Coated positive electrode material, preparation method thereof and lithium ion battery

Abstract

The present application relates to a kind of coated positive electrode material and its preparation method and lithium ion battery, the coated positive electrode material includes positive electrode material and the coating layer coated on the surface of positive electrode material, the coating layer includes conductive polymer, and the conductive polymer includes ethanol-based n-type conductive polymer.The present application provides a kind of ethanol-based n-type conductive polymer surface coated positive electrode material, and conductive polymer material is clean and environmental protection, which can form physical barrier between positive electrode material and electrolyte, reduce interface side reaction, improve the cycle stability and capacity retention rate of material, prolong battery life.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery cathode materials, and relates to a coated cathode material, in particular to a coated cathode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are gradually widely used due to their higher weight and volume energy density, longer service life, lower self-discharge rate and other advantages. Among many cathode materials, ternary cathodes are widely concerned due to their high specific capacity, low cost and environmental friendliness. However, there are still problems such as cation mixing, rock salt phase generation and oxygen loss, surface residual lithium, electrode / electrolyte interface side reaction and particle cracking, which lead to poor cycle stability and rate performance. At present, surface coating is one of the key strategies to improve the performance of ternary materials.

[0003] CN 108258224A discloses a ternary cathode material coated with metal oxide and a preparation method thereof. First, a medium barrier discharge plasma assisted high-energy ball milling method is used to mix the precursor and lithium source. The uniformly mixed powder is calcined to obtain a ternary cathode material. Then, the ternary cathode material and nano-sized metal oxide powder are mixed in proportion. The mixture is subjected to discharge ball milling to obtain a ternary cathode material coated with metal oxide. The invention only needs to use one-step discharge ball milling by reasonably adjusting the ball powder mass ratio and the rotation speed of the ball mill, without the need for complicated chemical synthesis or heat treatment. The method can prepare a ternary cathode material coated with metal oxide, which improves the conductivity of the surface of the cathode material and effectively inhibits the reaction between the surface of the cathode and the electrolyte, thereby improving the cycle stability and having good application prospects.

[0004] CN 109755484A discloses a modified ternary cathode material and a preparation method thereof. The material includes a base and a coating layer coated on the outer surface of the base. The base is composed of a material represented by the formula Li α (Ni 0.6 Co 0.2 Mn 0.2 ) 1-x M x O2, wherein M represents a metal element, 0.9≤α≤1.2, 0<x≤0.1. The coating layer is composed of a material selected from metal oxides and / or metal fluorides. In this way, the discharge capacity of the material is improved by doping, and the cycle performance of the material is improved by coating. The preparation method is as follows: a nickel-cobalt-manganese ternary precursor, a lithium source and a dopant are mixed, then one-time sintering is performed in an oxygen atmosphere, and finally a coating agent is mixed and two-time sintering is performed to obtain the modified ternary cathode material. The particle size of the modified ternary cathode material is uniform, and the material capacity, cycle performance and high-temperature storage performance are superior.

[0005] CN 108630913A provides a conductive double electric layer coated ternary positive electrode material and a preparation method. The invention coats the material surface with inorganic conductive coating through wet coating, which forms effective Li + ion conductor, improves Li + transport capacity; the second layer is an organic conductive layer, which has good electronic conductivity and effectively increases the material conductivity. The organic conductive layer has a "sponge" effect, which can reduce the breakage of the material during extrusion and effectively protect the structural integrity of the material. The coating of the double electric layer reduces the decrease of material conductivity caused by the coating layer under normal circumstances. The coating of the organic conductive layer can further reduce the occurrence of surface side reactions, improve the surface structure, and buffer the extrusion between materials to protect the material structure. Through the above mechanism, the cycle performance of the material is greatly improved.

[0006] CN 112758994A provides a conductive polymer and transition metal oxide coated high-nickel positive electrode material and a preparation method. The center layer is a spherical high-nickel ternary material, and the surface of the center layer is a coating layer. The coating layer has a three-layer structure of poly 3,4-ethylenedioxythiophene / polystyrene sulfonate PEDOT:PSS, MnO2, and poly 3,4-ethylenedioxythiophene / polystyrene sulfonate PEDOT:PSS from inside to outside. The chemical formula of the high-nickel ternary material is Li z Ni x Co y Mn 1-x-y O2, wherein 0.75≤x≤0.85, 0.075≤y≤0.125, and 1.0≤z≤1.1. The invention has higher discharge capacity, better cycle stability and rate performance. The surface coating layer can effectively reduce the residual amount of lithium ions on the surface of the cathode material, thereby greatly inhibiting the propagation of LiF and HF during the cycle process, and reducing the dissolution of transition metal ions and the formation of cycle electrode cracks.

[0007] The above technical solution uses commonly used metal oxides, metal fluorides, inorganic lithium ion conductors, etc. as coating materials, which need to be calcined at a high temperature of 500-900℃, and are prone to uneven coating. The conductive polymer can be coated by a miscible-coating-drying process, but NMP with high boiling point and environmental hazards is commonly used as a solvent.

[0008] Therefore, it is of great significance to develop new coating materials with excellent performance and environmental friendliness and optimize the coating process for promoting the progress of ternary material modification technology. SUMMARY

[0009] To solve the above technical problems, the application provides a coated positive electrode material, a preparation method thereof and a lithium ion battery.

[0010] To achieve the above purpose, the application adopts the following technical solutions.

[0011] In the first aspect, the application provides a coated positive electrode material, which comprises a positive electrode material and a coating layer coated on the surface of the positive electrode material, wherein the coating layer comprises a conductive polymer.

[0012] The conductive polymer comprises an ethanol-based n-type conductive polymer.

[0013] The application provides an ethanol-based n-type conductive polymer coated positive electrode material, which is clean and environmentally friendly, can form a physical barrier between the positive electrode material and the electrolyte, reduce the interface side reaction, improve the cycle stability and capacity retention rate of the material, and prolong the service life of the battery.

[0014] Preferably, the conductive polymer comprises polybenzoimidazobenzophenanthroline: polyethyleneimine (BBL: PEI), wherein the chemical formula of BBL is:

[0015]

[0016] The polymer BBL with conductive electron carriers is a porous nanogel, and the surface is adsorbed with the polymer PEI. Due to the introduction of PEI, the π-π stacking distance of BBL is shortened, and the π-π stacking order is enhanced. This microstructure is very beneficial to charge transport.

[0017] The BBL: PEI has good flexibility, and as a coating material, it can improve the mechanical properties of the positive electrode material, so that the coated electrode does not produce cracks or crushing after cycling. At the same time, the BBL: PEI has good solvent resistance and thermal stability, thereby ensuring that the coated positive electrode material has stable performance in different solvents and high temperature environments.

[0018] Preferably, the mass percentage content of PEI in the BBL: PEI is 5-70 wt%, for example, it can be 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt% or 70 wt%, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably, the mass percentage content of PEI is 40-60 wt%.

[0019] Preferably, the cathode material comprises any one or a combination of at least two of nickel cobalt manganese (NCM) ternary material, nickel cobalt aluminum (NCA) ternary material or nickel cobalt manganese aluminum (NCMA) quaternary material, typical but non-limiting combinations include a combination of NCM ternary material and NCA ternary material, NCA ternary material and NCMA quaternary material, a combination of NCM ternary material and NCMA quaternary material, a combination of NCM ternary material, NCA ternary material and NCMA quaternary material.

[0020] Preferably, the mass of the coating layer is 1-3wt% of the mass of the cathode material, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%, but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0021] Preferably, the thickness of the coating layer is 20-30nm, for example, it can be 20nm, 22nm, 24nm, 26nm, 28nm or 30nm, but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0022] Preferably, the particle size range of the coated cathode material is a median particle size of 3-16μm, for example, it can be 3μm, 5μm, 8μm, 10μm, 14μm or 16μm, but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0023] In a second aspect, the present application provides a preparation method of the coated cathode material according to the first aspect, the preparation method comprising the following steps:

[0024] Mixing the cathode material, the ethanol-based n-type conductive polymer and the solvent, stirring and drying to obtain the coated cathode material.

[0025] The present application provides a wet coating process using an ethanol-based n-type conductive polymer as a coating raw material, which does not need high-temperature curing, is simple to operate, requires a lower drying temperature for the mixture, has a low energy consumption throughout the process, and has the advantage of reducing costs.

[0026] Preferably, the ethanol-based n-type conductive polymer comprises BBL:PEI.

[0027] Preferably, the BBL:PEI is prepared by a method comprising the following steps:

[0028] After preparing the polymer BBL into BBL nanogel, the polymer dopant PEI is adsorbed on the surface of the BBL nanogel to obtain the BBL:PEI.

[0029] Preferably, the polymer dopant PEI comprises a chain structure PEI and / or a cross-linking structure PEI, preferably a chain structure PEI.

[0030] The chemical formula of the chain structure PEI is as follows:

[0031]

[0032] The chemical formula of the cross-linking structure PEI is as follows:

[0033]

[0034] Preferably, the solvent comprises ethanol.

[0035] Preferably, the solid-liquid ratio after mixing the positive electrode material, the ethanol-based n-type conductive polymer, and the solvent is 1:(30-70), which can be 1:30, 1:40, 1:50, 1:60, or 1:70, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0036] Preferably, the temperature of the stirring is 45-50℃, which can be 45℃, 46℃, 47℃, 48℃, 49℃, or 50℃, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0037] Preferably, the time of the stirring is 1-4h, which can be 1h, 1.5h, 2h, 3h, 3.5h, or 4h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0038] Preferably, the stirring speed is 600-1500rpm, which can be 600rpm, 800rpm, 1000rpm, 1200rpm, or 1500rpm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0039] Preferably, the drying method comprises rotary evaporation and / or oven drying.

[0040] Preferably, the temperature of the drying is 40-65℃, which can be 45℃, 50℃, 55℃, 60℃, or 65℃, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0041] As a preferred technical solution of the preparation method of the second aspect of the application, the preparation method comprises the following steps:

[0042] The mixing of the positive electrode material, BBL:PEI and ethanol, with a solid-liquid ratio of 1:(30-70) g / mL, at a temperature of 45-50℃, stirring for 1-4h, with a stirring speed of 600-1500rpm, and rotary evaporation and / or drying at a temperature of 40-65℃, to obtain the coated positive electrode material.

[0043] In a third aspect, the present application provides a lithium ion battery containing the coated positive electrode material of the first aspect.

[0044] Compared with the prior art, the present application has at least the following beneficial effects:

[0045] (1) The present application provides an ethanol-based n-type conductive polymer surface-coated positive electrode material. The conductive polymer material is clean and environmentally friendly. It can form a physical barrier between the positive electrode material and the electrolyte, reduce the interface side reaction, improve the cycle stability and capacity retention rate of the material, and prolong the battery life.

[0046] (2) The BBL:PEI has good flexibility, which can improve the mechanical properties of the positive electrode material, so that the coated electrode does not produce cracks or crushing after cycling. At the same time, BBL:PEI has good solvent resistance and thermal stability, so as to ensure the performance stability of the coated positive electrode material in different solvents and high temperature environment.

[0047] (3) The present application provides a wet coating process using ethanol-based n-type conductive polymer as coating raw material, which does not need high temperature curing, is simple to operate, requires lower drying temperature for the mixture, has low energy consumption throughout, and has the advantage of reducing cost. DETAILED DESCRIPTION

[0048] To facilitate understanding of the present application, the present application is illustrated by the following examples. Those skilled in the art should understand that the examples are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0049] Example 1

[0050] The present example provides a coated positive electrode material, which includes NCM811 ternary positive electrode material and a coating layer coated on the surface of the positive electrode material, and the coating layer includes conductive polymer BBL:PEI. The particle size range of the coated positive electrode material is a median particle size of 10μm.

[0051] The mass of the coating layer is 2wt% of the mass of the positive electrode material, and the thickness is 25nm.

[0052] The mass percentage of PEI in the conductive polymer BBL:PEI is 50wt%, and the PEI has a chain structure.

[0053] The preparation method of the coated positive electrode material comprises the following steps:

[0054] The positive electrode material, BBL:PEI and ethanol are mixed at a solid-liquid ratio of 1:50 g / mL, stirred at 48℃ for 2h, the stirring speed is 1000rpm, rotary evaporation and / or drying are carried out at 50℃, and the coated positive electrode material is obtained.

[0055] Example 2

[0056] The coated positive electrode material comprises an NCM811 ternary positive electrode material and a coating layer coated on the surface of the positive electrode material, the coating layer comprises a conductive polymer BBL:PEI, and the particle size range of the coated positive electrode material is a median particle size of 3μm.

[0057] The mass of the coating layer is 1.6wt% of the mass of the positive electrode material, and the thickness is 20nm.

[0058] The mass percentage of PEI in the conductive polymer BBL:PEI is 3wt%, and the PEI has a crosslinked structure.

[0059] The preparation method of the coated positive electrode material comprises the following steps:

[0060] The positive electrode material, BBL:PEI and ethanol are mixed at a solid-liquid ratio of 1:30 g / mL, stirred at 45℃ for 4h, the stirring speed is 600rpm, rotary evaporation and / or drying are carried out at 40℃, and the coated positive electrode material is obtained.

[0061] Example 3

[0062] The coated positive electrode material comprises an NCM811 ternary positive electrode material and a coating layer coated on the surface of the positive electrode material, the coating layer comprises a conductive polymer BBL:PEI, and the particle size range of the coated positive electrode material is a median particle size of 16μm.

[0063] The mass of the coating layer is 2.4wt% of the mass of the positive electrode material, and the thickness is 30nm.

[0064] The mass percentage of PEI in the conductive polymer BBL:PEI is 70wt%, and the PEI has a chain structure and a crosslinked structure.

[0065] The preparation method of the coated positive electrode material comprises the following steps:

[0066] The positive electrode material, BBL:PEI and ethanol are mixed, the solid-liquid ratio is 1:70 g / mL, the temperature is 50℃, the stirring speed is 1500 rpm, the stirring time is 1h, the rotary evaporation and / or drying is carried out at 65℃, and the coated positive electrode material is obtained.

[0067] Example 4

[0068] This example provides a coated positive electrode material, which is different from example 1 only in that the mass percentage of PEI in BBL:PEI is 3wt%.

[0069] Example 5

[0070] This example provides a coated positive electrode material, which is different from example 1 only in that the mass percentage of PEI in BBL:PEI is 75wt%.

[0071] Example 6

[0072] This example provides a coated positive electrode material, which is different from example 1 in that the mass of the coating layer is 0.5wt% of the mass of the positive electrode material, and the thickness of the coating layer is 15nm.

[0073] Example 7

[0074] This example provides a coated positive electrode material, which is different from example 1 only in that the mass of the coating layer is 4wt% of the mass of the positive electrode material, and the thickness of the coating layer is 35nm.

[0075] Example 8

[0076] This example provides a coated positive electrode material, which is different from example 1 only in that the positive electrode material is NCA811.

[0077] Example 9

[0078] This example provides a coated positive electrode material, which is different from example 1 only in that the positive electrode material is LiNi 0.80 Co 0.10 Mn 0.09 Al 0.01 O2.

[0079] Comparative Example 1

[0080] This comparative example provides a NCM811 positive electrode material.

[0081] Comparative Example 2

[0082] The comparative example provides a coated positive electrode material, which is only different from the example 1 in that BBL:PEI is replaced by equal mass of poly 3,4-ethylenedioxythiophene:polystyrene sulfonic acid (PEDOT:PSS). The PEDOT:PSS is an NMP-based p-type conductive polymer.

[0083] The above obtained positive electrode material is prepared into a positive electrode sheet and assembled into a lithium ion battery according to the standard of GB31241-2014 for electrochemical performance test.

[0084] Test conditions:

[0085] Normal temperature cycle: 25℃, 2C charging, 2C discharging, cycle for 500 times;

[0086] High temperature cycle: 45℃, 2C charging, 2C discharging, cycle for 500 times.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089] Test No. 25°C cycle 500 cycles capacity retention rate 45°C cycle 500 cycles capacity retention rate Example 1 93.6％ 91.3％ Example 2 92.1％ 90.1％ Example 3 92.8％ 90.4％ Example 4 90.5％ 89.8％ Example 5 91.6％ 90.7％ Example 6 88.2％ 87.3％ Example 7 87.9％ 87.3％ Example 8 92.6％ 91.2％ Example 9 92.5％ 90.8％ Comparative Example 1 85.4％ 83.9％ Comparative Example 2 87.6％ 86.8％

[0090] From Table 1, the following conclusions are drawn:

[0091] (1) From the examples 1-3 and examples 8, 9, it is known that the present application provides an ethanol-based n-type conductive polymer surface coated positive electrode material. The conductive polymer material is clean and environmentally friendly. It can form a physical barrier between the positive electrode material and the electrolyte, reduce the interface side reaction, improve the cycle stability and capacity retention rate of the material, and prolong the battery life.

[0092] (2) From the comparison of examples 4, 5 and example 1, it is known that when the mass percentage of PEI in the conductive polymer BBL:PEI is not within the preferred range of the present application, the coating effect is poor, which is not conducive to improving the cycle stability and capacity retention rate of the material, and prolonging the battery life.

[0093] (3) From the comparison of examples 6, 7 and example 1, it is known that when the mass of the coating layer and the thickness of the coating layer are not within the preferred range of the present application, the coating effect is poor, which is not conducive to improving the cycle stability and capacity retention rate of the material, and prolonging the battery life.

[0094] (4) From the comparison of comparative example 1 and example 1, it is known that the coated positive electrode material provided by the present application improves the side reaction between the interfaces. The capacity retention rate is improved by 8.2% at 25℃ for 500 cycles, and the capacity retention rate is improved by 7.4% at 45℃ for 500 cycles.

[0095] (5)From the comparison of Comparative Example 2 and Example 1, it can be seen that the BBL:PEI according to the application has good flexibility, and as a coating material, can improve the mechanical properties of the positive electrode material, so that the electrode after coating does not produce cracks or crushing after cycling; at the same time, the BBL:PEI has good solvent resistance and thermal stability, thereby ensuring that the coated positive electrode material has stable performance in different solvents and high temperature environments; and the ethanol BBL:PEI can be used in clean solvents, improving the environmental protection and cleanliness of the process, and PEDOT:PSS needs to be used in solvents such as NMP.

[0096] In summary, the application provides an ethanol-based n-type conductive polymer surface-coated positive electrode material, and the conductive polymer material is clean and environmentally friendly, which can form a physical barrier between the positive electrode material and the electrolyte, reduce the interface side reaction, improve the cycle stability and capacity retention rate of the material, and prolong the battery life.

[0097] The application is described by the above examples to illustrate the detailed process equipment and process flow of the application, but the application is not limited to the above detailed process equipment and process flow, that is, it does not mean that the application must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the application, equivalent replacement of each raw material of the product of the application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the application.

Claims

1. A coated cathode material, characterized in that, The coated positive electrode material includes a positive electrode material and a coating layer covering the surface of the positive electrode material, wherein the coating layer includes a conductive polymer. The conductive polymer includes an ethanol-based n-type conductive polymer; The conductive polymer includes BBL:PEI; The mass percentage of PEI in BBL:PEI is 5-70 wt%.

2. The coated cathode material according to claim 1, characterized in that, The mass percentage of PEI in BBL:PEI is 40-60 wt%.

3. The coated cathode material according to claim 1, characterized in that, The cathode material includes any one or a combination of at least two of the following: NCM ternary material, NCA ternary material, or NCMA quaternary material.

4. The coated cathode material according to claim 1, characterized in that, The mass of the coating layer is 1 to 3 wt% of the mass of the cathode material.

5. The coated cathode material according to claim 1, characterized in that, The thickness of the coating layer is 20–30 nm.

6. The coated cathode material according to claim 1, characterized in that, The median particle size of the coated cathode material is 3–16 μm.

7. A method for preparing a coated cathode material according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: The coated positive electrode material is obtained by mixing the positive electrode material, the ethanol-based n-type conductive polymer and the solvent, stirring and drying.

8. The preparation method according to claim 7, characterized in that, The ethanol-based n-type conductive polymer includes BBL:PEI.

9. The preparation method according to claim 7, characterized in that, The BBL:PEI is prepared by the following method, which includes the following steps: After preparing BBL nanogel from polymer BBL, polymer dopant PEI is adsorbed onto the surface of BBL nanogel to obtain BBL:PEI.

10. The preparation method according to claim 9, characterized in that, The polymer dopant PEI includes chain-like PEI and / or cross-linked PEI.

11. The preparation method according to claim 10, characterized in that, The polymer dopant PEI is a chain-like PEI.

12. The preparation method according to claim 7, characterized in that, The solvent includes ethanol.

13. The preparation method according to claim 7, characterized in that, The solid-liquid ratio of the mixed positive electrode material, ethanol-based n-type conductive polymer and solvent is 1:(30-70), with units of g / mL.

14. The preparation method according to claim 7, characterized in that, The stirring temperature is 45–50°C.

15. The preparation method according to claim 7, characterized in that, The stirring time is 1 to 4 hours.

16. The preparation method according to claim 7, characterized in that, The stirring speed is 600-1500 rpm.

17. The preparation method according to claim 7, characterized in that, The drying methods include rotary evaporation and / or baking.

18. The preparation method according to claim 7, characterized in that, The drying temperature is 40–65°C.

19. The preparation method according to claim 7, characterized in that, The preparation method includes the following steps: The positive electrode material, BBL:PEI and ethanol are mixed at a solid-liquid ratio of 1:(30-70), in g / mL. The mixture is stirred at 45-50℃ for 1-4 hours at a stirring speed of 600-1500 rpm. The mixture is then subjected to rotary evaporation and / or drying at 40-65℃ to obtain the coated positive electrode material.

20. A lithium-ion battery, characterized in that, The lithium-ion battery contains the coated positive electrode material as described in any one of claims 1-6.

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