Solid-phase preparation method of lithium nickel manganese oxide positive electrode material

Abstract

The invention discloses a solid-phase preparation method of a lithium nickel manganese oxide positive electrode material, and relates to the technical field of lithium ion battery manufacturing. The preparation method comprises the following steps: weighing a nickel source, a manganese source and a lithium source in a ball milling tank according to the proportion of lithium nickel manganese oxide, adding deionized water and zirconium oxide beads, and carrying out ball milling and mixing to obtain precursor slurry, performing solid-liquid separation on the precursor slurry to obtain a filter cake, re-homogenizing and stirring the filter cake by using a low-surface-tension organic solvent, performing solid-liquid separation again after sufficient dispersion to obtain a filter cake, drying and grinding to obtain loose porous precursor powder; performing heat treatment on the precursor powder in an air or oxygen atmosphere to obtain the lithium nickel manganese oxide positive electrode material; the precursor is obtained through a one-step solid phase method and solvent exchange, the lithium nickel manganese oxide positive electrode which is low in trivalent manganese content and good in stability can be obtained through one-step sintering, the technological process is simple, and production energy consumption is low.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically to a solid-phase preparation method for lithium nickel manganese oxide cathode material. Background Technology

[0002] With the rapid development of electric vehicles and other fields, the research and development of lithium-ion batteries is increasingly moving towards lower cost, higher energy density, and longer cycle life. Existing cathode materials, such as layered ternary lithium-ion batteries, suffer from high cost and limited resources due to cobalt; spinel lithium manganese oxide exhibits poor cycle stability; and lithium iron phosphate batteries struggle to meet high-performance energy density requirements, failing to fully satisfy market demands. Therefore, there is an urgent need to develop cathode materials that offer lower cost, higher energy density, and better cycle performance. Spinel lithium nickel manganese oxide, developed from lithium manganese oxide, uses Ni... 2+ Replace part of Mn 3+ This causes the average oxidation state of Mn to become +4, reducing the oxidation state of Mn. 3+ Content, to avoid its Jahn-Teller effect and Mn 2+ The dissolution process significantly improves cycle stability; the voltage platform reaches around 4.7V, and the energy density can reach the level of ternary batteries; at the same time, lithium nickel manganese oxide is cobalt-free, which has a significant cost advantage over ternary batteries, meeting the needs of battery cost reduction and supply chain security. Therefore, the research on lithium nickel manganese oxide has become one of the important directions.

[0003] Lithium nickel manganese oxide (LiMO) preparation methods can be broadly classified into solid-phase and liquid-phase methods. Solid-phase methods, compared to liquid-phase methods, offer advantages such as simpler operation, lower equipment costs, suitability for mass production, controllable energy consumption, and environmental friendliness, making them a mainstream method for cathode material preparation. However, the preparation process is still under development and improvement. Patent CN102931395B discloses a method for preparing lithium nickel manganese oxide (LiMO) cathode material for lithium-ion batteries. This invention involves mixing nickel salt, manganese salt, lithium salt, and citric acid in a ball mill jar according to a specific cation molar ratio, then adding additives such as citric acid to the jar. The resulting slurry is dried to obtain powder. After grinding and pressing the powder into blocks, it undergoes high-temperature heat treatment in an air atmosphere, followed by sintering and subsequent crushing to obtain the LiMO cathode. However, pressing the powder into blocks in this method can easily affect oxygen permeation efficiency, leading to an increase in trivalent manganese content. Furthermore, subsequent crushing can damage the cathode crystal structure, affecting stability. Patent CN110217833B describes a process where a manganese source and a nickel source are weighed, mixed, and ball-milled, and then the mixture is dried into powder. A certain amount of oxalic acid is weighed, and the mixture of oxalic acid, lithium source, and the dried manganese and nickel sources is ball-milled. A certain amount of PEG is added to the mixture and stirred to obtain a blackish-gray gel-like mixture. This blackish-gray gel-like mixture is preheated. The preheated mixture is first kept at 300°C for 1–5 hours, then heated to 800°C and kept at 800°C for 1–5 hours, and then annealed to room temperature to obtain a lithium nickel manganese oxide cathode material. This patent describes a process where, in order to reduce the trivalent manganese content in the lithium nickel manganese oxide cathode, various additives are often added or an annealing process is added to reduce oxygen defects generated during the sintering process. Summary of the Invention

[0004] The purpose of this invention is to provide a solid-state preparation method for lithium nickel manganese oxide cathode materials, so as to solve the problem that existing solid-state methods still need improvement.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a solid-phase preparation method for lithium nickel manganese oxide cathode material, comprising the following specific contents:

[0006] S1 Ball milling and mixing; according to the ratio of nickel, manganese and lithium oxide, weigh the nickel source, manganese source and lithium source into the ball milling jar, with the lithium source in excess, add deionized water and zirconium oxide beads, and ball mill and mix to obtain the precursor slurry;

[0007] S2 solvent exchange; the precursor slurry is separated into solid and liquid to obtain a filter cake. The filter cake is homogenized and stirred again with a low surface tension organic solvent. After being fully dispersed, it is separated into solid and liquid again to obtain a filter cake. After drying, it is ground to obtain a loose and porous precursor powder.

[0008] S3 heat treatment: The precursor powder is heat-treated in an air or oxygen atmosphere to obtain lithium nickel manganese oxide cathode material.

[0009] Preferably, in step S1 above, the nickel source is one or more of nickel hydroxide, nickel oxide, nickel carbonate, and basic nickel carbonate; the manganese source is one or more of manganese tetroxide, manganese dioxide, manganese carbonate, and manganese oxalate; and the lithium source is one or more of lithium carbonate and lithium hydroxide. The molar ratio of nickel, manganese, and lithium in the nickel source, manganese source, and lithium source is 1:3:(2.1 to 2.4).

[0010] Preferably, in step S1 above, the mass ratio of deionized water to the total mass of the three raw materials is (0.9-1.3):1, the mass ratio of zirconia beads to the total mass of the three raw materials is (3-5):1, the ball milling time is 1-5 hours, and the ball milling speed is 300-500 rpm.

[0011] Preferably, in step S2 above, the surface tension of the low surface tension organic solvent does not exceed 30 mN / m under the conditions of 20°C and 1 atmosphere.

[0012] Preferably, the low surface tension organic solvent is selected from one or more of ethanol, isopropanol, and n-butanol.

[0013] Preferably, in step S2 above, the homogenization speed is 4000-8000 rpm, the time is 20-60 min, the stirring speed is 500-800 rpm, and the time is 4-8 h.

[0014] Preferably, in step S2 above, the solid-liquid separation method is one of vacuum filtration, pressure filtration, or centrifugation.

[0015] Preferably, in step S3 above, the heat treatment temperature is 750–950°C and the heat treatment time is 8–20 h.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. The solid-phase preparation method of the lithium nickel manganese oxide cathode material uses water as a medium during ball milling to dissolve part of the lithium carbonate, allowing it to enter the channels of the nickel and manganese sources, thereby improving the dispersion effect of the lithium source. After solid-liquid separation and solvent recovery, excess lithium salt in the solution is recovered, while avoiding segregation during the drying process of lithium carbonate. After ball milling, the water in the precursor is removed by solvent exchange, which avoids severe particle agglomeration and caking after drying, resulting in a loose and porous structure that facilitates air diffusion into the deep layer, improving sintering efficiency. At the same time, it can reduce the trivalent manganese content and improve the stability of lithium nickel manganese oxide.

[0018] 2. The solid-phase preparation method of this lithium nickel manganese oxide cathode material obtains a precursor with uniform particle distribution and relatively small particle size by solvent exchange and drying. After heat treatment, the cathode particles with uniform particle size distribution can be obtained by simple grinding. However, the ordinary solid-phase heat treatment generally produces dense large-particle powder with poor processing performance, which requires further crushing and sieving, and is prone to damaging the crystal structure and affecting its stability.

[0019] 3. Compared with conventional methods of pre-calcination compaction and post-sintering crushing, the preparation method of this invention uses ball milling slurry to exchange solvent and then dry to obtain a loose and porous precursor, which is conducive to oxygen permeation and reduces the trivalent manganese content. At the same time, the cathode does not need to be crushed after sintering, which can preserve its complete crystal structure and improve stability. On the other hand, by separating solid and liquid and using solvent to exchange residual water in the slurry, lithium carbonate segregation during the drying process can be reduced, which is beneficial to the uniformity of element distribution of the cathode material.

[0020] 4. Conventional methods require an additional annealing process to reduce the trivalent manganese content in lithium nickel manganese oxide, which not only reduces production efficiency but also increases energy consumption. The preparation method of this invention uses a one-step ball milling and one-step sintering method, which can obtain a lithium nickel manganese oxide cathode with low trivalent manganese content and good stability without further hot annealing, simplifying the process and reducing production energy consumption. Attached Figure Description

[0021] Figure 1 This is an XRD image of the sample prepared in Example 1 of this invention.

[0022] Figure 2 These are scanning electron microscope (SEM) images of the samples prepared in Example 1 of this invention.

[0023] Figure 3 This is a scanning electron microscope (SEM) image of the sample prepared in Comparative Example 1 of this invention.

[0024] Figure 4 This is a scanning electron microscope (SEM) image of the sample prepared in Comparative Example 2 of this invention.

[0025] Figure 5 These are the capacity test curves of Embodiment 1, Comparative Example 1, and Comparative Example 2 of this invention under a charge / discharge current of 0.1C. Detailed Implementation

[0026] A solid-phase preparation method for lithium nickel manganese oxide cathode material includes the following specific steps:

[0027] S1 Ball milling and mixing; Weigh the nickel source, manganese source, and lithium source into the ball mill jar according to the ratio of nickel-manganese-lithium oxide, with the lithium source in excess. Specifically, the molar ratio of nickel, manganese, and lithium in the nickel source, manganese source, and lithium source can be 1:3:(2.1~2.4). Part of the excess lithium is recovered after dissolving lithium carbonate in the next solid-liquid separation step, and the other part is lost due to lithium volatilization during the heat treatment process. Add deionized water and zirconium oxide beads, and ball mill to obtain the precursor slurry. For reference, the ball milling time is 1~5h, and the ball milling speed is 300~500rpm.

[0028] For reference, the nickel source can be one or more of nickel hydroxide, nickel monoxide, nickel carbonate, and basic nickel carbonate; the manganese source can be one or more of manganese tetroxide, manganese dioxide, manganese carbonate, and manganese oxalate; and the lithium source can be one or more of lithium carbonate and lithium hydroxide.

[0029] In a preferred embodiment, the mass ratio of deionized water to the total mass of the three raw materials is (0.9–1.3):1, and the mass ratio of zirconia beads to the total mass of the three raw materials is (3–5):1.

[0030] S2 solvent exchange; the precursor slurry is separated into solid and liquid to obtain a filter cake. The filter cake is re-homogenized and stirred with a low surface tension organic solvent. After being fully dispersed, it is separated into solid and liquid again to obtain a filter cake. After drying, it is ground to obtain a loose and porous precursor powder (the two solid-liquid separations can be selected as needed from vacuum filtration, pressure filtration, centrifugation, etc., and excess lithium can be recovered from the filtrate).

[0031] The low surface tension organic solvent is further preferably an organic solvent with a surface tension not exceeding 30 mN / m under the conditions of 20°C and 1 atm, such as one or more of ethanol, isopropanol, and n-butanol, and of course acetonitrile can also be used;

[0032] Solvent exchange can not only remove moisture from the precursor and prevent severe particle agglomeration and caking after drying, resulting in a loose and porous structure that facilitates air diffusion into the deeper layers and improves sintering efficiency, but also reduce the trivalent manganese content and improve the stability of lithium nickel manganese oxide.

[0033] In a preferred embodiment, the homogenization speed is selected as 4000-8000 rpm, the time can be controlled as 20-60 min, the stirring speed is selected as 500-800 rpm, and the time can be controlled as 4-8 h.

[0034] S3 Heat Treatment: The precursor powder is heat-treated in an air or oxygen atmosphere to obtain lithium nickel manganese oxide cathode material. For reference, the heat treatment temperature can be 750-950℃ and the heat treatment time can be 8-20h.

[0035] Example 1

[0036] Weigh out 68.6 g of manganese tetroxide, 27.8 g of nickel hydroxide, and 25.1 g of lithium carbonate, and add them to 133 ml of deionized water (liquid-to-solid ratio 1.1). The mass of added zirconia beads is 492.1 g (material-to-bead ratio 4). The ball milling speed is 500 rpm, and the milling time is 2 h. After ball milling, the resulting slurry is filtered, washed several times with ethanol, and the filter cake is removed and redispersed with ethanol. After homogenization, the mixture is stirred and dispersed for 6 h, and then filtered again to remove moisture from the filter cake. The resulting filter cake is dried to obtain the heat-treated precursor. After grinding the heat-treated precursor, it is heat-treated in air at 900℃ for 12 h to obtain the desired lithium nickel manganese oxide cathode.

[0037] Comparative Example 1

[0038] This embodiment is based on Example 1, except that there is no solvent exchange step; the filter cake obtained by vacuum filtration is directly dried, ground, and then heat-treated. The SEM image of the sample prepared in this comparative example is attached. Figure 3 The sample particles were unevenly distributed and severely agglomerated, with a tap density of 1.5 g / cm³. 3 The installed coin cell has a 0.1C discharge specific capacity of 109 mAh / g and a capacity retention rate of 64.3% after 1000 cycles at 1C.

[0039] Comparative Example 2

[0040] This embodiment is based on Example 1, except that there is no solvent exchange step. The filter cake obtained by vacuum filtration is directly dried, ground, and then heat-treated. After heat treatment, the positive electrode is crushed. The SEM image of the sample prepared in this comparative example is attached. Figure 4 The sample crystals were severely damaged, with a tap density of 2.0 g / cm³. 3 The 0.1C discharge specific capacity of the installed button cell is 118 mAh / g, and the capacity retention rate is 59.1% after 1000 cycles at 1C.

[0041] Example 2

[0042] This embodiment is based on Example 1, except that the mass of lithium carbonate added is changed to 26.6 g.

[0043] Example 3

[0044] This embodiment is based on Example 1, except that the manganese source is replaced with manganese dioxide, with an added mass of 39.1g, the nickel source is replaced with nickel carbonate, with an added mass of 35.6g, the water added is 111 ml, and the zirconium oxide beads are added with a mass of 405.2g.

[0045] Example 4

[0046] This embodiment is carried out with reference to Embodiment 1, except that the mass of water added during ball milling is 108.7 g, the amount of zirconia beads added is 604.1 g, that is, the liquid-solid ratio of the ball milling step is 0.9, and the ball-to-material ratio is 5:1.

[0047] Example 5

[0048] This embodiment is based on Embodiment 1, except that the mass of water added in the ball milling step is 157.1 g, and the mass of zirconia beads added is 362.5 g, that is, the liquid-solid ratio in the ball milling step is 1.3, and the ball-to-material ratio is 3:1.

[0049] Example 6

[0050] This embodiment is based on Embodiment 1, except that the ball milling speed is 300 rpm and the ball milling time is 5 hours.

[0051] Example 7

[0052] This embodiment is based on Embodiment 1, except that the ball milling speed is 400 rpm and the ball milling time is 3 hours.

[0053] Example 8

[0054] This embodiment is based on Example 1, except that the solvent exchange dispersion time is changed to 4 hours.

[0055] Example 9

[0056] This embodiment is based on Example 1, except that the solvent used for solvent exchange is changed to isopropanol.

[0057] Example 10

[0058] This embodiment is based on Embodiment 1, except that the heat treatment temperature is changed to 750℃ and the heat treatment time is changed to 20h.

[0059] Example 11

[0060] This embodiment is based on Embodiment 1, except that the heat treatment temperature is changed to 950℃ and the heat treatment time is changed to 8h.

[0061] The XRD pattern of the lithium nickel manganese oxide cathode material prepared in Example 1 is shown in the patent appendix. Figure 1 LiNi is a spinel phase. 0.5 Mn 1.5 O4, the sample phase has high purity and good crystallinity. SEM images are attached. Figure 2 Comparative Example 1 (with appendix) Figure 3 ) and Comparative Example 2 (attached) Figure 4 The positive electrode has a complete crystal structure with no obvious agglomeration, and the tap density of the sample obtained is 2.1 g / cm³. 3 It exhibits higher volumetric energy density. The particle size distribution of the sample, D10, D50, and D90, are 2.3, 5.6, and 8.7 μm, respectively. Compared with comparative examples 1 and 2, the particle size distribution is more uniform, resulting in better processing performance and electrochemical performance.

[0062] The performance of the cathode material is tested using standard button cell testing methods. The battery assembly and performance testing mainly include the following steps:

[0063] ① Positive electrode preparation: The prepared lithium nickel manganese oxide material, conductive agent Super P, and binder PVDF are mixed in a weight ratio of 8:1:1 to form a positive electrode slurry, which is coated on one side of the aluminum foil surface and dried to obtain a positive electrode sheet.

[0064] ② Button battery assembly: The button battery is assembled in the following order: negative electrode shell, lithium sheet, separator, electrolyte, positive electrode sheet, gasket, spring sheet and positive electrode shell. The electrolyte solute is 1M LiPF6, the solvent volume ratio is EC:DMC:DEC=1:1:1, and the separator is a polyethylene porous membrane.

[0065] ③ Battery capacity test: The test voltage is 3.5-4.95 V. The constant current step is used for charging and then for discharging. The charge and discharge current for capacity test is 0.1C, and the charge and discharge current for cycle test is 1C.

[0066] Example 1: The charge-discharge curve of the coin cell at 0.1C obtained from the positive electrode is shown in the appendix. Figure 5 The 0.1C discharge specific capacity is 138 mAh / g, while the cathode samples prepared in Comparative Examples 1 and 2 show no significant Mn content at around 3.9-4.1 V. 3+ / Mn 4+ The charge-discharge plateau indicates that the positive electrode Mn was successfully prepared. 3+ With a low content, it has better cycling stability, with a capacity retention rate of 90.5% after 1000 cycles at 1C, which is significantly better than the 64.3% and 59.1% of comparative examples 2 and 3, respectively.

[0067] The following table compares the particle size, tap density, battery capacity, and cycle stability test results of the cathode material samples obtained in the examples and comparative examples:

[0068]

[0069] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0070] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A solid-phase preparation method for lithium nickel manganese oxide cathode material, characterized in that, Includes the following specific content: S1 Ball milling and mixing; according to the ratio of nickel, manganese and lithium oxide, weigh the nickel source, manganese source and lithium source into the ball milling jar, with the lithium source in excess, add deionized water and zirconium oxide beads, and ball mill and mix to obtain the precursor slurry; S2 solvent exchange; the precursor slurry is separated into solid and liquid to obtain a filter cake. The filter cake is homogenized and stirred again with a low surface tension organic solvent. After being fully dispersed, it is separated into solid and liquid again to obtain a filter cake. After drying, it is ground to obtain a loose and porous precursor powder. S3 heat treatment: The precursor powder is heat-treated in an air or oxygen atmosphere to obtain lithium nickel manganese oxide cathode material.

2. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S1, the nickel source is one or more of nickel hydroxide, nickel oxide, nickel carbonate, and basic nickel carbonate; the manganese source is one or more of manganese tetroxide, manganese dioxide, manganese carbonate, and manganese oxalate; and the lithium source is one or more of lithium carbonate and lithium hydroxide. The molar ratio of nickel, manganese, and lithium in the nickel, manganese, and lithium sources is 1:3:(2.1 to 2.4).

3. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S1, the mass ratio of deionized water to the total mass of the three raw materials is (0.9-1.3):1, the mass ratio of zirconia beads to the total mass of the three raw materials is (3-5):1, the ball milling time is 1-5 hours, and the ball milling speed is 300-500 rpm.

4. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S2, the surface tension of the low surface tension organic solvent does not exceed 30 mN / m under the conditions of 20°C and 1 atmosphere.

5. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 4, characterized in that: The low surface tension organic solvent is selected from one or more of ethanol, isopropanol, and n-butanol.

6. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S2, the homogenization speed is 4000-8000 rpm and the time is 20-60 min, the stirring speed is 500-800 rpm and the time is 4-8 h.

7. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S2, the solid-liquid separation method is one of vacuum filtration, pressure filtration, or centrifugation.

8. The solid-phase preparation method of lithium nickel manganese oxide cathode material according to claim 1, characterized in that: In step S3, the heat treatment temperature is 750–950℃ and the heat treatment time is 8–20h.

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