Method for reactivating failed hard carbon negative electrode material and application thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a method for reactivating a failed hard carbon negative electrode material and application thereof, and the method comprises the following steps: putting a failed hard carbon negative electrode sheet into ethylene glycol dimethyl ether for ultrasonic cleaning and then drying; and placing the dried hard carbon negative electrode plate in a mold, and carrying out reactivating treatment by using cold plasma to obtain an activated hard carbon negative electrode plate. Reactivation treatment of the failed hard carbon electrode plate is achieved through cold plasma, the failed hard carbon electrode plate is cleaned with ethylene glycol dimethyl ether, residual sodium salt and glass fibers on the surface of the electrode plate are removed, cold plasma treatment is facilitated, and direct etching of a solid electrolyte layer is facilitated; harmful gas and waste liquid are not generated in the process of etching the surface of the electrode plate by adopting the gas-phase plasma, so that the problems of high cost, energy consumption, harmful gas emission, acid waste, extra treatment cost and the like caused by the recovery process of the failed hard carbon electrode plate as a negative electrode material are solved, and the economic benefit is favorably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method for reactivating a failed hard carbon negative electrode material and an application thereof. Background Art

[0002] With the continuous expansion of the new energy market, the use of lithium-ion batteries has increased dramatically, but the reserves of lithium resources are limited, so sodium-ion batteries with more abundant resources have attracted much attention. Sodium-ion batteries are composed of electrolytes, diaphragm materials, positive and negative electrode materials, etc. Among them, negative electrode materials account for a large proportion and directly affect battery performance. Hard carbon negative electrodes are the most commercially promising, but such hard carbon negative electrode materials are undervalued as waste materials after failure, and the operating costs of large-scale stacking are high, so recycling needs to be considered. Recycling is divided into physical recycling and chemical recycling. Physical recycling separates some effective ingredients through mechanical crushing, but the cost is high and the benefits are low. Chemical recycling will produce acidic waste, harmful gases, etc., which is not environmentally friendly and has the problem of high cost and low benefits.

[0003] Therefore, there is an urgent need to develop a method for reactivating failed hard carbon negative electrode materials and their applications, so that the hard carbon negative electrode materials can be directly activated and reused from a failed state through more economical and environmentally friendly means. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reactivating failed hard carbon negative electrode materials and its application, so as to directly activate and reuse the hard carbon negative electrode materials from the failed state through relatively economical and environmentally friendly means, thereby solving the problems of high cost, low benefit and low reuse rate of existing methods for recovering failed hard carbon negative electrode materials.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for reactivating a failed hard carbon negative electrode material, characterized in that it comprises the following steps:

[0006] 1) The failed hard carbon negative electrode sheet is ultrasonically cleaned in ethylene glycol dimethyl ether and then dried;

[0007] 2) placing the dried hard carbon negative electrode sheet in a mold and performing reactivation treatment using cold plasma to obtain an activated hard carbon negative electrode sheet.

[0008] A further technical solution is that the ultrasonic cleaning time in 1) is 10 to 30 seconds. The ultrasonic cleaning time is related to the active sites restored by the electrode material after activation. If the ultrasonic time is too short, it will not be able to effectively remove the glass fibers, sodium salts and other substances that damage the electrode active sites on the surface of the electrode sheet. If the ultrasonic time is too long, it may cause irreversible damage to the electrode material, resulting in the loss of active hard carbon material.

[0009] A further technical solution is that the drying in 1) is carried out in a vacuum drying oven at 55-60° C. for 12-36 hours.

[0010] A further technical solution is that the generation mode of the cold plasma in the above 2) is one of dielectric barrier discharge, DC glow discharge, pulsed glow discharge, magnetron discharge, capacitively coupled radio frequency discharge, inductively coupled radio frequency discharge or microwave discharge, the generation power is 100W to 300W, and the cold plasma treatment time is 1min to 5min.

[0011] A further technical solution is that the cold plasma atmosphere in 2) is one or more of nitrogen, ammonia, fluorine, hydrogen fluoride, nitrogen trifluoride, phosphine and hydrogen sulfide. During the reactivation process, the gas in the cold plasma atmosphere can be used to dope the hard carbon material. When the atmosphere is a nitrogen-containing element, nitrogen atoms can be introduced into the hard carbon material. After cold plasma treatment, the SEI layer of the material is etched and nitrogen elements are doped into the hard carbon material at the same time, so that the hard carbon material has more active sites and faster ion transport kinetics, which is beneficial to the transmission of ions and is beneficial to improving the rate performance, cycle performance and first-cycle coulomb efficiency of the battery.

[0012] A further technical solution is that the activated hard carbon negative electrode sheet is used to prepare a negative electrode for a sodium ion battery.

[0013] A further technical solution is that the activated hard carbon negative electrode sheet is placed in a vacuum drying oven for drying and then used as the negative electrode of a sodium ion battery.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention realizes the reactivation treatment of failed hard carbon electrode sheets through cold plasma. First, ethylene glycol dimethyl ether is used to clean the failed hard carbon electrode sheets to remove the sodium salt and glass fiber remaining on the surface of the electrode sheets, so that the subsequent plasma treatment is more conducive to directly etching the solid electrolyte layer (SEI); secondly, the process of etching the surface of the electrode sheets by gas phase plasma does not produce harmful gases and waste liquids, which solves the problems of high cost and energy consumption, harmful gas emissions, acidic waste and additional disposal costs caused by the recycling process of failed hard carbon electrode sheets as negative electrode materials, and helps to improve economic benefits.

[0016] (2) The present invention utilizes cold plasma to etch the surface of the hard carbon material electrode sheet to reduce the excessively thick SEI during the battery cycle. At the same time, nitrogen doping can be introduced into the hard carbon material during the treatment process to improve the intrinsic conductivity of the hard carbon material, which is beneficial to the reversible deintercalation of sodium ions. The hard carbon material recovered by the present invention can reach more than 95% of the original capacity of the hard carbon material, providing a new idea for the recovery of hard carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is a SEM comparison of the reactivated and failed hard carbon negative electrode materials prepared in Example 1.

[0018] Figure 2 This is a SEM comparison picture of the cleaned hard carbon negative electrode material and the uncleaned material in Example 5.

[0019] Figure 3 This is a cycle capacity diagram of the original hard carbon material in Example 1 cycled to failure.

[0020] Figure 4 This is a cycle performance diagram of the reactivated hard carbon material prepared in Example 1.

[0021] Figure 5 This is the cycle performance diagram of the reactivated hard carbon material prepared in Example 2.

[0022] Figure 6 This is a battery cycle performance diagram after the electrode sheet prepared in Example 3 is assembled into a battery.

[0023] Figure 7 This is a battery cycle performance diagram after the electrode sheet prepared in Comparative Example 1 is assembled into a battery.

[0024] Figure 8 This is a battery cycle performance diagram after the electrode sheet prepared in Comparative Example 1 is assembled into a battery. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] A method for reactivating a spent hard carbon negative electrode material comprises the following steps:

[0028] Step (1), placing the failed hard carbon negative electrode sheet in an ethylene glycol dimethyl ether solution for ultrasonic cleaning for 10 seconds, and then placing it in a vacuum drying oven at 60° C. for 24 hours to obtain a hard carbon electrode sheet to be activated;

[0029] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0030] Step (3), using DBD cold plasma with a power of 100W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 1 minute, a reactivated hard carbon negative electrode material can be obtained.

[0031] Example 2

[0032] A method for reactivating a spent hard carbon negative electrode material comprises the following steps:

[0033] Step (1), placing the failed hard carbon negative electrode sheet in an ethylene glycol dimethyl ether solution for ultrasonic cleaning for 20 seconds, and then placing it in a vacuum drying oven at 60° C. for 24 hours to obtain a hard carbon electrode sheet to be activated;

[0034] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0035] Step (3), using DBD cold plasma with a power of 100W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 2 minutes, a reactivated hard carbon negative electrode material can be obtained.

[0036] Example 3

[0037] A method for reactivating a spent hard carbon negative electrode material comprises the following steps:

[0038] Step (1), placing the failed hard carbon negative electrode sheet in an ethylene glycol dimethyl ether solution for ultrasonic cleaning for 30 seconds, and then placing it in a vacuum drying oven at 60° C. for 24 hours to obtain a hard carbon electrode sheet to be activated;

[0039] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0040] Step (3), using DBD cold plasma with a power of 100W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 3 minutes, a reactivated hard carbon negative electrode material can be obtained.

[0041] Example 4

[0042] A method for reactivating a spent hard carbon negative electrode material comprises the following steps:

[0043] Step (1), placing the failed hard carbon negative electrode sheet in an ethylene glycol dimethyl ether solution for ultrasonic cleaning for 20 seconds, and then placing it in a vacuum drying oven at 60° C. for 24 hours to obtain a hard carbon electrode sheet to be activated;

[0044] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0045] Step (3), using DBD cold plasma with a power of 50W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 3 minutes, a reactivated hard carbon negative electrode material can be obtained.

[0046] Example 5

[0047] A method for reactivating a spent hard carbon negative electrode material comprises the following steps:

[0048] Step (1), placing the failed hard carbon negative electrode sheet in an ethylene glycol dimethyl ether solution for ultrasonic cleaning for 20 seconds, and then placing it in a vacuum drying oven at 60° C. for 24 hours to obtain a hard carbon electrode sheet to be activated;

[0049] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0050] Step (3), using DBD cold plasma with a power of 200W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 3 minutes, a reactivated hard carbon negative electrode material can be obtained.

[0051] Comparative Example 1

[0052] The hard carbon negative electrode material is directly subjected to cold plasma treatment without cleaning or drying, comprising the following steps:

[0053] Step (1), placing the failed hard carbon negative electrode sheet in a vacuum drying oven at 60° C. and drying for 24 h;

[0054] Step (2), placing the dried hard carbon electrode sheet in a glass mold, transferring it to a cold plasma instrument, connecting a gas cylinder and the mold, and pre-ventilating it for 1 minute;

[0055] Step (3), using DBD cold plasma with a power of 100W and a nitrogen atmosphere to treat the pretreated hard carbon electrode sheet for 3 minutes, a reactivated hard carbon negative electrode material can be obtained.

[0056] Example 6

[0057] The electrode sheets prepared in Examples 1 to 5 were used as the negative electrode of the sodium ion battery to test its charge and discharge performance. 1M NaF6 dissolved in ethylene glycol dimethyl ether (DME) was used as the electrolyte. The outer shell was made of stainless steel, the positive electrode was made of a metal sodium sheet, and the positive electrode was separated from the negative electrode by a glass fiber diaphragm to assemble into a button battery. Finally, the assembled button battery was subjected to an electrochemical test with a voltage range of 0.01V to 3V and a test temperature of room temperature. The commercially available hard carbon materials used in the above-described embodiments were purchased from B&T.

[0058] SEM image of failed hard carbon material Figure 1 (a) and Figure 2 (b). Figure 2 (b) It can be clearly seen that the surface of the failed hard carbon electrode has many small bulges and small cracks and is covered with a layer of sodium salt, such as Figure 1As shown, after cold plasma treatment, the surface-coated SEI and sodium salt are removed, exposing the active carbon material surface, which is conducive to better electrochemical performance of the electrode material.

[0059] like Figure 2 As shown in (a) and (b), compared with the SEM images of cleaned and uncleaned hard carbon materials, it can be clearly seen that the surface of the cleaned electrode sheet has been removed by most of the surface, and the smoother surface proves that the plasma successfully activates the activity of the electrode material, which is conducive to the electrode material to exert better electrochemical performance. Figure 3 As shown, the hard carbon material is 0.1Ag -1 The initial capacity at the current density is 275.9 mAh g -1 After 275 cycles, its capacity is only 182.9 mAh g -1 (66.3% of the initial capacity).

[0060] After cleaning, plasma treatment and drying, the cells were reassembled and then electrochemically tested. Figure 4 As shown in the figure, the electrode material treated with DBD plasma at a power of 100 W and a nitrogen atmosphere for 1 min after cleaning, and its capacity recovered to 225 mAh g at the same current density. -1 , which is 81.8% of the initial capacity, such as Figure 5 and 6 As shown in the figure, the materials treated for 2 min and 3 min under the same conditions showed 233.1 mAh g -1 and 261.3mAh g -1 The capacity of the material treated for 3min recovered to 94.7% of the initial capacity, reaching a smaller capacity loss of 95% of the initial capacity.

[0061] In order to compare the treatment effects under different powers, the best treatment time was 3 min and the DBD plasma treatment was performed with 50 W and 200 W power respectively (Example 4 and Example 5). The results are as follows: Figure 7 and 8 As shown, the capacity of the electrode treated with 200W is 156mAh g -1 The processing power may be too high, the electrode sheet curls, and its surface area is reduced when the battery is installed, resulting in the inability to fully receive the sodium ions from the positive electrode material, causing capacity loss. When the processing power is 50W, the capacity of the material is only 96mAh g -1 This is because the smaller processing power cannot remove the SEI and sodium salt on the surface of the material. On the contrary, the oxygen that the electrode sheet contacts during the drying and processing process causes a passivation layer to form on the surface, resulting in surface inactivation and a large loss of capacity.

[0062] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for reactivating a spent hard carbon negative electrode material, characterized in that: The following steps are involved: 1) The failed hard carbon negative electrode sheet is ultrasonically cleaned in ethylene glycol dimethyl ether and then dried; 2) placing the dried hard carbon negative electrode sheet in a mold and performing reactivation treatment using cold plasma to obtain an activated hard carbon negative electrode sheet.

2. A method for reactivating a spent hard carbon negative electrode material according to claim 1, characterized in that: The ultrasonic cleaning time in 1) is 10 to 30 seconds.

3. A method for reactivating a spent hard carbon negative electrode material according to claim 1, characterized in that: The drying in 1) is carried out in a vacuum drying oven at 55-60° C. for 12-36 hours.

4. A method for reactivating a spent hard carbon negative electrode material according to claim 1, characterized in that: The generation mode of the cold plasma in the above 2) is one of dielectric barrier discharge, DC glow discharge, pulse glow discharge, magnetron discharge, capacitively coupled radio frequency discharge, inductively coupled radio frequency discharge or microwave discharge, the generation power is 100W to 300W, and the cold plasma treatment time is 1min to 5min.

5. The method for reactivating a spent hard carbon negative electrode material according to claim 1, characterized in that: The cold plasma atmosphere in the above 2) is one or more of nitrogen, ammonia, fluorine, hydrogen fluoride, nitrogen trifluoride, phosphine and hydrogen sulfide.

6. A method for reactivating a spent hard carbon negative electrode material according to any one of claims 1 to 5, characterized in that: The activated hard carbon negative electrode sheet is used to prepare the negative electrode of a sodium ion battery.

7. The activated hard carbon negative electrode sheet according to claim 6, characterized in that: The activated hard carbon negative electrode sheet is placed in a vacuum drying oven for drying and then used as a negative electrode of a sodium ion battery.

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