Preparation method of Zr-doped modified lithium-rich manganese-based positive electrode material

Abstract

A preparation method of a Zr-doped modified lithium-rich manganese-based positive electrode material comprises the following steps: weighing lithium acetate dihydrate, manganese acetate tetrahydrate, a zirconium acetate aqueous solution and citric acid monohydrate, dissolving in deionized water, and uniformly stirring to obtain a precursor solution; and carrying out spray pyrolysis on the precursor solution, sintering the obtained precursor in a muffle furnace in an air atmosphere at a high temperature, and cooling to room temperature after sintering to obtain the Zr-doped modified lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material prepared by the invention is low in cost and suitable for large-scale production and application; the material has high specific discharge capacity, high capacity retention rate and high rate performance; the Zr element is only added into the precursor solution in the precursor preparation process, so that the lattice structure of the lithium-rich manganese base can be stabilized; when the electric capacity and the capacity retention ratio are high, the discharge capacities can reach 152.7 mAh.g <-1 > and 130.8 mAh.g <-1 > respectively under the high magnification of 5C and 10C.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for lithium-ion secondary batteries, and particularly to a preparation method of a Zr-doped modified lithium-rich manganese-based cathode material. Background Art

[0002] Due to advantages such as high energy density, long cycle life, and no memory effect, lithium-ion batteries have become one of the most widely used electrochemical energy storage devices. Especially driven by the new energy electric vehicle industry, lithium-ion battery technology has been vigorously developed. However, with the continuous increase in the demand for driving range, higher requirements are also put forward for the energy density of lithium-ion batteries. As an important part of lithium-ion batteries, the cathode material directly determines the energy density of the battery. Unfortunately, the actual specific capacity of existing commercial cathode materials is almost an order of magnitude smaller than that of anode materials, making it difficult to meet the demand for greater driving range in new energy electric vehicles.

[0003] Lithium-rich manganese-based cathode materials are regarded as an ideal choice for the cathode materials of next-generation high-energy density lithium-ion batteries because of their extremely high theoretical specific capacity (greater than 350 mAh g -1 ) and reversible specific capacity (greater than 280 mAh g -1 ) and moderate average voltage (about 3.6 V). However, lithium-rich manganese-based cathode materials also face some challenges, such as low electronic conductivity and ionic conductivity, and lattice oxygen evolution, resulting in low initial Coulomb efficiency, poor cycle performance and rate performance of lithium-rich manganese-based cathode materials, which limits their commercial application.

[0004] Element doping can stabilize the layered structure of the bulk material and inhibit cation mixing, thereby improving the structural stability and electrochemical performance of lithium-rich manganese-based cathode materials. CN 119050340 A discloses "an anion and cation co-doped lithium-rich manganese-based cathode material, its preparation method and application", and the chemical general formula of the cathode material is LiA 1-w [Li 1-x-2y Ni x Co y Mn 2-2x-y / 3 O 2-z B z , where A is Na and B is F or S. The preparation method includes the following steps: (1) mixing the nickel-cobalt-manganese ternary precursor Ni x Co y Mn 2-2x-y / 3 (OH) a, where 0.05 < x ≤ 0.25, 0.05 ≤ y ≤ 0.25, 0.7 ≤ x + 2y ≤ 1, 1.5 ≤ a ≤ 3. It is placed in an aqueous solution of a compound containing elements A and B, stirred to fully dissolve the sample, and transferred to a polytetrafluoroethylene reaction kettle for hydrothermal reaction; after the reaction, the sample is cooled and left to stand, then centrifuged, washed, and dried; (2) The treated precursor and lithium carbonate are placed in a mortar and ground, pre-calcined after being fully mixed, then the temperature is raised for calcination, and after cooling with the furnace, it is fully ground to obtain a lithium-rich manganese-based cathode material co-doped with cations and anions. Additionally, "A cobalt-free magnesium-doped lithium-rich manganese-based cathode material and its preparation method" is disclosed in the patent application number "CN 118867225 A". The chemical formula of the cobalt-free magnesium-doped lithium-rich manganese-based cathode material is: Li(Ni x Mn 1-x )Mg y O2; where 0.1 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.1. The preparation method includes: (1) Mixing nickel salt, manganese salt, magnesium salt, and deionized water to obtain a metal salt solution; (2) Adding the metal salt solution, precipitant solution, and complexing agent solution into the bottom liquid in parallel for coprecipitation reaction to obtain a lithium-rich manganese-based precursor; (3) Mixing the lithium-rich manganese-based precursor and lithium salt for primary calcination to obtain a lithium-rich manganese-based intermediate; (4) Mixing the lithium-rich manganese-based intermediate and lithium salt solution, separating the solid and liquid, and then performing secondary calcination to obtain a cobalt-free magnesium-doped lithium-rich manganese-based cathode material. In the doping modification of these lithium-rich manganese-based cathode materials, adding multiple elements simultaneously will increase the preparation cost of the cathode material; in addition, when the total amount of doping elements introduced is large, it will not only increase the preparation cost but also directly affect the structure of the cathode material, and the effect of performance improvement is not obvious. SUMMARY OF THE INVENTION

[0005] The technical problem to be solved by the present invention is to provide a preparation method of a Zr-doped modified lithium-rich manganese-based cathode material with simple process, low cost, strong operability, and stable electrochemical performance.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a Zr-doped modified lithium-rich manganese-based cathode material, the specific steps are as follows:

[0008] (1) Prepare a precursor solution

[0009] Weigh lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, cobalt acetate tetrahydrate, and zirconium acetate aqueous solution according to a molar ratio of 1.2:0.54:0.13:0.13:(0.0005 - 0.005), add them to deionized water, and then add a complexing agent to the deionized water. The molar ratio of the complexing agent to lithium acetate dihydrate is 1:6.24, and stir evenly to obtain a precursor solution;

[0010] (2) Prepare a precursor

[0011] The precursor solution is subjected to spray pyrolysis. The inlet air temperature for spray pyrolysis is 230 °C, and the outlet air temperature is 110 °C - 115 °C to obtain the precursor material.

[0012] (3) Prepare the Zr-doped modified lithium-rich manganese-based cathode material

[0013] Place the precursor material in an alumina crucible, heat it to 1000 °C in a muffle furnace, sinter for 20 min. After sintering is completed, cool the muffle furnace to room temperature to obtain the Zr-doped modified lithium-rich manganese-based cathode material. During the whole process, a blower is used to blow air into the muffle furnace.

[0014] Furthermore, the molar ratio of lithium acetate dihydrate, nickel acetate tetrahydrate, cobalt acetate tetrahydrate, manganese acetate tetrahydrate and zirconium acetate is 1.2:0.54:0.13:0.13:0.001.

[0015] Furthermore, the complexing agent is citric acid monohydrate.

[0016] Furthermore, in step (1), the molar volume ratio of the complexing agent to deionized water is 0.06 mol / L.

[0017] Furthermore, the heating rate in the muffle furnace is 3 °C / min -1 .

[0018] Furthermore, the mass concentration of the zirconium acetate aqueous solution is 15%.

[0019] The beneficial effects of the present invention are as follows:

[0020] The raw material components are inexpensive, and it has a high discharge specific capacity, high capacity retention rate and high rate performance. Only by adding Zr element to the precursor solution during the preparation of the precursor, the lattice structure of the lithium-rich manganese-based material can be stabilized. After cycling 500 times at 1C, the capacity retention rate of the cathode material is as high as 95.2%. At high rates of 5C and 10C, the discharge capacities can reach 152.7 mAh / g -1 and 130.8 mAh / g -1 . Brief Description of the Drawings

[0021] Figure 1 is the XRD pattern before cycling of the present invention (Comparative Example 1 and Example 2);

[0022] Figure 2 is the SEM image before cycling of the present invention (Comparative Example 1 and Example 2);

[0023] Figure 3 is the Raman spectrum before cycling of the present invention (Comparative Example 1 and Example 2);

[0024] Figure 4 are the HRTEM images of the present invention (Comparative Example 1 and Example 2) after 500 cycles;

[0025] Figure 5 are the XPS images of the present invention (Comparative Example 1 and Example 2) before cycling;

[0026] Figure 6 is the first charge-discharge curve of the present invention (Comparative Example 1 and Example 2);

[0027] Figure 7 is the cycling performance graph of the present invention (Comparative Example 1 and Example 2) at 1C;

[0028] Figure 8 is the rate performance comparison graph of the present invention (Comparative Example 1 and Example 2);

[0029] Figure 9 is the discharge specific energy graph of the present invention (Comparative Example 1 and Example 2) at 1C;

[0030] Figure 10 is the CV curve comparison graph of the present invention (Comparative Example 1 and Example 2) at different scan rates;

[0031] Figure 11 is the peak current vs. square root of scan rate curve comparison graph of the present invention (Comparative Example 1 and Example 2);

[0032] Figure 12 The present invention (Comparative Example 1 and Example 2) is the EIS comparison graph before and after 500 cycles;

[0033] Figure 13 is the GITT comparison graph during the first cycle of the present invention (Comparative Example 1 and Example 2). Detailed implementation manners

[0034] The present invention can be implemented in many different forms and is not limited to the embodiments described herein. The present invention will be further described below with reference to the drawings and embodiments.

[0035] Example 1

[0036] Step 1, prepare a precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 0.163 g of a 15% zirconium acetate aqueous solution by mass fraction, and 63.042 g of citric acid monohydrate, add them to 500 mL of deionized water and stir for 1 h to obtain a precursor solution;

[0037] Step 2, Preparation of precursor: The precursor solution was subjected to spray pyrolysis to obtain the precursor. The inlet air temperature was set at 230 °C, the fan size was 25, the needle passing rate was 20, the peristaltic pump injection speed was 20 - 25, and the outlet air temperature was controlled between 110 °C and 115 °C;

[0038] Step 3, Transfer the precursor obtained in Step 2 to an alumina crucible and perform high-temperature sintering in a muffle furnace. The sintering conditions were as follows: heating to 1000 °C at a rate of 3 °C / min, holding for 20 minutes. During sintering, air was continuously blown into the furnace with a blower, and then it was naturally cooled to room temperature. The brownish-black product was ground into powder with a mortar to obtain a Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.0005.

[0039] Example 2

[0040] Step 1, Preparation of precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 0.327 g of 15% zirconium acetate aqueous solution by mass fraction, and 63.042 g of citric acid monohydrate, add them to 500 mL of deionized water and stir for 1 h to obtain the precursor solution;

[0041] Step 2, Preparation of precursor: The precursor solution was subjected to spray pyrolysis to obtain the precursor. The inlet air temperature was set at 230 °C, the fan size was 25, the needle passing rate was 20, the peristaltic pump injection speed was 20 - 25, and the outlet air temperature was controlled between 110 °C and 115 °C;

[0042] Step 3, Transfer the precursor obtained in Step 2 to an alumina crucible and perform high-temperature sintering in a muffle furnace. The sintering conditions were as follows: heating to 1000 °C at a rate of 3 °C / min, holding for 20 min. During sintering, air was continuously blown into the furnace with a blower, and then it was naturally cooled to room temperature. The brownish-black product was ground into powder with a mortar to obtain a Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.001. See Figure 1 It can be seen that the Zr-doped and modified lithium-rich manganese-based material prepared in Example 2 consists of two phases, R-3m and C2 / m, and the peak shape is good. The (003) peak is slightly shifted to the left, indicating that the lattice spacing of the lithium-rich manganese-based material slightly increases, which is beneficial to the transfer of Li + ; After Zr doping, there are no any additional diffraction peaks for the lithium-rich material, indicating that no extra impurity phases are formed after Zr doping. The ratio of (003) / (104) is 1.493, indicating that the degree of Li / Ni mixing in the material after Zr doping is relatively low.

[0043] See Figure 2 and Figure 3, the size of the Li-rich manganese-based material doped with Zr prepared in Example 2 is uniform, and the primary particle size is about 200-400 nm and uniform, indicating that the overall morphology of the primary particles has not changed after Zr doping. The two main peaks at 485 and 595 cm -1 are respectively related to the E g (O-M-O bending) and A 1g (M-O stretching) vibration modes of the R-3m layered structure, while some weak peaks in the range of 350-450 cm -1 can be attributed to the phonon vibration of the C2 / m monoclinic phase Li2MnO3.

[0044] See Figure 4 , it can be seen from the HRTEM-EDS energy spectrum that the distributions of Mn, Ni, Co, O, and Zr elements in Example 2 are very uniform, and there is no element segregation phenomenon. After 500 cycles, obvious spinel phase transformation occurred on the surface and subsurface of the particles in Comparative Example 1, and many structural voids were generated, and the particle structure was severely damaged. On the contrary, the surface and subsurface of the particles in Example 2 still maintained a good layered phase, indicating that Zr doping effectively stabilized the lattice structure of the Li-rich manganese-based material, which also enabled Example 2 to have a stable Li + transfer during the cycling process, which is beneficial to the improvement of the cycling performance and rate performance. Moreover, it can be found that a uniform CEI film is formed on the surface of Example 2, which is beneficial to reducing the side reactions at the interface between the Li-rich manganese-based material and the electrolyte.

[0045] See Figure 5 , characteristic peaks of Zr 3d 3 / 2 and Zr 3d 5 / 2 were found at the binding energies of 185.5 eV and 182.2 eV, indicating that Zr elements were doped into the Li-rich manganese-based matrix phase, which is consistent with the Figure 4 EDS energy spectrum results. There are a total of four peaks in the O 1s spectrum. The peaks at the binding energies of 529.9 eV and 531.7 eV correspond to lattice oxygen and oxygen vacancies respectively, while the oxygen peak positions of 531.7 eV and 535.9 eV correspond to the CMC binder. Before cycling, the proportions of lattice oxygen, oxygen vacancies, and CMC binder in Example 2 were 32.5%, 26.7%, and 40.8% respectively. However, the proportions of lattice oxygen, oxygen vacancies, and CMC binder in Comparative Example 1 were 41.0%, 22.9%, and 36.1% respectively. In comparison, the proportion of oxygen vacancies in Example 2 increased, which is beneficial to improving the electronic conductivity.

[0046] Next, the preparation of the positive electrode material, the assembly of the battery, and the testing of the electrochemical performance of Example 2 prepared by the present invention will be carried out:

[0047] I. Preparation of the positive electrode sheet and assembly of the CR2025 coin cell

[0048] (1) Preparation of the positive electrode sheet using the lithium-rich manganese-based positive electrode material of Example 2:

[0049] Weigh 253 mg of the lithium-rich manganese-based positive electrode material of Example 2, 32 mg of Super P conductive agent, and 1250 mg of an aqueous CMC solution with a mass fraction of 1.2%. Place them in a polytetrafluoroethylene ball milling tank, add 10 agate ball milling beads with a diameter of 6 mm, seal it, and ball mill at a speed of 400 rpm / min for 6 h to obtain a mixed slurry. Coat it on the aluminum foil using a 0.15 mm scraper, place it in a vacuum drying oven and dry it at 115 °C for 10 h. Cut it into a positive electrode sheet with a diameter of 10 mm. After weighing, place the cut positive electrode sheet in a vacuum drying oven at 115 °C for 10 h again.

[0050] (2) Assembly of the CR2025 coin cell:

[0051] Assemble the battery in a glove box filled with argon with the water and oxygen content both less than 0.01 ppm. The positive electrode is the prepared positive electrode sheet, the lithium metal sheet is used as the reference electrode and the counter electrode, the separator is Celgard-2400, and the electrolyte is the commercial electrolyte LBC-3045I(G). Assemble the CR2025 coin cell and let it stand at 60 °C for 24 h.

[0052] II. Electrochemical performance test of the CR2025 coin cell

[0053] Refer to Figure 6 , and use the constant current charge-discharge method to conduct a cycle performance test on the battery. The test voltage window is 2.0 - 4.8 V. The initial discharge specific capacity at a current density of 0.1C (20 mAg -1 ) is 291.1 mAh g -1 , and the initial Coulomb efficiency is 85.0%.

[0054] Refer to Figure 7 , after being activated 3 times at 0.1C, the initial discharge specific capacity at a current density of 1C is 217.7 mAh g -1 , and the discharge specific capacity after 500 cycles is 207.2 mAh g -1 , and the capacity retention rate is as high as 95.2%.

[0055] Refer to Figure 8 , conduct a rate performance test on the battery. The test voltage window is 2.0 - 4.8 V, and the current densities are 0.1C, 0.5C, 1C, 2C, 5C, and 10C respectively. The discharge specific capacities at high rates of 2C, 5C, and 10C are 182.4 mAh g -1 , 152.7 mAh g-1 and 130.8 mAh g -1 , when the current density is restored to 0.1 C, it still has a discharge specific capacity of 278.2 mAh g -1 .

[0056] See Figure 9 , after cycling 500 times at 1 C, the energy density of Example 2 is 618.10 Wh kg -1 , and the energy retention rate is as high as 80.0%.

[0057] See Figure 10 and Figure 11 , the CV curves of the test battery at sweep rates of 0.1 mV s -1 , 0.2 mV s -1 , 0.4 mV s -1 , 0.6 mV s -1 , 0.8 mV s -1 and 1 mV s -1 were tested. The peak current of the oxidation peak in the CV curve was linearly fitted with the square root of the scan rate (v 1 / 2 ). It was found that there was a good linear relationship between the two. The slope of the fitting straight line was 2.887, which was significantly greater than the slope of the fitting straight line of Comparative Example 1, 2.173, indicating that the kinetic performance had been significantly improved.

[0058] See Figure 12 , EIS test was carried out on Example 2 with an amplitude of 10 mV and a frequency range of 100 kHz to 100 mHz. Before cycling, the solution internal resistance R s and charge transfer resistance R ct of Example 2 were approximately 5.3 Ω and 146.7 Ω respectively. After 500 cycles, a CEI layer was formed on the positive electrode surface, so a CEI layer impedance R sf was generated, approximately 38.9 Ω. At this time, the charge transfer resistance R ct was approximately 19.7 Ω, both of which were smaller than R sf and R ct in Comparative Example 1, indicating that Example 2 had fast electron and ion mobilities. In addition, Example 2 had better rate performance.

[0059] See Figure 13 , a galvanostatic intermittent titration test (GITT) was carried out on Example 2 with a pulse current of 20 mA g -1 , a pulse time of 30 min, and a relaxation time of 2 h. For Example 2, when the voltage reached 4.4 V during charging, the D Li + value was the smallest, and the value was approximately 1.567×10 -12, which matches the anion oxidation reaction caused by the activation of Li2MnO3, which is usually related to the release of O and the reordering of the structure, ultimately leading to Li + During both the charging process from 3.2 V to 4.4 V and the discharging process from 3.4 V to 4.5 V, the D Li + value of Example 2 is higher than that of Comparative Example 1, indicating that the sample of Example 2 has a higher Li + diffusion coefficient, improving the ionic conductivity and effectively enhancing the kinetic performance. This result is also consistent with the Figure 11 and Figure 12 test results.

[0060] During both the charging process from 3.2 to 4.4 V and the discharging process from 3.4 to 4.5 V, the D Li + value of Example 2 is higher than that of Comparative Example 1.

[0061] Example 3

[0062] Step 1, prepare the precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 0.982 g of a 15% zirconium acetate aqueous solution by mass fraction, and 63.042 g of citric acid monohydrate, add them to 500 mL of deionized water and stir for 1 h to obtain the precursor solution;

[0063] Step 2, prepare the precursor: Perform spray pyrolysis on the precursor solution to obtain the precursor. Set the inlet air temperature to 230 °C, the fan size to 25, the through-pin rate to 20, the peristaltic pump injection speed to 20 - 25, and control the outlet air temperature between 110 °C and 115 °C;

[0064] Step 3, transfer the precursor in Step 2 to an alumina crucible, and perform high-temperature sintering in a muffle furnace. The sintering conditions are: heat up to 1000 °C at a rate of 3 °C / min, hold for 20 minutes, continuously blow air into the furnace with a blower during sintering, then naturally cool to room temperature, and grind the brownish-black product into powder with a mortar to obtain the Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.003.

[0065] Example 4

[0066] Step 1, prepare the precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 1.637 g of a 15% zirconium acetate aqueous solution by mass fraction, and 63.042 g of citric acid monohydrate, add them to 500 mL of deionized water and stir for 1 h to obtain the precursor solution;

[0067] Step 2: Prepare the precursor: Spray pyrolyze the precursor solution to obtain the precursor. Set the inlet air temperature at 230°C, the blower size at 25, the needle passing rate at 20, the peristaltic pump injection speed at 20 - 25, and control the outlet air temperature between 110°C and 115°C.

[0068] Step 3: Transfer the precursor obtained in Step 2 to an alumina crucible and perform high-temperature sintering in a muffle furnace. The sintering conditions are as follows: Heat up to 1000°C at a rate of 3°C / min, hold for 20 minutes. Continuously blow air into the furnace with a blower during sintering, and then naturally cool to room temperature. Grind the brownish-black product into powder with a mortar to obtain the Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.005.

[0069] Example 5

[0070] Step 1: Prepare the precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 2.292 g of 15% zirconium acetate aqueous solution by mass, and 63.042 g of citric acid monohydrate. Add them to 500 mL of deionized water and stir for 1 h to obtain the precursor solution.

[0071] Step 2: Prepare the precursor: Spray pyrolyze the precursor solution to obtain the precursor. Set the inlet air temperature at 230°C, the blower size at 25, the needle passing rate at 20, the peristaltic pump injection speed at 20 - 25, and control the outlet air temperature between 110°C and 115°C.

[0072] Step 3: Transfer the precursor obtained in Step 2 to an alumina crucible and perform high-temperature sintering in a muffle furnace. The sintering conditions are as follows: Heat up to 1000°C at a rate of 3°C / min, hold for 20 minutes. Continuously blow air into the furnace with a blower during sintering, and then naturally cool to room temperature. Grind the brownish-black product into powder with a mortar to obtain the Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.007.

[0073] The following provides a comparative example for comparison with the present invention:

[0074] Comparative Example 1

[0075] The preparation method of Comparative Example 1 is the same as that of Example 1, except that when preparing the precursor solution, weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, and 63.042 g of citric acid monohydrate, without adding zirconium acetate, and the other process flows are exactly the same.

[0076] Comparative Example 2

[0077] Step 1: Prepare the precursor solution: Weigh 19.098 g of lithium acetate dihydrate, 4.852 g of nickel acetate tetrahydrate, 4.857 g of cobalt acetate tetrahydrate, 19.852 g of manganese acetate tetrahydrate, 3.274 g of zirconium acetate aqueous solution with a mass fraction of 15%, and 63.042 g of citric acid monohydrate. Add them to 500 mL of deionized water and stir for 1 h to obtain the precursor solution;

[0078] Step 2: Prepare the precursor: Perform spray pyrolysis on the precursor solution to obtain the precursor. Set the inlet air temperature to 230 °C, the blower size to 25, the through-pin rate to 20, and the peristaltic pump injection speed to 20 - 25. Control the outlet air temperature between 110 °C and 115 °C;

[0079] Step 3: Transfer the precursor obtained in Step 2 to an alumina crucible and perform high-temperature sintering in a muffle furnace. The sintering conditions are as follows: Heat up to 1000 °C at a rate of 3 °C / min, hold for 20 minutes. Continuously blow air into the furnace with a blower during sintering, and then naturally cool to room temperature. Grind the brownish-black product into powder with a mortar to obtain the Zr-doped lithium-rich manganese-based cathode material. Grind the brownish-black product into powder with a mortar to obtain the Zr-doped lithium-rich manganese-based cathode material, denoted as Zr-0.01.

[0080] Table 1 Electrochemical performance of Examples 1 - 5 and Comparative Examples 1 and 2 of the present invention

[0081]

[0082] Note: The 1C current density is 200 mA / g -1 , and the first charge and discharge current densities are 20 mA / g -1 .

[0083] As shown in Table 1, compared with Comparative Examples 1 and 2, Example 2 has improved first discharge capacity and first Coulombic efficiency. After 500 cycles at 1C, the remaining discharge capacity and capacity retention rate of Example 2 are 207.3 mAh / g -1 and 95.2%, significantly higher than those of Comparative Examples 1 and 2. At 5C and 10C rates, the discharge capacities of Example 2 are 152.8 mAh / g -1 and 130.3 mAh / g -1 , respectively, higher than those of Comparative Examples 1 and 2.

[0084] Next, perform electrochemical performance testing on the pure-phase lithium-rich manganese-based cathode material prepared in Comparative Example 1:

[0085] I. The preparation of the electrode sheet of the pure-phase lithium-rich manganese-based cathode material in Comparative Example 1 is the same as that in Example 2 for the CR2025 type coin cell.

[0086] II. Electrochemical Performance Test of CR2025 Button Batteries:

[0087] See Figure 6 , the CR2025 button battery assembled in Comparative Example 1 was subjected to constant current charge and discharge tests, and the test voltage window was 2.0 - 4.8V. The initial discharge specific capacity at a current density of 0.1C was 285.6 mAh g -1 ; the initial Coulombic efficiency was 84.1%.

[0088] See Figure 7 , after being activated 3 times at 0.1C, the initial discharge specific capacity at a current density of 1C was 213.2 mAh g -1 , the discharge specific capacity after 500 cycles was 173.4 mAh g -1 , and the capacity retention rate was 81.3%.

[0089] See Figure 8 , the rate performance of the battery was tested, the test voltage window was 2.0 - 4.8V, and the current density conditions were 0.1C, 0.5C, 1C, 2C, 5C, and 10C. The discharge specific capacities at high rates of 2C, 5C, and 10C were 160.7 mAh g -1 , 131.0 mAh g -1 and 107.5 mAh g -1 , when the current density returned to 0.1C, the discharge specific capacity at this time was 257.1 mAh g -1 .

[0090] See Figure 9 , after cycling 500 times at a current density of 1C, the remaining energy density of Comparative Example 1 was 510.3 Wh kg -1 , and the energy retention rate was 67.8%.

[0091] See Figure 10 and Figure 11 , the CV curves of the test battery were tested at sweep rates of 0.1 mV s -1 , 0.2 mV s -1 , 0.4 mV s -1 , 0.6 mV s -1 , 0.8 mV s -1 and 1 mV s -1 . The peak current of the CV curve test was linearly fitted with the square root of the sweep rate. There was a good linear relationship between the peak current of the oxidation peak and the square root of the scan rate. The slope of the fitted straight line was 2.173, which was significantly smaller than the slope of the straight line in Example 2.

[0092] See Figure 12, the EIS test was carried out on Comparative Example 1 with an amplitude of 10 mV and a frequency range of 100 kHz to 100 mHz. Before cycling, the ohmic internal resistance R s and charge transfer resistance R ct of Comparative Example 1 were approximately 5.2 Ω and 147.0 Ω, respectively. After 500 cycles, a CEI layer was formed on the surface of the positive electrode of the battery, so a CEI layer impedance R sf was generated, which was approximately 49.8 Ω. At this time, the charge transfer resistance R ct of Comparative Example 1 was approximately 33.2 Ω.

[0093] See Figure 13 , the GITT test was carried out on Comparative Example 1 with a pulse current of 20 mA g -1 , a pulse time of 30 min, and a relaxation time of 2 h. For Comparative Example 1, when the voltage reached 4.4 V during charging, the D Li + value was the smallest, and the value was approximately 1.148×10 -12 , which was consistent with the anion oxidation reaction caused by the activation of Li2MnO3, which was usually related to the release of O and the reordering of the structure, ultimately resulting in poor Li + diffusion ability.

[0094] The above are only specific embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of Zr-doped modified lithium-rich manganese-based cathode material, characterized in that: The specific steps are as follows: (1) Prepare the precursor solution: Weigh lithium acetate dihydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, cobalt acetate tetrahydrate, and zirconium acetate aqueous solution according to the molar ratio of 1.2:0.54:0.13:0.13:(0.0005 - 0.005), add them to deionized water, and then add a complexing agent to the deionized water. The molar ratio of the complexing agent to lithium acetate dihydrate is 1:6.24, and stir evenly to obtain the precursor solution; (2) Prepare the precursor: Perform spray pyrolysis on the precursor solution. The inlet air temperature for spray pyrolysis is 230 °C, and the outlet air temperature is 110 °C - 115 °C to obtain the precursor material; (3) Prepare the Zr-doped modified lithium-rich manganese-based cathode material Place the precursor material in an alumina crucible, heat it to 1000 °C in a muffle furnace, sinter for 20 minutes. After sintering, cool the muffle furnace to room temperature. During the whole process, use a blower to blow air into the muffle furnace to obtain the Zr-doped modified lithium-rich manganese-based cathode material.

2. The preparation method of the Zr-doped modified lithium-rich manganese-based cathode material according to claim 1, characterized in that: The molar ratio of the lithium acetate dihydrate, nickel acetate tetrahydrate, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and zirconium acetate is 1.2:0.54:0.13:0.13:0.

001.

3. The preparation method of the Zr-doped modified lithium-rich manganese-based cathode material according to claim 1, characterized in that: The complexing agent is citric acid monohydrate.

4. The preparation method of the Zr-doped modified lithium-rich manganese-based cathode material according to claim 1, characterized in that: In step (1), the molar volume ratio of the complexing agent to deionized water is 0.06 mol / L.

5. The preparation method of the Zr-doped modified lithium-rich manganese-based cathode material according to claim 1, characterized in that: The heating rate in the muffle furnace is 3 °C·min -1 .

6. The preparation method of the Zr-doped modified lithium-rich manganese-based cathode material according to claim 1, characterized in that: The mass concentration of the zirconium acetate aqueous solution is 15%.

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