Modified ternary positive electrode material and preparation method and application thereof

Abstract

The application provides a modified ternary positive electrode material and a preparation method and application thereof. The modified ternary positive electrode material comprises a ternary positive electrode material matrix and a coating layer. The coating layer comprises a first coating layer existing on the surface of the ternary positive electrode material matrix and a second coating layer existing on the surface of the first coating layer. The first coating layer comprises Al2O3. The second coating layer comprises Li3AlF6 and LiF. The modified ternary positive electrode material provided by the application has high specific capacity, excellent cycle stability and excellent rate performance by doping boron elements in the matrix phase and constructing a specific double-layer coating layer on the surface of the matrix.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a modified ternary cathode material, its preparation method, and its application. Background Technology

[0002] As new energy vehicles evolve towards 800V high-voltage platforms, high-nickel ternary cathode materials (NCM / NCA) have become the mainstream choice due to their energy density advantage. However, their development faces three major technical bottlenecks: 1) Poor structural stability: lattice distortion leads to a volume expansion rate of >10% during long-term cycling (capacity decay of >20% after 1C / 1000 cycles); 2) Interface contact failure: poor electrolyte wettability (contact angle >45°) causes an increase in ion transport impedance (>10mΩ·cm²); 3) Thermal safety risks: the oxygen evolution reaction initiation temperature is <300℃ (UL2849 standard requires this temperature to be >325℃), resulting in a high probability of thermal runaway.

[0003] To address the above issues, the industry currently employs bulk doping (such as Mg, Ti, etc.) or surface coating (such as Al2O3, ZrO2, phosphate, etc.) for modification. However, these two modification methods still have the following limitations: 1) Although bulk doping can stabilize the crystal lattice, it is difficult to suppress the side reactions caused by residual alkali on the surface; 2) Although surface coating can physically isolate the electrolyte, if the ionic conductivity of the coating layer is poor or it cannot effectively consume residual alkali, it will increase the impedance and degrade the rate performance.

[0004] Therefore, there is an urgent need for a synergistically modified ternary cathode material that can combine strengthening the bulk structure with eliminating interfacial residual alkali and optimizing cycle and rate performance. Summary of the Invention

[0005] This invention provides a modified ternary cathode material, its preparation method, and its application, in order to solve the problem that the modified ternary cathode material in the prior art cannot effectively eliminate residual alkali on the surface, resulting in poor cycle and rate performance.

[0006] In a first aspect, the present invention provides a modified ternary cathode material, comprising a ternary cathode material matrix and a coating layer, wherein the coating layer comprises a first coating layer present on the surface of the ternary cathode material matrix and a second coating layer present on the surface of the first coating layer; the chemical formula of the ternary cathode material matrix is ​​Li. m Ni x Co y Al z B aO2, wherein 1.01≤m≤1.05, 0.8≤x≤0.86, 0.1≤y≤0.15, 0.03≤z≤0.035, 0.005≤a≤0.02, x+y+z+a=1; the first coating layer includes Al2O3; the second coating layer includes Li3AlF6 and LiF.

[0007] In one alternative implementation, the thickness of the first coating layer is 3-10 nm.

[0008] In one alternative embodiment, the thickness of the second coating layer is 5-15 nm.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned modified ternary cathode material, comprising the following steps: Step S1: Mix the ternary cathode material precursor, lithium source, and boron source in the first stage, and sinter to obtain the ternary cathode material matrix. Step S2: Disperse the ternary cathode material matrix in a solvent, add an aluminum source solution and a precipitant for a second mixing and a first heat treatment to obtain a ternary cathode material coated with a first coating layer; Step S3: The ternary cathode material coated with the first coating layer and lithium fluoride are mixed in the third step and subjected to the second heat treatment to obtain the modified ternary cathode material.

[0010] In one optional embodiment, the ratio of the total number of moles of metal elements in the ternary cathode material precursor, the number of moles of boron in the boron source, and the number of moles of lithium in the lithium source is 0.98-0.995:0.005-0.02:1.01-1.05.

[0011] In one optional embodiment, the mass ratio of the ternary cathode material matrix to the volume ratio of the solvent is 1g:15-25mL.

[0012] In one optional embodiment, the ratio of the mass of the ternary cathode material matrix to the molar number of aluminum elements in the aluminum source is 1g:0.05-1mmol.

[0013] In one optional embodiment, the mass ratio of the aluminum source to the volume ratio of the solvent is 0.01-0.05 g: 10 mL.

[0014] In one alternative embodiment, the precipitant adjusts the pH of the reaction system to 8.5-9.5.

[0015] In one optional embodiment, the mass ratio of the ternary cathode material coated by the first coating layer to lithium fluoride is 1:0.005-0.02.

[0016] In one optional embodiment, the chemical formula of the ternary cathode material precursor is Ni.x Co y Al z (OH)₂, where 0.8≤x≤0.86, 0.1≤y≤0.15, and 0.03≤z≤0.035.

[0017] In one alternative embodiment, the lithium source comprises lithium hydroxide.

[0018] In one alternative embodiment, the boron source includes at least one of boric acid, boron trioxide, trimethyl borate, and triethyl borate.

[0019] In one alternative embodiment, the solvent includes at least one selected from ethanol, methanol, isopropanol, n-butanol, acetone, and acetonitrile.

[0020] In one optional embodiment, the aluminum source includes at least one of aluminum nitrate, aluminum nitrate hydrate, aluminum chloride, aluminum sulfate, aluminum acetylacetone, and aluminum isopropoxide.

[0021] In one alternative embodiment, the precipitant includes at least one of ammonia, sodium hydroxide, potassium hydroxide, ammonium bicarbonate, and urea.

[0022] In one alternative embodiment, the first mixing speed is 300-500 rpm and the time is 10-30 min.

[0023] In one optional embodiment, the sintering operation includes heating from room temperature to 450-550°C at a rate of 4-6°C / min under an oxygen atmosphere, holding at that temperature for 3-5 hours, and then continuing to heat to 750-850°C at a rate of 4-6°C / min, holding at that temperature for 10-15 hours.

[0024] In one alternative embodiment, the dispersion method includes ultrasound; optionally, the frequency of the ultrasound is 30-50 kHz and the duration is 20-40 min.

[0025] In one alternative embodiment, the second mixing speed is 400-600 rpm and the time is 1-3 hours.

[0026] In one optional embodiment, the first heat treatment is performed by raising the temperature from room temperature to 400-600°C at a heating rate of 2-4°C / min in an oxygen-containing atmosphere and holding the temperature for 2-4 hours.

[0027] In one alternative embodiment, the third mixing operation includes mixing for 10-30 minutes at a rotation speed of 2000-3000 rpm under an inert gas atmosphere.

[0028] In one alternative embodiment, the second heat treatment is performed by heating at 300-400°C for 1-3 hours in an inert gas and / or nitrogen atmosphere.

[0029] Thirdly, the present invention provides a positive electrode sheet, comprising: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer is the modified ternary positive electrode material described above or the modified ternary positive electrode material prepared by the above preparation method.

[0030] Fourthly, the present invention provides a secondary battery comprising the aforementioned positive electrode sheet.

[0031] Fifthly, the present invention provides an electrical device including the aforementioned secondary battery.

[0032] Compared with the prior art, the present invention has the following beneficial effects: 1. The modified ternary cathode material provided by this invention has the following advantages: Firstly, the boron ion radius is small, allowing the boron doped in the bulk matrix to enter the interlayer gap of the transition metal layer in the ternary cathode material precursor. Furthermore, the BO bond energy is much greater than the Ni-O bond energy, effectively suppressing anisotropic deformation and microcrack growth during cycling, stabilizing the bulk lattice, and simultaneously broadening the Li-O bond width. + On the one hand, diffusion channels are improved, enhancing ionic conductivity; on the other hand, by constructing a specific double-layer coating on the substrate surface, multi-dimensional performance synergistic optimization is achieved. The first coating layer on the substrate surface includes Al2O3, which effectively physically blocks direct contact between the electrolyte and the active material. The second coating layer, present on the surface of the first coating layer, includes Li3AlF6, a fast ion conductor with a cryolite structure, and LiF, which not only serve as lithium-ion channels but also form a dense protective network, significantly reducing residual alkali content and interfacial impedance, and improving interfacial ion transport efficiency. Therefore, the modified ternary cathode material provided by this invention possesses high specific capacity, excellent cycle stability, and outstanding rate performance.

[0033] 2. The preparation method of the modified ternary cathode material provided by the present invention firstly sintersects the ternary cathode material precursor with a boron source to obtain a boron-doped cathode material matrix; then, it forms an Al2O3 coating layer by liquid phase coating with an aluminum source and heat treatment; finally, it introduces LiF for secondary heat treatment to generate Li3AlF6 fast ion conductor in situ, chemically bonding the originally independent Al2O3 nanoparticles and LiF particles at the interface, and forming a second coating layer with the residual LiF. This results in a modified ternary cathode material with high capacity, long cycle life, and high rate capability. The process is simple, convenient, requires no special production equipment, has good compatibility with existing production processes, and is suitable for large-scale industrial applications. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a scanning electron microscope image of the modified ternary cathode material after cycling in Example 1 of this invention; Figure 2 This is a scanning electron microscope image of the modified ternary cathode material of Comparative Example 1 of the present invention after cycling; Figure 3 This is a scanning electron microscope image of the modified ternary cathode material of Comparative Example 2 of this invention after cycling. Detailed Implementation

[0036] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0037] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] Example 1 This embodiment provides a modified ternary cathode material, including a ternary cathode material matrix (chemical formula Li). 1.03 Ni 0.8 Co 0.15 Al 0.04 B 0.01 The ternary cathode material matrix comprises Al2O3 and a coating layer, wherein the coating layer comprises a first coating layer present on the surface of the ternary cathode material matrix and a second coating layer present on the surface of the first coating layer; the first coating layer comprises Al2O3; the second coating layer comprises Li3AlF6 and LiF; the thickness of the first coating layer is 5 nm; and the thickness of the second coating layer is 10 nm.

[0039] This embodiment also provides a method for preparing the above-mentioned modified ternary cathode material, including the following steps: (1) The ternary cathode material precursor (Ni) was selected according to the ratio of the total number of moles of metal elements in the ternary cathode material precursor, the number of moles of boron in the boron source, and the number of moles of lithium in the lithium source being 0.99:0.01:1.03. 0.8 Co 0.15 Al 0.04 (OH)2), boric acid and LiOH•H2O were mixed at 400 rpm for 20 min; then the mixture was placed in a box furnace and heated from room temperature to 500℃ at a rate of 5℃ / min under a pure oxygen atmosphere and held for 4 h, and then heated to 800℃ at a rate of 5℃ / min and held for 12 h. After natural cooling, it was taken out, crushed by a mechanical pulverizer, and passed through a 300-mesh sieve to obtain the ternary cathode material matrix; (2) 5g of ternary cathode material matrix was added to 100mL of anhydrous ethanol and ultrasonically dispersed at 40kHz for 30min. Then, 10mL of ethanol solution containing 0.026g of aluminum nitrate nonahydrate was added dropwise under stirring at 500rpm. Ammonia was then added dropwise to adjust the pH to 9.0. The mixture was stirred continuously for 2h, filtered, washed three times with anhydrous ethanol, and vacuum dried at 80℃. The resulting dry powder was placed in a box furnace and heated from room temperature to 500℃ at a heating rate of 3℃ / min under an oxygen atmosphere (flow rate of 100mL / min). The temperature was maintained for 3h to obtain Al2O3-coated ternary cathode material. (3) Take 4.95g of Al2O3-coated ternary cathode material and mix it with 0.05g of LiF powder. Place it in a high-speed mixer, introduce argon gas, and mix at 2500rpm for 20min. Then transfer the mixture to a tube furnace and heat treat it at 350℃ for 2h under argon atmosphere. After cooling, pass it through a 200-mesh sieve to obtain the modified ternary cathode material.

[0040] Example 2 This embodiment provides a modified ternary cathode material, including a ternary cathode material matrix (chemical formula Li). 1.0 2Ni 0.85 Co 0.10 Al 0.045 B 0.005 The ternary cathode material matrix comprises Al2O3 and a coating layer, wherein the coating layer comprises a first coating layer present on the surface of the ternary cathode material matrix and a second coating layer present on the surface of the first coating layer; the first coating layer comprises Al2O3; the second coating layer comprises Li3AlF6 and LiF; the thickness of the first coating layer is 4 nm; and the thickness of the second coating layer is 8 nm.

[0041] This embodiment also provides a method for preparing the above-mentioned modified ternary cathode material, including the following steps: (1) The ternary cathode material precursor (Ni) is taken according to the ratio of the total number of moles of metal elements in the ternary cathode material precursor, the number of moles of boron in the boron source, and the number of moles of lithium in the lithium source being 0.95:0.005:1.02. 0.85 Co 0.10 Al 0.045 (OH)2), boron trioxide and LiOH•H2O were mixed at 300 rpm for 30 min; then the mixture was placed in a box furnace and heated from room temperature to 550℃ at a rate of 4℃ / min under a pure oxygen atmosphere and held for 3 h, and then heated to 850℃ at a rate of 4℃ / min and held for 10 h. After natural cooling, it was taken out, crushed by a mechanical pulverizer, and passed through a 300-mesh sieve to obtain the ternary cathode material matrix; (2) 5g of ternary cathode material matrix was added to 75mL of anhydrous ethanol and ultrasonically dispersed at 50kHz for 20min. Then, 10mL of ethanol solution containing 0.019g of aluminum nitrate nonahydrate was added dropwise under stirring at 600rpm. Ammonia was then added dropwise to adjust the pH to 9.5. The mixture was stirred for 1h, filtered, washed three times with anhydrous ethanol, and vacuum dried at 80℃. The resulting dry powder was placed in a box furnace and heated from room temperature to 400℃ at a heating rate of 2℃ / min under an air atmosphere (flow rate of 50mL / min). The temperature was maintained for 4h to obtain Al2O3-coated ternary cathode material. (3) Take 4.97g of Al2O3-coated ternary cathode material and mix it with 0.03g of LiF powder. Place it in a high-speed mixer, introduce argon gas, and mix at 2000rpm for 30min. Then transfer the mixture to a tube furnace and heat treat it at 400℃ for 1h under argon atmosphere. After cooling, pass it through a 200-mesh sieve to obtain the modified ternary cathode material.

[0042] Example 3 This embodiment provides a modified ternary cathode material, including a ternary cathode material matrix (chemical formula L). 1.05 iNi 0.85 Co 0.10 Al 0.03 B 0.02 The ternary cathode material matrix comprises Al2O3 and a coating layer, wherein the coating layer comprises a first coating layer present on the surface of the ternary cathode material matrix and a second coating layer present on the surface of the first coating layer; the first coating layer comprises Al2O3; the second coating layer comprises Li3AlF6 and LiF; the thickness of the first coating layer is 6 nm; and the thickness of the second coating layer is 12 nm.

[0043] This embodiment also provides a method for preparing the above-mentioned modified ternary cathode material, including the following steps: (1) The ternary cathode material precursor (Ni) was selected according to the ratio of the total number of moles of metal elements in the ternary cathode material precursor, the number of moles of boron in the boron source, and the number of moles of lithium in the lithium source being 0.98:0.02:1.05. 0.85 Co 0.10 Al 0.03 (OH)2), boron trioxide and LiOH•H2O were mixed at 500 rpm for 10 min; then the mixture was placed in a box furnace and heated from room temperature to 450℃ at a rate of 6℃ / min under a pure oxygen atmosphere and held for 5 h, and then heated to 750℃ at a rate of 6℃ / min and held for 15 h. After natural cooling, it was taken out, crushed by a mechanical pulverizer, and passed through a 300-mesh sieve to obtain the ternary cathode material matrix; (2) 5g of ternary cathode material matrix was added to 125mL of anhydrous ethanol and ultrasonically dispersed at 30kHz for 40min. Then, 10mL of ethanol solution containing 0.035g of aluminum nitrate nonahydrate was added dropwise while stirring at 400rpm. Ammonia was then added dropwise to adjust the pH to 8.5. The mixture was stirred continuously for 3h, filtered, washed three times with anhydrous ethanol, and vacuum dried at 80℃. The resulting dry powder was placed in a box furnace and heated from room temperature to 600℃ at a heating rate of 4℃ / min under an oxygen atmosphere (flow rate of 200mL / min). The temperature was maintained for 2h to obtain Al2O3-coated ternary cathode material. (3) Take 4.91g of Al2O3-coated ternary cathode material and mix it with 0.09g of LiF powder. Place it in a high-speed mixer, introduce argon gas, and mix at 3000rpm for 10min. Then transfer the mixture to a tube furnace and heat treat it at 300℃ for 3h under argon atmosphere. After cooling, pass it through a 200-mesh sieve to obtain the modified ternary cathode material.

[0044] Comparative Example 1 This comparative example provides a ternary cathode material, the preparation method of which includes the following steps: (1) taking ternary cathode material precursor (Ni) according to the ratio of the total number of moles of metal elements in the ternary cathode material precursor to the number of moles of lithium elements in the lithium source of 1:1.03. 0.8 Co 0.15 Al 0.04 (OH)2) and LiOH•H2O were mixed at 400 rpm for 20 min; then the mixture was placed in a box furnace and heated from room temperature to 500℃ at a rate of 5℃ / min under a pure oxygen atmosphere and held for 4 h. Then the temperature was increased to 800℃ at a rate of 5℃ / min and held for 12 h. After natural cooling, the mixture was taken out, pulverized by a mechanical pulverizer, and passed through a 300-mesh sieve to obtain ternary cathode material.

[0045] Comparative Example 2 This comparative example provides a modified ternary cathode material, the preparation method of which is basically the same as that of Example 1, except that steps (2) and (3) are omitted, and the ternary cathode material matrix obtained in step (1) is directly used as the modified ternary cathode material.

[0046] Comparative Example 3 This comparative example provides a modified ternary cathode material, the preparation method of which is basically the same as that of Example 1, except that step (3) is omitted and the Al2O3-coated ternary cathode material obtained in step (2) is directly used as the modified ternary cathode material.

[0047] Comparative Example 4 This comparative example provides a modified ternary cathode material, the preparation method of which is basically the same as that of Example 1, except that step (2) is omitted and in step (3) the same mass of ternary cathode material matrix is ​​used instead of Al2O3 coated ternary cathode material.

[0048] Experimental Example 1 1. The positive electrode materials obtained in each embodiment and comparative example are assembled into coin cells. The preparation method of the coin cells is as follows: The positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-4, polyvinylidene fluoride, and conductive carbon black were homogenized in a mass ratio of 95:3:2 to obtain a slurry. Aluminum foil was then laid flat on a coating machine and coated with the prepared slurry (area density 13.5 mg / cm²). 2 Compacted density 2.8 mg / cm³ 2 The cells were dried in an 80°C forced-air drying oven for 3 hours. Then, the cells were punched, weighed, and the electrodes were baked to obtain the positive electrode. All battery assembly steps were carried out in a glove box filled with high-purity argon (H2O<0.1ppm, O2<0.1ppm). A 15mm diameter lithium metal sheet was used as the negative electrode. A Celgard 2400 polypropylene microporous membrane was used. The electrolyte was a solution of ethylene carbonate and diethyl carbonate (volume ratio 1:1) containing 1M LiPF6. The negative electrode shell, negative electrode sheet (lithium sheet), electrolyte were added, the membrane was laid, the positive electrode sheet was added, electrolyte was added, the positive electrode shell was covered, and the cell was sealed with a sealing machine to obtain a button cell. The assembled battery was tested after standing at 25°C for 12 hours.

[0049] 2. Perform performance tests on the button cells prepared above. (1) Charge and discharge test: The electrical performance was tested using the Blue Electric test system within the range of cutoff voltage of 2.5V-4.25V. The charge and discharge process was as follows: In the first round, the battery was charged to 4.25V with a constant current of 0.2C and then discharged to 2.5V with a constant current of 0.2C to obtain the 0.2C discharge capacity. The 0.2C initial discharge specific capacity was calculated based on the 0.2C discharge capacity / mass of positive electrode material. In the second round, the battery was charged to 4.25V with a constant current of 0.2C and then discharged to 2.5V with a constant current of 1C. In the third round, the battery was charged to 4.25V with a constant current of 0.2C and then discharged to 2.5V with a constant current of 1C. (2) Cyclic performance test: Within the cutoff voltage range of 2.5V-4.25V, the first 3 cycles of charging and discharging are the same as above. Starting from the 4th cycle, charge at 1C constant current to 4.25V, and then discharge at 1C constant current to 2.5V. Cycle up to 53 cycles. The capacity retention rate after 50 cycles = discharge capacity of the 53rd cycle / discharge capacity of the 4th cycle × 100%; (3) Rate performance test: Within the cutoff voltage range of 2.5V-4.25V, the first 3 cycles of charging and discharging are the same as above. Starting from the 4th cycle, charge at 5C constant current to 4.25V, and then discharge at 5C constant current to 2.5V. Cycle up to 53 cycles. The 5C rate capacity retention rate = discharge capacity of the 53rd cycle / discharge capacity of the 4th cycle × 100%; 3. Test Results Table 1 Performance Test Results

[0050] As shown in Table 1, the cathode materials of Examples 1-3 of this invention exhibit high discharge specific capacity and initial coulombic efficiency at 0.2C, and their cycle performance and rate performance are significantly superior to those of the comparative examples. Comparative Example 1, lacking both doping and coating, shows the worst performance; Comparative Example 2, with only boron doping, cannot effectively eliminate residual alkali, resulting in severe interfacial side reactions and poor electrochemical performance; Comparative Example 3, with only Al2O3 coating, has high interfacial impedance and cannot achieve a synergistic improvement in cycle performance and rate performance; Comparative Example 4, lacking an Al2O3 inner layer, cannot generate the Li3AlF6 fast ion phase, resulting in poor performance. These findings demonstrate that the present invention, through boron doping in the bulk matrix and the construction of a specific bilayer coating on the matrix surface, achieves a synergistic effect, enabling the modified ternary cathode material to possess high specific capacity, excellent cycle stability, and outstanding rate performance.

[0051] Experimental Example 2 The batteries from Example 1 and Comparative Examples 1-2, after undergoing 50 cycles at 1C, were disassembled in an argon glove box. The positive electrode was removed, rinsed with dimethyl carbonate to remove the electrolyte, and the active material layer was scraped off. The obtained active material was then embedded in epoxy resin, polished, and platinum-sprayed. The cross-sectional morphology was observed using a scanning electron microscope (SEM) at an accelerating voltage of 5 kV. The results are as follows: Figure 1-3As shown, Figure 1 The modified ternary cathode material of the present invention has a complete secondary particle structure after cycling, with only a few particles having extremely short non-penetrating cracks with a width of <0.1m on the surface, and no obvious radial cracks. Figure 2 Using the undoped and unmodified cathode material of Comparative Example 1, there are a large number of penetrating radial cracks with a width of 0.5-2m inside the secondary particles, and the particles are severely broken. Figure 3 Using the cathode material of Comparative Example 2, which is doped only with boron, cracks with a width of 0.2-1 μm exist inside the secondary particles. This indicates that boron doping can suppress some microcracks, but without a coating layer, crack propagation cannot be completely avoided.

[0052] Experimental Example 3 The coin cells assembled in Example 1 were cycled for 10 cycles at 25°C at a 1C rate within a cutoff voltage range of 2.5-4.25V. After being discharged to 3.8V and allowed to stand for 2 hours, they were tested using an electrochemical workstation at a frequency range of 10. 5 Hz ~ 10 -2 The frequency is Hz, and the amplitude is 5mV. ZView software is required to obtain the values ​​of Rs, Rsf, and Rct through equivalent circuit model fitting. The total impedance is calculated by summing these three values, as shown in the table below.

[0053] Table 2 Electrochemical impedance results

[0054] Table 2 shows that the test system in this experiment exhibits good consistency based on the ohmic resistance Rs. Compared with Comparative Examples 1-4, Examples 1-3 of this invention show significantly lower film resistance, charge transfer resistance, and total impedance. Specifically, the total impedance of Example 1 is significantly lower than that of Comparative Example 1. Comparative Example 2, with only boron doping, still shows high Rsf and Rct, indicating that bulk modification alone cannot solve the interfacial impedance problem. Comparative Example 3, with only Al2O3 coating, shows higher Rsf and Rct than Example 1, proving that single oxide coating increases interfacial resistance due to the thickening of the insulating layer. Comparative Example 4, without an Al2O3 coating layer, also shows high Rsf and Rct, indicating that LiF coating alone cannot reduce interfacial impedance when the Li3AlF6 fast ion phase cannot be generated. These results demonstrate that the bulk doping and double-layer coating of this invention have a synergistic effect, effectively constructing a low-impedance ion transport channel and significantly optimizing interfacial dynamics.

[0055] Experiment Example 4 Take 2.00g of the positive electrode material from each example and comparative example and add it to 100mL of deionized water. After stirring magnetically for 30min, filter the solution. Titrate the filtrate with 0.1mol / L HCl standard solution. Use phenolphthalein as an indicator to determine the LiOH content and methyl orange as an indicator to determine the total alkali content. Calculate the Li2CO3 content by subtracting the LiOH content from the total alkali content. Perform three parallel tests and take the average value.

[0056] Table 3 Results of residual alkali content

[0057] As shown in Table 3, compared with Comparative Examples 1-4, the residual alkali content on the surface of the cathode material samples in Examples 1-3 was significantly reduced. Comparative Example 1, lacking both doping and coating, had a high residual alkali content. Comparative Example 2 only had boron doping and no coating layer, resulting in severe interfacial side reactions and failing to reduce residual alkali. Comparative Example 3 had only Al2O3 as its coating layer; Al2O3 is an inert oxide and cannot react with residual alkali, only reducing alkali dissolution through physical barrier. Comparative Example 4, lacking an Al2O3 inner layer, could not generate the Li3AlF6 fast ionic phase; only LiF was used for coating, resulting in a small contact area with residual alkali and insufficient reaction. These results indicate that the modified ternary cathode material provided by this invention can effectively suppress the formation of lithium salt byproducts on the cathode material surface and reduce the residual alkali level.

[0058] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A modified ternary cathode material, characterized in that, The ternary cathode material includes a ternary cathode material substrate and a coating layer. The coating layer comprises a first coating layer on the surface of the ternary cathode material substrate and a second coating layer on the surface of the first coating layer. The chemical formula of the ternary cathode material substrate is Li. m Ni x Co y Al z B a O2, wherein 1.01≤m≤1.05, 0.8≤x≤0.86, 0.1≤y≤0.15, 0.03≤z≤0.035, 0.005≤a≤0.02, x+y+z+a=1; the first coating layer includes Al2O3; the second coating layer includes Li3AlF6 and LiF.

2. The modified ternary cathode material according to claim 1, characterized in that, The thickness of the first coating layer is 3-10 nm; And / or, the thickness of the second coating layer is 5-15 nm.

3. The method for preparing the modified ternary cathode material according to claim 1 or 2, characterized in that, Includes the following steps: Step S1: Mix the ternary cathode material precursor, lithium source, and boron source in the first stage, and sinter to obtain the ternary cathode material matrix. Step S2: Disperse the ternary cathode material matrix in a solvent, add an aluminum source solution and a precipitant for a second mixing and a first heat treatment to obtain a ternary cathode material coated with a first coating layer; Step S3: The ternary cathode material coated with the first coating layer and lithium fluoride are mixed in the third step and subjected to the second heat treatment to obtain the modified ternary cathode material.

4. The method for preparing the modified ternary cathode material according to claim 3, characterized in that, The ratio of the total number of moles of metal elements in the ternary cathode material precursor, the number of moles of boron in the boron source, and the number of moles of lithium in the lithium source is 0.98-0.995:0.005-0.02:1.01-1.05; And / or, the mass ratio of the ternary cathode material matrix to the volume ratio of the solvent is 1g:15-25mL; And / or, the ratio of the mass of the ternary cathode material matrix to the molar number of aluminum elements in the aluminum source is 1g:0.05-1mmol; And / or, the mass ratio of the aluminum source to the volume ratio of the solvent is 0.01-0.05 g: 10 mL; And / or, the precipitant adjusts the pH of the reaction system to 8.5-9.5; And / or, the mass ratio of the ternary cathode material coated by the first coating layer to lithium fluoride is 1:0.005-0.

02.

5. The method for preparing the modified ternary cathode material according to claim 3, characterized in that, The chemical formula of the ternary cathode material precursor is Ni. x Co y Al z (OH)₂, where 0.8≤x≤0.86, 0.1≤y≤0.15, 0.03≤z≤0.035; And / or, the lithium source includes lithium hydroxide; And / or, the boron source includes at least one of boric acid, boron trioxide, trimethyl borate, and triethyl borate; And / or, the solvent includes at least one of ethanol, methanol, isopropanol, n-butanol, acetone, and acetonitrile; And / or, the aluminum source includes at least one of aluminum nitrate, aluminum nitrate hydrate, aluminum chloride, aluminum sulfate, aluminum acetylacetone, and aluminum isopropoxide; And / or, the precipitant includes at least one of ammonia, sodium hydroxide, potassium hydroxide, ammonium bicarbonate, and urea.

6. The method for preparing the modified ternary cathode material according to claim 3, characterized in that, The first mixing speed is 300-500 rpm, and the time is 10-30 min; And / or, the sintering operation includes heating from room temperature to 450~550℃ at a rate of 4-6℃ / min under an oxygen atmosphere, holding at that temperature for 3~5h, and then continuing to heat to 750~850℃ at a rate of 4-6℃ / min, holding at that temperature for 10~15h.

7. The method for preparing the modified ternary cathode material according to claim 3, characterized in that, The dispersion method includes ultrasound; optionally, the frequency of the ultrasound is 30-50 kHz and the duration is 20-40 min. And / or, the second mixing speed is 400-600 rpm, and the time is 1-3 h; And / or, the first heat treatment is performed by raising the temperature from room temperature to 400-600°C at a heating rate of 2-4°C / min in an oxygen-containing atmosphere and holding it at that temperature for 2-4 hours. And / or, the third mixing operation includes mixing for 10-30 minutes at a speed of 2000-3000 rpm under an inert gas atmosphere; And / or, the second heat treatment is performed by heating at 300-400°C for 1-3 hours in an inert gas and / or nitrogen atmosphere.

8. A positive electrode sheet, characterized in that, include: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the modified ternary positive electrode material as described in claim 1 or 2 or the modified ternary positive electrode material prepared by the preparation method described in any one of claims 3-7.

9. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

Images