Lithium powder negative electrode based on dry electrode process and applications

Abstract

The preparation method of lithium powder anode based on dry electrode process includes raw material premixing, "sandwich" structure assembly, and roll forming of lithium powder electrode sheet. Specifically, it includes three process steps and conditions. The lithium powder obtained by the method is applied to lithium battery by embedding lithium powder into the mesh pores of copper mesh and bonding it tightly to the surface of copper mesh and copper foil under the bonding effect of polyethylene oxide (PEO) to form a "sandwich" structure. The introduced mesh support and carbon nanotubes (CNTs) together play a supporting role. It has the advantages of overcoming the reactive failure of solvent and lithium powder in traditional wet process and the defects of existing dry process, and solving the defect of reactive failure of solvent and lithium powder in traditional wet process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for preparing lithium powder anodes based on a dry electrode process and its application. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, high operating voltage, small size, light weight, and zero pollution. In recent years, with the development of consumer electronics, electric vehicles, and large-scale energy storage, higher demands have been placed on the energy density of lithium-ion batteries. However, further improvements in battery performance are largely limited by the development of anode materials. Currently, commercially widely used graphite anodes suffer from low theoretical specific capacity (372 mAh / g) and poor rate performance. Lithium metal anodes, with extremely high theoretical specific capacity (3860 mAh / g), face significant challenges in safety and cycle life due to severe dendrite formation, large volume expansion, and an unstable solid electrolyte interphase (SEI) film.

[0003] To improve the performance of lithium metal anodes, researchers have conducted numerous studies, including increasing the electrode reaction area by processing lithium metal into powder. This helps to homogenize current distribution, reduce local current density, thereby suppressing dendrite growth and improving the rate performance and cycle stability of the electrode. For example, patent CN111725515A uses a wet process to directly coat lithium powder slurry onto the surface of a silicon-based anode to create a pre-lithiated anode sheet. The coin cell assembly using this pre-lithiated anode showed a 19% improvement in first-time efficiency and a 3% improvement in capacity retention, indicating that the lithium powder supplementation agent offsets the irreversible lithium loss caused by the formation of the SEI film, improving the overall capacity and energy density of the battery. However, traditional wet processes involve the use of toxic solvents (such as NMP) and the reactive failure of the solvent with the lithium powder, which is detrimental to fully realizing the lithium powder supplementation effect. Another example is a similar patent... The invention patent CN102437313A describes a lithium powder anode constructed using micron-sized lithium metal powder as the active material and combined with a three-dimensional porous current collector (such as copper foam). The pulverization of lithium metal effectively increases the specific surface area of ​​the electrode. Furthermore, due to the large number of pores in the powder electrode, it can improve the interfacial compatibility between the electrolyte and lithium metal, reduce the reaction impedance of the electrode, and effectively improve the discharge rate characteristics of the battery. However, since no binder is used in its powder electrode, it is prone to structural collapse and active material shedding during cycling, resulting in rapid capacity decay.

[0004] Therefore, it is of great significance to develop and apply a dry electrode process for preparing lithium powder anodes. Summary of the Invention

[0005] The objective of this invention is to overcome the shortcomings of the prior art and propose a method for preparing and applying lithium powder anodes based on a dry electrode process. This method can overcome the reactive failure of solvent and lithium powder in traditional wet processes and the defects of existing dry processes, and can also solve the defect of reactive failure of solvent and lithium powder in traditional wet processes.

[0006] The preparation method of lithium powder anode based on dry electrode process includes raw material premixing, "sandwich" structure assembly and roll forming of lithium powder electrode sheet, specifically including the following process steps and conditions: 1) Raw material premixing: In an argon atmosphere glove box, lithium powder, conductive agent and low melting point binder are premixed in a mortar to obtain a mixed powder; 2) "Sandwich" structure assembly: First, place the copper foil on a horizontal plane, then spread the mixed powder evenly on the copper foil through a sieve, and finally cover it with a mesh support structure to form a "sandwich" composite structure. 3) Roll pressing to prepare lithium powder electrode sheets: The "sandwich" structure is hot rolled using a roller press, which makes the softened binder bond with the conductive powder and lithium powder, and presses the copper foil, mixed powder and mesh support together. After adjusting the roller gap and rolling three times in a row, the "sandwich" structure lithium powder negative electrode sheet is obtained.

[0007] Applying the lithium powder obtained by the above method to lithium batteries involves embedding the lithium powder into the mesh holes of a copper mesh, and then, with the bonding effect of polyethylene oxide (PEO), adhering it tightly to the surface of the copper mesh and copper foil to form a "sandwich" structure. The introduced mesh support and carbon nanotubes (CNTs) together play a supporting role.

[0008] Compared with the prior art, the present invention has the following innovations, advantages or effects: (1) The dry electrode process is used to directly prepare lithium powder anodes, which completely eliminates the complex processes such as slurry stirring, coating and high temperature drying in the traditional wet process. This not only completely avoids the use of toxic solvents (such as NMP) and subsequent recycling problems, but also significantly reduces production energy consumption and overall cost.

[0009] (2) A “sandwich” structure lithium powder anode was creatively constructed. The mesh support and carbon nanotube (CNT) conductive network introduced therein can effectively buffer the huge volume change of lithium during the deposition / stripping process while synergistically improving the electronic conductivity of the electrode, thereby improving the structural stability and cycle life of the lithium powder anode.

[0010] (3) For the dry preparation of highly active lithium powder anodes, traditional polytetrafluoroethylene (PTFE) binders are no longer suitable due to inherent defects such as low-temperature embrittlement, weak interfacial adhesion, and easy deactivation of lithium powder during mixing. This invention preferably uses polyethylene oxide (PEO) as an alternative, which, with its lower thermal softening temperature, can achieve a firm and uniform bond between the electrode components and the current collector under mild hot-pressing conditions. This choice not only effectively avoids damage to the active material caused by high-shear mixing but also enhances the stability of the electrode structure through the flexible network formed by PEO.

[0011] (4) Compared with traditional lithium foil electrodes, the lithium powder anode prepared by the present invention has an extremely high specific surface area, which is beneficial to homogenize the current distribution and reduce the local current density, thereby inhibiting dendrite growth and improving the cycle stability of the electrode; and because there are a large number of pores in the powder electrode, the interfacial compatibility between the electrolyte and metallic lithium is improved, the reaction impedance of the electrode is reduced, and the rate performance of the electrode is improved. Attached Figure Description

[0012] Figure 1 This invention provides a schematic diagram of a process for preparing lithium powder anodes and lithium powder electrode sheets based on a dry electrode process.

[0013] Figure 2 This is a schematic diagram of the cycle number-capacity retention rate curve of the CR2032 coin cell assembled with the lithium powder anode prepared in Example 1 of the present invention.

[0014] Figure 3 This is a schematic diagram of the cycle number-capacity retention rate curve of the CR2032 coin cell assembled with the lithium powder negative electrode sheet prepared in Example 1 of the present invention.

[0015] Figure 4 This is a schematic diagram showing the total time-voltage comparison curves of the lithium powder anode and the lithium sheet anode symmetrical battery prepared in Example 1 of the present invention.

[0016] The present invention will be further described in detail below with reference to the accompanying drawings. Detailed Implementation

[0017] like Figures 1-4 As shown, the preparation method of lithium powder anode based on dry electrode process includes raw material premixing, "sandwich" structure assembly and roll forming of lithium powder electrode sheet, specifically including the following process steps and conditions: 1) Raw material premixing: In an argon atmosphere glove box, lithium powder, conductive agent and low melting point binder are premixed in a mortar to obtain a mixed powder; 2) "Sandwich" structure assembly: First, place the copper foil on a horizontal plane, then spread the mixed powder evenly on the copper foil through a sieve, and finally cover it with a mesh support structure to form a "sandwich" composite structure. 3) Roll pressing to prepare lithium powder electrode sheets: The "sandwich" structure is hot rolled using a roller press, which makes the softened binder bond with the conductive powder and lithium powder, and presses the copper foil, mixed powder and mesh support together. After adjusting the roller gap and rolling three times in a row, the "sandwich" structure lithium powder negative electrode sheet is obtained.

[0018] This method can be further... The average particle size of the lithium powder in step 1) is 500 nm.

[0019] In step 1), the conductive agent is at least one of superconducting carbon black (SP), graphene, and carbon nanotubes (CNT).

[0020] In step 1), the conductive agent is carbon nanotubes (CNTs), whose network structure can better buffer the volume expansion of the lithium powder anode during cycling and improve structural stability.

[0021] In step 1), the low-melting-point binder is at least one of polyethylene oxide (PEO) and styrene-butadiene rubber (SBR).

[0022] In step 1), the mass ratio of lithium powder, polyethylene oxide (PEO), and carbon nanotubes (CNTs) is 8:1:1.

[0023] The total mass of the mixed powder in step 1) is 0.5~1.5 g.

[0024] In step 2), the copper foil has a size of Φ150×70 mm and a thickness of 8μm.

[0025] In step 2), the mesh support is any one of copper mesh, copper / nickel foam mesh, or nickel foam, with dimensions of Φ150×70 mm and a thickness of 100~150μm.

[0026] In step 2), the copper / nickel mesh of the mesh support has a mesh size of 400 mesh.

[0027] In step 2), the porosity of the mesh support foam copper / foam nickel is 96~98%, and the pore size is 130ppi.

[0028] In step 3), the sieve is a 2000-mesh sieve.

[0029] In step 3), the hot rolling temperature is 65~85℃.

[0030] In step 3), the roller pressing is performed three times, and the roller gap width changes sequentially to 500μm, 300μm, and 200μm.

[0031] In step 3), the roll pressure is 2T and the roll linear speed is 5~10mm / s.

[0032] In step 3), the lithium powder negative electrode sheet has a size of Φ150×70 mm and a thickness of 100~200μm.

[0033] Applying the lithium powder obtained by the method described in claims 1 to 16 to lithium batteries involves embedding the lithium powder into the mesh holes of a copper mesh, and then, under the bonding effect of polyethylene oxide (PEO), adhering it tightly to the surface of the copper mesh and copper foil to form a "sandwich" structure. The introduced mesh support and carbon nanotubes (CNTs) together provide support. Example

[0034] In an argon-filled glove box (O2 / H2O < 1 ppm), 1.2 g of lithium powder, 0.15 g of CNT, and 0.15 g of PEO were weighed and mixed in a mortar. Then, a copper foil with dimensions of Φ150×70 mm was placed horizontally on a stainless steel plate, and the premixed powder was evenly spread on the copper foil through a sieve. Finally, a copper mesh was placed on the mixed powder to form a "sandwich" structure. After preheating the roller press to 80℃ and holding it at that temperature for 30 min, the "sandwich" composite structure was fed into the roller gap at a linear speed of 8 mm / s for hot rolling. After adjusting the roller gap and rolling continuously for 3 times, a composite lithium powder anode with a thickness of 200 μm was obtained. Example

[0035] Replace the copper mesh in Example 1 with copper foam, and the remaining steps are the same as in Example 1. Example

[0036] Replace the PEO adhesive in Example 1 with SBR, and the remaining steps are the same as in Example 1. Example

[0037] Replace the PEO binder in Example 1 with PTFE, and the remaining steps are the same as in Example 1. Example

[0038] Replace the CNT conductive agent in Example 1 with SP, and the remaining steps are the same as in Example 1. Example

[0039] Remove the copper mesh support from Example 1, and the remaining steps are the same as in Example 1. Example

[0040] Remove the conductive agent and adhesive from Example 1, and the remaining steps are the same as in Example 1.

[0041] Electrical performance testing: The lithium powder anode sheet and commercial lithium sheet (Φ16×0.5mm) prepared in Example 1 were used as symmetrical electrodes and encapsulated together with a PE separator and electrolyte in a CR2032 coin cell. After standing for 24 h, the battery was subjected to repeated constant current deposition and stripping processes. The current density was set to 0.5 mA / cm², and the areal capacity of a single deposition or stripping was set to 0.5 mAh / cm².

[0042] The lithium powder anode sheets prepared in Examples 1-7 above were combined with PE separators and LFP cathode sheets to fabricate 0.6mAh CR2032 coin cells. After standing for 24 hours, formation was performed by charge-discharge at a 0.1C rate for 5 weeks, and charge-discharge performance was tested at a 1C rate. The electrolyte ratio was LiPF6:EC:DEC:PP:FEC = 12:30:50:3:5; the cathode ratio was LFP:SP:PVDF = 80:10:10; the specific test results are shown in Table 1.

[0043] Table 1. Electrical performance test results of lithium powder anode sheets prepared using Examples 1-7 Examples Initial efficiency (%) Cycle life (weeks) Capacity retention CR = 80% Example 1 99.64 557 Example 2 99.72 416 Example 3 98.65 420 Example 4 89.96 67 Example 5 99.68 400 Example 6 94.04 32 Example 7 99.68 411 from Figure 4 The comparative analysis of the total time-voltage curves of the symmetrical cells shown indicates that the initial microstructure of the electrode active material has a decisive influence on its electrochemical stability. The symmetrical cell assembled from the lithium powder anode prepared in Example 1 exhibited a low deposition overpotential (approximately 0.02V) in the early stages of cycling. This is attributed to its large specific surface area effectively reducing the local current density, thereby inducing more uniform initial lithium deposition behavior. In subsequent long-term cycling, the overpotential of this system stabilized at approximately 0.06V, and no significant degradation occurred after more than 1000 hours of continuous operation. The voltage curve remained highly symmetrical, confirming its excellent interfacial stability and cycle life. In contrast, the symmetrical cell using a conventional lithium sheet anode had an initial overpotential of 0.06V, and after approximately 330 hours of cycling, the voltage curve exhibited drastic fluctuations and short-circuit characteristics, indicating severe lithium dendrite growth and uncontrollable side reactions at the interface. The comparative results clearly reveal that by constructing a composite lithium powder anode structure with a high specific surface area, the kinetics of lithium deposition can be effectively controlled, dendrite formation can be suppressed, and thus the cycle stability can be far superior to that of traditional lithium metal anodes.

[0044] A comparison of the electrical performance test results of the lithium powder anode sheets prepared in Examples 1-7 shows that Example 1 (copper mesh / PEO / CNT reference system) exhibits the best comprehensive performance, confirming the effectiveness of the synergistic design principle of "rigid two-dimensional conductive framework - ion-conductive bonding network - one-dimensional flexible conductive agent". Example 2 (replaced with copper foam) shows that the three-dimensional framework of copper foam is relatively fragile and prone to local collapse under repeated stress during electrode pressing or battery cycling, affecting long-term cycling stability. Example 6 (removal of the support) shows a sharp performance degradation, directly proving that the mechanical stability and current homogenization provided by the support are the basis for the system's cyclicability. Example 7 (retaining only the copper mesh) shows only a slight performance decrease, further demonstrating the dominant function of the copper mesh in current collection and mechanical support, which can partially compensate for the lack of binder and conductive agent. Example 3 (SBR binder) shows a decrease in cycle life, highlighting the electrochemical activity advantage of PEO as an ion conductor in homogenizing lithium ion flow and guiding uniform deposition, which is not possessed by the purely physical binder SBR. The performance degradation in Example 5 (SP conductive agent) demonstrates that CNTs not only provide electronic pathways, but the CNT network also acts as a "skeleton" to bind the active material, buffering volume changes and enhancing the overall mechanical integrity of the electrode. This has a synergistic reinforcing effect with the flexible network of the PEO binder. Example 4 (PTFE binder) showed a significant decrease in both initial efficiency and cycle life, attributed to side reactions during PTFE fiberization leading to active lithium loss and interface deterioration, highlighting the importance of binder chemical stability and electrode material compatibility.

[0045] Overview: The realization of high-performance lithium powder anodes relies on the systematic matching of three components: a robust and conductive two-dimensional support framework, an active binder with ion conduction and interface stabilization functions, and a one-dimensional conductive network that can maintain long-range connectivity. Among them, the support is the necessary foundation for maintaining structural integrity and electrochemical cycling, while the optimized selection of binders and conductive agents is the key to further improving interface stability and long-cycle performance.

[0046] As described above, the present invention can be well implemented. The above embodiments are only the best implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are all included within the protection scope of the present invention.

Claims

1. A method for preparing lithium powder anodes based on dry electrode technology, characterized in that... The process includes raw material premixing, "sandwich" structure assembly, and roll forming to prepare lithium powder electrodes. Specifically, it includes the following process steps and conditions: 1) Raw material premixing: In an argon atmosphere glove box, lithium powder, conductive agent and low melting point binder are premixed in a mortar to obtain a mixed powder; 2) "Sandwich" structure assembly: First, place the copper foil on a horizontal plane, then spread the mixed powder evenly on the copper foil through a sieve, and finally cover it with a mesh support structure to form a "sandwich" composite structure. 3) Roll pressing to prepare lithium powder electrode sheets: The "sandwich" structure is hot rolled using a roller press, which makes the softened binder bond with the conductive powder and lithium powder, and presses the copper foil, mixed powder and mesh support together. After adjusting the roller gap and rolling three times in a row, the "sandwich" structure lithium powder negative electrode sheet is obtained.

2. The method according to claim 1, characterized in that: The average particle size of the lithium powder in step 1) is 500 nm.

3. The method according to claim 1, characterized in that: In step 1), the conductive agent is at least one of superconducting carbon black (SP), graphene, and carbon nanotubes (CNT).

4. The method according to claim 1, characterized in that: In step 1), the conductive agent is carbon nanotubes (CNTs), whose network structure can better buffer the volume expansion of the lithium powder anode during cycling and improve structural stability.

5. The method according to claim 1, characterized in that: In step 1), the low-melting-point binder is at least one of polyethylene oxide (PEO) and styrene-butadiene rubber (SBR).

6. The method according to claim 1, characterized in that: In step 1), the mass ratio of lithium powder, polyethylene oxide (PEO), and carbon nanotubes (CNTs) is 8:1:

1.

7. The method according to claim 1, 2, 3, 4, 5, or 6, characterized in that: The total mass of the mixed powder in step 1) is 0.5~1.5 g.

8. The method according to claim 1, characterized in that: In step 2), the copper foil has a size of Φ150×70 mm and a thickness of 8μm.

9. The method according to claim 1, characterized in that: In step 2), the mesh support is any one of copper mesh, copper / nickel foam mesh, or nickel foam, with dimensions of Φ150×70 mm and a thickness of 100~150μm.

10. The method according to claim 1, characterized in that: In step 2), the copper / nickel mesh of the mesh support has a mesh size of 400 mesh.

11. The method according to claim 1, 8, 9, or 10, characterized in that: In step 2), the porosity of the mesh support foam copper / foam nickel is 96~98%, and the pore size is 130ppi.

12. The method according to claim 1, characterized in that: In step 3), the sieve is a 2000-mesh sieve.

13. The method according to claim 1, characterized in that: In step 3), the hot rolling temperature is 65~85℃.

14. The method according to claim 1, characterized in that: In step 3), the roller pressing is performed three times, and the roller gap width changes sequentially to 500μm, 300μm, and 200μm.

15. The method according to claim 1, 12, 13, or 14, characterized in that: In step 3), the roll pressure is 2T and the roll linear speed is 5~10mm / s.

16. The method according to claim 1, characterized in that: In step 3), the lithium powder negative electrode sheet has a size of Φ150×70mm and a thickness of 100~200μm.

17. Applying the lithium powder obtained by the method described in claims 1-16 to a lithium battery, characterized in that... Lithium powder is embedded into the mesh openings of a copper mesh and bonded tightly to the surface of the copper mesh and copper foil by the adhesive effect of polyethylene oxide (PEO), forming a "sandwich" structure. The introduced mesh support and carbon nanotubes (CNTs) work together to provide support.

Images