A method for pre-sodiuming hard carbon anode material and a sodium-ion battery anode

Abstract

This invention provides a method for pre-sodiuming hard carbon anode materials and a sodium-ion battery anode. The pre-sodiuming method includes: mixing hard carbon material with a pre-sodiuming agent and then subjecting it to cold plasma for pre-sodiuming treatment to obtain pre-sodiumed hard carbon anode material. This invention solves the problems of low first-cycle coulombic efficiency, poor cycle stability, and poor rate performance of sodium-ion batteries prepared with hard carbon as the anode material by using cold plasma to achieve solid-phase pre-sodiuming technology.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more specifically, to a method for pre-sodiuming electrode materials and an electrode sheet. Background Technology

[0002] Lithium-ion batteries have been widely used in various fields such as automobiles, energy storage, ships, and communication base stations in recent years due to their excellent performance. However, the uneven geographical distribution and limited reserves of lithium resources have led to their high price, prompting researchers to turn to cheaper sodium-ion batteries. The main components of a sodium-ion battery include electrolyte, separator material, and positive and negative electrode materials. The negative electrode material accounts for a large proportion, as its performance directly affects the performance of the sodium-ion battery, and its cost directly determines the overall battery cost. There are many types of negative electrode materials for sodium-ion batteries, such as carbon materials (hard carbon, soft carbon), alloys, metal oxides, metal sulfides, phosphorus, and MXenes. Hard carbon materials have attracted much attention due to their excellent physical / chemical stability, good conductivity, and electrochemical stability. However, hard carbon-based negative electrodes have also revealed some significant problems, including low initial coulombic efficiency, poor cycle stability, and poor rate performance.

[0003] Currently, pre-sodiumization technology is the most commonly used method to solve the problems of low first-cycle coulombic efficiency and poor cycle stability of hard carbon-based anodes. Traditional pre-sodiumization methods mainly include four types: electrochemical methods, chemical methods, sodium metal physical methods, and short-circuit methods. However, traditional pre-sodiumization methods have high requirements for the operating environment, complex operating processes, high safety hazards, and generate large amounts of organic waste liquid, which are not conducive to industrial-scale promotion. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for pre-sodiuming hard carbon anode materials that is low in cost, simple to operate, environmentally friendly, has a short production cycle, and is easy to industrialize.

[0005] One aspect of the present invention provides a method for pre-sodiuming a hard carbon anode material, which may include the following steps: mixing hard carbon material with a pre-sodiuming agent and then placing it in cold plasma for pre-sodiuming treatment to obtain a pre-sodiumed hard carbon anode material.

[0006] Furthermore, the mass ratio of hard carbon material to pre-sodiumizing agent is 1:(0.0005~0.05).

[0007] Furthermore, the pre-sodiumizing agent is one or more of sodium sulfide, sodium carbonate, sodium chloride, sodium sulfate, sodium nitrate, sodium fluoride, sodium bicarbonate, and sodium acetate.

[0008] Furthermore, the power of the cold plasma generation is 100W to 300W, and the plasma treatment time is 0 to 20 minutes.

[0009] Furthermore, the cold plasma atmosphere is one or more of argon, oxygen, nitrogen, hydrogen, ammonia, methane, phosphine, and hydrogen sulfide.

[0010] Furthermore, cold plasma can be generated through dielectric barrier discharge, DC glow discharge, pulsed glow discharge, magnetron discharge, capacitively coupled radio frequency discharge, inductively coupled radio frequency discharge, or microwave discharge.

[0011] Another aspect of the present invention provides a sodium-ion battery anode, which may include the hard carbon anode material pre-sodiumized by the above-described hard carbon anode material pre-sodiumization method.

[0012] Another aspect of the present invention provides a method for preparing a sodium-ion battery anode, which may include the following steps: mixing the hard carbon anode material pre-sodiumized by the above-described hard carbon anode material pre-sodiumization method with a conductive agent and a binder to form a slurry; coating the slurry onto a current collector to obtain a sodium-ion battery anode.

[0013] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0014] (1) This invention uses cold plasma to achieve solid-phase pre-sodiumization, which solves the problems of low first-cycle coulombic efficiency, poor cycle stability and poor rate performance of sodium-ion batteries made with hard carbon as the negative electrode material.

[0015] (2) The method of the present invention has the advantages of low cost, simple operation, environmental friendliness, short production cycle and easy industrialization, and has very important industrialization value. Attached Figure Description

[0016] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 The image shows the SEM image of the pre-sodiumized hard carbon anode material prepared in Example 1.

[0018] Figure 2 XPS image of the pre-sodiumized hard carbon material prepared in Example 1.

[0019] Figure 3 The image shows a CV comparison between the hard carbon material prepared in Example 2 and the hard carbon material prepared in Comparative Example 1.

[0020] Figure 4 The image shows the battery cycle performance after the electrode sheet prepared in Example 3 is assembled into a battery.

[0021] Figure 5 The image shows the battery cycle performance after the electrode sheet prepared in Example 4 was assembled into a battery.

[0022] Figure 6 The image shows the battery cycle performance after the electrode sheet prepared in Comparative Example 1 is assembled into a battery. Detailed Implementation

[0023] In the following, a method for pre-sodiuming a hard carbon anode material and a sodium-ion battery anode according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0024] One aspect of the present invention provides a method for pre-sodiuming a hard carbon anode material. In some embodiments, the method for pre-sodiuming a hard carbon anode material may include the following steps:

[0025] Hard carbon material is mixed with a pre-sodiumizing agent and then subjected to pre-sodiumization treatment in cold plasma (DBD) to obtain pre-sodiumized hard carbon anode material.

[0026] In summary, pre-sodiumizing hard carbon materials using cold plasma can give them more electroactive sites, thereby enabling faster ion transport kinetics. This is beneficial for ion transport and allows the prepared sodium-ion batteries to have high first-cycle coulombic efficiency, good cycle stability, and good rate performance.

[0027] In some embodiments, the mass ratio of hard carbon material to pre-sodiumizing agent can be 1:(0.0005–0.05). This mass ratio affects the amount of active sodium and other substances entering the hard carbon material. For example, the mass ratio can be 1:(0.005–0.045), 1:(0.009–0.041), 1:(0.01–0.038), 1:(0.015–0.032), 1:(0.021–0.029), or a combination thereof. Preferably, the mass ratio of hard carbon material to pre-sodiumizing agent can be 1:(0.01–0.05). Within this preferred range, the hard carbon material contains suitable active sodium to achieve sodiumization, and the pre-sodiumizing agent content is not too high, resulting in excessive residue that could affect the reversible capacity and energy density of the electrode material.

[0028] In some implementations, the presodiumizing agent may be one or more of sodium sulfide, sodium carbonate, sodium chloride, sodium sulfate, sodium nitrate, sodium fluoride, sodium bicarbonate, and sodium acetate.

[0029] In summary, by using the aforementioned pre-sodiumizing agent and then treating it with cold plasma, active sodium can be introduced into the hard carbon material during the pre-sodiumization process, while other elements and / or oxygen-containing functional groups that are beneficial to the performance of the hard carbon material can be doped, thus giving the hard carbon material more active sites. For example, when the pre-sodiumizing agent is sodium sulfide, Na2S can be introduced into the hard carbon material after cold plasma treatment, achieving the simultaneous introduction of active sodium and elemental sulfur (S). The introduction of sulfur can give the pre-sodiumized hard carbon material pseudocapacitive characteristics after being assembled into a battery, which can accelerate mass transfer, improve cycle performance, and improve the initial coulombic efficiency. Furthermore, the doping of Na2S will first form a stable SEI with the electrolyte, which is beneficial to the cycle stability of the battery. Preferably, when the mass ratio of hard carbon material to pre-sodiumizing agent is 1:(0.035~0.05), the button battery assembled from the hard carbon material after plasma treatment and Na2S doping exhibits better cycle stability. After 600 cycles at a current density of 3A / g, it still retains a capacity of over 170mAh / g, with a capacity retention rate of over 80%, and the charge / discharge efficiency remains around 100%. The introduction of active sodium and S doping simultaneously enhances the pseudocapacitive properties of the hard carbon material, resulting in high cycle performance and high initial coulombic efficiency. For example, when the pre-sodiumizing agent is sodium fluoride, the cold plasma treatment of the hard carbon material introduces fluorine along with active sodium, further improving the pseudocapacitive properties and thus enhancing the cycle performance and initial coulombic efficiency of the battery. Similarly, when the pre-sodiumizing agent is sodium nitrate, the cold plasma treatment of the hard carbon material introduces nitrogen along with active sodium. Similarly, when the pre-sodiuming agent is sodium sulfate, the hard carbon material will introduce sulfur along with active sodium after cold plasma treatment; when the pre-sodiuming agent is sodium acetate or sodium bicarbonate, the hard carbon material will also introduce oxygen-containing functional groups for doping along with active sodium after cold plasma treatment, which can further improve the pseudocapacitive characteristics of the hard carbon material, thereby enhancing the cycle performance and first coulombic efficiency of the battery.

[0030] In some implementations, the power of the cold plasma generator can be between 100W and 300W, and the cold plasma treatment time can be no more than 20 minutes. At these power and treatment times, excessive power or long treatment times will not cause the disordered structures in the hard carbon material to transform into ordered structures, thus affecting the cycling stability of the hard carbon material. For example, the power of the cold plasma generator can be a combination of 120W–280W, 135W–265W, 148W–251W, 163W–218W, or higher. The cold plasma treatment time can be a combination of 3–17 minutes, 7–15 minutes, 9–13 minutes, 10–12 minutes, or higher.

[0031] In some implementations, the cold plasma atmosphere can be one or more of argon, oxygen, nitrogen, hydrogen, ammonia, methane, phosphine, and hydrogen sulfide. During the pre-sodiumization process, the gas in the cold plasma atmosphere can dope the hard carbon anode material. For example, when the atmosphere is nitrogen, nitrogen can be introduced into the hard carbon material for doping. When the atmosphere is oxygen, oxygen-containing functional groups can be introduced into the hard carbon material. Simultaneous doping of the hard carbon material by introducing active sodium, sulfur, or fluorine from the pre-sodiumization agent, as well as elements from the atmosphere, through cold plasma treatment can give the hard carbon material more active sites, thereby giving the electrode material faster ion transport kinetics. This is beneficial for ion transport and improves the rate performance, cycle performance, and initial coulombic efficiency of the battery.

[0032] In some implementations, the cold plasma can be generated by dielectric barrier discharge, DC glow discharge, pulsed glow discharge, magnetron discharge, capacitively coupled radio frequency discharge, inductively coupled radio frequency discharge, or microwave discharge. Of course, the cold plasma generation method of the present invention is not limited to these; any method capable of generating cold plasma is acceptable.

[0033] In some implementations, the pre-sodiumation method may further include the following specific steps:

[0034] Step (1) involves grinding and mixing commercially available hard carbon material with a pre-sodium reagent at a set mass ratio to obtain a uniformly mixed pretreated powder material.

[0035] Step (2): The pretreated powder material is evenly spread in a specially made glass mold, transferred to the cold plasma instrument, connected to the gas cylinder and the mold, and pre-ventilated. For example, pre-ventilate for 2 to 5 minutes.

[0036] Step (3) involves modifying the pretreated material with cold plasma to obtain the pre-sodiumized hard carbon material.

[0037] Another aspect of the present invention provides a sodium-ion battery anode. In some embodiments, the sodium-ion battery anode comprises a hard carbon anode material pre-sodium-treated by the aforementioned hard carbon anode material pre-sodium-treatment method.

[0038] Another aspect of the present invention provides a method for preparing a sodium-ion battery negative electrode, which may include the following steps:

[0039] S01, the pre-sodium-treated hard carbon anode material described above is mixed with a conductive agent and a binder to form a slurry;

[0040] SO2 is used to coat the slurry onto the current collector to obtain the negative electrode of the sodium-ion battery.

[0041] In some embodiments, the conductive agent can be any one of materials such as carbon black, graphite, graphene, carbon fiber, and Super P. The adhesive can be a composite adhesive composed of any one of styrene-butadiene rubber, polytetrafluoroethylene, and aqueous polyacrylate with sodium carboxymethyl cellulose. In some embodiments, the mass ratio of the pre-sodium-treated hard carbon material, the conductive agent, and the adhesive can be adjusted according to actual conditions. For example, the mass ratio of the pre-sodium-treated hard carbon material, carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) can be 80:10:5:5.

[0042] In some implementations, the current collector can be aluminum foil, copper foil, copper mesh, or copper foam, etc.

[0043] Another aspect of the present invention provides a sodium-ion battery, wherein in some embodiments, the sodium-ion battery includes a sodium-ion battery negative electrode prepared by the sodium-ion battery negative electrode preparation method described above.

[0044] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0045] Example 1

[0046] A method for pre-sodiuming hard carbon anode materials includes the following steps:

[0047] Step (1): Weigh commercially available hard carbon material and Na2S at a mass ratio of 1:0.005 and grind and mix them in an agate mortar for 10 minutes to obtain a uniformly mixed pretreated powder material.

[0048] Step (2): Spread the pretreated powder material evenly in a special glass mold, transfer it to the DBD instrument, connect the gas cylinder and the mold, and pre-ventilate it for 3 minutes.

[0049] Step (3) involves treating the pretreated powder material with a power of 150W and a nitrogen atmosphere for 6 minutes to obtain the pre-sodiumized hard carbon material.

[0050] SEM images of the pre-sodium-treated hard carbon material are shown below. Figure 1 As shown. From Figure 1 It can be seen that the surface of the treated hard carbon contains many fine particles, combined with... Figure 2 The XPS image of the pre-sodium-treated hard carbon material shown indicates that the fine particles are Na2S particles incorporated after treatment.

[0051] Electrode sheets are prepared using pre-sodium-treated hard carbon material. The preparation method includes the following steps:

[0052] S01, mix the pre-sodium-treated hard carbon material according to the ratio of hard carbon: carbon black: CMC: SBR = 80:10:5:5, and grind for 35 minutes to obtain a slurry;

[0053] S02, the slurry is uniformly coated onto the negative electrode current collector aluminum foil using a coating machine. The coating thickness of the slurry is 0.05 mm. The aluminum foil carrying the slurry is placed in a vacuum oven and dried at 55°C for 7 hours to obtain a hard carbon material electrode sheet.

[0054] Example 2

[0055] A method for pre-sodiuming hard carbon anode materials includes the following steps:

[0056] Step (1): Weigh commercially available hard carbon material and Na2S at a mass ratio of 1:0.02 and grind and mix them in an agate mortar for 10 minutes to obtain a uniformly mixed pretreated powder material.

[0057] Step (2): Spread the pretreated powder material evenly in a special glass mold, transfer it to the DBD instrument, connect the gas cylinder and the mold, and pre-ventilate it for 3 minutes.

[0058] Step (3) involves treating the pretreated powder material with a power of 150W and a nitrogen atmosphere for 6 minutes to obtain the pre-sodiumized hard carbon material.

[0059] Electrode sheets are prepared using pre-sodium-treated hard carbon material. The preparation method includes the following steps:

[0060] S01, the pre-sodium-treated hard carbon material is mixed according to the ratio of hard carbon:carbon black:CMC:SBR = 80:10:5:5, and ground for 55 minutes to obtain a slurry;

[0061] S02, the slurry is uniformly coated onto the negative electrode current collector aluminum foil using a coating machine. The coating thickness of the slurry is 0.05 mm. The aluminum foil carrying the slurry is placed in a vacuum oven and dried at 110°C for 20 h to obtain a hard carbon material electrode sheet.

[0062] Example 3

[0063] A method for pre-sodiuming hard carbon anode materials includes the following steps:

[0064] Step (1): Weigh commercially available hard carbon material and Na2S at a mass ratio of 1:0.035 and grind and mix them in an agate mortar for 10 minutes to obtain a uniformly mixed pretreated powder material.

[0065] Step (2): Spread the pretreated powder material evenly in a special glass mold, transfer it to the DBD instrument, connect the gas cylinder and the mold, and pre-ventilate it for 3 minutes.

[0066] Step (3) involves treating the pretreated powder material with a power of 150W and a nitrogen atmosphere for 6 minutes to obtain the pre-sodiumized hard carbon material.

[0067] Electrode sheets are prepared using pre-sodium-treated hard carbon material. The preparation method includes the following steps:

[0068] S01, the pre-sodium-treated hard carbon material is mixed according to the ratio of hard carbon:carbon black:CMC:SBR = 80:10:5:5, and ground for 40 minutes to obtain a slurry;

[0069] S02, the slurry is uniformly coated onto the negative electrode current collector aluminum foil using a coating machine. The coating thickness of the slurry is 0.05 mm. The aluminum foil carrying the slurry is placed in a vacuum oven and dried at 80°C for 15 h to obtain a hard carbon material electrode sheet.

[0070] Example 4

[0071] A method for pre-sodiuming hard carbon anode materials includes the following steps:

[0072] Step (1): Weigh commercially available hard carbon material and Na2S at a mass ratio of 1:0.05 and grind and mix them in an agate mortar for 10 minutes to obtain a uniformly mixed pretreated material.

[0073] Step (2): Spread the pretreated powder material evenly in a special glass mold, transfer it to the DBD instrument, connect the gas cylinder and the mold, and pre-ventilate it for 3 minutes.

[0074] Step (3) involves treating the pretreated material with a DBD plasma of 150W in a nitrogen atmosphere for 6 minutes to obtain the pre-sodiumized hard carbon material.

[0075] Electrode sheets are prepared using pre-sodium-treated hard carbon material. The preparation method includes the following steps:

[0076] S01, the pre-sodium-treated hard carbon material is mixed according to the ratio of hard carbon:carbon black:CMC:SBR = 80:10:5:5, and ground for 45 minutes to obtain a slurry;

[0077] S02, the slurry is uniformly coated onto the negative electrode current collector aluminum foil using a coating machine. The coating thickness of the slurry is 0.05 mm. The aluminum foil carrying the slurry is placed in a vacuum oven and dried at 65°C for 15 h to obtain a hard carbon material electrode sheet.

[0078] Comparative Example 1

[0079] Cold plasma treatment of hard carbon anode materials includes the following steps:

[0080] Step (1): Place commercially available hard carbon material in an agate mortar and grind for 10 minutes to obtain pretreated powder material;

[0081] Step (2): Spread the pretreated powder material evenly in a special glass mold, transfer it to the DBD instrument, connect the gas cylinder and the mold, and pre-ventilate it for 3 minutes.

[0082] Step (3) involves treating the pretreated powder material with a power of 150W and a nitrogen atmosphere for 6 minutes to obtain the treated hard carbon material.

[0083] Electrode sheets are prepared using treated hard carbon material. The preparation method includes the following steps:

[0084] S01, the modified hard carbon material is mixed according to the ratio of hard carbon:carbon black:CMC:SBR = 80:10:5:5, and ground for 40 minutes to obtain a slurry;

[0085] S02, the slurry is uniformly coated onto the negative electrode current collector aluminum foil using a coating machine. The coating thickness of the slurry is 0.05 mm. The aluminum foil carrying the slurry is placed in a vacuum oven and dried at 110°C for 20 h to obtain a hard carbon material electrode sheet.

[0086] The electrode sheets prepared in Examples 1-4 and Comparative Example 1 were used as the negative electrodes of the batteries, and their charge-discharge performance was tested. 1M NaF6 dissolved in dimethyl glycol ether (DME) was used as the electrolyte. The outer casing was made of stainless steel, and the positive electrode was a sodium metal sheet. A glass fiber separator was used to separate the positive and negative electrodes, assembling them into coin cells. Finally, electrochemical tests were performed on the above coin cells, with a voltage range of 0.01V to 3V, and the test temperature was room temperature. The commercially available hard carbon used in the above examples was purchased from BTR.

[0087] Figure 3 The figure shows a CV comparison between the hard carbon material prepared in Example 2 and the hard carbon material prepared in Comparative Example 1, where Example 2 refers to Example 2. As can be seen from the figure, the hard carbon material after pre-sodium treatment has a larger peak area and peak current, indicating that the material has faster ion transport kinetics, which is beneficial for ion transport and will result in better rate performance of the battery. Figure 4 The figure shows the battery cycle performance after the electrode sheet prepared in Example 3 is assembled into a battery, where Example 3 refers to Example 3. Figure 5 The figure shows the battery cycle performance after the electrode sheet prepared in Example 4 is assembled into a battery, where Example 4 refers to Example 4. Figure 6 The image shows the cycle performance of the battery assembled from the electrode sheets prepared in Comparative Example 1. Figure 4 ,5 Compared to 6, the button battery assembled from hard carbon material after DBD treatment and Na2S doping exhibits better cycle stability. After 600 cycles at a current density of 3 A / g, the capacity remains at 174.4 mAh / g, with a capacity retention of over 80%, and the charge / discharge efficiency remains around 100%. This demonstrates that the introduction of sulfur (S) after Na2S doping imparts pseudocapacitive properties to the hard carbon material, accelerating mass transfer, improving battery cycle performance and initial coulombic efficiency; furthermore, the addition of Na2S initially forms a stable SEI with the electrolyte, which is beneficial to the battery's cycle stability. (Comparison) Figure 6 After DBD treatment, without Na2S doping, the capacity rapidly decayed to 110 mAh / g after 220 cycles at a current density of 3 A / g, which is significantly worse than the capacity retention of the pre-sodium-treated hard carbon material after 600 cycles.

[0088] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for pre-sodiumizing a hard carbon negative electrode material, characterized in that, The method comprises the following steps: The hard carbon material is mixed with a pre-sodium agent and then placed in a cold plasma for pre-sodium treatment to obtain a pre-sodium hard carbon negative electrode material, wherein The mass ratio of the hard carbon material to the pre-sodium agent is 1:(0.0005-0.05). The pre-sodium agent is one or more of sodium sulfide, sodium carbonate, sodium chloride, sodium sulfate, sodium nitrate, sodium fluoride, sodium bicarbonate, and sodium acetate. 2.The method of pre-sodiumizing hard carbon negative electrode material according to claim 1, characterized in that, The power of the cold plasma is 100-300 W, and the cold plasma treatment time is not more than 20 min. 3.The method of pre-sodiumizing hard carbon negative electrode material according to claim 1 or 2, characterized in that, The cold plasma atmosphere is one or more of argon, oxygen, nitrogen, hydrogen, ammonia, methane, phosphine, and hydrogen sulfide. 4.The method of pre-sodiumizing hard carbon negative electrode material according to claim 1 or 2, characterized in that, The cold plasma is generated by dielectric barrier discharge, direct current glow discharge, pulse glow discharge, magnetic control discharge, capacitive coupling radio frequency discharge, inductive coupling radio frequency discharge, or microwave discharge.

5. A sodium-ion battery anode, characterized in that, The pre-sodium hard carbon negative electrode material is obtained by the pre-sodium method of any one of claims 1-4.

6. The method of claim 5, wherein the sodium-ion battery anode is prepared by, The method comprises the following steps: The pre-sodium hard carbon negative electrode material obtained by the pre-sodium method of any one of claims 1-4 is mixed with a conductive agent and a binder to form a slurry; The slurry is coated on a current collector to obtain a sodium ion battery negative electrode.

7. A sodium-ion battery, characterized in that, The sodium ion battery negative electrode is prepared by the method of claim 6.

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