A double-coated lithium-rich manganese-based positive electrode material and a preparation method thereof

Abstract

The application relates to the field of power battery positive electrode materials, in particular to a double-layer coated lithium-rich manganese-based positive electrode material and a preparation method. The lithium-rich manganese-based positive electrode material is prepared from a nickel salt, a manganese source and lithium carbonate, then a LiCrTiO4 coating layer is formed on the surface of the lithium-rich manganese-based positive electrode material through epitaxial growth, then the coated lithium-rich manganese-based positive electrode material is immersed in a lithium titanate precursor liquid, and a stable lithium titanate crystal coating layer is formed on the surface of the lithium-rich manganese-based positive electrode material through calcination. The lithium-rich manganese-based positive electrode material prepared by the method contains a double-layer lithium coating layer, is rich in lithium, has good structural stability, good rate performance and cycle performance, and when used as a positive electrode material, the capacity retention rate is still above 83% after 2000 cycles, and the application prospect is good.

Description

TECHNICAL FIELD

[0001] The application relates to the field of power battery positive electrode materials, in particular to a double-layer coated lithium-rich manganese-based positive electrode material and a preparation method. BACKGROUND

[0002] Lithium ion batteries are currently the most widely used energy storage devices, and lithium-rich manganese-based positive electrodes are the most potential positive electrode materials for the next generation of lithium ion batteries. The lithium-rich manganese-based positive electrode has the following advantages: high energy density (up to 1200 Wh / kg), good thermal stability (close to lithium iron phosphate), high tap density (close to NCM ternary material), and low unit price (close to lithium iron phosphate). In summary, the lithium-rich manganese-based layered material has the potential to be used as a high-energy-density lithium ion battery positive electrode. However, the crystal structure of the lithium-rich manganese-based positive electrode is unstable during the cycling process, which can cause the dissolution of transition metal ions, and oxygen ions can also participate in the redox reaction at high voltage, leading to oxygen precipitation, thereby resulting in poor cycling stability, poor rate performance and obvious reaction pressure drop of the lithium-rich manganese-based positive electrode during use, which limits the commercial application of the lithium-rich manganese-based positive electrode.

[0003] Surface coating can isolate the contact between the electrode material surface and the electrolyte, inhibit the dissolution of divalent manganese ions through the electrode surface, and partially inhibit the side reactions and oxygen precipitation, thereby achieving the purpose of stabilizing the crystal structure of the lithium-rich manganese-based positive electrode. For example, Chinese patent application CN116632216A discloses a lithium-rich manganese-based positive electrode material with a surface multi-component integrated coating and a preparation method thereof, which uses the thermal decomposition reaction of ammonium dihydrogen phosphate to construct a coating layer with a stable spinel phase manganese-based material as an inner layer and lithium phosphate as an outer layer on the surface of the material. For another example, Chinese patent application CN116722124A discloses a lithium-rich manganese-based positive electrode material coated with bismuth fluoride / lithium fluoride and a preparation method thereof, which uses a wet chemical method to wrap fluorine sources and bismuth sources onto the surface of the lithium-rich manganese-based layered positive electrode primary particles, and then in-situ synthesizes a bismuth fluoride / lithium fluoride in-situ coating layer on the surface of the lithium-rich manganese-based positive electrode through high-temperature calcination. For another example, Chinese patent No. CN116711104A discloses a positive electrode material, a preparation method and application thereof, which uses Mn4O(PO3)2 to coat the manganese-based positive electrode material.

[0004] The above-mentioned different forms of coating can avoid direct contact between the positive electrode material and the electrolyte, inhibit the occurrence of side reactions and the dissolution of transition metal ions. However, since the coating materials and the positive electrode materials in the above-mentioned methods do not match the crystal lattice, there will be an amorphous interface between the coating layer and the positive electrode material that hinders the transmission of lithium ions, thereby affecting the rate performance of the lithium-rich manganese-based positive electrode material. In view of the above problems, the epitaxial growth coating method can better eliminate the amorphous interface between the coating material and the lithium-rich manganese-based positive electrode material, but the epitaxial growth coating is uncontrollable and may produce crystal defects, thereby affecting the electrochemical performance of the lithium-rich manganese-based positive electrode material. SUMMARY

[0005] In order to solve the problems of poor cycle stability and rate performance of the existing lithium-rich manganese-based positive electrode material, the application provides a double-coated lithium-rich manganese-based positive electrode material and a preparation method. The method provided by the application forms a coating layer on the surface of the lithium-rich manganese-based positive electrode material by epitaxial coating method, reduces the amorphous interface and is conducive to forming a channel for lithium ion transmission, and further coats a lithium titanate layer to stabilize the structure of the lithium-rich manganese-based positive electrode material. Finally, the lithium-rich manganese-based positive electrode material prepared by the application has good cycle stability and rate performance. The specific technical solutions are as follows:

[0006] In a first aspect, the application provides a preparation method of a double-coated lithium-rich manganese-based positive electrode material, comprising the following steps:

[0007] Step 1: mixing a solution of nickel salt and manganese salt and an ammonia solution of sodium carbonate to obtain a mixed solution, adjusting and keeping the pH of the mixed solution at 7.0-8.5 to obtain a solid-liquid mixture;

[0008] Step 2: filtering, washing and drying to obtain a solid-phase precipitate, mixing and then ball milling the solid-phase precipitate after adding lithium carbonate, and then sintering and pulverizing to obtain a lithium-rich manganese-based positive electrode powder;

[0009] Step 3: dissolving metal nitrate in alcohol, then adding the lithium-rich manganese-based positive electrode powder, stirring and drying to obtain a lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer;

[0010] Step 4: placing the lithium-rich manganese-based positive electrode precursor containing the epitaxial coating layer in a lithium titanate precursor liquid, stirring and drying, and finally sintering to obtain a double-coated lithium-rich manganese-based positive electrode material.

[0011] Specifically, the nickel salt in step 1 is at least one of nickel nitrate or nickel sulfate.

[0012] Specifically, the manganese salt in step 1 is at least one of manganese nitrate and manganese sulfate.

[0013] Specifically, the concentration of the solution of the nickel salt and the manganese salt in step 1 is 1.5-3 mol / L, and the molar ratio of the manganese salt and the nickel salt is 2.5-3.5:1, calculated based on Mn and Ni respectively.

[0014] Specifically, the concentration of the ammonia solution of sodium carbonate (Na2CO3) in step 1 is 2.5-3.5 mol / L; wherein the molar ratio of Na2CO3 and NH4OH in the solution is 3-5:1.

[0015] Specifically, step 1 further comprises the step of adding a salt solution of doping ions for stirring and reaction, or / and step 2 further comprises the step of adding an oxide for reaction.

[0016] More specifically, the doping ions are selected from at least one of Sc, V, Fe, Mo or W, and the concentration of the salt solution of the doping ions is 0.1-0.15 mol / L.

[0017] Specifically, the temperature of the drying in step 2 is 100-120℃, and the time is 20-30h.

[0018] Specifically, the reagent for the washing in step 2 is water.

[0019] Specifically, the sintering process in step 2 is as follows:

[0020] First, the temperature is raised to 400-500℃ at a rate of 4-6℃ / min, and the temperature is kept for 5-7h, then the temperature is raised to 750-850℃ at a rate of 4-6℃ / min, and the temperature is kept for 10-14h, finally the temperature is reduced to room temperature at a rate of 4-6℃ / min.

[0021] Specifically, the concentration of the metal nitrate in alcohol in step 3 is 0.4-0.6 mol / L.

[0022] Specifically, the metal nitrate in step 3 is a combination of lithium nitrate, chromium nitrate and titanium nitrate, and the molar ratio of the lithium nitrate, the chromium nitrate and the titanium nitrate is 1-1.05:1:1.

[0023] Specifically, in step 4, the lithium-rich manganese-based positive electrode precursor containing the epitaxial coating layer is placed in the lithium titanate precursor liquid until the solid content is 30-50%.

[0024] Specifically, the sintering temperature in step 4 is 400-600℃.

[0025] Specifically, the preparation method of the lithium titanate precursor liquid in step 4 is as follows:

[0026] 0.5-1 parts by weight of lithium hydroxide is weighed, 200-500 parts by weight of deionized water is added, and ultrasonic dispersion is performed for 30-50min, 2-4 parts by weight of oxalic acid with a concentration of 20-50wt% is added to obtain a mixed solution, 0.1-0.3 parts by weight of tetrabutyl titanate is weighed, 100-300 parts by weight of deionized water is added, and ultrasonic dispersion is performed for 20-30min to obtain a titanium source solution, the titanium source solution is added dropwise into the above mixed solution, and microwave treatment is performed to obtain a lithium titanate precursor liquid.

[0027] In a second aspect of the present application, a double-coated lithium-rich manganese-based positive electrode material prepared by the above method is provided.

[0028] The beneficial effects brought by the present application are as follows:

[0029] The lithium-rich manganese-based positive electrode material is prepared from a nickel salt, a manganese source and lithium carbonate, and then a LiCrTiO4 coating layer is formed on the surface of the lithium-rich manganese-based positive electrode material through epitaxial growth coating, so that the amorphous interface formed by lattice mismatch between the coating material and the lithium-rich manganese-based positive electrode material is avoided, the lithium-rich manganese-based positive electrode material prepared through double-layer coating does not contain the amorphous interface, and the three-dimensional network structure of the lithium titanate coating layer further constructs a lithium ion transmission channel, so that the rate performance of the lithium-rich manganese-based positive electrode material is greatly improved.

[0030] In addition, the lithium-rich manganese-based positive electrode material after epitaxial coating is immersed in a lithium titanate precursor liquid, and a lithium titanate crystal coating layer is formed on the surface of the lithium-rich manganese-based positive electrode material through calcination, the lithium titanate crystal has a three-dimensional network structure and high stability, can stabilize the structure of the prepared lithium-rich manganese-based positive electrode material, and avoids the problem that the cycle performance improvement is limited due to the lattice defects generated by epitaxial growth coating.

[0031] Finally, the lithium-rich manganese-based positive electrode material prepared through double-layer coating has good electrochemical performance, has a relatively high charge and discharge capacity, and when used as a positive electrode material, the capacity retention rate is still above 83% under the condition of 2000 cycles of long cycle. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Capacity diagram of the lithium-rich manganese-based positive electrode material prepared for Examples 1-2 and Comparative Examples 1-2;

[0033] Figure 2 Rate performance diagram of the lithium-rich manganese-based positive electrode material prepared for Examples 1-2 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0034] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0035] The specific preparation method of the lithium titanate precursor liquid in the embodiments and comparative examples of the present application is as follows:

[0036] Take 0.8 parts by weight of lithium hydroxide, add 350 parts by weight of deionized water, ultrasonic dispersion for 40 min, add 3 parts by weight of 35wt% oxalic acid, to obtain a mixed solution, take 0.2 parts by weight of tetrabutyl titanate, add 200 parts by weight of deionized water, ultrasonic dispersion for 25 min, to obtain a titanium source solution, drop the titanium source solution into the above mixed solution, microwave treatment, to obtain a lithium titanate precursor liquid.

[0037] Example 1

[0038] Step 1, take 2mol / L manganese sulfate and nickel sulfate solution (molar ratio of Mn, Ni is 3:1) and 2mol / L ammonia solution of Na2CO3 (molar ratio of Na2CO3 and NH4OH is 4:1) to obtain a mixed solution, adjust and keep the pH of the mixed solution at 7.5, to obtain a solid-liquid mixture;

[0039] Step 2, filter, water washing and drying at 110℃ for 20h to obtain solid-phase precipitated Mn 0.75 Ni 0.25 CO3, the molar ratio of Mn 0.75 Ni 0.25 CO3 and Li2CO3 is 1:1.05, add Li2CO3 and mix, then ball mill, then heat to 800℃ at a heating rate of 5℃ / min, keep for 12h, then cool to room temperature at a cooling rate of 5℃ / min, then powderize to obtain lithium-rich manganese-based positive electrode powder;

[0040] Step 3, dissolve lithium nitrate, chromium nitrate and titanium nitrate in alcohol to obtain a solution with a total metal ion concentration of 0.5mol / L, then add the lithium-rich manganese-based positive electrode powder to obtain a lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer;

[0041] Step 4, add the lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer to the lithium titanate precursor liquid to a solid content of 30%, stir and dry, and finally sinter at 400℃ to obtain a lithium-rich manganese-based positive electrode material coated with LiCrTiO4 and lithium titanate.

[0042] Comparative Example 1

[0043] Step 1, take 2mol / L manganese sulfate and nickel sulfate solution (molar ratio of Mn, Ni is 3:1) and 2mol / L ammonia solution of Na2CO3 (molar ratio of Na2CO3 and NH4OH is 4:1) to obtain a mixed solution, adjust and keep the pH of the mixed solution at 7.5, to obtain a solid-liquid mixture;

[0044] Step 2, filter, water washing and drying at 110℃ for 20h to obtain solid-phase precipitated Mn 0.75 Ni0.25 CO3, by Mn 0.75 Ni 0.25 CO3, and Li2CO3 was added in a molar ratio of 1:1.05, Li2CO3 was added to obtain a lithium-rich manganese-based layered positive electrode precursor, then the temperature was raised to 800°C at a rate of 5°C / min for 12 hours, then the temperature was lowered to room temperature at a rate of 5°C / min, and then powderization was performed to obtain a lithium-rich manganese-based positive electrode material.

[0045] Example 2

[0046] Step 1, a solution of 2 mol / L manganese nitrate and nickel nitrate (molar ratio of Mn, Ni was 2.5:1) and 3 mol / L Na2CO3 ammonia solution (molar ratio of Na2CO3 and NH4OH was 3:1) were mixed to obtain a mixed solution, the pH of the mixed solution was adjusted and maintained at 8.5, then 0.12 mol / L Sc, V, Fe sulfate mixed solution was added in a molar ratio of Ni to Sc, V, Fe of 95:1:1:1, and stirred to obtain a solid-liquid mixture;

[0047] Step 2, filtration, water washing and drying at 100°C for 30h to obtain a solid-phase precipitate Mn 0.75 Ni 0.25 CO3, by Mn 0.75 Ni 0.25 CO3, and Li2CO3 was added in a molar ratio of 1:1.05, then MoO3 and WO3 were added in a molar ratio of Sc, V, Fe to Mo, W of 1:1:1:1:1, and then ball milling was performed, then the temperature was raised to 800°C at a rate of 5°C / min for 12 hours, then the temperature was lowered to room temperature at a rate of 5°C / min, and then powderization was performed to obtain a lithium-rich manganese-based positive electrode powder;

[0048] Step 3, lithium nitrate, chromium nitrate and titanium nitrate were dissolved in alcohol to prepare a solution with a total metal ion concentration of 0.4 mol / L in a molar ratio of 1:1:1, then the above lithium-rich manganese-based positive electrode powder was added and stirred to dryness to obtain a lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer;

[0049] Step 4, the lithium-rich manganese-based positive electrode precursor containing the epitaxial coating layer was placed in a lithium titanate precursor liquid to a solid content of 40%, stirred and dried, and finally sintered at 500°C to obtain a lithium-rich manganese-based positive electrode material coated with LiCrTiO4 and lithium titanate.

[0050] Comparative Example 2

[0051] Step 1, take 2 mol / L manganese sulfate and nickel sulfate solution (molar ratio of Mn, Ni is 2.5:1) and 3 mol / L Na2CO3 ammonia solution (molar ratio of Na2CO3 and NH4OH is 3:1) to get a mixed solution, adjust and keep the pH of the mixed solution at 8.5, then add 0.1 mol / L Sc, V, Fe sulfate mixed solution according to the molar ratio of Ni to Sc, V, Fe 95:1:1:1, stir and react to get a solid-liquid mixture;

[0052] Step 2, filter, water wash and dry at 100℃ for 30h to get solid phase precipitation Mn 0.75 Ni 0.25 CO3, add Li2CO3 according to the molar ratio of Mn 0.75 Ni 0.25 CO3 to Li2CO3 1:1.05, then add MoO3 and WO3 according to the molar ratio of Sc, V, Fe to Mo, W 1:1:1:1:1, ball mill after mixing, get lithium-rich manganese-based layered positive electrode precursor, then heat to 800℃ at a heating rate of 5℃ / min, keep for 12 hours, then cool to room temperature at a cooling rate of 5℃ / min, then powder to get lithium-rich manganese-based positive electrode powder;

[0053] Step 3, the lithium-rich manganese-based positive electrode powder is placed in the lithium titanate precursor liquid to a solid content of 30%, stirred and dried, and finally sintered at 500℃ to get lithium titanate coated lithium-rich manganese-based positive electrode material.

[0054] Example 3

[0055] Step 1, take 2 mol / L manganese sulfate and nickel nitrate solution (molar ratio of Mn, Ni is 3.5:1) and 1.5 mol / L Na2CO3 ammonia solution (molar ratio of Na2CO3 and NH4OH is 5:1) to get a mixed solution, adjust and keep the pH of the mixed solution at 7.0, get a solid-liquid mixture;

[0056] Step 2, filter, water wash and dry at 120℃ for 25h to get solid phase precipitation Mn 0.75 Ni 0.25 CO3, add Li2CO3 according to the molar ratio of Mn 0.75 Ni 0.25 CO3 to Li2CO3 1:1.05, ball mill after mixing, then heat to 800℃ at a heating rate of 4℃ / min, keep for 12 hours, then cool to room temperature at a cooling rate of 6℃ / min, then powder to get lithium-rich manganese-based positive electrode powder;

[0057] Step 3, lithium nitrate, chromium nitrate and titanium nitrate are dissolved in alcohol to form a solution with a total metal ion concentration of 0.6 mol / L according to a molar ratio of 1.05:1:1, then the lithium-rich manganese-based positive electrode powder is added and stirred and dried to obtain a lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer;

[0058] Step 4, the lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer is placed in a lithium titanate precursor liquid to a solid content of 50%, stirred and dried, and finally sintered at 600°C to obtain a lithium-rich manganese-based positive electrode material coated with LiCrTiO4 and lithium titanate.

[0059] Comparative Example 3

[0060] Comparative Example 3 is different from Example 3 in that Step 4 is different. Step 4 of Comparative Example 3 is specifically:

[0061] Step 4, the lithium-rich manganese-based positive electrode precursor containing an epitaxial coating layer is placed in a lithium titanate precursor liquid to a solid content of 50%, stirred and dried, and finally sintered at 600°C to obtain a lithium-rich manganese-based positive electrode material coated with LiCrTiO4 and lithium titanate.

[0062] Performance test

[0063] The lithium-rich manganese-based positive electrode materials prepared in the examples and comparative examples are assembled into button cells, and then subjected to electrochemical tests under certain voltage (2.0-4.8V) and charge-discharge conditions of 0.1C to 5C. The test results are shown in Figure 1 、 Figure 2 and Table 1.

[0064] Table 1

[0065] Test item Example 1 Comparative Example 1 Example 2 Comparative Example 2 Example 3 Comparative Example 3 2000 cycle capacity retention 84.3％ 69.3％ 86.2％ 74.6％ 83.6％ 71.0％

[0066] From Figure 1 、 Figure 2 and Table 1, it can be seen that the lithium-rich manganese-based positive electrode material prepared by the method of the present application has good rate performance; the lithium-rich manganese-based positive electrode material of Comparative Example 1 has poor charge-discharge capacity, cycle performance and rate performance because it is not coated; the lithium-rich manganese-based positive electrode material of Comparative Example 2 has relatively low charge-discharge capacity and relatively low capacity retention rate after long cycle because it is only coated with lithium titanate; the lithium-rich manganese-based positive electrode material of Comparative Example 3 has low capacity retention rate after long cycle because the epitaxial growth coating produces lattice defects, which reduces the stability of the material after long cycle.

[0067] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a double-layer coated lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: Step 1: Mix solutions of nickel salt and manganese salt with an ammonia solution of sodium carbonate to obtain a mixed solution. Adjust and maintain the pH of the mixed solution at 7.0-8.5 to obtain a solid-liquid mixture. Step 2: After filtration, washing and drying, a solid precipitate is obtained. Lithium carbonate is added to the solid precipitate and mixed. The mixture is then ball-milled, sintered and pulverized to obtain lithium-rich manganese-based cathode powder. Step 3: Dissolve the metal nitrate in alcohol, then add lithium-rich manganese-based cathode powder, stir and dry to obtain a lithium-rich manganese-based cathode precursor with an epitaxial coating layer; the metal nitrate is a combination of lithium nitrate, chromium nitrate and titanium nitrate; the epitaxial coating layer is a LiCrTiO4 coating layer. Step 4: Place the lithium-rich manganese-based cathode precursor containing the epitaxial coating layer in a lithium titanate precursor liquid, stir and dry, and finally sinter to obtain a double-layer coated lithium-rich manganese-based cathode material; the double coating is a LiCrTiO4 coating layer and a lithium titanate crystal coating layer.

2. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The nickel salt mentioned in step 1 is at least one of nickel nitrate or nickel sulfate, and the manganese salt is at least one of manganese nitrate and manganese sulfate.

3. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The concentration of the nickel salt and manganese salt solution in step 1 is 1.5~3 mol / L, and the molar ratio of manganese salt and nickel salt, calculated as Mn and Ni respectively, is 2.5~3.5 :

1.

4. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The concentration of the ammonia solution of sodium carbonate in step 1 is 2.5~3.5 mol / L.

5. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, Step 1 also includes the steps of adding a salt solution containing doped ions and stirring to react, or / and adding an oxide containing doped ions in step 2 to react.

6. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 5, characterized in that, The dopant ion is selected from at least one of Sc, V, Fe, Mo or W.

7. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 5, characterized in that, The concentration of the salt solution containing the doped ions is 0.1~0.15 mol / L.

8. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The concentration of the metal nitrate in alcohol in step 3 is 0.4~0.6 mol / L.

9. The method for preparing the double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The sintering temperature in step 4 is 400~600℃.

10. A double-layer coated lithium-rich manganese-based cathode material prepared by the method according to any one of claims 1 to 9.

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