Preparation method of cobalt-free binary positive electrode material

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, in particular to a preparation method of a cobalt-free binary positive electrode material, which comprises the following steps: step 1, weighing Ni0. 6Mn0. 4 (OH) 2 and Li2CO3 according to a molar ratio; 2, carrying out wet ball milling on the weighed raw materials to obtain a mixed raw material; 3, drying the mixed raw material to obtain a primary raw material; step 4, sieving the dried raw material with a standard sieve to obtain a secondary raw material; and 5, carrying out three-stage gradient calcination on the secondary raw material to obtain NM64 positive electrode material powder. The invention provides an optimization process scheme combining gradient heating and dynamic lithium compensation, and aims to realize uniform distribution of nickel / manganese atoms in the material, reduce the Li / Ni mixed arrangement degree and finally obtain the high-performance cobalt-free binary positive electrode material with excellent structural stability.

Description

Technical Field

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

[0002] Lithium-ion batteries have become the core power source for electric vehicles and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. However, the current mainstream cathode materials have obvious limitations: although ternary materials (such as NCM, NCA) have a high specific capacity of about 270 mAh / g, their dependence on cobalt resources leads to high costs and prominent supply chain risks; although lithium iron phosphate (LiFePO4) has a cost advantage, its theoretical specific capacity of 170 mAh / g limits the room for improvement of its energy density.

[0003] In this context, the cobalt-free binary layered cathode material (LiNi x Mn 1-x O2) has become a promising alternative due to its high specific capacity (close to the level of ternary materials) and low-cost advantage. The electrochemical performance of this material mainly depends on three key factors: crystal structure stability, cationic order degree, and the ability to inhibit interfacial side reactions, and these characteristics are all closely related to the preparation process parameters.

[0004] Currently, the preparation of cobalt-free binary cathode materials mainly uses the high-temperature solid-state method, which has the advantages of simple process and easy industrialization, but still faces many technical challenges in practical applications: firstly, the mixing uniformity of the precursor directly affects the material performance, insufficient ball milling time will lead to uneven element distribution and cause local composition segregation; secondly, the control of the calcination temperature is particularly crucial, too low temperature will exacerbate Li / Ni mixing, while too high temperature will cause the migration of transition metal ions and the precipitation of lattice oxygen; finally, the lithium ratio (Li / M) needs to be precisely controlled, excessive lithium ratio will form inert phases such as Li2O, and insufficient lithium ratio will be difficult to compensate for high-temperature lithium volatilization, both of which will affect the material performance. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of the influence of the preparation process on the microstructure and performance of the cobalt-free binary cathode material LiNi 0.6 Mn 0.4 O2 (NM64), and propose a preparation method of a cobalt-free binary cathode material.

[0006] The technical solution adopted by the present invention to solve its technical problems: A preparation method of a cobalt-free binary cathode material, comprising the following steps: Step 1, Ni 0.6 Mn 0.4 (OH)2 and Li2CO3 are weighed according to the molar ratio. Step 2: Wet ball-mill the weighed raw materials to obtain mixed raw materials; Step 3: Dry the mixed raw materials to obtain primary raw materials; Step 4: Pass the dried raw materials through a standard sieve to obtain secondary raw materials; Step 5: Subject the secondary raw materials to three-stage gradient calcination to obtain NM64 cathode material powder.

[0007] Preferably, in Step 1, the lithium ratio (Li / M) is 1:1.000 to 1:1.035.

[0008] Preferably, in Step 2, during wet ball-milling, zirconia is used as the grinding ball, anhydrous ethanol is used as the ball-milling medium, and the time is 0.5 h to 3 h.

[0009] Preferably, in Step 3, during drying, the temperature is 80°C to 120°C, and the time is 10 to 12 h.

[0010] Preferably, in Step 4, a standard sieve with 300 to 325 mesh is used.

[0011] Preferably, in Step 5, the three-stage gradient calcination includes the first-stage calcination, the second-stage calcination, and the third-stage calcination, where in the first-stage calcination, the temperature is 300°C to 500°C, and the holding time is 2 - 4 h; in the second-stage calcination, the temperature is 700°C to 750°C, and the holding time is 4 - 6 h; in the third-stage calcination, the temperature is 800°C to 1000°C, and the holding time is 8 - 12 h; The heating rate during each stage of calcination is 3 to 5 °C / min.

[0012] A cathode material obtained by the preparation method of the cobalt-free binary cathode material according to the item.

[0013] A lithium battery, including the cathode material obtained by the preparation method of the cobalt-free binary cathode material.

[0014] Preferably, the capacity retention rate of the lithium battery is 65% to 70%, and the discharge specific capacity is 160 to 170 mAh / g.

[0015] Preferably, the NM64 cathode material with the best performance is prepared under the conditions of a ball-milling time of 1 h, a calcination temperature of 920°C, a lithium ratio of 1.085, and a holding time of 10 h. Its initial discharge specific capacity is 172.6 mAh / g, and the cycle capacity retention rate is 77.1%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of a cobalt-free binary cathode material of the present invention uses the high-temperature solid-phase method to synthesize the NM64 cathode material with the best microstructure and electrochemical performance by adjusting the ball milling mixing time, calcination temperature, and lithium ratio before calcination. An optimized process scheme of gradient heating combined with dynamic lithium compensation is proposed to achieve uniform distribution of nickel / manganese atoms in the material, reduce the degree of Li / Ni mixing, and finally obtain a high-performance cobalt-free binary cathode material with excellent structural stability, which can provide an alternative material for lithium-ion battery cathode materials and has broad application prospects.

[0017] Furthermore, the preparation process parameters are limited to adjust the internal structure of the cathode material. Among them, the ball milling time (0.5 h - 3 h), calcination temperature (800°C - 1000°C), and lithium ratio (Li / M = 1:1.0 - 1:1.035) enable the prepared NM64 to have better microstructure and electrochemical performance. When applied in lithium batteries, its initial discharge specific capacity at 0.1 C, 2.8 - 4.3 V is 172.6 mAh / g, and the cycle capacity retention rate at 1.0 C, 2.8 - 4.3 V at room temperature of 25°C is 77.1%. Brief Description of the Drawings

[0018] Figure 1 is the flow chart of the preparation method of a cobalt-free binary cathode material of the present invention; Figure 2 is the SEM image of the cathode material after different ball milling times and calcination by the method of the present invention; Figure 3 is the SEM image of the cathode material at different calcination temperatures by the method of the present invention; Figure 4 is the SEM image of the cathode material with different lithium ratios by the method of the present invention. Detailed Description of the Invention

[0019] The following further elaborates on the present invention through specific embodiments, which are explanations rather than limitations of the present invention.

[0020] The present invention discloses a preparation method of a cobalt-free binary cathode material. Referring to Figure 1 , it includes the following steps: Step 1, Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio, and the lithium ratio (Li / M) is 1:1.000 - 1:1.035; Step 2, 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 medium. It is placed in a planetary ball mill for wet ball milling for 0.5 h - 3 h to obtain a mixed raw material; Step 3, pour out the ball-milled mixture and place it in an oven to dry at 80 °C to 120 °C for 10 to 12 h to obtain the mixture; Step 4, pass the dried mixture through a standard sieve with 300 to 325 mesh and store it sealed; Step 5, because there is a relatively large amount of raw materials after sieving, weigh 15 to 20 g of the sieved material, and then place the mixed material in a high-temperature furnace for three-stage calcination (the heating rate for each step of calcination is 3 to 5 °C / min). First, heat it to 300 °C to 500 °C and hold for 2 to 4 h, then continue to heat to 700 °C to 750 °C and hold for 4 to 6 h, and then heat to 800 °C to 1000 °C and hold for 8 to 12 h to synthesize the NM64 cathode material powder.

[0021] In order to clarify the performance of the NM64 cathode material powder, the following steps are used to make the battery for grinding and sieving: Step 6, grind the calcined and synthesized NM64 cathode material in an agate mortar and then pass it through a standard sieve; Step 7, make a slurry: weigh the NM64 cathode material, carbon black, N-methylpyrrolidone and polyvinylidene fluoride in a certain mass ratio, and put them into a vacuum mixer and stir for 30 to 50 min; Step 8, coating: pour the slurry into a scraper, and after setting a certain speed for the push rod, it will be automatically coated, and then dried at a temperature of 80 °C to 120 °C on the machine; Step 9, assemble the button cell: finally, put the uniform-quality electrode sheet into a glove box to assemble the CR2032 button cell. First, put the electrode sheet into the positive electrode shell, then put in the separator and drop in the electrolyte, and then put in the lithium sheet, gasket, spring piece, and negative electrode shell in sequence. Finally, put the assembled button cell into a pneumatic sealing machine for encapsulation and detection.

[0022] Example 1: Step 1, batching: Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio of the chemical equation, and the lithium ratio (Li / M) is 1:1.085; Step 2, mixing: put the weighed raw materials into a polytetrafluoroethylene ball milling tank, use zirconia as the grinding balls, and anhydrous ethanol as the ball milling aid, and place it in a ball mill for wet ball milling for 1 h to obtain the mixed material; Step 3, drying: pour out the ball-milled mixture and place it in an oven to dry at 80 for 12 h to obtain the dried mixture; Step 4, sieving: pass the dried mixture through a standard sieve with 300 mesh and store it sealed; Step 5, Calcination: Weigh 18 g of the mixed material and place it in a high-temperature furnace for three-stage calcination. First, heat it to 500 °C and hold for 2 h, then continue to heat to 780 °C and hold for 5 h, and finally heat to 960 °C and hold for 10 h to synthesize the NM64 cathode material powder; Step 6, Grinding and Sieving: Grind the synthesized NM64 cathode material by calcination in an agate mortar and then pass it through a standard sieve of 325 mesh; Step 7: Weigh the NM64 cathode material, carbon black, N-methylpyrrolidone, and polyvinylidene fluoride in a mass ratio of 90:5:5, and put them into a vacuum mixer and stir for 30 min; Step 8, Coating: Pour the slurry into the scraper, set a certain speed for the push rod for automatic coating, then dry it at 80 °C on the machine, and finally transfer it to a vacuum drying oven and dry it at 120 °C for 8 h; Step 9: Finally, put the uniform-quality electrode sheet into a glove box to assemble the CR2032 button cell. First, put the electrode sheet into the positive electrode case, then put in a 20 mm separator and drop in the electrolyte, and then sequentially put in the lithium sheet, spacer, spring sheet, and negative electrode case. Finally, put the assembled button cell into a pneumatic sealing machine for encapsulation.

[0023] Example 2: Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio of the chemical equation, and the others are the same as in Example 1, and the ball milling time is 0.5 h.

[0024] Example 3: Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio of the chemical equation, and the others are the same as in Example 1, and the ball milling time is 2 h.

[0025] Example 4: Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio of the chemical equation, and the others are the same as in Example 1, and the ball milling time is 3 h.

[0026] Example 5: Ni 0.6 Mn 0.4 (OH)2 (99.99%), Li2CO3 (99.99%) are weighed according to the molar ratio of the chemical equation, and the others are the same as in Example 1, and the calcination temperature is 800 °C.

[0027] Example 6: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, and the calcination temperature is 840 °C.

[0028] Example 7: Ni0.6Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, and the calcination temperature is 880 °C.

[0029] Example 8: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, and the calcination temperature is 920 °C.

[0030] Example 9: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, and the calcination temperature is 1000 °C.

[0031] Example 10: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, and the lithium ratio (Li / M) is 1:1.000.

[0032] Example 11: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, the lithium ratio is 1:1.035, and the calcination temperature is 920 °C.

[0033] Example 12: Ni 0.6 Mn 0.4 (OH)2(99.99%), Li2CO3(99.99%) are weighed according to the molar ratio of the chemical equation. Other conditions are the same as in Example 1, the lithium ratio is 1:1.06, and the calcination temperature is 920 °C.

[0034] Example 13: Ni 0.6 Mn0.4 (OH)2 (99.99%) and Li2CO3 (99.99%) were weighed according to the molar ratio of the chemical equation. Other conditions were the same as in Example 1. The lithium ratio was 1:1.110, and the calcination temperature was 920 °C.

[0035] Example 14: Ni 0.6 Mn 0.4 (OH)2 (99.99%) and Li2CO3 (99.99%) were weighed according to the molar ratio of the chemical equation. Other conditions were the same as in Example 1. The lithium ratio was 1:1.135, and the calcination temperature was 920 °C.

[0036] The electrochemical data of the above Examples 1 to 14 are shown in Table 1 below, which summarizes the initial discharge specific capacity, cycle capacity retention rate, and discharge specific capacity data after 100 cycles of the examples.

[0037] Table 1 shows the electrochemical data of Examples 1 to 14 in the voltage range of 2.8 V to 4.2 V

[0038] From the data in the above table, it can be seen that the best-performing NM64 cathode material was prepared under the conditions of ball milling time of 1 h, calcination temperature of 920 °C, lithium ratio of 1.085, and holding time of 10 h. Its initial discharge specific capacity was 172.6 mAh / g, and the cycle capacity retention rate was 77.1%. This is because the reasonable ball milling time retained the full mixing of the precursor particles and the lithium salt, avoiding segregation. The reasonable control of the temperature and lithium ratio during calcination synergistically improved the electrochemical performance of the NM64 cathode material.

[0039] Figure 2 SEM images of the cathode materials after different ball milling times and calcination are shown. As the ball milling time increased, the morphology of the precursor was gradually broken. By observing the sintered cathode materials, it was found that the cathode materials ball milled for 2 h and 3 h had serious agglomeration, which would lead to a decrease in the utilization rate of the active material and have an adverse effect on the electrochemical performance. As shown in Table 1, the capacity retention rates of the cathode materials ball milled for 2 h and 3 h after calcination were only 47.9% and 5.7%, respectively. While the cathode materials ball milled for 0.5 h and 1 h had better dispersion after calcination, which was beneficial to reducing local stress concentration, inhibiting particle breakage and interfacial side reactions. When the ball milling time was 1 h, the mixing uniformity and electrical properties of the active material were the best.

[0040] Figure 3SEM images of the cathode materials within different calcination temperature ranges are shown. With the increase in temperature, the primary particles of the cathode materials show an obvious tendency to increase, and the secondary particles gradually change into the single-crystal-like morphology at 1000 °C. Reasonably regulating the morphology of the cathode materials is crucial for their electrical properties. The decrease in specific capacity of the NM64 cathode material with the increase in temperature can be attributed to the increase in the size of primary particles. When the calcination temperature is 800 °C, due to the unstable crystal structure of small particles, during the charge-discharge cycle process, after multiple insertions and extractions of Li, the secondary particles are prone to pulverization. Its capacity retention rate and discharge specific capacity at the 100th cycle are only 29.3% (46.7 mAh / g). When the calcination temperatures are 800 °C, 920 °C, and 960 °C, good cycle stability is demonstrated. After 100 charge-discharge cycles, the capacity retention rates are 75.7%, 77.1%, and 71.2% respectively, and the electrical properties are the best when the calcination temperature is 920 °C. The capacity retention rates of the samples at 960 °C and 1000 °C after 100 cycles are only 55.1% and 9.1% respectively. The electrochemical stability decreases sharply, which may be because the morphology and uniformity of the single-crystal-like particles sintered by three-stage firing are relatively poor.

[0041] Figure 4 SEM images of the cathode materials within different lithium ratio ranges are shown. When the lithium ratio increases, the size of the primary particles of NM64 also increases. This may be because a higher lithium ratio may change the chemical potential of the reaction system, thereby affecting the reaction rate and crystal growth kinetics. Within a certain range, increasing the lithium ratio may accelerate the reaction rate, enabling the crystal to have more time and conditions for growth, and thus leading to an increase in the size of primary particles. The lithium ratio has little effect on the electrochemical properties of the NM64 material. When the sintering temperature is 920 °C and the lithium ratio is 1.085, the cycle performance of the material is the best. The capacity retention rate and discharge specific capacity after 100 cycles are 77.1% (119.2 mAh / g).

[0042] The above are only the preferred embodiments of the present invention and are not used to limit the technical solutions of the present invention. Those skilled in the art should understand that without departing from the spirit and principle of the present invention, the technical solutions can be subject to several simple modifications and substitutions, and these modifications and substitutions also fall within the protection scope covered by the claims.

Claims

1. A preparation method of a cobalt-free binary cathode material, characterized in that, It includes the following steps: Step 1, Ni 0.6 Mn 0.4 (OH)2 and Li2CO3 are weighed according to the molar ratio; Step 2: Wet ball-mill the weighed raw materials to obtain mixed raw materials; Step 3: Dry the mixed raw materials to obtain primary raw materials; Step 4: Pass the dried raw materials through a standard sieve to obtain secondary raw materials; Step 5: Subject the secondary raw materials to three-stage gradient calcination to obtain NM64 cathode material powder.

2. The preparation method of the cobalt-free binary cathode material according to claim 1, characterized in that, In Step 1, the lithium ratio (Li / M) is 1:1.000 to 1:1.

035.

3. The preparation method of the cobalt-free binary cathode material according to claim 1, characterized in that In Step 2, during wet ball-milling, zirconia is used as the grinding ball, anhydrous ethanol is used as the ball-milling medium, and the time is 0.5 h to 3 h.

4. The preparation method of the cobalt-free binary cathode material according to claim 1, wherein In Step 3, during drying, the temperature is 80°C to 120°C and the time is 10 to 12 h.

5. The preparation method of the cobalt-free binary cathode material according to claim 1, wherein, In Step 4, a standard sieve with 300 to 325 mesh is used.

6. The preparation method of the cobalt-free binary cathode material according to claim 1, wherein, In Step 5, the three-stage gradient calcination includes the first-stage calcination, the second-stage calcination, and the third-stage calcination, where in the first-stage calcination, the temperature is 300°C to 500°C and the holding time is 2 to 4 h; in the second-stage calcination, the temperature is 700°C to 750°C and the holding time is 4 to 6 h; in the third-stage calcination, the temperature is 800°C to 1000°C and the holding time is 8 to 12 h; the heating rate during each stage of calcination is 3 to 5 °C / min.

7. A cathode material obtained by the method for preparing a cobalt-free binary cathode material according to any one of claims 1 to 6.

8. A lithium battery, characterized in that, It includes the cathode material obtained by the method for preparing a cobalt-free binary cathode material according to any one of claims 1 to 6.

9. The lithium battery according to claim 8, wherein, The capacity retention rate of this lithium battery is 65% to 70%, and the discharge specific capacity is 160 to 170 mAh / g.

10. The lithium battery according to claim 8, characterized in that, The NM64 cathode material with the best performance is prepared under the conditions of a ball-milling time of 1 h, a calcination temperature of 920°C, a lithium ratio of 1.085, and a holding time of 10 h. Its initial discharge specific capacity is 172.6 mAh / g, and the cyclic capacity retention rate is 77.1%.

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