A high-tap-density lithium-rich manganese-based cathode material and its preparation method

Abstract

This application relates to the field of battery cathode materials, and in particular to a high-tap-density lithium-rich manganese-based cathode material and its preparation method. In this application, phosphate and oxalate are used as precipitants, and a certain amount of polymer resin is added. The polymer resin participates in the oxalate precipitation process, followed by sintering. Simultaneously, high-speed stirring and ultrasonic treatment are used to obtain a relatively dense particle system, which also improves the temperature tolerance of the processing. This method enables the achievement of high tap density and good electrical performance even with certain temperature fluctuations.

Description

Technical Field

[0001] This application relates to the field of battery cathode materials, and in particular to a high tap density lithium-rich manganese-based cathode material and its preparation method. Background Technology

[0002] Lithium-rich manganese-based cathode (LR-NMC) is one of the most promising high-energy-density cathode systems in the lithium-ion battery field in recent years. With its "high manganese, low cobalt" composition design, it balances ultra-high energy density with cost advantages, making it a strong candidate for the "ultimate cathode" in all-solid-state batteries. Its core feature is a "layer-to-layer" composite structure (Li₂MnO₃·LiMO₂, M = Ni, Co, Mn, etc.), which combines cations (Ni / Co / Mn) and anions (O₂, Co, Co, Mn, etc.). 2- Simultaneously participates in redox reactions, achieving >250 mAh·g -1 Its reversible specific capacity is far higher than that of lithium iron phosphate (160 mAh·g). -1 ) and conventional high-nickel ternary lithium batteries (200mAh·g) -1 The theoretical mass energy density can reach 1000 Wh kg. -1 It has broad market prospects.

[0003] Typically, lithium-rich manganese-based cathode materials are obtained by precipitating lithium, manganese, and other doped metals or non-metals with carbonates, followed by sintering. Currently, some studies indicate that doping lithium-rich manganese-based cathode materials with phosphorus and boron can improve electrode stability, and by using phosphorus and boron as fluxes, the tap density of the prepared cathode material can be increased.

[0004] Typically, in the above-mentioned scheme, boron is added in the form of borates and boron oxides, while phosphorus is added to the system in the form of phosphates and phosphorus pentoxides. The sintering process usually follows this sequence: First, initial heating decomposes the carbonates, hydroxides, and ammonium salts, resulting in dehydration and degassing. Heating continues until the lithium salt initially melts and diffuses, forming a preliminary framework template. Further heating causes the lithium salt to diffuse, and Li₂MnO₃ clusters begin to nucleate in the Mn-rich region, while secondary melting and particle formation reduce the porosity. Finally, Li₂MnO₃ and LiMO₃ achieve lattice-matched rearrangement at a higher temperature, ultimately forming the electrode material.

[0005] In the above process, although adding boron and phosphorus can lower the overall sintering temperature, their melting range overlaps with the temperature range of gas generation and drainage. Therefore, during the melting process, their flow will cause gas discharge to be obstructed. Based on the resistivity of boron and phosphorus elements themselves, the heating process needs to be controlled more precisely. Even small temperature disturbances will have a significant impact on the performance of the system, which undoubtedly reduces the yield and increases the production cost of enterprises. Summary of the Invention

[0006] To address the aforementioned issues, the purpose of this application is to provide a lithium-rich manganese-based cathode material and a corresponding preparation method, which incorporates a gas discharge channel during the granulation process, enabling the achievement of good tap density and electrical performance without the need for precise temperature control during preparation.

[0007] First, this application provides a method for preparing a high-tap-density lithium-rich manganese-based cathode material, wherein the chemical formula of the lithium-rich manganese-based cathode material is Li. 1+x Mn y M z O r A w P q M can be any one of nickel, cobalt, iron, titanium, copper, molybdenum, chromium, zirconium, magnesium, and aluminum, and A can be any number of sulfur and boron; where 0 < x ≤ 1, 0 < y ≤ 1, 0 ≤ z < 0.5, 0 ≤ w ≤ 0.1, 0 ≤ q ≤ 0.1, and r = 1 + x + y + z. Its preparation method includes the following steps: S1. According to the chemical formula, take lithium, manganese and water-soluble or alcohol-soluble salts of component M, add solvent to dissolve them, and obtain the first slurry; S2. Add a precipitant to the first slurry for co-precipitation, wherein the precipitant contains the following components: a. At least one of sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, ammonium phosphate, ammonium hydrogen phosphate, and diammonium hydrogen phosphate; b. Water-soluble oxalate; c. A polymer resin, wherein the polymer resin is at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polylactic acid; S3. The dispersion system is dried in a spray dryer to obtain spherical precursor powder; S4. The precursor powder is sintered, cooled, and then pulverized to obtain the target product.

[0008] In the above scheme, a precipitation-granulation-sintering process is used to prepare lithium-rich manganese-based cathode materials. The key step is the precipitation step. In this step, compared with the commonly used grinding-granulation-sintering process in existing technologies, an oxalic acid precipitation method is used to prepare the precursor. During the precipitation process, some phosphorus is introduced by means of phosphate, and a portion of polymer resin is added. In the above scheme, the polymer resin can act as a template in the system and also as a certain nanoscale dispersant. On the one hand, during the sintering process, the polymer resin will first carbonize at high temperature and then be completely burned off, which is conducive to the discharge of residual gases. On the other hand, it can also act as a steric hindrance and bridging agent, forming a physical barrier less than 10 nm thick on the surface of the primary crystal nuclei, reducing the attraction of van der Waals forces between molecules. In the above process, the resulting structure is more compact, further improving the tap density of the system. On the other hand, when polymer resins are involved in the sintering process, since the reaction temperature is close to the temperature at which ammonium phosphate produces gas and the decomposition temperature of carbonates in the system, the polymer resin will first absorb heat during the sintering process, which delays the generation of gas in the system. The mesoporous channels formed subsequently help the gas to escape, and the channels gradually close during the subsequent sintering process. Therefore, overall, even if sintering is carried out at a relatively wide temperature range, the tap density can be improved.

[0009] In the above scheme, the water-soluble salt or alcohol-soluble salt is preferably a nitrate, acetate, carbonate, or fluoride salt. In Li 1+x Mn y M z O r A w P q In this system, M is preferably a nickel-cobalt mixture, wherein the molar amount of nickel is 0.2 to 0.3 times that of manganese, and the molar amount of cobalt is 0.2 to 0.3 times that of manganese. A is preferably boron, and in the system 0.001≤w≤0.002, 0.001≤q≤0.002.

[0010] Preferably, in step S4 sintering, two sintering steps are performed, in the following order: S4-1. Heat the temperature to 500-650℃ for a second heat treatment, and the heat treatment time is 1-10 hours. S4-2. Sinter at a temperature not lower than 900℃ for 5 to 20 hours. After cooling, pulverize to obtain the target product.

[0011] Overall, the above process still adopts a two-stage sintering method. The first stage can use a higher temperature, which achieves the effects of drainage and degassing. On the other hand, this process can also promote the transformation of polymer. In addition, the polymer is less likely to produce ash during sintering, which can better improve the tap density and reduce the resistivity.

[0012] Preferably, in step S2, the polymer resin is polyvinyl alcohol. More preferably, the mass of the polymer resin is 0.5% to 1% of the mass of manganese in the system. Experiments have shown that polyvinyl alcohol maintains the morphology of the product well during sintering and can achieve a higher overall tap density. Even with temperature fluctuations, it can achieve high density and high capacity retention.

[0013] Preferably, in step S2, during the precipitation process, the mixture is stirred at a high speed of 500-1000 rpm, and / or; In step S2, during the precipitation process, ultrasonic treatment at 60–100 kHz is applied, and / or; In step S2, the temperature is controlled at 80–100°C.

[0014] High-speed stirring and / or ultrasonic treatment helps improve the dispersibility of the polymer, enabling it to better disperse the precipitated solid materials. It also helps to form more uniform drainage and gas generation channels during sintering. After uniform dispersion, the resulting size is more stable, thus reducing the adverse effects of the polymer on the tap density during subsequent sintering to form closed channels.

[0015] Preferably, during the precipitation process in step S2, the pH value is controlled at 4–6. In the above scheme, the pH can be controlled using a buffer system of phosphate and hydrogen phosphate to keep the system in a weakly acidic state. This process can reduce the formation of hydroxide co-precipitates in the system and further improve the uniformity of particle formation.

[0016] In addition, this application also relates to lithium-rich manganese-based cathode materials prepared by the above-mentioned preparation method, which have a high tap density (reaching not less than 2.3 g / cm³). 3 It has good electrical performance (discharge specific capacity of not less than 200mAh / g in the first week and retention rate of not less than 93% after 100 cycles).

[0017] In summary, this application provides a preparation scheme for lithium-rich manganese-based cathode materials. By introducing a combustion aid and a portion of organic polymer resin, the requirements for temperature control are reduced. High tap density and good electrical performance can be achieved by sintering within a certain temperature range. Detailed Implementation

[0018] The technical solution of this application will be further described below through specific embodiments.

[0019] In this application, by introducing some high molecular polymers, especially polyvinyl alcohol, the overall tap density and electrical properties are kept good even when there are fluctuations in temperature control.

[0020] Example 1: A method for preparing a high-tap-density lithium-rich manganese-based cathode material, the overall chemical formula of which is Li. 1.15 Mn 0.54 Ni 0.20 Co 0.11 O2B 0.002 P 0.002 The specific preparation method is as follows: S1. According to the above chemical formula, dissolve lithium carbonate, manganese acetate, nickel acetate, and cobalt acetate in water to prepare a solution with a total metal ion concentration of 1 mol·L⁻¹. -1 The solution system yields the first slurry; A precipitant is added to the first slurry. The specific precipitant is as follows: The mixed system of diammonium hydrogen phosphate and diammonium dihydrogen phosphate was prepared into a solution system with pH=4.5, and a 1 mol·L⁻¹ solution was prepared. -1 Aqueous solution; Ammonium oxalate, prepared in 1 mol·L⁻¹ -1 Aqueous solution; Polyvinyl alcohol, specifically brand name PVA0588, was added at a rate of 0.5% of the manganese mass and dispersed using a small amount of water and ethanol solution. After adding the precipitant, the temperature was controlled at 90±10℃, the stirring speed was controlled at 800rpm, and ultrasonic treatment at 80KHZ was applied. The reaction time was controlled at 12h. S3. Adjust the solid slurry by adding a small amount of water to control the overall solid content at 120g / L, and then spray dry it at an air inlet temperature of 250℃. S4. The dried particles from step S3 are sintered. To verify that this application has low requirements for sintering conditions, two different sintering methods are used in this embodiment and each of the following embodiments: Method 1: The sintering process specifically includes the following steps: S4-1. Heat the temperature to 500℃ for a second heat treatment, and the heat treatment time is 10 hours. S4-2. Sintering is carried out at 1200℃ for 5 hours. After cooling, the product is pulverized to obtain the target product.

[0021] Method 2: The sintering process specifically includes the following steps: S4-1. Heat the temperature to 650℃ for a second heat treatment, and the heat treatment time is 1 hour. S4-2. Sintering is carried out at 1000℃ for 20 hours. After cooling, the product is pulverized to obtain the target product.

[0022] To verify the effect of the polymer resin in the system, the examples shown in Table 1 were set up. All of them were based on Example 1, with the polymer resin used and its mass intersecting with manganese adjusted, while keeping other reaction conditions unchanged.

[0023] It should be noted that, since polylactic acid is poorly soluble in water, in Examples 10 and 11, the additional solvent was replaced with a mixture of ethyl acetate and water in a volume ratio of 1:9.

[0024] Example 12 differs from Example 1 in that, in step S2, no ultrasonic treatment is applied during the precipitation process.

[0025] Example 13 differs from Example 1 in that, in step S2, the stirring speed is controlled at 150 rpm during the sedimentation process.

[0026] Experiments were conducted on Example 1 and the comparative example described above. The experimental part included two forms: density detection and electrical performance detection. The specific method for electrical performance detection is as follows: The above-mentioned positive electrode material was mixed uniformly with acetylene black and PVDF at a mass ratio of 8:1:1. Then, NMP was added as a solvent to adjust the solid content to 45%. The coating was applied to an aluminum foil with a thickness of 120 µm. After drying at 120℃ for 2 min + 80℃ for 2 min, the electrode was punched into a 14 mm electrode sheet. Lithium was used as the negative electrode, Celgard 2325 was selected as the separator, and the electrolyte system was 1M LiPF6 + EC / EMC / DMC + 2%VC + 1%LiPO2F2 (where EC:EMC:DMC = 3:4:3). The initial charge-discharge specific capacity was measured at room temperature in the voltage range of 0.1C and 2.0-4.8V. The capacity retention rate was measured after 100 cycles in the voltage range of 2.0C and 2.5-4.7V.

[0027] The results of the above embodiments and comparative examples are shown in Table 2.

[0028] The above experiments show that after adding a small amount of polymer resin, the sintering system can achieve stable sintering under two different sintering conditions. It has a high initial discharge specific capacity, a high retention rate after 100 cycles, and a high tap density. Therefore, it is proven that adding a certain amount of polymer can have a positive effect on the stability of sintering and reduce product defects caused by unstable temperature control during the sintering process.

[0029] Among a variety of polymers, PVA0588 and PVA1788 provide higher tap density overall. This may be because the polyhydroxyl groups with polyvinyl alcohol structure can form coordination structures with some metal ions in the early stage, which further adjusts the overall porosity. It may also be because polyvinyl alcohol has a better auxiliary effect on the polymer, which further improves the tap density. At the same time, due to the lower ash content during sintering, it exhibits stronger electrical properties overall.

[0030] Furthermore, by comparing Example 12 and Example 13, it can be seen that during the sedimentation process in the above examples, it is very necessary to apply high-speed stirring and ultrasonic treatment, which can significantly improve the tap density of the system and significantly enhance the dispersion performance of the organic system.

[0031] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a high-tap-density lithium-rich manganese-based cathode material, characterized in that, The chemical formula of the lithium-rich manganese-based cathode material is Li 1+x Mn y M z O r A w P q M can be any one of nickel, cobalt, iron, titanium, copper, molybdenum, chromium, zirconium, magnesium, and aluminum, and A can be any number of sulfur and boron; where 0 < x ≤ 1, 0 < y ≤ 1, 0 ≤ z < 0.5, 0 ≤ w ≤ 0.1, 0 ≤ q ≤ 0.1, and r = 1 + x + y + z. Its preparation method includes the following steps: S1. According to the chemical formula, take lithium, manganese and water-soluble or alcohol-soluble salts of component M, add solvent to dissolve them, and obtain the first slurry; S2. Add a precipitant to the first slurry for co-precipitation, wherein the precipitant contains the following components: a. At least one of sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, ammonium phosphate, ammonium hydrogen phosphate, and diammonium hydrogen phosphate; b. Water-soluble oxalate; c. A polymer resin, wherein the polymer resin is at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polylactic acid; S3. The dispersion system is dried in a spray dryer to obtain spherical precursor powder; S4. The precursor powder is sintered, cooled, and then pulverized to obtain the target product.

2. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S4, the sintering process involves two sintering steps, in the following order: S4-1. Heat the temperature to 500-650℃ for a second heat treatment, and the heat treatment time is 1-10 hours. S4-2. Sinter at a temperature not lower than 900℃ for 5 to 20 hours. After cooling, pulverize to obtain the target product.

3. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S2, the polymer resin is polyvinyl alcohol.

4. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 3, characterized in that, The mass of the polymer resin is 0.5 to 1% of the mass of manganese in the system.

5. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 3, characterized in that, In step S2, during the precipitation process, high-speed stirring is performed at 500–1000 rpm, and / or; In step S2, during the precipitation process, ultrasonic treatment at 60–100 kHz is applied, and / or; In step S2, the temperature is controlled at 80–100°C.

6. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, During the precipitation process in step S2, the pH value is controlled at 4 to 6.

7. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S3, the spray inlet air temperature is controlled at 200-250℃.

8. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S1, the water-soluble salt or alcohol-soluble salt is a nitrate, acetate, carbonate, or fluoride.

9. The method for preparing a high-tap-density lithium-rich manganese-based cathode material according to claim 1, characterized in that, Li 1+x Mn y M z O r A w P q In this system, M represents a nickel-cobalt mixture, where the molar amount of nickel is 0.2 to 0.3 times that of manganese, and the molar amount of cobalt is 0.2 to 0.3 times that of manganese. And / or, A is boron, and in the system 0.001≤w≤0.002, 0.001≤q≤0.

002.

10. The high tap density lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 9.

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