High-strength dry-method electrode, preparation method thereof and lithium ion battery

Abstract

The invention provides a high-strength dry electrode, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The high-strength dry-method electrode is prepared by adopting a composite binder, the composite binder is composed of fibrous polytetrafluoroethylene and a polymer serving as a network node, and the polymer serving as the network node is one or a mixture of polyurethane, polyether-ether-ketone, polyamide or a protein cross-linking system. According to the invention, the specific polymer is introduced as a network node and is interspersed and anchored with the PTFE fiber to form a unique three-dimensional double-network structure, so that the tensile strength and flexibility of the dry-method electrode film are remarkably enhanced, the problems of easy breakage, powder falling and the like in the preparation process of the existing dry-method electrode are effectively solved, and the preparation method is particularly suitable for a large-scale roll-to-roll production process. The electrode prepared by the composite binder has excellent mechanical performance and electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-strength dry electrode, its preparation method, and a lithium-ion battery containing the electrode. Background Technology

[0002] Dry electrode technology is considered a key technology for next-generation high-performance batteries due to its advantages such as eliminating the need for toxic solvents, simple processing, low cost, and high energy density. This technology typically involves directly rolling a mixture of active materials, conductive agents, and binders (most commonly polytetrafluoroethylene, PTFE) into an electrode film. PTFE, as a fibrous material, can form a three-dimensional network structure under shear force, binding the active material particles and giving the electrode a certain strength.

[0003] However, a single PTFE binder network has significant shortcomings: First, the PTFE fiber network is prone to slippage at the nodes when subjected to tensile stress, resulting in limited tensile strength of the electrode film; second, the electrodes bonded with pure PTFE lack flexibility and are prone to cracking during winding or rolling; third, the electrode edges are prone to problems such as powder shedding and burrs, which seriously affect the efficiency of subsequent roll-to-roll production and the safety of the battery.

[0004] To improve the mechanical properties of dry-process electrodes, some existing technologies have been explored. For example, some patents disclose a scheme using a composite of a fibrous binder and a thermally molten coating binder, aiming to improve performance. However, such schemes rely on the molten flow and reshaping of the binder, and their reinforcing effect is limited by the uniformity of the coating. Furthermore, instability may be introduced due to thermal history, thus limiting their ability to improve the mechanical strength of the electrode.

[0005] Therefore, there is an urgent need in this field to develop a novel dry electrode fabrication process that can fundamentally enhance the mechanical strength, especially tensile strength and flexibility, of dry electrodes without relying on a hot-melting process. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-strength dry electrode, a method for preparing the same, and a lithium-ion battery containing the electrode. The dry electrode is prepared using a composite binder, which constructs a unique three-dimensional dual-network structure, significantly improving the tensile strength, flexibility, and processability of the dry electrode.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention proposes a method for preparing a high-strength dry electrode, comprising the following steps: S1: Dry mixing of electrode active material, conductive agent, polytetrafluoroethylene and polymer as network nodes to obtain mixed powder; S2: The mixed powder is sheared to fibrousize the polytetrafluoroethylene and combine with the polymer, which serves as the network node, to form a three-dimensional double network structure, thereby obtaining the electrode material; S3: The electrode material is rolled to form a dry electrode film.

[0008] Preferably, the polymer used as a network node is one of polyurethane, polyetheretherketone, polyamide, or a protein crosslinking system.

[0009] Preferably, the polyurethane is an anionic waterborne polyurethane containing tertiary amine groups. This type of polyurethane has good hydrophobicity and can undergo better crosslinking.

[0010] Preferably, the protein cross-linking system is a cross-linked network formed by soybean protein, casein, or gelatin through an aldehyde cross-linking agent. The aldehyde cross-linking agent can be glutaraldehyde or glyoxal.

[0011] Preferably, the mass ratio of the polytetrafluoroethylene to the polymer serving as the network node is 1:99 to 99:1, and more preferably 10:90 to 50:50.

[0012] Furthermore, in step S1, the dry mixing is ball milling or high-speed stirring; and / or, in step S2, the shearing treatment is a multi-step fiberization treatment, including high-speed shearing followed by low-speed dispersion.

[0013] Secondly, the present invention also proposes a high-strength dry electrode, which is prepared by the preparation method described above.

[0014] Furthermore, the high-strength dry electrode includes an electrode active material, a conductive agent, polytetrafluoroethylene (PTFE), and a polymer serving as network nodes; the PTFE and the polymer serving as network nodes constitute a composite binder, and the composite binder accounts for 1% to 10% of the mass of the dry electrode.

[0015] Thirdly, the present invention also proposes a lithium-ion battery comprising the high-strength dry electrode as described above.

[0016] Compared with the prior art, the present invention has the following significant advantages: 1. Structural Innovation, Synergistic Enhancement: This invention creatively introduces a specific polymer as a "network node" during the dry electrode fabrication process. This polymer interweaves and anchors with PTFE fibers, forming a stable "three-dimensional dual-network structure." In this structure, the PTFE fibers provide overall support and toughness as a continuous skeleton, while the polymers, acting as network nodes, firmly "lock" the nodes of the PTFE fiber network through molecular chain entanglement, hydrogen bonding, ionic interactions, or covalent cross-linking, greatly limiting fiber slippage under stress. This structure effectively disperses stress and prevents PTFE fiber node slippage, resulting in a significant improvement in the electrode's tensile strength and flexibility on a macroscopic scale.

[0017] 2. Excellent performance and suitable for production: The dry electrode prepared by the composite binder process of this invention has a tensile strength that is significantly higher than that of traditional PTFE electrodes and existing composite binder electrodes (exceeding 0.6MPa). At the same time, the electrode edge is intact and the roughness is low, which effectively solves the problem of powder shedding and perfectly matches the high requirements of roll-to-roll production process.

[0018] 3. Wide range of applications: The composite binder system (PTFE + network node polymer) used in this invention can be widely used in the dry electrode preparation of various positive and negative electrode active materials (such as lithium iron phosphate, ternary materials, graphite, silicon carbide, etc.), and is suitable for various energy storage devices such as lithium-ion batteries, sodium-ion batteries and supercapacitors.

[0019] 4. Excellent electrochemical performance: Since the electrode preparation process of this invention uses a composite binder to improve mechanical properties without introducing components that are harmful to electrochemical performance or blocking the internal ion transport channels of the electrode, the prepared electrode exhibits capacity performance, cycle stability and rate performance that are comparable to or even better than those of the prior art after being assembled into a battery. Attached Figure Description

[0020] Figure 1 This is an appearance diagram of the electrode film prepared in Example 1.

[0021] Figure 2 This is a comparison graph of the tensile stress-strain curves of the electrode film prepared in Comparative Example 1 (pure PTFE) and Example 1.

[0022] Figure 3 This is a schematic diagram of the winding of the dry electrode film prepared in Example 1 of the present invention.

[0023] Figure 4 These are the charge-discharge curves of the full battery assembled in Embodiments 1 and 3 of this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] In this invention, the polymers used as network nodes are preferably polyurethane (PU), polyetheretherketone (PEEK), polyamide (PA), or protein crosslinking systems. These materials themselves possess good mechanical strength, toughness, or reactivity, and can interact well with PTFE fibers.

[0026] When using a protein cross-linking system, for example, soybean protein powder can be reacted in situ with a small amount of cross-linking agent such as glutaraldehyde during the mixing process to form cross-linked network nodes.

[0027] The composite binder can be prepared directly during the dry mixing process of the electrode materials without prior synthesis.

[0028] Example 1: A dry electrode for the positive electrode

[0029] raw material: Active material: ternary material NCM811, 81 wt% Electrolyte powder: Li6PS5Cl, 15 wt% Conductive agent: Acetylene black, 2 wt% PTFE: 1 wt% Polymer used as network nodes: polyurethane powder, 1 wt%; Preparation method: 1. Place all the above raw materials in a high-speed mixer and dry mix at 1000 rpm for 5 minutes to obtain a uniform mixed powder.

[0030] 2. The mixed powder is then sheared at 4000 rpm for 3 minutes to fully fiberize the PTFE, embedding and anchoring the polyurethane powder at the nodes of the PTFE fiber network. The mixture is then dispersed at 300 rpm for 3 minutes to obtain a uniformly sized electrode material.

[0031] 3. The obtained electrode material is rolled into a self-supporting electrode film with a thickness of 170 μm by a two-roll press at 80℃ and 20 N / mm pressure.

[0032] Example 2: A dry electrode for the negative electrode

[0033] raw material: Active material: artificial graphite, 97 wt% Conductive agent: carbon nanotubes, 1 wt% PTFE: 1 wt% Polymer used as network nodes: polyamide powder, 1 wt%; The preparation method is the same as in Example 1.

[0034] Example 3: A dry-process electrolyte membrane for solid-state batteries

[0035] raw material: Electrolyte powder: Li6PS5Cl, 98 wt% PTFE: 1 wt% Polyurethane powder, used as a network node, 1 wt% The preparation method is the same as in Example 1.

[0036] Comparative Example 1: Pure PTFE binder electrode

[0037] The raw materials and preparation methods are basically the same as in Example 1, except that 1 wt% of polyurethane powder is replaced with an equal amount of PTFE, that is, the total PTFE content is 2 wt%.

[0038] Comparative Example 2: Existing composite binder electrode

[0039] The composite binder was made of 1 wt% fibrous PTFE and 1 wt% polyethylene (PE, as a heat-melting coating adhesive), and the remaining components and preparation method were the same as in Example 1.

[0040] Performance testing: The performance of the electrode films prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was tested, and the results are shown in the table below.

[0041] Table 1: Comparison of Electrode Membrane Performance Test Results

[0042] Test Result Analysis: Comparative Example 2: Existing composite binders using a combination of fibrous binders and thermally molten coating binders aim to improve performance. However, such solutions rely on the melt flow and reshaping of the binder, and their reinforcing effect is limited by the uniformity of the coating. Furthermore, instability may be introduced due to thermal history, thus limiting their ability to improve the mechanical strength of the electrodes.

[0043] As can be clearly seen from the data in Table 1, the dry electrodes prepared in Examples 1 and 2 of the present invention are significantly superior to Comparative Example 1 (pure PTFE) and Comparative Example 2 (existing composite binder) in terms of tensile strength, elongation at break and flexibility.

[0044] Figure 1 The smooth appearance and edges of the sample from Example 1 are shown. Figure 2 The image shows a comparison of the tensile stress-strain curves of the electrode film prepared in Comparative Example 1 (pure PTFE) and Example 1, demonstrating the excellent tensile properties of the electrode film in Example 1. This fully proves the effectiveness and superiority of the "three-dimensional dual-network structure" proposed in this invention in improving the mechanical properties of dry electrodes.

[0045] Figure 3 This is a schematic diagram of the winding of the dry electrode film prepared in Example 1 of the present invention, which demonstrates the good flexibility of the electrode film in Example 1 and its perfect match for the high requirements of roll-to-roll production process.

[0046] The lithium-free, all-solid-state pouch cells assembled using Examples 1 and 3 exhibited excellent battery performance. Figure 4 The initial coulombic efficiency was 91.57% (initial charge specific capacity 221.59mAh / g, initial discharge specific capacity 202.8mAh / g).

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a high-strength dry electrode, characterized in that, Includes the following steps: S1: Dry mixing of electrode active material, conductive agent, polytetrafluoroethylene and polymer as network nodes to obtain mixed powder; S2: The mixed powder is sheared to fibrousize the polytetrafluoroethylene and combine with the polymer, which serves as the network node, to form a three-dimensional double network structure, thereby obtaining the electrode material; S3: The electrode material is rolled to form a dry electrode film; The polymer used as a network node is one of polyurethane, polyetheretherketone, polyamide, or a protein crosslinking system.

2. The method for preparing a high-strength dry electrode according to claim 1, characterized in that, The polyurethane is an anionic waterborne polyurethane containing tertiary amine groups.

3. The method for preparing a high-strength dry electrode according to claim 1, characterized in that, The protein cross-linking system is a cross-linked network formed by soybean protein, casein, or gelatin through an aldehyde cross-linking agent.

4. The method for preparing a high-strength dry electrode according to claim 1, characterized in that, The mass ratio of the polytetrafluoroethylene to the polymer serving as the network node is from 10:90 to 50:

50.

5. The method for preparing a high-strength dry electrode according to claim 1, characterized in that, In step S1, the dry mixing is ball milling or high-speed stirring; and / or, in step S2, the shearing treatment is a multi-step fiberization treatment, including high-speed shearing followed by low-speed dispersion.

6. A high-strength dry electrode, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. A high-strength dry electrode according to claim 6, characterized in that, It includes an electrode active material, a conductive agent, polytetrafluoroethylene (PTFE), and a polymer as a network node; the PTFE and the polymer as a network node constitute a composite binder, and the composite binder accounts for 1% to 10% of the mass of the dry electrode.

8. A lithium-ion battery, characterized in that, It includes the high-strength dry electrode as described in claim 6 or 7.

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