Single-crystal lithium-rich manganese-based positive electrode material, preparation method thereof and battery

Abstract

The application discloses a single-crystal lithium-rich manganese-based positive electrode material and a preparation method and a battery thereof, and belongs to the technical field of batteries. The molecular formula of the single-crystal lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiMO2, wherein 0 < x < 1, and M comprises at least one of Ni, Co, Mn, Al, V, Cr and Fe. The single-crystal lithium-rich manganese-based positive electrode material has a single-crystal morphology and a complete layered structure, has high mechanical strength and bonding strength, can improve the cycle performance of the lithium-rich manganese-based positive electrode material, slow down side reactions such as gas production, and improve the comprehensive performance of the lithium-rich manganese-based positive electrode material. The battery prepared from the single-crystal lithium-rich manganese-based positive electrode material has higher capacity and initial efficiency at a low voltage.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of batteries, in particular, to a single-crystal lithium-rich manganese-based positive electrode material and a preparation method thereof and a battery. BACKGROUND

[0002] Lithium ion batteries are widely used in electric vehicles, portable electronic products and in grid storage systems, bringing great convenience to human life. However, with the rapid development of human society, the industry has put forward higher requirements for the energy density of lithium ion batteries for electric vehicles, consumer (3C) electronic products and energy storage devices. Developing high specific capacity and high voltage positive electrode materials to improve the energy density of batteries has become a research hotspot. Lithium-rich manganese-based positive electrodes have attracted the in-depth research of many experts and scholars in the industry due to their high specific capacity, good thermal stability, good cycle performance, wide charge-discharge voltage range, low price, environmental friendliness and other advantages, and have great development potential.

[0003] Currently, the preparation method of lithium-rich manganese-based positive electrode materials mainly adopts co-precipitation-high temperature solid phase method, and the morphology is micron-sized secondary spherical particles formed by the aggregation of hundreds of nanometer primary particles. The mechanical strength of this secondary spherical particle material structure is low and the firmness is poor. Under high compaction conditions, these secondary spherical particles are easily crushed, leading to phenomena such as exposure of internal particles, increased side reactions and metal ion leaching, and are easily broken in the cycle, forming intergranular cracks, and electrolyte easily invades the inside of the secondary particles, aggravating the side reactions of the material and the electrolyte, thereby causing serious capacity decay. At the same time, the primary particle size is too small and has many structural defects, which easily collapses under high voltage charging and discharging, the interface side reaction is difficult to inhibit during the charging and discharging process, causing material structure damage, in addition, the secondary spherical particles also easily lead to swelling and other safety problems.

[0004] In view of this, the present disclosure is proposed. SUMMARY

[0005] One of the purposes of the present disclosure includes providing a single-crystal lithium-rich manganese-based positive electrode material with high single-crystallization degree and complete layered structure, which can effectively improve the above-mentioned problems.

[0006] The second purpose of the present disclosure includes providing a preparation method of the single-crystal lithium-rich manganese-based positive electrode material.

[0007] The third purpose of the present disclosure includes providing a battery comprising the single-crystal lithium-rich manganese-based positive electrode material.

[0008] The present disclosure can be achieved as follows:

[0009] In a first aspect, the present disclosure provides a single-crystal lithium-rich manganese-based cathode material, having a molecular formula of xLi2MnO3·(1-x)LiMO2, wherein 0

[0010] The single-crystal lithium-rich manganese-based cathode material has a single-crystal morphology and a complete layered structure.

[0011] In an optional embodiment, the single-crystal lithium-rich manganese-based cathode material has a smooth surface.

[0012] In an optional embodiment, the single-crystal lithium-rich manganese-based cathode material exhibits a superlattice peak of Li2MnO3 between θ = 20°-22°.

[0013] In an optional embodiment, the single-crystal lithium-rich manganese-based cathode material has an α-NaFeO2 structure of a typical space group of R-3m.

[0014] In an optional embodiment, the single-crystal lithium-rich manganese-based cathode material does not have a spinel structure.

[0015] In a second aspect, the present disclosure provides a method for preparing the single-crystal lithium-rich manganese-based cathode material according to any one of the preceding embodiments, comprising the following steps: performing first sintering on a mixture of a lithium-rich manganese-based cathode material precursor and a first lithium source in an oxygen-free environment to obtain a first sintering product having both a layered structure and a spinel structure; and performing second sintering on a mixture of the first sintering product and a second lithium source in an oxygen-containing environment to convert the spinel structure in the first sintering product into a layered structure.

[0016] In an optional embodiment, the lithium-rich manganese-based cathode material precursor is a Me(OH)2 precursor or a MeCO3 precursor, wherein Me includes at least one of Ni, Co, Mn, Al, V, Cr, and Fe.

[0017] In an optional embodiment, the lithium-rich manganese-based cathode material precursor has a particle size D 50 = 1 μm-15 μm.

[0018] In an optional embodiment, the molar ratio of transition metals in the lithium-rich manganese-based cathode material precursor to lithium in the first lithium source is (1:1)-(1:1.05).

[0019] In an optional embodiment, the first lithium source includes LiOH or Li2CO3.

[0020] In an optional embodiment, the oxygen-free environment is an inert gas environment or a vacuum environment.

[0021] In an optional embodiment, the inert gas environment includes a nitrogen gas environment or an argon gas environment.

[0022] In an optional embodiment, the inert gas environment corresponds to a gas flow rate > 0 m 3 / h and ≤ 20 m 3 / h.

[0023] In an optional embodiment, the first sintering comprises: first holding at 450-700℃ for 3-10h, and then holding at 800-1100℃ for 3-15h.

[0024] In an optional embodiment, the molar ratio of the transition metal to lithium in the second lithium source in the sintered product is (1:0.1)-(1:0.6).

[0025] In an optional embodiment, the second lithium source comprises LiOH or Li2CO3.

[0026] In an optional embodiment, the oxygen-containing environment is an air environment or an oxygen environment.

[0027] In an optional embodiment, the oxygen-containing environment corresponds to a gas flow rate of 1 m 3 / h-20 m 3 / h.

[0028] In an optional embodiment, the second sintering comprises: first holding at 650-750℃ for 0.5-5h, and then holding at 800-1100℃ for 2-10h.

[0029] In a third aspect, the present disclosure provides a battery containing the single-crystal lithium-rich manganese-based positive electrode material of any one of the preceding embodiments.

[0030] The beneficial effects of the present disclosure include:

[0031] The single-crystal lithium-rich manganese-based positive electrode material provided by the present disclosure has a single-crystal morphology and a complete layered structure, has higher mechanical strength and bonding strength than the secondary spherical particle lithium-rich manganese-based positive electrode material, can effectively avoid particle breakage under high compaction, avoid electrolyte intrusion into the interior of the secondary particles, and slow down the side reactions of the material and the electrolyte. In addition, the single-crystal lithium-rich manganese-based positive electrode material has better cycle performance, can slow down side reactions such as gas production, and improve the comprehensive performance of the lithium-rich manganese-based positive electrode material. The battery prepared therefrom can have higher capacity and initial efficiency at low voltage. BRIEF DESCRIPTION OF DRAWINGS

[0032] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the accompanying drawings required for 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, without creative efforts, other related drawings can also be obtained based on these drawings.

[0033] Figure 1 SEM image of the lithium-rich manganese-based cathode material in Comparative Example 1 of the present disclosure;

[0034] Figure 2 SEM image of the lithium-rich manganese-based cathode material in Comparative Example 2 of the present disclosure;

[0035] Figure 3 SEM image of the first fired product in Test Example 1 of the present disclosure;

[0036] Figure 4 SEM image of the second fired product in Test Example 1 of the present disclosure;

[0037] Figure 5 XRD pattern of the single crystal lithium-rich manganese-based cathode material in Test Example 1 of the present disclosure;

[0038] Figure 6 First cycle charge-discharge result graph of the battery corresponding to Example 1 in Test Example 2 of the present disclosure. Detailed implementation manners

[0039] 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 not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0040] The single crystal lithium-rich manganese-based cathode material, its preparation method, and the battery provided by the present disclosure will be specifically described below.

[0041] The present disclosure provides a single crystal lithium-rich manganese-based cathode material with the molecular formula xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M includes at least one of Ni, Co, Mn, Al, V, Cr, and Fe; this single crystal lithium-rich manganese-based cathode material has a single crystal morphology and a complete layered structure.

[0042] Compared with the secondary spherical particle manganese-rich cathode material, the single-crystal lithium-rich manganese-based cathode material has higher mechanical strength and bonding strength, can effectively avoid particle breakage under high compaction, avoid electrolyte intrusion into the secondary particle, and slow down the side reaction between the material and the electrolyte. In addition, the single-crystal lithium-rich manganese-based cathode material has better cycle performance, can slow down the side reaction such as gas production, and improve the comprehensive performance of the lithium-rich manganese-based cathode material.

[0043] In the present disclosure, the single-crystal lithium-rich manganese-based cathode material has a D 50 = 1 μm-15 μm, which is beneficial to more easily form a single-crystal morphology in the first sintering.

[0044] In some embodiments, the single-crystal lithium-rich manganese-based cathode material has a smooth and flat surface, so that the surface attachments and impurities are less, which is beneficial to improve the cycle performance of the material.

[0045] In the present disclosure, the single-crystal lithium-rich manganese-based cathode material has a superlattice peak of Li2MnO3 between θ = 20°-22°, so that the material can have the characteristics of high specific capacity, high voltage, and high energy density.

[0046] In addition, the single-crystal lithium-rich manganese-based cathode material has a typical α-NaFeO2 structure of space group R-3m, which can make the material have higher capacity at low voltage.

[0047] It should be noted that the single-crystal lithium-rich manganese-based cathode material in the present disclosure has no spinel structure, and the spinel structure is completely converted into a layered structure, which can improve the reversible specific capacity of the material.

[0048] Correspondingly, the present disclosure also provides a preparation method of the single-crystal lithium-rich manganese-based cathode material, which can include the following steps: performing first sintering on a mixture of a lithium-rich manganese-based cathode material precursor and a first lithium source in an oxygen-free environment to obtain a first sintering product having both a layered structure and a spinel structure; and performing second sintering on a mixture of the first sintering product and a second lithium source in an oxygen-containing environment to convert the spinel structure in the first sintering product into a layered structure.

[0049] For reference, the lithium-rich manganese-based cathode material precursor can be, for example, a Me(OH)2 precursor or a MeCO3 precursor. That is, in some embodiments, the Me(OH)2 precursor can be used, and in other embodiments, the MeCO3 precursor can be used. The Me in the precursor can include at least one of Ni, Co, Mn, Al, V, Cr, and Fe, and specifically, the selection of M corresponds to Me in the molecular formula of the single-crystal lithium-rich manganese-based cathode material.

[0050] The above lithium-rich manganese-based positive electrode material precursor can be directly purchased or prepared by referring to a conventional coprecipitation method.

[0051] In the present disclosure, the particle size D 50 of the lithium-rich manganese-based positive electrode material precursor is 1 μm-15 μm, such as 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm or 15 μm, etc., and can also be any other value within the range of 1 μm-15 μm.

[0052] If the particle size of the lithium-rich manganese-based positive electrode material precursor is less than 1 μm, it is not conducive to industrial production (the particles are too small, and the yield of the precursor is low); if the particle size of the lithium-rich manganese-based positive electrode material precursor is greater than 15 μm, it is not conducive to the formation of single crystals, or it is easy to cause the internal hollow of the formed single crystals.

[0053] The molar ratio of transition metal to lithium in the first lithium source in the lithium-rich manganese-based positive electrode material precursor can be (1:1)-(1:1.05), such as 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04 or 1:1.05, etc., and can also be any other value within the range of (1:1)-(1:1.05).

[0054] The first lithium source can include LiOH or Li2CO3.

[0055] In the present disclosure, the first sintering is performed in an oxygen-free environment, which can be an inert gas environment or a vacuum environment, for example.

[0056] The inert gas environment can include a nitrogen gas environment or an argon gas environment. The gas flow corresponding to the inert gas environment is >0 m 3 / h and ≤20 m 3 / h, such as 2 m 3 / h, 5 m 3 / h, 8 m 3 / h, 10 m 3 / h, 12 m 3 / h, 15 m 3 / h, 18 m 3 / h or 20 m 3 / h, etc.

[0057] If the gas flow during the first sintering process exceeds 20 m 3 / h, more lithium ions are likely to volatilize.

[0058] It should be noted that the present disclosure can successfully prepare a single crystal product with a single crystal morphology by performing the first sintering in an oxygen-free environment. If there is oxygen during the first sintering process, the prepared one-sintered product will have a polycrystalline morphology, which is not conducive to the formation of a single crystal morphology.

[0059] The first sintering in the present disclosure is to first keep the material at a low temperature zone for a period of time to decompose the material, and then to increase the temperature and keep the material at a period of time to react the material. The low temperature zone decomposes the material refers to decomposing the Me(OH)2 precursor or the MeCO3 precursor into MeO, decomposing the LiOH or the Li2CO3 into Li2O.

[0060] For reference, the first sintering includes: first keeping at 450-700℃ for 3-10h, and then keeping at 800-1100℃ for 3-15h.

[0061] That is, the temperature of the low temperature zone in the first sintering process is 450-700℃, such as 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃, and the keeping time of the low temperature zone in the first sintering process is 3-10h, such as 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0062] If the temperature of the low temperature zone in the first sintering process is less than 450℃, it is not conducive to the decomposition of the precursor and the lithium salt; if the temperature of the low temperature zone in the first sintering process is higher than 700℃, the precursor and the lithium salt cannot be fully decomposed and have already begun to react, resulting in that the material decomposes and reacts at the same time, which can cause defects in the material. Similarly, if the keeping time of the low temperature zone in the first sintering process is less than 3h, it is not conducive to the decomposition of the precursor and the lithium salt; if the keeping time of the low temperature zone in the first sintering process is longer than 10h, more spinel structures can be generated, which is not conducive to the transformation of the layered structure in the second sintering process.

[0063] The increased temperature in the first sintering process is 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃, and the keeping time of the increased temperature in the first sintering process is 3-15h, such as 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.

[0064] If the increased temperature in the first sintering process is less than 800℃, it can easily lead to a low crystallinity of the layered structure; if the increased temperature in the first sintering process is higher than 1100℃, it can easily lead to a large loss of lithium ion evaporation. Similarly, if the keeping time of the increased temperature in the first sintering process is less than 3h, it is not conducive to the formation of single crystal morphology; if the keeping time of the increased temperature in the first sintering process is longer than 15h, it can easily lead to a large loss of lithium ion evaporation.

[0065] The present disclosure can prepare a one-sintering product with single crystal morphology without adding any fluxing agent by sintering in the above manner. The one-sintering product has both layered structure and spinel structure.

[0066] It should be noted that after the above oxygen-free sintering, the obtained first sintering product particles may have agglomeration phenomenon, and the sample surface is uneven, which indicates that the reaction in the sintering process is insufficient, resulting in that lithium ions do not completely enter the crystal lattice. There may also be attachments on the surface of the first sintering sample, and the attachments may be lithium sources that do not react completely or metal oxides after dehydration of the precursor.

[0067] Based on this, the present disclosure adds a second lithium source and performs a second sintering in an oxygen-containing atmosphere to improve the above problems and promote the complete conversion of the spinel structure into a layered structure.

[0068] Before adding the second lithium source, the first sintering product can also be crushed and sieved to make its D 50 = 1 μm-15 μm.

[0069] For reference, the molar ratio of transition metal to lithium of the second lithium source in the first sintering product can be (1:0.1)-(1:0.6), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5 or 1:0.6, etc.

[0070] Similarly, the second lithium source can also include LiOH or Li2CO3.

[0071] In the present disclosure, the oxygen-containing environment can be an air environment or an oxygen environment. Exemplarily, the gas flow corresponding to the oxygen-containing environment can be 1 m 3 / h-20 m 3 / h, such as 1 m 3 / h, 2 m 3 / h, 5 m 3 / h, 8 m 3 / h, 10 m 3 / h, 12 m 3 / h, 15 m 3 / h, 18 m 3 / h or 20 m 3 / h, etc.

[0072] In the present disclosure, the second sintering is first kept at a low temperature for a period of time to decompose the added second lithium source, and then the temperature is raised and kept for a period of time to react the material.

[0073] For reference, the second sintering includes: first keeping at 650°C-750°C for 0.5h-5h, and then keeping at 800°C-1100°C for 2h-10h.

[0074] That is, the temperature of the low-temperature zone in the second sintering process is 650-750℃, such as 650℃, 680℃, 700℃, 720℃ or 750℃, and the holding time of the low-temperature zone in the second sintering process is 0.5-5h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0075] If the temperature of the low-temperature zone in the second sintering process is less than 650℃, the decomposed lithium oxide is not conducive to diffusion into the single crystal; if the temperature of the low-temperature zone in the second sintering process is higher than 750℃, the surface layer will preferentially form a layered structure, and the core will still be a spinel structure, which is not conducive to the formation of a complete layered structure in the single crystal. Similarly, if the holding time of the low-temperature zone in the second sintering process is less than 0.5h, it is not conducive to the formation of a layered structure; if the holding time of the low-temperature zone in the second sintering process is longer than 5h, it is easy to cause more loss of lithium ion evaporation.

[0076] The temperature after the increase in the second sintering process is 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃, and the holding time after the increase in the second sintering process is 2-10h, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0077] If the temperature after the increase in the second sintering process is less than 800℃, it is not conducive to the formation of a complete layered structure; if the temperature after the increase in the second sintering process is higher than 1100℃, it is easy to cause more loss of lithium ion evaporation. Similarly, if the holding time after the increase in the second sintering process is less than 2h, it is conducive to the formation of a complete layered structure; if the holding time after the increase in the second sintering process is longer than 10h, it is easy to cause more loss of lithium ion evaporation.

[0078] The present disclosure can completely convert the spinel structure in the material to a layered structure by the second sintering in the above manner, and make the surface of the second sintering product smooth and flat, exhibit a superlattice peak of Li2MnO3 between θ=20-22° and have a typical α-NaFeO2 structure belonging to the space group R-3m.

[0079] Further, the second sintering product can be crushed and sieved according to the required particle size.

[0080] Further, the second sintering product can be crushed and sieved according to the required particle size.

[0081] In addition, the present disclosure also provides a battery containing the single-crystal lithium-rich manganese-based positive electrode material described above, which has a higher specific capacity and initial efficiency.

[0082] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0083] Example 1

[0084] This embodiment provides a single-crystal lithium-rich manganese-based cathode material, the preparation method of which includes the following steps:

[0085] S1: Take 100g of D 50 Ni, a lithium-rich manganese-based cathode material precursor with a diameter of 5.5 μm. 0.40 Mn 0.60 (OH)₂ and 42g of Li₂CO₃ were mixed evenly (the molar ratio of transition metal in the precursor to lithium in Li₂CO₃ was 1.05:1), and then placed in a sintering furnace, through which 5m³ of sulfur dioxide was introduced. 3 Nitrogen gas was used as a protective gas to maintain an oxygen-free environment in the sintering furnace. The furnace was held at 550°C for 4 hours, then the temperature was increased to 850°C and held for 12 hours. The furnace was then cooled to room temperature to obtain the first sintered product.

[0086] The aforementioned lithium-rich manganese-based cathode material precursor Ni 0.40 Mn 0.60 (OH)₂ was prepared by the following method:

[0087] A nickel-manganese metal sulfate solution A (total metal concentration of 2 mol / L) was prepared with a nickel-manganese molar ratio of 4:6. A mixed solution B consisting of a 5 mol / L complexing agent (ammonia) and a 10 mol / L precipitant (NaOH) was also prepared. The agitator in the reactor was submerged in deionized water (stirring speed 50 rpm), and nitrogen gas was passed through the deionized water to prevent manganese oxidation. Then, solutions A and B were introduced into the reactor to generate Ni. 0.40 Mn 0.60 (OH)₂ compound, wherein the flow rate of solution A is 50 mL / min, and the flow rate of solution B is determined according to the pH value in the reactor to maintain the pH value in the reactor at 10-12, and the precipitation reaction temperature is 60℃. Ni is obtained by filtering, washing, drying, and sieving the above materials. 0.40 Mn 0.60 (OH)2 precursor.

[0088] S2: The primary calcination product is crushed and sieved to improve the D content of the primary calcination product. 50 =5.5μm.

[0089] S3: Mix 50g of the sintered product after sieving S2 with 5g of lithium carbonate until homogeneous, then place it in a sintering furnace and purge with 10m³ of gas. 3 / h air, and then the temperature was increased to 800℃ and maintained for 8h, and then the furnace was cooled to room temperature, to obtain a two-burn product.

[0090] S4: The two-burn product was crushed and sieved to obtain D 50 = 5.5μm single-crystal lithium-rich manganese-based positive electrode material.

[0091] Example 2

[0092] The difference between this example and Example 1 is that in S1, the lithium-rich manganese-based positive electrode material precursor is D 50 = 6.5μm Ni 0.37 Mn 0.63 (OH)2; and in S3, the amount of lithium carbonate was 8g.

[0093] The preparation method of the above-mentioned lithium-rich manganese-based positive electrode material precursor Ni 0.37 Mn 0.63 (OH)2refers to the preparation of the Ni 0.40 Mn 0.60 (OH)2precursor in Example 1, except that the molar ratio of nickel to manganese in the metal salt solution A was 4:6.

[0094] Example 3

[0095] This example provides a single-crystal lithium-rich manganese-based positive electrode material, and the preparation method thereof comprises the following steps:

[0096] S1: 100g of D 50 = 1μm lithium-rich manganese-based positive electrode material precursor Ni 0.40 Mn 0.60 (OH)2and LiOH were mixed uniformly (the molar ratio of transition metals in the precursor to lithium in LiOH was 1:1), and then placed in a sintering furnace, and 10m 3 / h nitrogen gas was introduced as a protective gas to maintain an oxygen-free environment in the sintering furnace, and the temperature was maintained at 450℃ for 5h, and then the temperature was increased to 800℃ and maintained for 15h, and then the furnace was cooled to room temperature, to obtain a one-burn product.

[0097] The source of the above-mentioned lithium-rich manganese-based positive electrode material precursor Ni 0.40 Mn 0.60 (OH)2is the same as in Example 1.

[0098] S2: The one-burn product was crushed and sieved to make the D 50 = 1μm of the one-burn product.

[0099] S3: Mix 50g of the sintered product after sieving S2 with LiOH until homogeneous (the molar ratio of transition metal in the sintered product to lithium in LiOH is 1:0.1), then place it in a sintering furnace and purge with 10m³ of sulfur dioxide. 3 The furnace is heated to 650℃ for 5 hours with air at a constant temperature, then the temperature is increased to 900℃ and held for 10 hours. The furnace is then cooled to room temperature to obtain the second-burned product.

[0100] S4: The secondary calcination product is crushed and sieved to obtain D. 50 =1μm single-crystal lithium-rich manganese-based cathode material.

[0101] Example 4

[0102] This embodiment provides a single-crystal lithium-rich manganese-based cathode material, the preparation method of which includes the following steps:

[0103] S1: Take 100g of D 50 Ni, a lithium-rich manganese-based cathode material precursor with a diameter of 15 μm 0.40 Mn 0.60 CO3 and LiOH were mixed evenly (the molar ratio of transition metal to lithium in the precursor was 1:1.03), and then placed in a sintering furnace, through which 20m³ of oxygen was introduced. 3 Nitrogen gas was used as a protective gas to maintain an oxygen-free environment in the sintering furnace. The furnace was held at 700°C for 3 hours, then the temperature was increased to 1100°C and held for 5 hours. The furnace was then cooled to room temperature to obtain the first-burned product.

[0104] The aforementioned lithium-rich manganese-based cathode material precursor Ni 0.40 Mn 0.60 The method for preparing CO3 is the same as that for Ni in Example 1. 0.40 Mn 0.60 The preparation of the (OH)2 precursor differs in that the precipitant is replaced with a 2 mol / L Na2CO3 solution, and the metal salt solution and sodium carbonate solution are introduced into the reaction vessel at the same flow rate to stabilize the pH value at 7-8. The remaining procedures and conditions are the same.

[0105] S2: The primary calcination product is crushed and sieved to improve the D content of the primary calcination product. 50 =15μm.

[0106] S3: Mix 50g of the sintered product after sieving S2 with LiOH until homogeneous (the molar ratio of transition metal in the sintered product to lithium in LiOH is 1:0.6), then place it in a sintering furnace and introduce 10m³ of sulfuric acid. 3 / h of air was heated at 750℃ for 0.5h, then the temperature was increased to 1100℃ and held for 2h, and then cooled to room temperature in the furnace to obtain the second calcination product.

[0107] S4: The double-sintered product is crushed and sieved to obtain D 50 = 15 μm single-crystal lithium-rich manganese-based positive electrode material.

[0108] Comparative Example 1

[0109] The difference between this comparative example and Example 1 is that the particle size D 50 = 20 μm of the lithium-rich manganese-based positive electrode material precursor.

[0110] The SEM image of the lithium-rich manganese-based positive electrode material obtained in this comparative example is shown in FIG. 2, and the results show that when the particle size of the precursor is too large, the lithium-rich manganese-based positive electrode material obtained has defects such as bubbles and cracks inside. Figure 1

[0111] Comparative Example 2

[0112] The difference between this comparative example and Example 1 is that in the first sintering process, an equal amount of air is used instead of nitrogen; that is, the first sintering is performed in an oxygen-containing environment.

[0113] The SEM image of the lithium-rich manganese-based positive electrode material obtained in this comparative example is shown in FIG. 3, and the results show that when the first sintering is performed in an oxygen-containing environment, the lithium-rich manganese-based positive electrode material obtained has a polycrystalline morphology. Figure 2

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 1 is that in the first sintering process, the temperature in the low-temperature zone is 400°C.

[0116] Comparative Example 4

[0117] The difference between this comparative example and Example 1 is that in the first sintering process, the temperature in the low-temperature zone is 800°C.

[0118] Comparative Example 5

[0119] The difference between this comparative example and Example 1 is that the second sintering is not performed, and the first-sintered product is directly used as the positive electrode material.

[0120] The structure of the lithium-rich manganese-based positive electrode material obtained in this comparative example includes a layered structure and a spinel structure.

[0121] Comparative Example 6

[0122] The difference between this comparative example and Example 1 is that in the second sintering process, an equal amount of nitrogen is used instead of air; that is, the second sintering is performed in an oxygen-free environment.

[0123] The structure of the lithium-rich manganese-based positive electrode material obtained in this comparative example includes a layered structure and a spinel structure.

[0124] Comparative Example 7​​

[0125] The difference between the present comparative example and Example 1 is that the air flow is 0.5 m 3 / h during the second sintering process.

[0126] Test Example 1

[0127] Taking Example 1 as an example, the first sintered product and the second sintered product obtained during the preparation process are compared:

[0128] ① The SEM images of the first sintered product and the second sintered product are shown in Figure 3 and Figure 4 respectively.

[0129] As can be seen from Figure 3 , after the first sintering in an oxygen-free environment, the single crystal material particles appear to be agglomerated, and the surface of the sample is uneven, indicating that the reaction during the first sintering process is not sufficient, resulting in lithium ions not completely entering the crystal lattice. The attachments on the surface of the first sintered sample may be lithium sources that have not completely reacted or metal oxides after dehydration of the precursor.

[0130] As can be seen from Figure 4 , after the second sintering for lithium supplementation, the agglomerated particles form individual particles, and the particle surface is smooth and complete, indicating that the reaction between materials is sufficient.

[0131] ② The XRD images of the first sintered product and the second sintered product are shown in Figure 5 .

[0132] As can be seen from Figure 5 , the first sintered single crystal sample obtained after the first sintering in an oxygen-free environment does not have a Li2MnO3 superlattice peak between θ = 20°-22°, and the phase only matches the layered structure and spinel structure. After the second sintering, the sample presents a Li2MnO3 superlattice peak between θ = 20°-22°, the lithium-rich manganese-based positive electrode material has a typical α-NaFeO2 structure, belongs to the R-3m space group, and the (006) / (012) and (018) / (110) peaks are obviously split, indicating that the layered structure is complete, and the phase matching does not match the spinel phase, indicating that the spinel phase is converted into a complete layered structure during the second sintering process.

[0133] Test Example 2

[0134] Taking the lithium-rich manganese-based positive electrode materials obtained in Examples 1-4 and Comparative Examples 1-6 as examples, batteries were prepared according to the following methods respectively:

[0135] The single crystal morphology lithium-rich manganese-based positive electrode material, super carbon black and polyvinylidene fluoride (PVDF) are weighed according to the mass ratio of 9:0.5:0.5, mixed thoroughly, coated on an aluminum foil, and placed in a vacuum drying oven at 100°C for 5h. After taking out, the aluminum foil is placed on a rolling machine and rolled several times, and then a round piece is cut out. The round piece is used as a positive electrode, a lithium metal sheet is used as a negative electrode, a polypropylene microporous membrane is used as a separator, and 1mol / L LiPF6+EC / DMC / EMC is used as an electrolyte. The assembly of a CR2430 stainless steel button cell is completed in an argon-filled glove box with a water content of less than 0.1ppm. After standing for 10h, the charge and discharge performance is tested under the conditions of a voltage of 2.5-4.8V and a rate of 0.1C.

[0136] The first cycle charge and discharge result diagram of the battery corresponding to Example 1 is shown in Figure 6 As can be seen from Figure 6 , the initial charge specific capacity of the battery is 287.1mAh / g, the first cycle discharge specific capacity is 225.4mAh / g, and the first efficiency is 78.5%.

[0137] The first cycle charge and discharge results of the batteries obtained in the remaining examples and comparative examples are summarized in Table 1.

[0138] Table 1: First cycle charge and discharge results

[0139]

[0140] As can be seen from Table 1, the single crystal lithium-rich manganese-based positive electrode material prepared by the present disclosure can further obtain a battery with high specific capacity and high first efficiency.

[0141] Industrial applicability

[0142] The single crystal lithium-rich manganese-based positive electrode material provided by the present disclosure has a single crystal morphology and a complete layered structure, and has higher mechanical strength and bonding strength than the secondary spherical particle manganese-based positive electrode material. It can effectively avoid particle breakage under high compaction, avoid the intrusion of electrolyte into the interior of the secondary particle, and slow down the side reactions of the material and the electrolyte. In addition, the single crystal lithium-rich manganese-based positive electrode material has good cycle performance, can slow down the side reactions such as gas production, and improve the comprehensive performance of the lithium-rich manganese-based positive electrode material. The battery prepared therefrom can have higher capacity and first efficiency at low voltage.

Claims

1. A single-crystal lithium-rich manganese-based cathode material, characterized in that, The molecular formula of the single-crystal lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M includes at least one of Ni, Co, Mn, Al, V, Cr, and Fe; The single-crystal lithium-rich manganese-based cathode material has a single-crystal morphology and a complete layered structure; The single-crystal lithium-rich manganese-based cathode material has no spinel structure; The preparation of the single-crystal lithium-rich manganese-based cathode material includes the following steps: sintering the mixture of the lithium-rich manganese-based cathode material precursor and the first lithium source in an oxygen-free environment for the first time to obtain a first-sintered product with both a layered structure and a spinel structure; sintering the mixture of the first-sintered product and the second lithium source in an oxygen-containing environment for the second time to convert the spinel structure in the first-sintered product into a layered structure; the first sintering includes: first maintaining the temperature at 450°C - 700°C for 3h - 10h, and then maintaining the temperature at 800°C - 1100°C for 3h - 15h.

2. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The surface of the single-crystal lithium-rich manganese-based cathode material is smooth and flat.

3. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The single-crystal lithium-rich manganese-based cathode material exhibits a superlattice peak of Li2MnO3 between θ = 20° - 22°.

4. The single-crystal lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The single-crystal lithium-rich manganese-based cathode material has a typical α-NaFeO2 structure belonging to the R-3m space group.

5. A method for preparing a single-crystal lithium-rich manganese-based cathode material as described in any one of claims 1-4, characterized in that, Including the following steps: Sintering the mixture of the lithium-rich manganese-based cathode material precursor and the first lithium source in an oxygen-free environment for the first time to obtain a first-sintered product with both a layered structure and a spinel structure; Sintering the mixture of the first-sintered product and the second lithium source in an oxygen-containing environment for the second time to convert the spinel structure in the first-sintered product into a layered structure; The first sintering includes: first maintaining the temperature at 450°C - 700°C for 3h - 10h, and then maintaining the temperature at 800°C - 1100°C for 3h - 15h.

6. The preparation method according to claim 5, characterized in that, The lithium-rich manganese-based cathode material precursor is a Me(OH)2 precursor or a MeCO3 precursor, and Me includes at least one of Ni, Co, Mn, Al, V, Cr, and Fe.

7. The preparation method according to claim 6, characterized in that, The particle size D of the lithium-rich manganese-based cathode material precursor 50 =1μm-15μm.

8. The preparation method according to claim 6, characterized in that, The molar ratio of the transition metal in the lithium-rich manganese-based cathode material precursor to the lithium in the first lithium source is (1:1) - (1:1.05).

9. The preparation method according to claim 8, characterized in that, [[ID=十三]]The first lithium source includes LiOH or Li2CO3.

10. The preparation method according to claim 5, characterized in that, The oxygen-free environment is an inert gas environment or a vacuum environment.

11. The preparation method according to claim 10, characterized in that, The inert gas environment includes a nitrogen environment or an argon environment.

12. The preparation method according to claim 11, characterized in that, Gas flow rate > 0 m³ / s in an inert gas environment 3 / h and ≤20m 3 / h.

13. The preparation method according to claim 5, characterized in that, The molar ratio of the transition metal in the first-sintered product to the lithium in the second lithium source is (1:0.1) - (1:0.6).

14. The preparation method according to claim 13, characterized in that, The second lithium source includes LiOH or Li2CO3.

15. The preparation method according to claim 5, characterized in that, The oxygen-containing environment is an air environment or an oxygen environment.

16. The preparation method according to claim 15, characterized in that, The gas flow rate corresponding to an aerobic environment is 1 m³ / s. 3 / h-20m 3 / h.

17. The preparation method according to claim 5, characterized in that, The second sintering includes: first maintaining the temperature at 650°C - 750°C for 0.5h - 5h, and then maintaining the temperature at 800°C - 1100°C for 2h - 10h.

18. A battery, characterized in that, Containing the single-crystal lithium-rich manganese-based cathode material according to any one of claims 1 - 4.

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