Single crystal lithium nickel manganese oxide synthesized by a multi-stage step sintering method and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion battery positive electrode materials, and discloses a single-crystal lithium nickel manganese oxide synthesized by a multi-section step sintering method and a preparation method thereof, which is characterized in that a synthesis temperature curve has multiple steps, that is, multiple stages of rapid material temperature rising and then temperature falling occur in the heating process. The method comprises the following steps: short-time heating of mixed raw materials by infrared radiation heating to discharge water vapor; short-time heating of the mixed raw materials by biological fuel and fossil fuel to accelerate decomposition of lithium carbonate and discharge of CO2 and other gases that are not conducive to synthesis of the lithium nickel manganese oxide; acceleration of growth of the single-crystal lithium nickel manganese oxide by a gradient thermal field; and single-crystal lithium nickel manganese oxide is obtained after the temperature is lowered, the temperature is raised again and cooling. The single-crystal lithium nickel manganese oxide has good processing performance, better cycle performance and high-temperature storage performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a single-crystal lithium nickel manganese oxide synthesized by a multi-stage step sintering method and its preparation method. Background Technology

[0002] Traditional polycrystalline high-voltage lithium nickel manganese oxide typically exhibits irreversible structural and electrochemical losses under high voltage, significantly reducing its stability. Micron-sized "secondary" particles are usually composed of many "primary" nanoparticles, allowing the electrolyte to permeate into the interior through the gaps between grains. The random crystal orientation of these primary particles leads to significant stress during cycling, resulting in cracks. Especially under full charge, the anisotropy of lattice contraction generates localized stress along grain boundaries, causing structural damage. Even during the first stage of charging, microcracks can form between grains. Electrolyte seeps into these microcracks, causing direct contact between the battery's positive electrode and the electrolyte. These microcracks disrupt the mechanical integrity of the positive electrode material, promote volume changes and crack formation, further impairing the material's cycle performance and reducing the efficiency of the positive electrode electrochemical reaction. In contrast, polycrystalline high-voltage lithium nickel manganese oxide... + and Ni 4+ The severe mixing within the crystal lattice makes it easier for microcracks to form inside the crystal. Therefore, suppressing the formation of microcracks is key to improving the mechanical strength of lithium nickel manganese oxide cathode materials and inhibiting the rapid capacity decay of the material.

[0003] Research has found that single-crystal lithium nickel manganese oxide (LiNOO) has micron-sized particles. The "single-crystal" morphology limits surface reactions and particle cracking, offering advantages such as resistance to mechanical fracturing and gas evolution, thus improving battery cycle and thermal stability. Single crystals completely eliminate interparticle stress, eliminating grain boundaries for electrolyte penetration and reducing pathways for atomic oxygen diffusion from the material's interior to the exterior. Another benefit is high density; the crystal itself is not only free of porosity but can also withstand greater forces during rolling without cracking. Therefore, single-crystal morphologies grown with specific crystal facet advantages possess excellent high-voltage stability, high mechanical strength, and a stable structure, holding promise for solving problems such as structural damage and cycle performance issues under high voltage in traditional polycrystalline high-voltage LiNOO materials.

[0004] For example, patent CN201611029096X discloses a large single-crystal lithium nickel manganese oxide cathode material and its preparation method; patent CN2019106224263 discloses a method for preparing micron-sized single-crystal lithium nickel manganese oxide cathode material; patent CN2022116125073 discloses a method for preparing chamfered single-crystal lithium nickel manganese oxide cathode material; and patent CN2023109510687 discloses a method for preparing single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal faces. None of these methods involve the specific process for the directional growth of the advantageous interfaces of single-crystal lithium nickel manganese oxide. The stability of single-crystal lithium manganese oxide during synthesis at voltages greater than 4.8V still needs further improvement, and the cycling performance of lithium nickel manganese oxide cathode materials in the 3.0-4.9V cycling process cannot be improved. Those skilled in the art urgently need to develop a multi-stage sintering method for synthesizing single-crystal lithium nickel manganese oxide and its preparation method to meet current application market and performance requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a single-crystal lithium nickel manganese oxide synthesized by a multi-stage stepped sintering method and its preparation method. The aim is to solve the problem of microcrack formation inside lithium nickel manganese oxide cathode materials, improve the mechanical strength of lithium nickel manganese oxide cathode materials, and enhance battery cycle performance and high-temperature storage performance.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A single-crystal lithium nickel manganese oxide synthesized by a multi-stage stepped sintering method, the preparation method of the single-crystal lithium nickel manganese oxide comprising the following steps:

[0008] (1) The combustion aid, lithium salt and lithium nickel manganese oxide precursor are mixed evenly according to the molar ratio to obtain a mixed raw material;

[0009] (2) In the first stage, the infrared radiation heating method is used to raise the temperature to T1, and the heating time is t1, so that the mixed raw materials can be discharged more quickly. The mixed raw materials contain free water and crystal water. The infrared radiation heating is turned off to lower the temperature of the mixed raw materials.

[0010] (3) In the second stage, the combustion aid is used to carry out an oxidation reaction, which releases a large amount of heat and raises the temperature of the mixed raw materials to T2. The heating time is t2, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the end, the temperature of the mixed raw materials decreases.

[0011] (4) In the third stage, microwave heating is used to raise the temperature to T3 for a time of t3, so as to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes;

[0012] (5) After turning off microwave heating, control the sintering temperature of the mixed raw materials and carry out the synthesis reaction;

[0013] (6) During the cooling stage, microwave heating or infrared heating is used to raise the temperature to 800°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained.

[0014] Preferably, in step (1), the molar ratio of combustion aid, lithium salt and lithium nickel manganese oxide precursor is 0.001-0.1:0.48-0.58:1.

[0015] Preferably, in (1), the combustion aid is one of bioethanol, biobutanol, phosphate ester, triethyl phosphate, microcrystalline wax, liquid paraffin, liquid resin, polyethylene wax, glycerol, glycerol fatty acid, biodiesel, and toner.

[0016] Preferably, in step (2), during the infrared heating process, the infrared radiation wavelength is 200μm-1μm, the heating rate is 10-80℃ / s, and the instantaneous heat flux density reaches 0.01-1MW / m³. 2 Preferably, the infrared radiation wavelength is 50μm-2μm, the heating rate is 20-50℃ / s, and the instantaneous heat flux density reaches 0.1-0.5MW / m³. 2 More preferably, the infrared radiation wavelength is 20μm-2.5μm, the heating rate is 20-40℃ / s, and the instantaneous heat flux density reaches 0.2-0.4MW / m³. 2 T1 is 150-300℃, and t1 is 0.1-1h.

[0017] Preferably, in step (3), the heating temperature T2 of the combustion aid is 700-950℃ and the heating time t2 is 0.01-0.2h.

[0018] Preferably, in step (4), the microwave heating temperature T3 is 750-1200℃ and the heating time t3 is 0.1-2h.

[0019] Preferably, in step (5), the sintering temperature is 820-980℃ and the synthesis reaction time is 12-24h.

[0020] Preferably, the preparation temperature curve exhibits multiple step-like characteristic peaks, meaning that during the heating process, there are multiple stages where the material temperature rises rapidly and then falls. The total heating time for synthesis is t, and the synthesis temperature is T. The first stage has a time of t1 and a maximum temperature of T1, the second stage has a time of t2 and a maximum temperature of T2, and the Nth stage has a time of t... n The highest temperature is T n The following relationships are satisfied: T1×t≥T×t1, T2×t≥T×t2, ..., T n ×t≥T×t n , where 2≤n≤3.

[0021] Preferably, the total heating time t is 3-20h and the synthesis temperature T is 600-1200℃. More preferably, the total heating time t is 6-10h and the synthesis temperature T is 800-1000℃.

[0022] Preferably, the heating method used is one or more of the following: electric heating, infrared radiation heating, microwave heating, combustion additive heating, heat flow heating, and Joule heating.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] Typically, the sintering curve of lithium nickel manganese oxide cathode material is trapezoidal. The raw material is heated from room temperature to the sintering temperature at a fixed heating rate, sintered for a certain time, and then cooled naturally to obtain the lithium nickel manganese oxide cathode material. Uniform heating and cooling rates are not conducive to obtaining disordered phase lithium nickel manganese oxide. The electronic conductivity of disordered spinel is 2-3 orders of magnitude higher than that of ordered spinel. Therefore, disordered phase lithium nickel manganese oxide has better rate performance and is suitable for high-rate charge and discharge. The electrochemical performance of lithium nickel manganese oxide is closely related to the exposed crystal faces on the material surface. (111) The crystal face is dominated by closely packed oxygen atoms and is the advantageous growth interface of spinel structure; (100) The crystal face has a moderate distribution of Mn, Ni and Li metal ions, which can avoid the deterioration of cycle performance caused by excessive dissolution of Mn; (110) The crystal face has a large number of ion channels, which can improve the migration rate of lithium ions. The multi-stage stepped sintering method can rapidly heat up and cool down the material, thereby increasing the relative growth rate of the (100) and (110) crystal planes through rapid temperature changes, increasing the proportion of the (100) and (110) crystal planes on the material surface, and thus improving the cycle performance and rate performance of the single crystal lithium nickel manganese oxide cathode material.

[0025] The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method described in this invention and its preparation method also have other beneficial effects. 1) Because mid-wave infrared radiators have high heating efficiency for water-containing materials, mid-wave infrared radiation can be well absorbed by water and directly converted into heat, thereby accelerating the evaporation of water and the drying of materials. Therefore, using infrared radiation heating to make the raw materials infrared radiation can accelerate the evaporation of free water and crystal water in the raw materials, and can also make Ni 0.25 Mn 0.751) Hydroxide ions in (OH)2 accelerate decomposition and improve the chemical activity of the raw materials. 2) During the heating process, the heat generated by the combustion of the combustion aid is used to rapidly heat the mixed raw materials to 650-950℃, so that lithium carbonate decomposes rapidly and CO2 gas is released. 3) During the heating process, microwave heating is used to rapidly raise the temperature of the mixed raw materials to 750-1200℃, which increases the relative growth rate of the (100) and (110) crystal planes of lithium nickel manganese oxide and increases the proportion of (100) and (110) crystal planes on the material surface. 4) During the cooling process, microwave heating or infrared heating is used to reheat the material, release the lattice stress inside the material, and reduce crystal defects and surface oxygen defects in the material. Attached Figure Description

[0026] Figure 1 The figure shows the temperature curve of the preparation process in Example 1. As can be seen from the figure, the preparation temperature curve exhibits multiple step-like characteristic peaks.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the single-crystal lithium nickel manganese oxide prepared in Example 1. As can be seen from the image, the lithium nickel manganese oxide has a single-crystal morphology, and obvious (100) and (110) crystal planes can be observed on the surface.

[0028] Figure 3 To compare the temperature curves of the preparation process in Example 1, it can be seen from the figure that the preparation temperature curves are trapezoidal;

[0029] Figure 4 The scanning electron microscope image of the single crystal lithium nickel manganese oxide in Comparative Example 1 shows that the prepared lithium nickel manganese oxide has a polycrystalline morphology, and obvious (111) crystal planes can be observed on the surface. The (100) and (110) crystal planes account for a very small proportion and are not obvious.

[0030] Figure 5 A comparison graph of the cycle performance of batteries was prepared for Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the embodiments described below are merely some embodiments of the present invention. For those skilled in the art, other implementation methods can be obtained based on these embodiments without creative effort. Example 1

[0032] (1) Triethyl phosphate combustion aid, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly in a molar ratio of 0.003:0.25:1 to obtain a mixed raw material;

[0033] (2) In the first stage, the infrared radiation heating method was used to raise the temperature to 150℃, and the heating time was 0.5h. The infrared radiation wavelength was 20μm, the heating rate was 40℃ / s, and the instantaneous heat flux density reached 0.3MW / m. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials to 90°C, and then continue to raise the temperature.

[0034] (3) In the second stage, triethyl phosphate undergoes an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 700°C. The heating time is 0.01h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the process is completed, the temperature of the mixed raw materials decreases to 240°C and continues to rise.

[0035] (4) In the third stage, when the temperature of the mixed raw materials is raised to 800°C, microwave heating is used to raise the temperature to 1000°C for 2 hours to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0036] (5) Control the total heating time to 6 hours, turn off microwave heating, control the sintering temperature of the mixed raw materials to 900°C, and carry out the synthesis reaction for 16 hours;

[0037] (6) During the cooling stage, microwave heating is used to raise the temperature to 800°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 2

[0038] (1) Bioethanol, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly at a molar ratio of 0.002:0.25:1 to obtain a mixed raw material;

[0039] (2) In the first stage, the temperature was raised to 300℃ using infrared radiation heating for 1 hour. The infrared radiation wavelength was 5μm, the heating rate was 30℃ / s, and the instantaneous heat flux density reached 0.2MW / m³. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials to 140°C, and continue to raise the temperature.

[0040] (3) In the second stage, bioethanol is used to undergo an oxidation reaction, which releases a large amount of heat and rapidly raises the temperature of the mixed raw materials to 950°C. The heating time is 0.01h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the reaction is completed, the temperature of the mixed raw materials decreases to 400°C and continues to rise.

[0041] (4) In the third stage, when the temperature of the mixed raw materials is raised to 850°C, microwave heating is used to raise the temperature to 1000°C for 1 hour to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0042] (5) Control the total heating time to 8h, turn off microwave heating, control the sintering temperature of mixed raw materials to 900℃, and carry out the synthesis reaction for 18h;

[0043] (6) During the cooling stage, infrared heating is used to raise the temperature to 700°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 3

[0044] (1) Microcrystalline wax, glycerol fatty acids, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly in a molar ratio of 0.0005:0.0005:0.25:1 to obtain a mixed raw material;

[0045] (2) In the first stage, the temperature was raised to 200℃ using infrared radiation heating method, with a heating time of 0.5h. The infrared radiation wavelength was 40μm, the heating rate was 100℃ / s, and the instantaneous heat flux density reached 0.4MW / m³. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials. When the temperature drops to 100°C, continue to raise the temperature.

[0046] (3) In the second stage, microcrystalline wax and glycerol fatty acids undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 800°C. The heating time is 0.1h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the reaction is completed, the temperature of the mixed raw materials decreases to 415°C and continues to rise.

[0047] (4) In the third stage, when the temperature of the mixed raw materials is raised to 850°C, microwave heating is used to raise the temperature to 1000°C for 2 hours to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0048] (5) Control the total heating time to 10h, turn off microwave heating, control the sintering temperature of mixed raw materials to 950℃, and carry out the synthesis reaction for 12h;

[0049] (6) During the cooling stage, infrared heating is used to raise the temperature to 800°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 4

[0050] (1) Polyethylene wax, carbon powder, LiOH·H2O and Ni0.25 Mn 0.75 O is mixed evenly in a molar ratio of 0.0002:0.0001:0.51:1 to obtain a mixed raw material;

[0051] (2) In the first stage, the infrared radiation heating method was used to raise the temperature to 300℃ for 1 hour. The infrared radiation wavelength was 100μm, the heating rate was 60℃ / s, and the instantaneous heat flux density reached 0.25MW / m. 2 This accelerates the removal of free water and crystal water from the mixed raw materials. The infrared radiation heating is then turned off, causing the temperature of the mixed raw materials to drop to 160°C. The temperature is then raised again.

[0052] (3) In the second stage, polyethylene wax and carbon powder undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 1000℃. The heating time is 0.1h, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the reaction is completed, the temperature of the mixed raw materials decreases to 605℃ and continues to rise.

[0053] (4) In the third stage, when the temperature of the mixed raw material is raised to 750°C, the temperature of the mixed raw material is rapidly increased to 1000°C for 0.5 hours to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0054] (5) Control the total heating time to 6 hours, turn off microwave heating, control the sintering temperature of the mixed raw materials to 850°C, and carry out the synthesis reaction for 20 hours;

[0055] (6) During the cooling stage, infrared heating is used to raise the temperature to 600°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 5

[0056] (1) Glycerol, triethyl phosphate, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly in a molar ratio of 0.005:0.01:0.26:1 to obtain a mixed raw material;

[0057] (2) In the first stage, the temperature was raised to 200℃ using infrared radiation heating for 0.5 hours. The infrared radiation wavelength was 20μm, the heating rate was 50℃ / s, and the instantaneous heat flux density reached 0.15MW / m³. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Infrared radiation heating is used to lower the temperature of the mixed raw materials to 160°C, and the temperature is then raised again.

[0058] (3) In the second stage, glycerol and triethyl phosphate undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 950°C. The heating time is 0.2h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the reaction is complete, the temperature of the mixed raw materials decreases to 550°C and continues to rise.

[0059] (4) In the third stage, when the temperature of the mixed raw materials is raised to 800°C, microwave heating is used to raise the temperature to 1050°C for 0.1 h to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0060] (5) Control the total heating time to 3 hours, turn off microwave heating, control the sintering temperature of the mixed raw materials to 900°C, and carry out the synthesis reaction for 15 hours;

[0061] (6) During the cooling stage, microwave heating is used to raise the temperature to 750°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 6

[0062] (1) Triethyl phosphate, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly at a molar ratio of 0.06:0.255:1 to obtain a mixed raw material;

[0063] (2) In the first stage, the temperature was raised to 250℃ using infrared radiation heating method, with a heating time of 0.2h. The infrared radiation wavelength was 10μm, the heating rate was 50℃ / s, and the instantaneous heat flux density reached 0.3MW / m³. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and water of crystallization. Turn off infrared radiation heating to lower the temperature of the mixed raw materials to 180°C, and then continue to raise the temperature.

[0064] (3) In the second stage, triethyl phosphate undergoes an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 700°C. The heating time is 0.01h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the reaction is complete, the temperature of the mixed raw materials decreases to 480°C and continues to rise.

[0065] (4) In the third stage, when the temperature of the mixed raw materials is raised to 800°C, microwave heating is used to raise the temperature to 1200°C for 1 hour to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0066] (5) Control the total heating time to 20h, turn off microwave heating, control the sintering temperature of mixed raw materials to 980℃, and carry out the synthesis reaction for 15h;

[0067] (6) During the cooling stage, microwave heating is used to raise the temperature to 800°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 7

[0068] (1) Liquid resin, triethyl phosphate, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly in a molar ratio of 0.001:0.01:0.25:1 to obtain a mixed raw material;

[0069] (2) The first stage of infrared radiation heating method raises the temperature to 250℃ in 0.1h, with an infrared radiation wavelength of 40μm, a heating rate of 80℃ / s, and an instantaneous heat flux density of 0.4MW / m³. 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials to 120°C, and continue to raise the temperature.

[0070] (3) In the second stage, liquid resin and triethyl phosphate undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 950°C. The heating time is 0.1h, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the reaction is complete, the temperature of the mixed raw materials decreases to 550°C and continues to rise.

[0071] (4) In the third stage, when the temperature of the mixed raw materials is raised to 800°C, microwave heating is used to raise the temperature to 1100°C for 0.5 hours to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0072] (5) Control the total heating time to 10h, turn off microwave heating, control the sintering temperature of mixed raw materials to 930℃, and carry out the synthesis reaction for 18h;

[0073] (6) During the cooling stage, infrared heating is used to raise the temperature to 850°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 8

[0074] (1) Add carbon powder, LiOH·H2O and Ni 0.25 Mn 0.75 O is mixed evenly in a molar ratio of 0.02:0.52:1 to obtain a mixed raw material;

[0075] (2) In the first stage, the temperature was raised to 300℃ using infrared radiation heating for 0.5 hours. The infrared radiation wavelength was 3μm, the heating rate was 50℃ / s, and the instantaneous heat flux density reached 0.25MW / m³. 2To accelerate the removal of free water and crystal water contained in LiOH·H2O, turn off infrared radiation heating to lower the temperature of the mixed raw materials to 125℃, and continue to raise the temperature.

[0076] (3) In the second stage, the carbon powder undergoes an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 950°C. The heating time is 0.05h, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the carbon powder reaction is complete, the temperature of the mixed raw materials decreases to 315°C and continues to rise.

[0077] (4) In the third stage, when the temperature of the mixed raw material is raised to 650°C, microwave heating is used to rapidly raise the temperature of the mixed raw material to 950°C for 1 hour, so as to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0078] (5) Control the total heating time to 15h, turn off microwave heating, control the sintering temperature of mixed raw materials to 820℃, and carry out the synthesis reaction for 24h;

[0079] (6) During the cooling stage, microwave heating is used to raise the temperature to 600°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 9

[0080] (1) Bioethanol, triethyl phosphate, LiOH·H2O and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly in a molar ratio of 0.002:0.005:0.25:1 to obtain a mixed raw material;

[0081] (2) In the first stage, the temperature was raised to 150℃ using infrared radiation heating method, with a heating time of 0.5h. The infrared radiation wavelength was 100μm, the heating rate was 40℃ / s, and the instantaneous heat flux density reached 0.15MW / m. 2 Accelerate the discharge of LiOH·H2O and Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials. When the temperature drops to 80°C, continue to raise the temperature.

[0082] (3) In the second stage, bioethanol and triethyl phosphate undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 900°C. The heating time is 0.1h, which accelerates the release of carbon dioxide gas from the mixed raw materials. After the bioethanol and triethyl phosphate have reacted, the temperature of the mixed raw materials decreases to 420°C and continues to rise.

[0083] (4) In the third stage, when the temperature of the mixed raw materials is raised to 760°C, microwave heating is used to raise the temperature to 1000°C for 1 hour to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0084] (5) Control the total heating time to 8h, turn off microwave heating, control the sintering temperature of mixed raw materials to 850℃, and carry out the synthesis reaction for 20h;

[0085] (6) During the cooling stage, microwave heating is used to raise the temperature to 650°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. Example 10

[0086] (1) Triethyl phosphate, microcrystalline wax, LiOH·H2O and Ni 0.25 Mn 0.75 O 3.5 The raw materials were mixed evenly according to a molar ratio of 0.03:0.02:0.25:1 to obtain a mixed raw material;

[0087] (2) In the first stage, the temperature was raised to 250℃ using infrared radiation heating for 0.5 hours. The infrared radiation wavelength was 50μm, the heating rate was 20℃ / s, and the instantaneous heat flux density reached 0.1MW / m³. 2 Accelerate the discharge of LiOH·H2O and Ni 0.25 Mn 0.75 (OH)2 contains free water and crystal water. Turn off infrared radiation heating to lower the temperature of the mixed raw materials to 105℃, and continue to raise the temperature.

[0088] (3) In the second stage, triethyl phosphate and microcrystalline wax undergo an oxidation reaction, releasing a large amount of heat and rapidly raising the temperature of the mixed raw materials to 700°C. The heating time is 0.2h, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the reaction of triethyl phosphate and microcrystalline wax is completed, the temperature of the mixed raw materials decreases to 460°C and continues to rise.

[0089] (4) In the third stage, when the temperature of the mixed raw materials is raised to 750°C, microwave heating is used to raise the temperature to 1100°C for 0.5 hours to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes.

[0090] (5) Control the total heating time to 20h, turn off microwave heating, control the sintering temperature of mixed raw materials to 870℃, and carry out the synthesis reaction for 18h;

[0091] (6) During the cooling stage, infrared heating is used to raise the temperature to 720°C. After cooling, single-crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained.

[0092] Comparative Example 1

[0093] (1) Mix Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly at a molar ratio of 0.25:1 to obtain a mixed raw material;

[0094] (2) The mixture was heated to 900°C using electric heating and the synthesis reaction was carried out at 900°C for 16 hours.

[0095] (3) After cooling, single-crystal lithium nickel manganese oxide is obtained.

[0096] Comparative Example 2

[0097] (1) Triethyl phosphate, Li2CO3 and Ni 0.25 Mn 0.75 (OH)2 is mixed evenly at a molar ratio of 0.003:0.25:1 to obtain a mixed raw material;

[0098] (2) The infrared radiation heating method was used to raise the temperature to 300℃, the heating time was 0.5h, the infrared radiation wavelength was controlled at 20μm, the heating rate was 40℃ / s, and the instantaneous heat flux density reached 0.3MW / m 2 Accelerate the discharge of Ni 0.25 Mn 0.75 (OH)2 contains free water and water of crystallization; turn off infrared radiation heating to lower the temperature of the mixed raw materials to 115℃, and continue to raise the temperature.

[0099] (3) When the temperature of the mixed raw materials rises to 900℃, the temperature of the mixed raw materials is controlled at 900℃ and the synthesis reaction is carried out for 16 hours;

[0100] (4) During the cooling stage, infrared heating is used to raise the temperature to 800°C. After cooling, single-crystal lithium nickel manganese oxide is obtained.

[0101] The specific surface area of ​​the high-voltage lithium nickel manganese oxide cathode materials prepared in the embodiments and comparative examples of the present invention was measured, and the results are shown in Table 1.

[0102] Table 1 is a comparison table of the specific surface area of ​​Examples 1-10 of the present invention and Comparative Examples 1 and 2.

[0103]

[0104] As can be seen from Table 1, the specific surface area of ​​Examples 1-10 is significantly smaller than that of Comparative Example 1 and Comparative Example 2.

[0105] The powder internal resistance of the high-voltage lithium nickel manganese oxide cathode materials prepared in the embodiments and comparative examples of the present invention was tested, and the results are shown in 2.

[0106] Table 2 is a comparison table of specific surface areas between Examples 1-10 of the present invention and Comparative Examples 1 and 2.

[0107]

[0108] As can be seen from Table 2, the powder internal resistance of Examples 1-10 is significantly lower than that of Comparative Example 1 and Comparative Example 2.

[0109] The compaction density of the high-voltage lithium nickel manganese oxide cathode materials prepared in the embodiments and comparative examples of the present invention was tested, and the results are shown in Table 3.

[0110] Table 3 is a comparison table of the compaction density of Examples 1-10 of the present invention and Comparative Examples 1 and 2.

[0111]

[0112] As can be seen from Table 3, the compaction density of Examples 1-10 is significantly higher than that of Comparative Example 1 and Comparative Example 2.

[0113] The positive electrode materials from Examples 1, 1, and 2 were used to fabricate lithium-ion batteries. Specifically, 9g of the positive electrode material, 0.5g of acetylene black, and a 5% solids content polyvinylidene fluoride solution were mixed at room temperature and pressure to form a slurry, which was then uniformly coated onto the surface of aluminum foil to obtain an electrode sheet. The electrode sheet obtained in the previous step was dried at 80°C, pressed, and cut into pieces with an area of ​​1.32 cm². 2 A circular thin sheet is used as the positive electrode, a pure lithium sheet is used as the negative electrode, and a 1 mol / L solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) of LiPF6 is used as the electrolyte, wherein the volume ratio of EC to DMC is 1:1. The lithium-ion battery is then assembled in an argon-filled glove box.

[0114] The room temperature rate capability and cycle performance of the prepared lithium-ion batteries were tested, and the results are shown in the table below. Figure 5 , Figure 5 A comparison chart of the cycle performance of batteries for Example 1, Comparative Example 1 and Comparative Example 2 of the present invention was prepared.

[0115] Figure 5 This is a comparison chart of the cycle performance of batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0116] Depend on Figure 5It can be seen that the battery prepared in Example 1 has a 0.2C discharge specific capacity of 127.7 mAh / g, a 1.0C discharge specific capacity of 127.2 mAh / g, a 1C / 0.2C ratio of 99.6%, and a capacity retention rate of 98.3% after 50 cycles at 1.0C. The battery prepared in Comparative Example 1 has a 0.2C discharge specific capacity of 125.5 mAh / g, a 1.0C discharge specific capacity of 124.4 mAh / g, a 1C / 0.2C ratio of 99.1%, and a capacity retention rate of 93.6% after 50 cycles at 1.0C. The battery prepared in Comparative Example 2 has a 0.2C discharge specific capacity of 124.6 mAh / g, a 1.0C discharge specific capacity of 121.5 mAh / g, a 1C / 0.2C ratio of 97.5%, and a capacity retention rate of 69.0% after 50 cycles at 1.0C. The rate performance and cycle performance of Example 1 are better than those of Comparative Example 1 and Comparative Example 2.

[0117] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A single-crystal lithium nickel manganese oxide synthesized by a multi-stage stepped sintering method, characterized in that, The preparation method of the single-crystal lithium nickel manganese oxide includes the following steps: (1) The combustion aid, lithium salt and lithium nickel manganese oxide precursor are mixed evenly according to the molar ratio to obtain a mixed raw material; the combustion aid is one of the following: bioethanol, biobutanol, phosphate ester, triethyl phosphate, microcrystalline wax, liquid paraffin, liquid resin, polyethylene wax, glycerol, glycerol fatty acid, biodiesel and carbon powder. (2) In the first stage, the infrared radiation heating method is used to raise the temperature to T1, and the heating time is t1, so that the mixed raw materials can be discharged more quickly. The mixed raw materials contain free water and crystal water. The infrared radiation heating is turned off to lower the temperature of the mixed raw materials. (3) In the second stage, the combustion aid is used to carry out an oxidation reaction, which releases a large amount of heat and raises the temperature of the mixed raw materials to T2. The heating time is t2, which accelerates the discharge of carbon dioxide gas from the mixed raw materials. After the end, the temperature of the mixed raw materials decreases. (4) In the third stage, microwave heating is used to raise the temperature to T3 for a time of t3, so as to accelerate the growth of lithium nickel manganese oxide (100) and (110) crystal planes; (5) After turning off microwave heating, control the sintering temperature of the mixed raw materials and carry out the synthesis reaction; (6) During the cooling stage, microwave heating or infrared heating is used to raise the temperature to 800°C. During the cooling process, microwave heating or infrared heating is used to raise the temperature of the material again, release the lattice stress inside the material, reduce the crystal defects and surface oxygen defects of the material, and after cooling, single crystal lithium nickel manganese oxide synthesized by multi-stage step sintering method is obtained. The preparation temperature curve exhibits multiple step-like characteristic peaks, meaning that during the heating process, there are multiple stages where the material temperature rises rapidly and then falls. The total heating time for synthesis is t, the synthesis temperature is T, the first stage time is t1 and the highest temperature is T1, the second stage time is t2 and the highest temperature is T2, and the third stage time is t3 and the highest temperature is T3, satisfying the following relationships: T1×t≥T×t1, T2×t≥T×t2, T3×t≥T×t3, where 2≤n≤3.

2. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, In (1), the molar ratio of combustion aid, lithium salt and lithium nickel manganese oxide precursor is 0.001-0.1:0.48-0.58:

1.

3. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, In (2), during the infrared heating process, the infrared radiation wavelength is 200μm-1μm, the heating rate is 10-80℃ / s, and the instantaneous heat flux density reaches 0.01-1MW / m³. 2 T1 is 150-300℃, and t1 is 0.1-1h.

4. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, In (3), the heating temperature T2 of the combustion aid is 700-950℃ and the heating time t2 is 0.01-0.2h.

5. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, In (4), the microwave heating temperature T3 is 750-1200℃ and the heating time t3 is 0.1-2h.

6. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, In step (5), the sintering temperature is 820-980℃ and the synthesis reaction time is 12-24h.

7. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, The total heating time t is 3-20h, and the synthesis temperature T is 600-1200℃.

8. The single-crystal lithium nickel manganese oxide synthesized by the multi-stage stepped sintering method according to claim 1, characterized in that, The heating and temperature rise method is one or more of the following: electric heating, infrared radiation heating, microwave heating, combustion additive heating, heat flow heating, and Joule heating.

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