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

Abstract

The invention provides preparation and application of a high-nickel layered positive electrode material coated with lithium ferric sulfate, and a uniform and stable polyanion coating material is generated on the surface of a high-nickel layered positive electrode in situ through spray drying. The coating layer directly grown on the surface of the high-nickel positive electrode in a nucleation manner has structural coherence, and the high-nickel layered structure and the bulk phase of the lithium ferric sulfate can be better connected, so that the ion migration barrier is reduced. The obtained lithium ferric sulfate coated high-nickel layered positive electrode material has the advantages of the two positive electrode materials, the characteristic of high specific energy is stably exerted, and the comprehensive performance is obviously improved. The synthesis method is simple, effective and low in cost, and the prepared material is uniform in surface coating and suitable for large-scale production.

Description

Technical Field

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

[0002] Since 2015, electric vehicles, including hybrid vehicles and pure electric vehicles, have developed rapidly. As the core component of the energy storage system of electric vehicles, lithium-ion batteries have high energy and long cycle life requirements. Layered cathode materials have the advantage of weight capacity, which helps to alleviate users' mileage anxiety. Although high-nickel layered cathode 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 studies have shown that in practical applications, the structure of high-nickel layered cathode materials will gradually deteriorate as the number of cycles increases, especially the surface gradually transforms into spinel and rock salt phases, and the ion migration barrier increases. In addition, side reactions increase, the electrolyte is gradually consumed, and the entire battery system is heading towards extinction. In order to improve the cycle stability of high-nickel layered cathode materials, people have done a lot of research from both the bulk and surface aspects, but it still cannot meet people's pursuit of high specific energy and long-life lithium-ion battery performance.

[0004] The polyanion cathode material system has excellent cycle stability and high safety, and complements the advantages and disadvantages of high-nickel layered cathode materials. The organic 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 use common lithium iron phosphate-coated ternary positive electrode materials to improve the overall performance of the positive electrode materials. However, due to the poor uniformity of physical coating and the complexity of in-situ synthesis process, most of the existing methods cannot achieve the desired effect and are difficult to expand production. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a preparation and application of a lithium iron sulfate-coated high-nickel layered positive electrode material.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

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

[0009] (1) adding lithium sulfate, ferrous sulfate, an antioxidant and a carbon source into an appropriate amount of deionized water in proportion, and dispersing by ultrasonication to obtain a uniform solution;

[0010] (2) adding high nickel positive electrode powder to solution I, stirring to obtain a uniform mixed solution II, and spray drying the mixed solution II to obtain powder;

[0011] (3) The obtained powder is placed in a crucible, and the crucible is placed in a heating device for high temperature treatment, the temperature is raised to 200°C to 400°C and calcined for 3h to 15h, the calcination atmosphere is an inert gas, and the temperature is lowered and cooled after the calcination to obtain a lithium iron sulfate-coated high-nickel layered positive electrode material in the crucible.

[0012] The molar ratio of lithium sulfate, lithium iron sulfate and antioxidant is 1:1:0.05, the carbon source accounts for 5% of the mass of lithium iron sulfate; and the total mass of lithium sulfate and lithium iron sulfate accounts for 2% to 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 redox graphene.

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

[0015] Preferably, in step (2), the high nickel cathode 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, 0≤1-xy<0.4.

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

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

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

[0019] A lithium ion battery, wherein the positive electrode material of the battery adopts the high-nickel layered positive electrode material coated with lithium iron sulfate described in the present invention.

[0020] Beneficial Effects

[0021] The present invention provides a high-nickel layered positive electrode material coated with lithium iron sulfate, wherein the lithium iron sulfate is uniformly synthesized on the surface of the layered positive electrode by a spray drying method, and a stable polyanion positive electrode material is uniformly coated on the surface without affecting the performance of the layered positive electrode. Compared with the common lithium iron phosphate, lithium iron sulfate has a lower synthesis temperature and a shorter synthesis time, thereby reducing the influence of inert gas calcination on the high-nickel layered positive electrode and reducing its oxygen deficiency phenomenon. Compared with the ordinary solid phase physical coating method, the coating layer that directly nucleates and grows on the surface of the high-nickel positive electrode has structural coherence, and the high-nickel layered structure and the bulk phase of lithium iron sulfate can be better connected, reducing the ion migration barrier. The obtained high-nickel layered positive electrode material coated with lithium iron sulfate has the advantages of both positive electrode materials, stably exerts the characteristics of high specific energy, and meets people's pursuit of positive electrode material performance.

[0022] The present invention provides a high-nickel layered positive electrode material coated with lithium iron sulfate. A lithium iron sulfate coating layer is in situ grown on the surface of the high-nickel layered positive electrode material by spray drying. The method is simple, effective, and low-cost. The surface of the prepared material is evenly coated and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 2 This is a voltage capacity diagram for the first two cycles of a battery assembled with the high-nickel positive electrode material coated with lithium iron sulfate prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with specific embodiments.

[0026] In the following examples or comparative examples:

[0027] Assembly of button cells: At room temperature, a working electrode is first prepared by mixing the material prepared in the embodiment or comparative example with a binder and a conductive agent in a ratio of 8:1:1 to prepare a uniform slurry; then, the obtained slurry is evenly applied to an aluminum foil with a scraper, and vacuum dried at 100°C for 12 hours to obtain a working electrode; finally, a punching machine is used to press the aluminum foil coated with the sample into a small disc with a diameter of 1.1 cm as the positive electrode, a lithium sheet as the negative electrode material, and a 1.0M LiPF6 carbonate electrolyte to prepare a button cell.

[0028] The blue electric system is used to detect electrochemical performance. The test voltage range is 2.7-4.3V, the test temperature is 30°C, and the test current density is 1C (1C=200mA / g).

[0029] Example 1

[0030] 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, and 5.955 mg of CNT (5% of Li2Fe(SO4)2) were dissolved in 20 ml of deionized water and ultrasonically dispersed for 1 h to obtain a uniform solution. Then 2.382 g of Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 positive electrode material was added to the solution and stirred at 1000 rpm for 15 min until uniform. The resulting mixed solution was spray dried at 200 °C to obtain powder, and then heated at 300 °C for 10 h under argon atmosphere to obtain Li2Fe(SO4)2@Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 composite sample, lithium iron sulfate accounts for about 4.8% of the total mass of the composite positive electrode material.

[0031] The energy spectrum of the composite layered cathode material is as follows Figure 1 As shown, the results show that Fe and S elements are evenly distributed on the surface of the composite material, indicating that the surface of the high-nickel material is evenly coated with a lithium iron sulfate layer.

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

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

[0034] Example 2

[0035] 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, and 5.955 mg of CNT (5% of Li2Fe(SO4)2) were dissolved in 20 ml of deionized water and ultrasonically dispersed for 1 h to obtain a uniform solution. Then 1.985 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material was added to the solution and stirred at 1000 rpm for 15 min until uniform. The obtained mixed solution was spray dried at 200°C to obtain powder, and then heated at 300°C for 10 h under argon atmosphere to obtain Example 2, where lithium iron sulfate accounted for about 5.7% of the total mass of the composite positive electrode material.

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

[0037] Example 3

[0038] 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, and 5.955 mg of CNT (5% of Li2Fe(SO4)2) were dissolved in 20 ml of deionized water and ultrasonically dispersed for 1 h to obtain a uniform solution. Then 4 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material was added to the solution and stirred at 1000 rpm for 15 min until uniform. The obtained mixed solution was spray dried at 200°C to obtain powder, and then heated at 300°C for 10 h under argon atmosphere to obtain Example 3, wherein lithium iron sulfate accounted 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. After 200 cycles, the capacity retention rate is 91.7%.

[0040] Example 4

[0041] 33 mg (0.3 mmol) of Li2SO4, 86.1 mg (0.3 mmol) of FeSO4 7H2O, 2.64 mg (0.015 mmol) of VC, and 5.955 mg of CNT (5% of Li2Fe(SO4)2) were dissolved in 20 ml of deionized water and ultrasonically dispersed for 1 h to obtain a uniform solution. Then 1.5 g of Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material was added to the solution and stirred at 1000 rpm for 15 min until uniform. The obtained mixed solution was spray dried at 200°C to obtain powder, and then heated at 300°C for 10 h under argon atmosphere to obtain Example 4, where lithium iron sulfate accounted 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. After 200 cycles, the capacity retention rate is 92.3%.

[0043] Comparative Example 1

[0044] Take Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 positive electrode material was used as comparative example 1, and was directly prepared into electrode sheets and assembled into batteries. The cycle performance of the obtained batteries is shown in Table 1. After 200 cycles, the capacity retention rate was 87.9%.

[0045] Comparative Example 2

[0046] Take 2g of Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 positive electrode material was added to deionized water and stirred at 1000 rpm for 15 min until uniform. The obtained solution was spray dried at 200°C to obtain powder, and then heated at 300°C for 10 h under argon atmosphere to obtain comparative example 2.

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

[0048]

[0049]

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

Claims

1. A high nickel layered positive electrode material coated with lithium iron sulfate, characterized in that: The material is prepared by the following method, and the method steps are as follows: A high-nickel layered positive electrode material coated with lithium iron sulfate, the material is prepared by the following method, the method steps are as follows: (1) adding lithium sulfate, ferrous sulfate, an antioxidant and a carbon source into an appropriate amount of deionized water in proportion, and dispersing by ultrasonication to obtain a uniform solution; (2) adding high nickel positive electrode powder to solution I, stirring to obtain a uniform mixed solution II, and spray drying the mixed solution II to obtain powder; (3) The obtained powder is placed in a crucible, and the crucible is placed in a heating device for high temperature treatment, the temperature is raised to 200°C to 400°C and calcined for 3h to 15h, the calcination atmosphere is an inert gas, and the temperature is lowered and cooled after the calcination to obtain a lithium iron sulfate-coated high-nickel layered positive electrode material in the crucible. The molar ratio of lithium sulfate, lithium iron sulfate and antioxidant is 1:1:0.05, the carbon source accounts for 5% of the mass of lithium iron sulfate; and the total mass of lithium sulfate and lithium iron sulfate accounts for 2% to 10% of the mass of the high-nickel layered positive electrode.

2. A high nickel layered positive electrode material coated with lithium iron sulfate as claimed in claim 1, characterized in that: In step (1), the antioxidant is ascorbic acid or citric acid; and the carbon source is carbon nanoparticles, carbon nanotubes or redox graphene.

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

4. A high nickel layered positive electrode material coated with lithium iron sulfate as claimed in claim 1, characterized in that: 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, 0≤1-xy<0.

4.

5. A high nickel layered positive electrode material coated with lithium iron sulfate as claimed in claim 1, characterized in that: In step (2), the stirring temperature is room temperature, the rotation speed is 500-1500 rpm, the stirring time is 0.25h-1h; and the spray drying temperature is 150-250°C.

6. A high nickel layered positive electrode material coated with lithium iron sulfate as claimed in claim 1, characterized in that: In step (3), the heating device used is a tubular furnace, and an inert gas is introduced during the calcination process. The inert gas is nitrogen or argon, and the gas flow rate is 50cfm to 300cfm.

7. A high nickel layered positive electrode material coated with lithium iron sulfate 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 to 15 μm, wherein the lithium iron sulfate coating layer accounts for 2% to 9% of the total mass of the positive electrode material, more preferably 4% to 7%, and the thickness of the lithium iron sulfate coating layer is 5 to 100 nm, more preferably 10 to 20 nm.

8. A lithium ion battery, characterized in that: The positive electrode material of the battery adopts a high-nickel layered positive electrode material coated with lithium iron sulfate as described in any one of claims 1 to 7.

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