Medium-nickel cobalt-free positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a medium-nickel cobalt-free positive electrode material and a preparation method thereof, and the method comprises the following steps: step 1, proportioning according to a designed stoichiometric ratio of Li (Ni < 0.6 > Mn < 0.4 >) < 1-x > Mo < x > O < 2 >; step 2, wet ball milling; step 3, drying the mixed raw materials to constant weight; step 4, screening for the first time; 5, a sintering product is obtained through three-step calcination treatment; step 6, grinding the sintered product; and step 7, screening for the second time to obtain a Li (Ni < 0.6 > Mn < 0.4 >) < 1-x > Mo < x > O < 2 > sample. The morphology of the original positive electrode material and the size of primary particles are regulated and controlled through Mo doping, and the electrochemical performance of the positive electrode material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically to a medium-nickel cobalt-free cathode material and a preparation method thereof. Background Art

[0002] Binary cobalt-free cathode materials have been developed to reduce the cost of ternary cathode materials containing cobalt. The successful research and development of binary cobalt-free cathode materials avoid the expensive and complex factor of cobalt. It not only realizes a significant reduction in cost in raw material procurement, but also effectively reduces various costs such as energy consumption, labor input, and equipment loss in the production process by simplifying the production process. Its influence is profound and extensive.

[0003] For example, CN114744196A discloses a cobalt-free cathode material doped and coated with C and a preparation method and a lithium-ion battery thereof. The cobalt-free cathode material includes a cobalt-free cathode material core and a carbon coating layer provided on the surface of the cobalt-free cathode material core. C elements are doped in the crystal lattice of the cobalt-free cathode material core. Stable C anchoring is achieved by doping C elements inside the crystal lattice, and at the same time, a good lithium-ion migration network and channels are formed by carbon coating. The above factors comprehensively improve the electrochemical performance of the material.

[0004] Although binary cobalt-free cathode materials have significant cost advantages, they are prone to rapid capacity decay during long-term cycling. This problem is mainly attributed to the structural stability defects of the materials: during repeated charge and discharge processes, the crystal lattice of cobalt-free materials is prone to distortion, resulting in blocked lithium-ion diffusion channels, and continuously reducing the reversible intercalation / deintercalation efficiency of lithium ions; at the same time, the large voltage polarization characteristics of the materials will exacerbate the electrode polarization phenomenon. These two factors jointly restrict. Summary of the Invention

[0005] Aiming at the problems of large voltage polarization and poor cycle stability of LiNi 0.6 Mn 0.4 O2 during the electrochemical cycling process, the present invention provides a medium-nickel cobalt-free cathode material and a preparation method thereof.

[0006] The present invention is realized through the following technical solutions: A preparation method of a medium-nickel cobalt-free cathode material, comprising the following steps: Step 1, proportion Li2CO3, Ni 0.6 Mn 0.4 (OH)2, MoO3 according to the stoichiometric ratio of Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2; Step 2, wet ball-mill the raw materials in Step 1 to obtain mixed raw materials; Step 3, drying the mixed raw materials to constant weight to obtain a dry mixture; Step 4, performing a first screening on the dry mixture to obtain materials with uniform particle size; Step 5, subjecting the materials obtained in Step 4 to three-step calcination treatment to obtain a sintered product; Step 6, grinding the sintered product to obtain Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder; Step 7, performing a second screening on the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder to obtain a Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 sample.

[0007] Preferably, in Step 2, during wet ball milling, zirconia is used as the grinding balls, absolute ethanol is used as the ball milling aid, and the ball milling time is 1 - 4 h.

[0008] Preferably, in Step 3, during drying, the temperature is 80 - 110 °C.

[0009] Preferably, in Step 4, the first screening is carried out using a 300-mesh standard sieve.

[0010] Preferably, in Step 5, the three-step calcination includes the first calcination, the second calcination, and the third calcination, where during the first calcination, the temperature is 300 - 600 °C, and the heat preservation time is 1 - 3 h during the second calcination, the temperature is 600 - 750 °C, and the heat preservation time is 2 - 5 h during the third calcination, the temperature is 950 - 1100 °C, and the heat preservation time is 8 - 12 h.

[0011] Preferably, in Step 5, during the three-stage calcination process, the heating rate is always maintained at 4 °C / min.

[0012] Preferably, in Step 7, the second screening is carried out using a 325-mesh standard sieve.

[0013] A cathode material obtained by the method for preparing a medium-nickel cobalt-free cathode material as described above.

[0014] A lithium battery comprising the cathode material obtained by the method for preparing a medium-nickel cobalt-free cathode material.

[0015] Preferably, after 100 cycles at a high rate of 1C, the capacity retention rate of the lithium battery is 86.83%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: A method for preparing a medium-nickel cobalt-free cathode material of the present invention realizes the regulation of the morphology and the size of primary particles of the original cathode material by Mo doping, and improves its electrochemical performance. Specifically, with LiNi 0.6 Mn 0.4 O2 as the matrix, Mo 6+ doping is adopted, and Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 samples are synthesized by the high-temperature solid-state method. After the lithiation reaction is completed, as the sintering temperature continuously increases, the primary particles of the LiNi 0.6 Mn 0.4 O2 cathode material will break through the grain boundary limitation and fuse into larger and irregularly shaped new primary particles. However, when Mo 6+ is introduced in the sintering stage, Mo will enter the grain boundary, inhibit the migration and fusion of the grain boundary, thereby inhibiting the continuous growth of primary particles and maintaining the spherical primary particle morphology. The shortened diffusion path of lithium ions and the reduced charge transfer resistance in such smaller spherical primary particles NMM promote the improvement of the kinetic performance of their insertion and extraction. In addition, the spherical primary particle morphology is beneficial to the uniform distribution of the electrolyte on the particle surface. This optimized spatial arrangement accelerates the ion exchange at the electrode-electrolyte interface, enabling a large number of lithium ions to participate in the surface redox reaction simultaneously, thereby improving the electrochemical performance of the said material.

[0017] Furthermore, based on the thermogravimetric analysis results, a three-stage sintering process is designed: first, the temperature is raised to 500°C and held for 2 h to fully decompose the organic matter and moisture, then the temperature is raised to 780°C and held for 3 h. In this holding stage, the lithiation reaction mainly occurs to form a layered phase, while the primary grains are still in the nanometer size and the overall is a polycrystalline morphology. Finally, the temperature is raised to 920°C for grain growth and held for 10 h.

[0018] A lithium ion battery of the present invention has excellent charge and discharge capacity and Coulomb efficiency. After 100 cycles at a high rate of 1C, the capacity retention rate of the lithium ion battery using the modified cathode material of the present invention is 77.61% without modification, while it is 86.83% after modification, and the modified battery exhibits a smaller voltage plan and more excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a method for preparing a medium-nickel cobalt-free cathode material of the present invention; Figure 2 is the thermogravimetric curve of the calcination process of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode material; Figure 3 are the XRD patterns of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode materials prepared in Examples 1-4; Figure 4 are the SEM images of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode materials prepared in Examples 1-4; Figure 5 is the mechanism analysis diagram of Mo doping to inhibit the growth of primary particles and control the spherical morphology of primary particles; Figure 6 are the rate performances of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode materials prepared in Examples 1-4; Figure 7 are the changes in the discharge medium voltage during the charge and discharge cycle of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode materials prepared in Examples 1-4; Figure 8 are the electrochemical cycling performance images of the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 cathode materials prepared in Examples 1-4. Detailed implementation manners

[0020] The following further describes the present invention in detail with specific examples, which are explanations of the present invention rather than limitations.

[0021] The present invention discloses a method for preparing a medium-nickel and cobalt-free cathode material. Referring to Figure 1 , the method includes the following steps: Step 1, mix Li2CO3 (99.99%), Ni 0.6 Mn 0.4 (OH)2 (99.99%), and MoO3 (99.99%) according to the designed Li(Ni 0.6 Mn0.4 ) 1-x Mo x Prepare the mixture according to the stoichiometric ratio of Mo to O2; Step 2: Wet ball mill the raw materials in Step 1 to obtain a mixed raw material. Specifically, put the weighed raw materials into a polytetrafluoroethylene ball mill tank, use zirconia as the grinding balls, and anhydrous ethanol as the ball milling aid, and place them in a ball mill for wet ball milling for 1 - 4 h.

[0022] Step 3: Dry the mixed raw material at 80 - 110 °C until constant weight to obtain a dry mixture; Step 4: Screen the dry mixture for the first time using a 300 - mesh standard sieve to obtain a material with uniform particle size; Step 5: Obtain a sintered product by subjecting the material obtained in Step 4 to three - step calcination. Specifically, the three - step calcination includes the first - step calcination, the second - step calcination, and the third - step calcination. Among them, During the first - step calcination, the temperature is 300 - 600 °C and the heat - preservation time is 1 - 3 h During the second - step calcination, the temperature is 600 - 750 °C and the heat - preservation time is 2 - 5 h During the third - step calcination, the temperature is 950 - 1100 °C and the heat - preservation time is 8 - 12 h; During the three - stage calcination process, the heating rate is always maintained at 4 °C / min.

[0023] Step 6: Grind the sintered product to obtain Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder; Step 7: Screen the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder for the second time using a 325 - mesh standard sieve to obtain Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 sample.

[0024] In the present invention, the sintering process of the LiNi 0.6 Mn 0.4 O2 cathode material is obtained from the thermogravimetric curve analysis (as Figure 2), in the thermogravimetric curve, below 209.3 °C, as the temperature gradually rises from room temperature, the initial stage of the thermogravimetric curve shows a stable trend, indicating that within this temperature range, the sample has basically not undergone obvious mass changes and the substance is in a relatively stable state. In the temperature range from 209.3 °C to 511.7 °C, as the temperature steadily rises, the thermogravimetric curve begins to show a significant downward trend, which clearly indicates that the sample has undergone a decomposition reaction within this temperature range, mainly the decomposition of moisture and organic matter, which also leads to a gradual decrease in mass, a decrease of approximately 18.04%. In the temperature range of 511 °C to 815.6 °C of the thermogravimetric curve, there is an obvious weight loss step, which corresponds to the lithiation reaction process, and its chemical equation is: 2Ni 0.6 Mn 0.4 (OH)2 + Li2CO3 + O2 → 2LiNi 0.6 Mn 0.4 O2 + CO2 + 2H2O. When the temperature reaches 815.6 °C, the thermogravimetric curve flattens out and the mass remains basically constant, which means that the synthesis reaction has been basically completed and the remaining substance has reached a relatively stable state.

[0025] The present invention also discloses a positive electrode material obtained according to the preparation method of the medium nickel cobalt-free positive electrode material.

[0026] The present invention also discloses a lithium battery, which includes the positive electrode material obtained by the preparation method of the medium nickel cobalt-free positive electrode material, and after cycling 100 times at a high rate of 1C, the capacity retention rate of the lithium battery is 86.83%.

[0027] Example 1 Step 1, ingredient preparation: Li2CO3 (99.99%), Ni 0.6 Mn 0.4 (OH)2 (99.99%), MoO3 (99.99%) are proportioned according to the stoichiometric ratio of Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2; Step 2, mixing: The weighed raw materials are put into a polytetrafluoroethylene ball milling tank, zirconia is used as the grinding ball, and anhydrous ethanol is used as the ball milling assistant, and it is placed in a ball mill for wet ball milling for 1 h to obtain a mixed raw material; Step 3, drying: The ball milled slurry is poured out and placed in an oven to be dried at 80 °C to 110 °C until constant weight to obtain a dried raw material mixture; Step 4, screening: The raw material mixture is first passed through a 300-mesh standard sieve to screen out coarse particles and impurities, so that the obtained material has a relatively uniform particle size distribution.

[0028] Step 5, Sintering: The raw material mixture is subjected to three-step calcination treatment: First, preheat at 500 °C, second, calcine at 780 °C after the preheating is completed, and third, calcine at 920 °C.

[0029] Step 6, Grinding: Take out the LiNi 0.6 Mn 0.4 O2 obtained by sintering and place it in an agate mortar for physical grinding; Step 7, Secondary Screening: Pass the ground LiNi 0.6 Mn 0.4 O2 powder through a standard sieve with 325 mesh to obtain a LiNi 0.6 Mn 0.4 O2 sample with a more uniform particle size distribution Example 2: Weigh Ni 0.6 Mn 0.4 )(OH)2, MoO3 (99.99%) according to the chemical formula Li(Ni 0.99 Mo 0.01 O2, and the others are the same as in Example 1. 0.6 Mn 0.4 (OH)2, MoO3 (99.99%), and the others are the same as in Example 1.

[0030] Example 3: Weigh Ni 0.6 Mn 0.4 )(OH)2, MoO3 (99.99%) according to the chemical formula Li(Ni 0.98 Mo 0.02 O2, and the others are the same as in Example 1. 0.6 Mn 0.4 (OH)2, MoO3 (99.99%), and the others are the same as in Example 1.

[0031] Example 4: Weigh Ni 0.6 Mn 0.4 )(OH)2, MoO3 (99.99%) according to the chemical formula Li(Ni 0.97 Mo 0.03 O2, and the others are the same as in Example 1. 0.6 Mn 0.4 (OH)2, MoO3 (99.99%), and the others are the same as in Example 1.

[0032] Table 1 XRD crystal structures of the cathode materials obtained in Examples 1 to 4

[0033] Table 2 Electrochemical cycling performance of the cathode materials obtained in Examples 1 to 4

[0034] Figure 3For the XRD patterns of implementation 1 to 4, XRD analysis proved that all cathodes exhibited a hexagonal R-3m space group α-NaFeO2 type layered crystal structure.

[0035] Figure 4 The SEM images of 1 to 4 reflect the grain refinement caused by the introduction of Mo. The data in Table 1 show that Mo doping broadens the lithium ion insertion and extraction channels and reduces the degree of lithium-nickel mixing.

[0036] Figure 5 This is a mechanism analysis diagram of how Mo doping inhibits the growth of primary particles and controls the primary particles to maintain a spherical morphology.

[0037] Figure 6 is the rate performance of Examples 1 to 4, Figure 5 The data in the above table collectively indicate that Mo-doped Examples 2 and 3 have better rate performance than that of Raw Material Example 1.

[0038] Figure 7 The figure shows the change of the discharge intermediate voltage of Examples 1 to 4 during the charge and discharge cycle, indicating that Example 2 has a lower voltage platform attenuation than Example 1.

[0039] Figure 8 Table 2 and Table 3 are the electrochemical cycle performance images of Examples 1 to 4, which together indicate that Examples 2, 3, and 4 have better electrochemical stability than the raw material Example 1.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A preparation method of a medium-nickel and cobalt-free cathode material, characterized in that, It includes the following steps: Step 1, mix Li2CO3, Ni 0.6 Mn 0.4 (OH)2, and MoO3 according to the stoichiometric ratio of Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2; Step 2: Wet ball-mill the raw materials in Step 1 to obtain mixed raw materials; Step 3: Dry the mixed raw materials to constant weight to obtain a dry mixture; Step 4: Conduct the first screening on the dry mixture to obtain materials with uniform particle size; Step 5: Subject the materials obtained in Step 4 to three-step calcination treatment to obtain a sintered product; Step 6, grind the sintered product for 0.5 - 3 h to obtain Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder; Step 7, perform a second screening on the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 powder to obtain the Li(Ni 0.6 Mn 0.4 ) 1-x Mo x O2 sample.

2. The preparation method of the medium nickel and cobalt-free cathode material according to claim 1, wherein In Step 2, during wet ball-milling, zirconia is used as the grinding balls, absolute ethanol is used as the ball-milling assistant, and the ball-milling time is 1 - 4 h.

3. The preparation method of the medium-nickel and cobalt-free cathode material according to claim 1, wherein, In Step 3, during drying, the temperature is 80 - 110 °C.

4. The preparation method of the medium-nickel and cobalt-free cathode material according to claim 1, wherein, In Step 4, the first screening is carried out using a 300-mesh standard sieve.

5. The method for preparing the medium-nickel and cobalt-free cathode material according to claim 1, wherein In Step 5, the three-step calcination includes the first-step calcination, the second-step calcination, and the third-step calcination. Among them, during the first-step calcination, the temperature is 300 - 600 °C, and the heat preservation time is 1 - 3 h during the second-step calcination, the temperature is 600 - 750 °C, and the heat preservation time is 2 - 5 h during the third-step calcination, the temperature is 950 - 1100 °C, and the heat preservation time is 8 - 12 h.

6. The method for preparing a medium nickel and cobalt-free cathode material according to claim 1, wherein In Step 5, during the three-stage calcination process, the heating rate is always maintained at 4 °C / min.

7. The method for preparing the medium-nickel and cobalt-free cathode material according to claim 1, wherein In Step 7, the second screening is carried out using a 325-mesh standard sieve.

8. A positive electrode material obtained by the method for preparing a medium-nickel and cobalt-free positive electrode material according to any one of claims 1 - 7.

9. A lithium battery, characterized in that, It contains a positive electrode material obtained by the method for preparing a medium-nickel and cobalt-free positive electrode material according to any one of claims 1 - 7.

10. The lithium battery according to claim 9, characterized in that, After cycling 100 laps at a high rate of 1C, the capacity retention rate of the lithium battery is 86.83%.

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