A method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure

Abstract

This invention discloses a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes. The method involves adding a low eutectic point lithium salt system to alcohol for grinding, adding a nickel-manganese precursor, grinding and drying, sintering twice, centrifuging and washing, and vacuum drying to obtain the single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes. The low eutectic point lithium salt system is a lithium salt composition capable of undergoing a eutectic reaction, including two of lithium hydroxide, lithium nitrate, lithium carbonate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate. The preparation method of this invention is applicable to preparing single-crystal lithium nickel manganese oxide cathode materials with (111), (110), and (100) planes as the main exposed crystal planes, resulting in significantly improved electrochemical cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and relates to a lithium nickel manganese oxide cathode material, specifically a method for preparing a single-crystal lithium nickel manganese oxide cathode material with a specific exposed crystal facet. Background Technology

[0002] Among various energy storage technologies, lithium-ion batteries (LIBs) are considered one of the most successful energy storage technologies due to their high energy density, long cycle life, and environmental friendliness.

[0003] Lithium nickel manganese oxide (LiMO) has a high operating voltage of up to 4.7V and an energy density of up to 650Wh / kg, far exceeding the energy density of lithium manganese oxide and lithium iron phosphate (<500Wh / kg), and approaching that of the ternary layered cathode NCM111. Furthermore, LiMO exhibits good thermal stability and high safety performance, and its cost is lower due to the absence of expensive cobalt. In addition, LiMO possesses a three-dimensional lithium-ion channel for Li-ion exchange. + Rapid diffusion results in excellent rate performance during charge and discharge. All these advantages indicate that high-voltage spinel nickel-manganese oxide is a promising candidate cathode material for next-generation high-performance lithium-ion batteries, capable of meeting the ever-expanding energy density demands. However, some inherent drawbacks limit its commercial application, such as poor rate performance and severe capacity decay.

[0004] The electrochemical performance of lithium nickel manganese oxide is related not only to its crystal structure (space group, disorder, impurity phase, etc.), particle size and distribution, but also to the crystal orientation of the material. By controlling the crystal orientation, side reactions and the dissolution of transition metals at the electrode / electrolyte interface can be suppressed: (100) facet has a moderate distribution of Mn, Ni and Li metal ions on the crystal surface, which can avoid severe Mn dissolution without harming the transport kinetics of Li ions; (110) facet has a large number of ion channels and has excellent Li ion transport kinetics; (111) facet is dominated by closely packed oxygen atoms, showing good protection for the crystal surface structure.

[0005] Patent CN 115465900 A discloses a spinel-phase lithium nickel manganese oxide cathode material, its preparation method, and a battery. Specifically, it discloses the use of organic additives from Fu-Electronics Group to induce the material to grow along the (111) and (100) crystal planes with lower surface energy. However, its preparation method is complex and the process is cumbersome, making it difficult to scale up to industrial production. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes, so as to solve the problems of poor rate performance and severe capacity decay inherent in lithium nickel manganese oxide in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal faces involves grinding a low eutectic point lithium salt system with alcohol, adding a nickel-manganese precursor, grinding and drying, sintering twice, centrifuging and washing, and vacuum drying to obtain the single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal faces.

[0009] The low eutectic point lithium salt system is a lithium salt composition capable of undergoing a eutectic reaction, including two of lithium hydroxide, lithium nitrate, lithium carbonate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate.

[0010] As a limitation, the proportions of the low eutectic point lithium salt system are the proportions that allow the lithium salt to undergo a eutectic reaction.

[0011] As another limitation, the dominant exposed crystal plane of the single-crystal lithium nickel manganese oxide cathode material is at least one of the (111) plane, (110) plane and (100) plane.

[0012] As a third limitation, the amount of lithium salt system with nickel-manganese precursor added is such that the molar amount of lithium is 60% of the total molar amount of manganese and nickel.

[0013] As a fourth limitation, the nickel-manganese precursor is a combination of a nickel source and a manganese source or a nickel-manganese binary product.

[0014] The nickel source is nickel acetate, nickel nitrate, nickel carbonate, or nickel chloride;

[0015] The manganese source is manganese acetate, manganese nitrate, manganese carbonate, or manganese chloride;

[0016] The nickel-manganese binary product is Ni. 0.5 Mn 1.5 (CO3)2 or Ni 0.25 Mn 0.75 (OH)2;

[0017] The ratio of the nickel-manganese precursor is: the molar ratio of nickel to manganese is 1:3.

[0018] As a fifth limitation, the drying process is carried out at a temperature of 65-75°C for 1 hour.

[0019] As a sixth limitation, the two sintering processes are as follows: the first sintering is performed at a temperature of 200-350℃ for 2-2.5 hours; the second sintering is performed at a temperature of 750-900℃ for 6-10 hours.

[0020] As a seventh limitation, the centrifugal washing is performed three times: the first washing uses deionized water, the speed is 6000 rpm, and the washing time is 5 min; the second washing uses anhydrous ethanol, the speed is 6000 rpm, and the washing time is 5 min; the third washing uses deionized water, the speed is 6000 rpm, and the washing time is 5 min.

[0021] As an eighth limitation, the vacuum drying is performed at a temperature of 65-75°C for 12 hours.

[0022] By adopting the above technical solution, the technical progress achieved by this invention compared with the prior art is as follows:

[0023] ① The present invention provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal face exposure. By controlling the type and ratio of the low eutectic point lithium salt system, the reaction temperature required for lithium salt melting is reduced. After the lithium salt melts, it undergoes a solid-liquid reaction with the nickel source and manganese source, which reduces the nucleation and growth temperature and time of lithium nickel manganese oxide. Thus, lithium nickel manganese oxide cathode material with specific crystal face exposure can be obtained at a lower sintering temperature. The main exposed crystal faces are (111), (110) and (100) faces. To a certain extent, this solves the inherent disadvantage of poor cycle stability of lithium nickel manganese oxide. After 500 cycles at 1C, the capacity retention rate can reach about 86%, and the cycle performance is greatly improved.

[0024] ② The present invention provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure. By selecting a low eutectic point lithium salt system, the sintering temperature and sintering time can be reduced, thereby avoiding problems such as disordered phase growth and impurity generation at high temperatures, and thus improving the electrochemical performance of the material.

[0025] ③ The present invention provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure, wherein the molten salt system is all lithium salt, which reduces the introduction of other impurity elements during the preparation process;

[0026] ④ The present invention provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal face exposure. It only requires simple grinding and mixing of nickel manganese precursor and lithium salt system, and material generation and crystal growth can be achieved by sintering, and finally the target product is obtained. This method solves the shortcomings of the three-step co-precipitation-hydrothermal-calcination method and the sol-gel method, such as complex and cumbersome synthesis process, many control conditions, and long time consumption.

[0027] ⑤ The present invention provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure. The amount of molten salt (low eutectic point lithium salt system) used is greatly reduced compared with other reported molten salt methods. At the same time, the sintering temperature and time are also reduced, which reduces the production cost. In addition, the preparation steps are simple and the required equipment is readily available, making it more suitable for industrial production.

[0028] The preparation method of the present invention is applicable to the preparation of single-crystal lithium nickel manganese oxide cathode materials with (111), (110) and (100) planes as the main exposed crystal planes, and the electrochemical cycle performance of the prepared lithium nickel manganese oxide is greatly improved. Attached Figure Description

[0029] Figure 1 This is a SEM image of the single-crystal lithium nickel manganese oxide cathode material LNMO-1 in Example 1;

[0030] Figure 2 The image shows the XRD pattern of LNMO-1, the single-crystal lithium nickel manganese oxide cathode material in Example 1.

[0031] Figure 3 This is a SEM image of the single-crystal lithium nickel manganese oxide cathode material LNMO-2 in Example 1;

[0032] Figure 4 The image shows the XRD pattern of the single-crystal lithium nickel manganese oxide cathode material LNMO-2 in Example 1.

[0033] Figure 5 The charge-discharge curves of the single-crystal lithium nickel manganese oxide cathode material LNMO-1 in Example 1 at 1C rate for the 5th and 500th cycles;

[0034] Figure 6 The charge-discharge curves of the single-crystal lithium nickel manganese oxide cathode material LNMO-2 in Example 1 at 1C rate for the 5th and 500th cycles;

[0035] Figure 7 The graph shows the cycling performance of the single-crystal lithium nickel manganese oxide cathode materials LNMO-1 and LNMO-2 and the lithium nickel manganese oxide cathode material β1 at a 1C rate in Example 1. Detailed Implementation

[0036] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are only for explaining the present invention and do not limit the present invention.

[0037] Example 1: Preparation method of single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes

[0038] This embodiment prepared two single-crystal lithium nickel manganese oxide cathode materials with specific exposed crystal planes and studied their performance, specifically including the following steps performed in sequence:

[0039] I. Sample Preparation

[0040] 1. Preparation of LNMO-1, a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes.

[0041] S1. Weigh 0.0012 mol of the LiNO3-LiCl molten salt system (molar ratio 0.88:0.21) and place it in an agate mortar. Add alcohol and grind for 10 min to uniformly disperse the molten salt in the alcohol to form a homogeneous multi-component molten salt system. Then add 0.02 mol of the precursor Ni. 0.25 Mn 0.75 Continue grinding (OH)2 for 30 minutes until the alcohol evaporates to obtain a black paste-like substance;

[0042] S2. Place the black paste-like substance in a forced-air drying oven and dry it at 70°C for 1 hour. Then, grind the dried substance in a mortar to obtain a black fluffy powder, so that the material is less likely to clump during the subsequent sintering process.

[0043] S3. Place the black, fluffy powder into a 50 mL alumina-covered crucible, and place the crucible in a muffle furnace for two sintering processes: the first sintering at 350℃ for 2 hours to remove moisture from the material and ensure the molten salt is in a molten state; the second sintering at 800℃ for 10 hours to allow the material to react uniformly and form LiNi. 0.5 Mn 1.5 O4 crystals were grown and sintered. The resulting material was then ground in an agate mortar to obtain a black powder.

[0044] S4. The black powder was centrifuged and washed: the first wash was with deionized water at 6000 rpm for 5 min; the second wash was with anhydrous ethanol at 6000 rpm for 5 min; the third wash was with deionized water at 6000 rpm for 5 min. The precipitate was retained by centrifugation and dried in a vacuum drying oven at 70℃ for 12 h. After grinding, the single-crystal lithium nickel manganese oxide cathode material LNMO-1 with specific exposed crystal faces was obtained.

[0045] 2. Preparation of LNMO-2, a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes.

[0046] S1. Weigh 0.0012 mol of the LiNO3-LiOH molten salt system (molar ratio 0.6:0.4) and place it in an agate mortar. Add alcohol and grind for 10 min to uniformly disperse the molten salt in the alcohol to form a homogeneous multi-component molten salt system. Then add 0.01 mol of the precursor Ni. 0.5 Mn 1.5 Continue grinding (CO3)2 for 30 minutes until the alcohol evaporates to obtain a black paste-like substance;

[0047] S2. Place the black paste-like substance in a forced-air drying oven and dry it at 70°C for 1 hour. Then, grind the dried substance in a mortar to obtain a black fluffy powder, so that the material is less likely to clump during the subsequent sintering process.

[0048] S3. Place the black, fluffy powder into a 50 mL alumina-covered crucible, and place the crucible in a muffle furnace for two sintering processes: the first sintering at 350℃ for 2 hours to remove moisture from the material and ensure the molten salt is in a molten state; the second sintering at 800℃ for 10 hours to allow the material to react uniformly and form LiNi. 0.5 Mn 1.5 O4 crystals were grown and sintered. The resulting material was then ground in an agate mortar to obtain a black powder.

[0049] S4. The black powder was centrifuged and washed: the first wash was with deionized water at 6000 rpm for 5 min; the second wash was with anhydrous ethanol at 6000 rpm for 5 min; the third wash was with deionized water at 6000 rpm for 5 min. The precipitate was retained by centrifugation and dried in a vacuum drying oven at 70℃ for 12 h. After grinding, the single-crystal lithium nickel manganese oxide cathode material LNMO-2 with specific exposed crystal faces was obtained.

[0050] 3. Preparation of lithium nickel manganese oxide cathode material β1

[0051] S1. Add 0.0105 mol of lithium nitrate to alcohol and grind for 10 min, then add 0.02 mol of precursor Ni. 0.25 Mn 0.75 Grind (OH)2 for 30 minutes until the alcohol evaporates to obtain a black paste-like substance;

[0052] S2. Place the black paste-like substance in a forced-air drying oven and dry it at 70°C for 1 hour. Then, grind the dried substance in a mortar to obtain a black fluffy powder, so that the material is less likely to clump during the subsequent sintering process.

[0053] S3. Place the black, fluffy powder into a 50 mL alumina-covered crucible, and place the crucible in a muffle furnace for two sintering processes: the first sintering at 350℃ for 2 hours to remove moisture from the material and ensure the molten salt is in a molten state; the second sintering at 800℃ for 10 hours to allow the material to react uniformly and form LiNi. 0.5 Mn 1.5 O4 crystals are grown and sintered. The resulting material is then ground in an agate mortar to obtain lithium nickel manganese oxide cathode material β1.

[0054] II. Scanning Electron Microscopy and X-ray Diffraction Experiments

[0055] Scanning electron microscope (SEM) images of single-crystal lithium nickel manganese oxide cathode materials LNMO-1 and LNMO-2 with specific exposed crystal planes were taken, and X-ray diffraction experiments were performed. The results are as follows: Figure 1-4 As shown:

[0056] Depend on Figure 1 It can be seen that the main exposed crystal planes of LNMO-1 are the (111) plane and the (110) plane;

[0057] Depend on Figure 2 It can be seen that the diffraction peaks of LNMO-1 correspond to those of standard LiNi. 0.5 Mn 1.5 The presence of no impurity peaks on the O4 card indicates that single-crystal lithium nickel manganese oxide material has been successfully synthesized.

[0058] Depend on Figure 3 It can be seen that the main exposed crystal planes of LNMO-2 are the (111) plane, the (110) plane, and the (100) plane;

[0059] Depend on Figure 4 It can be seen that the diffraction peaks of LNMO-2 correspond to those of standard LiNi. 0.5 Mn 1.5 The absence of impurity peaks on the O4 card indicates successful synthesis of single-crystal lithium nickel manganese oxide material.

[0060] III. Charge and Discharge Test

[0061] Single-crystal lithium nickel manganese oxide cathode materials LNMO-1, LNMO-2, and β1 with specific exposed crystal planes were used as cathode active materials. These were mixed with acetylene black (a conductive agent) and PVDF (dissolved in NMP) (a binder) to form cathode sheets. The mass ratio of cathode active material, conductive agent, and binder was 85:10:5. Using the lithium sheet as the counter electrode, 2032 coin cells were assembled and subjected to constant current charge-discharge tests at voltages of 3-4.9V. The test results are as follows: Figure 5-7 As shown:

[0062] Depend on Figure 5 It can be seen that LNMO-1 has two charge / discharge platforms, Ni 2+ / Ni 3+ and Ni 3+ / Ni 4+ The redox process exhibits a plateau at approximately 4.6-4.7 V, Mn 4+ / Mn 3+ The process showed a plateau of approximately 4.0V, and the prepared LNMO-1 sample conformed to the typical charge-discharge curve of lithium nickel manganese oxide materials.

[0063] Depend on Figure 6 It can be seen that LNMO-2 has two charge / discharge platforms, Ni2+ / Ni 3+ and Ni 3+ / Ni 4+ The redox process exhibits a plateau at approximately 4.6-4.7 V, Mn 4+ / Mn 3+ The process showed a plateau of approximately 4.0V, and the prepared LNMO-2 sample conformed to the typical charge-discharge curve of lithium nickel manganese oxide materials.

[0064] Depend on Figure 7 It can be seen that LNMO-1 has excellent cycling performance, with a capacity retention of 86.4% after 500 cycles at 1C, while LNMO-2 has a capacity retention of 84.1%, which is much higher than the 36.9% of lithium nickel manganese oxide cathode material β1.

[0065] Examples 2-6: Preparation methods of single-crystal lithium nickel manganese oxide cathode materials with specific exposed crystal planes

[0066] Examples 2-6 are methods for preparing single-crystal lithium nickel manganese oxide cathode materials with specific exposed crystal planes. Their preparation methods are basically the same as steps S1-S4 in Example 1 for preparing single-crystal lithium nickel manganese oxide cathode material LNMO-1, differing only in the amount of raw materials and process parameters. See Table 1 for details.

[0067] Table 1. Summary of Control Parameters for Examples 2-6

[0068]

[0069] The contents of other parts of Examples 2-6 are the same as those of Example 1, and the single-crystal lithium nickel manganese oxide cathode materials obtained are LNMO-3 to LNMO-7, respectively.

Claims

1. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific exposed crystal planes, characterized in that, It involves adding alcohol to a low eutectic point lithium salt system for grinding, adding a nickel-manganese precursor, grinding and drying, sintering twice, centrifuging and washing, and vacuum drying to obtain the single-crystal nickel-manganese lithium oxide cathode material with specific exposed crystal faces. The low eutectic point lithium salt system is a lithium salt composition capable of undergoing a eutectic reaction, including two of lithium hydroxide, lithium nitrate, lithium carbonate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate. The dominant exposed crystal plane of the single-crystal lithium nickel manganese oxide cathode material is at least one of the (111) plane, (110) plane, and (100) plane; The two sintering processes are as follows: the first sintering is performed at a temperature of 200-350℃ for 2-2.5 hours; the second sintering is performed at a temperature of 750-900℃ for 6-10 hours. The nickel-manganese precursor is a combination of a nickel source and a manganese source or a nickel-manganese binary product. The ratio of the nickel-manganese precursor is: the molar ratio of nickel to manganese is 1:

3.

2. The method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure according to claim 1, characterized in that, The ratio of the low eutectic point lithium salt system is the ratio that allows the lithium salt to undergo a eutectic reaction.

3. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with exposed specific crystal planes according to claim 1 or 2, characterized in that, The amount of lithium salt system with low eutectic point and nickel-manganese precursor added is such that the molar amount of lithium is 60% of the total molar amount of manganese and nickel.

4. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with a specific exposed crystal plane according to claim 1 or 2, characterized in that, The nickel source is nickel acetate, nickel nitrate, nickel carbonate, or nickel chloride; The manganese source is manganese acetate, manganese nitrate, manganese carbonate, or manganese chloride; The nickel-manganese binary product is Ni 0.5 Mn 1.5 (CO3)2 or Ni 0.25 Mn 0.75 (OH)2.

5. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with a specific exposed crystal plane according to claim 1 or 2, characterized in that, The drying process is carried out at a temperature of 65-75℃ for 1 hour.

6. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with specific crystal plane exposure according to claim 1 or 2, characterized in that, The centrifugal washing process consisted of three cycles: the first wash used deionized water at a speed of 6000 rpm for 5 minutes; the second wash used anhydrous ethanol at a speed of 6000 rpm for 5 minutes; and the third wash used deionized water at a speed of 6000 rpm for 5 minutes.

7. A method for preparing a single-crystal lithium nickel manganese oxide cathode material with a specific exposed crystal plane according to claim 1 or 2, characterized in that, The vacuum drying process is carried out at a temperature of 65-75℃ for 12 hours.

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