Preparation method of iron stearate modified lithium-rich manganese-based positive electrode material

Abstract

The invention provides a preparation method of an iron stearate modified lithium-rich manganese-based positive electrode material, which comprises the following steps: placing an original lithium-rich manganese-based material in an alcoholic solution of iron stearate, carrying out ultrasonic treatment, carrying out suction filtration, and carrying out secondary calcination on the obtained solid phase to obtain the iron stearate modified lithium-rich manganese-based positive electrode material. The iron source and the environment are optimized to perform synchronous interaction influence on the doping and coating processes, so that the microdynamics is changed, and the first coulombic efficiency of the lithium-rich manganese-based material is improved.

Description

Technical Field

[0001] The invention belongs to the field of preparation of lithium ion battery positive electrode materials, and particularly relates to a preparation method of an iron stearate modified lithium-rich manganese-based positive electrode material, and particularly relates to a preparation method of an iron stearate modified lithium-rich manganese-based positive electrode material with high first coulombic efficiency. Background Art

[0002] Lithium-ion batteries are mainly composed of positive electrode materials, negative electrode materials, electrolytes, separators, etc. Among them, the positive electrode material is the key to lithium-ion batteries, and its cost accounts for about half of the entire battery. The discharge specific capacity of the positive electrode material also determines the energy density of the entire battery.

[0003] At present, lithium iron phosphate LiFeO4 and ternary NCM are the more common positive electrode materials in the lithium-ion battery industry. Although lithium iron phosphate LiFeO4 has the advantages of long service life and high safety, after years of development, its energy density has approached the theoretical value and is difficult to meet the current market demand. The energy density of ternary NCM is higher, but it contains expensive cobalt elements and has a high cost. In addition, it also faces the problem of thermal stability. In this context, lithium-rich manganese-based Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 has attracted much attention due to its high energy density and low cost, and is regarded as the next generation of positive electrode materials. However, lithium-rich manganese-based positive electrode materials have problems with low initial coulombic efficiency, poor cycle life, and poor rate performance in their applications, which seriously affect the commercialization process of lithium-rich manganese-based materials. Some technologies use different ion doping to improve the electrochemical properties of lithium-rich manganese-based positive electrode materials, but the doping modification effects of different ions are not the same. Doped ions from different sources also have unpredictable effects on electrochemical performance. Differences in structural adaptability, thermal stability, and reaction kinetics make it difficult to achieve the expected improvement and optimization of the doping effect.

[0004] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing an iron stearate-modified lithium-rich manganese-based positive electrode material with low cost and high first coulombic efficiency.

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

[0007] A method for preparing an iron stearate modified lithium-rich manganese-based positive electrode material comprises the following steps:

[0008] The original lithium-rich manganese-based material is placed in an alcohol solution of iron stearate, and filtered after ultrasonication. The obtained solid phase is calcined twice to obtain an iron stearate-modified lithium-rich manganese-based positive electrode material.

[0009] In some embodiments, the original lithium-rich manganese-based material has the following general formula: Li 1+x Ni y Co z Mn 1-x-y-z O2, 0<x≤0.3, 0<y≤0.2, 0<z≤0.2, x+y+z<0.5; It is beneficial to improve the specific capacity and working voltage platform of lithium-rich manganese-based. Further preferred, 0.05<x≤0.3, 0.1<y≤0.15, 0.1<z≤0.15, x+y+z<0.5, the optimized ratio is beneficial to further optimize and improve the structural stability and lithium content of the original lithium-rich manganese-based material.

[0010] In some embodiments, the concentration of iron stearate in the alcohol solution of iron stearate is 0.001-0.002 mol / L. A good concentration is conducive to enhancing the coordination effect of the alcohol solvent on iron stearate on the surface of the lithium-rich manganese-based material. The alcohol solution includes but is not limited to small molecule alcohol solutions such as ethanol solution and methanol solution.

[0011] In some schemes, the ultrasonic time is preferably more than 1 hour, which is conducive to the full dispersion and adhesion of each material in the solvent.

[0012] In some schemes, the secondary calcination temperature is 340-390°C and the time is 60-120 minutes. The optimized calcination conditions are conducive to the fully stable doping of iron ions, and are also conducive to the decomposition of stearate to form a good carbon coating and a stable doping layer.

[0013] In some embodiments, the original lithium-rich manganese-based material can be directly purchased or prepared by itself. As an exemplary preparation method, the manganese-based precursor material and lithium carbonate can be fully mixed according to the stoichiometric ratio of the manganese-based precursor with a slight excess, and then sintered once.

[0014] Among them, the manganese-based precursor can be a nickel-cobalt-manganese carbonate compound, a representative general formula of which is Ni α Co β Mn γ CO3, 0.1≤α≤0.2, 0.1≤β≤0.2, 0.6≤γ≤0.8, α+β+γ=1.

[0015] Among them, the feeding ratio of manganese-based precursor material to lithium carbonate is preferably a molar ratio of (1.3-1.6):1.

[0016] Among them, the staged heating in the primary sintering process is beneficial to the structural integrity and performance optimization of the original lithium-rich manganese-based material. The primary sintering program can be set as: 330-380℃ insulation for 4-6h, 790-810℃ insulation for 4-6h, 820-840℃ insulation for 4-12h, and the heating rate is 3-10° / min.

[0017] Beneficial effects of the present invention:

[0018] The present invention firstly adopts a specific iron source, ferrous stearate, to dope and modify the lithium-rich manganese-based material. Ferrous stearate is a long-chain fatty acid iron salt. During the reaction, the long chain of ferrous stearate is opened to generate long chains and free iron ions. The long chain itself contains more carbon, which can be further deposited on the surface of the lithium-rich manganese-based material to play a role of carbon coating, thereby improving the ionic conductivity of the lithium-rich manganese-based material. Under the combined action of ultrasound, the above-mentioned unique structure, and the environment mediated by the alcohol solvent, the iron ions are attached to the surface of the lithium-rich manganese-based material, and after secondary sintering, they play a better role of surface doping. The iron ion doping can expand the interlayer spacing of the lithium-rich manganese-based material, which is beneficial to Li + The transport of Li can also inhibit the migration of Ni to the Li layer to a certain extent; in addition, the bond energy of iron-oxygen bond (397.5 kJ / mol) is higher than that of nickel-oxygen (366 kJ / mol) and manganese-oxygen (362 kJ / mol), which is beneficial to inhibit the precipitation of lattice oxygen in the first cycle of lithium-rich manganese-based materials.

[0019] Therefore, the present invention adopts an ultrasonic method to carry out liquid phase treatment of iron stearate modified lithium manganese-based materials combined with secondary sintering, which simultaneously plays the role of doping and coating, and the doping and coating processes synchronously interact with each other, changing the microdynamics. The method is simple and effective, and improves the first coulombic efficiency of the lithium-rich manganese-based material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the first charge and discharge curve of the lithium-rich manganese-based positive electrode material modified by iron stearate in the embodiment of the present invention and the comparative example;

[0021] Figure 2 It is the X-ray diffraction analysis of the lithium-rich manganese-based positive electrode material modified by iron stearate in the embodiment of the present invention and the comparative example;

[0022] Figure 3 is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 1);

[0023] Figure 4 is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 2);

[0024] Figure 5 is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 3);

[0025] Figure 6 is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 4);

[0026] Figure 7is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 5);

[0027] Figure 8 is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 6);

[0028] Fig. 9 It is a SEM image of the iron stearate modified lithium-rich manganese-based positive electrode material of the present invention (corresponding to Example 7). DETAILED DESCRIPTION

[0029] Example 1

[0030] (1) Preparation of raw materials

[0031] Weigh 10gNi 0.16 Co 0.16 Mn 0.68 CO3 precursor, 4.588g Li2CO3 were put into the ball mill for ball milling, 300r for one hour and 350r for one hour, the ball-to-material ratio was 1:1, and sintering was performed after mixing evenly. The sintering procedure was 350° for 5h, 800° for 5h, 825° for 8h, and the heating rate was 5° / min. After sintering, the original Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based materials.

[0032] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0033] Dissolve iron stearate in alcohol to prepare a 0.0013 mol / L solution. Put the original material into the solution for ultrasonication. After ultrasonication for 2 hours, filter the solution three times, filter out the original material, and calcine it at 365° for 60 minutes. During the whole process, compressed air is blown into the muffle furnace, and the furnace is cooled to obtain the iron stearate modified lithium-rich manganese-based positive electrode material.

[0034] 1. Assemble CR2032 stainless steel button battery

[0035] (1) Production of positive electrode sheets for lithium-ion batteries:

[0036] The iron stearate modified lithium-rich manganese-based positive electrode material, Super P, and PVDF were weighed in a mass ratio of 8:1:1 and placed in a mixing tank. Two zirconia beads with a diameter of 4 mm were added. After mixing with a degassing machine, they were coated on aluminum foil with a 50μm scraper. They were dried in a blast drying oven at 80° for 2h and vacuum dried at 120° for 7h. After drying, they were cut into 12mm diameter pole pieces to obtain the positive electrode of the lithium-ion battery.

[0037] (2) Assemble CR2032 stainless steel button battery

[0038] Using the metal lithium sheet as the negative electrode, 30μL of 1.2mol LiFP6 in FEC:EMC=2:8 basic electrolyte was dripped into it, and the CR2032 stainless steel button battery was assembled in a glove box filled with argon gas and with a moisture content of less than 0.01ppm. After standing at 25℃ for 5h, its charge and discharge performance was tested.

[0039] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0040] The first discharge capacity at a current density of 25 mA / g was 291.43 mAh / g, and the first coulombic efficiency was 88.09%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g was 234.41 mAh / g.

[0041] Example 2

[0042] (1) Preparation of raw materials

[0043] The preparation of the original material is the same as in Example 1.

[0044] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0045] The difference from Example 1 is that the concentration of iron stearate is 0.0015 mol / L.

[0046] 1. Assemble the CR2032 stainless steel button battery as in Example 1.

[0047] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0048] The first discharge capacity at a current density of 25 mA / g is 299.55 mAh / g, and the first coulombic efficiency is 88.92%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 240.75 mAh / g.

[0049] Example 3

[0050] (1) Preparation of raw materials

[0051] The preparation of the original material is the same as in Example 1

[0052] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0053] The difference from Example 1 is that the concentration is 0.0017 mol / L.

[0054] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0055] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0056] The first discharge capacity at a current density of 25 mA / g is 294.74 mAh / g, and the first coulombic efficiency is 88.17%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 236.98 mAh / g.

[0057] Example 4

[0058] (1) Preparation of raw materials

[0059] The preparation of the original material is the same as in Example 1

[0060] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0061] The difference from Example 2 is that the concentration is 345°C and the secondary sintering temperature is kept at 60 minutes.

[0062] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0063] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0064] The first discharge capacity at a current density of 25 mA / g is 297.13 mAh / g, and the first coulombic efficiency is 89.02%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 240.75 mAh / g.

[0065] Example 5

[0066] (1) Preparation of raw materials

[0067] The preparation of the original material is the same as in Example 1

[0068] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0069] The difference from Example 2 is that the secondary sintering temperature is 385° and the temperature is maintained for 60 minutes.

[0070] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0071] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0072] The first discharge capacity at a current density of 25 mA / g is 295.94 mAh / g, and the first coulombic efficiency is 88.41%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 236.47 mAh / g.

[0073] Example 6 Iron stearate lithium-rich manganese-based modified sample

[0074] (1) Preparation of raw materials

[0075] The preparation of the original material is the same as in Example 1

[0076] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0077] The difference from Example 2 is that the secondary sintering holding time is 90 minutes.

[0078] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0079] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0080] The first discharge capacity at a current density of 25 mA / g is 292.31 mAh / g, and the first coulombic efficiency is 88.72%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 234.17 mAh / g.

[0081] Example 7

[0082] (1) Preparation of raw materials

[0083] The preparation of the original material is the same as in Example 1

[0084] (2) Preparation of lithium-rich manganese-based positive electrode materials modified by iron stearate

[0085] The difference from Example 2 is that the secondary sintering holding time is 120 minutes.

[0086] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0087] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0088] The first discharge capacity at a current density of 25 mA / g is 293.94 mAh / g, and the first coulombic efficiency is 88.46%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 236.89 mAh / g.

[0089] Comparative Example 1

[0090] (1) Preparation of raw materials

[0091] The preparation of the original material is the same as in Example 1

[0092] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0093] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0094] The first discharge capacity at a current density of 25 mA / g is 293.94 mAh / g, and the first coulombic efficiency is 88.46%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 236.89 mAh / g.

[0095] Comparative Example 2

[0096] (1) Preparation of raw materials

[0097] The preparation of the original material is the same as in Example 1

[0098] (2) Preparation of stearic acid-modified lithium-rich manganese-based positive electrode materials

[0099] Dissolve stearic acid in alcohol to prepare a 0.0015 mol / L solution. Place the original material in the solution for ultrasonic treatment. After ultrasonic treatment for 2 hours, filter the solution three times to remove the original material, and calcine at 370° for 60 minutes. During the whole process, compressed air is blown into the muffle furnace, and the furnace is cooled to obtain a stearic acid-modified lithium-rich manganese-based positive electrode material.

[0100] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0101] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0102] The first discharge capacity at a current density of 25 mA / g is 293.94 mAh / g, and the first coulombic efficiency is 88.46%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 236.89 mAh / g.

[0103] Comparative Example 3

[0104] (1) Preparation of raw materials

[0105] The preparation of the original material is the same as in Example 1

[0106] (2) Preparation of iron oleate-modified lithium-rich manganese-based cathode materials

[0107] Dissolve ferric oleate in alcohol to prepare a 0.0015 mol / L solution. Put the original material into the solution for ultrasonic treatment. After ultrasonic treatment for 2 hours, filter the solution three times to filter out the original material and calcine it at 370° for 60 minutes. During the whole process, compressed air is blown into the muffle furnace, and the furnace is cooled to obtain a stearic acid-modified lithium-rich manganese-based positive electrode material.

[0108] 1. Assemble CR2032 stainless steel button battery as in Example 1.

[0109] 2. Electrochemical performance test of CR2032 stainless steel button battery

[0110] The first discharge capacity at a current density of 25 mA / g is 226.14 mAh / g, and the first coulombic efficiency is 78.52%. After three activations at 25 mA / g, the first discharge capacity at a current density of 250 mA / g is 159.88 mAh / g.

[0111] Table 1 Electrochemical performance of the embodiments of the present invention and the comparative examples

[0112]

[0113] It can be seen from Examples 1-7 of the present invention that the iron stearate modified lithium-rich manganese-based positive electrode material prepared by the present invention shows excellent first discharge specific capacity and first coulomb efficiency. The material has a first coulomb efficiency of more than 88% at 0.1C, and a first discharge specific capacity of more than 234 mAh / g at 1C. With iron stearate as the iron source dopant, the 003 / 104 crystal plane ratio in the layered structure of the material reaches 1.55-2.02 ( Figure 2 ), which is conducive to the diffusion and transmission of lithium ions. SEM shows that the material has uniform particles and surface morphology ( Figure 3-9 ), which is beneficial to improve the electrochemical stability of the material.

[0114] Comparative Example 1 is the original lithium-rich manganese-based material, Comparative Example 2 is the stearic acid-modified lithium-rich manganese-based material, and Comparative Example 3 is the iron oleate modification. The three have no obvious improvement in the first effect. And the unsuitable modification method is like Comparative Example 3. Although iron oleate and iron stearate are both long-chain fatty acid iron salts, the modified material has a certain degree of performance reduction compared to the original lithium-rich manganese-based material of Comparative Example 1.

[0115] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. Although the embodiments of the present invention have been shown and described above, it can be understood that the above-described embodiments are exemplary and cannot be understood as limitations of the present invention. Those of ordinary skill in the art can change, modify, replace and deform the above-described embodiments within the scope of the present invention. In addition, those of ordinary skill in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

Claims

1. A method for preparing a lithium-rich manganese-based positive electrode material modified by iron stearate, comprising the following steps: The original lithium-rich manganese-based material is placed in an alcohol solution of iron stearate, and filtered after ultrasonication. The obtained solid phase is calcined twice to obtain an iron stearate-modified lithium-rich manganese-based positive electrode material.

2. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The original lithium-rich manganese-based material has the following general formula: Li 1+x Ni y Co z Mn 1-x-y-z O2, 0<x≤0.3, 0<y≤0.2, 0<z≤0.2, x+y+z<0.5; More preferably, 0.05<x≤0.3, 0.1<y≤0.15, 0.1<z≤0.15, x+y+z<0.

5.

3. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: In the alcohol solution of ferric stearate, the concentration of ferric stearate is 0.001-0.002 mol / L.

4. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The alcohol solution includes one or more of an ethanol solution and a methanol solution.

5. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The ultrasonic time is more than 1h.

6. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The secondary calcination temperature is 340-390°C and the time is 60-120min.

7. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The original lithium-rich manganese-based material is obtained by the following method: a manganese-based precursor material and lithium carbonate are fully mixed according to a stoichiometric ratio in which the manganese-based precursor is slightly excessive, and then sintered once.

8. The method for preparing the iron stearate modified lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: The manganese-based precursor is a nickel-cobalt-manganese carbonate compound with the general formula Ni α Co β Mn γ CO3, 0.1≤α≤0.2, 0.1≤β≤0.2, 0.6≤γ≤0.8, α+β+γ=1; The feeding ratio of the manganese-based precursor material to lithium carbonate is a molar ratio (1.3-1.6): 1; The primary sintering procedure is: 330-380°C for 4-6h, 790-810°C for 4-6h, 820-840°C for 4-12h, and a heating rate of 3-10° / min.

9. The iron stearate modified lithium-rich manganese-based positive electrode material obtained by the method according to any one of claims 1 to 8.

10. The iron stearate modified lithium-rich manganese-based positive electrode material according to claim 9, characterized in that: The material has a first coulombic efficiency of more than 88% at 0.1C; Further preferably, the material has a first discharge specific capacity of greater than 234 mAh / g at 1C, and a 003 / 104 crystal plane ratio in the layered structure of the material reaches 1.55-2.02.

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