentoxide, lithium iron phosphate, and phosphate esters, preferably at least one of lithium phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium pyrophosphate, nickel phosphate, and manganese phosphate.

[0074] The fluorine source is primarily a fluorine-containing compound, such as at least one of lithium fluoride, hydrogen fluoride, ammonium fluoride, sodium fluoride, copper fluoride, cerium fluoride, lanthanum fluoride, cobalt fluoride, manganese fluoride, nickel fluoride, and polytetrafluoroethylene. Preferably, it is at least one of lithium fluoride and ammonium fluoride.

[0075] The aluminum source, phosphorus source, and fluorine source can also be at least one of Al-PF compounds, such as aluminum fluoride, sodium hexafluoroaluminate, fluoroaluminate, aluminum phosphate, aluminum monohydrogen phosphate, aluminum dihydrogen phosphate, aluminum tripolyphosphate, and lithium difluorophosphate. Preferably, it is at least one of aluminum fluoride, aluminum phosphate, aluminum tripolyphosphate, and lithium difluorophosphate.

[0076] It should be noted that when the aluminum, phosphorus, or fluorine source does not contain lithium, the capacity of the prepared positive electrode active material will decrease slightly. This is because some phosphate ions will combine with lithium in the positive electrode matrix material to form a stable lithium phosphate phase, which will cause some lithium in the positive electrode matrix material to be consumed, resulting in lithium loss during the charging and discharging process and causing a decrease in capacity.

[0077] The preparation method provided by the present invention can prepare the positive electrode active material of the first aspect mentioned above, and the positive electrode active material can be applied to lithium-ion batteries to improve the cycle performance of lithium-ion batteries.

[0078] In some embodiments of the present invention, the mass ratio of the positive electrode substrate material to the total mass of the aluminum source, phosphorus source, and fluorine source is 1:0.01-0.5;

[0079] And / or, the mass ratio of the aluminum source, phosphorus source, and fluorine source is 1:0.3-15:0.2-5.

[0080] This invention controls the mass ratio of the positive electrode substrate material to the total mass of the aluminum, phosphorus, and fluorine sources. By keeping the mass ratio of the aluminum, phosphorus, and fluorine sources within a suitable range, a coating layer and a transition layer with appropriate mass proportions can be obtained. Furthermore, the coating layer and the transition layer can have suitable thicknesses, thereby achieving complete coating of the positive electrode substrate material by the transition layer and the coating layer. This suppresses the contact between the positive electrode substrate material and the electrolyte, reduces the occurrence of interfacial side reactions, improves the structural stability and interfacial stability of the positive electrode active material, and ultimately improves the cycle stability of the lithium-ion battery.

[0081] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material as described above or the positive electrode active material prepared by the preparation method described above.

[0082] The positive electrode sheet of the present invention can be prepared using conventional techniques in the art. Specifically, the above-mentioned positive electrode active material, conductive agent and binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry. Then, the positive electrode active layer slurry is coated on at least one functional surface of the positive electrode current collector, and after drying, the positive electrode sheet of the present invention can be obtained.

[0083] This invention does not specifically limit the types of conductive agents and adhesives. The conductive agents, adhesives and other components can all be conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber and styrene-acrylic rubber.

[0084] The present invention does not specifically limit the coating method, and any coating method such as gravure coating, extrusion coating, spraying, screen printing, etc. can be used to achieve the coating of the positive electrode active layer slurry.

[0085] Since the positive electrode sheet provided by the present invention includes the above-mentioned positive electrode active material, the positive electrode sheet used in lithium-ion batteries can improve the rate performance and cycle performance of lithium-ion batteries.

[0086] Fourthly, the present invention provides a lithium-ion battery, comprising the positive electrode sheet as described above.

[0087] The lithium-ion battery of the present invention includes, in addition to the positive electrode, a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as a PP film or a PE film.

[0088] The lithium-ion battery of the present invention can be prepared using conventional methods in the art. Specifically, the positive electrode, separator and negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding process. Then, the lithium-ion battery can be obtained by baking, liquid injection, formation and packaging.

[0089] Since the lithium-ion battery provided by the present invention includes the above-mentioned positive electrode, the lithium-ion battery has excellent rate performance and cycle performance.

[0090] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0091] Example 1

[0092] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0093] 1000g LiNi 0.5 Mn 1.495 Nb 0.004 O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.6 Al 0.02 (PO 3.95 F 0.1 ) 0.2 F 0.06 The chemical composition of the transition layer is Li 1.046 Ni 0.48 Mn 1.44 Nb 0.004 Al 0.01 P 0.04 F 0.02 O 3.99 The chemical composition of the cathode active material is as follows: the molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.51% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.22%. The coating layer has a thickness of 18 nm, the transition layer has a thickness of 2.5 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.14. The positive electrode substrate material is a single crystal material with a particle size of 8 μm.

[0094] Example 2

[0095] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0096] 1000g Li 1.03 Ni 0.5 Mn 1.48 Nb 0.01O4, 2.8g LiF, 10.4g Al2O3, and 18g Li3PO4 (Al2O3 and Li3PO4 were both treated with an air jet mill for 3 hours and passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0312, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:0.87:0.37. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.2 Al 0.12 (PO 3.98 F 0.04 ) 0.1 F 0.26 The chemical composition of the transition layer is Li. 1.038 Ni 0.44 Mn 1.423 Nb 0.01 Al 0.08 P 0.02 F 0.0 2O 3.99 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.90% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.32%. The coating layer has a thickness of 20 nm, the transition layer has a thickness of 4 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.2. The positive electrode substrate material is a single-crystal material with a particle size of 6 μm.

[0097] Example 3

[0098] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0099] 1000g Li 1.06 Ni 0.48 Mn 1.485 Nb 0.008 O4, 10.2g AlF3, and 18.5g LiH2PO4 (AlF3 and LiH2PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0287, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:1.68:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.1 Al 0.09 (PO 3.90 F 0.2 ) 0.08 F 0.13 Chemical composition, the chemical formula of the transition layer is Li 1.07 Ni 0.425Mn 1.47 Nb 0.008 Al 0.03 P 0.05 F 0.08 O 3. 96 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.33% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.39%. The coating layer has a thickness of 19.5 nm, the transition layer has a thickness of 4 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.205. The positive electrode substrate material is a polycrystalline material with a particle size of 12 μm.

[0100] Example 4

[0101] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0102] 1000g Li 1.07 Ni 0.465 Mn 1.48 Nb 0.016 O4, 10g LiPO2F2, and 10g Al2O3 (both LiPO2F2 and Al2O3 were treated with an air jet mill for 3 hours and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.02, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:0.54:0.67. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.08 Al 0.11 (PO 3.93 F 0.14 ) 0.05 F 0.26 The chemical composition of the transition layer is Li. 1.074 Ni 0.44 Mn 1.394 Nb 0.016 Al 0.08 P 0.03 F 0.06 O 3.97 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.01% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.43%. The coating layer has a thickness of 17.6 nm, the transition layer has a thickness of 3.5 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.2. The positive electrode substrate is a polycrystalline material with a particle size of 15 μm.

[0103] Example 5

[0104] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0105] 1000g LiNi 0.5 Mn 1.497 Nb 0.004 O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 850℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.4 Al 0.018 (PO 3.95 F 0.1 ) 0.15 F 0.04 The chemical composition of the transition layer is Li 1.048 Ni 0.441 Mn 1.435 Nb 0.004 Al 0.02 P 0.05 F 0.02 O 3.99 The chemical composition of the cathode active material is as follows: the molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.84% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.28%. The coating layer has a thickness of 17.8 nm, the transition layer has a thickness of 3.2 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.18. The positive electrode substrate material is a single crystal material with a particle size of 8 μm.

[0106] Example 6

[0107] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0108] 1000g LiNi 0.5 Mn 1.497 Nb 0.004 O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 950℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.16 Al 0.008 (PO 3.90F 0.2 ) 0.06 F 0.004， The chemical composition of the transition layer is Li. 1.2 Ni 0.38 Mn 1.34 Nb 0.004 Al 0.06 P 0.08 F 0.06 O 3.97 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 0.72% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.95%. The coating layer has a thickness of 11.6 nm, and the transition layer has a thickness of 13.8 nm, with a thickness ratio of 1:1.19. The positive electrode substrate material is a single-crystal material with a particle size of 8 μm.

[0109] Example 7

[0110] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0111] 1000g LiNi 0.5 Mn 1.497 Nb 0.004 O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 6 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.62 Al 0.025 (PO 3.96 F 0.08 ) 0.22 F 0.03 The chemical composition of the transition layer is Li. 1.034 Ni 0.49 Mn 1.448 Nb 0.004 Al 0.008 P 0.03 F 0.01 O 3.995 In this process, the molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.67% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.16%. The coating layer has a thickness of 18.6 nm, the transition layer has a thickness of 2.5 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.13. The positive electrode substrate material is a single-crystal material with a particle size of 8 μm.

[0112] Example 8

[0113] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0114] 1000g LiNi 0.5 Mn 1.497 Nb 0.004 O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 10 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.56 Al 0.018 (PO 3.94 F 0.12 ) 0.2 F 0.014 The chemical composition of the transition layer is Li. 1.05 Ni 0.476 Mn 1.4255 Nb 0.004 Al 0.012 P 0.048 F 0.04 O 3.98 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.39% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.29%. The coating layer has a thickness of 17.5 nm, the transition layer has a thickness of 3.3 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.19. The positive electrode substrate material is a single-crystal material with a particle size of 8 μm.

[0115] Example 9

[0116] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0117] 1000g Li 1.01 Ni 0.49 Mn 1.495 Ta 0.006O4, 5.3g AlF3, and 30.6g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0359, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:4.81:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.62 Al 0.05 (PO 3.96 F 0.08 ) 0.22 F 0.11 The chemical composition of the transition layer is Li. 1.03 Ni 0.48 Mn 1.425 Ta 0.006 Al 0.01 P 0.05 F 0.0 6O 3.97 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.88% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.31%. The coating layer has a thickness of 20.5 nm, the transition layer has a thickness of 3.1 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.15. The positive electrode substrate material is a single-crystal material with a particle size of 6 μm.

[0118] Example 10

[0119] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0120] 1000g Li 1.03 Ni 0.486 Mn 1.477 Ta 0.018 O4, 2.8g LiF, 15g AlH2P3O 10 (LiF, AlH2P3O) 10 After being treated by air jet milling for 3 hours and then sieved through a 10,000-mesh screen, the mixture was thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0178, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:3.44:1.43. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.15 Al 0.04 (PO 3.97 F 0.06 ) 0.08 F 0.03 The chemical composition of the transition layer is Li.1.038 Ni 0.48 Mn 1.402 Ta 0.018 Al 0.018 P 0.05 F 0.02 O 3.99 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.03% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.25%. The coating layer has a thickness of 10.2 nm, the transition layer has a thickness of 0.92 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.088. The positive electrode substrate material is a polycrystalline material with a particle size of 26 μm.

[0121] Example 11

[0122] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0123] 1000g Li 1.02 Ni 0.48 Mn 1.49 Mo 0.01 W 0.01 O4, 6.8g AlF3, and 22.5g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0293, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:2.76:2.12. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Li... 0.5 Al 0.05 (PO 3.95 F 0.1 ) 0.15 F 0.2 The chemical composition of the transition layer is Li. 1.05 Ni 0.465 Mn 1.4 Mo 0.01 W 0.01 Al 0.02 P 0.06 F 0.0 4O 3.98 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.3% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.34%. The coating layer has a thickness of 19.6 nm, the transition layer has a thickness of 4.8 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.24. The positive electrode substrate material is a single-crystal material with a particle size of 4 μm.

[0124] Example 12

[0125] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0126] 1000g Li 0.98 Ni 0.49 Mn 1.507 Mo 0.003 W 0.001 O4, 4.2g NH4F, and 20.8g AlPO4 (NH4F and AlPO4 were milled for 8 hours and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.025, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:1.15:0.58. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Al... 0.12 (PO 3.96 F 0.08 ) 0.1 F 0.06 The chemical composition of the transition layer is Li. 0.98 Ni 0.486 Mn 1.4265 Mo 0.003 W 0.001 Al 0.05 P 0.06 F 0.03 O 3.985 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 1.4% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.38%. The coating layer has a thickness of 16.2 nm, the transition layer has a thickness of 1.9 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.12. The positive electrode substrate material is a single-crystal material with a particle size of 8 μm.

[0127] Example 13

[0128] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0129] 1000g LiNi 0.5 Mn 1.4925 Mo 0.002 W 0.008O4, 6.5g AlF3, and 22.6g NH4H2PO4 (AlF3 and NH4H2PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0291, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:2.91:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The coating layer contains Al... 0.08 (PO 3.98 F 0.04 ) 0.06 F 0.06 The chemical composition of the transition layer is LiNi. 0.492 Mn 1.419 Mo 0.002 W 0.008 Al 0.02 P 0.0 5F 0.04 O 3.98 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 0.90% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.28%. The coating layer has a thickness of 18.5 nm, the transition layer has a thickness of 3.3 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.18. The positive electrode substrate material is a polycrystalline material with a particle size of 8 μm.

[0130] Example 14

[0131] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0132] 1000g LiNi 0.8 Co 0.1 Mn 0.1 O2, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The chemical formula of the coating layer is Li. 0.6 Al 0.02 (PO 3.95 F 0.1 ) 0.2 F 0.06 The chemical formula of the transition layer is Li 1.02 Ni 0.8 Co 0.1 Mn 0.06Al 0.01 P 0.022 F 0.04 O 1.98 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.51% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.18%. The coating layer has a thickness of 16.5 nm, the transition layer has a thickness of 2.5 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.15. The positive electrode substrate material is a polycrystalline material with a particle size of 15 μm.

[0133] Example 15

[0134] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0135] 1000g LiFe 0.4 Mn 0.6 PO4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10,000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The chemical formula of the coating layer is Li. 0.6 Al 0.02 (PO 3.95 F 0.1 ) 0.2 F 0.06 The chemical formula of the transition layer is Li 1.03 Fe 0.4 Mn 0.42 Al 0.01 F 0.06 P 1.06 O 3.97 In this process, the molar amounts of aluminum and fluorine in the transition layer are both less than those in the coating layer, and the difference between the molar amounts of phosphorus in the transition layer and the coating layer is less than 1. The coating layer accounts for 2.51% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.35%. The coating layer has a thickness of 18.8 nm, the transition layer has a thickness of 4 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.21. The positive electrode substrate material is a single-crystal material with a particle size of 6 μm.

[0136] Example 16

[0137] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0138] 1000g LiMn2O4, 2.5g AlF3, and 27.8g Li3PO4 (AlF3 and Li3PO4 were treated in a sand mill for 8 hours, dried, and then passed through a 10000-mesh sieve) were thoroughly mixed and sintered at 750℃ for 8 hours. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:9.17:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained. The chemical formula of the coating layer is Li. 0.6 Al 0.02 (PO 3.95 F 0.1 ) 0.2 F 0.06 The chemical formula of the transition layer is Li 1.05 Mn 1.863 Al 0.01 P 0.08 F 0.04 O 3.98 The molar amounts of aluminum, phosphorus, and fluorine in the transition layer are all less than those in the coating layer. The coating layer accounts for 2.51% of the mass fraction of the positive electrode active material, while the transition layer accounts for 0.39%. The coating layer has a thickness of 26.3 nm, the transition layer has a thickness of 8.5 nm, and the thickness ratio of the coating layer to the transition layer is 1:0.32. The positive electrode substrate material is a polycrystalline material with a particle size of 3 μm.

[0139] Comparative Example 1

[0140] Comparative Example 1 has a chemical composition of LiNi 0.5 Mn 1.5 The lithium nickel manganese oxide positive electrode active material of O4 was not doped with metal ions or coated on the surface.

[0141] Comparative Example 2

[0142] Comparative Example 2 has a chemical composition of LiNi 0.5 Mn 1.947 Nb 0.004 The lithium nickel manganese oxide positive electrode active material of O4 was not surface coated.

[0143] Comparative Example 3

[0144] Comparative Example 3 has a chemical composition of Li 1.01 Ni 0.49 Mn 1.495 Ta 0.006 The lithium nickel manganese oxide positive electrode active material of O4 was not surface coated.

[0145] Comparative Example 4

[0146] Comparative Example 4 has a chemical composition of Li 1.02 Ni0.48 Mn 1.49 Mo 0.01 W 0.01 The lithium nickel manganese oxide positive electrode active material of O4 was not surface coated.

[0147] Comparative Example 5

[0148] The preparation method of the positive electrode active material of Comparative Example 5 includes the following steps:

[0149] 1000g LiNi 0.5 Mn 1.947 Nb 0.004 After thoroughly mixing O4 and 10.4g Al2O3, the mixture was sintered at 500℃ for 10h, and then crushed and sieved to obtain lithium nickel manganese oxide positive electrode active material.

[0150] Comparative Example 6

[0151] The preparation method of the positive electrode active material of Comparative Example 6 includes the following steps:

[0152] 1000g LiNi 0.5 Mn 1.947 Nb 0.004 After thoroughly mixing O4 and 18g Li3PO4, the mixture was sintered at 500℃ for 10h, and then crushed and sieved to obtain lithium nickel manganese oxide positive electrode active material.

[0153] Comparative Example 7

[0154] The preparation method of the positive electrode active material of Comparative Example 7 includes the following steps:

[0155] 1000g LiNi 0.5 Mn 1.947 Nb 0.004 After thoroughly mixing O4 and 2.8g LiF, the mixture was sintered at 500℃ for 10h, and then crushed and sieved to obtain lithium nickel manganese oxide positive electrode active material.

[0156] Comparative Example 8

[0157] The preparation method of the positive electrode active material of Comparative Example 8 includes the following steps:

[0158] 1000g Li 1.01 Ni 0.49 Mn 1.495 Ta 0.006 After thoroughly mixing O4, 10.4g Al2O3, and 18g Li3PO4, the mixture was sintered at 750℃ for 8 hours. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained.

[0159] Comparative Example 9

[0160] The preparation method of the positive electrode active material of Comparative Example 9 includes the following steps:

[0161] 1000g Li 1.01 Ni 0.49 Mn 1.495 Ta 0.006 After thoroughly mixing O4, 2.8g LiF, and 10.4g Al2O3, the mixture was sintered at 750℃ for 8 hours. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained.

[0162] Comparative Example 10

[0163] The preparation method of the positive electrode active material of Comparative Example 10 includes the following steps:

[0164] 1000g Li 1.01 Ni 0.49 Mn 1.495 Ta 0.006 After thoroughly mixing O4 and 6g LiPO2F2, the mixture was sintered at 750℃ for 8 hours. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained.

[0165] Comparative Example 11

[0166] The preparation method of the positive electrode active material of Comparative Example 11 includes the following steps:

[0167] 1000g Li 1.02 Ni 0.48 Mn 1.49 Mo 0.01 W 0.01 O4, 2.5g AlF3, and 27.8g Li3PO4 were thoroughly mixed and sintered at 500℃ for 10h. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.0303, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:0.87:0.37. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained.

[0168] Comparative Example 12

[0169] The preparation method of the positive electrode active material of Comparative Example 12 includes the following steps:

[0170] 1000g Li 1.06 Ni 0.48 Mn 1.485 Nb 0.008O4, 10.2g AlF3, and 18.5g LiH2PO4 were thoroughly mixed and sintered at 500℃ for 10h. The mass ratio of the positive electrode matrix material to the total mass of the aluminum, phosphorus, and fluorine sources was 1:0.287, and the mass ratio of the aluminum, phosphorus, and fluorine sources was 1:1.68:2.11. After crushing and sieving, lithium nickel manganese oxide positive electrode active material was obtained.

[0171] Comparative Example 13

[0172] The preparation method of the positive electrode active material of Comparative Example 13 includes the following steps:

[0173] 1.39 g of Al(NO3)3·9H2O was dissolved in 100 mL of deionized water to prepare an aluminum nitrate solution. 10.0 g of LiNi was then dissolved in the solution. 0.8 Co 0.1 Mn 0.1 O2 was added to the aluminum nitrate solution and stirred to disperse, thus obtaining a primary mixture. 0.31 g of NH4F and 0.12 g of (NH4)2HPO4 were weighed and dissolved in 20 mL of deionized water to prepare a fluoride and phosphate mixed solution. Under continuous stirring, the prepared fluoride and phosphate solutions were added dropwise to the primary mixture. After reacting for 2 hours, the mixture was allowed to stand, washed, filtered, and dried. Then, it was sintered at 400 °C for 5 hours under an inert atmosphere to obtain a composite positive electrode active material coated with an AlF3 / AlPO4 composite coating layer.

[0174] Comparative Example 14

[0175] The preparation method of the positive electrode active material of Comparative Example 14 includes the following steps:

[0176] 1) Add 1 kg of LiNi 0.8 Co 0.1 Mn 0.1 O2 is added to a high-speed mixer, nitrogen protection is activated (pressure 0.2 MPa), and stirring is performed continuously at 1200 rpm; 80g (Al2O3) is added. 0.6 (TiO2) 0.4 The alcohol phase sol (solid content 10wt%) was added by spraying and stirred at low speed until homogeneous; then heated to 80℃ and dried for 2 hours.

[0177] 2) Stir slowly in an oxygen atmosphere (oxygen concentration of 20%), gradually heat to 350℃, keep at that temperature for 3 hours, and then cool down;

[0178] 3) When the temperature is lowered to 30℃, 27.38g of lithium difluorophosphate is added under high-speed stirring in a nitrogen atmosphere, and stirring is continued for 90min to obtain the positive electrode active material. The stoichiometric formula of this positive electrode active material is LiNi. 0.8 Co 0.1 Mn0.1 O2·0.015((Al2O3) 0.6 (TiO2) 0.4 )·0.02LiPO2F2.

[0179] Comparative Example 15

[0180] The preparation method of the positive electrode active material of Comparative Example 15 includes the following steps:

[0181] 1) Lithium difluorophosphate (average particle size: 1100 nm), lithium phosphate (average particle size: 130 nm), and LiNi 0.8 Co 0.1 Mn 0.1 O2 (D50 is about 12μm) was mixed evenly in a mixer at a mass ratio of 0.5:0.2:100, and then heat-treated at 350℃ in an oxygen atmosphere for 12 hours to obtain the positive electrode active material.

[0182] Comparative Example 16

[0183] The preparation method of the positive electrode active material of Comparative Example 16 includes the following steps:

[0184] 1) LiNi 0.8 Co 0.1 Mn 0.1 O2, LiOH, NH4H2PO4, NH4F, and Al2O3 were weighed in a molar ratio of 1.0:1.1:1.0:1.0:0.5 and ball-milled at 200 rpm for 2 hours to ensure thorough mixing. The finely mixed powder was then placed in a tube furnace and sintered at 600℃ for 3 hours under a high-purity oxygen flow of 99.999%, with a heating rate of 5℃ / min. The mixture was then allowed to cool naturally. This yielded LAPF@NCM811, a positive electrode active material of lithium aluminum fluoride coated with ternary NCM811.

[0185] Comparative Example 17

[0186] The preparation method of the positive electrode active material of Comparative Example 17 includes the following steps:

[0187] 1) Preparation of LiAlPO4F material: 100g of lithium carbonate, aluminum hydroxide, ammonium dihydrogen phosphate, and ammonium fluoride were weighed according to a molar ratio of 0.5:1:1. The powder was dispersed in deionized water using a planetary ball mill and ground for 3 hours. The ball-to-powder ratio was 5:1, and the ratio of grinding solvent to powder was 2:1. The grinding balls were made of zirconia balls with a diameter of 5mm. After grinding, the slurry was dried at 100℃. The dried powder was placed in an alumina crucible and heated to 500℃ at a rate of 2℃ / min, held for 6 hours, and then allowed to cool naturally to obtain LiAlPO4F powder material. The LiAlPO4F powder was then sand-milled for 3 hours, with the final particle size controlled within 80nm.

[0188] 2) Preparation of LiAlPO4F@NCM811 powder: The positive electrode active material NCM (D50 = 8μm) was coated using a coating machine (the mass of LiAlPO4F powder was 1% of the mass of the positive electrode active material). After coating, the powder was calcined at 600℃ for 4h to obtain LiAlPO4F@NCM811 powder.

[0189] 3) Preparation of PAA@LiAlPO4F@NCM811 powder dispersion: Weigh 1g of PAA into 1000mL of deionized water (1g / L), add 101g of the above-prepared LiAlPO4F@NCM811 powder, then add 5g of dilute sulfuric acid (8M) and 0.51g of ethanol. Some of the carboxyl groups of PAA undergo esterification to generate ester groups. Stir magnetically for 1h to allow PAA to adsorb onto the surface of LiAlPO4F, thus obtaining PAA@LiAlPO4F@NCM811 powder dispersion;

[0190] 4) Preparation of PAA-diaminoferrocene@LiAlPO4F@NCM811 powder dispersion: The dispersion prepared above was evaporated to dryness and dissolved again in 500 mL of acetone. 0.7 g of formic acid was added, and the mixture was stirred magnetically for 1 h to convert the carboxyl ester group to a carboxyl group. 0.6 g of phosphorus trichloride and 0.1 g of aluminum trichloride were added as catalysts, and the mixture was stirred magnetically at 80 °C for 3 h to convert the carboxyl group to an acyl chloride group. 0.8 g of diaminoferrocene and 0.1 g of 4-dimethylaminopyridine were added, and the mixture was stirred at -10 °C for 30 min to form a PAA-diaminoferrocene gel network coating the LiAlPO4F@NCM811 particles, thus obtaining the PAA-diaminoferrocene@LiAlPO4F@NCM811 powder dispersion.

[0191] 5) Preparation of PAA-diaminoferrocene@LiAlPO4F@NCM811 powder: The PAA-diaminoferrocene@LiAlPO4F@NCM811 powder dispersion prepared above was stirred and 0.7g of PEG was added. PEG introduced the ether chain into the PAA-diaminoferrocene gel network to obtain PAA-diaminoferrocene@LiAlPO4F@NCM811 powder dispersion;

[0192] The powder dispersion was washed with water and then spray-dried at an inlet air temperature of 200°C and an outlet air temperature of 70°C to obtain PAA-diaminoferrocene@LiAlPO4F@NCM811 powder with a particle size of approximately 8 μm.

[0193] Experimental example:

[0194] 1. Surface smoothness: The surface smoothness was tested using a scanning electron microscope (Hitachi Regulus 8100 / SU 8010) at an accelerating voltage of 5kV, a magnification of 50K, and a working distance of 8.1mm. The area of ​​non-point-like coatings on the surface of the positive electrode active material was measured as the area of ​​the field of view at that magnification.

[0195] 2. Coating or transition layer thickness: The thickness of the coating and transition layers was characterized using field emission transmission electron microscopy (Talos F200X, Thermo Fisher Scientific, USA). Anhydrous ethanol was typically used to disperse the powder sample, and the accelerating voltage was 60 kV.

[0196] 3. Chemical formulas of the coating layer and transition layer: The coated sample was etched with 1 mol / L nitric acid solution for 20–60 min, with the specific etching depth being the coating layer thickness measured by transmission electron microscopy. The etched coating layer was characterized using inductively coupled plasma optical emission spectrometry (ICP-OES) on an Optima 7000 / Avio 500. The content of each element in the coating layer was quantitatively determined, and the chemical formula of the coating layer (Li) was calculated based on the content of each element. a1 Al b1 (PO 4-δ F 2δ ) c1 F d1 The chemical formula of the manganese-containing matrix material was determined by a combination of X-ray diffraction (Brook D8A A25) and ICP testing. The contents of lithium, aluminum, phosphorus, and fluorine in the transition layer were calculated by subtracting the contents of each element in the coating layer from the contents of the additives. The chemical formula of the transition layer (Li) was deduced based on the doping of lithium, aluminum, phosphorus, and fluorine into the positive electrode active material. a2 Ni x1 Co y1 Mn z1 M e Fe f Alb2 P c2 F d2 O g ).

[0197] 4. Mass fraction of coating layer and transition layer: Based on the chemical formula and element content of the coating layer and transition layer in Experiment Example 3, the mass of the coating layer and transition layer is calculated as m1 = M1*a1 + M2*b1 + M3*c1 + M4*(2δC1+d1) + M5*(4-δ)C1, where M1, M2, M3, M4, and M5 are the relative atomic masses of lithium, aluminum, phosphorus, fluorine, and oxygen, respectively. The ratio of these masses to the mass of the positive electrode active material is the mass fraction of the coating layer. Similarly, the mass fraction of the transition layer can be calculated.

[0198] 5. Specific capacity: At 25°C and normal pressure (0.1MPa), the positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) of each embodiment and comparative example were thoroughly mixed in N-methylpyrrolidone solvent at a mass percentage ratio of 95:3:2 to obtain a positive electrode slurry. The positive electrode slurry was coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet containing a positive electrode active layer with a thickness of 100μm. Then, the positive electrode sheet was punched into small discs with a diameter of 12mm using a film die. After drying and weighing, the discs were assembled into a coin cell in a glove box under Ar protective atmosphere using a 2025 coin cell case, with a Li metal disc as the negative electrode and conventional high-voltage lithium cobalt oxide electrolyte. The battery was charged at a constant current rate of 0.1C / 0.33C to the upper limit voltage, and then charged at a constant voltage rate until the current equals 0.05C. The charging capacity at this point is recorded as the first charge specific capacity. After resting for 5 minutes, the battery was discharged at a constant current rate of 0.1C / 0.33C to the lower limit voltage. The discharge capacity at this point is recorded as the first discharge specific capacity. The voltage window for lithium nickel manganese oxide is 3.5-4.95V, for nickel cobalt manganese ternary materials it is 2.8-4.3V, for lithium manganese iron phosphate it is 2.5-4.3V, and for lithium manganese oxide it is 3-4.35V.

[0199] 6. Initial Coulombic Efficiency: Assemble the coin cell according to the method in the coin cell capacity test, charge it at a constant current rate of 0.1C to the upper limit voltage, and then charge it at a constant voltage rate of 0.05C at the upper limit voltage. The charging capacity at this time is recorded as the first charge specific capacity. After that, let it stand for 5 minutes, and then discharge it at a constant current rate of 0.1C to the lower limit voltage. The discharge capacity at this time is recorded as the battery's first discharge specific capacity. The obtained discharge specific capacity / charging specific capacity is the initial coulombic efficiency.

[0200] 7. Capacity retention after 100 cycles at 1C: Following the method described in the coin cell capacity test, the positive electrode active material was coated to form a positive electrode sheet, and graphite was used as the negative electrode. A full cell was constructed with a polyethylene separator and an electrolyte (LiPF6 electrolyte, EC / DMC solvent). At 25°C, the cell was charged at a constant current of 1C to the upper limit voltage, then charged at a constant voltage of 0.5C to the lower limit voltage, and finally discharged at a constant voltage of 1C to the lower limit voltage. This charge-discharge cycle was repeated 100 times. The discharge capacity Q1 at the first cycle and Q at the 100th cycle were measured. 100 The capacity retention rate after 100 cycles is Q = Q 100 / Q1*100%.

[0201] 8. Number of cycles at 80% capacity retention: For the full cells prepared above, charge them at a constant current rate of 0.1C to the upper limit voltage at 25℃ / 45℃, then charge them at a constant voltage rate of 0.05C at the upper limit voltage, let them stand for 5 minutes, and then discharge them at a constant current rate of 0.1C to the lower limit voltage. Repeat this cycle test until the capacity decays to 80%, and record the number of cycles.

[0202] 9. 28-day capacity retention rate: After the soft-pack full battery is formed, the air bag is removed and it is sealed. The initial capacity after formation is tested. After charging to the upper limit voltage and storing for 28 days, the remaining capacity of the battery is tested. The ratio of the remaining battery capacity to the initial capacity is the 28-day storage capacity retention rate.

[0203] 10. High-temperature storage gas generation performance: The positive active material was coated into a positive electrode sheet according to the method in the coin cell capacity test to prepare a positive soft pack battery. The soft pack battery before storage was placed in water and the initial volume V0 of the soft pack battery was tested by the water displacement method. The temperature was controlled at 70℃. After storage for 28 days, the volume V1 of the soft pack battery was tested again by the water displacement method. The volume change (V1-V0) / V0 was calculated to obtain the gas generation performance during high-temperature storage.

[0204] 11. BET change rate σ: σ=(BET1-BET2) / BET1, where BET1 is the specific surface area of ​​the positive electrode matrix material and BET2 is the specific surface area of ​​the positive electrode active material.

[0205] Figure 1 Here is a SEM image of the positive electrode active material prepared in Example 1;

[0206] Figure 2 Here is a SEM image of the positive electrode active material prepared in Example 3;

[0207] Figure 3 Here is a SEM image of the positive electrode active material prepared in Example 9;

[0208] Figure 4 SEM image of the positive electrode active material prepared in Example 11;

[0209] from Figure 1-4 It can be seen that the positive electrode active materials of Examples 1, 9 and 11 have relatively rounded particle shapes, no adhesion, smooth surfaces and no small particles. The surface of the positive electrode active material of Example 3 is also very smooth, indicating that the aluminum source, phosphorus source and fluorine source have entered the surface interface of the positive electrode matrix material.

[0210] Figure 5 Here is a SEM image of the positive electrode active material prepared in Comparative Example 1;

[0211] from Figure 5 It can be seen that the undoped single crystal particles prepared in Comparative Example 1 have poor dispersion.

[0212] Figure 6 Here is a SEM image of the positive electrode active material prepared in Comparative Example 2;

[0213] Figure 7 Here is a SEM image of the positive electrode active material prepared in Comparative Example 3;

[0214] Figure 8 Here is a SEM image of the positive electrode active material prepared in Comparative Example 4;

[0215] from Figure 6-8 It can be seen that the single crystal particles in Comparative Examples 2-4 have good dispersion, indicating that the transition metal elements Nb, Ta, Mo, and W have a significant dispersing effect on the single crystal materials.

[0216] Figure 9 Here is a SEM image of the positive electrode active material prepared in Comparative Example 5;

[0217] from Figure 9 It can be seen that the positive electrode active material prepared at low temperature in Comparative Example 5 has many fine particles on the surface of the aluminum-coated material, which are dotted and unevenly coated.

[0218] Figure 10 The image shows a SEM image of the positive electrode active material prepared in Comparative Example 11.

[0219] Figure 11 The image shows the SEM image of the positive electrode active material prepared in Comparative Example 12.

[0220] from Figure 10 , 11 It can be seen that in the positive electrode active materials prepared at low temperature in Comparative Example 11 (single crystal) and Comparative Example 12 (polycrystalline), aluminum, phosphorus and fluorine elements are dot-like coated on the surface of lithium nickel manganese oxide material, and the coating is uneven.

[0221] Table 1

[0222]

[0223]

[0224] As shown in Table 1, compared with the comparative example, the positive electrode active material provided by the present invention includes a positive electrode substrate material, a transition layer, and a coating layer, and the surface smoothness of the positive electrode active material is limited, so as to achieve complete and uniform coating of the positive electrode substrate material by the coating layer, suppress the direct contact between the positive electrode substrate material and the electrolyte, reduce the occurrence of interfacial side reactions, enhance the structural stability and interfacial stability of the material, and improve the cycle performance of lithium-ion batteries when applied to lithium-ion batteries.

[0225] As can be seen from Comparative Example 1, the positive electrode active material without transition metal doping and surface coating has very poor specific capacity, cycle performance, and high-temperature storage performance.

[0226] As can be seen from Comparative Examples 2-4, the positive electrode active material without surface coating exhibits poor high-temperature cycling and high-temperature storage performance. This is because the surface stability of the positive electrode matrix material is poor, making it prone to interfacial side reactions at high temperatures, leading to electrolyte oxidative decomposition and the degradation of transition metal Mn. 2+ Leaching leads to decreased performance during high-temperature cycling and high-temperature storage.

[0227] As can be seen from Comparative Examples 5-7, the specific surface area of ​​the positive electrode active material obtained by low-temperature sintering is significantly increased, and the surface smoothness is less than 30%. This indicates that at low temperatures, the coating material is mainly distributed in a dotted pattern on the surface of the positive electrode active material (e.g., ...). Figure 8 As shown in the figure, this coating method has poor uniformity. Areas with thin coating layers are easily corroded by hydrofluoric acid in the electrolyte. It can also lead to the positive electrode active material surface not being completely coated. The coating layer is not tightly adhered to the material surface and is prone to falling off under long-term cycling, which causes rapid capacity decay, resulting in poor cycle performance and poor high-temperature storage performance.

[0228] As can be seen from Comparative Example 8, the cycle performance needs to be improved and the high-temperature storage performance is also poor when no fluorine is added. This is because fluoride ions have an important acid-resistant effect. The presence of fluoride ions can effectively inhibit the interfacial reaction between hydrofluoric acid in the electrolyte and the positive electrode active material, thus reducing gas production.

[0229] As can be seen from Comparative Example 9, without the addition of phosphorus, the capacity decreased, the cycle performance was poor, and the high-temperature storage performance was also poor. This is because phosphate has good conductivity, which is conducive to the transport of lithium ions and does not significantly reduce the capacity during cycling.

[0230] As can be seen from Comparative Example 10, without the addition of aluminum, both cycle performance and high-temperature storage performance need improvement. This is because the alumina coating has low electrochemical activity, which can directly block the contact between the electrolyte and the surface of the positive electrode active material, inhibiting the transition metal Mn. 2+ The dissolution of aluminum and phosphorus is facilitated by their low melting point. Furthermore, both aluminum and phosphorus are low-melting-point substances, and their co-coating process promotes eutectic effects, aiding in surface doping.

[0231] As can be seen from Comparative Example 11, low-temperature sintering increases the specific surface area of ​​the positive electrode active material, indicating that no surface gradient doped transition layer or coating layer is formed. Figure 9 The morphology shows that at low temperatures, the coating layer still exists in the form of dot-like coating, and its cycle performance is poor due to the unevenness of the coating layer.

[0232] As can be seen from Comparative Examples 12-17, the specific surface area of ​​lithium aluminum, phosphorus, and fluorine nickel cobalt manganese oxide coated at low temperature is significantly larger than that of lithium coated at high temperature (Example 14), and the surface smoothness is also much lower. Its coating effect is poor, resulting in poor overall battery capacity and cycle life.

[0233] 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, It includes a positive electrode substrate material, a transition layer, and a coating layer; the transition layer covers the surface of the positive electrode substrate material, and the coating layer covers the surface of the transition layer; The surface smoothness of the positive electrode active material is >95%; The positive electrode substrate material includes manganese. The chemical formula of the coating layer is Li. a1 Al b1 (PO 4-δ F 2δ ) c1 F d1 Where, 0≤a1≤1.0, 0.001≤b1≤0.2, 0.01≤c1≤0.5, 0.01≤d1≤0.5, 0.01≤δ≤0.2, d1=a1+3b1-3c1; The chemical formula of the transition layer is Li. a2 Ni x1 Co y1 Mn z1 M e Fe f Al b2 P c2 F d2 O g , 0.95≤a2≤1.20, 0≤x1≤0.95, 0≤y1≤0.25, 0.05≤z1≤1.60, 0.001≤e≤0.02, 0≤f≤0.65, 1.5≤g≤4.5, 0.001≤b2≤0.1, 0.01≤c2≤1.2, 0.005≤d2≤0.1, M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

2. The positive electrode active material according to claim 1, characterized in that, b2≤b1, d2≤d1; c2>1, c2-1≤c1; c2<1, c2≤c1.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The coating layer accounts for 0.5-3.0% of the mass fraction of the positive electrode active material; The transition layer accounts for 0.05-1.0% of the mass fraction of the positive electrode active material.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The thickness ratio of the covering layer to the transition layer is 1:0.01-0.5; And / or, the thickness of the coating layer is 5-30 nm; the thickness of the transition layer is 0.5-10 nm.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The positive electrode substrate material is a single crystal material, and the average particle size of the positive electrode substrate material is 0.2-20 μm; Alternatively, the positive electrode substrate material is a polycrystalline material, and the average particle size of the positive electrode substrate material is 3-50 μm.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, The cathode substrate material includes LiNi. 0.5 Mn 1.5-x M x O4, LiMn 2-x M x O4, LiMn 0.6-x Fe 0.4 M x PO4, Li(Ni) y Co z Mn 1-y-z ) 1-x M x At least one of O2; wherein 0.001≤x≤0.050, 0.50≤y≤0.095, 0.001≤z≤0.02, and M includes at least one of Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, and S.

7. A method for preparing a positive electrode active material as described in any one of claims 1-6, characterized in that, Includes the following steps: After nano-sizing of aluminum, phosphorus, and fluorine sources, they are mixed with the positive electrode matrix material to obtain a mixed system. The mixed system is then sintered at 700-1000℃ for 5-10 hours to obtain the positive electrode active material.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the positive electrode substrate material to the total mass of the aluminum source, phosphorus source, and fluorine source is 1:0.01-0.5; And / or, the mass ratio of the aluminum source, phosphorus source, and fluorine source is 1:0.3-15:0.2-5.

9. A positive electrode plate, characterized in that, This includes the positive electrode active material according to any one of claims 1-6, and the positive electrode active material prepared by the preparation method according to claim 7 or 8.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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