A high-capacity high-nickel cobalt-free cathode material, its preparation method and application

Abstract

The present invention discloses a high-rate and high-nickel cobalt-free cathode material, a preparation method thereof, and an application thereof. The chemical formula of the cathode material is LiNi x Mn 1‑x‑y‑z M y N z O2, M is one or more of Al, Zr, Y, W, Nb, Ce, Ti, Mg, Sr, B, P or Si, N is an MBene material coating layer, 0.5

Description

Technical Field

[0001] The present invention belongs to the technical field of high-nickel and cobalt-free cathode materials for lithium-ion batteries, and particularly relates to a high-rate high-nickel and cobalt-free cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the extreme pursuit of high energy density and low cost by people, the nickel content of the cathode material for lithium-ion batteries is getting higher and higher, and the cobalt content is getting lower and lower or even cobalt-free. These two factors of the increase in nickel content and the absence of cobalt lead to an increase in residual lithium in the cathode material, serious lithium-nickel mixing, poor thermal stability, easy particle breakage, and poor rate performance and cycle stability. For ultra-high-nickel and cobalt-free materials with Ni>90%, these problems are more prominent.

[0003] The traditional coating operation generally directly mixes the coating with the cathode material matrix by dry or wet method, and then obtains the coated and modified cathode material through low-temperature annealing. Due to the uneven surface of the cathode material matrix, the binding force between the coating layer and the cathode material matrix is weak, and the coating layer fails to completely cover the entire particle surface, resulting in poor stability in the later-stage electrical performance. The traditional coating is generally a metal oxide, which is difficult to fully react with the residual lithium on the surface of the cathode material matrix. Because the residual lithium is relatively dense at the pits or gaps of the particles, the coating is difficult to fully contact, resulting in a considerable part still existing in the initial oxide state finally, and then leading to poor surface conductivity of the cathode material, which is not conducive to the later-stage electrical performance.

[0004] Patent document CN118248856A discloses a preparation method of a cathode material for an aqueous zinc-ion battery based on the composite of single-layer MoB MBene and 1T-MoS2. The specific process is as follows: MoB MBene is ultrasonically treated to obtain single-layer MoB MBene, which is then mixed with MoO3, urea, and thioacetamide and placed in an autoclave to react at 200 °C for 12 h, and then washed with absolute ethanol and distilled water and freeze-dried to obtain the product. To further improve the performance, aniline, hydrochloric acid, and ammonium persulfate are added to the material at low temperature and reacted for 12 h, and a layer of polyaniline can be coated on the material, whose function is to enhance the structural stability of the material. This patent uses single-layer MoB MBene as the skeleton to in-situ grow 1T-MoS2 outside, making the prepared electrode material have excellent electronic conductivity and good structural stability, and the coated polyaniline further ensures the cycle stability of the material during charge and discharge. However, the material prepared in this patent is the cathode material for an aqueous zinc-ion battery, and single-layer MoB MBene serves as the skeleton during the preparation process of the cathode material for an aqueous zinc-ion battery to realize the in-situ growth of 1T-MoS2 and the coating of the polyaniline coating layer. Patent document CN118522875A discloses a modified cathode material, its preparation method and application. The modified cathode material includes a cathode material matrix and a coating layer provided on the surface of the cathode material matrix. The coating layer includes a fluoropolymer and a metal oxide-coated MBene nanomaterial. This modified cathode material has excellent charge and discharge performance and cycle performance at a high cut-off voltage. In the coating modification process of this patent, the prepared coating layer includes a fluoropolymer and a metal oxide-coated MBene nanomaterial, not a single MBene nanomaterial. And during the coating modification process, the fluoropolymer and the metal oxide-coated MBene nanomaterial are added to a second organic solvent for dispersion, and then the second organic solvent dispersion of the cathode material matrix is added, stirred to evaporate to dryness and dried to obtain a powder; the powder is subjected to a fusion reaction to obtain the modified cathode material. The coating modification step adopts a direct wet mixing method, which cannot effectively achieve the dense and uniform coating of the fluoropolymer and the metal oxide-coated MBene nanomaterial on the surface of the cathode material matrix to a certain extent, and cannot effectively ensure the stable coating of the fluoropolymer and the metal oxide-coated MBene nanomaterial on the surface of the cathode material matrix, thereby effectively preventing the peeling and falling off of the coating layer. Summary of the Invention

[0005] The present invention aims to solve the problems in the prior art that the binding force between the coating layer and the cathode material matrix of the high-nickel cobalt-free cathode material is poor, and the conductivity and chemical stability of the coating layer material are poor. As a result, the surface stability of the modified cathode material is poor, the viscosity changes greatly during the preparation of the lithium-ion battery slurry, and the rate performance and cycle stability of the prepared lithium-ion battery are poor. The present invention provides a high-rate high-nickel cobalt-free cathode material and a preparation method thereof. The high-nickel cobalt-free cathode material prepared by this method has a porous structure inside and a coating layer of MBene material with stable chemical properties and high conductivity on the surface. When used in lithium-ion batteries, the viscosity change of the slurry is small, and the rate performance of the prepared lithium-ion battery is good and the cycle stability is significantly improved.

[0006] To solve the above technical problems, the present invention adopts the following technical solution. A high-rate high-nickel cobalt-free cathode material has the chemical formula LiNi x Mn 1-x-y-z M y N z O2, where M is one or more of Al, Zr, Y, W, Nb, Ce, Ti, Mg, Sr, B, P, or Si, and N is a coating layer of MBene material. The MBene material is one or more of MoB, Mo 1.33 B, Zr2B2, MnB, Cr2B2, Fe2B2, or TiB. 0.5 < x < 1, 0 < y < 0.1, 0 < z < 0.1, and 0 < x + y + z < 1.

[0007] The MBene material is a two-dimensional transition metal boride with diversity and tunability. Its structure and properties can be adjusted by changing the M element, doping the M' element, forming different surface functional groups, etc. This kind of material has good mechanical strength and hardness, and at the same time has certain chemical stability, acid and alkali corrosion resistance, and oxidation resistance, and has good lithium-ion diffusion ability and charge transfer ability, which can achieve high capacity, high stability, and high rate performance. For the cathode material of lithium-ion batteries, it is an excellent coating material.

[0008] The present invention provides a method for preparing a high-rate high-nickel cobalt-free cathode material. The specific process is as follows: A porous precursor is selected for lithium doping sintering to obtain a cathode material matrix, and then the cathode material matrix is polished with an abrasive. After the polishing treatment is completed, the abrasive and the fine powder generated by polishing are separated. Finally, it is coated with an MBene-based material and then subjected to annealing sintering to obtain a high-rate high-nickel cobalt-free cathode material with a porous structure inside and a coating layer with stable chemical properties and high conductivity on the surface. The abrasive is a powder or dispersion of one or more of cerium oxide, silicon oxide, zirconium oxide, aluminum oxide, iron oxide, chromium oxide, or stearic acid; preferably one or more of cerium oxide, silicon oxide, zirconium oxide, or aluminum oxide, because the metal elements in cerium oxide, silicon oxide, zirconium oxide, and aluminum oxide are relatively harmless to the cathode material matrix, and even if a small part remains on the surface of the cathode material matrix, it will not have an adverse effect on the later performance of the cathode material.

[0009] Further, it is specified that the D50 of the abrasive particles is 10 nm to 50 μm. If the particle size of the abrasive is too large, it will cause greater damage to the cathode material matrix during the polishing process, easily leading to particle cracks or even breakage, resulting in poor later electrical performance. If the particle size of the abrasive is too small, the polishing force is weak and the polishing efficiency is low.

[0010] Further, it is specified that the dosage of the abrasive accounts for 1% to 20% of the weight of the cathode material matrix. If the dosage of the abrasive is too much, it will increase the cost of the abrasive raw material and the separation from the cathode material matrix. If the dosage of the abrasive is too little, the polishing time will be prolonged and the polishing efficiency will be low.

[0011] Further, it is specified that the method for polishing the cathode material matrix is selected from one or more of high-speed mixing polishing, grinding polishing, ball milling polishing, or fusion machine polishing.

[0012] Further, it is specified that the separation method of the polished cathode material matrix from the abrasive and the fine powder generated by polishing is selected from one or more of cyclone separation, ultrasonic sieving separation, centrifugal separation, membrane filtration separation, sedimentation separation, or magnetic separation; preferably one or more of cyclone separation or ultrasonic sieving separation.

[0013] Further, it is specified that after the separation of the polished cathode material matrix from the abrasive and the fine powder generated by polishing, the residual ratio of the abrasive is within 5% of the weight of the added abrasive. If the residual ratio of the abrasive is too much, it will cause an increase in non-active components in the finally prepared cathode material and a decrease in battery capacity.

[0014] Further limitation: the sphericity of the particles of the polished cathode material matrix is 85% - 100%; if the sphericity of the cathode material matrix particles is too low, the sphericity is relatively poor, indicating that the polishing effect is not good. When the MBene-based material is coated later, the coating effect at the sharp corners or gaps is poor, and it is difficult to form a dense and uniform coating layer, which is not conducive to the later electrical performance.

[0015] Further limitation: the coating method of the MBene-based material is selected from one or more of solid-phase reaction method, spray drying method, hydrothermal or solvothermal method, sol-gel method, microemulsion coating method, heterogeneous nucleation method, supercritical fluid method, chemical vapor deposition method or microencapsulation method; preferably one or more of solid-phase reaction method or spray drying method.

[0016] The present invention also provides a lithium-ion battery, and the positive electrode of the lithium-ion battery is prepared from the above high-rate high-nickel cobalt-free cathode material.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] 1. The present invention selects the MBene-based material as the coating layer. On the one hand, the surface chemical properties of the high-nickel cobalt-free cathode material are stable, and the slurry stability is higher during the preparation of the lithium-ion battery slurry, the viscosity change is small, and the side reaction with the electrolyte during the cycle is reduced, thereby achieving better cycle stability of the lithium-ion battery; on the other hand, the ionic conductivity of the MBene-based material is high, and the rate performance of the lithium-ion battery prepared from the high-nickel cobalt-free cathode material coated with the MBene-based material is better.

[0019] 2. The present invention first polishes the cathode material matrix before coating. On the one hand, it can make the sphericity of the cathode material matrix particles higher, the fluidity better, and there are fewer sharp corners, pits or protruding particles on the surface, making it easier to achieve a dense and uniform coating on the surface of the cathode material matrix particles; on the other hand, it is beneficial to make the coating layer combine more tightly and firmly with the cathode material matrix, so that the coating layer is not easy to peel off or fall off during the charge and discharge process of the high-nickel cobalt-free cathode material, and the long-term electrical performance is more stable and the cycle life is longer. Description of the Drawings

[0020] Figure 1 It is the change curve of the slurry viscosity for the full battery prepared from the cathode materials in Examples 1 - 3 and Comparative Examples 1 - 2.

[0021] Figure 2 It is the rate performance curve for the full battery prepared from the cathode materials in Examples 1 - 3 and Comparative Examples 1 - 2.

[0022] Figure 3 It is the cycle performance curve for the full battery prepared from the cathode materials in Examples 1 - 3 and Comparative Examples 1 - 2. Detailed Embodiments

[0023] The above content of the present invention will be further described in detail through the following embodiments. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention. Embodiment 1

[0024] Select Ni 0.92 Mn 0.075 B 0.005 (OH)2 porous precursor, and sinter with lithium hydroxide at a ratio of 1:1.05 at 760 °C to obtain the cathode material matrix LiNi 0.92 Mn 0.075 B 0.005 O2; then polish the cathode material matrix with cerium oxide powder with a D50 of 1 μm accounting for 10% of the weight of the cathode material matrix. The specific operation process is to add the cathode material matrix and cerium oxide into a grinding machine, start automatic grinding until the sphericity of the cathode material matrix reaches 94%, and then perform cyclone separation to remove cerium oxide and the ground fine powder until the residual weight ratio of cerium oxide is below 5%; coat the Mo 1.33 B dispersion on the surface of the polished cathode material matrix by spray drying method, and then anneal at 600 °C for 6 hours to obtain LiNi 0.91 Mn 0.075 B 0.005 (Mo 1.33 B) 0.01 O2 cathode material. Embodiment 2

[0025] Select Ni 0.94 Mn 0.04 W 0.02 (OH)2 porous precursor, and sinter with lithium hydroxide at a ratio of 1:1.05 at 740 °C to obtain the cathode material matrix LiNi 0.94 Mn 0.04 W 0.02 O2; then polish the cathode material matrix with silicon oxide powder with a D50 of 5 μm accounting for 5% of the weight of the cathode material matrix. The specific operation process is to add the cathode material matrix and silicon oxide into a fusion machine, adjust the rotor speed to adjust the pressure of the abrasive powder ejected from the fixed indenter until the sphericity of the cathode material matrix reaches 92%, and then pass through an ultrasonic vibrating screen to separate and remove silicon oxide and the ground fine powder until the residual weight ratio of silicon oxide is below 5%; add the Fe2B2 dispersion and the polished cathode material matrix into a high-pressure reaction kettle with a polytetrafluoroethylene lining, add the dispersant ethylene glycol at the same time, react at 120 °C for 12 hours, separate the solid and liquid of the obtained product and wash it, then put it into a vacuum oven and dry it at 80 °C for 10 hours, and then anneal at 600 °C for 6 hours to obtain LiNi 0.93 Mn0.04 W 0.02 (Fe2B2) 0.01 O2 cathode material. Example 3

[0026] Select Ni 0.96 Mn 0.03 Al 0.01 (OH)2 porous precursor is sintered with lithium hydroxide at a ratio of 1:1.05 at 720 °C to obtain the cathode material matrix LiNi 0.96 Mn 0.03 Al 0.01 O2; then the cathode material matrix is polished with a zirconia dispersion with a solid content of 15 wt% and a D50 of 500 nm. The zirconia particles in the zirconia dispersion account for 15% of the weight of the cathode material matrix. The specific operation process is to add the cathode material matrix and zirconia to a ball mill, and at the same time add polyurethane balls and absolute ethanol, and carry out wet polishing until the sphericity of the cathode material matrix reaches 90%. After the polishing is completed, first take out the polyurethane balls, and then carry out centrifugal separation. The pore size of the filter cloth is 2 μm to remove the zirconia and the fine powder ground out, and the filter cake is vacuum dried until the residual weight ratio of zirconia is below 5% to obtain the polished cathode material matrix powder; the TiB powder and the polished cathode material matrix powder are fully mixed evenly by the high-speed mixing method, and then annealed at 650 °C for 6 hours to obtain LiNi 0.93 Mn 0.03 Al 0.01 (TiB) 0.03 O2 cathode material.

[0027] Comparative Example 1

[0028] It is basically the same as the steps of Example 1, except that: the cathode material matrix is not polished before Mo 1.33 B coating.

[0029] Comparative Example 2

[0030] It is basically the same as the steps of Example 1, except that: the polished cathode material matrix is not coated with Mo 1.33 B material.

[0031] Particle sphericity (roundness) test

[0032] By combining electron microscopy technology and image processing technology, using image processing software, the electron microscopy image of the sample is binarized, and the obtained image is regarded as the two-dimensional projection of the particle group. The number of pixels forming each particle projection is statistically calculated, and then converted into the pixel area, pixel perimeter, etc. of each particle. Based on this information, the software can accurately calculate the sphericity (roundness) description parameters of any particle in the image.

[0033] Electrical performance test

[0034] 1. Electrical performance test:

[0035] The full - electric involved is a soft - pack battery of model 604062, and its specific manufacturing steps are as follows:

[0036] Step 1): Mix the main materials: SP: CNT: PVDF in a weight ratio of 95.5%: 1.0%: 1.7%: 1.8%, and perform high - speed stirring and dispersion in a double - planetary power mixer to obtain the full - electric slurry;

[0037] Step 2): Coating, baking, rolling, cutting, winding, injecting electrolyte, and sealing the full - electric slurry to obtain a soft - pack battery of model 604062.

[0038] 2. Viscosity change test:

[0039] Take 150 mL of the full - electric slurry obtained in Step 1), place it in an environment with a relative humidity ≤ 60% with an open mouth, measure the viscosity every hour, and place it for a total of 17 hours.

[0040] 3. Rate performance test:

[0041] For the soft - pack battery of model 604062 obtained in Step 2), at room temperature of 23 ± 2 °C, within the voltage range of 2.75 - 4.2 V, charge at 1C, and discharge at 1C, 2C, 3C, 4C, and 5C respectively, and calculate the discharge capacity ratios of 1C / 1C, 2C / 1C, 3C / 1C, 4C / 1C, and 5C / 1C respectively.

[0042] 4. Cycle performance test:

[0043] For the soft - pack battery of model 604062 obtained in Step 2), at room temperature of 23 ± 2 °C, within the voltage range of 2.75 - 4.2 V, perform 1C charge - discharge cycle tests until the capacity decays to 80% of the capacity in the first week.

[0044] Perform pulp viscosity tests, rate performance tests, and cycle stability tests on the full - electrics made from the positive electrode materials obtained in Examples 1 - 3 and Comparative Examples 1 - 2, and respectively obtain Figures 1 - 3 .

[0045] From Figure 1It can be seen that the pulp viscosities of the cathode materials prepared in Examples 1 to 3 are significantly lower, and the fluctuation range is relatively small, indicating that the stability of the slurry state is better with the extension of the storage time; the pulp viscosity of the cathode material prepared in Comparative Example 1 is close to that of Examples 1 to 3 at the initial stage of placement. As time goes by, the pulp viscosity begins to fluctuate greatly, indicating that the slurry stability gradually deteriorates. This is because the cathode material matrix was not polished before coating, resulting in a weak bonding force between the coating layer and the cathode material matrix. In the processes of sieving the finished cathode material by an ultrasonic vibrating screen and high-speed stirring of the slurry for making a soft-pack battery, there is a great possibility that part of the coating layer will peel off or fall off, resulting in the exposure of the relatively high residual alkali internal surface of the cathode material, and then leading to a large fluctuation in the viscosity of the slurry with the extension of the placement time.

[0046] From Figure 2 It can be seen that the rate performance of the full-electricity prepared from the cathode materials in Examples 1 to 3 is significantly better than that of Comparative Examples 1 to 2, indicating that using a porous structure precursor for sintering, first polishing the cathode material matrix, and then coating a highly conductive MBene-based material as the coating layer can effectively improve the rate performance of the full-electricity prepared from the cathode material.

[0047] From Figure 3 It can be seen that the cycle life and cycle stability of the full-electricity prepared from the cathode materials in Examples 1 to 3 are significantly better than those of Comparative Examples 1 to 2, indicating that the coating layer on the surface of the cathode material fully plays the role of isolating the erosion of the electrolyte and inhibiting side reactions, thus making the cycle stability of the prepared full-electricity better; the coating layer on the surface of the cathode material plays the role of improving the ionic conductivity, thus making the rate performance of the prepared full-electricity better.

[0048] The above examples describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above examples. What is described in the above examples and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-capacity and high-nickel cobalt-free cathode material, characterized in that: The chemical formula of the high-capacity high-nickel cobalt-free cathode material is LiNi x Mn 1-x-y-z M y N z O2, where M is one or more of Al, Zr, Y, W, Nb, Ce, Ti, Mg, Sr, B, P, or Si, and N is a coating layer of MBene material, and the MBene material is one or more of MoB, Mo 1.33 B, Zr2B2, MnB, Cr2B2, Fe2B2, or TiB, 0.5 < x < 1, 0 < y < 0.1, 0 < z < 0.1, 0 < x + y + z < 1; The specific preparation process of the high-rate high-nickel cobalt-free cathode material is as follows: a porous precursor is selected for lithium doping sintering to obtain a cathode material matrix, and then the cathode material matrix is polished with a polishing agent. After the polishing treatment is completed, the polishing agent and the fine powder generated by polishing are separated. Finally, it is coated with an MBene-based material and then annealed and sintered to obtain a high-rate high-nickel cobalt-free cathode material with a porous structure inside and a coating layer with stable chemical properties and high conductivity on the surface; the polishing agent is a powder or dispersion of one or more of cerium oxide, silicon oxide, zirconium oxide or aluminum oxide, and the D50 of the polishing agent particles is 10 nm to 50 μm; the dosage of the polishing agent accounts for 1% to 20% of the weight of the cathode material matrix; after the polished cathode material matrix is separated from the polishing agent and the fine powder generated by polishing, the residual ratio of the polishing agent is within 5% of the weight of the added polishing agent; the sphericity of the particles of the polished cathode material matrix is 85% to 100%.

2. The high-capacity high-nickel cobalt-free cathode material according to claim 1, wherein: The method for polishing the cathode material matrix is selected from one or more of high-speed mixing polishing, grinding polishing, ball milling polishing or fusion machine polishing.

3. The high-capacity high-nickel cobalt-free cathode material according to claim 1, characterized in that: The separation method of the polished cathode material matrix from the polishing agent and the fine powder generated by polishing is selected from one or more of cyclone separation, ultrasonic sieving separation, centrifugal separation, membrane filtration separation, sedimentation separation or magnetic separation.

4. The high-capacity high-nickel cobalt-free cathode material according to claim 1, characterized in that: The coating method of the MBene-based material is selected from one or more of solid-phase reaction method, spray drying method, hydrothermal or solvothermal method, sol-gel method, microemulsion coating method, heterogeneous nucleation method, supercritical fluid method, chemical vapor deposition method or microencapsulation method.

5. A lithium-ion battery, characterized in that: The positive electrode of the lithium-ion battery is prepared from the high-rate high-nickel cobalt-free cathode material described in any one of claims 1 to 4.

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