A cobalt-free lithium-rich single-crystalline cathode material with adjustable crystal planes, its preparation method and application

Abstract

The present invention discloses a cobalt-free lithium-rich single-crystal cathode material with adjustable crystal planes, a preparation method thereof, and applications. The molecular formula of the cobalt-free lithium-rich single-crystal cathode material with adjustable crystal planes is Li1+xNiyMn0.8 yO2. The cobalt-free lithium-rich single-crystal cathode material is single-crystal particles with a size between 0.2 - 5 μm. The top and bottom surfaces of the single-crystal particles are (001) crystal planes, and at least one of the {012} or {010} active crystal planes with fast lithium-ion transport channels is exposed on the side surfaces. The preparation method of the present invention uses a eutectic mixed salt with a lower melting point, combines the surface energies of different crystal planes of the cobalt-free lithium-rich single-crystal cathode crystal, and realizes the controllable exposure of its crystal planes by adjusting the molar ratios of the precursor, the eutectic mixed salt, and the two salts in the eutectic mixed salt, which can improve the electrochemical performance of the cobalt-free lithium-rich single-crystal cathode material. The process of the present invention is simple in operation and low in production cost, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for lithium-ion batteries, and particularly to a facet-adjustable cobalt-free lithium-rich single-crystal cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high charge and discharge efficiency, low self-discharge rate, etc., and are widely used in modern industrial and life fields. With the rapid development of 3C electronic devices and electric vehicles, high-capacity lithium-ion power batteries have become the focus of the development of global new energy and technology. The capacity of lithium-ion batteries depends on their cathode materials. Seeking a cathode material with low cost, high energy density, long cycle life, and excellent rate performance is the key point of current technological research.

[0003] So far, the specific capacities of the developed lithium-ion cathode materials (such as spinel-type lithium manganate LiMn2O4, lithium cobaltate LiCoO2, ternary material NCM) are all lower than 200 mAh / g, which cannot meet the requirements of current industry and daily use for high-capacity lithium-ion power batteries. Therefore, it is necessary to continue to develop a high-capacity lithium-ion battery cathode material.

[0004] After years of research, cobalt-free lithium-rich manganese-based layered oxide cathode materials have become the first choice for the next generation of high-capacity lithium-ion battery cathode materials due to their ultra-high theoretical capacity (250 mAh / g), non-toxic cobalt-free, and low cost. At present, the widely studied cobalt-free lithium-rich layered oxide cathode materials are mostly spherical secondary particle aggregates composed of primary particles, which are prone to fragmentation during the cycling process. Excessive nanoparticle gaps lead to a large number of interfacial reactions consuming the electrolyte and generating more side reactions, thereby affecting their electrochemical performance. Moreover, the high specific capacity of the lithium-rich manganese-based layered oxide cathode originates from the oxygen anion reaction of the Li2MnO3 component at voltages higher than 4.5 V. This reaction will cause the Mn element in its surface layer to migrate from the transition metal layer to the lithium layer, resulting in an irreversible "layered-spinel" phase transition, and then leading to voltage drop and material capacity decay during the cycling process. These problems have severely restricted the commercialization of lithium-rich manganese-based layered oxide cathodes. From the perspective of morphology and crystal structure design, single-crystal cathode materials can maintain a complete morphology under the same pressure due to their complete crystal structure, while aggregate cathode materials are prone to structural collapse due to their secondary aggregate structure; during the battery cycling process, the thermal release temperature of single-crystal materials is much lower than that of aggregate cathode materials, and thus they have better thermal stability. Therefore, single-crystal cathode materials have the advantages of high mechanical strength, stable structure, good thermal stability, etc., and have significant advantages in cycling stability compared with aggregate cathode materials during the cycling process. However, the kinetic performance of single-crystal cathode materials is low, resulting in poor rate performance. By adjusting the crystal facets of single-crystal materials, exposing active crystal facets with lithium-ion channels is an effective method.

[0005] The Chinese patent document with the publication number CN113497227A discloses a single-crystal-like lithium-rich layered oxide cathode material with an adjustable full concentration gradient and its preparation. However, this single-crystal material does not perform crystal plane regulation from the perspective of crystal structure and contains a trace amount of Co element.

[0006] The Chinese patent document with the publication number CN114628657A discloses a cobalt-free lithium-rich single-crystal-like gradient material and its preparation method. Although the prepared cobalt-free lithium-rich manganese-based layered oxide single-crystal cathode material regulates the changes of Ni and Mn elements inside the particles, it still cannot regulate the crystal structure of the single-crystal material. Summary of the Invention

[0007] The first object of the present invention is to provide a crystal plane adjustable cobalt-free lithium-rich single-crystal cathode material, the second object is to provide a preparation method of the above material, and the third object of the present invention is to provide an application of the above material in the cathode material of a lithium-ion battery.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a crystal plane adjustable cobalt-free lithium-rich single-crystal cathode material. The molecular formula of the crystal plane adjustable cobalt-free lithium-rich single-crystal cathode material is Li 1+x Ni y Mn 0.8-y O2, where 0 < x < 0.25 and 0 < y < 0.8. Preferably, the crystal plane adjustable cobalt-free lithium-rich single-crystal cathode material is single-crystal-like particles with a size between 0.2 - 5 μm. The single-crystal-like particles have a sheet structure or a polyhedron structure with the top and bottom surfaces being (001) crystal planes, and at least one of the side surfaces exposing {012} or {010} active crystal planes with fast lithium-ion transport channels. The sum of the exposure ratios of the {012} active crystal plane and the {010} active crystal plane is 0.15 - 0.65;

[0010] In the second aspect, the present invention provides a preparation method of the above material, including the following steps:

[0011] (1) Prepare a cobalt-free lithium-rich single-crystal cathode material precursor from manganese salt and nickel salt by a solid-phase method or a co-precipitation method;

[0012] (2) Uniformly mix the cobalt-free lithium-rich single-crystal cathode material precursor, lithium source and eutectic mixed salt and then calcine to obtain a sintered product; wash and heat-treat the sintered product to obtain the crystal plane adjustable cobalt-free lithium-rich single-crystal cathode material.

[0013] Preferably, the manganese salt is any one of manganese carbonate, manganese nitrate or manganese acetate; the nickel salt is any one of nickel carbonate, nickel nitrate or nickel acetate.

[0014] Preferably, in the step (1), in the solid-phase method, the manganese salt and the nickel salt are uniformly mixed to obtain a precursor of a cobalt-free lithium-rich single-crystal cathode material; the molar ratio of Mn in the manganese salt to Ni in the nickel salt is 0.8 - y:y, where 0 < y < 0.8.

[0015] Preferably, in the step (1), in the co-precipitation method, the manganese salt and the nickel salt are dissolved in deionized water to prepare solution A; under the protection of a protective gas, solution A, an alkali solution, and ammonia water are mixed for a co-precipitation reaction to obtain a suspension; the suspension is filtered, washed, and dried to obtain a precursor of a cobalt-free lithium-rich single-crystal cathode material; the molar ratio of Mn in the manganese salt to Ni in the nickel salt is 0.8 - y:y, where 0 < y < 0.8. Compared with the solid-phase method, using the precursor prepared by the co-precipitation method can make the product particles more uniform and the electrochemical performance more consistent.

[0016] More preferably, the alkali solution is any one of sodium hydroxide solution, sodium carbonate solution or sodium bicarbonate solution; the total concentration of manganese ions and nickel ions in solution A is 1 - 4 mol / L, the concentration of the alkali solution is 1 - 6 mol / L, the concentration of ammonia water is 1 - 5 mol / L, and the volume ratio of solution A, the alkali solution, and ammonia water is 1:1:1 - 3; the pH value of the suspension is 9.5 - 11.5, the co-precipitation reaction temperature is 40 - 70 °C, and the reaction time is 0.5 - 5 hours.

[0017] Preferably, in the step (2), the molar ratio of the precursor of the cobalt-free lithium-rich single-crystal cathode material, the lithium source and the eutectic mixed salt is 1:1 - 4:2 - 32; the lithium source is any one of lithium hydroxide, lithium carbonate, lithium nitrate or lithium acetate; the eutectic mixed salt is a mixed salt of a chloride salt and a fluoride salt or a mixed salt of a chloride salt and an oxygen-containing salt; the molar ratio of the chloride salt to the fluoride salt is 1 - 30:1; the molar ratio of the chloride salt to the oxygen-containing salt is 1 - 30:1.

[0018] More preferably, the chloride salt is any one of lithium chloride, sodium chloride, potassium chloride, cesium chloride, strontium chloride or barium chloride; the fluoride salt is any one of lithium fluoride, sodium fluoride, potassium fluoride or cesium fluoride; the oxygen-containing salt is any one of sodium sulfate, sodium carbonate, sodium pyrophosphate, sodium hydroxide, potassium sulfate, potassium carbonate, potassium pyrophosphate or potassium hydroxide.

[0019] Preferably, in the step (2), the calcination reaction process is as follows: heating up to 400-600 °C at a heating rate of 5 °C / min, pre-sintering for 2-5 h, then continuing to heat up to 800-1000 °C at a heating rate of 2 °C / min and maintaining for 6-12 h; the heat treatment temperature is 200-400 °C and the heat treatment time is 1-3 h.

[0020] Thirdly, the present invention provides an application of the above material in a cathode material for a lithium-ion battery.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The cobalt-free lithium-rich single-crystal cathode material with adjustable crystal planes prepared by the technical solution of the present invention is single-crystal particles with a size between 0.2-5 μm. This size characteristic is beneficial to improving the tap density of the cobalt-free lithium-rich single-crystal cathode material with adjustable crystal planes; the single-crystal particles have a sheet-like structure or a polyhedral structure with the top and bottom surfaces being (001) crystal planes and at least one of the side surfaces exposing {012} or {010} active crystal planes with fast lithium-ion transport channels, and the sum of the exposure ratios of the two active crystal planes is 0.15-0.65. The exposure of the active crystal planes can effectively improve the lithium-ion transport rate and enhance the reversible specific capacity and rate performance of this material.

[0023] 2. The preparation method of the present invention uses a eutectic mixed salt with a lower melting point, which can provide a liquid-phase reaction environment during heating. Due to the different adsorption effects between different molten salt ions and different crystal planes of the single-crystal cathode material, combined with the surface energy of different crystal planes of the cobalt-free lithium-rich single-crystal cathode crystal, by adjusting the molar ratio of the precursor, the eutectic mixed salt, and the two salts in the eutectic mixed salt, the growth orientation of the single-crystal can be controlled, and the controllable exposure of its crystal planes can be realized.

[0024] 3. The cobalt-free lithium-rich single-crystal cathode material with active crystal planes prepared by the present invention, as a cathode material for a lithium-ion battery, can still maintain a reversible specific capacity of 167.9-179.5 mAhg -1 after 100 charge-discharge cycles at a current density of 1C, and the reversible specific capacity at a high current density of 5C is 145.0-155.3 mAh / g, which is much higher than the reversible specific capacity of 131.6-146.1 mAh / g after 100 cycles at 1C and the reversible specific capacity of 113.5-118.1 mAh / g at 5C of the cobalt-free lithium-rich single-crystal cathode material without active crystal planes. Description of the Drawings

[0025] Figure 1 It is a SEM image of the cobalt-free lithium-rich single-crystal cathode material with {010} crystal planes prepared in Example 1 of the present invention;

[0026] Figure 2Element distribution map of the cobalt-free lithium-rich single-crystal cathode material with {010} crystal plane prepared in Example 1 of the present invention;

[0027] Figure 3 SEM image of the cobalt-free lithium-rich single-crystal cathode material with {012} crystal plane prepared in Example 2 of the present invention;

[0028] Figure 4 SEM image of the cobalt-free lithium-rich single-crystal cathode material with {010} and {012} crystal planes prepared in Example 3 of the present invention;

[0029] Figure 5 SEM image of the cobalt-free lithium-rich single-crystal cathode material without exposed crystal plane in Comparative Example 1;

[0030] Figure 6 SEM image of the cobalt-free lithium-rich single-crystal cathode material without exposed crystal plane in Comparative Example 2;

[0031] Figure 7 XRD patterns of the cobalt-free lithium-rich single-crystal cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 of the present invention; Detailed implementation manners

[0032] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples. Example 1

[0033] The precursor is selected as Mn 0.75 Ni 0.25 (OH)2, and this precursor is prepared by a co-precipitation reaction. The specific steps are as follows: Dissolve nickel sulfate hexahydrate and manganese sulfate monohydrate in deionized water according to the stoichiometric ratio to prepare solution A with a total concentration of manganese ions and nickel ions of 2 mol / L; and prepare an aqueous solution with a concentration of sodium hydroxide of 4 mol / L and an ammonia water concentration of 1 mol / L. Add solution A, the alkali solution and ammonia water to the reaction kettle under N2 protection according to a volume ratio of 1:1:1, adjust the pH value to 11, the reaction temperature to 55 °C, and the reaction time to 3 h. After washing the co-precipitation product with water, dry it in vacuum at 50 °C to obtain the Mn 0.75 Ni 0.25 (OH)2 precursor.

[0034] The obtained Mn 0.75 Ni 0.25(OH)2 precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.3:4. The molten salt consists of potassium chloride and potassium sulfate, and their molar ratio is 3:1. After mixing the reactants evenly, they are placed in a crucible. Then, the crucible is placed in a muffle furnace and heated at a heating rate of 5 °C / min, held at 400 °C for 5 h, and then continuously heated at a heating rate of 2 °C / min to 900 °C, held for 12 h, and then cooled with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then subjected to secondary heat treatment at 200 °C for 3 h to obtain a Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystalline cathode material with a {010} crystal plane exposure ratio of 0.43. Example 2

[0035] Mn 0.75 Ni 0.25 (OH)2 precursor is prepared in the same way as in Example 1. The obtained Mn 0.75 Ni 0.25 (OH)2 precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.5:4. The molten salt consists of potassium chloride and potassium fluoride, and their molar ratio is 4:1. After mixing the reactants evenly, they are placed in a crucible. Then, the crucible is placed in a muffle furnace and heated at a heating rate of 5 °C / min, held at 600 °C for 2 h, and then continuously heated at a heating rate of 2 °C / min to 900 °C, held for 12 h, and then cooled with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then subjected to secondary heat treatment at 300 °C for 2 h to obtain a Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystalline cathode material with a {012} crystal plane exposure ratio of 0.65. Example 3

[0036] Mn 0.75 Ni 0.25 (OH)2 precursor is prepared in the same way as in Example 1. The obtained Mn 0.75 Ni 0.25(OH)2 precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.5:16. The molten salt consists of sodium chloride and potassium fluoride, and the molar ratio of the two is 30:1. The reactants are mixed evenly and placed in a crucible. Then, the crucible is placed in a muffle furnace and heated at a heating rate of 5 °C / min. After holding at 500 °C for 5 h, it is continuously heated to 1000 °C at a heating rate of 2 °C / min and held for 6 h, followed by furnace cooling. The obtained sintered product is washed three times with deionized water and absolute ethanol respectively, and then heat-treated at 400 °C for 2 h to obtain Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystal cathode material, and the exposure ratios of {010} and {012} are 0.2 and 0.4 respectively. Example 4

[0037] Mn 0.75 Ni 0.25 CO3 precursor is prepared by co-precipitation reaction. The specific steps are as follows: Nickel sulfate hexahydrate and manganese sulfate monohydrate are dissolved in deionized water according to the stoichiometric ratio to prepare solution A with a total concentration of manganese ions and nickel ions of 2 mol / L. A sodium carbonate aqueous solution with a concentration of 2 mol / L and an ammonia aqueous solution with a concentration of 5 mol / L are prepared. Solution A, sodium carbonate alkali solution, and ammonia aqueous solution are simultaneously added to a reaction kettle under N2 protection at a volume ratio of 1:1:3. The pH value of the reaction suspension is controlled to be 10, the reaction temperature is 55 °C, and the reaction time is 3 h. The product is washed with water and dried in vacuum at 80 °C to obtain Mn 0.75 Ni 0.25 CO3 precursor.

[0038] The obtained Mn 0.75 Ni 0.25 CO3 precursor powder, lithium carbonate, and molten salt are in a molar ratio of 1:1.5:8. The molten salt consists of potassium chloride and potassium fluoride, and the molar ratio of the two is 7:1. The reactants are mixed evenly and placed in a crucible. Then, the crucible is placed in a muffle furnace and heated at a heating rate of 5 °C / min. After holding at 500 °C for 5 h, it is continuously heated to 900 °C at a heating rate of 2 °C / min and held for 10 h, followed by furnace cooling. The obtained sintered product is washed three times with deionized water and absolute ethanol respectively, and then heat-treated at 400 °C for 1 h to obtain Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystal cathode material, and the exposure ratio of the {012} crystal plane is 0.6. Example 5

[0039] Mn 0.75 Ni 0.25The preparation method of the CO3 precursor is the same as that in Example 4. The obtained Mn 0.75 Ni 0.25 CO3 precursor powder, lithium carbonate, and molten salt are in a molar ratio of 1:1.5:16. The molten salt composition is lithium chloride and potassium fluoride, and the molar ratio of the two is 15:1. After mixing the reactants evenly, place them in a crucible; then place the crucible in a muffle furnace, heat it at a heating rate of 5 °C / min, hold at 500 °C for 5 h, continue to heat at a heating rate of 2 °C / min to 800 °C, hold for 8 h and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then heat-treated at 200 °C for 3 h to obtain the Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystalline cathode material, and the exposure ratios of {010} and {012} are 0.15 and 0.45 respectively. Example 6

[0040] Mn 0.75 Ni 0.25 (OH)2 precursor is prepared in the same way as in Example 1. The obtained Mn 0.75 Ni 0.25 (OH)2 precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.5:4. The molten salt composition is potassium chloride and potassium pyrophosphate, and the molar ratio of the two is 4:1. After mixing the reactants evenly, place them in a crucible; then place the crucible in a muffle furnace, heat it at a heating rate of 5 °C / min, hold at 400 °C for 5 h, continue to heat at a heating rate of 2 °C / min to 900 °C, hold for 12 h and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then heat-treated at 300 °C for 2 h to obtain the Li 1.2 Mn 0.6 Ni 0.2 O2 cobalt-free lithium-rich single-crystalline cathode material, and the exposure ratio of the {012} crystal plane is 0.45. Example 7

[0041] Mn 0.75 Ni 0.25 The preparation method of the CO3 precursor is the same as that in Example 4. The obtained Mn 0.75 Ni 0.25The CO3 precursor powder, lithium carbonate, and molten salt are in a molar ratio of 1:4:32. The molten salt consists of potassium chloride and potassium pyrophosphate, and their molar ratio is 30:1. After mixing the reactants evenly, place them in a crucible. Then, place the crucible in a muffle furnace and heat it at a heating rate of 5 °C / min, hold at 500 °C for 2 h, continue to heat at a heating rate of 2 °C / min to 900 °C, hold for 8 h, and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then subjected to secondary heat treatment at 300 °C for 2 h to obtain a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2 Mn 0.6 Ni 0.2 O2 with a {012} crystal plane exposure ratio of 0.35. Example 8

[0042] A precursor powder obtained by uniformly mixing nickel carbonate and manganese carbonate in a stoichiometric ratio (1:3); the obtained precursor powder, lithium carbonate, and molten salt are in a molar ratio of 1:1.3:4. The molten salt consists of potassium chloride and sodium fluoride, and their molar ratio is 4:1. After mixing the reactants evenly, place them in a crucible. Then, place the crucible in a muffle furnace and heat it at a heating rate of 5 °C / min, hold at 600 °C for 2 h, continue to heat at a heating rate of 2 °C / min to 850 °C, hold for 12 h, and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then subjected to secondary heat treatment at 200 °C for 3 h to obtain a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2 Mn 0.6 Ni 0.2 O2 with a {012} crystal plane exposure ratio of 0.4. Example 9

[0043] A precursor powder obtained by uniformly mixing nickel nitrate and manganese nitrate in a stoichiometric ratio (1:3); the obtained precursor powder, lithium nitrate, and molten salt are in a molar ratio of 1:1.3:2. The molten salt consists of potassium chloride and lithium fluoride, and their molar ratio is 1:1. After mixing the reactants evenly, place them in a crucible. Then, place the crucible in a muffle furnace and heat it at a heating rate of 5 °C / min, hold at 500 °C for 3 h, continue to heat at a heating rate of 2 °C / min to 900 °C, hold for 12 h, and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then subjected to secondary heat treatment at 400 °C for 1 h to obtain a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2 Mn 0.6 Ni 0.2 O2 with a {012} crystal plane exposure ratio of 0.46. Example 10

[0044] A precursor powder obtained by uniformly mixing nickel acetate and manganese acetate in a stoichiometric ratio of 1:3; the obtained precursor powder, lithium nitrate, and molten salt are mixed in a molar ratio of 1:1.3:4, where the molten salt composition is sodium chloride and potassium pyrophosphate, and the molar ratio of the two is 3:1. After mixing the reactants evenly, they are placed in a crucible; then the crucible is placed in a muffle furnace, heated at a heating rate of 5 °C / min, held at 600 °C for 2 h, and then continued to be heated at a heating rate of 2 °C / min to 900 °C. After holding for 12 h, it is cooled with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then after secondary heat treatment at 400 °C for 1 h, a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2 Mn 0.6 Ni 0.2 O2 with a cobalt-free lithium-rich single-crystalline cathode material, and the exposure ratio of the {012} crystal plane is 0.42. Example 11

[0045] A precursor powder obtained by uniformly mixing nickel acetate and manganese nitrate in a stoichiometric ratio of 1:3; the obtained precursor powder, lithium nitrate, and molten salt are mixed in a molar ratio of 1:2:12, where the molten salt composition is cesium chloride and potassium carbonate, and the molar ratio is 11:1. After mixing the reactants evenly, they are placed in a crucible; then the crucible is placed in a muffle furnace, heated at a heating rate of 5 °C / min, held at 400 °C for 5 h, and then continued to be heated at a heating rate of 2 °C / min to 800 °C. After holding for 12 h, it is cooled with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then after secondary heat treatment at 400 °C for 1 h, a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2 Mn 0.6 Ni 0.2 O2 with a cobalt-free lithium-rich single-crystalline cathode material, and the exposure ratio of the {012} crystal plane is 0.45. Example 12

[0046] Mn 0.75 Ni 0.25 (OH)2 is prepared in the same way as in Example 1. The obtained Mn 0.75 Ni 0.25 (OH)2 precursor powder, lithium hydroxide, and molten salt are mixed in a molar ratio of 1:1:4, where the molten salt composition is lithium chloride and potassium sulfate, and the molar ratio is 2:1. After mixing the reactants evenly, they are placed in a crucible; then the crucible is placed in a muffle furnace, heated at a heating rate of 5 °C / min, held at 500 °C for 3 h, and then continued to be heated at a heating rate of 2 °C / min to 900 °C. After holding for 10 h, it is cooled with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then after secondary heat treatment at 300 °C for 2 h, a cobalt-free lithium-rich single-crystalline cathode material of Li 1.2Mn 0.6 Ni 0.2 Cobalt-free lithium-rich single-crystalline cathode material with O2, the exposure ratio of the {010} crystal plane is 0.35. Comparative Example 1

[0047] Precursor powder obtained by uniformly mixing nickel acetate and manganese acetate in a stoichiometric ratio (1:3); the obtained precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.3:2, where the molten salt is potassium chloride. After mixing the reactants evenly, place them in a crucible; then place the crucible in a muffle furnace, heat it at a heating rate of 5 °C / min, hold at 500 °C for 5 h, continue to heat at a heating rate of 2 °C / min to 1000 °C, hold for 10 h and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then heat-treated at 300 °C for 2 h to obtain a cobalt-free lithium-rich single-crystalline cathode material without crystal plane exposure. Comparative Example 2

[0048] Mn 0.75 Ni 0.25 (OH)2 precursor preparation method is the same as in Example 1. The obtained Mn 0.75 Ni 0.25 (OH)2 precursor powder, lithium hydroxide, and molten salt are in a molar ratio of 1:1.3:64, where the molten salt is potassium chloride and potassium fluoride, and the ratio of the two is 30:1. After mixing the reactants evenly, place them in a crucible; then place the crucible in a muffle furnace, heat it at a heating rate of 5 °C / min, hold at 500 °C for 5 h, continue to heat at a heating rate of 2 °C / min to 900 °C, hold for 10 h and then cool with the furnace. The obtained sintered product is washed three times with deionized water and anhydrous ethanol respectively, and then heat-treated at 300 °C for 2 h to obtain a cobalt-free lithium-rich single-crystalline cathode material without crystal plane exposure.

[0049] The morphologies and phases of the products prepared in Examples 1-3 and Comparative Examples 1-2 were analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Figure 1 SEM image of the cobalt-free lithium-rich single-crystalline with exposed active crystal planes prepared in Example 1. From Figure 1 it can be clearly observed that the cobalt-free lithium-rich single-crystalline sample particles prepared in Example 1 are in a flake structure. The top and bottom surfaces of this flake structure are (001) crystal planes and present a hexagonal shape, the side surfaces expose the {010} crystal plane, and the width of the top and bottom surfaces of this flake structure is 0.7 microns, and the thickness is about 0.2 microns; the {010} crystal plane exposed on the side of the cobalt-free lithium-rich single-crystalline sample with this flake structure prepared by regulating the binary molten salt of potassium chloride and potassium sulfate is suitable for the rapid migration of lithium ions, which is beneficial to the diffusion of lithium ions during the electrochemical cycling process and is expected to improve the rate performance of the material; Figure 2 Element distribution map of this sample. FromFigure 2 It can be seen from [the figure] that the distribution of manganese and nickel elements in the prepared cobalt-free lithium-rich single-crystal cathode material is uniform and conforms to the molar ratio of 3:1 in the prepared single-crystal material. Figure 3 Figure 3 is a SEM image of the cobalt-free lithium-rich single-crystal cathode material with exposed {012} crystal plane active crystal plane prepared in Example 2. It can be clearly observed from this figure that the sample prepared in Example 2 has a flake structure with the {012} crystal plane exposed on the side. The width of this flake structure is about 0.6 microns and the thickness is about 0.15 microns. The cobalt-free lithium-rich single-crystal sample prepared by regulating the binary molten salt of potassium chloride and potassium fluoride has a flake structure with the (001) crystal plane on the top and bottom and the {012} crystal plane exposed on the side. The {012} crystal plane family also has channels suitable for rapid lithium-ion transport, which can promote the diffusion of lithium ions and improve the rate performance of the material. Figure 4 Figure 5 is a SEM image of the cobalt-free lithium-rich single-crystal cathode material prepared in Example 3. It can be clearly observed that the structure of the cobalt-free lithium-rich single-crystal sample in Example 3 is a polyhedral structure with the (001) crystal plane on the top and bottom and the {010} and {012} crystal planes exposed on the side. The particle size is about 0.8 microns. The {010} and {012} crystal plane families exposed on the side can promote lithium-ion transport and improve the rate performance. Figure 5 and Figure 6 Figures 7 and 8 are SEM images of the samples prepared in Comparative Example 1 and Comparative Example 2 respectively. It can be clearly observed that the morphologies of the cobalt-free lithium-rich single-crystal cathode materials prepared in Comparative Example 1 and Comparative Example 2 are spherical particles with particle sizes of 1 micron and 0.8 micron respectively. No active crystal planes suitable for rapid lithium-ion transport are exposed. Therefore, the diffusion of lithium ions in this material is slow and the rate performance is poor. Figure 7 Figure 9 is the XRD pattern of the samples prepared in Examples 1-3 and Comparative Examples 1-2. It can be seen from this pattern that the five prepared samples are all pure-phase cobalt-free lithium-rich single-crystal cathode materials without the generation of impurity phases. In the above Examples 1-12, the particles of the cobalt-free lithium-rich single-crystal cathode material prepared using hydroxides or carbonates obtained by the coprecipitation method are more uniform, and the electrochemical performance consistency as an electrode material test is better.

[0050] Application Example 1

[0051] The cobalt-free lithium-rich single-crystal cathode materials obtained in Examples 1-12 and Comparative Examples 1-2 were used to prepare lithium-ion battery cathode sheets by the following method: Using the cobalt-free lithium-rich single-crystal cathode material as the active substance, acetylene black as the conductive agent, and PVDF as the binder, after mixing evenly at a mass ratio of 80:10:10, NMP was used as the solvent to prepare a slurry. The slurry was evenly coated on the aluminum foil, dried at 80 °C, and then dried under vacuum at 100 °C for 12 hours to make a cathode sheet with a diameter of 8 microns, which was pressed to the required thickness of the cathode sheet for standby. Using a lithium metal sheet as the counter electrode, a Celgard 2400 membrane as the separator, and 1 mol / L LiPF6 / EC+DEC (volume ratio 1:1) as the electrolyte, a CR2032 coin cell was assembled in a glove box. The obtained battery was tested for its electrochemical performance using a Blue Electric Battery Test System CT2001A tester. In the cyclic test, the charge-discharge voltage range for the first three cycles was 2-4.8 V, and the charge-discharge voltage for the subsequent cycles was 2-4.6 V. In the rate test, the charge-discharge voltage range was 2-4.8 V.

[0052]

[0053] Table 1 compares the electrochemical performances of Examples 1-12 and Comparative Examples 1-2. It can be seen that Examples 1-12 have better electrochemical performances. For the samples of Examples 1-12, the single-crystal morphology structure exposes at least one of the {012} or {010} active crystal planes with fast lithium-ion transport channels, which can promote the diffusion of lithium ions in the material and improve the reversible specific capacity and rate performance of the material during the electrochemical cycling process. The samples of Examples 1-12 have a reversible specific capacity of 167.9-179.5 mAh g -1 after cycling 100 times at a current density of 1C (1C = 250 mA g -1 , with an average reversible specific capacity of 173.4 mAh g -1 , and a reversible specific capacity of 145.0-155.3 mAh g -1 after cycling 10 times at 5C, with an average reversible specific capacity of 149.5 mAh g -1 . While the samples prepared in Comparative Examples 1-2 have a spherical structure without the exposure of active crystal planes with fast lithium-ion transport channels, and lithium ions diffuse slowly in this type of material. The samples of Comparative Examples 1-2 have a reversible specific capacity of 131.6-146.1 mAh g -1 after cycling 100 times at a current density of 1C (1C = 250 mA g -1 , with an average reversible specific capacity of 138.9 mAh g -1 , and a reversible specific capacity of 113.8 -118.1 mAh g -1 after cycling 10 times at 5C, with an average reversible specific capacity of 115.9 mAh g -1Therefore, the cobalt-free lithium-rich single-crystal cathode material with facet activity can increase the reversible specific capacity by up to 24.8% and 28.9% respectively under the conditions of current densities of 1C and 5C. Through the comparative analysis of the electrochemical performance and morphological characteristics of Examples 1-12 and Comparative Examples 1-2, it can be seen that by adjusting the precursor, eutectic mixed salt, and the molar ratio of the two salts in the eutectic mixed salt, the growth orientation of single-crystal crystals can be controlled. With the reaction conditions of appropriate precursor, eutectic mixed salt, and the molar ratio of the two salts in the eutectic mixed salt, the prepared cobalt-free lithium-rich single-crystal cathode material particles have a flake structure or polyhedron structure with the top and bottom being (001) crystal planes and at least one of the side surfaces exposing the {012} or {010} active crystal planes with fast lithium-ion transport channels; the single crystals prepared under the reaction conditions without appropriate precursor, eutectic mixed salt, and the molar ratio of the two salts in the eutectic mixed salt are spherical particles. Therefore, the technical solution provided by the present invention can control the crystal growth of the cobalt-free lithium-rich single-crystal cathode material, expose the active crystal planes with fast lithium-ion transport channels, and further improve its reversible specific capacity and rate performance during the electrochemical cycling process. This shows that the beneficial effects brought by this technical solution can better make up for the defects of the existing technical solutions, thereby obtaining materials with excellent performance.

[0054] The specific embodiments described above further elaborate on the present invention, but these descriptions should not be construed as limitations on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane, characterized in that: The molecular formula of the cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane is Li 1+x Ni y Mn 0.8-y O2, where 0 <x<0.25,0<y<0.8; The cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane is a single crystal particle with a size between 0.2 and 5 μm, and the single crystal particle has a sheet structure or a polyhedral structure with the top and bottom surfaces being (001) crystal planes, and at least one of {012} or {010} active crystal planes with lithium ion fast transport channels exposed on the side, and the sum of the exposure ratios of {012} active crystal planes to {010} active crystal planes is 0.15-0.65; The method for preparing the cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane comprises the following steps: (1) preparing a cobalt-free lithium-rich single crystal cathode material precursor by using a solid phase method or a co-precipitation method with a manganese salt and a nickel salt; (2) uniformly mixing a cobalt-free lithium-rich single crystal positive electrode material precursor, a lithium source and a eutectic mixed salt, and then calcining the mixture to obtain a sintered product; washing and heat treating the sintered product to obtain a cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal surface; The molar ratio of the cobalt-free lithium-rich single crystal positive electrode material precursor, the lithium source and the eutectic mixed salt is 1:1-4:2-32; the lithium source is any one of lithium hydroxide, lithium carbonate, lithium nitrate or lithium acetate; the eutectic mixed salt is a mixed salt of chloride and fluoride or a mixed salt of chloride and oxygen-containing acid salt; the molar ratio of chloride and fluoride is 1-30:1; the molar ratio of chloride and oxygen-containing acid salt is 1-30:1; The calcination reaction process is: heating to 400-600°C at a heating rate of 5°C / min, pre-sintering for 2-5h, and then heating to 800-1000°C at a heating rate of 2°C / min, and maintaining for 6-12h; the heat treatment temperature is 200-400°C, and the heat treatment time is 1-3h.

2. The crystal plane adjustable cobalt-free lithium-rich single crystal positive electrode material according to claim 1, characterized in that: The manganese salt is any one of manganese carbonate, manganese nitrate or manganese acetate; the nickel salt is any one of nickel carbonate, nickel nitrate or nickel acetate.

3. The crystal plane adjustable cobalt-free lithium-rich single crystal positive electrode material according to claim 1, characterized in that: In the step (1), the solid phase method is to mix the manganese salt and the nickel salt evenly to obtain a cobalt-free lithium-rich single crystal positive electrode material precursor; the molar ratio of Mn in the manganese salt to Ni in the nickel salt is 0.8-y:y, where 0 <y<0.8。 4. The crystal plane adjustable cobalt-free lithium-rich single crystal positive electrode material according to claim 1, characterized in that: In the step (1), the coprecipitation method is to dissolve the manganese salt and the nickel salt in deionized water to prepare a solution A; under the protection of a protective gas, the solution A, an alkali solution and an ammonia solution are mixed to perform a coprecipitation reaction to obtain a suspension; Filtering, washing and drying to obtain a cobalt-free lithium-rich single crystal positive electrode material precursor; the molar ratio of Mn in the manganese salt to Ni in the nickel salt is 0.8-y:y, where 0 <y<0.8。 5. The crystal plane adjustable cobalt-free lithium-rich single crystal positive electrode material according to claim 4, characterized in that: The alkali solution is any one of sodium hydroxide solution, sodium carbonate solution or sodium bicarbonate solution; the total concentration of manganese ions and nickel ions in the solution A is 1-4 mol / L, the alkali solution concentration is 1-6 mol / L, the ammonia concentration is 1-5 mol / L, and the volume ratio of the solution A, the alkali solution and the ammonia solution is 1:1:1-3; the pH value of the suspension is 9.5-11.5, the coprecipitation reaction temperature is 40-70°C, and the reaction time is 0.5-5 hours.

6. The crystal plane adjustable cobalt-free lithium-rich single crystal positive electrode material according to claim 1, characterized in that: In the step (2), the chloride salt is any one of lithium chloride, sodium chloride, potassium chloride, cesium chloride, strontium chloride or barium chloride; the fluoride salt is any one of lithium fluoride, sodium fluoride, potassium fluoride or cesium fluoride; the oxyacid salt is any one of sodium sulfate, sodium carbonate, sodium pyrophosphate, sodium hydroxide, potassium sulfate, potassium carbonate, potassium pyrophosphate or potassium hydroxide.

7. An application of the cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane as claimed in claim 1, characterized in that: The cobalt-free lithium-rich single crystal positive electrode material with adjustable crystal plane is applied to positive electrode materials of lithium-ion batteries.

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