Negative electrode based on specific solid electrolyte gradient mixing and preparation method and application thereof

Abstract

The invention relates to the field of batteries, in particular to a negative electrode based on specific solid electrolyte gradient mixing and a preparation method and application thereof. Comprising a current collector, a first layer of slurry and a second layer of slurry, wherein the content of the solid electrolyte in the first layer of slurry is smaller than that in the second layer of slurry; lLZO / LATP and a binder synergistically form a multi-layer interface under gradient concentration, and the interface contact resistance is reduced by more than 30% compared with that of a single-layer structure; a conduction path of LLZO / LATP is optimized through gradient distribution, the ionic conductivity of the upper layer is improved by 50%, and the problem of uneven distribution is solved; the electron blocking characteristic of LLZO / LATP in the high-concentration layer reduces electron migration, and the self-discharge rate is reduced to be less than 5% / month; through matching of the binder and the solid electrolyte, the stability of the slurry is improved, and the coating defect rate is reduced; gradient design relieves lithium dendrite growth, and the cycle life is prolonged by 20%.

Description

Technical Field

[0001] This invention relates to the field of batteries, and in particular to a negative electrode based on gradient mixing of a specific solid electrolyte, its preparation method, and its application. Background Technology

[0002] In recent years, solid-state batteries have become a research hotspot due to their advantages in safety and energy density; however, the practical application of solid-state electrolytes still faces challenges. In particular, commonly used solid-state electrolytes such as LLZO (Li7La3Zr2O)... 12 ) and LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3) Although it has high ionic conductivity, its distribution in the electrode and interfacial contact are prominent issues. Under a single coating process, solid electrolytes such as LLZO / LATP tend to aggregate in the electrode, resulting in discontinuous ion conduction paths and a significant decrease in ionic conductivity in areas far from the current collector. LLZO / LATP has a solid-solid contact with the electrode active material, resulting in high interfacial impedance, and volume changes during charging and discharging exacerbate contact failure. Existing gradient concentration designs are mostly designed for liquid electrolytes or general-purpose materials, without considering the particle characteristics (such as particle size and surface energy) of solid electrolytes such as LLZO / LATP, leading to limited optimization effects. LLZO / LATP is prone to adverse reactions with binders and solvents in the slurry, affecting coating uniformity and electrode stability.

[0003] Therefore, there is an urgent need to provide an electrode tailored to the material properties of specific solid electrolytes such as LLZO / LATP. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a negative electrode based on gradient mixing of a specific solid electrolyte, its preparation method, and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention is to provide a negative electrode based on a gradient mixing of a specific solid electrolyte, comprising: a current collector and a first slurry layer and a second slurry layer sequentially coated on the surface of the current collector;

[0007] The first slurry layer and the second slurry layer each include: negative electrode active material, solid electrolyte, conductive agent, binder and additives; the solid electrolyte content in the first slurry layer is less than the solid electrolyte content in the second slurry layer.

[0008] Preferably, the negative electrode active material includes at least one of graphite and silicon-based materials.

[0009] Preferably, the solid electrolyte is Li7La3Zr2O 12 Or Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0010] Preferably, the adhesive comprises at least one of sodium carboxymethyl cellulose, polyvinylidene fluoride, and polyacrylic acid.

[0011] Preferably, in the first slurry layer, the mass ratio of the negative electrode active material, solid electrolyte, conductive agent, binder and additive is 97:2:1.5:1.0:0.5;

[0012] In the second slurry, the mass ratio of negative electrode active material, solid electrolyte, conductive agent, binder and additive is 97:5:1.5:1.0:0.5.

[0013] Preferably, the thickness ratio of the first slurry layer to the second slurry layer is 1:(1-2).

[0014] The second aspect of the present invention is to provide a method for preparing the above-mentioned negative electrode based on a specific solid electrolyte gradient mixing, the steps of which include: mixing a negative electrode active material, a solid electrolyte, a conductive agent, a binder and an additive in a certain proportion to prepare a first slurry and a second slurry; continuously coating the first slurry and the second slurry on a copper foil current collector and then drying and cold pressing to obtain the negative electrode.

[0015] A third aspect of the present invention is to provide an application of the above-mentioned negative electrode based on a specific solid electrolyte gradient mixing in a solid-state battery, the steps of which include: winding and assembling the negative electrode and the positive electrode separator, and then performing a liquid injection and capacity testing process to obtain the solid-state battery.

[0016] Preferably, the preparation steps of the positive electrode include: mixing the positive electrode active material, conductive agent, binder and dispersant in a mass ratio of 96.5:2.0:1.2:0.3, adding N-methylpyrrolidone, stirring evenly, coating the slurry onto an aluminum foil current collector, drying and cold pressing to obtain the positive electrode.

[0017] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0018] (1) Significantly reduced interfacial impedance: LLZO / LATP forms a multi-layered interface in synergy with the binder under gradient concentration, and the interfacial contact resistance is reduced by more than 30% compared with the single-layer structure;

[0019] (2) Improved ionic conductivity: The gradient distribution optimizes the conduction path of LLZO / LATP, increasing the ionic conductivity of the upper layer by 50% and solving the problem of uneven distribution;

[0020] (3) Self-discharge inhibition: The electron blocking properties of LLZO / LATP in the high-concentration layer reduce electron migration, and the self-discharge rate is reduced to below 5% / month;

[0021] (4) Enhanced process compatibility: By matching the binder with the solid electrolyte, the stability of the slurry is improved and the coating defect rate is reduced;

[0022] (5) Enhanced safety: Gradient design mitigates lithium dendrite growth and extends cycle life by 20%. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0026] Example 1

[0027] This embodiment provides a method for preparing a negative electrode based on gradient mixing of a specific solid electrolyte, the steps of which include:

[0028] 1. Prepare the first layer of slurry by mixing the negative electrode active material (graphite), solid electrolyte (LLZO with a particle size of 1μm and a concentration of 20wt%), conductive agent, binder (sodium carboxymethyl cellulose) and additives in a mass ratio of 97:2:1.5:1.0:0.5.

[0029] 2. Prepare the second slurry by mixing the negative electrode active material (graphite), solid electrolyte (LLZO with a particle size of 1μm and a concentration of 35wt%), conductive agent, binder (polyvinylidene fluoride) and additives in a mass ratio of 97:5:1.5:1.0:0.5.

[0030] 3. Prepare a double-layer electrode by continuously coating two layers of slurry onto a copper foil current collector with a thickness ratio of 1:1-2 and a total areal density of 15-25 mg / cm². After drying and cold pressing, the electrode thickness is 160 μm.

[0031] Example 2

[0032] This embodiment provides another method for preparing a negative electrode based on gradient mixing of a specific solid electrolyte, the steps of which include:

[0033] 1. Prepare the first layer of slurry by mixing the negative electrode active material (graphite), solid electrolyte (LATP with a particle size of 1.5μm and a concentration of 28wt%), conductive agent, binder (polyacrylic acid) and additives in a mass ratio of 97:2:1.5:1.0:0.5.

[0034] 2. Prepare the second slurry by mixing the negative electrode active material (graphite), solid electrolyte (LATP with a particle size of 1.5μm and a concentration of 35wt%), conductive agent, binder (polyvinylidene fluoride) and additives in a mass ratio of 97:5:1.5:1.0:0.5.

[0035] 3. Prepare a double-layer electrode by continuously coating two layers of slurry onto a copper foil current collector with a thickness ratio of 1:1-2 and a total areal density of 15-25 mg / cm². After drying and cold pressing, the electrode thickness is 160 μm.

[0036] Comparative Example 1

[0037] This comparative example provides a method for preparing a negative electrode, the steps of which include:

[0038] A single-layer negative electrode sheet was prepared, with the total LLZO content being the same as the sum of the two-layer slurry in Example 1, and the total proportion of other components (active material, conductive agent, etc.) also being consistent with that in Example 1.

[0039] Comparative Example 2

[0040] This comparative example provides another method for preparing a negative electrode, the steps of which include:

[0041] The solid electrolyte was replaced with a Li2SP2S5 glass-ceramic electrolyte, and everything else was the same as in Example 1.

[0042] Comparative Example 3

[0043] This comparative example provides another method for preparing a negative electrode, the steps of which include:

[0044] No solid electrolyte was added; only the active material, conductive agent, and binder were retained, and everything else was the same as in Example 1.

[0045] Comparative Example 4

[0046] This comparative example provides another method for preparing a negative electrode, the steps of which include:

[0047] A single-layer negative electrode sheet was prepared, with the total LATP content being the same as the sum of the two-layer slurry in Example 2, and the total proportion of other components also being consistent with that in Example 2.

[0048] Comparative Example 5

[0049] This comparative example provides another method for preparing a negative electrode, the steps of which include:

[0050] The solid electrolyte was replaced with a Li2SP2S5 glass-ceramic electrolyte, and everything else was the same as in Example 2.

[0051] Comparative Example 6

[0052] This comparative example provides another method for preparing a negative electrode, the steps of which include:

[0053] No solid electrolyte was added; only the active material, conductive agent, and binder were retained, and everything else was the same as in Example 2.

[0054] Detection Examples

[0055] Batteries were fabricated by assembling the negative and positive electrodes of Examples 1-2 and Comparative Examples 1-6, and the performance of the batteries was tested. The results are shown in Table 1-2.

[0056] Table 1

[0057]

[0058] Table 2

[0059]

[0060] In Example 1, hydrophilic sodium carboxymethyl cellulose promotes close contact between the first layer of LLZO and the copper foil current collector, while hydrophobic polyvinylidene fluoride effectively reduces the interfacial impedance with the subsequent solid electrolyte layer in the second layer. This gradient of the binder and the gradient distribution of LLZO produce a synergistic effect.

[0061] The superior performance of Example 2 demonstrates the synergistic effect between LATP's high bulk ionic conductivity and the gradient structure and binder system designed for it. Comparative Example 4 shows that without the gradient structure, the advantages of LATP cannot be fully realized; Comparative Example 5 demonstrates that this specific gradient structure is ineffective with other electrolyte materials, highlighting the specificity of the solution for LATP.

[0062] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A negative electrode based on gradient mixing of a specific solid electrolyte, characterized in that, include: A current collector and a first layer of slurry and a second layer of slurry sequentially coated on the surface of the current collector; The first slurry layer and the second slurry layer each include: negative electrode active material, solid electrolyte, conductive agent, binder and additives; the solid electrolyte content in the first slurry layer is less than the solid electrolyte content in the second slurry layer.

2. The negative electrode based on gradient mixing of a specific solid electrolyte according to claim 1, characterized in that, The negative electrode active material includes at least one of graphite and silicon-based materials.

3. The negative electrode based on gradient mixing of a specific solid electrolyte according to claim 1, characterized in that, The solid electrolyte is Li7La3Zr2O 12 Or Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

4. The negative electrode based on gradient mixing of a specific solid electrolyte according to claim 1, characterized in that, The adhesive includes at least one of sodium carboxymethyl cellulose, polyvinylidene fluoride, and polyacrylic acid.

5. The negative electrode based on gradient mixing of a specific solid electrolyte according to claim 1, characterized in that, In the first layer of slurry, the mass ratio of negative electrode active material, solid electrolyte, conductive agent, binder and additive is 97:2:1.5:1.0:0.5; In the second slurry, the mass ratio of negative electrode active material, solid electrolyte, conductive agent, binder and additive is 97:5:1.5:1.0:0.

5.

6. The negative electrode based on gradient mixing of a specific solid electrolyte according to claim 1, characterized in that, The thickness ratio of the first slurry layer to the second slurry layer is 1:(1-2).

7. A method for preparing a negative electrode based on a specific solid electrolyte gradient mixing as described in any one of claims 1-6, characterized in that, step include: A first slurry and a second slurry are prepared by mixing the negative electrode active material, solid electrolyte, conductive agent, binder and additives in a certain proportion. The first slurry and the second slurry are continuously coated on the copper foil current collector and then dried and cold pressed to obtain the negative electrode.

8. An application of a negative electrode based on a specific solid electrolyte gradient mixing as described in any one of claims 1-6 in a solid-state battery, characterized in that, step... include: After the negative electrode and positive electrode separator are wound and assembled, a liquid injection and capacity testing process is performed to obtain the solid-state battery.

9. The application according to claim 8, characterized in that, The preparation steps of the positive electrode include: mixing positive electrode active material, conductive agent, binder and dispersant in a mass ratio of 96.5:2.0:1.2:0.3, adding N-methylpyrrolidone, stirring evenly, coating the slurry onto an aluminum foil current collector, drying and cold pressing to obtain the positive electrode.

Images