A cathode material for lithium-ion batteries and a preparation method thereof

Abstract

The present invention discloses a cathode material for a lithium-ion battery and a preparation method thereof, belonging to the field of battery materials. The preparation method includes the following steps: (1) preparing a solution A by using manganese sulfate monohydrate and polyvinylpyrrolidone in water, adding a potassium ferricyanide solution to the solution A in a titration form and stirring for reaction, aging, filtering, and washing after the reaction is complete to obtain manganese ferricyanide; (2) dispersing manganese ferricyanide, a nickel source, a lithium source, polyimide, and an anionic surfactant uniformly in water and performing ball milling treatment, and then keeping the temperature at 750-950 °C for 15-20 h to obtain the cathode material for the lithium-ion battery. The material has a multi-layer flaky structure, which is beneficial to full contact with the electrolyte and can also effectively relieve the stress caused by the volume change of the cathode material during charge and discharge; in addition, the iron phase in the material can be stabilized in the oxide ion framework and maintain a higher valence state, and the nitrogen-containing carbon coating layer can make the charge and discharge capacity higher.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and particularly to a cathode material for a lithium-ion battery and a preparation method thereof. Background Art

[0002] Lithium cobalt oxide is the earliest commercialized cathode material for lithium-ion batteries. It has high energy density and good performance. However, due to the high toxicity and low resource content of cobalt itself, in order to reduce the cost of the material, nickel and manganese elements are used to dope and modify lithium cobalt oxide to reduce the relative content of cobalt. At the same time, the three metal elements can have a synergistic effect, and the prepared ternary material can also exhibit good electrochemical performance.

[0003] With the deepening of research, people began to use iron to completely replace cobalt in the ternary material. The prepared Li-Fe-Ni-Mn-O material has performance comparable to that of commercial ternary materials, and at the same time has lower production costs and higher safety. However, the introduction of iron directly leads to a change in the morphology of the ternary material, making it impossible to maintain a good layered structure, resulting in the inability to ensure its electrochemical stability during use. At the same time, iron itself also has certain instability, and it is easy to appear heterophase during the preparation process, affecting the product performance. Summary of the Invention

[0004] Based on the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a layered lithium-ion battery cathode Li-Fe-Ni-Mn-O composite material. This preparation method uses manganese ferrocyanide with a special morphology as the basic structure, and at the same time introduces a cross-linked nitrogen-containing polymer polyimide and a specific surfactant for mixing the precursors. Through the high-temperature solid-phase method, a Li-Fe-Ni-Mn-O composite material with a multi-layered flake structure can be effectively obtained. The synthesis path of this material is simple, and the multi-layered flake structure is conducive to the full contact of the electrolyte and can also effectively relieve the stress caused by the volume change of the cathode material during charge and discharge. In addition, through the doping and stabilization of nickel and manganese phases, the iron phase in the material can be effectively stabilized in the oxide ion framework and maintain a high valence state. Cooperating with the nitrogen-containing carbon coating layer with high conductivity can make the charge and discharge capacity higher. To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0005] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] A preparation method of a cathode material for a lithium-ion battery, comprising the following steps:

[0007] (1) Prepare solution A by dissolving manganese sulfate monohydrate and polyvinylpyrrolidone in water. Add a potassium ferrocyanide solution to solution A in a titration form and stir to react. After the reaction is complete, age, filter, and wash to obtain manganese ferrocyanide;

[0008] (2) Uniformly disperse manganese ferricyanide, nickel source, lithium source, polyimide, and anionic surfactant in water and perform ball milling treatment. Subsequently, keep the temperature at 750 - 950 °C for 15 - 20 h to obtain the positive electrode material for the lithium-ion battery.

[0009] In the preparation method of the positive electrode material for the lithium-ion battery of the present invention, in addition to serving as an iron source and a manganese source, the manganese ferricyanide obtained by the method has a special cubic nanostructure, and the interior of the structure is hollow. When it contacts and reacts with the nickel source and the lithium source, it can effectively improve the reaction diffusion degree of lithium ions. When the final Li-Fe-Ni-Mn-O composite material is sintered and synthesized, the cubic hollow nanostructure collapses due to stress and gradually transforms into multi-layered sheet-like structure fragments, effectively increasing the area of the product when contacting the electrolyte and alleviating the volume change stress during charge and discharge of the material; in addition, in the existing iron-doped Li-Fe-Ni-Mn-O or Li-Fe-Co-Ni-Mn-O materials, it is difficult to maintain a high valence state of the iron phase. However, in the technical solution of the present invention, the iron source is introduced in the form of manganese ferricyanide, and through the combination of manganese and the nickel element in the raw materials, the iron phase can be effectively maintained in the oxide ion framework, and the charge and discharge capacity of the overall material is effectively improved.

[0010] On the other hand, in the process of synthesizing ternary materials or Li-Fe-Ni-Mn-O materials by the traditional solid-phase method, the lithium source is usually introduced into the precursor by ball milling. Although this method is simple to operate, it is very easy to cause poor mixture uniformity and result in more raw material losses. The existing solutions mostly introduce organic solvents and some surfactants as dispersants to alleviate particle agglomeration. However, for the components dissolved in the solvent, they will also be lost as the solvent volatilizes or is consumed. For the insoluble components, they will still gradually stay at the bottom of the reaction vessel during ball milling, and the improvement of dispersion is limited. Therefore, the preparation method of the product of the present invention uses polyimide as an intermediate. In the case of water as the dispersion phase, polyimide can effectively crosslink or entrap each Li-Fe-Ni-Mn-O ternary positive electrode material precursor, and maintain good dispersibility under the action of the hydrophobic groups generated by the anionic surfactant (since the anionic surfactant is easy to generate hydrophobic groups in water, for water-soluble polyimide, it can effectively crosslink each precursor source when dissolved in water, and for oil-soluble polyimide, under the action of the hydrophobic groups, it can also be stably dispersed in water in molecular form and entrap each precursor source. Both action modes can effectively improve the dispersibility of the precursor source during mixing). After high-temperature sintering, the polyimide is transformed into a nitrogen-containing conductive carbon layer, which can not only protect the material structure but also effectively improve the conductivity of the overall material.

[0011] Preferably, the molar ratio of manganese sulfate monohydrate to the mass of polyvinylpyrrolidone in the solution A is (0.0025 - 0.0035) mol:(1 - 5) g, and the concentration of the solution A is 10 - 15 g / L.

[0012] Preferably, the concentration of the potassium ferricyanide solution is 5 - 10 g / L.

[0013] Preferably, the molar ratio of the sum of iron and manganese elements in manganese ferricyanide to the nickel element in the nickel source is n(Mn + Fe):n(Ni) = (9:1) - (8:2).

[0014] Preferably, the molar ratio of manganese, iron, nickel elements in manganese ferricyanide and nickel source, and lithium element in the lithium source is: n(Mn + Fe + Ni):n(Li) = 1:(1 - 1.05).

[0015] The Li-Fe-Ni-Mn-O composite material prepared with the above raw material ratio has a relatively high content of manganese element, which can effectively improve the discharge capacity and cycle stability of the overall material.

[0016] Preferably, the nickel source is at least one of nickel acetate and nickel carbonate; the lithium source is at least one of lithium acetate and lithium carbonate.

[0017] Preferably, the anionic surfactant is at least one of carboxylate anionic surfactants and sulfonate anionic surfactants.

[0018] Preferably, the mass ratio of manganese ferricyanide, nickel source, lithium source, polyimide and anionic surfactant is: m(manganese ferricyanide + nickel source + lithium source):m(polyimide):m(anionic surfactant) = 1:(0.4 - 0.6):(0.4 - 0.6).

[0019] The appropriate introduction of polyimide and anionic surfactant can effectively improve the dispersibility and uniformity of the raw materials during the dispersion process, and at the same time, it will not cause the raw materials to be completely separated from the water system and adhere to the grinding wall.

[0020] Another object of the present invention also lies in providing a lithium-ion battery cathode material prepared by the preparation method of the lithium-ion battery cathode material.

[0021] The Li-Fe-Ni-Mn-O composite material for lithium-ion battery cathode prepared by the method of the present invention constructs an ideal multi-layered structure through special raw material selection and synthesis process, effectively ensuring the stable performance of the product during lithium ion deintercalation and extraction. At the same time, due to the introduction of iron source in the form of manganese ferrocyanide and the use of N-containing polymer as an auxiliary processing reagent, the iron phase stability in the obtained material is high and the overall material purity is high. At the same time, due to the introduction of nitrogen element, the conductivity of the overall material is also significantly improved.

[0022] Another object of the present invention is to provide a positive electrode plate for a lithium-ion battery, wherein the positive electrode plate is prepared from the positive electrode material for a lithium-ion battery of the present invention.

[0023] The beneficial effect of the present invention is that the present invention provides a preparation method of a lithium ion battery positive electrode material with a layered structure. The preparation method uses manganese ferrocyanide with a special morphology as a basic structure, and introduces a cross-linked nitrogen-containing polymer polyimide and a specific anionic surfactant to mix the precursors. A Li-Fe-Ni-Mn-O composite material with a multilayer sheet structure can be effectively obtained by a high-temperature solid phase method. The material has a multilayer sheet structure, which is conducive to full contact with the electrolyte and can also effectively alleviate the stress caused by the volume change of the positive electrode material during the charge and discharge process; in addition, the iron phase in the material can be effectively stabilized in the oxide ion framework and maintain a higher valence state, and the high conductivity nitrogen-containing coated carbon layer can make the charge and discharge capacity higher. DETAILED DESCRIPTION

[0024] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, the purpose of which is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents, raw materials and instruments designed for the implementation of the present invention and comparative examples are all commonly used ordinary reagents, raw materials and instruments unless otherwise specified.

[0025] Example 1

[0026] An embodiment of the lithium ion battery positive electrode material and the preparation method thereof according to the present invention comprises the following steps:

[0027] (1) 0.003 mol of manganese sulfate monohydrate and 3 g of polyvinyl pyrrolidone are mixed with water and a small amount of ethanol to prepare a solution A with a concentration of 12 g / L, 12 g / L of potassium ferrocyanide solution is added to the solution A in a titration form and stirred to react until the turbidity of the solution no longer changes. After the reaction is complete, the solution is aged at room temperature for 24 hours, filtered, washed with water and ethanol respectively, and dried to obtain manganese ferrocyanide;

[0028] (2) Place manganese ferricyanide, nickel acetate, lithium acetate, polyimide, and anionic surfactant dodecyl glycidyl ether DEG (Senfeida Chemical Industry) in a ball milling jar, add 5 times the mass of water, disperse evenly, and perform ball milling treatment at a rate of 200 rpm for 24 h using a planetary ball mill. After drying the obtained mixed slurry at room temperature for 24 h, place it in an air atmosphere and keep it at 850 °C for 18 h to obtain the positive electrode material for the lithium-ion battery. Among them, according to the theoretical reaction product chemical formula Li(Mn 0.48 Fe 0.32 Ni 0.2 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 8:2; the mass ratio of manganese ferricyanide, nickel source, lithium source, polyimide, and anionic surfactant is: m(manganese ferricyanide + nickel source + lithium source):m(polyimide):m(anionic surfactant) = 1 g:0.5 g:0.5 g.

[0029] Example 2

[0030] The difference between this example and Example 1 is only that, according to the theoretical reaction product chemical formula Li(Mn 0.51 Fe 0.34 Ni 0.15 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 8.5:1.5.

[0031] Example 3

[0032] The difference between this example and Example 1 is only that, according to the theoretical reaction product chemical formula Li(Mn 0.54 Fe 0.36 Ni 0.1 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 9:1.

[0033] Example 4

[0034] The difference between this example and Example 1 is only that, according to the theoretical reaction product chemical formula Li(Mn 0.57 Fe 0.38 Ni 0.05 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 9.5:0.5.

[0035] Example 5

[0036] The difference between this embodiment and Embodiment 1 is only that the mass ratio of manganese ferrocyanide, nickel source, lithium source, polyimide and anionic surfactant is: m(manganese ferrocyanide + nickel source + lithium source): m(polyimide): m(anionic surfactant) = 1 g: 0.6 g: 0.6 g.

[0037] Example 6

[0038] The difference between this embodiment and Embodiment 1 is only that the mass ratio of manganese ferrocyanide, nickel source, lithium source, polyimide and anionic surfactant is: m(manganese ferrocyanide + nickel source + lithium source): m(polyimide): m(anionic surfactant) = 1 g: 0.8 g: 0.8 g.

[0039] Comparative Example 1

[0040] A lithium-ion battery cathode material and a preparation method thereof, comprising the following steps:

[0041] Put ferric acetate, manganese acetate, nickel acetate, lithium acetate, polyimide and anionic surfactant dodecyl glycerol ether into a ball milling tank, add 5 times the mass of water to disperse evenly, and use a planetary ball mill to carry out ball milling treatment at a rate of 200 rpm for 24 h. The obtained mixed slurry is dried at room temperature for 24 h and then placed in an air atmosphere and kept warm at 850 °C for 18 h to obtain the lithium-ion battery cathode material; among them, the metal elements in each mixture are calculated according to the theoretical reaction product chemical formula Li(Mn 0.48 Fe 0.32 Ni 0.2 )O2, and the element ratio is n(Mn + Fe + Ni): n(Li) = 1:1, n(Mn + Fe): n(Ni) = 8:2; the mass ratio of iron source, manganese source, nickel source, lithium source, polyimide and anionic surfactant is: m(iron source + manganese source + nickel source + lithium source): m(polyimide): m(anionic surfactant) = 1 g: 0.5 g: 0.5 g.

[0042] Comparative Example 2

[0043] A lithium-ion battery cathode material and a preparation method thereof, comprising the following steps:

[0044] (1) Prepare a solution A with a concentration of 12 g / L by using 0.003 mol of manganese sulfate monohydrate and 3 g of polyvinylpyrrolidone with water and a small amount of ethanol. Add a 12 g / L potassium ferricyanide solution to solution A in a titration form and stir the reaction until the turbidity of the solution no longer changes. After the reaction is complete, age at room temperature for 24 h, filter, wash with water and ethanol respectively, and dry to obtain manganese ferrocyanide;

[0045] (2) Place manganese ferricyanide, nickel acetate, lithium acetate, and polyimide in a ball milling jar, add 5 times the mass of water to disperse evenly, and perform ball milling treatment at a rate of 200 rpm for 24 h using a planetary ball mill. After the obtained mixed slurry is dried at room temperature for 24 h, it is placed in an air atmosphere and kept at 850 °C for 18 h to obtain the positive electrode material for the lithium-ion battery; among them, according to the theoretical reaction product chemical formula Li(Mn 0.48 Fe 0.32 Ni 0.2 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 8:2; the mass ratio of manganese ferricyanide, nickel source, lithium source, and polyimide is: m(manganese ferricyanide + nickel source + lithium source):m(polyimide) = 1 g:0.5 g.

[0046] Comparative Example 3

[0047] A positive electrode material for a lithium-ion battery and a preparation method thereof, comprising the following steps:

[0048] (1) Prepare solution A with a concentration of 12 g / L by using 0.003 mol of manganese sulfate monohydrate and 3 g of polyvinylpyrrolidone with water and a small amount of ethanol. Add a 12 g / L potassium ferricyanide solution to solution A in a titration form and stir the reaction until the turbidity of the solution no longer changes. After the reaction is complete, age at room temperature for 24 h, filter, wash with water and ethanol respectively, and after drying, obtain manganese ferricyanide;

[0049] (2) Place manganese ferricyanide, nickel acetate, lithium acetate, and anionic surfactant dodecyl glycidyl ether in a ball milling jar, add 5 times the mass of water to disperse evenly, and perform ball milling treatment at a rate of 200 rpm for 24 h using a planetary ball mill. After the obtained mixed slurry is dried at room temperature for 24 h, it is placed in an air atmosphere and kept at 850 °C for 18 h to obtain the positive electrode material for the lithium-ion battery; among them, according to the theoretical reaction product chemical formula Li(Mn 0.48 Fe 0.32 Ni 0.2 )O2, the ratio of each element is calculated as n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 8:2; the mass ratio of manganese ferricyanide, nickel source, lithium source, and anionic surfactant is: m(manganese ferricyanide + nickel source + lithium source):m(anionic surfactant) = 1 g:0.5 g.

[0050] Comparative Example 4

[0051] An embodiment of the positive electrode material for a lithium-ion battery and a preparation method thereof according to the present invention, comprising the following steps:

[0052] (1) Dissolve 0.003 mol of manganese sulfate monohydrate and 3 g of polyvinylpyrrolidone in water and a small amount of ethanol to prepare solution A with a concentration of 12 g / L. Add a 12 g / L potassium ferricyanide solution to solution A in a titration form and stir to react until the turbidity of the solution no longer changes. After the reaction is complete, age at room temperature for 24 h, filter, wash with water and ethanol respectively, and dry to obtain manganese ferricyanide;

[0053] (2) Place manganese ferricyanide, nickel acetate, lithium acetate, polyimide, and non-ionic surfactant AEO-9 (Daixu Chemical) in a ball milling tank, add 5 times the mass of water to disperse evenly, and use a planetary ball mill to perform ball milling treatment at a rate of 200 rpm for 24 h. The obtained mixed slurry is dried at room temperature for 24 h and then placed in an air atmosphere and kept at 850 °C for 18 h to obtain the positive electrode material of the lithium-ion battery; among them, according to the theoretical reaction product chemical formula Li(Mn 0.48 Fe 0.32 Ni 0.2 )O2, the element ratio of each element is n(Mn + Fe + Ni):n(Li) = 1:1, n(Mn + Fe):n(Ni) = 8:2; the mass ratio of manganese ferricyanide, nickel source, lithium source, polyimide, and non-ionic surfactant is: m(manganese ferricyanide + nickel source + lithium source):m(polyimide):m(non-ionic surfactant) = 1 g:0.5 g:0.5 g.

[0054] Effect Example 1

[0055] To verify the electrochemical performance of the positive electrode material of the lithium-ion battery described in the present invention, mix the materials of each example and comparative example with conductive carbon black and PVDF according to a mass ratio of 8:1:1, add an appropriate amount of NMP to adjust the slurry, coat it on an aluminum foil, cut it after drying to prepare a positive electrode sheet, use a lithium metal as the negative electrode sheet, and a commercial polypropylene film as the separator to assemble a lithium-ion coin-type half cell. After the obtained battery is left standing for 12 h, perform 100 charge-discharge cycle tests at a voltage of 2 - 4.5 V and a rate of 0.2C at room temperature, then increase the rate to 1C and cycle 5 times, and finally return to a rate of 0.2C and cycle 5 times. The results are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] As can be seen from Table 1, the initial discharge specific capacity of the products obtained in each example is relatively high at low magnification, reaching over 155 mAh / g, and the capacity retention rate after 100 cycles also reaches over 80%. When the product undergoes high magnification cycling and then returns to low magnification cycling, its discharge specific capacity remains considerable, reaching up to 145 mAh / g at most. From Examples 1 to 4, it can be seen that as the nickel element content in the product decreases, its cycling stability improves to a certain extent, but the discharge capacity decreases. Considering the comprehensive performance, the product has better performance when n(Mn + Fe):n(Ni) is 9:1 - 8:2. From the comparison of the product performances of Example 1 with Examples 5 and 6, as the addition amounts of polyimide and surfactant increase excessively, the dispersibility of each precursor of the product is better, and the nitrogen element doping content also becomes higher. However, relatively speaking, it may cause the complete separation of each precursor from the aqueous phase during the mixing process, and the degree of uniform mixing becomes lower, which also affects the cycling performance and rate performance of the product. In contrast, the product of Comparative Example 1 was prepared using ordinary raw materials. Although surfactants and polyimide were finally introduced, the overall effect was poor, with poor cycling performance, low initial capacity, and poor rate performance. In Comparative Examples 2 and 3, surfactants and polyimide were not introduced respectively during the grinding and mixing of the precursors. Compared with the product of Example 1, their cycling performance and rate performance deteriorated significantly. The initial discharge specific capacity of the product of Comparative Example 3 was low, indicating that the lack of nitrogen element doping also affects the initial capacity of the product. The only difference between the product of Comparative Example 4 and Example 1 during the preparation process was the use of different types of surfactants. Obviously, its performance was equivalent to that of the product of Comparative Example 2 without introducing surfactants, indicating that non-ionic surfactants cannot effectively help the uniform mixing and dispersion of each precursor material, and this additive is not suitable for the preparation process system of the product described in the present invention.

[0060] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a cathode material for a lithium-ion battery, characterized in that, It includes the following steps: (1) Prepare solution A by dissolving manganese sulfate monohydrate and polyvinylpyrrolidone in water. Add potassium ferricyanide solution to solution A in a titration form and stir for reaction. After the reaction is complete, age, filter, and wash to obtain manganese ferricyanide; (2) Disperse manganese ferricyanide, nickel source, lithium source, polyimide, and anionic surfactant evenly in water and perform ball milling treatment. Then, keep it at 750 - 950 °C for 15 - 20 h to obtain the positive electrode material for the lithium-ion battery.

2. The preparation method of the cathode material of the lithium ion battery according to claim 1, wherein, In the solution A, the molar ratio of manganese sulfate monohydrate to the mass of polyvinylpyrrolidone is (0.0025 - 0.0035) mol:(1 - 5) g, and the concentration of the solution A is 10 - 15 g / L.

3. The preparation method of the lithium ion battery cathode material according to claim 1, wherein, The concentration of the potassium ferricyanide solution is 5 - 10 g / L.

4. The preparation method of the cathode material for a lithium-ion battery according to claim 1, characterized in that, The molar ratio of the sum of iron element and manganese element in the manganese ferricyanide to the nickel element in the nickel source is n(Mn + Fe):n(Ni) = (9:1) - (8:2).

5. The preparation method of the lithium ion battery cathode material according to claim 1, characterized in that, The total molar ratio of the manganese element, iron element in the manganese ferricyanide, and nickel element in the nickel source to the lithium element in the lithium source is: n(Mn + Fe + Ni):n(Li) = 1:(1 - 1.05).

6. The preparation method of the cathode material of the lithium ion battery according to claim 1, characterized in that, The nickel source is at least one of nickel acetate and nickel carbonate; the lithium source is at least one of lithium acetate and lithium carbonate.

7. The preparation method of the cathode material for lithium ion battery according to claim 1, characterized in that, The anionic surfactant is at least one of carboxylate anionic surfactant and sulfonate anionic surfactant.

8. The preparation method of the lithium ion battery cathode material according to claim 1, characterized in that, The mass ratio of manganese ferricyanide, nickel source, lithium source, polyimide, and anionic surfactant is: m(manganese ferricyanide + nickel source + lithium source):m(polyimide):m(anionic surfactant) = 1:(0.4 - 0.6):(0.4 - 0.6).

9. The positive electrode material for the lithium-ion battery prepared by the preparation method of the positive electrode material for the lithium-ion battery according to any one of claims 1 - 8.

10. A positive electrode sheet of a lithium-ion battery, characterized in that, The positive electrode plate is prepared from the positive electrode material for the lithium-ion battery according to claim 9.

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