A method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material

Abstract

The application discloses a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material, and comprises the following steps: (a) adding polyaniline into a solution containing a proton acid for treatment to obtain a proton acid doped PANI; (b) adding the proton acid doped PANI and PEG into organic solvents respectively to make them dissolve to obtain a first mixture; (c) adding inorganic functional materials and the high-nickel ternary positive electrode material into the first mixture respectively, and stirring and ultrasonicating; after the reaction is completed, performing vacuum distillation and collecting a black substance, and drying to obtain a high-nickel ternary positive electrode material composite layer with a pre-constructed conductive polymer on the surface, which is simple and easy to prepare.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to a method for surface modification of a positive electrode material, in particular to a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material. BACKGROUND

[0002] Lithium ion batteries have occupied most of the market of consumer electronic devices and power batteries in the present consumption field due to their high voltage, high energy density and long cycle life and many other advantages. The positive electrode material is the main bottleneck restricting the development of lithium ion batteries.

[0003] High-nickel ternary layered positive electrode material LiNi x Co y Mn 1-x-y O2(NCM) has a high specific energy density (> 270 mAhg -1 ), and is one of the most mainstream positive electrode materials of lithium ion batteries. In order to achieve long endurance and fast charging of lithium ion batteries, the positive electrode material needs to exhibit higher cycle stability and thermal stability. However, the high-nickel NCM positive electrode material usually has rapid capacity decay and structure and surface morphology degradation during the cycle process. A large number of studies have revealed that the failure mechanism of the high-nickel NCM positive electrode material involves the accumulation of anisotropic strain in the phase transition process to cause intergranular microcracks and harmful side reactions at the positive electrode-electrolyte contact interface. Therefore, a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material needs to be researched to inhibit the above-mentioned intergranular microcracks and harmful side reactions. SUMMARY

[0004] The application provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material to solve the above problems in the prior art.

[0005] To achieve the above purpose, the application provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material, which comprises the following steps:

[0006] (a) adding polyaniline into a solution containing a protonic acid for treatment to obtain protonic acid-doped PANI;

[0007] (b) adding the protonic acid-doped PANI and PEG into organic solvents respectively to dissolve them to obtain a first mixture;

[0008] (c) adding inorganic functional materials and high-nickel ternary positive electrode materials into the first mixture respectively, stirring and ultrasonicating; after the reaction is completed, performing vacuum distillation and collecting a black substance, and drying to obtain the conductive polymer CEI film.

[0009] Optimally, in step (a), the protonic acid is a mixed acid composed of phosphoric acid and hydrochloric acid, and the mass ratio of the polyaniline to the mixed acid is 1:10-15.

[0010] Further, the volume ratio of hydrochloric acid to phosphoric acid in the mixed acid is 1:1-3.

[0011] Preferably, the concentration of phosphoric acid is 85%, and the concentration of hydrochloric acid is 36-38%.

[0012] Optimally, in step (a), after the polyaniline is added to the solution containing the protonic acid, it is moved into a flask and heated to 40-80°C for stirring for 0.5-2h, followed by ultrasonic treatment; and then it is subjected to suction filtration with a filter membrane with a pore size of ≤0.45μm, washed with deionized water until neutral, and dried to obtain the protonic acid-doped PANI.

[0013] Optimally, in step (b), the PEG is one of PEG1500 and PEG2000.

[0014] Optimally, the organic solvent is N-methylpyrrolidone or / and N,N-dimethylformamide.

[0015] Optimally, the mass ratio of the protonic acid-doped PANI to the PEG is 1:1, and the ratio of the PEG to the organic solvent is 0.15-0.6g:20ml.

[0016] Optimally, in step (c), the inorganic functional material is one selected from the group consisting of multi-walled carbon nanotubes and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0017] Preferably, the high-nickel ternary positive electrode material is NCM811.

[0018] Further, in step (c), the mass ratio of the inorganic functional material, the high-nickel ternary positive electrode material, and the PEG is 4-5:150-250:3.

[0019] Further, in step (c), it is stirred at 50-70°C for 0.5-2h, and ultrasonic treatment is performed for 5-20min.

[0020] Compared with the prior art, the application has the following advantages: the method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary positive electrode material of the application is simple and easy to operate, and the surface of the high-nickel ternary positive electrode material is pre-constructed with a conductive polymer, by compounding PANI, PEG and inorganic functional materials with the high-nickel ternary positive electrode material, so that the PANI exhibits polarity compatible with the electrolyte through hydrogen bonding, and the production is simple and easy to operate; the positive electrode material and the electrolyte are isolated from direct contact, so as to inhibit the dissolution of transition metal ions at a high potential; the lithium ion migration of the positive electrode-electrolyte interface of the coating layer is improved; and the conductive polymer-inorganic functional material composite can also adapt to the volume change and reduce the generation of micro-cracks of the positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The cycle performance diagrams of LiNi8Co1Mn1O2 / Li batteries prepared from Examples 1-2 and Comparative Examples 1-2 are as follows: (a) discharge curve diagram, (b) discharge rate diagram, (c) charge-discharge diagram of Comparative Example 1 at different rates, (d) charge-discharge diagram of Example 1 at different rates, and (e) charge-discharge diagram of Example 2 at different rates.

[0022] Figure 2 The post-cycle 100 EIS comparison diagrams of LiNi8Co1Mn1O2 / Li batteries prepared from Examples 1-2 and Comparative Examples 1-2 are as follows:

[0023] Figure 3 The XRD diagrams of LiNi8Co1Mn1O2 / Li batteries prepared from Examples 1-2 and Comparative Examples 1-2 are as follows: (a) XRD diagram before cycling, (b) XRD diagram after 100 cycles, and (c) magnified XRD diagram of the (003) diffraction plane after 100 cycles.

[0024] Figure 4 The SEM diagrams of LiNi8Co1Mn1O2 / Li electrodes in LiNi8Co1Mn1O2 / Li batteries prepared from Examples 1-2 and Comparative Examples 1-2 are as follows: (a) Comparative Example 1, (b) partial magnified diagram of Comparative Example 1, (c) Example 1, (d) partial magnified diagram of Example 1, (e) Comparative Example 2, (f) partial magnified diagram of Comparative Example 2, (g) Example 2, and (h) partial magnified diagram of Example 2.

[0025] Figure 5 The TF-IR diagrams and thermogravimetry of Examples 1-2 and Comparative Examples 1-2 are as follows: (a) infrared diagram of each example and comparative example, and (b) thermogravimetric diagram of Example 1, Example 2 and Comparative Example 2. DETAILED DESCRIPTION

[0026] This invention discloses a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, comprising the following steps: (a) treating polyaniline in a solution containing protic acid to obtain protic acid-doped PANI; (b) dissolving the protic acid-doped PANI and PEG in an organic solvent to obtain a first mixture; (c) adding an inorganic functional material and the high-nickel ternary cathode material to the first mixture, stirring, and sonicating; after the reaction is complete, vacuum distillation is performed, a black substance is collected, and dried. By combining protic acid-doped PANI, PEG, and inorganic functional materials with the high-nickel ternary cathode material, PANI exhibits polarity compatible with the electrolyte through hydrogen bonds, resulting in a high-nickel ternary cathode material composite layer with a pre-constructed conductive polymer on the surface. This method is simple and easy to implement; it helps to isolate the cathode material from direct contact with the electrolyte, thereby inhibiting the dissolution of transition metal ions at high potentials; it improves lithium ion migration at the cathode-electrolyte interface of the coating layer; and the conductive polymer-inorganic functional material composite can adapt to volume changes, reducing the generation of microcracks in the cathode material.

[0027] In step (a), the protic acid is a mixed acid composed of phosphoric acid and hydrochloric acid, and the mass ratio of polyaniline to the mixed acid is 1:10-15. The volume ratio of hydrochloric acid to phosphoric acid in the mixed acid is 1:1-3; preferably, the concentration of phosphoric acid is 85% and the concentration of hydrochloric acid is 36-38%. In step (a), after adding the polyaniline to the solution containing the protic acid, it is transferred to a flask and heated to 40-80°C and stirred for 0.5-2 hours, followed by sonication; it is then filtered through a filter membrane with a pore size ≤0.45μm, washed with deionized water until neutral, and dried to obtain protic acid-doped PANI. In step (b), the PEG is one of PEG1500 / or PEG2000. The organic solvent is N-methylpyrrolidone and / or N,N-dimethylformamide. The mass ratio of the protic acid-doped PANI to the PEG is 1:1, and the ratio of the PEG to the organic solvent is 0.15-0.6g:20ml. In step (c), the inorganic functional material is selected from multi-walled carbon nanotubes and LiTFSI; preferably, the high-nickel ternary cathode material is NCM811. In step (c), the mass ratio of the inorganic functional material, the high-nickel ternary cathode material, and PEG is 4–5:150–250:3. In step (c), the mixture is stirred at 50–70°C for 0.5–2 hours and sonicated for 5–20 minutes.

[0028] The preferred embodiments of the present invention will be described in detail below.

[0029] Example 1

[0030] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, including the following steps:

[0031] (a) Add PANI (1g) to a mixed acid (HCl and H3PO4, volume ratio 1:2, commercially available concentrated hydrochloric acid and concentrated phosphoric acid) (the mass ratio of PANI to the mixed acid is 1:10). Then, transfer the mixed acid solution containing PANI into a flask, heat to 50°C and stir for 1 hour. Place it in an ultrasonic instrument and sonicate at room temperature for 3 hours. After sonication, transfer PANI to a Buchner funnel on a vacuum filtration flask (with a microporous filter membrane with a pore size of 0.45μm in the funnel), filter it by a circulating water vacuum pump, wash it with deionized water until neutral, transfer it to a clean petri dish, and place it in a vacuum drying oven at 60°C for 8 hours to obtain proton acid-doped PANI.

[0032] (b) Take PANI (0.03g) and PEG (0.03g) after step (a) and add them to a single-necked flask. Add 10ml of NMP solvent and stir at 50°C for 3h and sonicate for 0.5h until the protic acid-doped PANI and PEG are completely dissolved in NMP (organic solvent) to obtain the first mixture.

[0033] (c) Take 0.045g MWCNTs and 2g NCM811 and add them to the first mixture. Stir at 60℃ for 1h and sonicate for 10min. After the reaction is complete, transfer the single-necked flask to a rotary evaporator for vacuum distillation at 100rpm and 80℃. After the organic solvent has evaporated, collect the black substance. Place it in a vacuum oven at 80℃ for 5h. After the organic solvent has completely evaporated, collect the PANIPEG / inorganic functional material composite high-nickel ternary cathode material.

[0034] 0.2g of the above-mentioned high-nickel ternary cathode material, 0.025g of Super P and 0.025g of polyvinylidene fluoride (PVDF) were mixed with an appropriate amount of NMP slurry in a ratio of 8:1:1. The mixture was then coated, dried and sliced ​​to assemble a LiNi8Co1Mn1O2 / Li half cell (denoted as PANIPEG / CNTs@NCM).

[0035] Example 2

[0036] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (c), 0.045g of LiTFSI is added, denoted as PANIPEG / LiTFSI@NCM.

[0037] Example 3

[0038] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), the mass ratio of PANI to mixed acid is 1:10.

[0039] Example 4

[0040] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), the mass ratio of PANI to mixed acid is 1:15.

[0041] Example 5

[0042] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), the volume ratio of HCl to H3PO4 in the mixed acid is 1:1.

[0043] Example 6

[0044] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), the volume ratio of HCl to H3PO4 in the mixed acid is 1:3.

[0045] Example 7

[0046] This embodiment provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (b), the mass ratio of PANI and PEG after step (a) is 1:0.5.

[0047] Comparative Example 1

[0048] This example provides a method for preparing a half-cell, which is basically the same as that in Example 1, except that NCM811 is used directly without modification (denoted as Pristine NCM).

[0049] Comparative Example 2

[0050] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that MWCNTs (denoted as PANIPEG@NCM) are not added in step (c).

[0051] Comparative Example 3

[0052] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), only phosphoric acid is used.

[0053] Comparative Example 4

[0054] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (a), only hydrochloric acid is used.

[0055] Comparative Example 5

[0056] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that the mass ratio of PANI to mixed acid is 1:20 (with excess mixed acid).

[0057] Comparative Example 6

[0058] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that the mass ratio of PANI to mixed acid is 1:5 (too little mixed acid).

[0059] Comparative Example 7

[0060] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (b), the mass ratio of PANI and PEG after step (a) is 1:0.2 (too little PEG).

[0061] Comparative Example 8

[0062] This example provides a method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, which is basically the same as that in Example 1, except that in step (b), the mass ratio of PANI to PEG after step (a) is 1:2 (too much PEG).

[0063] The cathode materials and the prepared half-cells from Examples 1-7 and Comparative Examples 1-8 were subjected to performance tests, and the test results are shown in the figure. Figures 1 to 5 And Table 1.

[0064] Table 1. Half-cell performance data for Examples 1-7 and Comparative Examples 1-8

[0065]

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material, characterized in that, Includes the following steps: (a) Polyaniline is added to a solution containing protic acid for treatment to obtain protic acid-doped PANI; (b) The protic acid doped PANI and PEG are added to an organic solvent and dissolved to obtain a first mixture; (c) Add the inorganic functional material and the high-nickel ternary cathode material to the first mixture respectively, stir and sonicate; after the reaction is completed, perform vacuum distillation, collect the black substance, and dry it. In step (a), the protic acid is a mixed acid composed of phosphoric acid and hydrochloric acid, and the mass ratio of polyaniline to the mixed acid is 1:10~15; the volume ratio of hydrochloric acid to phosphoric acid in the mixed acid is 1:1~3; the concentration of phosphoric acid is 85%, and the concentration of hydrochloric acid is 36~38%; in step (c), the inorganic functional material is selected from multi-walled carbon nanotubes and lithium bis(trifluoromethanesulfonyl)imide.

2. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: In step (a), after adding the polyaniline to the solution containing protic acid, the solution is transferred to a flask and heated to 40-80°C and stirred for 0.5-2 hours, followed by sonication; the solution is then filtered using a filter membrane with a pore size ≤0.45μm, washed with deionized water until neutral, and dried to obtain protic acid-doped PANI.

3. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: In step (b), the PEG is one of PEG1500 or PEG2000.

4. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: The organic solvent is N-methylpyrrolidone or / and N,N-dimethylformamide.

5. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: The mass ratio of the protic acid-doped PANI to the PEG is 1:1, and the ratio of the PEG to the organic solvent is 0.15~0.6g:20ml.

6. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: In step (c), the high-nickel ternary cathode material is NCM811.

7. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: In step (c), the mass ratio of the inorganic functional material, the high-nickel ternary cathode material, and PEG is 4~5:150~250:

3.

8. The method for constructing a conductive polymer CEI film on the surface of a high-nickel ternary cathode material according to claim 1, characterized in that: In step (c), stir at 50~70℃ for 0.5~2h and sonicate for 5~20min.

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