Highly ordered single-crystal-like structure secondary particle ultrahigh nickel positive electrode and preparation method thereof

Abstract

The invention belongs to the technical field of chemical energy storage batteries, and provides a preparation method of a high-order single-crystal-like structure secondary particle ultra-high nickel positive electrode, which comprises the following steps: step 1, enabling a mixed alkali solution to pass through a microfiltration membrane in a microreactor, then carrying out contact reaction on the mixed alkali solution and a mixed salt solution, and collecting a material from a discharge port of the microreactor; step 2, transferring the material collected in the step 1 into an aging tank under the protection of nitrogen, stirring, then collecting solids, washing and drying to obtain an ultrahigh nickel positive electrode material precursor; and step 3, uniformly mixing the ultra-high nickel positive electrode material precursor with LiOH.H2O, and obtaining the finished product material of the secondary particle ultra-high nickel positive electrode with the single-crystal-like structure by adopting a step-by-step calcination method. According to the technical scheme, the technical problems that an ultrahigh nickel material is unstable in structure, rapid in circulation attenuation and the like are solved, meanwhile, high structural stability and high discharge performance are achieved, the microreactor amplification process is simple and easy to implement, cost consumption is greatly reduced, and the method can be suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical energy storage batteries, and particularly relates to a high-order single-crystal-structure secondary particle ultra-high-nickel positive electrode material and a preparation method thereof. BACKGROUND

[0002] The ultra-high-nickel positive electrode material is an ideal choice for high-energy-density lithium ion batteries due to its high specific capacity (≥220 mAh / g) and high working voltage (~3.8 V vs. Li+ / Li). The ultra-high-nickel positive electrode material can provide a higher discharge platform voltage and a greater reversible capacity due to its high nickel content (greater than 90%), and has a broad application prospect in the field of power batteries. However, with the increase of the nickel content, the structural stability of the material is significantly reduced, which becomes a major bottleneck restricting its commercial application.

[0003] The technical challenges brought by the ultra-high nickel content mainly manifest in three aspects: first, lattice stress and mechanical failure: Ni 3+ / Ni 4+ Oxidation-reduction reaction is accompanied by a dramatic change in lattice volume (H2-H3 phase transition), which is extremely easy to accumulate stress in the particle interior and induce micro-cracks; second, cationic disordering is intensified: Ni 2+ (0.069 nm) and Li + (0.076 nm) have similar ionic radii, and the kinetic driving is enhanced at high temperatures, leading to serious Ni 2 + / Li+ mixed occupation, which destroys the order of the layered structure; third, surface instability: high-activity Ni 4+ is easy to react with the electrolyte to form an unstable positive electrode electrolyte interface (CEI) film, which aggravates the interface side reaction and transition metal dissolution. These factors synergistically act on the material, significantly degrading the cycle life, rate performance and thermal safety performance of the material.

[0004] Further research reveals that the primary particle size of the ultra-high-nickel material significantly decreases with the increase of the nickel content, which is rooted in the high-nickel characteristics itself: the high-nickel environment intensifies the cationic disordering (Ni 2 + / Li+), significantly inhibiting the grain boundary migration and grain growth kinetics in the high-temperature sintering process; the decline of the thermal stability of the material and the enhancement of the lithium evaporation effect together cause the available sintering process window to be rapidly narrowed, which severely limits the grain growth.

[0005] However, the traditional preparation process not only fails to effectively overcome these inherent challenges, but also exacerbates the deterioration of the microstructure: the precursor synthesis (co-precipitation method) process, the low efficiency of conventional reaction kettle mixing, is prone to cause local concentration unevenness, leading to irregular particle morphology and wide particle size distribution (PSD) of the synthesized precursor. This structural unevenness of the precursor introduces congenital defects for subsequent sintering, which is not conducive to the formation of uniform and stable crystal structure. High-temperature calcination process, although the commonly used single-stage high-temperature treatment can promote crystallization, but in this process, it will cause serious lithium volatilization. Lithium loss not only destroys the stoichiometric ratio of the material, but more importantly, it exacerbates the tendency of Ni 3 + reduction to Ni 2+ . High concentration of Ni 2+ further worsens the degree of cationic disordering. The final result is to form a polycrystalline secondary particle material with low structural order, which has many internal grain boundaries and rich structural defects.

[0006] This process-induced fine-grained structure (small primary particles) and low structural order (high cationic disordering) form a vicious cycle: small grains significantly exacerbate the accumulation of internal stress during charging and discharging, and are more prone to cause micro-cracks. Rich grain boundaries and surface defects greatly increase the contact area and active sites with the electrolyte, exacerbating the interface side reactions of high-activity Ni 4+ and the formation of unstable CEI film. Both of them directly damage the electrochemical performance, structural stability and thermal safety of the material.

[0007] To inhibit the interface side reactions of high-nickel cathodes, researchers have proposed single-crystal cathode materials. However, single crystals have no internal grain boundaries, but their entire outer surface is exposed, and large single crystals are prone to crack as a whole under cyclic stress. In contrast, the outermost surface of the quasi-single-crystal secondary particles is exposed, and the contact surface between the internal primary particles is mostly buried, with a significantly lower effective specific surface area than single-crystal particles of the same size. The stress of quasi-single-crystal secondary particles may be dispersed at the grain boundaries or released by generating micro-cracks (without causing the whole particle to be crushed), which has a higher tolerance.

[0008] Therefore, breaking through the inherent defects of high-nickel materials and the limitations of traditional processes, and developing a new synthesis process that can prepare ultra-high-nickel cathode materials with high structural order (low cationic disordering) and stable microstructure (such as quasi-single-crystal secondary particles) is a key technical problem that needs to be solved to promote its commercial application. SUMMARY

[0009] (1) Technical problems to be solved

[0010] The technical problem to be solved by the present application is that the existing technology has technical problems such as unstable structure, serious cationic disordering and complex preparation process of ultra-high-nickel cathode materials.

[0011] (II) Technical Solution

[0012] To address the aforementioned technical problems, this invention provides a method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode, specifically comprising the following steps:

[0013] Step 1: Feed the mixed alkaline solution as the dispersed phase into one inlet of the microreactor, and feed the mixed salt solution as the continuous phase into the other inlet of the microreactor. Inside the microreactor, the mixed alkaline solution passes through a microfiltration membrane and reacts with the mixed salt solution. The material is then collected from the outlet of the microreactor.

[0014] Step 2: Transfer the material collected in Step 1 to an aging tank under nitrogen protection, stir at 40℃~50℃, then collect the solids and wash and dry them to obtain the ultra-high nickel cathode material precursor Ni. x M y (OH)2, where 0.9≤x≤1, 0≤y≤0.1, and M is cobalt, manganese, aluminum, molybdenum, titanium, niobium, or zirconium;

[0015] Step 3: After uniformly mixing the ultra-high nickel cathode material precursor obtained in Step 2 with LiOH·H2O at a molar ratio of 1:0.98 to 1:1.02, the mixture is then subjected to a stepwise calcination method under an O2 atmosphere to finally obtain the high-structural-order, near-single-crystal structure, secondary particle ultra-high nickel cathode material LiNi. x M y O2.

[0016] Furthermore, in step one, the mixed alkaline solution is prepared by mixing NaOH and ammonia in a molar ratio of 1.5:1 to 2:1, and the mixed salt solution is prepared by mixing soluble inorganic salts corresponding to nickel and M metal elements. The molar ratio of NaOH in the mixed alkaline solution to all metal ions in the mixed salt solution is 1.5:1 to 2:1; the feed flow rate ratio of the mixed alkaline solution to the mixed salt solution is 0.9:1 to 1:1.

[0017] Furthermore, in step one, the flow rate of the mixed alkaline solution is 18 mL / min to 20 mL / min, and the flow rate of the mixed salt solution is 20 mL / min.

[0018] Furthermore, the pore size of the microfiltration membrane in step one is 5μm to 10μm.

[0019] Furthermore, in step two, the stirring rate is 700–900 r / min, and the stirring time is 4–6 h.

[0020] Furthermore, the step-by-step calcination method in step three is specifically as follows:

[0021] First stage, low temperature stage: first raise the temperature to 400-500℃ at 5℃ / min and maintain it for 5-6 hours;

[0022] The second stage, the medium temperature range: increase the temperature to 650-700℃ at 3℃ / min and then maintain it for 6-8 hours;

[0023] The third stage, a short-term high-temperature phase: the temperature is increased to 800-850℃ at 3℃ / min and held for 5-10min, then increased to 900-950℃ at 3℃ / min and held for 5-10min.

[0024] The fourth stage, cooling and tempering stage: cool down to 650-700℃ at a rate of 2-3℃ / min and then hold for 3-5 hours;

[0025] Fifth stage, final rapid cooling: cool down to room temperature at a rate of 5℃ / min.

[0026] Furthermore, the mixed salt solution contains ethyl lactate as an antisolvent, which accounts for 5%-10% of the volume of the mixed salt solution.

[0027] Further, in step one, the total concentration of Ni and Co ions in the mixed salt solution is 0.1 mol / L, the molar ratio of Ni:Co is 0.9:0.1, and the mixed salt solution contains 5% vol of ethyl lactate as an antisolvent; the mixed alkaline solution is prepared by mixing 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution in a volume ratio of 0.882:1.

[0028] In step two, the mixed alkaline solution, as the dispersed phase, is fed into the microreactor through one inlet at a flow rate of 18.82 mL / min, while the mixed salt solution, as the continuous phase, is fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor is set to 50 °C. After passing through a 5 μm microfiltration membrane, the mixed alkaline solution is rapidly mixed and reacted with the mixed salt solution. The material flowing out of the microreactor is then transferred to an aging tank under nitrogen protection, where it is stirred at 700 r / min for 4 hours at 45 °C. The solids are collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2;

[0029] In step three, first Ni 0.9 Co 0.1(OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 6 h, then heated to 850℃ at a rate of 3℃ / min and held for 5 min, then heated to 950℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material.

[0030] Furthermore, in step one, the total concentration of Ni and Co ions in the mixed salt solution is 0.1 mol / L, the molar ratio of Ni:Co is 0.92:0.08, and the mixed salt solution contains 5% vol of ethyl lactate as an antisolvent; the mixed alkaline solution is prepared by mixing 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution in a volume ratio of 0.9:1.

[0031] In step two, the mixed alkaline solution, as the dispersed phase, is fed into the microreactor through one inlet at a flow rate of 20 mL / min, while the mixed salt solution, as the continuous phase, is fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor is set to 50 °C. After passing through a microfiltration membrane with a pore size of 5 μm, the mixed alkaline solution is rapidly mixed and reacted with the mixed salt solution. The material flowing out of the microreactor is then transferred to an aging tank under nitrogen protection, where it is stirred at 700 r / min for 4 h at 45 °C. The solids are collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2;

[0032] In step three, first Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 680℃ at a rate of 3℃ / min and held for 6 h, then heated to 820℃ at a rate of 3℃ / min and held for 5 min, then heated to 920℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.92 Co 0.08 O2 cathode material.

[0033] The present invention also includes a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode material prepared by the above method.

[0034] (III) Beneficial Effects

[0035] Compared with existing technologies, the present invention has the following beneficial effects: The highly ordered, near-single-crystal structure, secondary particle ultra-high nickel cathode prepared by the present invention has the following significant advantages: The micron-level reaction channels in the microreactor ensure rapid and uniform mixing of the reaction solution in a short time and precise control of the precursor synthesis process. Strict control over the mixing alkali ratio, mixed salt concentration, antisolvent content in the mixed salt, flow rate, and microfiltration membrane pore size of the microreactor prevents local supersaturation of the reactants, allowing the precursor to nucleate uniformly and grow into larger particles under low supersaturation, which is beneficial for uniform element distribution and particle size distribution in the ultra-high nickel cathode material precursor. Simultaneously, the aging process under nitrogen protection ensures the uniformity of precursor components and morphological regularity. Combined with a unique five-segment stepwise calcination curve design, it effectively suppresses lithium volatilization and Ni reduction, promoting grain growth (achieving a "single-crystal" structure). The prepared LiNi... x M y O2 (0.9≤x≤1) materials exhibit extremely low cation mixing (I (003) / I (104) The process exhibits a diffraction peak intensity ratio of 1.482 or 1.437, a relatively large primary particle size (approximately 2-3 μm), a highly consistent layered structure, and excellent electrochemical performance. This technology solves the technical challenges of unstable structure and rapid cycle decay in ultra-high nickel materials, while simultaneously achieving high structural stability and high discharge performance. Furthermore, the microreactor scale-up process is simple and easy to implement, significantly reducing costs and making it suitable for large-scale production. Attached Figure Description

[0036] Figure 1a , Figure 1b LiNi prepared based on Example 1 0.9 Co 0.1 Scanning electron microscope (SEM) image of O2.

[0037] Figure 2 LiNi prepared based on Example 1 0.9 Co 0.1 X-ray diffraction (XRD) pattern of O2.

[0038] Figure 3 LiNi prepared based on Example 1 0.9 Co 0.1 Figure 1 shows the cycle stability test results of the O2-assembled battery at 0.2C.

[0039] Figure 4a , Figure 4b LiNi prepared based on Example 2 0.92 Co 0.08 Scanning electron microscope (SEM) image of O2.

[0040] Figure 5LiNi prepared based on Example 2 0.92 Co 0.08 X-ray diffraction (XRD) pattern of O2.

[0041] Figure 6 LiNi prepared based on Example 2 0.92 Co 0.08 Figure 1 shows the cycle stability test results of the O2-assembled battery at 0.2C.

[0042] Figure 7a , Figure 7b LiNi prepared based on Comparative Example 1 0.9 Co 0.1 O2 scanning electron microscope (SEM) image.

[0043] Figure 8 LiNi prepared based on Comparative Example 1 0.9 Co 0.1 X-ray diffraction (XRD) pattern of O2.

[0044] Figure 9 LiNi prepared based on Comparative Example 1 0.9 Co 0.1 Figure 1 shows the cycle stability test results of the O2-assembled battery at 0.2C.

[0045] Figure 10a , Figure 10b LiNi prepared based on Comparative Example 2 0.9 Co 0.1 O2 scanning electron microscope (SEM) image.

[0046] Figure 11 LiNi prepared based on Comparative Example 2 0.9 Co 0.1 X-ray diffraction (XRD) pattern of O2.

[0047] Figure 12 LiNi prepared based on Comparative Example 2 0.9 Co 0.1 Figure 1 shows the cycle stability test results of the O2-assembled battery at 0.2C.

[0048] Figure 13a , Figure 13b LiNi prepared based on Comparative Example 3 0.9 Co 0.1 O2 scanning electron microscope (SEM) image.

[0049] Figure 14 LiNi prepared based on Comparative Example 3 0.9 Co 0.1 X-ray diffraction (XRD) pattern of O2.

[0050] Figure 15 LiNi prepared based on Comparative Example 3 0.9 Co 0.1 Figure 1 shows the cycle stability test results of the O2-assembled battery at 0.2C.

[0051] Figure 16 This is a process diagram of an ultra-high nickel cathode material with high structural order and its preparation method. Detailed Implementation

[0052] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0053] In the following embodiments:

[0054] Battery assembly: Ultra-high nickel cathode material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1. The homogeneous slurry was coated onto an aluminum film, vacuum dried, and then cut into sheets to serve as the cathode. In a vacuum glove box, lithium metal sheets were used as the anode, and Celgard 2300 was used as the separator. 1 mol / L... -1 LiPF6 / ethylene carbonate:dimethyl carbonate (volume ratio 1:1) was used as the electrolyte to assemble CR2025 coin cells; the assembled cells were tested on a LAND CT 2001A test system, and the charge and discharge voltage range was 2.75V to 4.3V.

[0055] Scanning electron microscope: Model FEIQuanta, Netherlands.

[0056] X-ray diffraction (XRD) test: The X-ray diffractometer used was the Rigaku Ultima IV-185 manufactured by Rigaku Corporation of Japan;

[0057] Battery cycle performance testing: LAND CT 2001A tester purchased from Wuhan Landian Electronics Co., Ltd.;

[0058] Example 1

[0059] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co = 0.9:0.1, and prepare a mixed salt solution with a total Ni and Co ion concentration of 0.1 mol / L using deionized water. The mixed salt solution contains 5% vol of ethyl lactate as an antisolvent.

[0060] Prepare 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution using deionized water, and mix the NaOH solution and ammonia solution at a volume ratio of 0.882:1 to obtain a mixed alkaline solution.

[0061] (2) A mixed alkaline solution and a mixed salt solution were pumped into the microreactor using a horizontal flow pump. The mixed alkaline solution, as the dispersed phase, was fed into the microreactor through one inlet at a flow rate of 18.82 mL / min, while the mixed salt solution, as the continuous phase, was fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor was set to 50 °C. The mixed alkaline solution was rapidly mixed with the mixed salt solution after passing through a microfiltration membrane with a pore size of 5 μm. The material flowing out of the microreactor was then transferred to an aging tank under nitrogen protection and stirred at 700 r / min for 4 h at 45 °C. The solids were collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2.

[0062] First Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 6 h, then heated to 850℃ at a rate of 3℃ / min and held for 5 min, then heated to 950℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material. The prepared cathode material was assembled into CR2025 coin cells for electrochemical performance testing.

[0063] The material characterization results show that the LiNi prepared in this invention... 0.9 Co 0.1 O2 ultra-high nickel cathode materials possess excellent structural and electrochemical properties. Figure 1a , Figure 1b The material exhibits a uniform particle size distribution and an irregular polyhedral morphology with primary particle sizes of approximately 2-3 μm. This characteristic primarily stems from two key process controls: First, the precisely controlled low-supersaturation environment within the antisolvent-containing microreactor promotes the growth of the Ni precursor. 0.9 Co 0.1 (OH)₂ achieves uniform nucleation and controllable growth; secondly, the optimized step-by-step calcination process further densifies the particles and promotes grain growth through a high-temperature melting-recrystallization mechanism (short-time treatment at 700-950℃). More importantly, Figure 2 XRD analysis of the material showed that I (003) / I (104)The diffraction peak intensity ratio reached 1.482, significantly higher than the 1.2 of conventional processes. This indicator fully demonstrates that the material possesses extremely low cation mixing degree and a highly ordered layered crystal structure. This structural advantage directly translates into excellent electrochemical performance. Figure 3 For LiNi 0.9 Co 0.1 The cycling performance of the O2 ultra-high nickel cathode material after 50 cycles at 0.2C is shown in the graph. The discharge capacity in the first cycle is 221.7 mAh / g, and it slightly increases with each cycle due to the gradual wetting of the material by the electrolyte. After 50 cycles, the discharge capacity still reaches 222 mAh / g, demonstrating excellent cycle stability. This is because the larger particle size reduces the specific surface area, which helps eliminate voids and grain boundaries within the cathode particles, reduces intergranular microcracks, and suppresses side reactions with the electrolyte. The well-defined layered crystal structure ensures efficient lithium-ion transport and excellent structural stability, providing crucial performance assurance for the application of ultra-high nickel materials in power batteries.

[0064] Example 2

[0065] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co = 0.92:0.08, and prepare a mixed salt solution with a total Ni and Co ion concentration of 0.1 mol / L using deionized water. The mixed salt solution contains 5% vol of ethyl lactate as an antisolvent.

[0066] Prepare 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution using deionized water, and mix the NaOH solution and ammonia solution at a volume ratio of 0.9:1 to obtain a mixed alkaline solution.

[0067] (2) A mixed alkaline solution and a mixed salt solution were pumped into the microreactor using a horizontal flow pump. The mixed alkaline solution, as the dispersed phase, was fed into the microreactor through one inlet at a flow rate of 20 mL / min, while the mixed salt solution, as the continuous phase, was fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor was set to 50 °C. The mixed alkaline solution was rapidly mixed with the mixed salt solution after passing through a microfiltration membrane with a pore size of 5 μm. The material flowing out of the microreactor was then transferred to an aging tank under nitrogen protection and stirred at 700 r / min for 4 h at 45 °C. The solids were collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2.

[0068] First Ni 0.9 Co 0.1(OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 680℃ at a rate of 3℃ / min and held for 6 h, then heated to 820℃ at a rate of 3℃ / min and held for 5 min, then heated to 920℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.92 Co 0.08 O2 cathode material. The prepared cathode material was assembled into CR2025 coin cells for electrochemical performance testing.

[0069] The material characterization results show that the LiNi prepared in this invention... 0.92 Co 0.08 O2 ultra-high nickel cathode materials possess excellent structural and electrochemical properties. Figure 4a , Figure 4b The material exhibits a uniform particle size distribution and an irregular polyhedral morphology with primary particle sizes of approximately 2 μm. This characteristic primarily stems from two key process controls: First, the precisely controlled low-supersaturation environment within the antisolvent-containing microreactor promotes the formation of the Ni precursor. 0.92 Co 0.08 (OH)₂ achieves uniform nucleation and controllable growth; secondly, the optimized step-by-step calcination process further densifies the particles and promotes grain growth through a high-temperature melting-recrystallization mechanism (short-time treatment at 680-920℃). More importantly, Figure 5 XRD analysis of the material showed that I (003) / I (104) The diffraction peak intensity ratio reached 1.437, significantly higher than the 1.2 of conventional processes. This indicator fully demonstrates that the material possesses extremely low cation mixing degree and a highly ordered layered crystal structure. This structural advantage directly translates into excellent electrochemical performance. Figure 6 For LiNi 0.92 Co 0.08 The cycling performance of the O2 ultra-high nickel cathode material after 50 cycles at 0.2C is shown in the graph. The discharge capacity in the first cycle is 225 mAh / g, and it increases slightly as the cycle progresses. This is due to the gradual wetting of the material by the electrolyte. After 50 cycles, the discharge capacity still reaches 224 mAh / g, demonstrating excellent cycle stability. This is because the larger particle size reduces the specific surface area, which helps to eliminate voids and grain boundaries inside the cathode particles, reduce intergranular microcracks, and suppress side reactions with the electrolyte. The good layered crystal structure ensures efficient lithium-ion transport and excellent structural stability, providing key performance guarantees for the application of ultra-high nickel materials in power batteries.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the calcination process is different.

[0072] The specific steps for Comparative Example 1 are as follows:

[0073] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co = 0.9:0.1, and prepare a mixed salt solution with a total Ni and Co ion concentration of 0.1 mol / L using deionized water. The mixed salt solution contains 5% vol of ethyl lactate as an antisolvent.

[0074] Prepare 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution using deionized water, and mix the NaOH solution and ammonia solution at a volume ratio of 0.882:1 to obtain a mixed alkaline solution.

[0075] (2) A mixed alkaline solution and a mixed salt solution were pumped into the microreactor using a horizontal flow pump. The mixed alkaline solution, as the dispersed phase, was fed into the microreactor through one inlet at a flow rate of 18.82 mL / min, while the mixed salt solution, as the continuous phase, was fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor was set to 50 °C. The mixed alkaline solution was rapidly mixed with the mixed salt solution after passing through a microfiltration membrane with a pore size of 5 μm. The material flowing out of the microreactor was then transferred to an aging tank under nitrogen protection and stirred at 700 r / min for 4 h at 45 °C. The solids were collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2.

[0076] Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed evenly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 12 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material. The prepared cathode material was assembled into CR2025 coin cells for electrochemical performance testing.

[0077] pass Figure 7a , Figure 7b It can be seen that the LiNi prepared in this comparative example using a conventional calcination process assisted by a microreactor containing an antisolvent 0.9 Co 0.1The O2 particles are spherical, and the primary particle size is significantly reduced compared to Examples 1 and 2. This is mainly because traditional two-stage calcination lacks the driving force for grain growth and the mixing and repair mechanism, failing to release the structural potential of the antisolvent precursor, thus limiting grain growth. Furthermore, through... Figure 8 The XRD diffraction pattern shows that material I (003) / I (104) The diffraction peak intensity ratio is 1.09, which indicates that the material exhibits significant cation mixing and a decrease in structural order. Figure 9 For LiNi 0.9 Co 0.1 The cycling performance of the O2 ultra-high nickel cathode material after 50 cycles at 0.2C is shown in the figure. The discharge capacity in the first cycle is 210.1 mAh / g, and the capacity decays to 191.7 mAh / g after 50 cycles, with a capacity retention of 91.2%. This is significantly lower than that of Examples 1 and 2. This is mainly due to the smaller primary particle size, which leads to an increased specific surface area, exacerbates the side reactions with the electrolyte, causes the cation mixing to gradually deteriorate, and induces phase transitions and cracks in the crystal structure during cycling, thereby accelerating the capacity decay. Even if the antisolvent-containing microreactor provides a high-quality precursor with uniform morphology and composition, if the calcination process is not designed properly (such as the traditional two-stage method), it is still impossible to obtain a near-single-crystal ultra-high nickel material with high structural order. This is because it lacks the "high-temperature driving force" to promote large grain growth and the "low-temperature ordering" to inhibit cation mixing, ultimately leading to a vicious cycle of "small grains + high mixing". However, the five-stage stepped calcination method proposed in this invention, through the synergistic design of "short-time high-temperature growth promotion" and "low-temperature tempering to control mixing", transforms the potential of the high-quality precursor into a highly stable near-single-crystal structure, solving this decisive bottleneck of the calcination process. This comparative result fully demonstrates the significant advantages of the antisolvent-containing microreactor combined with the stepped calcination process used in this invention in improving the performance of high-nickel cathode materials.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that the pore size of the microfiltration membrane in the microreactor is different.

[0080] The specific steps for Comparative Example 2 are as follows:

[0081] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co = 0.9:0.1, and prepare a mixed salt solution with a total Ni and Co ion concentration of 0.1 mol / L using deionized water;

[0082] Prepare 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution using deionized water, and mix the NaOH solution and ammonia solution at a volume ratio of 0.882:1 to obtain a mixed alkaline solution.

[0083] (2) A mixed alkaline solution and a mixed salt solution were pumped into the microreactor using a horizontal flow pump. The mixed alkaline solution, as the dispersed phase, was fed into the microreactor through one inlet at a flow rate of 18.82 mL / min, while the mixed salt solution, as the continuous phase, was fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor was set to 50 °C. The mixed alkaline solution was rapidly mixed with the mixed salt solution after passing through a 2 μm microfiltration membrane (using a small pore size and high shear rate to control the nucleation rate). The material flowing out of the microreactor was then transferred to an aging tank under nitrogen protection and stirred at 700 r / min for 4 h at 45 °C. The solids were collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2.

[0084] First Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 6 h, then heated to 850℃ at a rate of 3℃ / min and held for 5 min, then heated to 950℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material. The prepared cathode material was assembled into CR2025 coin cells for electrochemical performance testing.

[0085] pass Figure 10a , Figure 10b It can be seen that the LiNi prepared by the conventional microreactor process in this comparative example 0.9 Co 0.1 O2 particles are spherical with a relatively small primary particle size. This is mainly due to the reduced pore size to 2 μm, which increases shear force and inhibits aggregation. However, this physical constraint leads to particle breakage and limited growth, resulting in the smaller particle size. Furthermore, through... Figure 11 The XRD diffraction pattern shows that material I (003) / I (104) The diffraction peak intensity ratio is 1.18, indicating a high degree of material structural order. However, cation mixing still occurs. The five-stage calcination cooling and tempering stage can partially repair the cation mixing, allowing the initial state I... (003) / I (104) It is better than Comparative Example 1. Figure 12 For LiNi 0.9 Co 0.1The cycling performance of the O2 ultra-high nickel cathode material at 0.2C for 50 cycles is shown in the graph. The initial discharge capacity is 218.2 mAh / g, and the capacity decays to 204.5 mAh / g after 50 cycles, with a capacity retention of 93.7%. This is a significant decrease compared to Examples 1 and 2. This is mainly because the five-stage calcination only delays the decay but cannot stop it. It does not eliminate grain boundary defects in smaller grains, leading to an increase in specific surface area, which exacerbates side reactions with the electrolyte, causing a gradual deterioration of cation mixing. Defects in the crystal structure induce phase transitions and cracks during cycling, thereby accelerating capacity decay. This comparative result fully demonstrates the significant advantages of the antisolvent-containing microreactor combined with the five-stage stepped calcination process used in this invention in improving the performance of high-nickel cathode materials.

[0086] Comparative Example 3

[0087] LiNi was prepared using the traditional co-precipitation method. 0.9 Co 0.11 The specific steps for obtaining O2 are as follows:

[0088] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co = 90:10, and prepare a mixed salt solution with a total Ni and Co ion concentration of 2 mol / L using deionized water.

[0089] Prepare a mixed alkaline solution with a hydroxide concentration of 4 mol / L by mixing NaOH and ammonia water at a molar ratio of 1.5:1.

[0090] (2) Add 100 mL of deionized water as the reaction base solution to a reactor equipped with a stirrer, and adjust the pH of the deionized water to 11 with ammonia. Set the stirring speed in the reactor to 600 r / min and the reaction temperature to 55 °C. Then, use a peristaltic pump to pump the mixed salt solution and mixed alkali solution into the reactor at a speed of 4 rpm. After continuous feeding for 12 h, stop feeding, and then continue stirring with N2 for another 12 h. Filter, wash, and dry the precipitate produced by the reaction to obtain Ni. 0.9 Co 0.1 (OH)2.

[0091] Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed evenly in a ratio of 1:1.02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 12 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material. The prepared cathode material was assembled into CR2025 coin cells for electrochemical performance testing.

[0092] pass Figure 13a , Figure 13b It can be seen that the LiNi prepared by the conventional process in this comparative example 0.9 Co 0.1 O2 particles are spherical, with smaller primary particle sizes and a close packing. Furthermore, through... Figure 14 The XRD diffraction pattern shows that material I (003) / I (104) The diffraction peak intensity ratio is 1.06, which indicates that the material exhibits a certain degree of cation mixing and a decrease in structural order. Figure 15 For LiNi 0.9 Co 0.1 The cycling performance of the O2 ultra-high nickel cathode material at 0.2C for 50 cycles is shown in the graph. The initial discharge capacity is 221 mAh / g, and the capacity decays to 198.6 mAh / g after 50 cycles, with a capacity retention of 89.9%. This is a significant decrease compared to Examples 1 and 2. This is mainly because the smaller primary particle size leads to an increased specific surface area, and the crystal structure defects caused by cation mixing exacerbate phase transitions and crack formation during cycling, thereby accelerating capacity decay. This comparative result fully demonstrates the significant advantages of the microreactor combined with the stepped calcination process used in this invention in improving the performance of high-nickel cathode materials.

[0093] In summary, the highly ordered, near-single-crystal structure, secondary particle ultra-high nickel cathode material prepared by this invention has the following characteristics: LiNi x M y O2 (0.9≤x≤1), the primary particles that make up the secondary particles have a large particle size, and the material structure has a high degree of order. (003) / I (104) The intensity ratio of the diffraction peaks is 1.437-1.482.

[0094] The microreactor microfiltration membrane used in this invention has a pore size of 5μm to 10μm. At the same time, ethyl lactate is added to the mixed salt solution as an antisolvent, accounting for 5% to 10% of the volume of the mixed salt solution. This constitutes a dual mechanism of "microchannel mixing + antisolvent thermodynamic regulation", which ensures the uniformity of the precursor and the relatively large particle size of the primary particles.

[0095] In existing microreactor technologies, while microreactors improve mixing efficiency, the inherent rapid crystallization kinetics of high-nickel systems, coupled with the lack of supersaturation control, lead to explosive nucleation growth. This results in the rapid agglomeration of small primary particles into secondary particles. Using microfiltration membranes with 5μm–10μm diameters causes instantaneous accumulation of crystal nuclei at the membrane pores, ultimately clogging the microchannels. Typically, microfiltration membranes with pore sizes of 2μm–5μm are chosen to enhance micromixing, breaking down crystal nuclei through high shear force, resulting in particles with smaller sizes. This invention addresses this by adding an antisolvent (ethyl lactate) to the mixed salt solution to reduce the solubility of metal hydroxides, extending the nucleation window and suppressing explosive nucleation. Simultaneously, strict control of the microreactor's microfiltration membrane pore size allows for precise dispersion of the antisolvent through microchannels, synergistically maintaining global stability and low supersaturation, thus promoting grain growth. This provides low-defect "raw materials" for subsequent five-stage stepped calcination, resulting in lower grain boundary migration resistance during high-temperature sintering and facilitating the formation of large-size single-crystal-like particles.

[0096] The specific operation of the five-stage stepped calcination thermodynamic control method is as follows:

[0097] Low-temperature stage: First, increase the temperature to 400-500℃ at a rate of 5℃ / min and maintain it for 5-6 hours (to fully remove the precursor hydroxyl groups and residues, and avoid violent reactions at high temperatures).

[0098] Medium temperature range: Increase the temperature to 650-700℃ at a rate of 3℃ / min and hold for 6-8 hours (to promote initial crystallization and structural ordering; lithium volatilization is relatively controllable at this temperature).

[0099] The process involves short, stepped high-temperature phases: Increasing the temperature at 3℃ / min to 800-850℃ and holding for 5-10 minutes; then increasing the temperature at 3℃ / min to 900-950℃ and holding for 5-10 minutes (this promotes grain growth and densification. Although the high temperature increases the risk of lithium volatilization, the extremely short holding time (5-10 minutes) is crucial, aiming to minimize lithium loss while maximizing the driving force for grain growth. This is a key step in achieving large, "quasi-single-crystal" particles).

[0100] Cooling and tempering section: Cool to 650-700℃ at 2-3℃ / min and hold for 3-5 hours (this is the core of suppressing mixing). Holding at a relatively low temperature for an extended period (3-5 hours) allows Li+ and Ni to react. 2 +Providing sufficient time and kinetic conditions for ordered rearrangement significantly reduces cation mixing and repairs defects that may occur at high temperatures, while lithium volatilization is significantly reduced at this temperature.

[0101] Finally, rapidly cool down: cool to room temperature at 5℃ / min (to avoid phase transitions or defect regeneration that may occur during slow cooling).

[0102] The ultra-high nickel cathode materials prepared by the traditional two-stage calcination process and the five-stage stepped calcination thermodynamic control method have fundamental differences in material structure, performance and process objectives.

[0103] The five-stage step calcination method promotes the growth of large primary particles (forming a near-single-crystal structure) through an extremely short high-temperature sprint (800-950℃ / 5-10min), and has a dedicated low-temperature tempering stage (650-700℃ / 3-5h) to suppress cation mixing. At the same time, the high-temperature duration is strictly controlled to reduce lithium volatilization. In contrast, the traditional two-stage method, due to prolonged exposure to medium and high temperatures (750-850℃ / 12-24h), results in small grains (traditional polycrystalline), severe cation mixing, and a large loss of lithium, ultimately deteriorating the structural stability and electrochemical performance of the material.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode, characterized in that, Specifically, the steps include the following: Step 1: Feed the mixed alkaline solution as the dispersed phase into one inlet of the microreactor, and feed the mixed salt solution as the continuous phase into the other inlet of the microreactor. Inside the microreactor, the mixed alkaline solution passes through a microfiltration membrane and reacts with the mixed salt solution. The material is then collected from the outlet of the microreactor. Step 2: Transfer the material collected in Step 1 to an aging tank under nitrogen protection, stir at 40℃~50℃, then collect the solids and wash and dry them to obtain the ultra-high nickel cathode material precursor Ni. x M y (OH)2, where 0.9≤x≤1, 0≤y≤0.1, and M is cobalt, manganese, aluminum, molybdenum, titanium, niobium, or zirconium; Step 3: After uniformly mixing the ultra-high nickel cathode material precursor obtained in Step 2 with LiOH·H2O at a molar ratio of 1:0.98 to 1:1.02, the mixture is then subjected to a stepwise calcination method under an O2 atmosphere to finally obtain the high-structural-order, near-single-crystal structure, secondary particle ultra-high nickel cathode material LiNi. x M y O2.

2. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 1, characterized in that, In step one, the mixed alkaline solution is prepared by mixing NaOH and ammonia in a molar ratio of 1.5:1 to 2:1, and the mixed salt solution is prepared by mixing soluble inorganic salts corresponding to nickel and M metal elements. The molar ratio of NaOH in the mixed alkaline solution to all metal ions in the mixed salt solution is 1.5:1 to 2:1; the feed flow rate ratio of the mixed alkaline solution to the mixed salt solution is 0.9:1 to 1:

1.

3. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 2, characterized in that, In step one, the flow rate of the mixed alkaline solution is 18 mL / min to 20 mL / min, and the flow rate of the mixed salt solution is 20 mL / min.

4. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 3, characterized in that, In step one, the pore size of the microfiltration membrane is 5μm to 10μm.

5. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 4, characterized in that, In step two, the stirring rate is 700–900 r / min and the stirring time is 4–6 h.

6. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 5, characterized in that, The step-by-step calcination method in step three is as follows: First stage, low temperature stage: first raise the temperature to 400-500℃ at 5℃ / min and maintain it for 5-6 hours; The second stage, the medium temperature range: increase the temperature to 650-700℃ at 3℃ / min and then maintain it for 6-8 hours; The third stage, a short-term high-temperature phase: the temperature is increased to 800-850℃ at 3℃ / min and held for 5-10min, then increased to 900-950℃ at 3℃ / min and held for 5-10min. The fourth stage, cooling and tempering stage: cool down to 650-700℃ at a rate of 2-3℃ / min and then hold for 3-5 hours; Fifth stage, final rapid cooling: cool down to room temperature at a rate of 5℃ / min.

7. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 1, characterized in that, The mixed salt solution contains ethyl lactate as an antisolvent, which accounts for 5%-10% of the volume of the mixed salt solution.

8. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 1, characterized in that, The total concentration of Ni and Co ions in the mixed salt solution mentioned in step one is 0.1 mol / L, and the molar ratio of Ni:Co is 0.9:0.

1. The mixed salt solution contains 5% vol of ethyl lactate as an antisolvent. The mixed alkaline solution is prepared by mixing 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution in a volume ratio of 0.882:

1. In step two, the mixed alkaline solution, as the dispersed phase, is fed into the microreactor through one inlet at a flow rate of 18.82 mL / min, while the mixed salt solution, as the continuous phase, is fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor is set to 50 °C. After passing through a microfiltration membrane with a pore size of 5 μm, the mixed alkaline solution is rapidly mixed and reacted with the mixed salt solution. The material flowing out of the microreactor is then transferred to an aging tank under nitrogen protection, where it is stirred at 700 r / min for 4 hours at 45 °C. The solids are collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2; In step three, first Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.

02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 700℃ at a rate of 3℃ / min and held for 6 h, then heated to 850℃ at a rate of 3℃ / min and held for 5 min, then heated to 950℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.9 Co 0.1 O2 cathode material.

9. The method for preparing a highly ordered, single-crystal-like secondary particle ultra-high nickel cathode as described in claim 1, characterized in that, The total concentration of Ni and Co ions in the mixed salt solution mentioned in step one is 0.1 mol / L, and the molar ratio of Ni:Co is 0.92:0.

08. The mixed salt solution contains 5% vol of ethyl lactate as an antisolvent. The mixed alkaline solution is prepared by mixing 0.4 mol / L NaOH solution and 0.2 mol / L ammonia solution in a volume ratio of 0.9:

1. In step two, the mixed alkaline solution, as the dispersed phase, is fed into the microreactor through one inlet at a flow rate of 20 mL / min, while the mixed salt solution, as the continuous phase, is fed into the microreactor through the other inlet at a flow rate of 20 mL / min. The reaction temperature inside the microreactor is set to 50 °C. After passing through a microfiltration membrane with a pore size of 5 μm, the mixed alkaline solution is rapidly mixed and reacted with the mixed salt solution. The material flowing out of the microreactor is then transferred to an aging tank under nitrogen protection, where it is stirred at 700 r / min for 4 h at 45 °C. The solids are collected, washed, and dried to obtain Ni. 0.9 Co 0.1 (OH)2; In step three, first Ni 0.9 Co 0.1 (OH)₂ and LiOH·H₂O were mixed uniformly in a ratio of 1:1.

02. The mixture was first heated to 450℃ at a rate of 5℃ / min and held for 5 h, then heated to 680℃ at a rate of 3℃ / min and held for 6 h, then heated to 820℃ at a rate of 3℃ / min and held for 5 min, then heated to 920℃ at a rate of 3℃ / min and held for 5 min, then cooled to 680℃ at a rate of 2℃ / min and held for 5 h, and finally cooled to room temperature at a rate of 5℃ / min to prepare LiNi. 0.92 Co 0.08 O2 cathode material.

10. A highly ordered, single-crystal-like secondary particle ultra-high nickel cathode material prepared by the method described in any one of claims 1 to 7.

Images