Primary particle surface layer manganese gradient rock salt phase composite structure high nickel positive electrode and method of manufacturing same

Abstract

This invention belongs to the field of chemical energy storage battery technology and provides a method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure, including the following steps: Step 1, preparing a nickel-cobalt-manganese hydroxide precursor by co-precipitation; Step 2, preparing (Ni... x Co y Mn 1‑x‑y (OH)2) z ·(MnO2) 1‑z Materials; Step 3: After vacuum drying the material obtained in Step 2, mix it uniformly with LiOH·H2O at a molar ratio of 1:1.00 to 1:1.03, and then perform an intermittent high-temperature calcination process under an oxygen atmosphere to obtain a high-nickel cathode material with a manganese gradient distribution and a rock salt phase composite structure on the primary particle surface. The technical solution of this invention improves structural stability and long cycle life simultaneously through the synergistic effect of gradient composition buffering phase transformation stress and rock salt phase physical / chemical shielding.

Description

Technical Field

[0001] This invention belongs to the field of chemical energy storage battery technology, specifically relating to a high-nickel cathode material with a manganese gradient distribution and rock salt phase composite structure on the surface of primary particles and its preparation method. Background Technology

[0002] High-nickel layered cathode material LiNi 1-x-y Co x Mn y O2 (NCM) is a promising material (0.8≤x<1, 0<y<0.2). Compared with traditional LiCoO2, LiNiO2 and LiMnO2, it has become a research hotspot due to its ultra-high specific capacity (≥200mAh / g) and high energy density (≥800Wh / kg), and has become a core candidate material for next-generation power batteries.

[0003] High-nickel layered cathode materials generate a large amount of metastable Ni during charging. 4+ This valence state readily undergoes a reduction reaction with the electrolyte to generate Ni. 2+ This leads to Ni 2+ Occupying Li sites exacerbates cation mixing. While increasing Ni content can improve specific capacity, it significantly deteriorates cycling performance and structural stability. Introducing Mn can effectively enhance the structural stability of the material, but it reduces specific capacity.

[0004] Therefore, a reasonable composition control strategy should be to moderately reduce the Ni content while increasing the proportion and distribution of Mn, thereby achieving synergistic optimization of capacity characteristics and cycle stability, and extending the service life of the material. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The technical problem to be solved by this invention is: how to achieve synergistic optimization of capacity characteristics and cycle stability of high-nickel layered cathode materials.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention provides a method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure, comprising the following steps:

[0009] Step 1: Dissolve soluble inorganic salts of nickel, cobalt, and manganese in water to prepare a mixed salt solution of nickel, cobalt, and manganese. Prepare a mixed alkaline solution using sodium hydroxide and ammonia. Add water to the reaction vessel as the base solution, and adjust the pH to 10.5–11.0 using ammonia. Simultaneously, introduce N2 as a protective gas. Stir at 600–800 r / min. Add the mixed salt solution and mixed alkaline solution dropwise to the reaction vessel at a uniform rate, controlling the feeding time to 8–24 h. Simultaneously, control the reaction temperature to be stable at 50–60 °C and the pH to be stable within the range of 10.5–11.0. After the feeding is completed, continue to introduce N2 and stir for another 5–6 h. Filter, wash, and dry the obtained product to obtain the nickel, cobalt, and manganese hydroxide precursor.

[0010] Step 2: Disperse the nickel-cobalt-manganese hydroxide precursor in an aqueous ammonia solution with a concentration of 10-20 wt%. Add sodium aminosulfonate as a surfactant to the aqueous solution, and simultaneously add 1-3% potassium permanganate dropwise. Stir for 1-2 hours to mix thoroughly to obtain a mixed solution. Heat and stir in a water bath at 80-100℃ until dry. Wash with water and centrifuge to remove the supernatant. Repeat 2-3 times, and dry to obtain (Ni) x Co y Mn 1-x-y (OH)2) z ·(MnO2) 1-z Materials, wherein 0.8≤x<1, 0<y<0.2, 0.8≤z<1; the amount of sodium aminosulfonate used is 1‰~5% of the amount of potassium permanganate.

[0011] Step 3: After vacuum drying the material obtained in Step 2, mix it with LiOH·H2O at a molar ratio of 1:1.00 to 1:1.03 until homogeneous. Then, use an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, heat the material at a rate of 3 to 5 °C / min to 450 to 500 °C and calcine for 4 to 6 hours; in the second stage, heat the material at a rate of 2 °C / min to 700 to 750 °C and calcine for 10 to 12 hours; in the third stage, heat the material at a rate of 2 °C / min to 800 to 850 °C and calcine for 10 to 20 minutes; in the fourth stage, cool the material at a rate of 2 to 3 °C / min to 700 to 750 °C and continue calcining for 3 to 5 hours, and then cool the material to room temperature at a rate of 3 °C / min. This yields a high-nickel cathode material with a manganese gradient distribution and a rock salt phase composite structure on the surface of the primary particles.

[0012] Furthermore, the total concentration of nickel, cobalt, and manganese ions in the mixed salt solution in step one is 2.0–4.0 mol / L.

[0013] Furthermore, in step one: the molar ratio of nickel, cobalt, and manganese in the mixed salt solution is x:y:(1-xy).

[0014] Furthermore, the concentration of sodium hydroxide in the mixed alkaline solution in step one is 0.2–0.6 mol / L.

[0015] Furthermore, the mixed alkaline solution is prepared by mixing sodium hydroxide and ammonia water in a molar ratio of 0.8 to 4:1.

[0016] Furthermore, in step three, the vacuum drying temperature is 80–120°C, and the time is 12–24 hours.

[0017] Furthermore, the water is water with a purity of deionized water or higher.

[0018] Preferably, step one specifically involves: weighing NiSO4·6H2O, CoSO4·7H2O, and MnSO4·4H2O in a molar ratio of Ni:Co:Mn = 8:1:1, preparing a mixed salt solution with a total Ni, Co, and Mn ion concentration of 4 mol / L using deionized water, and then preparing a mixed alkaline solution with a NaOH concentration of 0.2 mol / L using deionized water and ammonia water in a molar ratio of 4:1.

[0019] 100 mL of deionized water was added to the reactor as the reaction base solution, and ammonia was added to adjust the pH to 11.0. The stirring speed was set to 600 r / min, and the reaction temperature was set to 55℃. The mixed salt solution and mixed alkali solution were slowly and uniformly pumped into the reactor, maintaining the pH at 11.0, and the feeding time was 12 h. After the feeding was completed, argon gas was continuously introduced and stirred for 5 h. After the reaction was completed, the precipitate was filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2;

[0020] Step two is as follows: 2g of nickel-cobalt-manganese hydroxide precursor is placed in an ammonia solution with a concentration of 10 w.t.%, and 1.30mg of sodium aminosulfonate is added as a surfactant. Simultaneously, potassium permanganate solution is added dropwise. After stirring for 2 hours to mix thoroughly, a mixed solution is obtained. This solution is then heated and stirred in a water bath at 100℃ until dry. After washing with water and centrifugation, the supernatant is removed. This process is repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.99 ·(MnO2) 0.01 Material;

[0021] Step three is as follows: The material obtained in step two is placed in a vacuum drying oven and dried at 120℃ for 12 hours. Then, it is mixed uniformly with LiOH·H2O at a molar ratio of 1:1.03, and subjected to an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, the temperature is increased to 450℃ at a rate of 3℃ / min and calcined for 6 hours; in the second stage, the temperature is increased to 750℃ at a rate of 2℃ / min and calcined for 10 hours; in the third stage, the temperature is increased to above 850℃ at a rate of 2℃ / min and calcined for 15 minutes, then decreased to 750℃ at a rate of 3℃ / min and calcined for another 5 hours, and finally decreased to room temperature at a rate of 3℃ / min. This yields a high-nickel cathode material Li(Ni) with a primary particle surface exhibiting a manganese gradient distribution and a rock salt phase composite structure. 0.8 Co 0.1 Mn 0.1 ) 0.99 Mn 0.01 O2.

[0022] Preferably, step one specifically involves: weighing NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co:Mn = 8:1:1, preparing a mixed salt solution with a total Ni, Co, and Mn ion concentration of 4 mol / L using deionized water, and then preparing a mixed alkaline solution with a NaOH concentration of 0.2 mol / L using deionized water and ammonia water in a molar ratio of 4:1.

[0023] Step two is as follows: 100 mL of deionized water is added to the reactor as the reaction base solution, and ammonia is added to adjust the pH to 11.0; the stirring speed is set to 600 r / min, and the reaction temperature is set to 55℃; the mixed salt solution and mixed alkali solution are slowly and uniformly pumped into the reactor, maintaining the pH at 11.0, with a feeding time of 12 h. After the feeding is completed, argon gas is continuously introduced for stirring for 5 h; after the reaction is completed, the precipitate is filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2;

[0024] 2g of nickel-cobalt-manganese hydroxide precursor was placed in an ammonia solution with a concentration of 10 w.t.%, and 2.60mg of sodium aminosulfonate was added dropwise as a surfactant. Potassium permanganate solution was added dropwise, and the mixture was stirred for 2 hours until homogeneous. The resulting solution was then heated in a water bath at 100℃ with stirring until dry. After washing with water and centrifugation, the supernatant was removed. This process was repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.96 ·(MnO2) 0.04 Material;

[0025] Step 3: Place the material obtained in Step 2 in a vacuum drying oven and dry at 120℃ for 12 hours. Then, mix it evenly with LiOH·H2O at a molar ratio of 1:1.03, and then perform an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, heat to 450℃ at a rate of 3℃ / min and calcine for 6 hours; in the second stage, heat to 750℃ at a rate of 2℃ / min and calcine for 10 hours; in the third stage, heat to above 850℃ at a rate of 2℃ / min and calcine for 20 minutes, then cool to 750℃ at a rate of 3℃ / min and continue calcining for 5 hours, and finally cool to room temperature at a rate of 3℃ / min. This yields a high-nickel cathode material Li(Ni) with a manganese gradient distribution and rock salt phase composite structure on the primary particle surface. 0.8 Co 0.1 Mn 0.1 ) 0.96 Mn 0.04 O2.

[0026] This invention also relates to a high-nickel cathode material with a primary particle surface manganese gradient rock salt phase composite structure prepared by the above method. The material uses a nickel-cobalt-manganese high-nickel ternary cathode material as a matrix. The primary particles of the matrix exhibit a decreasing concentration of Mn element from the surface layer to the subsurface layer, and the surface layer of the primary particles is a thin layer of rock salt phase NiO with a thickness of 1-5 nm.

[0027] (III) Beneficial Effects

[0028] Compared with the prior art, the present invention has the following beneficial effects: The material of the present invention uses nickel-cobalt-manganese layered cathode material as the matrix, and the precursor is a secondary particle formed by the agglomeration of primary particles. The primary particles of the matrix have a core region with uniform bulk distribution and a surface region with Mn content decreasing from the outside to the inside. The outermost layer of the primary particle surface is a thin layer of rock salt phase NiO. This composite structure maintains the stability of the layered structure by means of the uniform distribution of Mn element; the Mn content decreases from the surface to the bulk phase, which alleviates the charging and discharging stress; the outermost layer is a thin layer of rock salt phase NiO, which inhibits electrolyte erosion and Ni 4+ The reduction and charge compensation effects enhance the structural order. This composite structure simultaneously improves structural stability and long cycle life through the synergistic effect of gradient composition buffering phase transformation stress and rock salt phase physical / chemical shielding. Attached Figure Description

[0029] Figure 1 This is a cross-sectional Mn elemental distribution diagram of the high-nickel cathode material in Example 1;

[0030] Figure 2 This is a transmission electron microscope (TEM) image of the high-nickel cathode material in Example 1;

[0031] Figure 3The image shows the X-ray diffraction (XRD) pattern of the high-nickel cathode material in Example 1.

[0032] Figure 4 The graph shows the electrochemical performance of the high-nickel cathode material in Example 1.

[0033] Figure 5 The image shows the X-ray diffraction (XRD) pattern of the high-nickel cathode material in Example 2.

[0034] Figure 6 The graph shows the electrochemical performance of the high-nickel cathode material in Example 2.

[0035] Figure 7 The X-ray diffraction (XRD) pattern of the high-nickel cathode material in Comparative Example 1 is shown.

[0036] Figure 8 The image shows a transmission electron microscope (TEM) image of the high-nickel cathode material in Comparative Example 1.

[0037] Figure 9 The graph shows the electrochemical performance of the high-nickel cathode material in Comparative Example 1.

[0038] Figure 10 The X-ray diffraction (XRD) pattern of the high-nickel cathode material in Comparative Example 2 is shown.

[0039] Figure 11 The image shows a transmission electron microscope (TEM) image of the high-nickel cathode material in Comparative Example 2.

[0040] Figure 12 The cross-sectional Mn elemental distribution diagram of the high-nickel cathode material in Comparative Example 2 is shown.

[0041] Figure 13 The graph shows the electrochemical performance of the high-nickel cathode material in Comparative Example 2. Detailed Implementation

[0042] 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.

[0043] In the following embodiments and comparative examples:

[0044] XRD testing: The X-ray diffractometer used was the Rigaku Ultima IV-185 manufactured by Rigaku Corporation of Japan.

[0045] EDS testing: The energy dispersive spectrometer used was an Oxford INCA model X-ray energy dispersive spectrometer manufactured by Oxford Instruments (Shanghai) Co., Ltd.

[0046] TEM testing: The JEOL JEM-2100 field emission transmission electron microscope manufactured by Nippon Electronics Co., Ltd. was used.

[0047] Battery Assembly: The positive electrode material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 to form a slurry. After uniform mixing, the slurry was coated onto aluminum foil, then vacuum dried and cut into sheets to obtain the positive electrode sheet. A lithium metal sheet was used as the negative electrode, Celgard 2500 was used as the separator, and the concentration of LiPF6 in the electrolyte was 1 mol / L. The electrolyte solvent consisted of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. The CR2025 coin cell was assembled in a glove box. The electrochemical performance of the assembled battery was tested using a LANDCT 2001A tester (Wuhan Landian Electronics Co., Ltd.). The test temperature was 25℃, the test voltage range was 2.75-4.3V, and the charge and discharge were carried out at 0.2C (1C = 190mAh / g).

[0048] Battery cycle performance test: LAND CT 2001A tester purchased from Wuhan Landian Electronics Co., Ltd.

[0049] Example 1

[0050] (1) Weigh out NiSO4·6H2O, CoSO4·7H2O and MnSO4·4H2O in a molar ratio of Ni:Co:Mn = 8:1:1. Prepare a mixed salt solution with a total Ni, Co and Mn ion concentration of 4 mol / L using deionized water. Then prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water.

[0051] (2) Add 100 mL of deionized water to the reactor as the reaction base solution, and add ammonia to adjust the pH to 11.0. Set the stirring speed to 600 r / min and the reaction temperature to 55℃. Slowly and uniformly pump the mixed salt solution and mixed alkali solution into the reactor, maintaining the pH at 11.0. The feeding time is 12 h, and after the feeding is completed, continue stirring with argon gas for 5 h. After the reaction is complete, filter, wash, and dry the precipitate to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0052] (3) 2g of nickel cobalt manganese hydroxide precursor was placed in an ammonia solution with a concentration of 10 w.t.%, and 1.30mg of sodium aminosulfonate was added as a surfactant. Simultaneously, potassium permanganate solution (34.3mg potassium permanganate dissolved in 50ml water) was added dropwise. After stirring for 2 hours to obtain a homogeneous mixture, the solution was heated and evaporated to dryness in a water bath at 100℃. The solution was then washed with water and centrifuged to remove the supernatant. This process was repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.99 ·(MnO2) 0.01 Material.

[0053] (4) The material obtained in step (3) was placed in a vacuum drying oven and dried at 120°C for 12 hours. After that, it was mixed with LiOH·H2O at a molar ratio of 1:1.03 and then subjected to an intermittent high-temperature calcination process under an oxygen atmosphere: in the first stage, the temperature was increased to 450°C at a rate of 3°C / min and calcined for 6 hours; in the second stage, the temperature was increased to 750°C at a rate of 2°C / min and calcined for 10 hours; in the third stage, the temperature was increased to above 850°C at a rate of 2°C / min and calcined for 15 minutes; then the temperature was decreased to 750°C at a rate of 3°C / min and calcined for 5 hours; and then the temperature was decreased to room temperature at a rate of 3°C / min. This yielded a high-nickel cathode material Li(Ni) with a manganese gradient distribution and rock salt phase composite structure on the surface of the primary particles. 0.8 Co 0.1 Mn 0.1 ) 0.99 Mn 0.01 O2.

[0054] EDS analysis of the material revealed that the surface layer is doped with Mn, and the concentration of Mn decreases from the outside to the inside, forming a concentration gradient. Figure 1 As shown. The TEM test results of the material are as follows. Figure 2 As shown, the results indicate the formation of a thin rock salt phase layer approximately 2 nm thick on the surface of the material, which is attributed to the charge compensation effect induced by Mn doping. XRD results are as follows... Figure 3 As shown, where I (003) / I (104) With a strength of 1.25 and high structural order, this material exhibits excellent cycle stability: at a 0.2C rate, it retains up to 99.0% capacity after 50 cycles within a voltage range of 2.75-4.3V. Figure 4 As shown.

[0055] Elemental surface scanning analysis by EDS ( Figure 1This confirmed that the material surface region exhibits a significant manganese concentration gradient distribution, with the atomic percentage gradually decreasing from 18% in the surface layer to 11% in the subsurface layer, successfully constructing a gradient buffer structure of "externally rich manganese and internally poor manganese." High-resolution radio electron microscopy (HR-TEM) characterization showed... Figure 2 The material's primary particle surface formed a continuous rock salt phase NiO structure layer with a thickness of approximately 2.0 nm. The formation of this special phase structure can be attributed to Mn. 4+ The charge compensation effect induced by doping promotes Ni 2+ The structure was reconstructed through ordered migration to lithium sites. XRD results show that ( Figure 3 The characteristic peak intensity of the material is higher than that of I. (003) / I (104) Reaching 1.25, the layered structure exhibits low cation mixing, confirming that the Mn gradient distribution-rock salt phase composite structure effectively enhances the crystal structure's order. Electrochemical performance tests show ( Figure 4 The material retains 99.0% of its capacity after 50 cycles at a voltage window of 2.75-4.3V and a rate of 0.2C. The performance improvement mechanism can be analyzed as follows: the physical barrier of the surface rock salt phase inhibits electrolyte erosion (first layer of protection); the manganese gradient distribution buffers the H2-H3 phase transformation stress (second layer of buffering); and the ordered structure reduces lattice distortion (third layer of stabilization). The synergistic effect of these three factors significantly improves the structural integrity and cycle durability of the material.

[0056] Example 2

[0057] (1) Weigh NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co:Mn = 8:1:1. Prepare a mixed salt solution with a total Ni, Co and Mn ion concentration of 4 mol / L using deionized water. Then prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water.

[0058] (2) Add 100 mL of deionized water to the reactor as the reaction base solution, and add ammonia to adjust the pH to 11.0. Set the stirring speed to 600 r / min and the reaction temperature to 55℃. Slowly and uniformly pump the mixed salt solution and mixed alkali solution into the reactor, maintaining the pH at 11.0. The feeding time is 12 h, and after the feeding is completed, continue stirring with argon gas for 5 h. After the reaction is complete, filter, wash, and dry the precipitate to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0059] (3) 2g of nickel cobalt manganese hydroxide precursor was placed in an ammonia solution with a concentration of 10 w.t.%, and 2.60mg of sodium aminosulfonate was added as a surfactant. Simultaneously, potassium permanganate solution (137.2mg potassium permanganate dissolved in 50ml water) was added dropwise. After stirring for 2 hours to obtain a homogeneous mixture, the solution was heated and stirred in a water bath at 100℃ until dry. The solution was washed with water and centrifuged to remove the supernatant. This process was repeated three times to obtain (Ni 0.8 Co 0.1 Mn 0.1 (OH)2) 0.96 ·(MnO2) 0.04 Material.

[0060] (4) The material obtained in step (3) was placed in a vacuum drying oven and dried at 120°C for 12 hours. After that, it was mixed with LiOH·H2O at a molar ratio of 1:1.03 and then subjected to an intermittent high-temperature calcination process under an oxygen atmosphere: in the first stage, the temperature was increased to 450°C at a rate of 3°C / min and calcined for 6 hours; in the second stage, the temperature was increased to 750°C at a rate of 2°C / min and calcined for 10 hours; in the third stage, the temperature was increased to above 850°C at a rate of 2°C / min and calcined for 20 minutes; then the temperature was decreased to 750°C at a rate of 3°C / min and calcined for 5 hours; and then the temperature was decreased to room temperature at a rate of 3°C / min. This yielded a high-nickel cathode material Li(Ni) with a manganese gradient distribution and rock salt phase composite structure on the surface of the primary particles. 0.8 Co 0.1 Mn 0.1 ) 0.96 Mn 0.04 O2.

[0061] XRD results show that ( Figure 5 The characteristic peak intensity of the material is higher than that of I. (003) / I (104) Reaching 1.23, the layered structure exhibits low cation mixing, confirming that the Mn gradient distribution-rock salt phase composite structure effectively enhances the crystal structure's order. Electrochemical performance tests show ( Figure 6 The material retains 97.9% capacity after 50 cycles at a voltage window of 2.75-4.3V and a rate of 0.2C. The performance improvement mechanism can be analyzed as follows: the physical barrier of the surface rock salt phase inhibits electrolyte erosion (first layer of protection); the manganese gradient distribution buffers the H2-H3 phase transformation stress (second layer of buffering); and the ordered structure reduces lattice distortion (third layer of stabilization). The synergistic effect of the three factors significantly improves the structural integrity and cycle durability of the material.

[0062] Comparative Example 1

[0063] Step (3) of Comparative Example 1 differs from that of Example 1, but the rest remains the same. Specifically:

[0064] (1) Weigh out NiSO4·6H2O, CoSO4·7H2O and MnSO4·7H2O in a molar ratio of Ni:Co:Mn = 8:1:1. Prepare a mixed salt solution with a total Ni and Co ion concentration of 4 mol / L using deionized water. Then prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water.

[0065] (2) Add 100 mL of deionized water to the reactor as the reaction base solution, and add ammonia to adjust the pH to 11.0. Set the stirring speed to 600 r / min and the reaction temperature to 55℃. Slowly and uniformly pump the mixed salt solution and mixed alkali solution into the reactor, keeping the pH stable at 11.0. The feeding time is 12 h, and after the feeding is completed, continue stirring with argon gas for 5 h. After the reaction is complete, filter, wash, and dry the precipitate to obtain a nickel-cobalt cathode material precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0066] (3) Place 2g of nickel cobalt manganese hydroxide precursor in 50mL of distilled water, disperse 0.027g of manganese dioxide in 10mL of distilled water, and simultaneously add 0.0010g of polyvinylpyrrolidone (PVP). After stirring and mixing evenly, slowly add the mixture dropwise to the suspension of nickel cobalt manganese hydroxide. Heat and stir in a water bath at 100℃ until dry to obtain (Ni 0.8 Co 0.1 Mn 0.1 (OH)2) 0.99 ·(MnO2) 0.01 Material.

[0067] (4) The material obtained in step (3) was placed in a vacuum drying oven and dried at 120°C for 12 hours. After that, it was mixed with LiOH·H2O at a molar ratio of 1:1.03 and then subjected to an intermittent high-temperature calcination process under an oxygen atmosphere: in the first stage, the temperature was increased to 450°C at a rate of 3°C / min and calcined for 6 hours; in the second stage, the temperature was increased to 750°C at a rate of 2°C / min and calcined for 10 hours; in the third stage, the temperature was increased to above 850°C at a rate of 2°C / min and calcined for 15 minutes; then the temperature was decreased to 750°C at a rate of 3°C / min and calcined for 5 hours; and then the temperature was decreased to room temperature at a rate of 3°C / min to obtain the high-nickel cathode material Li(Ni 0.8 Co 0.1 Mn 0.1 ) 0.99 Mn 0.01 O2.

[0068] The XRD test results of the material are as follows: Figure 7As shown, the XRD patterns of the materials prepared in the comparative example show I (003) / I (104) The value was 1.13, significantly lower than that of the materials in Examples 1 and 2, indicating significant cation mixing in the material. The TEM test results of the material ( Figure 8 This result was further confirmed by TEM, which showed that a cation-mixed layer with uneven thickness distribution formed on the surface of the material. This was mainly due to the uneven distribution of additionally introduced Mn on the particle surface, fundamentally because the process in Comparative Example 1 could not achieve a uniform distribution of Mn on the particle surface. In subsequent cycles, the unevenly distributed cation-mixed layer on the surface acts as a reaction nucleus for phase transition, gradually diffusing from the surface into the interior of the material. The high cation mixing degree exacerbates lattice oxygen precipitation, ultimately leading to particle crack propagation and rapid capacity decay. The electrochemical performance results of the material are as follows: Figure 9 As shown, at a 0.2C rate, after 50 cycles in the voltage range of 2.75-4.3V, the capacity retention rate is only 90.8%, which is significantly lower than that of Examples 1 and 2.

[0069] Comparative Example 2

[0070] Step (4) of Comparative Example 2 differs from that of Example 1, but the rest remains the same. Specifically:

[0071] (1) Weigh out NiSO4·6H2O, CoSO4·7H2O and MnSO4·7H2O in a molar ratio of Ni:Co:Mn = 8:1:1. Prepare a mixed salt solution with a total Ni and Co ion concentration of 4 mol / L using deionized water. Then prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water.

[0072] (2) Add 100 mL of deionized water to the reactor as the reaction base solution, and add ammonia to adjust the pH to 11.0. Set the stirring speed to 600 r / min and the reaction temperature to 55℃. Slowly and uniformly pump the mixed salt solution and mixed alkali solution into the reactor, keeping the pH stable at 11.0. The feeding time is 12 h, and after the feeding is completed, continue stirring with argon gas for 5 h. After the reaction is complete, filter, wash, and dry the precipitate to obtain a nickel-cobalt cathode material precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0073] (3) 2g of nickel cobalt manganese hydroxide precursor was placed in an ammonia solution with a concentration of 10 w.t.%, and 1.30mg of sodium aminosulfonate was added as a surfactant. Simultaneously, potassium permanganate solution (34.3mg potassium permanganate dissolved in 50ml water) was added dropwise. After stirring for 2 hours to obtain a homogeneous mixture, the solution was heated and evaporated to dryness in a water bath at 100℃. The solution was then washed with water and centrifuged to remove the supernatant. This process was repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.99 ·(MnO2) 0.01 Material.

[0074] (4) The material obtained in step (3) is placed in a vacuum drying oven and dried at 120°C for 12 hours. After that, it is mixed with LiOH·H2O at a molar ratio of 1:1.03 and then calcined in an oxygen atmosphere using a traditional two-stage calcination process: first, calcined at 550°C for 6 hours at a heating rate of 3°C / min under an O2 atmosphere, and then calcined at 750°C for 12 hours at a heating rate of 2°C / min, finally obtaining the high-nickel cathode material Li(Ni 0.8 Co 0.1 Mn 0.1 ) 0.99 Mn 0.01 O2.

[0075] The XRD test results of the material are as follows: Figure 11 As shown, the XRD pattern of the material prepared in Comparative Example 2 shows I (003) / I (104) The value was 1.15, significantly lower than that of the materials in Examples 1 and 2, but better than that of Comparative Example 1 (1.13), indicating significant cation mixing in the material. The TEM test results of the material ( Figure 12 This result was further confirmed by TEM, which showed that a cation-mixed layer with a thickness of approximately 5 nm was formed on the surface of the material. Figure 13 As shown, no gradient distribution of Mn content was formed from the surface to the subsurface. Therefore, Comparative Example 2 did not form a composite structure of Mn concentration gradient and rock salt phase on the particle surface as in Examples 1 and 2, mainly due to the different calcination processes. In subsequent cycles, the cation mixing layer acts as a reaction nucleus for phase transition, gradually diffusing from the surface to the interior of the material. High cation mixing exacerbates lattice oxygen precipitation, ultimately leading to particle crack propagation and rapid capacity decay. The electrochemical performance results of the material are as follows: Figure 13 As shown, at a 0.2C rate, after 50 cycles in the voltage range of 2.75-4.3V, the capacity retention rate is only 93.0%, which is significantly lower than that of Examples 1 and 2.

[0076] Summarize

[0077] The principle of this invention is as follows:

[0078] Nickel-cobalt-manganese hydroxide precursors were prepared by co-precipitation. The precursors were dissolved in an ammonia solution containing sodium aminosulfonate, and potassium permanganate was added dropwise to ensure sufficient time for penetration into the secondary particles of the nickel-cobalt-manganese hydroxide precursor. Under the complexing effect of the ammonia solution, the potassium permanganate dissolved the exposed Ni... 2+ Isooxidation, MnO4 - The reaction is then reduced to MnO2, which is deposited on the particle surface. Furthermore, sodium aminosulfonate is used as a surfactant to regulate the reaction rate, ensuring uniform deposition of MnO2 on the primary particle surface. The intermittent high-temperature calcination process involves a first-stage low-temperature calcination of the precursor and lithium salt to form a layered framework, followed by a second-stage medium-temperature calcination of Li... + Mn embedded in a layered structure, uniformly deposited on the surface of primary particles 4+ Ni driven by charge compensation 2+ Ordered migration to Li sites forms ordered rock salt phase nuclei on the surface of primary particles. Since the surface Mn content is higher than the interior, the third stage of short-duration high-temperature calcination (800–850℃ for 10–20 min) stimulates the diffusion of Mn from high concentration to low concentration on the surface of the primary particles, establishing a concentration gradient. This short-duration heat treatment prevents Li volatilization caused by prolonged high temperatures. Simultaneously, the fourth stage continues calcination at 700–750℃ to eliminate grain boundary distortion through high-temperature thermodynamic relaxation, promoting the formation of surface Ni... 2+ The occupancy of Li sites transitions from short-range order to long-range order, ultimately forming a long-range ordered rock salt phase structure. Finally, after cooling to room temperature, a composite structure of manganese gradient distribution and rock salt phase forms on the surface of the primary grains.

[0079] The inventive point of this invention is:

[0080] Step (2) Preparation of (Ni) x Co y Mn 1-x-y (OH)2) z ·(MnO2) 1-z The material processing method differs from traditional approaches that typically involve first synthesizing a nickel-cobalt-manganese hydroxide precursor and then introducing MnO2 through physical mixing or post-treatment (such as coating or doping). The core innovation of this method lies in its use of potassium permanganate (KMnO4) in an alkaline environment (ammonia water containing a small amount of sodium aminosulfonate) to directly oxidize a portion of divalent manganese (MnO2). 2+ ) is tetravalent manganese (Mn) 4+This method involves in-situ formation of manganese dioxide (MnO2) on the surface of primary particles, which then simultaneously composites with a nickel-cobalt-manganese hydroxide precursor during a liquid-phase reaction. This achieves close contact and uniform mixing of the two phases (hydroxide and oxide phases) at the nanometer or micrometer scale. This one-step method directly constructs the composite structure in the solution phase, avoiding subsequent secondary processing steps (such as grinding, mixing, and secondary coating). The process is simpler, and the composite effect is more uniform and the bonding is tighter.

[0081] Utilizing the dual effects of the ammonia water environment: (1) Complexation: Ammonia water provides an alkaline environment, and more importantly, NH3 can react with Ni 2+ Co 2+ ,Mn 2+ A stable ammonia complex ([M(NH3)n) is formed. 2+ This helps control the release rate of metal ions, affects the morphology and uniformity of composite particles, inhibits excessive precipitation or aggregation of metal hydroxides, and helps to form a more uniform composite. (2) The reaction medium and stabilizer provide the necessary reaction environment for the reduction of potassium permanganate and the in-situ generation of MnO2. The presence of ammonia complexes also helps to stabilize the reaction system.

[0082] Sodium aminosulfonate was chosen for the following reasons: (1) Preventing precursor aggregation: Through the dual effects of electrostatic and steric hindrance, it ensures uniform dispersion of nickel-cobalt-manganese hydroxide in ammonia water, providing a homogeneous environment for subsequent oxidation reactions; (2) Promoting the oxidation efficiency of potassium permanganate: As a surfactant, it can enhance the oxidation efficiency of MnO4. - (2) Ions adsorption and electron transfer on the particle surface to achieve uniform coating of MnO2; (3) Reduce impurity residue: easy to remove during water washing (anionic characteristics), avoiding metal ion doping affecting the electrochemical performance of the material.

[0083] Step (3) Intermittent high-temperature calcination differs from conventional step calcination, which typically has only two main temperature ranges: low temperature range (~450-500℃): the main purpose is to form a preliminary mixture of lithium oxide and transition metal oxides, and the holding time is usually long, generally not less than 4-6 hours; high temperature range (~700-850℃): the main purpose is to achieve solid-state reaction, and the holding time is also long, generally not less than 10-15 hours, and the cooling is usually relatively simple (such as direct programmed cooling or slow cooling).

[0084] The core innovation of this intermittent high-temperature calcination process lies in:

[0085] Introducing ultra-high temperature short-time pulse (third stage): Breaking through the conventional temperature limit and holding time paradigm of high-nickel material calcination, by utilizing extreme conditions of >800℃ for 10-20 min, the gradient distribution of manganese ions and the formation of thin rock salt phase (Fm-3m) were selectively and controllably induced in the outermost layer of primary particles.

[0086] Four-stage precision temperature program: Unlike the traditional two-stage calcination, it achieves synergistic optimization of the bulk structure (good layered crystallinity) and surface microstructure (Mn gradient + rock salt composite phase) of the material through four stages with clear functions and finely controlled parameters (temperature, time, heating and cooling rate) (decomposition pre-calcination → main crystallization → surface reconstruction → relaxation stabilization).

[0087] Unique cooling-holding strategy (fourth stage): After the high-temperature pulse, instead of direct cooling, the temperature is first reduced to a medium temperature and then held for a long time. This step is crucial for stabilizing the special surface structure and potential damage to the repair phase induced by the high-temperature pulse, and is the key to ensuring the overall performance of the final material.

[0088] The precursor preparation process ensures the uniform distribution of MnO2, while the gradient calcination process enables the gradient distribution of Mn and forms a rock salt phase structure on the surface of the material.

[0089] In summary, the material described above utilizes a gradient structure design to construct a manganese element distribution system of "uniform bulk distribution - gradient decrease on the surface" within a high-nickel layered cathode material matrix (hereinafter referred to as the nickel-cobalt-manganese high-nickel ternary cathode material). During the synthesis stage of the high-nickel material precursor (i.e., the nickel-cobalt-manganese hydroxide precursor), uniform bulk manganese doping is achieved in the nickel-cobalt-manganese hydroxide, followed by gradient manganese doping through surface modification processes. Finally, intermittent high-temperature sintering treatment forms a manganese-rich concentration gradient structure on the surface. Specifically, Mn... 4+ The introduction of Ni induces a charge compensation mechanism. 2+ By selectively occupying Li sites, a rock salt phase structure layer (1-5 nm) of controllable thickness is constructed on the particle surface. This innovative structure achieves a performance breakthrough through a triple synergistic effect: gradient manganese distribution effectively alleviates the stress concentration phenomenon during the phase transition from hexagonal phase 2 to hexagonal phase 3 (H2-H3); the ordered rock salt phase surface layer blocks electrolyte erosion and inhibits irreversible phase transformation diffusion; and the charge compensation effect constructs the rock salt phase surface layer to improve structural order, thereby simultaneously improving the structural stability and long cycle life of the material.

[0090] 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 high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure, characterized in that, Includes the following steps: Step 1: Dissolve soluble inorganic salts of nickel, cobalt, and manganese in water to prepare a mixed salt solution of nickel, cobalt, and manganese. Prepare a mixed alkaline solution using sodium hydroxide and ammonia. Add water to the reaction vessel as the base solution and adjust the pH to 10.5-11.0 by adding ammonia. Simultaneously, introduce N2 as a protective gas and stir at a speed of 600-800 r / min. Add the mixed salt solution and mixed alkaline solution dropwise to the reaction vessel at a uniform rate, controlling the feeding time to 8-24 h. Simultaneously, control the reaction temperature to be stable at 50-60℃ and the pH to be stable within the range of 10.5-11.

0. After the feeding is completed, continue to introduce N2 and stir for another 5-6 h. Filter, wash, and dry the obtained product to obtain the nickel, cobalt, and manganese hydroxide precursor. Step 2: Disperse the nickel-cobalt-manganese hydroxide precursor in an aqueous ammonia solution with a concentration of 10-20 wt%. Add sodium aminosulfonate as a surfactant to the aqueous solution, and simultaneously add 1-3% potassium permanganate dropwise. Stir for 1-2 hours to mix thoroughly to obtain a mixed solution. Heat and stir in a water bath at 80-100℃ until dry. Wash with water and centrifuge to remove the supernatant. Repeat 2-3 times, and dry to obtain (Ni) x Co y Mn 1-x-y (OH)2) z ·(MnO2) 1-z Materials, wherein 0.8 ≤ x < 1, 0 < y < 0.2, 0.8 ≤ z < 1; the amount of sodium aminosulfonate used is 1‰~5% of the amount of potassium permanganate. Step 3: After vacuum drying the material obtained in Step 2, mix it with LiOH·H2O at a molar ratio of 1:1.00~1:1.03 until homogeneous. Then, use an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, heat the material at a rate of 3~5℃ / min to 450~500℃ and calcine for 4~6h; in the second stage, heat the material at a rate of 2℃ / min to 700~750℃ and calcine for 10~12h; in the third stage, heat the material at a rate of 2℃ / min to 800~850℃ and calcine for 10~20min; in the fourth stage, cool the material at a rate of 2~3℃ / min to 700~750℃ and continue calcining for 3~5h, and then cool the material at a rate of 3℃ / min to room temperature. This yields a high-nickel cathode material with a manganese gradient distribution and a rock salt phase composite structure on the surface of the primary particles.

2. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 1, characterized in that, The total concentration of nickel, cobalt, and manganese ions in the mixed salt solution in step one is 2.0~4.0 mol / L.

3. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 2, characterized in that, In step one: the molar ratio of nickel, cobalt and manganese in the mixed salt solution is x:y:(1-xy).

4. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 1, characterized in that, In step one, the concentration of sodium hydroxide in the mixed alkaline solution is 0.2~0.6 mol / L.

5. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 4, characterized in that, The mixed alkaline solution is prepared by mixing sodium hydroxide and ammonia water in a molar ratio of 0.8 to 4:

1.

6. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 1, characterized in that, In step three, the vacuum drying temperature is 80~120℃ and the time is 12~24h.

7. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 1, characterized in that, Step one is as follows: Weigh out NiSO4·6H2O, CoSO4·7H2O and MnSO4·4H2O in a molar ratio of Ni:Co:Mn=8:1:1, and prepare a mixed salt solution with a total Ni, Co and Mn ion concentration of 4 mol / L using deionized water. Then, prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water. 100 mL of deionized water was added to the reactor as the reaction base solution, and ammonia was added to adjust the pH to 11.

0. The stirring speed was set to 600 r / min, and the reaction temperature was set to 55℃. The mixed salt solution and mixed alkali solution were slowly and uniformly pumped into the reactor, maintaining the pH at 11.0, and the feeding time was 12 h. After the feeding was completed, argon gas was continuously introduced and stirred for 5 h. After the reaction was completed, the precipitate was filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2; Step two is as follows: 2g of nickel-cobalt-manganese hydroxide precursor is placed in an ammonia solution with a concentration of 10 w.t.%, and 1.30mg of sodium aminosulfonate is added as a surfactant. Simultaneously, potassium permanganate solution is added dropwise. After stirring for 2 hours to mix thoroughly, a mixed solution is obtained. This solution is then heated and stirred in a water bath at 100℃ until dry. After washing with water and centrifugation, the supernatant is removed. This process is repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.99 ·(MnO2) 0.01 Material; Step three is as follows: The material obtained in step two is placed in a vacuum drying oven and dried at 120℃ for 12 hours. Then, it is mixed uniformly with LiOH·H2O at a molar ratio of 1:1.03, and subjected to an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, the temperature is increased to 450℃ at a rate of 3℃ / min and calcined for 6 hours; in the second stage, the temperature is increased to 750℃ at a rate of 2℃ / min and calcined for 10 hours; in the third stage, the temperature is increased to above 850℃ at a rate of 2℃ / min and calcined for 15 minutes, then decreased to 750℃ at a rate of 3℃ / min and calcined for another 5 hours, and finally decreased to room temperature at a rate of 3℃ / min. This yields a high-nickel cathode material Li(Ni) with a primary particle surface exhibiting a manganese gradient distribution and a rock salt phase composite structure. 0.8 Co 0.1 Mn 0.1 ) 0.99 Mn 0.01 O2.

8. The method for preparing a high-nickel cathode with a primary particle surface manganese gradient rock salt phase composite structure as described in claim 1, characterized in that, Step one is as follows: Weigh out NiSO4·6H2O and CoSO4·7H2O in a molar ratio of Ni:Co:Mn = 8:1:1, and prepare a mixed salt solution with a total Ni, Co, and Mn ion concentration of 4 mol / L using deionized water. Then, prepare a mixed alkaline solution with a NaOH concentration of 0.2 mol / L by mixing NaOH and ammonia in a molar ratio of 4:1 using deionized water. Step two is as follows: 100 mL of deionized water is added to the reactor as the reaction base solution, and ammonia is added to adjust the pH to 11.0; the stirring speed is set to 600 r / min, and the reaction temperature is set to 55℃; the mixed salt solution and mixed alkali solution are slowly and uniformly pumped into the reactor, maintaining the pH at 11.0, with a feeding time of 12 h. After the feeding is completed, argon gas is continuously introduced for stirring for 5 h; after the reaction is completed, the precipitate is filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor with the molecular formula Ni. 0.8 Co 0.1 Mn 0.1 (OH)2; 2g of nickel-cobalt-manganese hydroxide precursor was placed in an ammonia solution with a concentration of 10 w.t.%, and 2.60mg of sodium aminosulfonate was added dropwise as a surfactant. Potassium permanganate solution was added dropwise, and the mixture was stirred for 2 hours until homogeneous. The resulting solution was then heated in a water bath at 100℃ with stirring until dry. After washing with water and centrifugation, the supernatant was removed. This process was repeated three times to obtain (Ni... 0.8 Co 0.1 Mn 0.1 (OH)2) 0.96 ·(MnO2) 0.04 Material; Step 3: Place the material obtained in Step 2 in a vacuum drying oven and dry at 120℃ for 12 hours. Then, mix it evenly with LiOH·H2O at a molar ratio of 1:1.03, and then perform an intermittent high-temperature calcination process under an oxygen atmosphere: In the first stage, the temperature is increased to 450℃ at a rate of 3℃ / min and calcined for 6 hours; in the second stage, the temperature is increased to 750℃ at a rate of 2℃ / min and calcined for 10 hours; in the third stage, the temperature is increased to above 850℃ at a rate of 2℃ / min and calcined for 20 minutes, then the temperature is decreased to 750℃ at a rate of 3℃ / min and calcined for another 5 hours, and then the temperature is decreased to room temperature at a rate of 3℃ / min. This yields a high-nickel cathode material Li(Ni) with a manganese gradient distribution and rock salt phase composite structure on the primary particle surface. 0.8 Co 0.1 Mn 0.1 ) 0.96 Mn 0.04 O2.

9. A high-nickel cathode material with a primary particle surface manganese gradient rock salt phase composite structure prepared by the method described in any one of claims 1 to 6, characterized in that, The high-nickel cathode material uses nickel-cobalt-manganese high-nickel ternary cathode material as the matrix. The primary particles of the matrix exhibit a decreasing concentration of Mn element from the surface layer to the subsurface layer, and the surface layer of the primary particles is a thin layer of rock salt phase NiO with a thickness of 1~5nm.

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