Monocrystal lithium-rich positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a single-crystal lithium-rich positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: mechanically mixing a transition metal source, nano metal powder and a lithium source to obtain a precursor mixture; and sintering, and cooling to room temperature along with a furnace to obtain the single crystal lithium-rich positive electrode material with the surface coated with the spinel layer and doped with the metal ions. The material has high tap density, excellent rate and cycling stability, and the preparation process is simple. According to the method, nano metal powder is adopted as a sintering aid additive, the single-crystal lithium-rich positive electrode material can be formed only through one-time calcination, and the calcination temperature is lower than that of a common single-crystal lithium-rich positive electrode material. Meanwhile, the nano metal powder can also be used as a doping coating agent, doping ions are formed in a single crystal particle body phase in the calcining process, a certain spinel coating layer is formed on the particle surface, and the multiplying power and the cycling stability of the material are improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a single-crystal lithium-rich cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as smartphones, 5G communications, low-altitude aircraft, electric vehicles, and industrial and commercial energy storage, the demand for high-energy-density, long-cycle-life lithium-ion batteries is constantly increasing. Lithium-rich cathode materials have attracted widespread attention due to their high discharge specific capacity, but their poor cycle stability, caused by voltage drop and oxygen evolution due to structural instability, severely limits their application. In particular, most common lithium-rich cathode materials are currently composed of micron-sized secondary spherical particles formed by the agglomeration of primary nanoparticles. The numerous gaps between primary particles result in a large contact area with the electrolyte, increasing battery side reactions and causing rapid capacity decay. Secondly, spherical secondary particles are prone to breakage during electrode preparation and electrochemical cycling, further degrading electrochemical performance. Thirdly, the tap density of spherical secondary particles and the compaction density of the electrode sheet are typically low, severely limiting the battery's energy density.

[0003] By preparing single-crystal materials, not only can their structural stability be improved to a certain extent, but their specific surface area can also be reduced, increasing their mechanical strength, thereby improving the cycle stability and the compaction density of the electrode. However, single-crystalization also brings other problems: the particle size of typical single-crystal cathode materials is about 3 micrometers, resulting in poor material kinetics and consequently poor rate performance. Reducing the particle size to the submicron level can improve its kinetics, but submicron-sized single-crystal materials have a larger specific surface area, leading to more surface side reactions with the electrolyte, which is detrimental to improving cycle stability, and also has limited effect on improving the compaction density of the electrode.

[0004] In addition, current technologies for preparing single-crystal lithium-rich cathode materials still face several challenges. For the commonly used molten salt method, the large amount of flux added in the early stages needs to be removed by water washing, which not only increases the complexity of the process but also results in the molten salt being highly corrosive to the sintering furnace and having poor environmental friendliness (CN116143200A). Patent CN116623295A provides a tantalum-zirconium co-doped cobalt-free lithium-rich manganese single-crystal cathode material and its preparation method, which uses ball milling and high-temperature sintering in a single step to obtain the target material. However, its particle size is in the submicron range, and its dispersibility is poor. Since current methods for preparing single-crystal lithium-rich cathode materials cannot simultaneously achieve both process simplicity and excellent overall performance, it is necessary to develop simple and efficient preparation methods to improve the performance of single-crystal lithium-rich cathode materials. Summary of the Invention

[0005] In view of the problems existing in the current technology for preparing single-crystal lithium-rich cathode materials, this invention provides a method for preparing single-crystal lithium-rich cathode materials with high tap density, excellent rate capability, and cycle stability, and with a simple process. This method uses nano-metal powder as a calcination aid, requiring only one calcination to form the single-crystal lithium-rich cathode material, and the calcination temperature is lower than that of typical single-crystal lithium-rich cathode materials. Simultaneously, the nano-metal powder can also act as a dopant coating agent, forming dopant ions in the bulk phase of the single-crystal particles during calcination and forming a spinel coating layer on the particle surface, thereby improving the rate capability and cycle stability of the material.

[0006] This invention provides a single-crystal lithium-rich cathode material, the chemical formula of which is: Li a Mn b Ni c Co d M e O2, where M is one or more of the elements Zn, Mg, Al, and Cu, and 1≤a≤1.6, 0<b≤0.6, 0<c≤0.3, 0≤d≤0.2, b+c+d =N, 0.01N≤e≤0.05N, and a+b+c+d+e=2; the D50 of the single-crystal lithium-rich cathode material is 1.2~2.3μm, and the compaction density is 3.3~3.7g / cm³. 3 .

[0007] This invention provides a method for preparing a single-crystal lithium-rich cathode material, specifically including the following steps:

[0008] Step S1: Prepare precursor mixture using solid-state method: Obtain precursor mixture by mechanically mixing transition metal source, nano metal powder and lithium source;

[0009] Step S2: The precursor mixture obtained in step S1 is first heated to 400-500℃ at a heating rate of 2-5℃ / min and pre-sintered for 2-5 hours, then heated to 850-920℃ at a heating rate of 5-10℃ / min and sintered for 10-15 hours, and then cooled to room temperature in the furnace to obtain the single-crystal lithium-rich cathode material with a surface coated with a spinel layer and metal ion doping.

[0010] Furthermore, the mechanical mixing in step S1 is mechanical ball milling with water or ethanol as the dispersion medium, followed by pressure filtration and drying to obtain the target product.

[0011] Furthermore, the solid content of the mechanical ball mill slurry is 40wt%~60wt%, the rotation speed is 300~800 rpm, and the time is 4~10h.

[0012] Furthermore, the lithium source is either lithium carbonate or lithium hydroxide, and the excess ratio of the lithium source is 3-8%.

[0013] Furthermore, the nano-metal powder is one or more of Zn, Mg, Al, and Cu, with a particle size of 10-100 nm, and the amount added is 1-5% of the total amount of transition metals.

[0014] Furthermore, the transition metal source is one or more of two or more corresponding oxides, hydroxides, carbonates or other insoluble salts of Ni, Co or Mn.

[0015] The present invention also provides a lithium-ion battery, which is prepared using the above-mentioned single-crystal lithium-rich cathode material.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention directly mixes transition metal compounds with nano-metal powder and lithium source and then calcines them once to obtain lithium-rich cathode material products. The whole process is simple and easy to realize large-scale automated industrial production.

[0018] 2. This invention uses nano-metal powder as a sintering aid, utilizing the self-heating effect of the metal powder to promote the growth of single crystal particles and reduce the crystal growth temperature. Furthermore, the metal powder is dispersed between the cathode precursor particles, simultaneously achieving metal ion doping and surface spinel layer coating, effectively improving the cycle stability and rate performance of the lithium-rich cathode material.

[0019] 3. The single-crystal lithium-rich cathode material prepared by this invention has a medium particle size of 1-3 micrometers and a large compaction density, which is beneficial to improving the energy density of the battery. Attached Figure Description

[0020] Figure 1 The morphology diagrams of the cathode materials corresponding to Example 1 and Comparative Example 1 are as follows: (a) Example 1, (b) Comparative Example 1-1, (c) Comparative Example 1-2, (d) Comparative Example 1-3;

[0021] Figure 2 Morphology diagrams of the cathode materials corresponding to Example 2 and Comparative Example 2: (a) Example 2, (b) Comparative Example 2;

[0022] Figure 3 Morphology diagrams of the cathode materials corresponding to Example 3 and Comparative Example 3: (a) Example 3, (b) Comparative Example 3;

[0023] Figure 4 The morphology diagrams of the cathode materials corresponding to Example 4 and Comparative Example 4 are shown: (a) Example 4, (b) Comparative Example 4. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0025] Example 1

[0026] A certain amount of Ni(OH)₂, MnO₂, Li(OH)₂, and nano-Mg powder were weighed and mechanically ball-milled with water as the dispersion medium (solid content: 60wt%, rotation speed: 300 rpm, time: 10 h). The mixture was then filtered and dried to obtain a precursor mixture. The precursor mixture was first pre-sintered at 500℃ for 2 h at a heating rate of 5℃ / min, then sintered at 920℃ for 10 h at a heating rate of 5℃ / min, and finally cooled to room temperature in the furnace to obtain the product with the composition Li. 1.11 Mn 0.58 Ni 0.29 Mg 0.02 O2 single-crystal lithium-rich cathode material. The excess ratio of Li(OH)2 is 5%, the D50 of nano-Mg powder is 30nm, and the amount added is 2% of the total amount of transition metals.

[0027] Comparative Example 1-1

[0028] The only difference from Example 1 is that Mg powder is not added.

[0029] Comparative Examples 1-2

[0030] The only difference from Example 1 is that the nano-Mg powder is replaced with MgO as a dopant.

[0031] Comparative Examples 1-3

[0032] The only difference from Example 1 is that nano-Mg powder is replaced with MgO as the dopant, and NaCl is added as a sintering aid, with the amount of NaCl added being three times the total mass of the precursor. The sample obtained after high-temperature sintering is then washed with water and dried to obtain the final product, a single-crystal lithium-rich cathode material, Li. 1.11 Mn 0.58 Ni 0.29 Mg 0.02 O2.

[0033] Example 2

[0034] A certain amount of Ni(OH)₂, Mn₂CO₃, Co₂O₃, Li₂CO₃, and nano-Zn powder were weighed and mechanically ball-milled with ethanol as the dispersion medium (solid content: 40wt%, rotation speed: 600 rpm, time: 8h). The mixture was then filtered and dried to obtain a precursor mixture. The precursor mixture was first pre-sintered at 400℃ for 5h at a heating rate of 2℃ / min, then sintered at 850℃ for 15h at a heating rate of 10℃ / min. Finally, it was cooled to room temperature in the furnace to obtain the product with the composition Li. 1.2 Mn 0.53 Ni 0.12 Co 0.12 Zn0.03 A single-crystal lithium-rich cathode material containing O2. The excess ratio of Li2CO3 is 8%, the D50 of nano-Zn powder is 50 nm, and the amount added is 3% of the total amount of transition metals.

[0035] Comparative Example 2

[0036] The only difference from Example 2 is that no Zn powder is added.

[0037] Example 3

[0038] A certain amount of NiO2, Mn2O3, Co2O3, Li(OH)2, and nano-Al powder were weighed and mechanically ball-milled with ethanol as the dispersion medium (solid content: 50wt%, rotation speed: 500 rpm, time: 6 h). The mixture was then filtered and dried to obtain a precursor mixture. The precursor mixture was first pre-sintered at 450℃ for 4 h at a heating rate of 5℃ / min, then sintered at 880℃ for 12 h at a heating rate of 10℃ / min. Finally, it was cooled to room temperature in the furnace to obtain the product with the composition Li. 1.25 Mn 0.4 Ni 0.15 Co 0.15 Al 0.05 O2 single-crystal lithium-rich cathode material. The excess ratio of Li(OH)2 is 6%, the D50 of nano-Al powder is 100nm, and the amount added is 5% of the total amount of transition metals.

[0039] Comparative Example 3

[0040] The only difference from Example 3 is that Al powder is not added.

[0041] Example 4

[0042] A certain amount of Ni(OH)₂, MnO₂, Co₂O₃, Li(OH)₂, and nano-Cu powder were weighed and mechanically ball-milled with water as the dispersion medium (solid content: 60wt%, rotation speed: 800 rpm, time: 4h). The mixture was then filtered and dried to obtain a precursor mixture. The precursor mixture was first heated to 400℃ at a heating rate of 2℃ / min and pre-sintered for 3h, then heated to 900℃ at a heating rate of 5℃ / min and sintered for 10h. Finally, it was cooled to room temperature in the furnace to obtain the product with the composition Li. 1.2 Mn 0.48 Ni 0.23 Co 0.08 Cu 0.01 O2 single-crystal lithium-rich cathode material. The excess ratio of Li(OH)2 is 3%, the D50 of nano-Cu powder is 10nm, and the amount added is 1% of the total amount of transition metals.

[0043] Comparative Example 4

[0044] The only difference from Example 4 is that Cu powder is not added.

[0045] Weigh 0.8g of the prepared positive electrode material, 0.1g of acetylene black, and 0.1g of polyvinylidene fluoride. Add an appropriate amount of N-N'-dimethylpyrrolidone, mix thoroughly, and coat onto aluminum foil. In an argon-atmospheric glove box, assemble a CR2016 coin cell using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1 mol / L LiPF6-EC+DEC (1:1) as the electrolyte. The testing instrument is a LAND CT2001 battery testing system. Charge-discharge cycle tests were performed on the battery within a voltage range of 2.0~4.8V using current densities of 0.1C and 1C.

[0046] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

[0047] Table 1 Performance test results of cathode materials

[0048]

Claims

1. A single-crystalline lithium-rich cathode material, characterized in that, The chemical formula of the positive electrode material is: Li a Mn b Ni c Co d M e O2, wherein M is one or more of elements Zn, Mg, Al, Cu, a is 1-1.6, b is 0-0.6, c is 0-0.3, d is 0-0.2, b+c+d=N, e is 0.01N-0.05N, and a+b+c+d+e=2; the D50 of the single-crystal lithium-rich positive electrode material is 1.2-2.3 microns, and the compaction density is 3.3-3.7 g / cm 3 .

2. The method for preparing a single-crystal lithium-rich cathode material as described in claim 1, characterized in that, Specifically comprising the following steps: Step S1: preparing a precursor mixture by a solid phase method: a transition metal source, a nano metal powder and a lithium source are mechanically mixed to obtain a precursor mixture; Step S2: the precursor mixture obtained in step S1 is first pre-sintered at a temperature increasing rate of 2-5 ℃ / min to 400-500 ℃ for 2-5 h, then sintered at a temperature increasing rate of 5-10 ℃ / min to 850-920 ℃ for 10-15 h, and then cooled to room temperature with the furnace, to obtain the single-crystal lithium-rich positive electrode material coated with a spinel layer and doped with metal ions on the surface.

3. The method of claim 2, wherein the single-crystal lithium-rich cathode material is prepared by the following steps: The mechanical mixing in step S1 is mechanical ball milling with water or ethanol as a dispersion medium, and the target product is obtained after pressure filtration and drying. ​ 4. The method of claim 3, wherein the single-crystal lithium-rich cathode material is prepared by the following steps: The solid content of the mechanical ball milling slurry is 40wt%-60wt%, the rotation speed is 300-800 rpm, and the time is 4-10 h. ​ 5. The method for preparing a single-crystal lithium-rich cathode material as described in claim 2, characterized in that, The lithium source is one of lithium carbonate or lithium hydroxide, and the excess ratio of the lithium source is 3-8%.

6. The method for preparing a single-crystal lithium-rich cathode material as described in claim 2, characterized in that, The nano metal powder is one or more of Zn, Mg, Al and Cu, the particle size is 10-100 nm, and the addition amount is 1-5% of the total amount of substance of the transition metal.

7. The method for preparing a single-crystal lithium-rich cathode material as described in claim 2, characterized in that, The transition metal source is one or more of oxides, hydroxides, carbonates or other insoluble salts of two or more of Ni, Co or Mn.

8. A lithium-ion battery, characterized by Prepared by using a single-crystal lithium-rich positive electrode material as claimed in claim 1.

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