Preparation and application of lithium iron sulfate-coated high-nickel layered positive electrode material

Abstract

The application provides preparation and application of a lithium iron sulfate-coated high-nickel layered positive electrode material, and in-situ generation of uniform and stable polyanion coating materials on the surface of the high-nickel layered positive electrode through spray drying, compared with common solid-phase physical coating methods, the coating layer directly nucleated and grown on the surface of the high-nickel positive electrode has structural coherence, the high-nickel layered structure and the bulk phase of lithium iron sulfate can be better connected, and the ion migration barrier is reduced. The obtained lithium iron sulfate-coated high-nickel layered positive electrode material well combines the advantages of the two kinds of positive electrode materials, stably exhibits the high specific energy characteristics, and the comprehensive performance is obviously improved. The synthesis method is simple and effective, the cost is low, the surface of the prepared material is uniformly coated, and the method is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to preparation and application of lithium iron sulfate-coated high-nickel layered positive electrode material and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] Since 2015, electric vehicles including hybrid electric vehicles and pure electric vehicles have developed rapidly. As a core component of the energy storage system of electric vehicles, lithium ion batteries are required to have high energy and long cycle life. Layered positive electrode materials have the advantage of high weight capacity, which helps to alleviate the range anxiety of users. Although high-nickel layered positive electrode materials with a nickel content of more than 80% can provide more capacity, there are still many difficulties in commercialization, especially in the power battery market.

[0003] Existing research shows that high-nickel layered positive electrode materials will gradually deteriorate in structure with an increase in the number of cycles in actual application, especially the gradual transition of the surface to spinel and rock salt phases, and the increase in ion migration barrier. In addition, the number of side reactions increases, and the electrolyte is gradually consumed, leading to the demise of the entire battery system. In order to improve the cycle stability of high-nickel layered positive electrode materials, people have made a lot of research from the bulk phase and the surface, but it still cannot meet people's pursuit of the performance of high specific energy and long life lithium ion batteries.

[0004] The polyanion positive electrode material system has excellent cycle stability and high safety, and is complementary to high-nickel layered positive electrode materials. The combination of the high specific energy characteristics of high-nickel materials and the high stability characteristics of lithium iron phosphate can better promote the development of long-range and long-life electric vehicles.

[0005] Existing related patents mainly apply common lithium iron phosphate-coated ternary positive electrode materials to improve the overall performance of the positive electrode material. However, due to the poor uniformity of physical coating, the complexity of in-situ synthesis process and other reasons, most of the existing methods cannot achieve the ideal effect, and it is difficult to expand production. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a preparation and application of lithium sulfate iron-coated high-nickel layered positive electrode material.

[0007] To achieve the above purpose, the technical scheme of the present application is as follows:

[0008] A lithium sulfate iron-coated high-nickel layered positive electrode material is prepared by the following method, and the method steps are as follows:

[0009] (1) Lithium sulfate, ferrous sulfate, an antioxidant and a carbon source are added to a proper amount of deionized water in proportion, and a uniform solution I is obtained through ultrasonic dispersion;

[0010] (2) adding high-nickel positive electrode powder into solution I to obtain a mixed solution П, and then performing spray drying on the mixed solution П to obtain a powder;

[0011] (3) placing the obtained powder into a crucible, and then placing the crucible into a heating device to perform high-temperature treatment, wherein the temperature is raised to 200-400℃ for calcination for 3-15h, the calcination atmosphere is inert gas, and after the calcination is completed, the temperature is lowered for cooling, and an iron lithium sulfate-coated high-nickel layered positive electrode material is obtained in the crucible.

[0012] In the formula, the molar ratio of lithium sulfate, iron lithium sulfate and antioxidant is 1:1:0.05, and the carbon source accounts for 5% of the mass of the iron lithium sulfate; the total mass of lithium sulfate and iron lithium sulfate accounts for 2%-10% of the mass of the high-nickel layered positive electrode.

[0013] Preferably, in step (1), the antioxidant is ascorbic acid or citric acid; and the carbon source is carbon nanoparticles, carbon nanotubes or reduced graphene oxide.

[0014] Preferably, in step (1), during ultrasonic dispersion, the ultrasonic intensity is 100-200 KHZ, and the ultrasonic time is 0.5-2h.

[0015] Preferably, in step (2), the high-nickel positive electrode powder is Li(Ni x A y M 1-x-y )O2, wherein A is Co or Fe, M is Mn, Al or W, 0.6≤x<1, 0≤y<0.4, and 0≤1-x-y<0.4.

[0016] Preferably, in step (2), the stirring temperature is room temperature, the stirring speed is 500-1500 rpm, and the stirring time is 0.25-1h; and the spray drying temperature is 150-250℃.

[0017] Preferably, in step (3), the heating device used is a tube furnace, inert gas is introduced during the calcination process, the inert gas is nitrogen or argon, and the gas flow rate is 50-300 cfm.

[0018] Preferably, the particle diameter of the iron lithium sulfate-coated high-nickel layered positive electrode material is 2-15μm, the iron lithium sulfate coating layer accounts for 2%-9% of the total mass of the positive electrode material, more preferably 4%-7%, and the thickness of the iron lithium sulfate coating layer is 5-100nm, more preferably 10-20nm.

[0019] A lithium ion battery, wherein the positive electrode material of the battery is the iron lithium sulfate-coated high-nickel layered positive electrode material according to the application.

[0020] Advantages

[0021] The application provides a lithium iron sulfate coated high-nickel layered positive electrode material, and lithium iron sulfate is uniformly synthesized on the surface of the layered positive electrode by a spray drying method, so that a stable polyanion positive electrode material is uniformly coated on the surface of the layered positive electrode without affecting the performance of the layered positive electrode. The synthesis temperature of lithium iron sulfate is lower than that of common lithium iron phosphate, and the synthesis time is shorter, so that the influence of inert gas calcination on the high-nickel layered positive electrode is reduced, and the oxygen loss phenomenon is reduced. Compared with the ordinary solid-phase physical coating method, the coating layer directly nucleated and grown on the surface of the high-nickel positive electrode has structural coherence, the high-nickel layered structure and the bulk phase of lithium iron sulfate can be better connected, and the ion migration barrier is reduced. The obtained lithium iron sulfate coated high-nickel layered positive electrode material has the advantages of the two kinds of positive electrode materials, can stably develop high specific energy characteristics, and meets the pursuit of people for the performance of the positive electrode material.

[0022] The application provides a lithium iron sulfate coated high-nickel layered positive electrode material, and lithium iron sulfate is uniformly synthesized on the surface of the layered positive electrode by a spray drying method, so that a stable polyanion positive electrode material is uniformly coated on the surface of the layered positive electrode without affecting the performance of the layered positive electrode. The synthesis temperature of lithium iron sulfate is lower than that of common lithium iron phosphate, and the synthesis time is shorter, so that the influence of inert gas calcination on the high-nickel layered positive electrode is reduced, and the oxygen loss phenomenon is reduced. Compared with the ordinary solid-phase physical coating method, the coating layer directly nucleated and grown on the surface of the high-nickel positive electrode has structural coherence, the high-nickel layered structure and the bulk phase of lithium iron sulfate can be better connected, and the ion migration barrier is reduced. The obtained lithium iron sulfate coated high-nickel layered positive electrode material has the advantages of the two kinds of positive electrode materials, can stably develop high specific energy characteristics, and meets the pursuit of people for the performance of the positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The energy spectrum (EDS) diagram of the lithium iron sulfate coated high-nickel positive electrode material prepared in Example 1.

[0024] Figure 2 The first two circle voltage capacity diagrams of the battery assembled by the lithium iron sulfate coated high-nickel positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0025] The application will be further described in detail below in combination with specific embodiments.

[0026] In the following examples or comparative examples:

[0027] Assembling of the button cell: at room temperature, first, a working electrode is prepared, the material prepared in the examples or comparative examples and a binder and a conductive agent are mixed in a ratio of 8:1:1 to prepare a uniform slurry; then, the obtained slurry is uniformly coated on an aluminum foil by using a doctor blade, and vacuum drying at 100 DEG C for 12 hours is performed to obtain the working electrode; finally, the aluminum foil coated with the sample is pressed into a small round sheet with a diameter of 1.1 cm as a positive electrode by using a sheet punching machine, lithium sheet is used as a negative electrode material, 1.0M LiPF6 carbonate electrolyte is prepared, and a button cell is prepared.

[0028] The Land system is used for detecting the electrochemical performance, the test voltage range is 2.7-4.3V, the test temperature is 30 DEG C, and the test current density is 1C (1C=200mA / g).

[0029] Example 1

[0030] Take 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, 5.955 mg of CNT (5% of Li2Fe(SO4)2) dissolved in 20 ml of deionized water, ultrasonic dispersion for 1 h to uniformity to obtain solution I. Take 2.382 g of Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 positive electrode material into the solution, high-speed stirring at 1000 rpm for 15 min to uniformity. The obtained mixed solution is spray dried at 200 ℃ to obtain a powder, and then heated at 300 ℃ for 10 h under an argon atmosphere to obtain a Li2Fe(SO4)2@Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 composite sample, and the lithium iron sulfate is about 4.8% of the total mass of the composite positive electrode material.

[0031] The energy spectrum of the composite layered positive electrode material is shown in Figure 1 The results show that the Fe element and S element are uniformly distributed on the surface of the composite material, indicating that the lithium iron sulfate layer is uniformly coated on the surface of the high-nickel material.

[0032] The first two circle voltage capacity results of the assembled battery are shown in Figure 2 As can be seen from the figure, the voltage platform of Example 1 in the first charge is similar to that of the polyanion positive electrode, but shows a high specific capacity of 267.7 mAh / g.

[0033] The cycle performance of the assembled battery is shown in Table 1, and the capacity retention rate is 93.6% after 200 cycles.

[0034] Example 2

[0035] Take 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, 5.955 mg of CNT (5% of Li2Fe(SO4)2) dissolved in 20 ml of deionized water, ultrasonic dispersion for 1 h to uniformity to obtain solution I. Take 2.382 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material into the solution, high-speed stirring at 1000 rpm for 15 min to uniformity. The obtained mixed solution is spray dried at 200 ℃ to obtain a powder, and then heated at 300 ℃ for 10 h under an argon atmosphere to obtain a Li2Fe(SO4)2@Li(Ni

[0036] The cycle performance of the assembled battery is shown in Table 1, and the capacity retention rate is 95.8% after 200 cycles.

[0037] Example 3

[0038] Take 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, 5.955 mg of CNT (5% of Li2Fe(SO4)2) and dissolve them in 20 ml of deionized water, ultrasonic dispersion for 1 h to get solution I. Then take 4 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material and add it to the solution, high-speed stirring at 1000 rpm for 15 min to uniform. The obtained mixed solution is dried by spray drying at 200°C to obtain a powder, and then heated at 300°C for 10 h under argon atmosphere to obtain Example 3, in which the lithium iron sulfate accounts for about 2.9% of the total mass of the composite positive electrode material.

[0039] The cycle performance of the assembled battery is shown in Table 1, and the capacity retention rate is 91.7% after 200 cycles.

[0040] Example 4

[0041] Take 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, 5.955 mg of CNT (5% of Li2Fe(SO4)2) and dissolve them in 20 ml of deionized water, ultrasonic dispersion for 1 h to get solution I. Then take 1.5 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material and add it to the solution, high-speed stirring at 1000 rpm for 15 min to uniform. The obtained mixed solution is dried by spray drying at 200°C to obtain a powder, and then heated at 300°C for 10 h under argon atmosphere to obtain Example 4, in which the lithium iron sulfate accounts for about 7.4% of the total mass of the composite positive electrode material.

[0042] The cycle performance of the assembled battery is shown in Table 1, and the capacity retention rate is 92.3% after 200 cycles.

[0043] Comparative Example 1

[0044] Take Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 positive electrode material as Comparative Example 1, directly prepared into an electrode sheet, assembled into a battery, and the cycle performance of the obtained battery is shown in Table 1, and the capacity retention rate is 87.9% after 200 cycles.

[0045] Comparative Example 2

[0046] Again, 2 g of Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 cathode material was added to deionized water and stirred at 1000 rpm for 15 min until uniform. The resulting solution was spray dried at 200°C to obtain a powder, which was then heated under an argon atmosphere at 300°C for 10 h to obtain Comparative Example 2.

[0047] The cycle performance of the assembled battery is shown in Table 1, and the capacity retention rate was 84.3% after 200 cycles.

[0048]

[0049]

[0050] Table 1. Performance comparison of different examples at 1C current density after 200 cycles.

Claims

1. A lithium iron sulfate-coated high-nickel layered cathode material, characterized in that: The material is prepared by the following method steps: (1) Lithium sulfate, ferrous sulfate, antioxidant and carbon source are added into a proper amount of deionized water in proportion, and a uniform solution I is obtained by ultrasonic dispersion; (2) High-nickel positive electrode powder is added into the solution I, and a uniform mixed solution II is obtained by stirring, and the mixed solution II is dried by spray drying to obtain a powder; (3) The obtained powder is placed in a crucible, and the crucible is placed in a heating device for high-temperature treatment, and the temperature is raised to 200-400℃ for calcination for 3-15h, and the calcination atmosphere is nitrogen or argon, and after the calcination is completed, the temperature is lowered for cooling, and a lithium iron sulfate coated high-nickel layered positive electrode material is obtained in the crucible; The molar ratio of lithium sulfate, ferrous sulfate and antioxidant is 1:1:0.05, and the carbon source accounts for 5% of the mass of lithium ferrous sulfate; the lithium ferrous sulfate coating layer accounts for 2%-4% of the total mass of the positive electrode material; the carbon source is carbon nanoparticles, carbon nanotubes or redox graphene; the high-nickel positive electrode powder is Li(Ni x A y M 1-x-y )O2, wherein A is Co or Fe, M is Mn, Al or W, 0.6<=x<1, 0<=y<0.4, and 0<=1-x-y<0.

4.

2. The lithium iron sulfate-coated high-nickel layered cathode material as claimed in claim 1, characterized in that: In step (1), the antioxidant is ascorbic acid or citric acid.

3. The lithium iron sulfate-coated high-nickel layered cathode material as claimed in claim 1, characterized in that: In step (1), the ultrasonic intensity is 100-200KHZ during ultrasonic dispersion, and the ultrasonic time is 0.5h-2h.

4. The lithium iron sulfate-coated high-nickel layered cathode material as claimed in claim 1, characterized in that: In step (2), the stirring temperature is room temperature, the stirring speed is 500-1500rpm, and the stirring time is 0.25h-1h; the spray drying temperature is 150-250℃.

5. The lithium iron sulfate-coated high-nickel layered cathode material as claimed in claim 1, characterized in that: In step (3), the heating device used is a tube furnace, and nitrogen or argon is introduced during the calcination process, and the gas flow is 50cfm-300cfm.

6. The lithium iron sulfate-coated high-nickel layered cathode material as claimed in claim 1, characterized in that: The particle diameter of the lithium iron sulfate coated high-nickel layered positive electrode material is 2-15μm, and the thickness of the lithium iron sulfate coating layer is 5-100nm.

7. A lithium-ion battery, characterized by: The positive electrode material of the battery uses a lithium iron sulfate coated high-nickel layered positive electrode material according to any one of claims 1-6.

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