Dry-method pole piece containing pre-buried electrolyte salt and preparation method and application of dry-method pole piece

Abstract

The invention provides a dry-method pole piece containing pre-buried electrolyte salt and a preparation method and application of the dry-method pole piece, and relates to the technical field of a dry-method electrode process. Electrolyte salt is distributed in a self-supporting membrane of the dry-method pole piece; the electrolyte salt is lithium salt or sodium salt; wherein the lithium salt is prepared from at least one of LiPF6, LiFSI, LiBOB, LiTFSI, LiBF4, LiDFOB and LiPO2F2, and the sodium salt is prepared from at least one of NaPF6, NaClO4, NaTFSI and NaBOB. According to the invention, the technical problems of difficult electrolyte infiltration and difficult ion diffusion of a dry-method pole piece are solved, and the technical effects of shortening the pole piece infiltration time, improving the ion migration rate and improving the electrochemical performance are achieved.

Description

Technical Field

[0001] This invention relates to the technical field of dry electrode technology, and in particular to a dry electrode sheet containing a pre-embedded electrolyte salt, its preparation method, and its application. Background Technology

[0002] Dry electrode process is a novel electrode preparation technology that uses solvent-free film formation technology. It involves mixing active materials, conductive agents (carbon nanotubes, carbon black) and binders, then shearing them at high speed to form a self-supporting film, which is then laminated onto the surface of a metal current collector (copper foil or aluminum foil).

[0003] Dry electrode manufacturing processes utilize solvent-free technology, avoiding side reactions between active materials, additives, and solvents such as NMP and water. However, the solvent-free process and multiple calendering densification steps result in a high proportion of closed pores in the electrode microstructure. Furthermore, the binders used are generally non-polar materials, making electrolyte wetting more difficult for the electrodes prepared using dry processes compared to traditional wet processes. Additionally, as electrode thickness increases, lithium-ion or sodium-ion diffusion becomes more challenging, limiting the battery's charge and discharge capabilities.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a dry electrode containing a pre-embedded electrolyte salt, which solves the technical problems of difficult electrolyte wetting and ion diffusion in dry electrodes, and can shorten the electrode wetting time, improve the ion migration rate and enhance electrochemical performance.

[0006] The second objective of this invention is to provide a method for preparing dry electrode sheets containing pre-embedded electrolyte salts, which is simple, has a high success rate, and is suitable for industrial production.

[0007] The third objective of this invention is to provide an application of a dry electrode containing a pre-embedded electrolyte salt, which is beneficial to improving electrochemical performance.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, a dry electrode containing pre-embedded electrolyte salts, wherein the electrolyte salts are distributed in the self-supporting membrane of the dry electrode. The electrolyte salt is a lithium salt or a sodium salt; The lithium salt includes at least one of LiPF6, LiFSI, LiBOB, LiTFSI, LiBF4, LiDFOB, and LiPO2F2; The sodium salt includes at least one of NaPF6, NaClO4, NaTFSI, and NaBOB.

[0009] Furthermore, the electrolyte salt accounts for 0.5%-5% of the mass of the self-supporting membrane.

[0010] Furthermore, the self-supporting membrane is composed of the following components by mass percentage: The active material is 85%-97.5%, the binder is 1%-5%, the conductive agent is 1%-5%, and the electrolyte salt is 0.5%-5%.

[0011] Furthermore, the thickness of the self-supporting membrane is 50μm-180μm.

[0012] Secondly, a method for preparing a dry electrode sheet according to any one of the above claims includes the following steps: (a) The active material, binder, conductive agent and electrolyte salt are premixed by slow mixing to obtain a premixed powder; (b) The premixed powder is rapidly sheared and mixed, sheared to a filamentous state, and then rolled and thinned to obtain a self-supporting film; (c) The self-supporting membrane is combined with a metal current collector to obtain the dry electrode.

[0013] Furthermore, in step (a), the linear velocity of the slow mixing is 5 m / s to 15 m / s.

[0014] Furthermore, in step (b), the linear velocity of the rapid shear mixing is 30 m / s to 50 m / s.

[0015] Furthermore, in step (b), the temperature of the roller pressing is 90°C-120°C.

[0016] Furthermore, in step (c), the composite method includes hot-pressing composite.

[0017] Thirdly, the application of any of the above-mentioned dry-process electrode sheets in the cell of a secondary battery.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: The dry-process electrode sheet containing pre-embedded electrolyte salt provided by this invention forms a high-concentration region of electrolyte salt locally after electrolyte injection, generating high osmotic pressure. This strongly drives the electrolyte to rapidly penetrate into the electrode sheet, effectively shortening the electrolyte wetting time of the electrode sheet in the cell manufacturing process. Furthermore, after electrolyte injection, the electrolyte salt in the electrode sheet gradually dissolves and forms a microporous structure, providing more migration channels for lithium or sodium ions and improving their migration rate. Cells prepared using this electrode sheet exhibit high-rate discharge and improved capacity retention. Due to the reduced electrode interface impedance and improved utilization of active materials, cells prepared using this electrode sheet have improved cycle life and electrochemical performance.

[0019] The method for preparing dry electrode sheets containing pre-embedded electrolyte salts provided by this invention is simple, has a high success rate, and is suitable for industrial production.

[0020] The application of the dry electrode containing pre-embedded electrolyte salt provided by this invention is beneficial to improving electrochemical performance. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the structure of a dry electrode sheet containing pre-embedded lithium salt provided in one embodiment of the present invention; Figure 2 This is a 4C rate discharge curve obtained from the experimental example of the present invention; Figure 3 This is a cyclic curve obtained from the experimental examples of the present invention.

[0023] Icons: 1-Electrolyte salt; 2-Self-supporting membrane; 3-Conductive substrate. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0025] According to a first aspect of the present invention, a dry electrode containing a pre-embedded electrolyte salt is provided, wherein the electrolyte salt is distributed in a self-supporting membrane of the dry electrode; The electrolyte salt can be a lithium salt or a sodium salt; The lithium salts include, but are not limited to, at least one of LiPF6, LiFSI, LiBOB, LiTFSI, LiBF4, LiDFOB and LiPO2F2; Sodium salts include, but are not limited to, at least one of NaPF6, NaClO4, NaTFSI, and NaBOB.

[0026] In this invention, after the dry electrode containing pre-embedded electrolyte salt is injected, the locally high concentration of lithium salt can create osmotic pressure, thereby promoting the wetting of the electrolyte. In addition, after the electrolyte salt gradually dissolves into the electrolyte, it can form micropores that remain in the electrode, serving as migration channels for lithium or sodium ions, thereby improving the migration rate of lithium or sodium ions.

[0027] It should be noted that, as Figure 1 As shown, the self-supporting membrane 2 (i.e., the active material layer with pre-embedded electrolyte salt) is composed of active material (active substance), binder, conductive agent and electrolyte salt 1. After the self-supporting membrane 2 and the conductive substrate 3 (i.e. the metal current collector) are combined, a dry electrode is formed.

[0028] In a preferred embodiment, the mass percentage of the electrolyte salt in the self-supporting membrane can be 0.5%-5%, with typical but non-limiting mass percentages being, for example, 0.5%, 1%, 2%, 3%, 4%, and 5%.

[0029] In this invention, the electrolyte salt distributed in a specific amount in the electrode can, on the one hand, create a high osmotic pressure, which helps to shorten the electrode wetting time. Specifically, after the electrolyte salt is injected, a high concentration area is formed locally, generating osmotic pressure, which strongly drives the electrolyte to quickly penetrate into the interior of the electrode, thus shortening the electrode wetting time. On the other hand, the electrolyte salt can form a microporous structure after dissolving, which helps to improve the migration rate of lithium ions or sodium ions. The battery cell prepared using this electrode can discharge at a high rate and improve the capacity retention rate. At the same time, due to the reduction of the electrode interface impedance, the utilization rate of active material is also improved, and the cycle life of the battery cell prepared using this electrode is improved.

[0030] In a preferred embodiment, the self-supporting membrane may consist of the following components by weight percentage: The active material is 85%-97.5%, the binder is 1%-5%, the conductive agent is 1%-5%, and the electrolyte salt is 0.5%-5%.

[0031] In this invention, typical but non-limiting mass percentages of the active material are, for example, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 97.5%; typical but non-limiting mass percentages of the binder are, for example, 1%, 2%, 3%, 4%, and 5%; typical but non-limiting mass percentages of the conductive agent are, for example, 1%, 2%, 3%, 4%, and 5%; and typical but non-limiting mass percentages of the electrolyte salt are, for example, 0.5%, 1%, 2%, 3%, 4%, and 5%.

[0032] In this invention, the active material can be common positive and negative electrode materials such as NCM, LFP, Prussian blue, and graphite, and the binder can be polymers such as PTFE or ultra-high molecular weight PET; the electrolyte salt can be a mixture of two or more electrolyte salts.

[0033] It should be noted that the self-supporting film is laminated onto the surface of the metal current collector, which is the conductive substrate and can be selected from copper foil, aluminum foil, composite copper foil, or composite aluminum foil.

[0034] In a preferred embodiment, the thickness of the monolayer self-supporting membrane can be 50 μm-180 μm, with typical but non-limiting thicknesses such as 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, and 180 μm.

[0035] According to a second aspect of the present invention, a method for preparing a dry electrode sheet as described in any one of the above claims is provided, comprising the following steps: (a) The active material, binder, conductive agent and electrolyte salt are premixed by slow mixing to obtain a premixed powder; (b) The premixed powder is rapidly sheared and mixed until it reaches a stringy state, and then thinned by (step-by-step) rolling to obtain a self-supporting film; (c) The self-supporting membrane is combined with a metal current collector to obtain a dry electrode.

[0036] The present invention provides a method for preparing dry electrode sheets containing pre-embedded electrolyte salts, which is simple in process, has a high success rate, and is suitable for industrial production.

[0037] In this invention, taking advantage of the solvent-free nature of dry electrodes, specific electrolyte salts can be added during the dry mixing stage for mixing, and the resulting mixture can then be used to prepare the electrode sheet. It should be noted that, in addition to adding electrolyte salts during the total mixing, electrolyte salts can also be added after the binder has been fiberized to a certain extent.

[0038] In a preferred embodiment, in step (a), the linear velocity of the slow mixing can be 5 m / s to 15 m / s, with typical but non-limiting linear velocities being, for example, 5 m / s, 10 m / s, and 15 m / s.

[0039] In a preferred embodiment, in step (b), the linear velocity of the rapid shear mixing can be 30 m / s to 50 m / s, with typical but non-limiting linear velocities being, for example, 30 m / s, 35 m / s, 40 m / s, 45 m / s, and 50 m / s.

[0040] In a preferred embodiment, in step (b), the rolling temperature can be 90°C-120°C, with typical but non-limiting temperatures such as 90°C, 100°C, 110°C, and 120°C.

[0041] In a preferred embodiment, in step (c), the composite method includes, but is not limited to, hot-pressing composite.

[0042] According to a third aspect of the present invention, the application of the dry-process electrode sheet described in any of the preceding claims in a cell of a secondary battery is provided.

[0043] The application of the dry electrode containing pre-embedded electrolyte salt in this invention is beneficial to improving electrochemical performance.

[0044] It should be noted that by using processes such as cutting and punching, dry electrode sheets can be prepared into appropriate sizes, and after assembly, they can form battery cells with different structures such as soft-pack and prismatic.

[0045] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0046] Example 1 A method for preparing a dry electrode containing pre-embedded lithium salt includes the following steps: (1) Nickel-cobalt-manganese ternary material (NCM613), conductive carbon black, carbon nanotubes (CNT), binder (PTFE) and lithium salt (LiTFSI) were premixed in a mass ratio of 93:2:1:2:2. The mixture was slowly mixed at an online speed of 10 m / s for 30 min, and the powder temperature was controlled to be <25℃ to obtain the premixed powder. (2) The obtained premixed powder is stirred using a high-speed shear machine at a linear speed of 40 m / s until the mixture becomes stringy, thus obtaining the mixture; (3) The mixture is granulated using a granulator. The granulated particle size is about 1mm-2mm, and granulated particles are obtained. (4) Using a multi-stage differential speed rolling equipment, the granulated particles are rolled thin to a thickness of 110 μm at a rolling temperature of 110℃ to obtain a self-supporting membrane. (5) Using a constant speed hot rolling press, the obtained self-supporting film is hot-pressed with a 15μm thick aluminum foil (metal current collector) at a composite temperature of 110℃ to obtain a dry electrode sheet.

[0047] In this embodiment, the obtained dry-process electrode sheet is compacted to a density of 3.3 g / cm³. 3A positive electrode sheet for battery assembly is obtained. This positive electrode sheet, together with a common graphite negative electrode sheet (graphite:CMC:SBR = 96:2:2), electrolyte, separator, and other auxiliary materials such as aluminum-plastic film and tabs, are assembled to form a 2000mAh soft-pack battery. The soft-pack battery is subjected to high-rate discharge at 4C, with a capacity retention rate of >92% relative to 0.2C rate; the capacity retention rate is >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle life is >2300 cycles.

[0048] Example 2 A method for preparing a dry electrode containing pre-embedded lithium salt includes the following steps: (1) Graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) were premixed in a mass ratio of 95:1:2:2 and mixed slowly at an online speed of 10m / s for 30min, while controlling the powder temperature to <25℃, to obtain premixed powder; (2) The obtained premixed powder is stirred using a high-speed shear machine at a linear speed of 35 m / s until the mixture becomes stringy, thus obtaining the mixture; (3) The mixture is granulated using a granulator. The granulated particle size is about 1mm-2mm, and granulated particles are obtained. (4) Using a multi-stage differential speed rolling equipment, the granulated particles are rolled thinned to a thickness of 90μm at a rolling temperature of 110℃ to obtain a self-supporting membrane. (5) Using a constant speed hot rolling press, the obtained self-supporting film is hot-pressed with an 8μm thick copper foil (metal current collector) at a composite temperature of 110℃ to obtain a dry electrode sheet.

[0049] In this embodiment, the obtained dry-process electrode sheet is compacted to a density of 1.6 g / cm³. 3 A negative electrode sheet for battery assembly is obtained. This negative electrode sheet, along with an LFP positive electrode sheet (LFP:SP:PVDF = 96:2:2), electrolyte, separator, and other auxiliary materials such as aluminum-plastic film and tabs, are assembled to form an 1800mAh soft-pack battery. The soft-pack battery is subjected to high-rate discharge at 4C, with a capacity retention rate of >85% relative to 0.2C rate; the capacity retention rate is >85% when charged at 0.5C and discharged at 1C, with a cycle life of >2900 cycles as the cutoff condition.

[0050] Example 3 The only difference between this embodiment and embodiment 2 is that in step (1), graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) are mixed in a mass ratio of 96:1:2:1. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0051] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >84% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2700 cycles.

[0052] Example 4 The only difference between this embodiment and embodiment 2 is that in step (1), graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) are mixed in a mass ratio of 94:1:2:3. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0053] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >86% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2950 cycles.

[0054] Example 5 The only difference between this embodiment and embodiment 2 is that in step (1), graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) are mixed in a mass ratio of 93:1:2:4. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0055] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >86.5% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2980 cycles.

[0056] Example 6 The only difference between this embodiment and embodiment 2 is that in step (1), graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) are mixed in a mass ratio of 92:1:2:5. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0057] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was discharged at a high rate of 4C, and the capacity retention rate was >86.1% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the number of cycles was >2800.

[0058] Example 7 The only difference between this embodiment and embodiment 2 is that in step (1), graphite, conductive carbon black, binder (PTFE) and lithium salt (LiTFSI) are mixed in a mass ratio of 91:1:2:6. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0059] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >83% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2500 cycles.

[0060] Example 8 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiPF6; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0061] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >84.5% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2800 cycles.

[0062] Example 9 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiFSI; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0063] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >84% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2700 cycles.

[0064] Example 10 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiBOB; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0065] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >85% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2800 cycles.

[0066] Example 11 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiBF4; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0067] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was discharged at a high rate of 4C, and the capacity retention rate was >84.2% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2850 cycles.

[0068] Example 12 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiDFOB; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0069] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >85% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C, and the cycle count was >2880 cycles.

[0070] Example 13 The only difference between this embodiment and embodiment 2 is that, in step (1), the lithium salt used is LiPO2F2; The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0071] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >84.5% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >2750 cycles.

[0072] Example 14 A method for preparing a dry electrode containing pre-embedded sodium salt includes the following steps: (1) Prussian blue, conductive carbon black, carbon nanotubes (CNT), binder (PTFE) and sodium salt (NaTFSI) of sodium battery cathode material were premixed in a mass ratio of 93:2:1:2:2. The mixture was slowly mixed at an online speed of 10 m / s for 30 min, and the powder temperature was controlled to be <25℃ to obtain premixed powder. (2) The obtained premixed powder is stirred using a high-speed shear machine at a linear speed of 35 m / s until the mixture becomes stringy, thus obtaining the mixture; (3) The mixture is granulated using a granulator. The granulated particle size is about 1mm-2mm, and granulated particles are obtained. (4) Using a multi-stage differential speed rolling equipment, the granulated particles are rolled thin to a thickness of 150μm at a rolling temperature of 110℃ to obtain a self-supporting membrane. (5) Using a constant speed hot rolling press, the obtained self-supporting film is hot-pressed with a 13μm thick aluminum foil at a composite temperature of 110℃ to obtain a dry electrode sheet.

[0073] In this embodiment, the obtained dry-process electrode sheet is compacted to a density of 1.8 g / cm³. 3 A positive electrode sheet for sodium battery assembly was obtained. This positive electrode sheet, along with a hard carbon negative electrode sheet (graphite:CMC:SBR:SP = 93:2:3:2), electrolyte, separator, and other auxiliary materials such as aluminum-plastic film and tabs, were assembled to form a 1500mAh soft-pack battery. The soft-pack battery was subjected to high-rate discharge at 4C, with a capacity retention rate of >94% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C, as the cutoff condition, and the cycle life was >1800 cycles.

[0074] Example 15 The only difference between this embodiment and embodiment 14 is that, in step (1), the sodium salt used is NaPF6; The remaining steps and parameters are the same as in Example 14, resulting in a dry electrode sheet.

[0075] The obtained dry-processed electrode sheets were assembled to form a 1500mAh soft-pack sodium battery. The soft-pack battery was subjected to high-rate discharge at 4C, with a capacity retention rate of >93% relative to 0.2C rate; the capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >1700 cycles.

[0076] Example 16 The only difference between this embodiment and embodiment 14 is that, in step (1), the sodium salt used is NaBOB; The remaining steps and parameters are the same as in Example 14, resulting in a dry electrode sheet.

[0077] The obtained dry-processed electrode sheets were assembled to form a 1500mAh soft-pack sodium battery. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was >93.5% relative to 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was >1750 cycles.

[0078] Comparative Example 1 The difference between this comparative example and Example 1 is that lithium salt (LiTFSI) was not added in step (1); that is, nickel-cobalt-manganese ternary material (NCM613), conductive carbon black, carbon nanotubes (CNT) and binder (PTFE) were mixed in a mass ratio of 95:2:1:2. The remaining steps and parameters are the same as in Example 1, resulting in a dry electrode sheet.

[0079] The obtained dry-process electrode sheets were assembled into a 2000mAh soft-pack battery according to the method of Example 1. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was 84.7% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C, and the cycle count was 1819 cycles.

[0080] Comparative Example 2 The difference between this comparative example and Example 2 is that in step (1), lithium salt (LiTFSI) was not added; that is, graphite, conductive carbon black and binder (PTFE) were mixed in a mass ratio of 97:1:2. The remaining steps and parameters are the same as in Example 2, resulting in a dry electrode sheet.

[0081] The obtained dry-process electrode sheets were assembled into an 1800mAh soft-pack battery according to the method of Example 2. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was 79.1% relative to the 0.2C rate. The capacity retention rate was >85% when charged at 0.5C and discharged at 1C as the cutoff condition, and the cycle count was 2300 cycles.

[0082] Comparative Example 3 The difference between this comparative example and Example 14 is that sodium salt (NaTFSI) was not added in step (1); that is, Russo blue, conductive carbon black, carbon nanotubes (CNTs) and binder (PTFE) were mixed in a mass ratio of 95:2:1:2. The remaining steps and parameters are the same as in Example 14, resulting in a dry electrode sheet.

[0083] The obtained dry-process electrode sheets were assembled into a 1500mAh soft-pack battery according to the method of Example 14. The soft-pack battery was subjected to high-rate discharge at 4C, and the capacity retention rate was 88.5% relative to the 0.2C rate. The battery was charged at 0.5C and discharged at 1C, and the capacity retention rate was >85% as the cutoff condition. The cycle count was 1500 cycles.

[0084] Test case Electrode wettability test: A wettability test method was designed based on the Lucas-Washburn permeation model. The specific operation was to cut the electrode sample into strips of 20mm×260mm, immerse the bottom of the electrode in the electrolyte for 20mm, observe the relationship between the electrolyte climbing height and time, and record the time required for a climbing height of 40mm. The results are shown in Table 1.

[0085] The data from Example 1 and Comparative Example 1 show that, on the one hand, the electrolyte salt forms a high-concentration region locally after injection, generating osmotic pressure and strongly driving the electrolyte to rapidly penetrate into the electrode, thus shortening the electrode wetting time from 380 min to 250 min; on the other hand, the electrolyte salt can form a microporous structure after dissolution, which is beneficial to improving the migration rate of lithium or sodium ions. The battery cell prepared using this electrode exhibits improved capacity retention at high discharge rates. At 4C high discharge rates, the 0.2C / 4C capacity retention can be increased from 84.7% to 92%. Figure 2 Simultaneously, due to the reduction in electrode interface impedance and the improvement in active material utilization, the cycle life of the battery cell prepared using this electrode can be increased by 29%. Figure 3 This is beneficial for improving electrochemical performance.

[0086] Table 1

[0087] In summary, this invention solves the technical problems of difficult electrolyte wetting and ion diffusion in dry-process electrodes, and achieves the technical effects of shortening electrode wetting time, improving ion migration rate and enhancing electrochemical performance.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dry-process electrode containing pre-embedded electrolyte salt, characterized in that, Electrolyte salts are distributed in the self-supporting membrane of the dry electrode. The electrolyte salt is a lithium salt or a sodium salt; The lithium salt includes at least one of LiPF6, LiFSI, LiBOB, LiTFSI, LiBF4, LiDFOB, and LiPO2F2; The sodium salt includes at least one of NaPF6, NaClO4, NaTFSI, and NaBOB.

2. The dry-process electrode sheet according to claim 1, characterized in that, The electrolyte salt accounts for 0.5%-5% of the mass of the self-supporting membrane.

3. The dry-process electrode sheet according to claim 1 or 2, characterized in that, The self-supporting membrane is composed of the following components by mass percentage: The active material is 85%-97.5%, the binder is 1%-5%, the conductive agent is 1%-5%, and the electrolyte salt is 0.5%-5%.

4. The dry-process electrode sheet according to claim 3, characterized in that, The thickness of the self-supporting membrane is 50μm-180μm.

5. A method for preparing a dry electrode according to any one of claims 1-4, characterized in that, Includes the following steps: (a) The active material, binder, conductive agent and electrolyte salt are premixed by slow mixing to obtain a premixed powder; (b) The premixed powder is rapidly sheared and mixed, sheared to a filamentous state, and then rolled and thinned to obtain a self-supporting film; (c) The self-supporting membrane is combined with a metal current collector to obtain the dry electrode.

6. The preparation method according to claim 5, characterized in that, In step (a), the linear velocity of the slow mixing is 5 m / s to 15 m / s.

7. The preparation method according to claim 5, characterized in that, In step (b), the linear velocity of the rapid shear mixing is 30 m / s-50 m / s.

8. The preparation method according to claim 5, characterized in that, In step (b), the temperature of the roller pressing is 90℃-120℃.

9. The preparation method according to claim 5, characterized in that, In step (c), the composite method includes hot-pressing composite.

10. The application of the dry-process electrode sheet according to any one of claims 1-4 in the cell of a secondary battery.

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