Bismuth metal anode, its preparation and application in sodium ion batteries

Abstract

The present invention belongs to the field of sodium-ion batteries, and specifically relates to a method for preparing a bismuth metal negative electrode, wherein a bismuth metal active layer is sputtered onto a current collector substrate by magnetron sputtering to prepare the bismuth metal negative electrode. The present invention also includes a bismuth metal negative electrode prepared by the preparation method and its application in a sodium-ion battery. The present invention innovatively uses ion sputtering to compound bismuth metal particles onto the current collector, which facilitates the preparation of a bismuth negative electrode suitable for sodium-ion batteries, with excellent sodium ion insertion and deinsertion efficiency and stability. In this way, a bismuth metal negative electrode that is suitable for a high-area-loaded positive electrode and has cycling stability under high current can be obtained.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and in particular relates to the technical field of sodium ion battery electrodes. Technical Background

[0002] In recent years, sodium-ion batteries have attracted widespread attention as a substitute for lithium-ion batteries. In addition to traditional carbon-based negative electrode materials, alloyed negative electrode materials are considered to be one of the excellent candidates for the new generation of high energy density / power density sodium-ion battery negative electrode materials due to their high theoretical specific capacity and suitable voltage platform. For example, metals such as bismuth, tin, antimony, and lead can all be used to store sodium by alloying with sodium. Among them, metal bismuth has low toxicity, is environmentally friendly, has abundant reserves, and has a high theoretical capacity and exhibits a suitable sodiumization voltage (average 0.55V (vs. Na + / Na)), and the layered structure of bismuth with a large interlayer spacing makes its volume expansion relatively smaller during the sodium insertion / extraction process, making it a very promising negative electrode material.

[0003] However, existing technologies primarily produce bismuth anodes through electroplating or by coating a mixture of bismuth powder and a binder onto a current collector, using traditional electrode sheet preparation methods. For example, Chinese patent publication CN116435495A discloses a bismuth electrode material, specifically describing the electrochemical reduction of a bismuth compound. Chinese patent publication CN113140723A discloses a coated, wide-temperature sodium-ion battery based on a metallic bismuth anode.

[0004] In summary, the existing bismuth anode material preparation process is complex and requires stringent conditions. Furthermore, bismuth powder generally requires pretreatment to suppress its volume expansion, thereby increasing the cycle life of the bismuth anode, which is detrimental to processing and cost control. Therefore, to avoid these issues, it is necessary to develop a simpler and more efficient method for producing bismuth anodes. Summary of the Invention

[0005] In order to solve the application performance of bismuth metal negative electrode in sodium metal battery, the first purpose of the present invention is to provide a preparation method of bismuth metal negative electrode for sodium ion battery, aiming to improve its application performance in sodium ion battery.

[0006] The second object of the present invention is to provide a bismuth metal negative electrode prepared by the preparation method and its application in sodium ion batteries.

[0007] The third object of the present invention is to provide a sodium ion battery comprising the bismuth metal negative electrode.

[0008] A method for preparing a bismuth metal negative electrode comprises sputtering a bismuth metal active layer on a current collector substrate by magnetron sputtering to prepare the bismuth metal negative electrode.

[0009] Different battery systems have different requirements for electrodes. For example, for lithium-ion and sodium-ion batteries, the radius of sodium ions is larger than that of lithium ions, and materials adapted for lithium-ion batteries are difficult to directly convert and adapt to sodium-ion battery applications. For example, for batteries with and without negative electrodes, the behavior of active ions in the electrodes is also different, and they also need to face different problems. For example, for the negative electrode of a sodium-ion battery, compared with a battery without a negative electrode, it needs to withstand the many problems caused by the frequent insertion and removal of sodium ions. The topic shifts to the present invention. In response to the problems with bismuth-containing negative electrodes, the present invention attempts to provide a negative electrode material in the industry that directly composites a metal bismuth layer on a current collector. However, studies have found that when such materials are used as negative electrodes for sodium-ion batteries, they need to solve the problems of large sodium ion insertion and removal impedance, and easy expansion, powdering and peeling. To address the problems faced by this idea, the present invention innovatively uses ion sputtering to compound bismuth metal particles on the current collector, which helps to prepare a bismuth negative electrode that is suitable for sodium ion batteries and has excellent sodium ion insertion and deinsertion efficiency and stability; not only that, it is also unexpectedly able to adapt to the application requirements of high surface load positive electrodes and large currents.

[0010] In the present invention, there is no special requirement for the current collector substrate, and any conductive current collector suitable for sodium ion batteries can be selected. For example, the current collector substrate can be at least one of aluminum foil, carbon-coated aluminum foil, and copper foil.

[0011] In the present invention, the metal bismuth composite layer is constructed on the current collector substrate through sputtering, which is crucial for improving the efficiency, pathway, and stability of sodium ion insertion and deintercalation. Furthermore, the study found that further optimizing and controlling the sputtering parameters and methods unexpectedly helped to further construct a physicochemical structure and stability that is compatible with sodium ion insertion and deintercalation, thereby further improving the performance of the prepared bismuth metal anode.

[0012] In the present invention, the magnetron sputtering stage adopts a DC power supply for sputtering.

[0013] In the present invention, the initial vacuum degree of sputtering is 1×10 -6 ~1×10 -4 Pa, preferably, the initial vacuum degree is 3×10 -6 ~4×10 -5 Pa, further 7×10 -6 ~1×10 -5 Pa.

[0014] In the present invention, the flow rate of argon gas during the sputtering process is 20 to 150 sccm, preferably, the flow rate of argon gas is 50 to 120 sccm, further preferably, 80 to 110 sccm.

[0015] In the present invention, the sputtering power is 10 to 80 W, preferably 20 to 65 W, and more preferably 25 to 55 W.

[0016] In the present invention, the total sputtering time is 5 to 120 minutes, preferably 5 to 90 minutes, and more preferably 30 to 70 minutes.

[0017] In the present invention, the sputtering process includes N sputtering processes, wherein adjacent sputtering stages are separated by a time interval of t, and the pressure of the system during the interval is negative pressure; N is 2 to 6; the time t is within 5 minutes; and the time of each sputtering stage is 0.1 to 2 times the average sputtering time.

[0018] The research of the present invention also shows that the innovative use of the multi-stage sputtering method, combined with processing parameters such as vacuum interval, can further optimize the distribution behavior and interface structure of metal bismuth on the current collector substrate, and can further optimize the efficiency and path of sodium ion insertion and deinsertion, which helps to further enhance its performance under high surface load positive electrode and high current.

[0019] In the present invention, N is 2 to 3; the time t is 1 to 5 minutes; and the time of each sputtering section is 0.5 to 1.5 times, and further 0.5 to 1 times, of the average sputtering time.

[0020] For example, in a preferred embodiment of the present invention, magnetron sputtering is performed using bismuth metal as a target and a current collector substrate as a substrate. The magnetron sputtering comprises a first stage of magnetron sputtering, followed by a second stage of magnetron sputtering after a period of time (t) under vacuum. In a further preferred embodiment, after the second stage of magnetron sputtering, a third stage of magnetron sputtering is performed after a period of time under vacuum.

[0021] Preferably, during the N-stage sputtering process, the power of the N-stage sputtering is 0.5 to 1 times the power of the N-1-stage sputtering. Preferably, during the N-stage sputtering process, the duration of the N-stage sputtering is 0.1 to 1 times the duration of the N-1-stage sputtering. The present invention also demonstrates that gradient control of the power and duration of multiple sputtering stages can further optimize the physical and chemical structure of the bismuth metal layer, helping to further improve the stability of the prepared cathode under high surface loads and high currents.

[0022] For example, the N-stage sputtering process is a two-stage sputtering process, wherein the power of the first stage magnetron sputtering is 25-35W, and the time of the first stage magnetron sputtering is 15-25 minutes; the power of the second stage magnetron sputtering is 20-30W, and the time of the second stage magnetron sputtering is 15-25 minutes; further preferably, the power of the first stage magnetron sputtering is 25-35W, and the time of the first stage magnetron sputtering is 20-25 minutes; the power of the second stage magnetron sputtering is 20-25W, and the time of the second stage magnetron sputtering is 20-25 minutes. The present invention shows that under this preferred condition, the sputtering mechanism and conditions can obtain better synergistic performance.

[0023] The present invention preferably adopts a three-stage sputtering process, wherein the power of each sputtering stage can be 25-35W, wherein the sputtering time of the first two stages is 20-25 minutes, and the sputtering time of the last stage is 10-25 minutes (preferably 10-15 minutes).

[0024] The present invention also provides a bismuth metal negative electrode prepared by the preparation method.

[0025] In the present invention, the preparation method can give the prepared material special physical and chemical characteristics, and the material with the characteristics prepared by the preparation method has more advantages in adaptability to high-surface-loaded positive electrodes, and can still obtain excellent electrochemical properties under large currents.

[0026] The bismuth metal negative electrode of the present invention has a bismuth metal layer loading of 0.5-6 mg cm -2 ; furthermore, it can be considered as 2-4 mg cm -2 .

[0027] The present invention also provides an application of the bismuth metal negative electrode, which is used as a negative electrode for preparing a sodium ion battery.

[0028] The present invention innovatively uses the bismuth metal negative electrode as the negative electrode. Based on its physical and chemical characteristics, it can solve the problems of unsatisfactory sodium ion embedding and de-embedding efficiency in the negative electrode and easy pulverization and peeling, and can improve its application performance in sodium ion batteries.

[0029] The present invention also provides a sodium ion battery, comprising a positive electrode, a barrier layer and a negative electrode that are composited in sequence, wherein the negative electrode is a bismuth metal negative electrode prepared by the preparation method of the present invention.

[0030] In the present invention, the sodium ion battery, except for the bismuth metal negative electrode of the present invention, can have other components and structures as known. In addition, the positive electrode of the present invention can be a conventional positive electrode, and further can be a conventional coated positive electrode. Furthermore, the surface loading of the positive electrode can be 2-27 mg cm -2; furthermore, it can be 10 to 20 mg cm -2 .

[0031] In the present invention, the barrier layer may be a diaphragm, or a solid or semi-solid electrolyte.

[0032] In addition, the sodium ion battery is also allowed to add a conventional electrolyte as needed. For example, when the barrier layer is a non-solid electrolyte, the system is allowed to add an electrolyte.

[0033] Beneficial effects

[0034] This invention provides, for the first time, a bismuth metal anode material with a bismuth metal layer directly composited onto a current collector via sputtering. The material is found to unexpectedly adapt to the sodium ion insertion and deinsertion requirements of sodium-ion battery anodes, improving the performance of these batteries. Furthermore, the use of multi-stage sputtering, coupled with optimal gradient control of the sputtering power and time, further enhances the physicochemical structure of the prepared material, further improving its performance in sodium-ion batteries.

[0035] The present invention studies show that the bismuth metal negative electrode prepared by the preparation method can adapt to the application requirements of high surface load positive electrode, and thus can still show excellent embedding and de-embedding efficiency and stability under high current. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the SEM image of the bismuth negative electrode obtained in Example 1

[0037] Figure 2 This is the SEM image of the bismuth negative electrode obtained in Example 1 after 100 cycles of half-cell assembly according to the test conditions.

[0038] Figure 3 The room temperature cycle performance diagram of the half-cell assembled with the bismuth negative electrode prepared in Example 1

[0039] Figure 4 The room temperature rate performance diagram of the half-cell assembled with the bismuth negative electrode prepared in Example 1

[0040] Figure 5 The room temperature cycle performance diagram of the full battery assembled with the bismuth negative electrode prepared in Example 1

[0041] Figure 6 The room temperature cycle performance diagram of the half-cell assembled with the scraped bismuth negative electrode prepared in Comparative Example 3 Specific embodiments

[0042] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0043] An optional method for preparing a bismuth negative electrode by magnetron sputtering of the present invention comprises the following steps:

[0044] 1) Install the bismuth target and place the clean current collector flat on the sample holder of the magnetron sputtering equipment chamber;

[0045] 2) Turn on the magnetron sputtering equipment and adjust the equipment to the required coating process;

[0046] 3) Using single-stage or step-by-step sputtering, a certain amount of metallic bismuth is sputtered on the surface of the current collector to obtain a bismuth negative electrode.

[0047] The negative electrode substrate of the present invention is made of one of aluminum foil, carbon-coated aluminum foil and copper foil;

[0048] In the present invention, aluminum foil, copper foil and other plain foils need to use plasma to clean impurities or oxides on the surface of the current collector.

[0049] In the present invention, a DC power supply is used for coating, and the initial vacuum degree of sputtering is 1×10 -6 ~1×10 -4 Pa, preferably, the vacuum degree is 3×10 -6 ~4×10 -5 Pa, further 7×10 -6 ~1×10 -5 Pa.

[0050] In the present invention, the flow rate of argon gas during the sputtering process is 20 to 150 sccm, preferably, the flow rate of argon gas is 50 to 120 sccm, further preferably, 80 to 110 sccm.

[0051] In the present invention, the sputtering power is 10 to 80 W, preferably 20 to 65 W, and further preferably 25 to 55 W.

[0052] In the present invention, the number of sputtering is 1 to 6 times, preferably 2 to 5 times, and further preferably 2 to 3 times.

[0053] In the present invention, the total magnetron sputtering time is controlled to be 5 to 120 minutes, preferably, the time is 5 to 90 minutes, further 30 to 70 minutes.

[0054] The bismuth negative electrode of the present invention is used for the preparation of sodium ion batteries.

[0055] In the present invention, the bismuth negative electrode of the present invention can be used to prepare a sodium ion battery based on conventional ideas.

[0056] The present invention also provides a button-type battery, which includes the bismuth negative electrode prepared by magnetron sputtering.

[0057] The structure of the button battery includes a positive electrode shell, a bismuth negative electrode, a polyethylene diaphragm, a glass fiber diaphragm, a positive electrode, a gasket, a spring, and a negative electrode shell in sequence.

[0058] The button cell of the present invention, apart from the bismuth negative electrode of the present invention, may have other components and structures that are well known. For example, the sodium sheet, separator, electrolyte, and battery structure may all be conventional.

[0059] For example, the positive electrode of the present invention may include a current collector and a positive electrode material composited on the surface thereof, wherein the positive electrode material includes a conventional sodium battery positive electrode active material, a conductive agent, and a binder.

[0060] For example, the positive electrode active material includes but is not limited to sodium vanadium phosphate, sodium vanadium fluoride phosphate, layered oxide positive electrode materials, and Prussian blue and its analogs positive electrode, etc., which are common positive electrode active materials with practical significance.

[0061] Test conditions

[0062] Preparation of positive electrode sheets: Weigh 0.8g of commercial sodium vanadium phosphate (NFPP) positive electrode material and mix with 0.1g of conductive carbon and grind for about 30 minutes. Then transfer it to a weighing bottle and add 2g of PVDF / NMP (N-methylpyrrolidone) solution with a PVDF content of 5%. Then add about 1mL of NMP and stir for 12h. Then, place the stirred mixture on the carbon-coated aluminum foil as the substrate and use a scraper to evenly spread it. Place it in a vacuum drying oven and dry it at 60℃ for 6h, then at 90℃ for 12h. Then take it out and cut it into positive electrode sheets with a diameter of 12mm. The ratio of active material, conductive carbon and binder is 8:1:1. The loading capacity of positive electrode material is about 14mg cm -2 Preparation of the sodium-ion battery electrolyte: 16.8 g of sodium hexafluorophosphate (NaPF6) was weighed and dissolved in 100 mL of ethylene glycol dimethyl ether (DME). 10 g of molecular sieves were added to remove any residual water in the DME to obtain a 1 M NaPF6 / DME electrolyte. The battery separators consisted of a 19 mm polyethylene membrane and a 19 mm glass fiber membrane.

[0063] A half-cell was assembled using sodium sheets, electrolyte, separator and corresponding bismuth negative electrode at a current density of 2Ag -2 The cycle stability was tested with 0.1Ag -2 , 0.2Ag-2 , 0.5Ag -2 , 1Ag -2 , 2Ag -2 , 5Ag -2 , 10Ag -2 The current density test rate performance is tested in the voltage range of 0 to 1.5V.

[0064] The cycling stability of the full battery was tested using the prepared cathode, electrolyte, separator, and corresponding bismuth anode. The loading of the cathode material was 14 ± 0.1 mg cm -2 The current density of the test is 2A g -2 The tested voltage range is 1.5~3.9V, and the specific capacity of the positive electrode active material is 100mAg -1 .

[0065] Example 1

[0066] After installing the bismuth target, place the current collector substrate (commercial carbon-coated aluminum foil in this case) flat on the sample holder, start magnetron sputtering, and wait until the initial vacuum reaches 1×10 -5 Pa, the magnetron sputtering process parameters were adjusted as follows: vacuum DC sputtering power 30W, argon flow rate 100sccm, sputtering times 2 times, each sputtering 23min, total sputtering time 46min, sample holder rotation speed 8r / min. The interval between adjacent sputtering steps was 4-5min, and the pressure of the system during the interval was controlled at 1×10 -5 Pa, metallic bismuth was sputtered onto carbon-coated aluminum foil, and the loading amount of bismuth negative electrode was 3±0.2 mg.

[0067] Example 2

[0068] Compared with Example 1, the only difference is that the current collector substrate is changed. The experimental groups are:

[0069] Group A: The current collector substrate is aluminum foil;

[0070] Group B: the current collector substrate is copper foil;

[0071] Other operations and parameters are the same as in Example 1.

[0072] The bismuth negative electrodes prepared in Example 1 and Example 2 were tested for the first coulombic efficiency (HCE) of the half-cell, the capacity retention rate (HCR) after 300 cycles, and the capacity retention rate (FCR) of the full-cell after 300 cycles according to the test conditions.

[0073] Table 1 The first coulombic efficiency and cycle stability of sodium ion half-cells and full cells assembled using different current collectors.

[0074] Half-cell Current collector substrate HCE HCR FCR Example 1 Carbon-coated aluminum foil 99.8％ 96.8％ 86.3％ Example 2-Group A aluminum foil 94.3％ 72.4％ 66.5％ Example 2-Group B copper foil 95.2％ 68.7％ 61.9％

[0075] It can be seen from Table 1 that the bismuth negative electrodes prepared using different current collector materials have high first coulombic efficiency and cycle stability.

[0076] Example 3

[0077] Compared with Example 1, the only difference is that the number of sputtering times, sputtering power, or total sputtering time is changed, and the sputtering time (min) and sputtering power (W) are marked as t1, t2, t3... and W1, W2, W3... respectively according to the number of sputtering times. The subsequent examples and comparative examples are consistent with this marking method. The experimental groups are:

[0078] Group A: Bismuth negative electrode was prepared using different sputtering times N, where the sputtering time was 46 / N min each time and the sputtering process and other parameters were the same.

[0079] The results of different sputtering times are shown in Table 2;

[0080] Table 2 The first coulombic efficiency and cycle stability of sodium ion half-cells and full cells assembled with bismuth anodes prepared with different sputtering times.

[0081] Number of sputtering HCE HCR FCR Example 3-A1 1 89.8％ 61.2％ 55.9％ Example 3-A2 3 97.3％ 88.6％ 79.8％ Example 3-A3 4 94.7％ 78.4％ 72.5％

[0082] Group B: Bismuth negative electrode was prepared using different sputtering powers.

[0083] The sputtering was performed using a two-stage sputtering process, with other operations and parameters being the same; the results are shown in Table 3;

[0084] Table 3 First coulombic efficiency and cycling stability of sodium ion half-cells and full cells assembled with bismuth anodes prepared with different sputtering powers.

[0085] <![CDATA[W1]]> t1 <![CDATA[W2]]> t2 HCE HCR FCR Example 3-B1 55 16 30 30 83.6％ 78.5％ 70.4％ Example 3-B2 30 30 55 16 80.8％ 73.7％ 67.2％ Example 3-B3 55 23 55 23 75.4％ 70.9％ 61.3％ Example 3-B4 30 23 20 23 99.9％ 97.6％ 89.5％

[0086] Other operations and parameters are the same as in Example 1.

[0087] Example 4

[0088] This embodiment further illustrates and optimizes the sputtering process parameters based on Example 3. Compared with Example 1, the only difference is that two or three of the sputtering times, sputtering power, and total sputtering time are changed simultaneously. Other operations and parameters are the same as in Example 1.

[0089] Table 4 The first coulombic efficiency and cycle stability of sodium ion half-cells and full cells assembled with bismuth negative electrodes prepared at different sputtering powers, different sputtering times and sputtering times.

[0090] <![CDATA[t1]]> <![CDATA[W1]]> <![CDATA[t2]]> <![CDATA[W2]]> <![CDATA[t3]]> <![CDATA[W3]]> HCE HCR FCR Example 4-Group A 23 30 23 30 13 30 96.7％ 87.5％ 78.1％ Example 4-Group B 23 30 23 30 23 30 95.3％ 86.0％ 76.6％ Example 4-Group C 20 30 20 30 10 30 99.8％ 94.2％ 86.2％

[0091] It can be seen from Table 2 that when the sputtering times are 2-3 times, the bismuth negative electrode has better performance.

[0092] It can be seen from Table 3 that, under the same total sputtering time, the use of a sputtering method with decreasing power can help to further improve the performance of the prepared bismuth negative electrode.

[0093] Comparative Example 1

[0094] Compared with Example 1, the only difference is that the target material used is Sb target or Sn target, and the other operations and parameters are the same as those in Example 1.

[0095] Comparative Example 2

[0096] Commercial bismuth powder electrodes were prepared using a similar blade coating method to that used for positive electrode sheets. Commercial bismuth powder (5-20 μm), conductive carbon, and PVDF binder were ground and mixed in a weight ratio of 8:1:1. An appropriate amount of NMP was added and magnetic stirring was performed for approximately 1 hour to form a uniform slurry. The slurry was then coated onto carbon-coated aluminum foil, with an active material loading of approximately 3 mg cm. -2 , and further vacuum dried at 80°C for 12h, and the obtained electrode piece was cut into electrode pieces with a diameter of 14mm to obtain a scraped bismuth negative electrode.

[0097] Comparative Example 3

[0098] A carbon-coated aluminum foil was used as the cathode and pure bismuth metal was used as the anode. The electrolyte was prepared by immersing the aluminum foil in an electrolyte solution consisting of 8 g bismuth nitrate, 3 g tartaric acid, 3 g polyethylene glycol, and 5 g NiCl dissolved in 200 mL dimethyl sulfoxide (DMSO). -2 The current density is used to reduce and deposit bismuth on the surface of the carbon-coated aluminum foil to form a bismuth layer, thereby obtaining an electroplated bismuth negative electrode (the bismuth content of the plated electrode is the same as that in Example 1).

[0099] Comparative Example 4

[0100] Compared with Example 1, the only difference is that the sputtering power used in the first sputtering is 100 W, and the other operations and parameters are the same as those in Example 1.

[0101] Comparative Example 5

[0102] Compared with Example 1, the only difference is that the second sputtering time is 80 minutes, and the other operations and parameters are the same as Example 1.

[0103] Table 5 shows the half-cell and full-cell performance tests of each comparative example according to the test conditions. The test results are as follows:

[0104]

[0105] Figure 1 This is the SEM image of the bismuth negative electrode obtained in Example 1. It can be seen that the bismuth negative electrode obtained by magnetron sputtering has a uniform morphology and a uniform structure. Figure 2The SEM image of the resulting bismuth anode assembled into a half-cell after 100 cycles under the aforementioned test conditions shows that the bismuth exhibits significant fibrillation after cycling and exhibits a regular, uniform interface under stress. Compared to Sn and Sb anodes prepared by magnetron sputtering, the Bi anode exhibits exceptionally superior stability, demonstrating the difficulty of deriving a Bi anode preparation process from existing magnetron sputtering techniques. Therefore, this magnetron sputtering strategy offers unique technical advantages for preparing Bi-based sodium-ion battery anodes.

[0106] Figure 3 and Figure 5 The figures are the cycle performance diagrams of half-cell and full-cell assembled with bismuth negative electrode prepared by the method described in Example 1, and it can be seen that its cycle performance is excellent. Figure 6 This is a rate performance diagram of a half-cell assembled with a bismuth negative electrode prepared by the method described in Example 1. The bismuth negative electrode has good rate performance.

Claims

1. A method for preparing a bismuth metal negative electrode, characterized in that: Using bismuth metal as a target and a current collector substrate as a base, a bismuth metal active layer is sputtered on the current collector substrate by magnetron sputtering to prepare the bismuth metal negative electrode; The sputtering process includes N sputtering stages, wherein adjacent sputtering stages are separated by a time interval of t, and the pressure of the system during the interval is negative pressure; N is 2 to 6; the time t is within 5 minutes; and the time of each sputtering stage is 0.1 to 2 times the average sputtering time; Sputtering power is 10~80 W; The total sputtering time is 30~70 min.

2. The method for preparing a bismuth metal negative electrode according to claim 1, wherein: The current collector substrate is at least one of current collector aluminum foil, carbon-coated aluminum foil, and copper foil.

3. The method for preparing a bismuth metal negative electrode according to claim 1, wherein: The magnetron sputtering stage uses a DC power supply for sputtering.

4. The method for preparing a bismuth metal negative electrode according to claim 1, wherein: The initial vacuum degree of sputtering is 1×10 −6 ~ 1×10 −4 Pa; The argon flow rate during the sputtering process was 20–150 sccm.

5. The method for preparing a bismuth metal negative electrode according to claim 4, wherein: The initial vacuum degree of sputtering is 3×10 -6 ~ 4×10 −5 Pa; The argon flow rate during the sputtering process was 50–120 sccm.

6. The method for preparing a bismuth metal negative electrode according to claim 4, wherein: The initial vacuum degree of sputtering is 7×10 -6 ~ 1×10 −5 Pa; argon flow rate is 80~110 sccm.

7. The method for preparing a bismuth metal negative electrode according to claim 1, wherein: The sputtering power is 20~65 W.

8. The method for preparing a bismuth metal negative electrode according to claim 7, wherein: The sputtering power is 25~55 W.

9. The method for preparing a bismuth metal negative electrode according to claim 1, wherein: The N is 2 to 3; the time t is 1 to 5 minutes; and the time of each sputtering section is 0.5 to 1.5 times of the average sputtering time.

10. The method for preparing a bismuth metal negative electrode according to claim 9, wherein: During the N-stage sputtering process, the power of the N-stage sputtering is 0.5 to 1 times the power of the N-1-stage sputtering; The time of the Nth sputtering stage is 0.1 to 1 times the time of the N-1th sputtering stage.

11. The method for preparing a bismuth metal negative electrode according to claim 10, wherein: The N-stage sputtering process consists of two-stage sputtering processes, wherein the power of the first stage magnetron sputtering is 25~35W, and the time of the first stage magnetron sputtering is 15~25min; the power of the second stage magnetron sputtering is 20~30W, and the time of the second stage magnetron sputtering is 15~25min.

12. The method for preparing a bismuth metal negative electrode according to claim 11, wherein: The N-stage sputtering process consists of two-stage sputtering process, wherein the power of the first stage magnetron sputtering is 25~35W, and the time of the first stage magnetron sputtering is 20~25min; the power of the second stage magnetron sputtering is 20~25W, and the time of the second stage magnetron sputtering is 20~25min.

13. The method for preparing a bismuth metal negative electrode according to claim 10, wherein: The N-stage sputtering process consists of three stages, wherein the power of each stage is 25-35W, the sputtering time of the first two stages is 20-25min, and the sputtering time of the last stage is 10-25min.

14. A bismuth metal negative electrode prepared by the preparation method according to any one of claims 1 to 13.

15. An application of a bismuth metal negative electrode prepared by the preparation method according to any one of claims 1 to 13, characterized in that: It is used as the negative electrode in the preparation of sodium ion batteries.

16. A sodium ion battery comprising a positive electrode, a barrier layer and a negative electrode which are compounded in sequence, wherein: The negative electrode is a bismuth metal negative electrode prepared by the preparation method according to any one of claims 1 to 13.

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