Method for producing a solid-state battery based on a lithium powder dry electrode

Abstract

The preparation method of the solid-state battery based on the lithium powder dry electrode comprises the following process steps in sequence: lithium powder dry electrode preparation, gel electrolyte preparation, solid-state battery packaging, and assembled button cell. The process is simple, the thickness of the solid-state electrolyte and the lithium negative electrode can be controlled to a low level, mass production is easy, the whole process is solvent-free, green and environmentally friendly, the safety and reliability of the battery are high, the lithium ion battery has obvious advantages in the first circle coulomb efficiency, cycle capacity retention rate, and specific capacity, etc.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and specifically to a method for preparing a solid-state battery based on a lithium powder dry electrode. Background Technology

[0002] With the rapid development and increasing demand for new energy vehicles, smart grids, and distributed energy storage systems, further improving energy storage technology is a key research objective at present. Lithium metal, due to its lower reduction potential (-3.04 V, compared to the standard hydrogen electrode) and ultra-high theoretical capacity of 3862 mAh / g, is considered a promising anode material. However, lithium metal has high reactivity, and uneven lithium deposition, lithium dendrite growth, and dead lithium formation during charging and discharging can all lead to severe capacity loss or even explosion in lithium metal batteries after long-term operation. By changing the electrolyte composition, optimizing the formation and distribution of the SEI film, and performing lithium anode interface engineering, it is possible to promote uniform lithium metal deposition and improve its safety to some extent. Currently, the main methods for lithium anode interface modification are as follows:

[0003] On the one hand, some people approach it from these three points:

[0004] 1. Preparation of artificial SEI: This refers to coating the surface of a lithium anode with an artificial SEI film through methods such as coating, deposition, or chemical reaction, thereby isolating the electrolyte from direct contact with the lithium anode. This method is simple and the process is controllable, but it is prone to problems such as difficulty in lithium-ion transport, increased internal resistance, and subsequent volume expansion caused by SEI film rupture.

[0005] 2. Preparation of Lithium Alloy Anodes: This refers to the process of incorporating active or inactive metal elements such as Mg, Al, and Sn into lithium foil through smelting or rolling, ensuring their uniform distribution within the lithium foil matrix, thereby effectively improving lithium deposition. This method can improve the performance of lithium anodes at low cost and high efficiency, and has the potential for large-scale application. Examples include "Gradient-Heterogeneous Lithium / Lithium–Magnesium Alloy for a Highly Stable Lithium Metal Anode" and the webpage: Gradient-Heterogeneous Lithium / Lithium–Magnesium Alloy for a Highly Stable Lithium Metal Anode (ACS Applied Materials & Interfaces).

[0006] 3. Lithium metal anode structure design: This refers to a well-designed porous structure that buffers volume changes during charge-discharge cycles, thereby reducing stress concentration, maintaining electrode structural integrity, and extending cycle life. This method can effectively improve lithium deposition behavior, but its preparation process is complex and not conducive to large-scale industrial applications.

[0007] On the other hand, some argue that liquid electrolytes inevitably undergo side reactions with lithium metal, leading to the loss of active lithium and a reduction in battery capacity. Furthermore, the thermal runaway of these reactions poses significant safety hazards. Therefore, the development of semi-solid and solid-state batteries is increasingly popular, including high-voltage anodes for ternary systems, lithium-sulfur batteries, and lithium-oxygen batteries. However, it remains challenging to simultaneously address cost and safety issues while pursuing higher capacity battery systems.

[0008] To address the aforementioned issues, several publications have revealed: CN116454282B, "An Artificial SEI Film for Protecting Lithium Anodes in Lithium Primary Batteries and Its Preparation Method," which involves spin-coating an inorganic lithium-containing compound / polycarbonate-based organic polymer composite film onto the surface of the lithium anode. This allows the spin-coated film to fully coat the lithium powder electrode, isolating it from the electrolyte and reducing side reactions, ultimately improving the battery's electrochemical and safety performance. However, its wet spin-coating process involves solvent preparation and organic solvent evaporation, which is environmentally unfriendly, and the low ionic conductivity of the coated composite film leads to a reduction in battery capacity. Another example is "Gradient-Heterogeneous Lithium / Lithium–Magnesium Alloy for a Highly Stable Lithium Metal." Anode disclosed "a gradient heterogeneous Li-Mg alloy anode composed of magnesium powder and lithium metal." This involves rolling a lithium block mixed with magnesium powder, repeatedly rolling, folding, and rolling the mixture in a rolling mill to obtain a uniformly mixed composite material with a thickness of approximately 0.3 mm. This provides abundant electrochemical active sites for lithium deposition. The solid solution structure of the lithium-magnesium alloy and the rapid diffusion of lithium ions enhance the stability of the lithium electrode. However, the incorporation of Mg leads to the formation of a passivation film composed of magnesium oxide, which hinders lithium ion diffusion, resulting in interfacial instability and uneven lithium deposition. CN117936802B, "Three-dimensional porous dual-alloy current collector, lithium metal anode, and primary / secondary battery for lithium metal anode," designs and fabricates a three-dimensional porous copper-zinc composite dual-phase alloy framework, and composites lithium metal within the framework to form a composite lithium anode. In this method, the three-dimensional framework has a large specific surface area, which is beneficial for reducing local current density and lithium dendrite formation. Chemically inert copper-zinc frameworks are beneficial for maintaining the structural stability of the negative electrode during delithiation / lithiation cycles and can effectively suppress volume changes during battery cycling. However, its preparation process is complex and lengthy, making it unsuitable for large-scale applications. CN119897353B, "A process for simultaneous surface smoothing and artificial SEI coating of lithium-containing metal strips, modified lithium-containing metal strips and their applications," uses a double-roll press to roll lithium-containing metal strips coated with an artificial SEI layer. Mechanical deformation activates the reaction between the lithium strip and the film-forming sacrificial agent, ultimately achieving a continuous, uniform, dense artificial SEI film composed of inorganic salts on the surface of the lithium-containing metal strip. This enables lithium negative electrode forming and surface modification, reduces processing costs, improves production efficiency, and simultaneously optimizes the performance of the lithium negative electrode. However, the mechanical and processing properties of the lithium metal are poor, and structural damage and cracking and differentiation of the lithium foil are inevitable during the preparation of the lithium negative electrode, affecting the final product performance. CN202111563740.2. "A composite solid polymer electrolyte and its preparation method" describes a wet coating process to prepare a composite solid polymer electrolyte with PEO as the matrix and incorporating lithium electrolyte, boron nitride, and a binder for use in solid-state batteries. The prepared solid electrolyte exhibits good flatness and high ionic conductivity, and the preparation process is relatively simple. However, the solid-solid contact between the solid electrolyte and the electrode has a relatively high contact resistance, which is detrimental to lithium-ion transport and leads to a decrease in battery capacity. Furthermore, although the ionic conductivity of the PEO-based composite solid electrolyte is improved to some extent, the electrochemical performance of this solid electrolyte at room temperature remains limited.

[0009] Therefore, it is of great significance to develop a method for preparing solid-state batteries based on lithium powder dry electrodes. Summary of the Invention

[0010] The objective of this invention is to overcome the shortcomings of the prior art and propose a method for preparing a solid-state battery based on a lithium powder dry electrode. This method can improve the surface state and properties of the lithium metal anode, slow down the growth of lithium dendrites during battery charging and discharging, and prevent side reactions and the formation of dead lithium.

[0011] The fabrication method and conditions for solid-state batteries based on lithium powder dry electrodes are as follows:

[0012] d1. Preparation of lithium powder dry electrode: Lithium powder, conductive agent and binder are mixed in a mass ratio of 2:1:1 to form powder. The powder is rolled into a flat and continuous thin sheet at 90 ℃ using a hot roller press, and then cut to obtain a lithium powder dry electrode negative electrode with a thickness of 100 μm.

[0013] d2. Preparation of gel electrolyte and solid-state battery encapsulation: LiPF6 and Mg(TFSI)2 were homogeneously dissolved in a mixed solvent of FEC / FEMC / EMC / DMC. Then, the polymerization monomers and initiators PETEA pentoerythritol tetraacrylate, DAP diethylallyl phosphate, HFBMA 2,2,3,4,4,4-hexafluorobutyl methacrylate, BPO benzoyl peroxide, and HMDS hexamethyldisilazane were added to the homogeneous solution and stirred evenly at room temperature.

[0014] d3. Assemble the button cell: After assembling, let the assembled cell stand at 65°C for 4 hours to allow the electrolyte to gel, and finally obtain a solid-state cell based on lithium powder dry electrode.

[0015] The innovation of this invention lies in:

[0016] (1) Solvent-free lithium powder dry electrode is prepared by hot pressing. This method is simple, easy to implement, green and environmentally friendly, and can produce a thin lithium anode with uniform distribution.

[0017] (2) By combining the dry electrode preparation process with the gel solid electrolyte preparation process and assembling coin cells, lithium powder dry electrodes were successfully applied to solid batteries, resulting in better battery performance. Compared with commercial lithium sheet anodes, the first-cycle coulombic efficiency was better, and the safety performance was relatively better.

[0018] Compared with the prior art, the advantages or positive effects of the present invention are as follows:

[0019] (1) The process is simple, the thickness of the solid electrolyte and lithium anode can be controlled to a low level, it is easy to prepare in large quantities, and there is no solvent throughout the process, making it green and environmentally friendly;

[0020] (2) The use of a novel gel solid electrolyte to replace the traditional liquid electrolyte reduces the possibility of explosion caused by thermal runaway of side reactions, effectively improving the safety and reliability of the battery;

[0021] (3) After assembling a button cell, using commercial LFP as the positive electrode and lithium powder dry electrode as the negative electrode, compared with traditional commercial lithium batteries, the lithium metal solid battery prepared by the method of this invention, which includes lithium powder dry electrode and gel solid electrolyte, has obvious advantages in terms of first-cycle coulombic efficiency and cycle capacity retention, further improving the specific capacity of lithium-ion batteries. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow for a solid-state battery based on a lithium powder dry electrode provided by the present invention.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings. Detailed Implementation

[0024] like Figure 1 As shown, the fabrication method of solid-state batteries based on lithium powder dry electrodes includes the following process steps and conditions:

[0025] d1. Preparation of lithium powder dry electrode: Lithium powder, conductive agent and binder are mixed in a mass ratio of 2:1:1 to form powder. The powder is rolled into a flat and continuous thin sheet at 90 ℃ using a hot roller press, and then cut to obtain a lithium powder dry electrode negative electrode with a thickness of 100 μm.

[0026] d2. Preparation of gel electrolyte and solid-state battery encapsulation: LiPF6 and Mg(TFSI)2 were homogeneously dissolved in a mixed solvent of FEC / FEMC / EMC / DMC. Then, the polymerization monomers and initiators PETEA pentoerythritol tetraacrylate, DAP diethylallyl phosphate, HFBMA 2,2,3,4,4,4-hexafluorobutyl methacrylate, BPO benzoyl peroxide, and HMDS hexamethyldisilazane were added to the homogeneous solution and stirred evenly at room temperature.

[0027] d3. Assemble the button cell: After assembling, let the assembled cell stand at 65°C for 4 hours to allow the electrolyte to gel, and finally obtain a solid-state cell based on lithium powder dry electrode.

[0028] This preparation method can be further...

[0029] The conductive agent in step d1 is carbon nanotubes.

[0030] In step d1, the adhesive is either SBR or PEO.

[0031] In step d1, the ratio of lithium powder: conductive agent: binder is 50~60wt%: 20~25wt%: 20~25wt%.

[0032] In step d2, the concentration of LiFP6 is 10~12.5 mol / L, and the concentration of TFSI2 is 0.3~0.5 mol / L.

[0033] In step d2, FEC:FEMC:EMC:DMC = 30 vol%: 14~15 vol%: 14~15 vol%: 40~42 vol%.

[0034] Comparative Example 1

[0035] Pure lithium foil anode - liquid LFP coin cell

[0036] Positive electrode: Commercially available LFP electrode sheet

[0037] Using separators, electrolytes, and assembly processes, and conventional coin cell technology.

[0038] Anode preparation: Commercially available pure lithium sheets.

[0039] Comparative Example 2

[0040] Lithium powder dry electrode negative electrode - liquid LFP coin cell

[0041] Positive electrode: Commercially available LFP electrode sheet

[0042] Using separators, electrolytes, and assembly processes, and conventional coin cell technology.

[0043] Negative electrode preparation: lithium powder dry electrode sheet.

[0044] Example 1

[0045] Phase 1: Preparation of lithium powder dry electrodes

[0046] Step 1: Ingredient Mixing

[0047] Formula (by mass): Lithium powder – 42~44% Conductive agent: Carbon nanotubes 28~29% Binder: PEO 28~29%.

[0048] The materials are added into a mixer filled with argon atmosphere in proportion and mixed thoroughly until a powder with uniform color is obtained.

[0049] Step 2: Spreading powder

[0050] The mixed powder was evenly spread on copper foil under an argon atmosphere, and a copper mesh with a size of 300 mesh and a thickness of about 50 μm was covered on the spread lithium powder.

[0051] Step 3: Hot pressing

[0052] Equipment: Electric heating double roller mill

[0053] Key parameters: areal density and thickness. The mass and thickness of the material per unit density in the overall lithium powder dry electrode are precisely controlled by adjusting the roller spacing and roller speed. The areal density and thickness of the lithium powder dry electrode are controlled to be <1.5% and <1.5%, respectively.

[0054] Phase 2: Preparation of gel electrolyte

[0055] The following steps are all performed in an environment filled with an argon protective atmosphere:

[0056] Step 1: Prepare the gel electrolyte base solution using LiPF6 and Mg(TFSI)2 as electrolyte salts and FEC / FEMC / EMC / DMC as a mixed solvent. Stir continuously at 60℃ for 4 hours to form a homogeneous solution. The concentration of LiPF6 is 12 mol / L, the concentration of Mg(TFSI)2 is 0.2 mol / L, and the ratio of FEC / FEMC / EMC / DMC is 3:1.5:1.5:4 by volume.

[0057] Step 2: Add the polymerizable monomers to the base solution. Take a certain mass of gel electrolyte base solution and add the polymerizable monomers and initiator in the following proportions: 1.5 wt% PETEA, 1.5 wt% DAP, 1 wt% HFBMA, 0.2 wt% BPO.

[0058] In addition, 15 μL of HMDS was added dropwise to remove the acidic substance HF from the solution.

[0059] Stir the solution evenly at room temperature for 4 hours until a clear and transparent homogeneous solution is formed.

[0060] Phase 3: Button cell assembly: The positive electrode uses commercial LFP electrode sheets, the negative electrode uses commercial alumina ceramic separator, the lithium powder dry electrode prepared in the first phase is used as the negative electrode, the prepared gel electrolyte is used as the battery electrolyte, and the button cell is assembled.

[0061] After sealing the battery with a sealing machine, let the battery stand for 8 hours to allow the gel electrolyte to be evenly distributed in the battery. Then place it in a vacuum drying oven for 4 hours at 65°C to achieve gelation of the electrolyte.

[0062] Phase 4: Battery Testing: The assembled battery was charged / discharged at a rate of 0.1C for the first cycle, and then cycled 100 times at a rate of 0.5C. The battery performance data is listed in Table 1.

[0063] Example 2

[0064] Unlike Example 1, Example 2 uses a mixture of PVDF and PTFE (PVDF to PTFE in a mass ratio of 1:1) as the binder required for the preparation of lithium powder dry electrodes, instead of PEO.

[0065] Example 3

[0066] Unlike Example 1, the lithium powder dry electrode preparation process in Example 4 is carried out at room temperature instead of 80°C as in Example 1.

[0067] Example 4

[0068] Unlike Example 1, the prepared gel electrolyte contained LiNO3 at a concentration of 0.65 mol / L in addition to the polymerizable monomer.

[0069] Example 5

[0070] Unlike Example 1, the prepared gel electrolyte did not contain the deacidifying agent HMDS.

[0071] The following table summarizes the effects of each example.

[0072] Comparative Example 1 140.16 96.93 99.41 The negative electrode uses commercially available lithium sheets. Comparative Example 2 160.16 99.43 99.26 The negative electrode uses a lithium powder dry electrode. Example 1 152.35 104.18 99.92 Lithium replenishment function of lithium powder dry electrode Example 2 152.09 98.41 99.15 Example 3 132.46 90.67 <80 Example 4 146.37 90.47 <80 Example 5 143.09 88.84 <80

[0073] Example 2 describes the preparation of lithium powder dry electrodes using PVDF and PTFE as binders. PVDF has a higher room temperature ionic conductivity than PEO, but its softening temperature and melting point are higher, and it is usually used as a binder in wet-coating electrodes. During the preparation of lithium powder dry electrodes, PVDF exhibits poor film-forming performance in solvent-free environments, resulting in low areal density and powder shedding, uneven surface distribution, and hindering the improvement of electrical performance. Example 3 describes the pressing of lithium powder dry electrodes at room temperature. The adhesive effect of PEO is weakened at room temperature. At high temperatures, the softened PEO is more conducive to the adhesion between the materials.

[0074] Based on the above data and analysis, in Example 4, a small amount of LiNO3 was added to the gel electrolyte in the hope of further improving the film-forming properties of the SEI film and the ionic conductivity of the electrolyte. However, LiNO3 has a certain inhibitory effect on polymer monomers, and inappropriate addition leads to a decrease in battery cycle performance. Example 5 did not add the acid remover HMDS. The presence of a small amount of HF accelerated the failure of the positive electrode and the loss of active lithium, hindering the improvement of battery electrochemical performance.

[0075] 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 a solid-state battery based on a lithium powder dry electrode, characterized in that... The process steps and conditions are as follows: d1. Preparation of lithium powder dry electrode: Lithium powder, conductive agent and binder are mixed in a mass ratio of 2:1:1 to form powder. The powder is rolled into a flat and continuous thin sheet at 90 ℃ using a hot roller press, and then cut to obtain a lithium powder dry electrode negative electrode with a thickness of 100 μm. d2. Preparation of gel electrolyte and solid-state battery encapsulation: LiPF6 and Mg(TFSI)2 were homogeneously dissolved in a mixed solvent of FEC / FEMC / EMC / DMC. Then, the polymerization monomers and initiators PETEA pentoerythritol tetraacrylate, DAP diethylallyl phosphate, HFBMA 2,2,3,4,4,4-hexafluorobutyl methacrylate, BPO benzoyl peroxide, and HMDS hexamethyldisilazane were added to the homogeneous solution and stirred evenly at room temperature. d3. Assemble the button cell: After assembling, let the assembled cell stand at 65°C for 4 hours to allow the electrolyte to gel, and finally obtain a solid-state cell based on lithium powder dry electrode.

2. The method according to claim 1, characterized in that: The conductive agent in step d1 is carbon nanotubes.

3. The method according to claim 1 or 2, characterized in that: In step d1, the adhesive is either SBR or PEO.

4. The method according to claim 1, characterized in that: In step d1, the ratio of lithium powder: conductive agent: binder is 50~60wt%: 20~25wt%: 20~25wt%.

5. The method according to claim 1, characterized in that: In step d2, the concentration of LiFP6 is 10~12.5 mol / L, and the concentration of TFSI2 is 0.3~0.5 mol / L.

6. The method according to claim 1 or 5, characterized in that: In step d2, FEC:FEMC:EMC:DMC = 30 vol%: 14~15 vol%: 14~15 vol%: 40~42 vol%.

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