Carbon-iodine-silver composite negative electrode protective layer material and preparation method and application thereof

Abstract

The application discloses a carbon-iodine-silver composite negative electrode protective layer material and a preparation method and application thereof. The preparation method of the carbon-iodine-silver composite negative electrode protective layer material comprises the following steps: mixing, grinding and calcining pitch, MgO and KOH to obtain a carbon precursor; washing the carbon precursor with an acid solution, and then drying; after drying, the carbon precursor is mixed with elemental iodine and then ground, and the mixture is placed in a reaction kettle to react, so that a C-I2 composite material is obtained; and the C-I2 composite material is mixed with Ag powder and then ground, so that the carbon-iodine-silver composite protective layer material is obtained. The AgI generated by the carbon-iodine-silver composite protective layer material prepared by the application can react with Li metal to generate LiI and Li-Ag alloy, which is very helpful for stabilizing the negative electrode / electrolyte interface. The carbon-iodine-silver composite protective layer material has good long cycle stability and excellent rate performance in a full solid-state lithium ion battery based on a sulfide electrolyte, and provides a new idea for the modification method of the negative electrode interface of a solid-state battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a carbon-iodine-silver composite negative electrode protective layer material and a preparation method and application thereof. BACKGROUND

[0002] The use of sulfide solid electrolytes (S-SSEs) with high ionic conductivity (>10 -3 Scm -1 ) and high mechanical strength for all-solid-state lithium ion batteries (ASSLIBs) is the best solution to address the high energy density requirements and the safety concerns associated with traditional lithium ion batteries. Currently, lithium ion batteries typically use graphite as the negative electrode material, which has the advantages of abundant source and stable electrochemical performance, but its theoretical capacity (370 mAh g -1 ) is low, resulting in a low energy density of the battery, which is difficult to meet the current demand. In contrast, lithium (Li) metal anodes have a high specific capacity (3860 mAh g -1 ) and low density, making them ideal negative electrode materials for high-energy-density all-solid-state batteries. However, due to the relatively low potential of lithium metal (-3.04 V vs. SHE), the anode / electrolyte interface is unstable, and there are interface problems such as electrolyte decomposition at low voltage and interfacial reactions. In addition, lithium metal anodes are prone to lithium dendrite formation, which poses a safety hazard such as short circuit for the battery. Therefore, finding a practical solution to address the Li anode / S-SSEs interface problem is the primary challenge for the advancement of lithium metal anode technology. SUMMARY

[0003] To solve the interface problem of lithium metal negative electrode, the present application proposes to introduce a simple carbon-iodine-silver (C-I2-Ag) composite protective layer between S-SSEs and Li metal anode, which can form both LiI alloy and Ag-Li alloy, thereby achieving the purpose of reducing interface activity and inhibiting lithium dendrite.

[0004] To achieve the above purpose, the technical solution adopted by the present application is:

[0005] The present application provides a preparation method of a carbon-iodine-silver composite negative electrode protective layer material, comprising the following steps:

[0006] (1) mixing, grinding and calcining pitch, MgO and KOH to obtain a carbon precursor;

[0007] (2) washing the carbon precursor with an acid solution, then drying, and mixing and grinding the dried carbon precursor with elemental iodine and placing it in a reaction kettle to react, to obtain a C-I2 composite material;

[0008] (3) mixing and grinding the C-I2 composite material with Ag powder to obtain the carbon-iodine-silver composite protective layer material.

[0009] Preferably, in step (1), the mass ratio of the pitch, MgO and KOH is 1:(3.5-4.5):(1-2); in some specific preferred embodiments of the present application, the mass ratio of the pitch, MgO and KOH is 1:4:1.5.

[0010] Preferably, in step (1), the calcination conditions are: first calcination at 28-32℃ for 1.8-2.2h, then heating to 140-160℃ at a heating rate of 4-6℃ / min for 0.4-0.6h, and then heating to 750-850℃ at a heating rate of 4-6℃ / min for 0.8-1.2h; in some specific preferred embodiments of the present application, the calcination conditions are: first calcination at 30℃ for 2h, then heating to 150℃ at a heating rate of 5℃ / min for 0.5h, and then heating to 800℃ at a heating rate of 5℃ / min for 1h. The calcination in the present application is carried out under an inert atmosphere.

[0011] In the present application, the carbon precursor is washed with an acid solution, and the specific acid and concentration are not limited, and in some specific embodiments of the present application, hydrochloric acid solution is used for washing.

[0012] Preferably, in step (2), the mass ratio of the carbon precursor to iodine after drying is 1:(2-3); in some specific preferred embodiments of the present application, the mass ratio of the carbon precursor to iodine after drying is 3:7.

[0013] Preferably, in step (2), the reaction temperature in the reaction kettle is 75-85℃, and the reaction time is 10-14h; further preferably, the reaction temperature in the reaction kettle is 78-82℃, and the reaction time is 11-13h.

[0014] Preferably, in step (3), the mass ratio of the C-I2 composite material to Ag powder is 1:(0.5-2.5).

[0015] Further preferably, in step (3), the mass ratio of the C-I2 composite material to Ag powder is 1:(1-2).

[0016] The second aspect of the present application provides a carbon-iodine-silver composite negative electrode protective layer material prepared by the preparation method.

[0017] The third aspect of the present application provides the use of the carbon-iodine-silver composite negative electrode protective layer material in the preparation of solid-state lithium ion batteries.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The carbon-iodine-silver (C-I2-Ag) composite protective layer obtained by the present application can enhance the long cycle stability of the battery.

[0020] (2) The carbon-iodine-silver (C-I2-Ag) composite protective layer obtained by the present application can form LiI and Li-Ag alloy with the solid-state lithium ion battery, LiI helps to passivate the interface, and Li-Ag alloy can inhibit lithium dendrites and stabilize the negative electrode interface. Compared with traditional LiF, LiI not only provides the same interface stability as LiF, but also does not have the problems of high toxicity, high cost, and complex synthesis process.

[0021] (3) The carbon-iodine-silver (C-I2-Ag) composite protective layer obtained by the present application has thermodynamic stability to lithium metal and any solid-state electrolyte, and has a low diffusion barrier to lithium ions, which is beneficial to the rapid transport of lithium ions on the interface.

[0022] (4) The reaction is complete, which is conducive to stable production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 SEM cross-section of the carbon-iodine-silver (C-I2-Ag) composite protective layer based on the full solid-state lithium ion battery of Li6PS5Cl electrolyte prepared in Example 2;

[0024] Figure 2 XRD pattern of the carbon-iodine-silver (C-I2-Ag) composite protective layer material prepared in Example 2;

[0025] Figure 3 Long cycle test graph of the full solid-state lithium ion battery based on Li6PS5Cl electrolyte of Example 1, Example 2, Example 3 and Comparative Example 1 at 0.5C;

[0026] Figure 4 Rate performance graph of the full solid-state lithium ion battery based on Li6PS5Cl electrolyte of Example 1, Example 2, Example 3 and Comparative Example 1;

[0027] Figure 5 Impedance and equivalent circuit of the full solid-state lithium ion battery based on Li6PS5Cl electrolyte of Example 1, Example 2, Example 3 and Comparative Example 1 after cycling;

[0028] Figure 6 Long cycle of the full solid-state lithium ion symmetric battery based on Li6PS5Cl electrolyte of Example 4 and Comparative Example 2 at 0.15mAcm -2 Current density. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application are further described below. It is to be understood that the description of these embodiments is intended to help understand the present application and is not intended to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0030] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available unless otherwise specified.

[0031] Example 1

[0032] This embodiment provides a preparation process of a carbon-iodine composite negative electrode protective layer (C-I2) battery and an assembly process of a full solid-state battery thereof:

[0033] (1) Put pitch, MgO and KOH in a mortar in a mass ratio of 1:4:1.5, grind for 30 min and mix uniformly; put the ground mixture into a crucible, and send it into a tube furnace under a pure nitrogen atmosphere. First, calcine at 30°C for 2h, then increase the temperature to 150°C at a rate of 5°C / min, calcine at 150°C for 0.5h, similarly increase the temperature to 800°C at a rate of 5°C / min, calcine at 800°C for 1h, and then naturally cool to room temperature to obtain a C precursor.

[0034] (2) Mix the C precursor with excess HCl and ultrapure water and stir for 12h, then wash with deionized water and perform suction filtration. Place the water-washed sample in an oven and dry at 60°C for 12h.

[0035] (3) Put the dried sample and iodine in a mortar in a mass ratio of 3:7, mix uniformly, and then put them into a Schlenk bottle, seal tightly with sealing tape, and then put them into a reaction kettle and react at 80°C for 12h to obtain a C-I2 composite material. Press the C-I2 composite material into a thin film with a thickness of about 50μm.

[0036] (4) According to the NCM811 mixed positive electrode material 6mg, Li6PS5Cl is 250mg, C-I2 composite material as a modification layer, lithium sheet as a negative electrode, add to the mold and press into a solid-state battery.

[0037] Example 2

[0038] This embodiment provides a preparation process of a carbon-iodine silver composite negative electrode protective layer (C-I2-Ag) battery and an assembly process of a full solid-state battery thereof:

[0039] (1) Put asphalt, MgO, and KOH into a mortar at a mass ratio of 1:4:1.5, grind for 30 min, and mix uniformly; put the ground mixture into a crucible, and send it into a tube furnace under a pure nitrogen atmosphere. First, calcine at 30°C for 2 h, then increase the temperature to 150°C at a rate of 5°C / min, calcine at 150°C for 0.5 h, increase the temperature to 800°C at a rate of 5°C / min, calcine at 800°C for 1 h, and then naturally cool to room temperature to obtain a C precursor.

[0040] (2) Mix the C precursor with 1M HCl and ultrapure water, stir for 12 h, then wash with deionized water and perform suction filtration. Place the washed sample in an oven, dry at 60°C for 12 h, and then cool to room temperature.

[0041] (3) Put the dried sample and iodine into a mortar at a mass ratio of 3:7, mix uniformly, place in a Schlenk bottle, seal tightly with sealing tape, place in a reaction kettle, and react at 80°C for 12 h to obtain a C-I2 composite material. Mix the C-I2 composite material with Ag powder at a mass ratio of 1:1 to obtain a C-I2:Ag=1:1 composite material. Press the composite material into a thin film with a thickness of about 50 μm.

[0042] (4) According to the NCM811 mixed positive electrode material 6 mg, Li6PS5Cl is 250 mg, C-I2:Ag=1:1 composite material as a modification layer, lithium sheet as a negative electrode, and add a mold to press into a solid-state battery.

[0043] Example 3

[0044] This example provides a preparation process of a carbon-iodine-silver composite negative electrode protection layer (C-I2-Ag) battery and an assembly process of a full solid-state battery thereof:

[0045] (1) Put asphalt, MgO, and KOH into a mortar at a mass ratio of 1:4:1.5, grind for 30 min, and mix uniformly; put the ground mixture into a crucible, and send it into a tube furnace under a pure nitrogen atmosphere. First, calcine at 30°C for 2 h, then increase the temperature to 150°C at a rate of 5°C / min, calcine at 150°C for 0.5 h, increase the temperature to 800°C at a rate of 5°C / min, calcine at 800°C for 1 h, and then naturally cool to room temperature to obtain a C precursor.

[0046] (2) Mix the C precursor with 1M HCl and ultrapure water, stir for 12 h, then wash with deionized water and perform suction filtration. Place the washed sample in an oven, dry at 60°C for 12 h, and then cool to room temperature.

[0047] (3) The dried sample and elemental iodine were mixed in a mortar at a mass ratio of 3:7, then placed in a Schlenk bottle, sealed with sealing tape, and placed in a reaction kettle. After reacting at 80°C for 12h, C-I2 composite material was obtained. The C-I2 composite material and Ag powder were mixed in a mortar at a mass ratio of 1:2 to obtain a C-I2:Ag=1:2 composite material. The composite material was pressed into a thin film with a thickness of about 50μm.

[0048] (4) A solid-state battery was prepared by adding NCM811 mixed cathode material 6mg, Li6PS5Cl 250mg, C-I2:Ag=1:2 composite material as a modification layer, and lithium sheet as an anode into a mold.

[0049] Example 4

[0050] This example provides a preparation process of a carbon-iodine-silver composite anode protection layer (C-I2-Ag) battery and an assembly process of a full solid-state battery thereof:

[0051] (1) The asphalt, MgO, and KOH were placed in a mortar at a mass ratio of 1:4:1.5 and ground for 30min. The mixed material was placed in a crucible and sent into a tube furnace under a pure nitrogen atmosphere. First, it was calcined at 30°C for 2h, then the temperature was increased to 150°C at a rate of 5°C / min, and calcined at 150°C for 0.5h. Similarly, the temperature was increased to 800°C at a rate of 5°C / min, and calcined at 800°C for 1h, then naturally cooled to room temperature to obtain C precursor.

[0052] (2) The C precursor was mixed with 1M HCl and ultrapure water and stirred for 12h, then washed with deionized water and filtered. The washed sample was placed in an oven and dried at 60°C for 12h.

[0053] (3) The dried sample and elemental iodine were mixed in a mortar at a mass ratio of 3:7, then placed in a Schlenk bottle, sealed with sealing tape, and placed in a reaction kettle. After reacting at 80°C for 12h, C-I2 composite material was obtained. The C-I2 composite material and Ag powder were mixed in a mortar at a mass ratio of 1:1 to obtain a C-I2:Ag=1:1 composite material. The composite material was pressed into a thin film with a thickness of about 50μm.

[0054] (4) A solid-state battery was prepared by adding lithium sheet, C-I2:Ag=1:1 composite material thin film, 250mg of Li6PS5Cl, C-I2:Ag=1:1 composite material thin film, and lithium sheet into a mold.

[0055] Comparative Example 1: Assembly of bare-Li full solid-state battery

[0056] According to NCM811 mixed positive electrode material 6mg, Li6PS5Cl is 250mg, lithium sheet as negative electrode, add to the mold and press into solid-state battery.

[0057] Comparative Example 2: Assembly of bare-Li all-solid-state symmetric battery

[0058] Lithium sheet, 250mg of Li6PS5Cl, lithium sheet are added to the mold and pressed into an all-solid-state symmetric battery.

[0059] The present application carries out the following tests on Example 1, Example 2, Example 3, Example 4 and Comparative Example 1, Comparative Example 2.

[0060] As shown in Figure 1 , cross-section SEM (scanning electron microscope) test is carried out on Example 2, and the cross-section of C-I2-Ag negative electrode is studied by scanning electron microscope, Figure 1 As shown in , there is a thin film between the lithium sheet and the Li6PS5Cl electrolyte, and the thickness is about 50μm.

[0061] Figure 2 As shown in , XRD (X-ray diffraction) test is carried out on Example 2 after cycling, and it is found that there are LiI and Li-Ag alloy signals in the XRD pattern of Example 2 after cycling, which proves that LiI and Li-Ag are generated at the negative electrode / electrolyte interface after cycling. LiI can passivate the interface and accelerate the ion transmission of the interface, and the alloy formed between Li and Ag is beneficial to inhibit the growth of dendrites.

[0062] Figure 3 As shown in , long cycle test at 0.5C rate is carried out on Example 1, Example 2, Example 3 and Comparative Example 1, and it is found that compared with Comparative Example 1, Example 1, Example 2 and Example 3 show more excellent cycle stability, and the excellent performance is more prominent in Example 2.

[0063] Figure 4 As shown in , rate cycle stability test at 0.1C, 0.2C, 0.5C and 1C is carried out on Example 1, Example 2, Example 3 and Comparative Example 1, and it is found that among all examples and comparative examples, Example 2 has excellent cycle stability.

[0064] Figure 5As shown, EIS (electrochemical impedance spectroscopy) tests were performed on Examples 1, 2, 3, and Comparative Example 1. The EIS data were fitted and analyzed using Zivw software. From the equivalent circuit diagram, it can be seen that the impedance spectrum consists of three parts: electrolyte impedance R1, negative electrode interface impedance R2, and charge transfer impedance R3. The impedance fitting results for each part of Example 2 and Comparative Example 1 are shown in Table 1. It can be seen that after ten charge-discharge cycles at 0.2C, the negative electrode interface impedance and charge transfer impedance of bare-Li (208.1Ω and 910.4Ω) are significantly higher than those of the 1:1 sample (180.6Ω and 529.4Ω). The high anode interface impedance and charge transfer impedance indicate a severe interfacial reaction at the bare-Li / electrolyte interface, with a large accumulation of interfacial byproducts leading to difficulty in ion transport and resulting in high impedance. The introduction of the C-I2-Ag interfacial modification layer inhibits the interfacial reaction and accelerates ion transport at the interface, thus resulting in a lower impedance value.

[0065] Table 1

[0066] Sample Cycle 1R 2R 3R bare 10 68.08 208.1 910.4 1:1 10 65.15 180.6 529.4

[0067] like Figure 6 As shown, for Example 4 and Comparative Example 2, at 0.15 mA / cm -2 Lithium plating / stripping cycle tests were conducted at a current density of [value missing]. The unmodified Li / Li symmetric cell showed a sudden voltage increase after approximately 800 hours, while the modified symmetric cell showed no significant change and did not short-circuit even after more than 1500 hours of cycling. Furthermore, the potential of Example 4 was significantly lower than that of Comparative Example 2, indicating that side reactions at the interface were effectively suppressed.

[0068] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-iodine-silver composite solid-state lithium metal anode protection layer material, characterized in that, The method comprises the following steps: (1) mixing and grinding asphalt, MgO and KOH, and then calcining to obtain a carbon precursor; the calcining conditions are as follows: first calcining at 28-32 ℃ for 1.8-2.2 h, then increasing the temperature to 140-160 ℃ at a temperature increasing rate of 4-6 ℃ / min for calcining for 0.4-0.6 h, and then increasing the temperature to 750-850 ℃ at a temperature increasing rate of 4-6 ℃ / min for calcining for 0.8-1.2 h; (2) washing the carbon precursor with an acid solution, and then drying, mixing and grinding the dried carbon precursor with iodine, and then placing the mixture in a reaction kettle for reaction to obtain a C-I2 composite material; the reaction temperature in the reaction kettle is 75-85 ℃, and the reaction time is 10-14 h; (3) mixing and grinding the C-I2 composite material with Ag powder to obtain the carbon-iodine-silver composite solid-state lithium metal negative electrode protection layer material.

2. The method for preparing the carbon-iodine-silver composite solid lithium metal anode protective layer material according to claim 1, characterized in that, In step (1), the mass ratio of the asphalt, MgO and KOH is 1:(3.5-4.5):(1-2).

3. The preparation method of the carbon-iodine-silver composite solid lithium metal anode protective layer material according to claim 1, characterized in that, In step (2), the mass ratio of the dried carbon precursor and iodine is 1:(2-3).

4. The preparation method of the carbon-iodine-silver composite solid lithium metal anode protective layer material according to claim 1, characterized in that, In step (3), the mass ratio of the C-I2 composite material and Ag powder is 1:(0.5-2.5).

5. The preparation method of the carbon-iodine-silver composite solid lithium metal anode protective layer material according to claim 1, characterized in that, In step (3), the mass ratio of the C-I2 composite material and Ag powder is 1:(1-2).

6. A carbon-iodine-silver composite solid-state lithium metal negative electrode protection layer material prepared by the preparation method in any one of claims 1-5.

7. Application of the carbon-iodine-silver composite solid-state lithium metal negative electrode protection layer material in claim 6 in the preparation of a solid-state lithium ion battery.

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