A bismuth electrode material and a method for preparing the same

Abstract

This application discloses a bismuth electrode material and its preparation method, belonging to the field of lithium-ion battery electrodes. The bismuth electrode material is obtained by electrochemical reduction of a bismuth compound. As a negative electrode material for lithium-ion batteries, the bismuth electrode material exhibits high energy density, good cycle stability, and excellent rate performance. Furthermore, the preparation process is simple.

Description

Technical Field

[0001] This application relates to a bismuth electrode material and its preparation method, belonging to the field of lithium-ion battery electrodes. Background Technology

[0002] Recently, with the development of portable electronic devices and electric vehicles (EVs), the demand for lithium-ion batteries (LIBs) has increased rapidly. To meet these demands, exploring novel electrode materials with high energy density and high safety is an effective approach. Commercially available lithium-ion batteries primarily use graphite anodes. However, graphite anodes have a low specific capacity (372 mAh·g). -1 The limited energy density of lithium-ion batteries restricts their development towards higher energy densities. Therefore, there is an urgent need to develop high-energy anode materials such as bismuth to improve the energy density of lithium-ion batteries.

[0003] Bismuth anodes possess high theoretical specific capacity, with a volumetric specific capacity reaching 3765 mAh·cm³. -3 It has five times the capacity of graphite anodes, making it one of the ideal anodes for lithium-ion batteries. However, lithium-ion batteries undergo significant volume changes during charging and discharging, leading to electrode structure pulverization, rapid capacity decay, and poor cycle stability. Summary of the Invention

[0004] According to the first aspect of this application, a bismuth electrode material is provided, obtained by electrochemical reduction of a bismuth compound. The bismuth electrode material exhibits high specific capacity and is used as the negative electrode in lithium-ion batteries, which possess high energy density. Furthermore, with increasing charge-discharge cycle count, the average particle size of the bismuth electrode material gradually decreases to the nanometer scale. This nanometer-scale particle size effectively mitigates volume changes in the bismuth electrode material during charge-discharge cycles, improving the cycle stability of the lithium-ion battery.

[0005] A bismuth electrode material is obtained by electrochemical reduction of a bismuth compound.

[0006] Optionally, the bismuth compound has an average particle size of 10 nm to 2 μm.

[0007] Optionally, the average particle size of the bismuth compound is selected from any value or a range between 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, and 2 μm.

[0008] Optionally, the bismuth compound is at least one of bismuth oxide and bismuth metal salt.

[0009] Optionally, the bismuth compound is a bismuth oxide or a bismuth metal salt.

[0010] Optionally, the bismuth compound has a nano-hollow cubic structure.

[0011] Optionally, the bismuth compound is at least one of bismuth vanadate, bismuth nitrate, and bismuth carbonate.

[0012] Optionally, the bismuth oxide is bismuth oxide.

[0013] For example, bismuth vanadate with nano-hollow cubic structure can be electrochemically reduced to a three-dimensional nanostructured bismuth electrode material.

[0014] According to a second aspect of this application, a method for preparing a bismuth electrode material is provided, comprising the following steps:

[0015] S1. A mixture containing bismuth compound, conductive additives and adhesive is coated on copper foil as the positive electrode, and metal is used as the negative electrode to form an electrochemical reaction device.

[0016] S2. Apply voltage or current between the positive and negative electrodes to electrochemically reduce the bismuth compound and prepare the bismuth electrode material.

[0017] Optionally, in step S1, the metal is an active metal.

[0018] Optionally, in step S1, the metal is lithium.

[0019] Optionally, in step S1, the conductive additive is carbon black.

[0020] Optionally, in step S1, the adhesive is polyvinylidene fluoride.

[0021] Optionally, in step S1, the mass ratio of the bismuth compound, the conductive additive, and the adhesive is 6-9:0.5-3.5:0.5-3.5.

[0022] Optionally, in step S1, the mass ratio of the bismuth compound, conductive additive, and binder is 7-9:0.5-2.5:0.5-2.5.

[0023] Optionally, in step S1, a membrane is further included between the positive and negative electrodes of the electrochemical device.

[0024] Optionally, the diaphragm is a microporous polypropylene membrane.

[0025] Optionally, the electrochemical device further includes an electrolyte;

[0026] The electrolyte is composed of lithium hexafluorophosphate as the solute and a mixture of ethylene carbonate and methyl ethyl carbonate as the solvent.

[0027] Optionally, the molar concentration of lithium hexafluorophosphate in the electrolyte is 0.8-1.2M.

[0028] Optionally, the volume ratio of ethylene carbonate to ethyl methyl carbonate in the solvent of the electrolyte is 1:1.

[0029] Optionally, in step S2, the ratio of the current density applied between the negative and positive electrodes to the mass of the bismuth compound is 80-120 mAh·g. -1 .

[0030] Optionally, the current density is independently selected from 80 mAh·g -1 85mAh·g -1 90mAh·g -1 95mAh·g -1 100mAh·g -1 105mAh·g -1 110mAh·g -1 115mAh·g -1 120mAh·g -1 Any value in the range or any value between the two.

[0031] Optionally, in step S2, the applied voltage ranges from 3.0V to 0.01V.

[0032] Optionally, in step S2, the electrochemical reduction is carried out under an inactive atmosphere.

[0033] Optionally, the inactive atmosphere is selected from at least one of nitrogen and argon.

[0034] In existing technologies, the preparation of bismuth via ion exchange is difficult to achieve. This invention solves this technical problem through electrochemical reduction. This is because in bismuth compound molecules, the positively charged region is concentrated near the bismuth (Bi) ions. When the bismuth compound is used as the positive electrode in an electrochemical device, the bismuth (Bi) in the positively charged region gains negatively charged electrons and is reduced to bismuth (Bi). Therefore, bismuth can be prepared through electrochemical reduction. Bismuth (Bi) is grown in situ on copper (Cu) foil, providing ample buffer space for the volume expansion of bismuth (Bi) during lithium-ion insertion / extraction. This fully utilizes the high capacity potential of the bismuth electrode material while mitigating the volume expansion effect during charge and discharge. Furthermore, the morphology of bismuth (Bi) continuously transforms during lithium-ion battery charge-discharge cycles, eventually transforming into a three-dimensional nanostructured bismuth electrode material. The three-dimensional nanostructure provides unique electron and lithium-ion transport channels and has a larger specific surface area; therefore, the bismuth electrode material prepared by this invention exhibits high energy density, good cycle stability, and excellent rate performance.

[0035] According to a third aspect of this application, an application of bismuth electrode material in lithium-ion batteries is provided. Bismuth (Bi) grown in situ on copper (Cu) foil can also be directly used as the negative electrode in lithium-ion batteries, assembled with lithium foil to form a lithium-ion half-cell, exhibiting high energy density, good cycle stability, and excellent rate performance. Bismuth (Bi) at 100 mA·g -1 The stable discharge specific capacity at current density is 497.5 mAh·g. -1 At 100 mA·g -1 After 200 cycles at the current density, the capacity retention rate was 63.9%. Meanwhile, the coulombic efficiency remained above 100%, and the maximum specific capacity of the battery during cycling reached 777.1 mAh·g. -1 .

[0036] The bismuth electrode materials described above and / or the bismuth electrode materials obtained by the preparation methods described above are used in lithium-ion batteries, zinc-ion batteries, sodium-ion batteries, potassium-ion batteries, and bismuth-ion batteries.

[0037] The beneficial effects that this application can produce include:

[0038] 1) The bismuth electrode material provided in this application, as a negative electrode material for lithium-ion batteries, has high energy density, good cycle stability and excellent rate performance.

[0039] 2) This application provides a method for preparing a bismuth electrode material, which involves the electrochemical reduction of a bismuth compound. Specifically, the electrochemical reduction of nano-hollow cubic bismuth vanadate yields a three-dimensional nanostructured bismuth electrode material, providing ample buffer space for the volume change of bismuth during lithium-ion insertion / extraction, thus improving its cycle stability. The three-dimensional nanostructure provides unique electron and lithium-ion transport channels and has a larger specific surface area, further improving the energy density, cycle stability, and rate performance of lithium-ion batteries.

[0040] 3) The application of metallic bismuth as a negative electrode material provided in this application in lithium-ion batteries, which exhibit high energy density, cycle stability, and rate performance. The bismuth electrode material, when used as the negative electrode of a lithium-ion battery, achieves a maximum specific capacity of 777.1 mAh·g. -1 100mA·g -1 The stable discharge specific capacity at the current density is 497.5 mAh·g. -1 After 200 cycles, the capacity retention rate was 63.9%, and the coulombic efficiency remained above 100%. Attached Figure Description

[0041] Figure 1 This is an X-ray diffraction pattern of the bismuth electrode material prepared in Example 3 of the present invention.

[0042] Figure 2 The image shows the microstructure of the bismuth electrode material prepared in Example 3 of this invention, with a scale bar of 1 μm.

[0043] Figure 3 The charge-discharge curves of the bismuth electrode material prepared in Example 3 of this invention for the first three cycles;

[0044] Figure 4 Rate curves of the bismuth electrode material prepared in Example 3 of this invention at different current densities;

[0045] Figure 5 The charge-discharge cycle curve of the bismuth electrode material prepared in Example 3 of this invention is shown. Detailed Implementation

[0046] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0047] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially, wherein:

[0048] Polyvinylidene fluoride (PVDF, HSV 900) was purchased from Arkema. Ethylenediaminetetraacetic acid disodium dihydrate (EDTA) and NaOH were purchased from Sinopharm Chemical Reagent Co., Ltd. Conductive carbon black was purchased from TIMCAL Graphite & Carbon. Nitric acid (65%–68%) was purchased from Xilong Chemical Co., Ltd. Ammonium metavanadate (NH4VO3) and bismuth nitrate (Bi(NO3)3·5H2O) were purchased from Aladdin. All chemicals were used directly according to the purchased methods without further purification.

[0049] The analysis method in the embodiments of this application is as follows:

[0050] The phase structures of bismuth vanadate and its discharge products were determined using a benchtop X-ray diffractometer (MiniFlex 600). The test conditions were Cu Kα target, voltage 40 kV, current 15 mA, scan rate 10° / min, and scan range 10°–80°. The morphology and size of bismuth vanadate and its discharge products were observed using a scanning electron microscope (SEM, SU8010) and a transmission electron microscope (TEM, JEM-2010). The sample structure was determined using a confocal Raman spectrometer (LabRAM HR) with a light source of 532 nm.

[0051] Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses were performed on an electrochemical workstation at Princeton, USA. The CV scan rate was 0.1 mV / s. -1The voltage range is 0.01–3V, and the EIS test frequency range is 0.01–100,000Hz. The assembled coin cells were subjected to constant current charge-discharge tests using the Xinwei Battery Testing System, with a test voltage of 0.01V–3.0V.

[0052] The battery was subjected to constant current charge-discharge testing at 30°C using a battery tester (CT-4008-5V50A-164, Neware China), with a voltage range of 3.0V-0.01V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed using an electrochemical workstation (Princeton PARSTAT MC). The scan rate for the cyclic voltammetry test was 0.1 mV / s. -1 .

[0053] Example 1

[0054] 1.1 Nano-Bi anode material and its preparation

[0055] CR2025 coin cells were assembled for electrochemical discharge, with nano-hollow cubic bismuth nitrate as the negative electrode material. The conductive additives and binders were carbon black (Super P, Timcal) and polyvinylidene fluoride (PVDF, HSV 900), respectively. Step 1: A slurry was prepared by mixing nano-hollow cubic BiVO4, PVDF, and Super P in a mass ratio of 8:1:1. This slurry was coated onto copper foil, dried, and then assembled into a coin cell casing with a Celgard 2500 microporous polypropylene membrane, a lithium metal sheet, and an electrolyte in a glove box under a high-purity argon atmosphere. The electrolyte was a mixture of 1.0 M LiPF6 dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EM) (1:1 volume ratio). After activation for 24 h, the BiVO4 electrode was connected to the positive electrode of the battery tester, and the lithium metal sheet was connected to the negative electrode. A 100 mAh g⁻¹ was applied. -1 A bismuth anode containing three-dimensional nano-bismuth anode material was prepared by using a constant current and a voltage ranging from 3.0V to 0.01V on the surface of a copper foil.

[0056] 1.2 Lithium-ion battery preparation

[0057] The negative electrode, separator, and lithium sheet were stacked sequentially and assembled into a CR2025 battery case in an assembly glove box under a high-purity argon atmosphere. Electrolyte was then added. The electrolyte was a mixture of 1.0M LiPF6 dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EM) (1:1 volume ratio).

[0058] Example 2

[0059] In step 1.1, the nano-hollow cubic bismuth nitrate is replaced with nano-hollow cubic bismuth carbonate, and the rest is the same as in Example 1.

[0060] Example 3

[0061] In step 1.1, the nano-hollow cubic bismuth nitrate is replaced with nano-hollow cubic bismuth vanadate, and the rest is the same as in Example 1.

[0062] The preparation method of nano-hollow cubic BiVO4 is as follows: First, a reaction solvent was prepared using 10 ml of 4M HNO3. Then, 2.42 g of bismuth nitrate (Bi(NO3)3·5H2O) was dissolved in 10 ml of nitric acid. Similarly, 0.585 g of ammonium metavanadate (NH4VO3) and 1 g of disodium ethylenediaminetetraacetate (EDTA) were dissolved in 10 ml of 4M NaOH solvent. Then, the NH4VO3 and EDTA solutions were added dropwise to the Bi(NO3)3·5H2O solution, stirred at room temperature for 30 min, and the NaOH solution was slowly added until a precipitate was formed, with the pH of the solution reaching approximately 7.5. Finally, the entire solution and precipitate were transferred together to a reaction vessel, placed in a stainless steel high-pressure reactor, and kept in an oven at 180°C for 24 h. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain nano-hollow cubic bismuth vanadate (BiVO4). Wash thoroughly with ultrapure water and ethanol (C2H5OH), and dry in an oven at 60°C for 8 hours for further characterization and application.

[0063] Example 4

[0064] In step 1.1, apply 100 mAh g -1 The constant current was converted into 80mAh g -1 Everything else is the same as in Example 1.

[0065] Example 5

[0066] In step 1.1, apply 100 mAh g -1 The constant current was converted into 120mAh g -1 Everything else is the same as in Example 1.

[0067] Example 6

[0068] In step 1.1, the electrolyte was changed from 1.0M LiPF6 to 0.8M LiPF6, and everything else was the same as in Example 1.

[0069] Example 7

[0070] In step 1.1, the electrolyte was changed from 1.0M LiPF6 to 1.2M LiPF6, and everything else was the same as in Example 1.

[0071] Analysis example

[0072] Figure 1 The X-ray diffraction pattern shows that the material prepared in Example 3 of this invention is a bismuth anode material.

[0073] Figure 2 As can be seen from the SEM microstructure, the bismuth anode material prepared in Example 3 of this invention exhibits a honeycomb-like three-dimensional nanostructure with an average particle size of approximately 500 nm.

[0074] Figure 3 The bismuth anode prepared in Example 3 was assembled with a lithium metal sheet into a lithium-ion battery. The charge-discharge curves for the first three cycles are shown. The discharge curve shows two voltage plateaus around 0.7V and 0.58V, corresponding to the formation of LiBi and Li3Bi, respectively. Due to V... 5+ The reduction of Bi exhibits a relatively broad voltage plateau at 1.2V. SEI film formation is thought to occur around the plateau at 0.01V. During charging, a voltage plateau around 0.98V corresponds to the dealloying of LiBi and Li3Bi. Interestingly, the voltage plateau disappears during the first charge cycle, occurring around 2.5V, and in the second and third charge cycles. According to previous reports, the voltage plateau at 2.5V is primarily caused by the oxidation of Bi to Bi ions.

[0075] Figure 4 For 100, 200, 500, 1000 and 100 mAh g respectively -1 The charge-discharge test curves at the specified current densities were obtained. The average discharge specific capacities of the bismuth anode material were 438.8, 308.2, 246.6, 142, and 265.3 mAh g⁻¹. -1 1000mAh g -1 The discharge specific capacity of bismuth anode material at current density is only 100 mAh g⁻¹. -1 The 36.6% loss at current density is attributed to electrolyte decomposition and the inevitable formation of the SEI film. Initial irreversible capacity loss at the electrode is a common characteristic of many anode materials.

[0076] Figure 5 The results show that the bismuth anode material at 100 mA·g -1 After 200 cycles at a current density, the capacity retention was 63.9%. The coulombic efficiency remained above 100%, and the maximum specific capacity of the battery during cycling reached 777.1 mAh g⁻¹. -1 It can be observed that the capacity decays rapidly within the first ten cycles. This phenomenon is attributed to the decomposition of the BiVO4 electrode material and the formation of the SEI layer. The capacity increase observed during cycling is attributed to the transformation of the honeycomb-like nano-Bi into a dandelion-like structure.

[0077] Table 1 compares the performance of the lithium battery assembled with the bismuth anode material in Example 3 of this invention with that of the prior art. It can be seen that the bismuth anode material prepared in Example 3 of this invention has a higher specific capacity.

[0078] Table 1 Comparison of existing technology with the bismuth anode material in Example 5 of this invention.

[0079]

[0080] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a bismuth electrode material, characterized in that, Includes the following steps: S1. A mixture containing bismuth compound, conductive additives and adhesive is coated on copper foil as the positive electrode, and lithium metal is used as the negative electrode to form an electrochemical reaction device. S2, applying 80-120 mAh.g between the positive and negative electrodes -1 constant current, voltage from 3.0 V to 0.01 V, electrochemically reducing the bismuth compound to produce a bismuth electrode material; The bismuth compound is at least one of bismuth vanadate, bismuth nitrate, and bismuth carbonate.

2. The method according to claim 1, characterized in that, The average particle size of the bismuth compound is 10 nm-2 μm.

3. The method according to claim 1, characterized in that, The bismuth electrode is a three-dimensional nanostructure.

4. The method according to claim 1, characterized in that, In step S1, the metal is an active metal; The conductive additive is carbon black; The adhesive is polyvinylidene fluoride.

5. The method according to claim 1, characterized in that, In step S1, the mass ratio of the bismuth compound, the conductive additive, and the adhesive is 6-9:0.5-3.5:0.5-3.

5.

6. The method according to claim 1, characterized in that, In step S1, the mass ratio of the bismuth compound, the conductive additive, and the adhesive is 7-9:0.5-2.5:0.5-2.

5.

7. The method according to claim 1, characterized in that, In step S1, a membrane is also included between the positive and negative electrodes of the electrochemical reaction device; The diaphragm is a microporous polypropylene membrane.

8. The method according to claim 1, characterized in that, The electrochemical reaction device also includes an electrolyte; The electrolyte is composed of lithium hexafluorophosphate as the solute and a mixture of ethylene carbonate and methyl ethyl carbonate as the solvent. The molar concentration of the lithium hexafluorophosphate is 0.8-1.2 M.

9. The bismuth electrode material obtained by the preparation method according to any one of claims 1-8 is used as an electrode for lithium-ion batteries, zinc-ion batteries, sodium-ion batteries, potassium-ion batteries, and bismuth-ion batteries.

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