Lithium-rich manganese-based positive electrode material, preparation method and use

Abstract

A lithium-rich manganese-based positive electrode material, a preparation method and the use. By constructing a lithium-deficient and manganese-deficient surface layer on the surface of an xLi2MnO3•(1-x)LiNiaCobMcO2 material, the removal of Li+ in the form of Li2O is reduced, thereby reducing lattice oxygen removal, thus mitigating unstable Mn elements on the surface layer of the material due to oxygen removal, and reducing the formation of a low-capacity spinel structure, wherein x is greater than 0 and less than or equal to 1, a+b+c=1, a is greater than 0 and less than 1, b is greater than or equal to 0 and less than 1, and c is greater than 0 and less than 1. The presence of a fast ion conductor layer can also improve the ion diffusion rate in the lithium-rich manganese-based positive electrode material, thereby effectively improving the ionic conductivity of the lithium-rich manganese-based positive electrode material, improving the capacity, and improving the rate performance and cycling performance.

Description

Lithium-rich manganese-based positive electrode material, preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of battery materials, and in particular to lithium-rich manganese-based positive electrode materials, preparation methods, and applications. Background Art

[0002] Layered lithium-rich manganese-based cathode materials have high capacity (>200mAhg -1 ), high energy density, and are considered promising cathode materials for lithium-ion batteries. However, such over-lithiated layered materials inevitably undergo oxygen evolution of the Li2MnO3 component during initial cycling, irreversible phase transition to an inactive phase after long-term cycling, and electrolyte decomposition, followed by accelerated surface degradation.

[0003] During the first charge of lithium-rich manganese-based cathode materials, part of the Li + It is released in the form of Li2O but cannot be re-embedded during the discharge process, resulting in a low initial charge and discharge efficiency of the material. At the same time, the release of Li2O will cause some lattice oxygen to be released, making the transition metal elements (such as Mn) in the surface layer of the material unstable due to the release of oxygen, thus forming a low-capacity spinel structure. This spinel structure gradually penetrates from the surface into the interior of the material, causing the discharge voltage to continue to drop, resulting in a continuous attenuation of capacity. Therefore, stabilizing the surface structure of the material is the key to maintaining the electrical performance during the cycle.

[0004] Currently, lithium-rich manganese-based cathode materials are mainly coated with metal oxides, fluorides or phosphates to stabilize the surface structure of the particles, avoid side reactions by isolating the electrolyte, and improve the performance of lithium-rich manganese-based cathode materials at room temperature and high temperature. However, the coating layer formed on the surface of the above materials is intermittent and discontinuous, and cannot fundamentally prevent Mn from migrating to the lithium site to form a spinel phase during the redox reaction.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure is to provide a lithium-rich manganese-based positive electrode material, a preparation method and an application, to construct a manganese-deficient and lithium-deficient surface, to reduce the migration of manganese to the lithium site, to reduce the Li2MnO3 content, to inhibit the transformation of the surface layered phase into the spinel phase, and to reduce the capacity decay of the lithium-rich manganese-based positive electrode material during the cycle.

[0008] The present disclosure is achieved as follows:

[0009] In a first aspect, the present disclosure provides a lithium-rich manganese-based positive electrode material, comprising a core and a first coating layer coated on the core, wherein:

[0010] The core has a chemical formula of xLi2MnO3·(1-x)LiNi a Co b M c O2, where 0 < x ≤ 1, a + b + c = 1, 0 < a < 1, 0 ≤ b < 1, 0 < c < 1, and the proportion of manganese on the surface of the core is lower than the average proportion of manganese in the core. M is selected from at least one of Mn, Cr, W, Mo, Nb, and Fe;

[0011] The first coating layer is a fast ion conductor layer with a general formula of Li m Me n O p , where m > 0, n > 0, p > 0.

[0012] In some embodiments, the average thickness of the first coating layer is 8 nm - 15 nm.

[0013] In some embodiments, a second coating layer is further coated on the first coating layer. The second coating layer is a carbon coating layer doped with fluorine and phosphorus.

[0014] In some embodiments, the average thickness of the second coating layer is 8 nm - 15 nm.

[0015] In some embodiments, the particle size of the core is 4 μm - 10 μm.

[0016] Second, the present disclosure provides a method for preparing the lithium-rich manganese-based cathode material according to any one of the foregoing embodiments, including coating the first coating layer on the core.

[0017] In some embodiments, it includes the preparation of the core: doping nickel and / or cobalt elements on the surface of the precursor to obtain a manganese-deficient precursor on the surface, and mixing the manganese-deficient precursor on the surface with a lithium source for primary sintering to obtain the core;

[0018] Where the precursor is at least one of an oxide containing nickel, cobalt, manganese, and M elements, a carbonate containing nickel, cobalt, manganese, and M elements, and a hydroxide containing nickel, cobalt, manganese, and M elements.

[0019] In some embodiments, ammonia water is used to adjust the mixed solution of the precursor, nickel salt, and / or cobalt salt to a pH of 9 - 11 while stirring to obtain a precursor with nickel hydroxide and / or cobalt hydroxide covered on the surface, which is the manganese-deficient precursor on the surface.

[0020] In some embodiments, the nickel salt is at least one of nickel sulfate, nickel oxalate, and nickel carbonate; the cobalt salt is at least one of cobalt sulfate, cobalt carbonate, and cobalt oxalate.

[0021] In some embodiments, the solid-liquid mass ratio of the mixed solution is 1:(1 - 2).

[0022] In some embodiments, the total mass ratio of the nickel salt and / or cobalt salt in the mixed solution to the precursor is 0.1%-2%.

[0023] In some embodiments, the thickness of the nickel hydroxide and / or cobalt hydroxide covering the surface of the precursor is 40 nm to 60 nm.

[0024] In some embodiments, the surface manganese-deficient precursor and the lithium salt are mixed in a molar ratio of 1:(1.2-1.5) and then sintered once.

[0025] In some embodiments, the primary sintering comprises:

[0026] The first stage of sintering is at 500-650℃ and kept at this temperature for 1-5 hours;

[0027] The second stage of sintering is at 850℃-950℃ and kept at this temperature for 10h-15h;

[0028] The first sintering stage and the second sintering stage are both performed in an oxygen atmosphere.

[0029] In some embodiments, the heating rate of the first sintering stage and / or the second sintering stage is 2° C. / min-5° C. / min.

[0030] In some embodiments, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium phosphate.

[0031] In some embodiments, coating with a first coating layer is further included: the core is mixed with an acid or salt containing Me and then subjected to secondary sintering to obtain the core coated with the first coating layer.

[0032] In some embodiments, the acid or salt containing Me is at least one of ammonium molybdate, molybdic acid, tungstic acid, ammonium tungstate, niobium oxalate, tantalum oxalate, and lanthanum nitrate.

[0033] In some embodiments, the mass of the Me-containing acid or salt is 0.1%-5% of the mass of the core.

[0034] In some embodiments, the secondary sintering temperature is 550° C.-800° C., the sintering time is 3 h-6 h, and the sintering atmosphere is an oxygen atmosphere.

[0035] In some embodiments, the method further includes coating with a second coating layer: mixing the core coated with the first coating layer, an organic solvent A, and an organic carbon source B, and evaporating the liquid to obtain a first intermediate; mixing the first intermediate and an organic carbon source C to obtain a second intermediate; and sintering the second intermediate three times to obtain a lithium-rich manganese-based positive electrode material.

[0036] The organic carbon source B is selected from reagents containing F element, and the organic carbon source C is selected from reagents containing P element.

[0037] In some embodiments, the organic solvent A is selected from one or more of ethanol, methanol, acetone, and DMF.

[0038] In some embodiments, the organic carbon source B is at least one of perfluorooctane sulfonic acid, perfluoroethane sulfonic acid, pentafluorostyrene and perfluorooctyltriethoxysilane.

[0039] In some embodiments, the organic carbon source C is at least one of triphenyl phosphate, methyl pyridinium, benfotiamine and dicyclohexyl phosphate.

[0040] In some embodiments, the total mass of the organic carbon source B and the organic carbon source C is 1%-5% of the mass of the core coated with the first coating layer.

[0041] In some embodiments, the mass of the organic carbon source B is 0.5%-1.5% of the mass of the core coated with the first coating layer, and the mass of the organic carbon source C is 0.5%-1.5% of the mass of the core coated with the first coating layer.

[0042] In some embodiments, the mass ratio of the organic solvent A to the mass of the core coated by the first coating layer is (1.8-2.2):1.

[0043] In some embodiments, the core coated with the first coating layer, the organic solvent A and the organic carbon source B are mixed and then evaporated to dryness at 70° C.-90° C.

[0044] In some embodiments, the temperature of the three sintering processes is 200° C.-450° C., and the sintering time is 3 h-6 h.

[0045] In a third aspect, the present disclosure provides a battery comprising the lithium-rich manganese-based positive electrode material described in any one of the aforementioned embodiments or the lithium-rich manganese-based positive electrode material obtained by the method described in any one of the aforementioned embodiments.

[0046] In a fourth aspect, the present disclosure provides an electrical device comprising the battery described in the aforementioned embodiment.

[0047] The present disclosure has the following beneficial effects:

[0048] The present invention discloses xLi2MnO3·(1-x)LiNi a Co b M c The surface of O2 material is constructed with lithium-deficient and manganese-deficient surface layers, which reduces Li +It is removed in the form of Li2O, thereby reducing the removal of lattice oxygen, and further alleviating the instability of the Mn element in the surface layer of the material due to oxygen removal, and reducing the formation of a low-capacity spinel structure.

[0049] In the present disclosure, the fast ion conductor layer can increase the ion diffusion rate between the lithium-rich manganese-based cathode materials, thereby effectively increasing the ionic conductivity of the lithium-rich manganese cathode materials, improving the capacity, and enhancing the rate and cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present disclosure, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0051] FIG. 1 is a flowchart for preparing a lithium-rich manganese-based cathode material;

[0052] FIG. 2 is an XRD diagram of the lithium-rich manganese-based cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 3;

[0053] FIG. 3 is an XRD diagram of the lithium-rich manganese-based cathode materials prepared in Example 1 and Example 3;

[0054] FIG. 4 is a cycling performance curve of the lithium-rich manganese-based cathode materials prepared in Example 1, 2, 3, and Comparative Example 1, 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0056] One embodiment of the present disclosure provides a lithium-rich manganese-based cathode material, including a core and a first coating layer coated on the core, wherein,

[0057] The chemical formula of the core is xLi2MnO3·(1-x)LiNi a Co b M c O2, 0 < x ≤ 1, a + b + c = 1, 0 < a < 1, 0 ≤ b < 1, 0 < c < 1, and the proportion of manganese element on the surface of the core is lower than the average proportion of manganese in the core, M is selected from at least one of Mn, Cr, W, Mo, Nb, and Fe;

[0058] The first coating layer is a fast ion conductor layer, the general formula of which is Li m Me n O p , m>0, n>0, p>0.

[0059] The main reason for the decrease in capacity of lithium-rich manganese-based cathode materials is Li + After being released in the form of Li2O, part of the lattice oxygen will be released, making the transition metal elements on the surface of the material unstable due to the release of oxygen, thus forming a low-capacity spinel structure. In order to reduce the release of lithium and manganese, the present invention adopts xLi2MnO3·(1-x)LiNi a Co b M c The surface of the O2 material is constructed with a lithium-deficient and manganese-deficient surface layer. The manganese element on the surface of the core is relatively low, which is called "surface manganese deficiency". The fast ion conductor layer contains lithium. During the preparation process, Me can react with the lithium in the core to form a fast ion conductor layer, which can evenly "pull out" the lithium in the shallow layer of the core, thereby constructing and realizing "surface lithium deficiency". At the same time, the fast ion conductor can increase the ion diffusion rate between the lithium-rich manganese-based positive electrode materials, thereby effectively improving the ion conductivity of the lithium-rich manganese-based positive electrode materials, increasing the capacity, and improving the rate and cycle performance; the fast ion conductor can also achieve the role of blocking the contact between the electrolyte and the core, thereby reducing the formation of low-capacity spinel structure, which is beneficial to the improvement of the material cycle performance.

[0060] In some embodiments, the average thickness of the first coating layer is 8 nm to 15 nm, specifically 8 nm, 10 nm, 12 nm, 14 nm, 15 nm, or any value between 8 nm and 15 nm. The fast ion conductor layer can increase the ion diffusion rate between the lithium-rich manganese-based positive electrode material, effectively increasing the capacity of the lithium-rich manganese-based positive electrode material and improving the rate performance. However, when the fast ion conductor layer is too thick, the capacity of the material will be reduced and the cycle performance will deteriorate.

[0061] In some embodiments, the first coating layer is further coated with a second coating layer, wherein the second coating layer is a carbon coating layer doped with fluorine and phosphorus. The presence of the carbon coating layer can further prevent the electrolyte from contacting the core and improve the material's conductivity. The combination of fluorine and phosphorus also improves the material's capacity and rate performance.

[0062] In some embodiments, the average thickness of the second coating layer is 8 nm to 15 nm, specifically 8 nm, 10 nm, 12 nm, 14 nm, 15 nm, or any value between 8 nm and 15 nm. Too large a thickness may also affect ion migration and reduce the electrical properties of the material.

[0063] In some embodiments, the core particle size is 4 μm-10 μm, specifically 4 μm, 6 μm, 8 μm, 10 μm or any value between 4 μm and 10 μm.

[0064] Another embodiment of the present disclosure provides a method for preparing the lithium-rich manganese-based positive electrode material according to any one of the aforementioned embodiments, comprising coating a first coating layer on the core.

[0065] In some embodiments, the core is prepared by doping nickel and / or cobalt on the surface of a precursor to obtain a surface manganese-deficient precursor, mixing the surface manganese-deficient precursor with a lithium source and sintering the mixture once to obtain the core;

[0066] The precursor is at least one of an oxide containing nickel, cobalt, manganese and M elements, a carbonate containing nickel, cobalt, manganese and M elements, and a hydroxide containing nickel, cobalt, manganese and M elements.

[0067] In this embodiment, manganese is diluted by doping nickel and cobalt on the surface of the precursor to reduce the content of manganese ions on the surface of the material, thereby obtaining a "manganese-deficient" surface. Although other metal ions can also be used to dilute manganese, considering the material capacity and the difficulty of combining with the precursor surface, nickel and cobalt are selected in this embodiment to dilute manganese. The precursor can be an existing conventional lithium-rich manganese-based positive electrode material precursor, such as a lithium-rich manganese-based positive electrode material precursor obtained by co-precipitation using ammonia water as a precipitant.

[0068] In some embodiments, a mixed solution of a precursor, a nickel salt and / or a cobalt salt is adjusted to a pH of 9-11 using ammonia water while stirring, and a precursor having a surface covered with nickel hydroxide and / or cobalt hydroxide is obtained, which is the surface manganese-deficient precursor. By adjusting the pH to 9, 10, 11 or any value between 9-11, the excess metal ions in the solution are uniformly precipitated and adsorbed onto the surface of the precursor, forming a structure in which the surface manganese-deficient nickel-rich internal elements are uniformly distributed, reducing the surface Li2MnO3 content in the subsequent primary sintering, suppressing the phase change during the post-treatment process, and reducing voltage decay. Stirring is conducive to uniform mixing of the precursor with the nickel salt and the cobalt salt, thereby allowing the hydroxide to be relatively uniformly precipitated on the surface of the precursor.

[0069] In some embodiments, the nickel salt is at least one of nickel sulfate, nickel oxalate, and nickel carbonate; and the cobalt salt is at least one of cobalt sulfate, cobalt carbonate, and cobalt oxalate.

[0070] In some embodiments, the solid-liquid mass ratio of the mixed solution is 1:(1-2), specifically, it can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, or any value between 1:(1-2). If the content of the precursor is too high, the frequency of collisions between the precursor particles increases during stirring, and the hydroxide precipitated on the surface of the precursor is easily detached due to the collision, which may result in a small amount of hydroxide attached to the surface of the precursor and uneven attachment. If the content of the precursor particles is too low, the water consumption will increase, and the surface area for the hydroxide to attach will be too small, which will increase the content of hydroxide not bound to the precursor, and also reduce the utilization rate of the raw materials.

[0071] In some embodiments, the total mass ratio of the nickel salt and / or cobalt salt in the mixed solution to the precursor is 0.1%-2%. In specific operations, the coprecipitation step can be continued until the precipitate no longer increases. At this time, the thickness of the hydroxide precipitate can be adjusted by adjusting the total mass ratio of the nickel salt and cobalt salt to the precursor. Of course, in other cases, the thickness of the hydroxide precipitate layer can also be controlled by controlling the coprecipitation time.

[0072] It should be noted that the specific amounts of nickel salt and cobalt salt can be reasonably selected according to the composition of the target product. In the actual preparation process, since the thickness of the hydroxide precipitation layer is relatively small, the impact on the overall core composition will not be too significant.

[0073] In some embodiments, the thickness of the nickel hydroxide and / or cobalt hydroxide covering the surface of the precursor is 40 nm to 60 nm. Too large a thickness may reduce the capacity.

[0074] In some embodiments, the surface manganese-deficient precursor and the lithium salt are mixed in a molar ratio of 1:(1.2-1.5) and then sintered once. Specifically, the surface manganese-deficient precursor and the lithium salt can be mixed in a molar ratio of 1:1.2, 1:1.3, 1:1.4, 1:1.5, or any value between 1:(1.2-1.5). Considering that a certain amount of lithium source is required for the subsequent preparation of the fast ion conductor layer, in this embodiment, the amount of lithium salt used in this application is greater than that used in the preparation of conventional lithium-rich manganese-based positive electrode materials.

[0075] In some embodiments, the primary sintering comprises:

[0076] The first stage sintering temperature is 500-650°C, specifically 500°C, 550°C, 600°C, 650°C or any value between 500-650°C, and the heat preservation time is 1-5h, specifically 1h, 2h, 3h, 4h, 5h or any value between 1h-5h;

[0077] The second stage sintering temperature is 850-950°C, specifically 830°C, 860°C, 890°C, 920°C, 950°C or any value between 850-950°C, and the heat preservation time is 10-15 hours, specifically 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or any value between 10 hours and 15 hours;

[0078] The first sintering stage and the second sintering stage are both performed in an oxygen atmosphere.

[0079] The first stage of sintering is used to fuse the surface manganese-deficient precursor and the lithium salt. The second stage of sintering is performed at a higher temperature, allowing the lithium source to penetrate the interior of the surface manganese-deficient precursor. Due to the limited penetration rate of the lithium source, the second stage of sintering also requires a relatively longer holding time. The oxygen atmosphere for sintering can be air or other oxygen-containing atmospheres.

[0080] In some embodiments, the heating rate of the first sintering stage and / or the second sintering stage is 2°C / min-5°C / min, specifically 2°C / min, 3°C / min, 4°C / min, 5°C / min or any value between 2°C / min and 5°C / min.

[0081] In some embodiments, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium phosphate.

[0082] In some embodiments, coating with a first coating layer is further included: the core is mixed with an acid or salt containing Me and then subjected to secondary sintering to obtain the core coated with the first coating layer.

[0083] The fast ion conductor can increase the ion diffusion rate between the lithium-rich manganese-based positive electrode materials, thereby effectively improving the ionic conductivity of the lithium-rich manganese-based positive electrode materials, increasing the capacity, and improving the rate and cycle performance.

[0084] In some embodiments, the acid or salt containing Me is at least one of ammonium molybdate, molybdic acid, tungstic acid, ammonium tungstate, niobium oxalate, tantalum oxalate, and lanthanum nitrate.

[0085] By utilizing the low melting point of the molten salt, the coating agent can melt and infiltrate the substrate well to form a uniform coating layer, thus solving the problem of conventional oxides, phosphides, and fluorides having high melting points and uneven coating. Although there are also methods of coating fast ion conductors on the core in the prior art, the timing of adding the fast ion conductors is different. If added during the first calcination, it cannot be guaranteed that the fast ion conductor is coated on the surface of the core. If the fast ion conductor is directly added during the second calcination, it cannot combine with the lithium in the shallow layer of the core and does not have the effect of "pulling out" the lithium on the surface of the core. In this embodiment, the acid or salt of Me with a lower melting point is used to uniformly coat the core with the acid or salt of Me, thereby facilitating the Me acid or salt to uniformly pull out the lithium in the shallow layer of the core, thereby facilitating the fast ion conductor layer to be uniformly coated on the surface of the core.

[0086] In some embodiments, the mass of the Me-containing acid or salt is 0.1%-5% of the mass of the core, specifically 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value between 0.1% and 5%. Excessive Me-containing acid or salt may prevent the shallow lithium layer in the core from fully reacting with it, resulting in some Me-containing acid or salt being unable to form a fast ion conductor, thus affecting the electrical performance of the product.

[0087] In some embodiments, the secondary sintering temperature is 550°C-800°C, specifically 550°C, 650°C, 700°C, 750°C, 800°C, or any value between 550°C-800°C, the sintering time is 3h-6h, specifically 3h, 4h, 5h, 6h, or any value between 3h-6h, and the sintering atmosphere is an oxygen atmosphere. The purpose of the secondary sintering is to melt the acid or salt of Me and simultaneously "pull out" the lithium in the shallow layer of the core, without requiring long-distance migration of ions. Therefore, the sintering temperature is lower than that of the primary sintering.

[0088] In some embodiments, the method further includes coating with a second coating layer: mixing the core coated with the first coating layer, an organic solvent A, and an organic carbon source B, and evaporating the liquid to obtain a first intermediate; mixing the first intermediate and an organic carbon source C to obtain a second intermediate; and sintering the second intermediate three times to obtain a lithium-rich manganese-based positive electrode material.

[0089] The organic carbon source B is selected from reagents containing F element, and the organic carbon source C is selected from reagents containing P element.

[0090] The three-firing low-temperature coating simultaneously introduces conductive carbon, F, and P elements, which can reduce the contact between the lithium-rich manganese-based positive electrode material and the electrolyte, avoid the occurrence of side reactions, and at the same time, the coating can inhibit the dissolution of manganese in the lithium-rich manganese-based positive electrode material, which is beneficial to improve the voltage decay of the electrolyte-modified lithium-rich manganese-based positive electrode material during the cycle and improve the long-term cycle stability of the lithium-rich manganese-based positive electrode material. In order to make the organic carbon source B and the organic carbon source C relatively uniformly coated on the core, the liquid organic carbon source B is first added to obtain the first intermediate, and then the solid organic carbon source C is added to obtain the second intermediate.

[0091] In some embodiments, the organic solvent A is selected from one or more of ethanol, methanol, acetone, and DMF.

[0092] In some embodiments, the organic carbon source B is at least one of perfluorooctane sulfonic acid, perfluoroethane sulfonic acid, pentafluorostyrene and perfluorooctyltriethoxysilane.

[0093] In some embodiments, the organic carbon source C is at least one of triphenyl phosphate, methyl pyridinium, benfotiamine and dicyclohexyl phosphate.

[0094] In some embodiments, the total mass of the organic carbon source B and the organic carbon source C is 1%-5% of the mass of the core coated with the first coating layer, specifically 1%, 2%, 3%, 4%, 5% or any value between 1% and 5%.

[0095] In some embodiments, the mass of the organic carbon source B is 0.5%-1.5% of the mass of the core coated with the first coating layer, specifically 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, or any value between 0.5% and 1.5%. The mass of the organic carbon source C is 0.5%-1.5% of the mass of the core coated with the first coating layer, specifically 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, or any value between 0.5% and 1.5%. Although fluorine and phosphorus can enter the lattice of the lithium-rich manganese positive electrode material, occupy oxygen vacancies, inhibit oxygen precipitation, and thus improve the stability of the core material, an excessively thick coating layer will also increase the difficulty of lithium ion migration and reduce capacity.

[0096] In some embodiments, the mass ratio of the organic solvent A to the mass of the core coated with the first coating layer is (1.8-2.2):1, specifically 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, or any value between (1.8-2.2):1. The organic solvent can be removed during the calcination, the main purpose of which is to ensure relatively uniform mixing of the raw materials.

[0097] In some embodiments, the core coated with the first coating layer, the organic solvent A, and the organic carbon source B are mixed and evaporated to dryness at 70° C. to 90° C., specifically 70° C., 75° C., 80° C., 85° C., 90° C., or any value between 70° C. and 90° C. In a specific operation, the liquid can be first evaporated by stirring at 70° C. to 90° C. until the liquid content is low, and then placed in an oven.

[0098] In some embodiments, the temperature of the three sinterings is 200°C-450°C, specifically 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or any value between 200°C-450°C, and the sintering time is 3h-6h, specifically 3h, 4h, 5h, 6h or any value between 3h-6h.

[0099] In a third aspect, the present disclosure provides a battery comprising the lithium-rich manganese-based positive electrode material described in any one of the aforementioned embodiments or the lithium-rich manganese-based positive electrode material obtained by the method described in any one of the aforementioned embodiments.

[0100] In a fourth aspect, the present disclosure provides an electrical device comprising the battery described in the aforementioned embodiment.

[0101] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0102] The precursor described in the embodiment of the present disclosure is obtained by mixing a nickel source, a cobalt source and a manganese source to obtain a ternary liquid, and the ternary liquid, liquid alkali and ammonia water are added to the bottom liquid in parallel to carry out a co-precipitation reaction; if other elements are required to be doped in the lithium-rich manganese-based positive electrode material, the ternary liquid may also include ions of the doping elements.

[0103] Example 1

[0104] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material, as shown in FIG1 , comprising the following steps:

[0105] (1) Ni 0.35 Mn 0.65 (OH)2 was dispersed in water at a solid-liquid mass ratio of 1:1.2, nickel sulfate was added, and ammonia water was added dropwise while mixing and stirring until the pH value was 11. After reacting for 30 minutes, the reaction liquid was filtered and the obtained solid was dried at 80°C for 12 hours. The amount of nickel sulfate added was 1% of the mass of the precursor.

[0106] (2) The precursor obtained in step (1) was uniformly mixed with lithium carbonate in a molar ratio of 1:1.35. The mixed material was placed in an air atmosphere, heated to 500°C at a rate of 2.5°C / min and sintered for 5 hours. Then, the temperature was increased to 950°C at a rate of 2.5°C / min and kept warm for 12 hours. The temperature was cooled along with the furnace and the sintered material was sieved through a 200-mesh sieve to obtain a primary sintered material.

[0107] (3) After the ammonium molybdate and the primary sintering material are uniformly mixed, the mixture is sintered at 800°C in an air atmosphere for 6 hours to obtain a secondary sintering material, wherein the amount of ammonium molybdate is 1 wt% of the primary sintering material.

[0108] (4) The secondary sintered material was added to ethanol at a mass ratio of 2:1, and perfluorooctyl triethoxysiloxane was added simultaneously. The mixture was stirred at 80°C until the solution evaporated, and then dried in an oven to obtain an intermediate 1, wherein the amount of perfluorooctyl triethoxysiloxane was 1 wt% of the secondary sintered material. Intermediate 1 was then mixed uniformly with methyl pyridinium phosphate at a mixing rate of 1800 rpm, wherein the amount of methyl pyridinium phosphate was 1 wt% of the intermediate 1. The mixing time was 15 minutes, and the mixture was sintered at 350°C for 4 hours in an air atmosphere to obtain a lithium-rich manganese-based positive electrode material with a double coating layer.

[0109] Example 2:

[0110] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material, which is different from embodiment 1 only in that step (4) is not performed.

[0111] Example 3:

[0112] This comparative example provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the elements of the coating layer 2 are different, and ammonium molybdate is replaced by aluminic acid.

[0113] Example 4:

[0114] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the ammonium molybdate in step (3) is replaced by an equimolar amount of Li2MoO4.

[0115] Example 5:

[0116] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the ammonium molybdate in step (3) is mixed with the precursor and the lithium salt in step (2) in advance, and the primary sintered material is directly sintered in step (3).

[0117] Example 6:

[0118] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the precursor in step (2) and the lithium salt are uniformly mixed in a molar ratio of 1:1.1.

[0119] Example 7:

[0120] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the precursor in step (2) and the lithium salt are uniformly mixed in a molar ratio of 1:1.6.

[0121] Example 8:

[0122] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the amount of nickel sulfate added in step (1) is 2.5% of the mass of the precursor.

[0123] Example 9:

[0124] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the amount of ammonium molybdate added in step (3) is 5% of the mass of the precursor.

[0125] Example 10:

[0126] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the amount of ammonium molybdate added in step (3) is 3% of the mass of the precursor.

[0127] Example 11:

[0128] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the amount of ammonium molybdate added in step (3) is 0.1% of the mass of the precursor.

[0129] Example 12:

[0130] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that in step (4), perfluorooctyltriethoxysiloxane and methylpyridinium phosphane are added simultaneously and the liquid is evaporated to dryness.

[0131] Example 13:

[0132] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that in step (4), perfluorooctyltriethoxysiloxane is replaced by polytetrafluoroethylene.

[0133] Example 14:

[0134] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that methyl pyridinium phos is replaced by pyrimidinium phos in step (4).

[0135] Example 15:

[0136] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that the precursor in step (1) is replaced by Ni0.40 Co 0.05 Mn 0.55 (OH)2.

[0137] Example 16:

[0138] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material, comprising the following steps:

[0139] (1) Ni 0.35 Mn 0.65 (OH)2 was dispersed in water in a solid-liquid mass ratio of 1:1, nickel sulfate and cobalt sulfate were added, and the mixture was stirred while adding ammonia water dropwise until the pH value reached 9. After 30 minutes, the reaction solution was filtered and the obtained solid was dried at 80°C for 12 hours. The total amount of nickel sulfate and cobalt sulfate added was 2% of the mass of the precursor.

[0140] (2) The precursor obtained in step (1) is uniformly mixed with lithium hydroxide in a molar ratio of 1:1.2. The mixed material is placed in an air atmosphere, heated to 550°C at a rate of 2°C / min and sintered for 5 hours. Then, the temperature is increased to 800°C at a rate of 2°C / min and kept at this temperature for 15 hours. The temperature is then lowered along with the furnace and the sintered material is sieved through a 200-mesh sieve to obtain a primary sintered material.

[0141] (3) After uniformly mixing tungstic acid and the primary sintered material, sintering was carried out in an air atmosphere at 550° C. for 3 hours to obtain a secondary sintered material, wherein the amount of tungstic acid used was 0.1 wt % of the primary sintered material.

[0142] (4) The secondary sintered material was added to ethanol at a mass ratio of 1.8:1, and perfluorooctane sulfonic acid was added simultaneously. The mixture was stirred at 70°C until the solution evaporated, and then placed in an oven to obtain an intermediate 1, wherein the amount of perfluorooctane sulfonic acid was 0.5 wt% of the secondary sintered material. Intermediate 1 was then mixed uniformly with triphenyl phosphate at a mixing rate of 1800 rpm, wherein the amount of triphenyl phosphate was 1.5 wt% of the intermediate 1. The mixing time was 15 minutes, and the mixture was sintered at 450°C for 3 hours in an air atmosphere to obtain a lithium-rich manganese-based positive electrode material with a double coating layer.

[0143] Example 17:

[0144] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material, comprising the following steps:

[0145] (1) Ni 0.35 Mn 0.65 (OH)2 was dispersed in water at a solid-liquid mass ratio of 1:2, nickel sulfate was added, and ammonia water was added dropwise while mixing and stirring until the pH value was 10. After 30 minutes, the reaction solution was filtered and the obtained solid was dried at 80°C for 12 hours. The amount of nickel sulfate added was 0.1% of the mass of the precursor.

[0146] (2) The precursor obtained in step (1) is uniformly mixed with lithium hydroxide in a molar ratio of 1:1.5. The mixed material is placed in an air atmosphere, heated to 650°C at a rate of 5°C / min and sintered for 1 hour. Then, the temperature is increased to 850°C at a rate of 5°C / min and kept at this temperature for 12 hours. The temperature is then lowered along with the furnace, and the sintered material is sieved through a 200-mesh sieve to obtain a primary sintered material.

[0147] (3) Niobium oxalate and the primary sintered material were mixed evenly and sintered in an air atmosphere at 750° C. for 4 hours to obtain a secondary sintered material, wherein the amount of niobium oxalate was 5 wt % of the primary sintered material.

[0148] (4) The secondary sintered material was added to ethanol at a mass ratio of 2.2:1, and pentafluorostyrene was added simultaneously. The mixture was stirred at 90°C until the solution evaporated, and then placed in an oven to obtain intermediate 1, wherein the amount of pentafluorostyrene was 1.5 wt% of the secondary sintered material. Intermediate 1 was then mixed uniformly with benfotiamine at a mixing rate of 1800 rpm, wherein the amount of benfotiamine was 0.5 wt% of the intermediate 1. The mixing time was 15 minutes, and the mixture was sintered at 200°C in an air atmosphere for 6 hours to obtain a lithium-rich manganese-based positive electrode material with a double coating layer.

[0149] Comparative Example 1

[0150] This comparative example provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that step (1) is not performed, and the precursor is directly mixed with the lithium salt.

[0151] Comparative Example 2:

[0152] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material, which is different from Example 1 only in that steps (3) and (4) are not performed.

[0153] Comparative Example 3:

[0154] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The only difference from Example 1 is that step (3) is not performed, and the primary sintered material is directly added to ethanol to perform step (4).

[0155] Performance testing:

[0156] The capacity and initial performance of the materials in the above-mentioned embodiments and comparative examples were studied using button half-cells. The experimental method is as follows: Positive electrode sheet: The positive electrode material, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were stirred and dispersed with the solvent NMP in a mass ratio of 92.5:5:2.5, coated on an aluminum foil substrate, and roller-pressed to obtain a positive electrode sheet. Negative electrode sheet: lithium sheet. Electrolyte: 1 mol / L LiPF6 solution, the solvent is a mixed solvent of EC and DMC, and the ratio of the two is 1:2. The charge cut-off voltage is 4.55V, and the discharge cut-off voltage is 2.3V. The cycle performance was tested using a full battery, with a charge cut-off voltage of 4.5V and a discharge cut-off voltage of 3.0V.

[0157] Batteries were prepared from the materials obtained in the above examples and comparative examples and tested. The results are shown in the following table.

[0158] Material characterization

[0159] The XRD phases of the cathode materials prepared in Example 1 and Comparative Example 1 are shown in Figure 2. As can be seen, Comparative Example 1 exhibits a characteristic spinel peak near 30-40° compared to Example 1, while the layered splitting peak near 38° is less pronounced, indicating a significant phase transition. Comparison of Example 4 with Comparative Example 3 reveals that even with only the precursor coating, without molten salt coating, a slight phase transition still occurs.

[0160] The XRD obtained by sintering the coating material used in Example 1 and Comparative Example 2 with the substrate at a ratio of 1%:1 is shown in Figure 3. It can be seen from the XRD that coating with molybdenum acid can form a lithium-containing fast ion conductor, while coating with aluminum cannot form a lithium-containing fast ion conductor layer. Therefore, only specific coating elements can do this.

[0161] The cycle performance of the embodiment and the comparative example is shown in Figure 4. It can be seen from Figure 4 that under the test conditions of voltage of 2.0~4.55V and rate of 1C, the material corresponding to Example 1 still has a capacity retention rate close to 100% after 80 cycles. However, the material corresponding to Comparative Example 1 has a discharge capacity of only 202.9mAh / g after 80 cycles at 1C, and its capacity retention rate is about 90%. The spinel phase transition produced during the subsequent heat treatment of the surface is the main reason affecting the electrochemical performance. Compared with Example 3, Example 2 has greatly improved capacity and capacity retention after surface coating. Compared with Example 2, Example 1 has improved cycle stability after secondary organic carbon coating.

[0162] Table 1 shows the test results of the electrical properties of the positive electrode materials obtained from each embodiment and comparative example. By comparing comparative example 1 with embodiment 1, combined with the XRD spectrum, after the secondary treatment of the precursor, the phase change in the subsequent heat treatment process is greatly curbed, and the capacity is greatly improved. Compared with comparative example 2, embodiment 2 is treated with molten salt on the surface to form a fast ion conductor, which increases the ion diffusion rate between the lithium-rich manganese-based positive electrode materials, effectively increases the capacity of the lithium-rich manganese positive electrode materials, and improves the rate performance. Compared with embodiment 1, embodiment 2 has a certain improvement in capacity and rate based on the conductivity of carbon and the effects of F and P after coating with organic carbon. Compared with embodiment 3, embodiment 1 does not form a fast ion layer on the surface after selecting other coating elements, does not have a lithium extraction effect, and has little effect on capacity improvement and cycle performance. Industrial Applicability

[0163] The present invention reduces the Mn content on the substrate surface by shallow surface doping of the precursor, suppresses the Li2MnO3 content on the substrate surface, and reduces surface phase change. Through two layers of coating, molten salt assists in reducing the Li content on the substrate surface, forming a structure with internal lithium-rich and surface lithium-poor, obtaining an outer layer coating of a fast ion conductor and improving the lithium ion transmission rate; a carbon coating layer is used to achieve full surface coating of the inner layer, limiting the reaction of lattice oxygen, encapsulating unstable oxygen, and improving the stability of oxygen in the lattice. The resulting positive electrode material can be used in the fields of 3C batteries and power batteries, especially under high cut-off voltage (≥4.5V) conditions, and has industrial applicability.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that: It comprises a core and a first coating layer coated on the core, wherein: The core has a chemical formula of xLi2MnO3·(1-x)LiNi a Co b M c O2, where 0 < x ≤ 1, a + b + c = 1, 0 < a < 1, 0 ≤ b < 1, 0 < c < 1, and the proportion of manganese element on the core surface is lower than the average proportion of manganese in the core. M is selected from at least one of Mn, Cr, W, Mo, Nb, and Fe; The first coating layer is a fast ion conductor layer, the general formula of which is Li m Me n O p , m>0, n>0, p>0.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The average thickness of the first coating layer is 8nm-15nm.

3. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The first coating layer is further coated with a second coating layer, and the second coating layer is a carbon coating layer doped with fluorine and phosphorus.

4. The lithium-rich manganese-based positive electrode material according to claim 3, characterized in that: The average thickness of the second coating layer is 8nm-15nm.

5. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The core particle size is 4 μm-10 μm.

6. A method for preparing the lithium-rich manganese-based positive electrode material according to any one of claims 1 to 5, characterized in that: The method comprises coating the core with a first coating layer.

7. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: The method comprises the following steps: doping nickel and / or cobalt elements on the surface of a precursor to obtain a surface manganese-deficient precursor, mixing the surface manganese-deficient precursor with a lithium source and performing a sintering operation to obtain a core; The precursor is at least one of an oxide containing nickel, cobalt, manganese and M elements, a carbonate containing nickel, cobalt, manganese and M elements, and a hydroxide containing nickel, cobalt, manganese and M elements.

8. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: A mixed solution of the precursor, nickel salt and / or cobalt salt is adjusted to pH 9-11 with ammonia water and stirred at the same time to obtain a precursor with nickel hydroxide and / or cobalt hydroxide covered on the surface, which is the surface manganese-deficient precursor.

9. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 8, characterized in that: The nickel salt is at least one of nickel sulfate, nickel oxalate and nickel carbonate; the cobalt salt is at least one of cobalt sulfate, cobalt carbonate and cobalt oxalate.

10. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 8, characterized in that: The solid-liquid mass ratio of the mixed solution is 1:(1-2).

11. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 8, characterized in that: The total mass ratio of the nickel salt and / or cobalt salt in the mixed solution to the precursor mass is 0.1%-2%.

12. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 8, characterized in that: The thickness of the nickel hydroxide and / or cobalt hydroxide covering the surface of the precursor is 40nm-60nm.

13. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: The surface manganese-deficient precursor and the lithium salt are mixed in a molar ratio of 1:(1.2-1.5) and then sintered once.

14. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: The primary sintering comprises: The first stage of sintering is at 500℃-650℃ and kept at this temperature for 1h-5h; The second stage is sintering at a temperature of 850-950°C for 10-15 hours; The first sintering stage and the second sintering stage are both performed in an oxygen atmosphere.

15. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 14, characterized in that: The heating rate of the first stage sintering and / or the second stage sintering is 2°C / min-5°C / min.

16. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium phosphate.

17. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: The method further comprises coating with a first coating layer: the core is mixed with an acid or salt containing Me and then subjected to secondary sintering to obtain the core coated with the first coating layer.

18. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 17, characterized in that: The acid or salt containing Me is at least one of ammonium molybdate, molybdic acid, tungstic acid, ammonium tungstate, niobium oxalate, tantalum oxalate and lanthanum nitrate.

19. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 17, characterized in that: The mass of the acid or salt containing Me is 0.1%-5% of the mass of the core.

20. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 17, characterized in that: The secondary sintering temperature is 550° C.-800° C., the sintering time is 3 h-6 h, and the sintering atmosphere is an oxygen atmosphere.

21. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: The method further comprises coating with a second coating layer: mixing the core coated with the first coating layer, the organic solvent A and the organic carbon source B, and then evaporating the liquid to obtain a first intermediate; mixing the first intermediate and the organic carbon source C to obtain a second intermediate; sintering the second intermediate three times to obtain a lithium-rich manganese-based positive electrode material; The organic carbon source B is selected from reagents containing F element, and the organic carbon source C is selected from reagents containing P element.

22. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The organic solvent A is selected from one or more of ethanol, methanol, acetone and DMF.

23. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The organic carbon source B is at least one of perfluorooctane sulfonic acid, perfluoroethane sulfonic acid, pentafluorostyrene and perfluorooctyltriethoxysilane.

24. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The organic carbon source C is at least one of triphenyl phosphate, methyl pyridinium, benfotiamine and dicyclohexyl phosphate.

25. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The total mass of the organic carbon source B and the organic carbon source C is 1%-5% of the mass of the core coated by the first coating layer.

26. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 25, characterized in that: The mass of the organic carbon source B is 0.5%-1.5% of the mass of the core coated by the first coating layer, and the mass of the organic carbon source C is 0.5%-1.5% of the mass of the core coated by the first coating layer.

27. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The mass ratio of the organic solvent A to the mass of the core coated by the first coating layer is (1.8-2.2):

1.

28. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The core coated with the first coating layer, the organic solvent A and the organic carbon source B are mixed and evaporated to dryness at 70° C.-90° C.

29. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 21, characterized in that: The temperature of the three sinterings is 200° C.-450° C., and the sintering time is 3 h-6 h.

30. A battery, characterized in that: It comprises the lithium-rich manganese-based positive electrode material described in any one of claims 1-5 or the lithium-rich manganese-based positive electrode material obtained by the method described in any one of claims 6-29.

31. An electrical equipment, characterized in that: Comprising the battery of claim 30.

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