Preparation method of cerium-tungsten composite modified core-shell lithium-rich manganese-based positive electrode material

Abstract

The invention relates to the technical field of positive electrode materials, in particular to a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based positive electrode material, which comprises the following steps: mixing a quaternary manganese-rich precursor and a lithium salt, sintering at a high temperature, cooling, crushing and sieving to obtain a primary sintered matrix; the method comprises the following steps: mixing a sintering matrix with a coating agent, sintering and modifying, and cooling, sieving and demagnetizing to obtain the cerium-tungsten composite modified core-shell lithium-rich manganese-based positive electrode material, the quaternary manganese-rich precursor is of a core-shell structure and is selected from at least one of a manganese-nickel-cobalt-aluminum quaternary precursor, a manganese-nickel-cobalt-tungsten quaternary precursor, a manganese-nickel-cobalt-zirconium quaternary precursor, a manganese-nickel-cobalt-magnesium quaternary precursor and a manganese-nickel-cobalt-titanium quaternary precursor; by adopting the quaternary manganese-rich precursor and adding the coating agent to the primary sintering matrix for modification, the obtained positive electrode material has obviously improved first charge-discharge specific capacity and rate capability, and the preparation process is simple and easy to popularize and implement.

Description

Technical Field

[0001] The invention relates to the technical field of positive electrode materials, and in particular to a method for preparing a cerium-tungsten composite-modified core-shell lithium-rich manganese-based positive electrode material. Background Art

[0002] Under normal voltage conditions, lithium-rich manganese-based cathode materials (LRM) have the best cycle stability among all commercial cathode materials. Secondly, under high voltage, they can exhibit very high gram capacity, making them ideal cathode materials for high energy density batteries and solid-state batteries. When the discharge voltage is above 3.5V, the gram capacity can reach 260mAh / g. At the same time, they are low-cobalt / cobalt-free, low-nickel, and high-manganese materials, which greatly reduces dependence on resources such as cobalt and nickel. They are currently the most competitive and promising cathode materials for power lithium-ion batteries.

[0003] Although LRM has many advantages, it also has many problems that need to be solved, such as low first coulombic efficiency (ICE), voltage decay and reduced energy density during the cycle. At the same time, due to the poor conductivity of Li2MnO3 (Mn 4+ Due to the presence of components with low electrical conductivity, the electrical conductivity of LRM positive electrode materials is generally low, and the rate performance is poor. In order to improve the rate performance, the primary particles are generally made smaller to reduce the lithium ion transmission distance. In this way, although the rate performance is improved, the specific surface area is generally larger, the contact area with the electrolyte is increased, and more side reactions are caused. A Chinese patent (authorization announcement number is CN116354418B) discloses a nickel-cobalt-manganese-aluminum quaternary precursor material, a preparation method thereof, and a positive electrode material. The preparation process of the positive electrode material involves the preparation of a total of eight solutions, including solution AG and base solution. The preparation process is complicated, and the 1C rate discharge of the prepared positive electrode material is 211mAh / g. The initial charge and discharge specific capacity and rate performance need to be further improved. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for preparing a cerium-tungsten composite modified core-shell lithium-rich manganese-based positive electrode material. By adopting a quaternary manganese-rich precursor and adding a coating agent to modify the monoalkyl matrix, the obtained positive electrode material has significantly improved initial charge and discharge specific capacity and rate performance, and the preparation process is simple and easy to promote and implement.

[0005] On the one hand, the present invention provides a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material, which at least includes the following steps: mixing a quaternary manganese-rich precursor and a lithium salt and then performing high-temperature sintering, cooling, crushing, and sieving to obtain a first-sintered matrix; mixing the first-sintered matrix with a coating agent and then performing sintering modification, and obtaining the cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material after cooling, sieving, and demagnetization; the quaternary manganese-rich precursor has a core-shell structure, and the quaternary manganese-rich precursor is selected from at least one of a manganese-nickel-cobalt-aluminum quaternary precursor, a manganese-nickel-cobalt-tungsten quaternary precursor, a manganese-nickel-cobalt-zirconium quaternary precursor, a manganese-nickel-cobalt-magnesium quaternary precursor, or a manganese-nickel-cobalt-titanium quaternary precursor.

[0006] In one embodiment, the quaternary manganese-rich precursor is a manganese-nickel-cobalt-aluminum quaternary precursor.

[0007] In one embodiment, the preparation method of the quaternary manganese-rich precursor at least includes the following steps:

[0008] (1) Prepare a mixed brine solution containing manganese ions, nickel ions, cobalt ions, and doped metal ions, and the doped metal ions include at least one of zirconium ions, tungsten ions, magnesium ions, aluminum ions, and titanium ions;

[0009] (2) Under the protection of a nitrogen atmosphere, control the stirring rate to be 450-650 rpm / h, add the mixed brine solution to a reaction kettle containing pure water at 50-70 °C at a rate of 2.5-3.5 L / h, and at the same time add a 5-7 mol / L sodium hydroxide aqueous solution and a 3-5 mol / L ammonia aqueous solution to the reaction kettle to control the pH of the system to be 11.5-12.5, and perform the first co-precipitation reaction to obtain the precursor inner core;

[0010] (3) When the particle size D50 of the precursor inner core is 2.0-4.0 μm, adjust the stirring rate to 550-750 rpm / h, pump the mixed brine solution into the reaction kettle at a rate of 1-2 L / h, and at the same time add a 3-5 mol / L sodium hydroxide aqueous solution and a 3-5 mol / L ammonia aqueous solution to the reaction kettle to control the pH of the system to be 10.5-11.5, perform the second co-precipitation to obtain precursor particles with a core-shell structure, and continue the reaction until the particle size D50 of the precursor particles is 4-6 μm, and then end the reaction to obtain a solid-liquid mixture;

[0011] (4) Centrifuge, wash, dry, and sieve the solid-liquid mixture to obtain the quaternary manganese-rich precursor.

[0012] In one embodiment, the molar ratio of manganese ions, nickel ions, cobalt ions, and doped metal ions in the mixed brine solution is (50-60):(35-40):(5-10):(1-3).

[0013] In one embodiment, the molar ratio of manganese ions, nickel ions, cobalt ions, and doped metal ions in the mixed brine solution is 54:38:7:1.

[0014] In one embodiment, the doped metal ion is aluminum ion.

[0015] In one embodiment, the total ion concentration of the mixed brine solution is 1.5 - 2.50 mol / L.

[0016] In one embodiment, the total ion concentration of the mixed brine solution is 2.00 mol / L.

[0017] The present invention prepares a quaternary manganese-rich precursor with a core-shell structure containing manganese, nickel, cobalt, and doped metal by itself. The element distribution is uniform, the crystal structure is further stabilized. By cooperating with the addition of a coating agent to coat and modify the sintered matrix for the first time, the obtained cathode material maintains a stable structure during charge and discharge. The first charge capacity > 236.1 mAh / g, the first discharge specific capacity > 194 mAh / g, and the first Coulombic efficiency > 82.2%. In particular, by controlling the molar ratio of manganese ions, nickel ions, cobalt ions, and doped metal ions and the conditions of the first and second co-precipitation reactions during the preparation of the quaternary manganese-rich precursor, it is ensured that the inner core part of the precursor has fine primary particles and loose distribution between particles, and the outer shell part is compact. During the subsequent high-temperature sintering process, a core-shell lithium-rich manganese-based cathode material with a porous interior is generated, shortening the lithium ion transmission distance and having excellent rate performance.

[0018] In one embodiment, the lithium salt is selected from one of lithium carbonate, lithium hydroxide, lithium nitrate, or lithium chloride.

[0019] In one embodiment, the lithium salt is lithium carbonate.

[0020] In one embodiment, the ratio of the total number of moles of metal elements in the quaternary manganese-rich precursor to the number of moles of lithium element in the lithium source (Me / Li) is 1:1.05 - 1.20.

[0021] In one embodiment, the ratio of the total number of moles of metal elements in the quaternary manganese-rich precursor to the number of moles of lithium element in the lithium source (Me / Li) is 1:1.06 - 1.12.

[0022] In one embodiment, the ratio of the total number of moles of metal elements in the quaternary manganese-rich precursor to the number of moles of lithium element in the lithium source (Me / Li) is 1:1.07 - 1.10.

[0023] In one embodiment, the ratio of the total number of moles of metal elements in the quaternary manganese-rich precursor to the number of moles of lithium element in the lithium source (Me / Li) is 1:1.08.

[0024] In one embodiment, the high-temperature sintering step includes: mixing a quaternary manganese-rich precursor and a lithium salt, placing them in a sintering furnace, controlling the heating rate at 2 - 5 °C / min, heating to 900 - 1000 °C, and holding for 10 - 20 h.

[0025] Furthermore, the present invention controls the ratio of the total molar amount of metal elements in the quaternary manganese-rich precursor to the molar amount of lithium element in the lithium source (Me / Li) and the addition amount of the coating agent, while ensuring a relatively high initial charge-discharge specific capacity and a relatively high initial Coulombic efficiency of the cathode material. The initial charge capacity > 238 mAh / g, the initial discharge specific capacity > 204 mAh / g, and the initial Coulombic efficiency > 86%.

[0026] In one embodiment, the particle size of the first-fired matrix is 4 - 7 μm.

[0027] In one embodiment, the coating agent is a mixture containing cerium element and tungsten element.

[0028] In one embodiment, the coating agent is a mixture containing cerium oxide and tungsten oxide.

[0029] The present invention coats and modifies the first-fired matrix with a mixture containing cerium element and tungsten element, reducing the surface impedance and accelerating the transmission of lithium ions, thereby improving the initial efficiency and the rate performance.

[0030] In one embodiment, the addition amount of the coating agent is 0.2 - 1% of the mass of the first-fired matrix.

[0031] In one embodiment, the addition amount of the coating agent is 0.3 - 0.7% of the mass of the first-fired matrix.

[0032] In one embodiment, the addition amount of the coating agent is 0.4 - 0.6% of the mass of the first-fired matrix.

[0033] In one embodiment, the addition amount of the coating agent is 0.5% of the mass of the first-fired matrix.

[0034] In one embodiment, the conditions for sintering modification are: the sintering temperature is 400 - 800 °C, and the sintering time is 8 - 12 h.

[0035] The cathode material provided by the present invention has a core-shell structure with loose pores inside, which can store more electrolyte and effectively alleviate the problem of insufficient electrolyte in the later stage of cycling.

[0036] Beneficial effects

[0037] 1. The present invention provides a preparation method of a core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite. By using a quaternary manganese-rich precursor and adding a coating agent to modify the matrix after the first calcination, the obtained cathode material has significantly improved initial charge-discharge specific capacity and rate performance, and the preparation process is simple and easy to promote and implement.

[0038] 2. The present invention self-prepares a quaternary manganese-rich precursor with a core-shell structure containing manganese, nickel, cobalt and doped metal, with uniform element distribution, further stabilizing the crystal structure. By cooperating with the addition of a coating agent to coat and modify the matrix after the first calcination, the obtained cathode material maintains a stable structure during charge and discharge, with an initial charge capacity > 236.1 mAh / g, an initial discharge specific capacity > 194 mAh / g, and an initial Coulomb efficiency > 82.2%.

[0039] 3. The present invention controls the molar ratios of manganese ions, nickel ions, cobalt ions and doped metal ions and the conditions of the first and second co-precipitation reactions during the preparation of the quaternary manganese-rich precursor, ensuring that the obtained precursor has a fine primary particle size, a loose distribution between particles in the inner core part and a compact outer shell part. During the subsequent high-temperature sintering process, a core-shell lithium-rich manganese-based cathode material with a porous interior is formed, shortening the lithium ion transmission distance and having excellent rate performance.

[0040] 4. The present invention controls the ratio of the total molar number of metal elements in the quaternary manganese-rich precursor to the molar number of lithium elements in the lithium source (Me / Li) and the addition amount of the coating agent, while ensuring a relatively high initial charge-discharge specific capacity and a relatively high initial Coulomb efficiency of the cathode material, with an initial charge capacity > 238 mAh / g, an initial discharge specific capacity > 204 mAh / g, and an initial Coulomb efficiency > 86%.

[0041] 5. The cathode material provided by the present invention has a core-shell structure with a porous interior, which can store more electrolyte and effectively alleviate the problem of insufficient electrolyte in the later stage of cycling. Description of the Drawings

[0042] Figure 1 It is a cross-sectional analysis diagram of the precursors and cathode materials in Example 1 and Comparative Example 1. In the figure, a is the precursor of Example 1, b is the cathode material of Example 1; c is the precursor of Comparative Example 1, and d is the cathode material of Comparative Example 1.

[0043] Figure 2 It is a rate performance result diagram of the cathode materials provided by Example 1 and Comparative Example 1 under the same test conditions. The upper and lower broken lines in the figure correspond to Example 1 and Comparative Example 1 respectively. Detailed Embodiments

[0044] Example 1

[0045] Example 1 of the present invention provides a preparation method of a core-shell lithium-rich manganese-based cathode material modified by cerium and tungsten, comprising the following steps: mixing a quaternary manganese-rich precursor and a lithium salt, followed by high-temperature sintering, cooling, crushing, and sieving to obtain a first-fired matrix; mixing the first-fired matrix with a coating agent, followed by sintering modification, cooling, sieving, and demagnetization to obtain the core-shell lithium-rich manganese-based cathode material modified by cerium and tungsten; the quaternary manganese-rich precursor is a manganese-nickel-cobalt-aluminum quaternary precursor.

[0046] The preparation method of the quaternary manganese-rich precursor comprises the following steps:

[0047] (1) Mix nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, and water to prepare a mixed brine solution containing manganese ions, nickel ions, cobalt ions, and aluminum ions;

[0048] (2) Under the protection of a nitrogen atmosphere, control the stirring rate at 500 rpm / h, add the mixed brine solution to a reaction kettle containing pure water at 60 °C at a rate of 3 L / h, and simultaneously add a 6 mol / L sodium hydroxide aqueous solution and a 4 mol / L ammonia aqueous solution to the reaction kettle to control the system pH to 11.8, and carry out the first co-precipitation reaction to obtain the precursor core;

[0049] (3) When the particle size D50 of the precursor core is 3.5 μm, adjust the stirring rate to 600 rpm / h, pump the mixed brine solution into the reaction kettle at a rate of 1.5 L / h, and simultaneously add a 4 mol / L sodium hydroxide aqueous solution and a 4 mol / L ammonia aqueous solution to the reaction kettle to control the system pH to 10.6, and carry out the second co-precipitation to obtain precursor particles with a core-shell structure. Continue the reaction until the particle size D50 of the precursor particles is 5.0 μm, and then end the reaction to obtain a solid-liquid mixture;

[0050] (4) Centrifuge, wash, dry, and screen the solid-liquid mixture to obtain the quaternary manganese-rich precursor.

[0051] The molar ratio of manganese ions, nickel ions, cobalt ions, and aluminum ions in the mixed brine solution is 54:38:7:1.

[0052] The total ion concentration of the mixed brine solution is 2.00 mol / L.

[0053] The lithium salt is lithium carbonate.

[0054] The ratio of the total molar number of metal elements in the quaternary manganese-rich precursor to the molar number of lithium elements in the lithium source (Me / Li) is 1:1.08.

[0055] The steps of the high-temperature sintering include: placing the quaternary manganese-rich precursor and the lithium salt in a sintering furnace, controlling the heating rate at 3 °C / min, and heating to 950 °C for insulation for 15 h.

[0056] The particle size of the first-fired matrix is 6 μm.

[0057] The coating agent is a mixture containing tungsten oxide and cerium oxide, and the contents of tungsten in tungsten oxide and cerium in cerium oxide respectively account for 50% of the mass of the coating agent.

[0058] The addition amount of the coating agent is 0.5% of the mass of the first-fired matrix.

[0059] The conditions for sintering modification are: the sintering temperature is 700 °C and the sintering time is 10 h.

[0060] Example 2

[0061] Example 2 of the present invention provides a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material. The specific implementation manner is the same as that of Example 1, except that the ratio of the total molar number of metal elements in the quaternary manganese-rich precursor to the molar number of lithium elements in the lithium source (Me / Li) is 1:1.06.

[0062] Example 3

[0063] Example 3 of the present invention provides a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material. The specific implementation manner is the same as that of Example 1, except that the ratio of the total molar number of metal elements in the quaternary manganese-rich precursor to the molar number of lithium elements in the lithium source (Me / Li) is 1:1.06.

[0064] Example 4

[0065] Example 4 of the present invention provides a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material. The specific implementation manner is the same as that of Example 1, except that the addition amount of the coating agent is 0.3% of the mass of the first-fired matrix.

[0066] Example 5

[0067] Example 5 of the present invention provides a preparation method of a cerium-tungsten composite modified core-shell lithium-rich manganese-based cathode material. The specific implementation manner is the same as that of Example 1, except that the addition amount of the coating agent is 0.7% of the mass of the first-fired matrix.

[0068] Comparative Example 1

[0069] Comparative Example 1 of the present invention provides a preparation method of an unmodified lithium-rich manganese-based cathode material, including the following steps: mixing the precursor Ni 0.38 Co 0.08 Mn 0.54 (OH)2 (D50 is 5.0 μm) and lithium carbonate, and then performing high-temperature sintering, and obtaining an unmodified lithium-rich manganese-based cathode material after cooling. The precursor Ni 0.38 Co0.08 Mn 0.54 The ratio (Me / Li) of the total molar amount of metal elements in (OH)2 to the molar amount of lithium element in the lithium source is 1:1.08

[0070] The conditions for the high-temperature sintering are as follows: the sintering temperature is 950 °C and the sintering time is 15 h.

[0071] Performance test

[0072] 1. Cross-section detection: Cross-sectional analysis was performed on the precursors and cathode materials in Example 1 and Comparative Example 1. The results are shown in Figure 1 and the analysis Figure 1 shows that, compared with the precursors and cathode materials provided in Comparative Example 1, the quaternary manganese-rich precursor and the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite provided in Example 1 have a core-shell structure with loose pores inside and dense outside.

[0073] 2. Capacity test: The cathode materials prepared in the examples and comparative examples were made into 2032-type coin cells and used in a blue electrochemical test cabinet to conduct electrochemical performance tests under specific test conditions. The test conditions and test results are shown in Table 1.

[0074] 3. Rate test: The cathode materials prepared in Example 1 and Comparative Example 1 were made into 2032-type coin cells and used in a blue electrochemical test cabinet to conduct different-rate discharge tests. The charge-discharge cut-off voltage was 2.3 - 4.55 V (0.1c). The test results are shown in Figure 2 and the analysis Figure 2 shows that the cathode material provided in Example 1 has better rate performance than the cathode material provided in Comparative Example 1.

[0075] Table 1

[0076]

[0077] It can be seen from the data in Table 1 that, compared with Comparative Example 1, the first charge capacity of the cathode materials obtained by the methods provided in Examples 1 - 5 > 236.1 mAh / g, the first discharge specific capacity > 194 mAh / g, and the first Coulombic efficiency > 82.2%. In particular, the cathode material provided in Example 1.

Claims

1. A preparation method of a core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite, characterized in that, It includes at least the following steps: Mix a quaternary manganese-rich precursor and a lithium salt, then conduct high-temperature sintering. After cooling, crushing, and sieving, a first-fired matrix is obtained. Mix the first-fired matrix with a coating agent and then conduct sintering modification. After cooling, sieving, and demagnetization, a core-shell lithium-rich manganese-based cathode material modified by cerium and tungsten is obtained. The quaternary manganese-rich precursor has a core-shell structure, and the quaternary manganese-rich precursor is selected from at least one of a manganese-nickel-cobalt-aluminum quaternary precursor, a manganese-nickel-cobalt-tungsten quaternary precursor, a manganese-nickel-cobalt-zirconium quaternary precursor, a manganese-nickel-cobalt-magnesium quaternary precursor, or a manganese-nickel-cobalt-titanium quaternary precursor.

2. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 1, characterized in that, The ratio of the total molar amount of metal elements in the quaternary manganese-rich precursor to the molar amount of lithium element in the lithium source is 1:1.07 - 1.

10.

3. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 2, characterized in that, The addition amount of the coating agent is 0.4 - 0.6% of the mass of the first-fired matrix.

4. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 3, characterized in that, The preparation method of the quaternary manganese-rich precursor includes at least the following steps: (1) Prepare a mixed brine solution containing manganese ions, nickel ions, cobalt ions, and doped metal ions. The doped metal ions include at least one of zirconium ions, tungsten ions, magnesium ions, aluminum ions, and titanium ions. (2) Under the protection of a nitrogen atmosphere, control the stirring rate at 450 - 650 rpm / h, and add the mixed brine solution to a reaction kettle containing pure water at 50 - 70 °C at a rate of 2.5 - 3.5 L / h. At the same time, add a 5 - 7 mol / L sodium hydroxide aqueous solution and a 3 - 5 mol / L ammonia aqueous solution to the reaction kettle to control the pH of the system at 11.5 - 12.5, and conduct the first co-precipitation reaction to obtain the precursor core. (3) When the particle size D50 of the precursor core is 2.0 - 4.0 μm, adjust the stirring rate to 550 - 750 rpm / h, and pump the mixed brine solution into the reaction kettle at a rate of 1 - 2 L / h. At the same time, add a 3 - 5 mol / L sodium hydroxide aqueous solution and a 3 - 5 mol / L ammonia aqueous solution to the reaction kettle to control the pH of the system at 10.5 - 11.5, and conduct the second co-precipitation to obtain precursor particles with a core-shell structure. Continue the reaction until the particle size D50 of the precursor particles is 4 - 6 μm, and then end the reaction to obtain a solid-liquid mixture. (4) Centrifuge, wash, dry, and sieve the solid-liquid mixture to obtain the quaternary manganese-rich precursor.

5. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 4, characterized in that, The molar ratio of manganese ions, nickel ions, cobalt ions, and doped metal ions in the mixed brine solution is (50 - 60):(35 - 40):(5 - 10):(1 - 3).

6. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 2, wherein, The total ion concentration of the mixed brine solution is 1.5 - 2.50 mol / L.

7. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 3, characterized in that, The lithium salt is selected from one of lithium carbonate, lithium hydroxide, lithium nitrate, or lithium chloride.

8. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 3, characterized in that, The steps of the high-temperature sintering include: Mix the quaternary manganese-rich precursor and the lithium salt, then place them in a sintering furnace, control the heating rate at 2 - 5 °C / min, and heat to 900 - 1000 °C and hold for 10 - 20 h.

9. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 3, characterized in that, The coating agent is a mixture containing cerium elements and tungsten elements.

10. The preparation method of the core-shell lithium-rich manganese-based cathode material modified by cerium-tungsten composite according to claim 3, characterized in that, The conditions for the sintering modification are: the sintering temperature is 400 - 800 °C, and the sintering time is 8 - 12 h.

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