Electrode plate for alkali metal ion liquid battery, manufacturing method and battery

Abstract

The invention relates to the technical field of batteries, and particularly provides an electrode plate for an alkali metal ion liquid battery, a manufacturing method and the battery. The electrode plate for the alkali metal ion liquid battery comprises a current collector, the active material coatings are sequentially coated on the same side of the current collector in the direction far away from the current collector; each active substance coating comprises an electrolyte additive, the electrolyte additive in each active substance coating can be dissolved in an electrolyte of the alkali metal ion liquid battery so as to form pores in each active substance layer, and the total volume of the pores of the coatings is gradually increased in the direction far away from the current collector. By improving the pore distribution of the coating of the pole piece, the rate and cycle performance of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically provides an electrode plate for an alkali metal ion liquid battery, a method for manufacturing an electrode plate for an alkali metal ion battery, a method for manufacturing a battery cell, and a battery. Background Art

[0002] The design and manufacture of electrode plates are key processes in the production of lithium-ion batteries. In the traditional design of electrode plate structures, for the electrode plate after rolling treatment, in the vertical direction from the current collector to the surface layer, the pore volume or porosity shows an obvious decreasing trend. As the compaction density of the electrode plate continuously increases, the porosity will also gradually decrease. Since the pore volume and pore distribution have a decisive influence on the diffusion of lithium ions in the liquid phase, the traditional pore structure of the electrode plate will greatly limit the rate performance and cycle life of the battery. Therefore, in order to break through this bottleneck and effectively increase the total pore volume of the electrode plate and improve its pore distribution in the vertical direction, it has become an important research direction for optimizing the electrode plate structure design and improving the overall performance of the battery.

[0003] Existing methods are complex in process and are not suitable for industrial mass production in terms of efficiency, energy consumption, and space. Therefore, it is necessary to develop a method suitable for mass production that can effectively improve the problem that the pore volume of the existing electrode plate gradually decreases in the vertical direction from the current collector to the surface layer after rolling, so as to improve the rate and cycle performance of the battery. Summary of the Invention

[0004] In order to overcome the above defects, the present invention provides an electrode plate for an alkali metal ion liquid battery, a method for manufacturing an electrode plate for an alkali metal ion battery, a method for manufacturing a battery cell, and a lithium-ion battery. The pore-forming electrolyte additives of different active material coatings are dissolved in the electrolyte to perform gradient pore formation, improve the pore distribution of the electrode plate, and improve the rate and cycle performance of the battery.

[0005] In a first aspect, the present invention provides an electrode plate for an alkali metal ion liquid battery, comprising:

[0006] A current collector;

[0007] A plurality of active material coatings are sequentially coated on the same side of the current collector in a direction away from the current collector; the active material coatings include electrolyte additives, and the electrolyte additives in each active material coating can be dissolved in the electrolyte of the alkali metal ion liquid battery to form pores in each active material layer, and in the direction away from the current collector, the total pore volume of the pores in the coating gradually increases.

[0008] Furthermore, at least one of the following is different between the electrolyte additives of each active material coating:

[0009] The types of electrolyte additives, the particle size of the electrolyte additives, and the volume ratio of the electrolyte additives in the electrode material of the coating where they are located, so that after the electrolyte additives are dissolved in the electrolyte, the pores in the corresponding coating can be formed, and along the direction away from the current collector, the total volume of the pores in the coating gradually increases.

[0010] Further, the active material coating further includes: active material, binder, and conductive agent; and / or

[0011] The types of the electrolyte additives in each active material coating include:

[0012] One or more of lithium salt crystals, organic electrolyte solvent crystals, and functional additive crystals.

[0013] Further, the lithium salt crystals include one or more of lithium chloride, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide;

[0014] The organic electrolyte solvent crystals include vinylene carbonate or ethylene vinylene carbonate;

[0015] The functional additive crystals include 1,3 - propanesultone.

[0016] Further, in each active material coating, the D50 particle size of the electrolyte additive is in the range of 0.1 - 50 μm.

[0017] Further, when the types of the electrolyte additives between the active material coatings are different, along the direction away from the current collector, the average pore - forming volume of the electrolyte additives in the coating gradually increases.

[0018] Further, when the particle sizes of the electrolyte additives between the active material coatings are different, along the direction away from the current collector, the particle size of the electrolyte additives in the coating gradually increases.

[0019] Further, when the volume ratios of the electrolyte additives in the electrode material of the coatings where they are located between the active material coatings are different, along the direction away from the current collector, the volume ratios in each coating gradually increase.

[0020] In a second aspect, the present invention provides a method for manufacturing an electrode plate for an alkali - metal ion battery, including:

[0021] Wet - mixing the electrode material with the electrolyte additives multiple times to form slurries for multiple active material coatings; wherein, each time during wet - mixing, at least one of the following of the electrolyte additives is different: the type of the electrolyte additive, the particle size of the electrolyte additive, and the volume ratio of the electrolyte additive in the electrode material of the coating where it is located;

[0022] Coat the slurries of the multiple coatings on the current collector in sequence.

[0023] In a third aspect, the present invention provides a method for preparing an electrode core, including:

[0024] Adopt the electrode tab described in the first aspect or the electrode tab prepared by using the preparation method described in the second aspect;

[0025] Roll press the tab at room temperature;

[0026] Based on the roll-pressed tab, wind or stack it to obtain an electrode core to be infiltrated;

[0027] Infiltrate the electrode core with an electrolyte.

[0028] Further, the infiltrating the electrode core with the electrolyte includes:

[0029] At 25°C - 90°C, inject the electrolyte into the electrode core and infiltrate for 2 - 72 h.

[0030] In a fourth aspect, the present invention provides a lithium-ion battery, including an electrode core obtained by using the preparation method in the third aspect.

[0031] One or more of the above technical solutions of the present invention have at least one or more of the following beneficial effects:

[0032] The present invention adopts a multi-layer coating technology, adds a specific pore-forming agent, namely an electrolyte additive, during the preparation of the slurry. After the electrode tab is made into an electrode core and the electrode core is infiltrated with the electrolyte, the pore-forming agent dissolves in the electrolyte to form pores. No additional equipment is added in the whole process.

[0033] By constructing active material coatings with multiple different pore-forming states on the electrode tab, the present invention effectively improves the pore distribution of the electrode tab in the vertical direction. This improvement not only significantly enhances the performance of the battery under high-rate discharge conditions, but also enables the battery to have excellent cycle stability. Description of the Drawings

[0034] Referring to the drawings, the disclosure of the present invention will become easier to understand. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the protection scope of the present invention. In addition, similar numbers in the drawings are used to represent similar components, where:

[0035] Figure 1 is a schematic flow chart of the main steps of the manufacturing method according to an embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the process of mixing an electrode material and a pore-forming agent according to an embodiment of the present invention;

[0037] Figure 3 is a schematic diagram of the electrode sheet before electrolyte injection (before removing the pore former) according to an embodiment of the present invention;

[0038] Figure 4 is a schematic diagram of the electrode sheet after electrolyte infiltration by injection (after removing the pore former) according to an embodiment of the present invention;

[0039] Figure 5 is the test result of the 0.5P cycle energy retention rate according to the present invention;

[0040] Figure 6 is the CP-SEM characterization result of the reference positive electrode according to the present invention;

[0041] Figure 7 is the CP-SEM characterization result of the positive electrode sheet of Example 1 according to the present invention.

[0042] List of Reference Numerals :

[0043] 1 active material powder; 2 binder; 3 conductive agent; 4 solvent; 5 pore former; 6 electrode material; 7 pores formed by non-pore formers; 8 electrolyte; 9 pores formed after removing the pore former. Detailed Embodiments

[0044] Some embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention.

[0045] Some embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention.

[0046] The present invention provides an electrode sheet for an alkali metal ion liquid battery, including:

[0047] Current collector;

[0048] A plurality of active material coatings are sequentially coated on the same side of the current collector in a direction away from the current collector; the active material coatings include electrolyte additives, and the electrolyte additives in each active material coating can be dissolved in the electrolyte of the alkali metal ion liquid battery to form pores in each active material layer, and in the direction away from the current collector, the total volume of the pores in the coating gradually increases.

[0049] In one embodiment, the active material coating further includes: active material, binder, and conductive agent; and / or

[0050] The electrolyte additives for each active material coating differ in at least one of the following:

[0051] The type of electrolyte additive, the particle size of the electrolyte additive and the volume proportion of the electrolyte additive in the electrode material of the coating in which it is located are so that the electrolyte additive can form the pores in the corresponding coating after being dissolved in the electrolyte, and the total volume of the pores in the coating gradually increases along the direction away from the current collector.

[0052] Since the total pore volume of each coating is different, it is necessary to use the electrolyte additive as a pore-forming agent in each coating, and adjust and differentiate the addition of the pore-forming agent. The pore-forming agents in each of the coatings are different in at least one of the following ways:

[0053] The type of pore former, the particle size of the pore former and the volume proportion of the pore former in the electrode material.

[0054] By varying any one or more of the above characteristics, coatings with different total pore volumes can be successfully formed. For example, different types of pore formers can be selected, or the same pore former with different particle sizes can be selected to form different pore size distributions in the coating. In addition, the volume proportion of the pore former in the electrode material can be adjusted to control the total pore volume of each coating. Through these methods, electrode coatings with specific pore structures can be flexibly designed and prepared to meet the needs of different application scenarios.

[0055] In one embodiment, the active material in the active material coating of the positive electrode plate is a positive electrode active material, and the active material in the active material coating of the negative electrode plate is a negative electrode active material.

[0056] The active material coatings of the positive electrode sheet and the negative electrode sheet are described in detail below.

[0057] In one embodiment, for the positive electrode plate, the active material coating includes: a positive electrode active material, a binder, a conductive agent and an electrolyte additive.

[0058] The positive electrode active material may be lithium iron phosphate. The binder may be PVDF (polyvinylidene fluoride). The conductive agent may be SP (Super P, a conductive carbon black material).

[0059] In one embodiment, for the negative electrode plate, the active material coating includes: a negative electrode active material, a binder, a conductive agent and an electrolyte additive.

[0060] The negative electrode active material may be graphite. The binder may be one or more of CMC (sodium carboxymethyl cellulose), PAA (polyacrylic acid) and SBR (styrene-butadiene rubber). The conductive agent may be SP (Super P, belonging to the conductive carbon black material).

[0061] In one embodiment, the types of the electrolyte additives in each active material coating include:

[0062] One or more of lithium salt crystals, organic electrolyte solvent crystals, and functional additive crystals. In one embodiment, the lithium salt crystals include one or more of lithium chloride (LiCl), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI);

[0063] The organic electrolyte solvent crystals include vinylene carbonate (VC) or vinylethylene carbonate (VEC);

[0064] The functional additive crystals include 1,3-propane sultone.

[0065] In the traditional battery manufacturing process, the pore-forming agents used in the solvent system of the positive electrode are often not suitable for the solvent system of the negative electrode. However, the present invention breaks this conventional limitation and proposes a new idea. The pore-forming agent has a certain solubility in the solvent. As long as this solubility does not cause other substances in the slurry mixing system to react, then this pore-forming agent can be used commonly in the positive electrode and the negative electrode. The solvent of the positive electrode sheet is usually water, and the solvent of the negative electrode sheet is usually NMP (N-methylpyrrolidone solvent). The addition amount of the solvent of the negative electrode sheet is such that the solid content of the active material coating of the negative electrode sheet is 55%. The addition amount of the solvent of the positive electrode sheet is such that the solid content of the active material coating of the positive electrode sheet is 62%.

[0066] Therefore, the method for controlling the pores of the electrode sheet proposed by the present invention has wide applicability and can meet the requirements of both the positive electrode and the negative electrode at the same time. This innovation not only simplifies the process flow of battery manufacturing, but also improves the production efficiency and the stability of battery performance.

[0067] These electrolyte additives used as pore-forming agents are all components with a certain solubility in the electrolyte. The pore-forming agent can stably occupy a certain space position during the mixing process with the electrode material. This occupation effect lays a solid foundation for the subsequent pore formation. When the electrolyte is injected into the battery cell, the pore-forming agent begins to play its unique role: they gradually dissolve in the electrolyte and are removed, and during this process, the space they originally occupied is transformed into pores inside the electrode material. The existence of these pores has an important impact on the performance of the lithium-ion battery. They not only provide a spacious channel for the rapid migration of lithium ions, but also enhance the contact area between the electrode material and the electrolyte, thereby improving the charge and discharge efficiency of the battery.

[0068] In one embodiment, in each active material coating, the D50 particle size of the electrolyte additive is in the range of 0.1 - 50 μm.

[0069] D50 is the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. Its physical meaning is that 50% of the particles are larger than it and 50% of the particles are smaller than it. D50 is also called the median diameter or median particle size. D50 is often used to represent the average particle size of the powder.

[0070] In one embodiment, when the types of electrolyte additives between the active material coatings are different, along the direction away from the current collector, the average single-pore pore-forming volume of the electrolyte additives in the coatings gradually increases.

[0071] In one embodiment, when the particle sizes of the electrolyte additives between the active material coatings are different, along the direction away from the current collector, the particle sizes of the electrolyte additives in the coatings gradually increase.

[0072] In one embodiment, when the volume ratios of the electrolyte additives in the electrode materials of their respective coatings are different between the active material coatings, along the direction away from the current collector, the volume ratios in each coating gradually increase.

[0073] The present invention also provides a method for manufacturing an electrode tab for an alkali metal ion battery, referring to Figure 1 , including:

[0074] S1, wet-mix the electrode material with the electrolyte additive multiple times to form slurries for multiple active material coatings; wherein, at least one of the following is different for the electrolyte additive each time of wet-mixing: the type of the electrolyte additive, the particle size of the electrolyte additive, and the volume ratio of the electrolyte additive in the electrode material of its respective coating;

[0075] S2, sequentially coat the slurries of the multiple coatings on the current collector.

[0076] After the electrode tab is immersed in the electrolyte, the electrolyte additive can dissolve in the electrolyte to form the pores in the corresponding coating, and along the direction away from the current collector, the total pore volume of the coating gradually increases.

[0077] In one embodiment, referring to Figure 2 , in step S1, when sequentially coating the slurries of the multiple coatings on the current collector, each time of coating the slurry on the current collector includes the following steps:

[0078] S11, mix the active material, conductive agent, binder, and electrolyte additive to obtain a dry powder mixture;

[0079] S12, add a solvent to the dry powder mixture to obtain a wet-mixed slurry;

[0080] S13, uniformly coat the wet-mixed slurry on the current collector. Referring toFigure 3 。

[0081] The present invention also provides a method for preparing an electrode core, comprising:

[0082] using the electrode sheet or the electrode sheet prepared by the preparation method described above;

[0083] rolling the sheet at room temperature;

[0084] winding or laminating the rolled sheet to obtain an electrode core to be infiltrated;

[0085] infiltrating the electrode core with an electrolyte.

[0086] In one embodiment, the step of infiltrating the electrode core with an electrolyte comprises:

[0087] injecting the electrolyte into the electrode core at 25°C - 90°C and infiltrating for 2 - 72 h.

[0088] Referring to Figure 4 , after infiltration, the pore-forming agent (electrolyte additive) gradually dissolves in the electrolyte and is removed. During this process, the space originally occupied by them is transformed into pores inside the electrode material. The pore-forming agent is ingeniously introduced into the electrode material to lay the foundation for the future pore structure. When the pore-forming agent is dispersed and dissolved in the electrolyte, the electrolyte, with its unique dissolving ability for the pore-forming agent, gradually breaks down the pore-forming agent molecules one by one, turning them into soluble ionic or molecular forms. As the pore-forming agent gradually dissolves, the space originally occupied by them in the electrode material gradually reveals, forming a pore structure.

[0089] In one embodiment, the electrolyte is injected into the electrode core at 45°C and infiltrated for 48 h.

[0090] The present invention optimizes the pore structure by precisely controlling the electrolyte soaking time and soaking temperature. Specifically, by adjusting the temperature range during the electrolyte infiltration process, i.e., selecting between 25°C and 90°C, and the length of the infiltration time, i.e., adjusting between 2 h and 72 h, the pore structure of the material can be effectively regulated and optimized. This method enables fine control of key characteristics such as the total pore volume, pore size, and its distribution of each coating of the material according to actual application requirements, thus meeting the specific requirements for the pore structure in different fields.

[0091] In one embodiment, when the sheet is infiltrated in the electrolyte and the pore-forming agent is dissolved in the electrolyte, the concentration range of the lithium salt in the electrolyte is 0.1 - 2 mol / L. The lithium salt here includes the lithium salt of the dissolved pore-forming agent and the lithium salt originally contained in the electrolyte.

[0092] In one embodiment, after the pore former is dissolved in the electrolyte, the pH value of the electrolyte ranges from 5 to 9.

[0093] A lithium-ion battery includes an electrode core obtained by using the preparation method.

[0094] The present invention also provides a lithium-ion battery including the electrode tab.

[0095] After preparing the electrode tab through different embodiments and comparative examples below, a battery is made.

[0096] In the following description, the layer closest to the current collector is the first layer, and the layers in the direction away from the current collector are the second layer and the third layer in sequence. The positive electrode material includes the active material lithium iron phosphate, the conductive agent SP, and the binder PVDF. The negative electrode material includes the active material graphite, the binders CMC, SBR, PAA, and the conductive agent SP.

[0097] Example 1 Multilayer Coating with Different Types of Pore Formers

[0098] In this example, between the electrolyte additives in each active material coating, the types of electrolyte additives are different. The pore-forming volume of VC is greater than that of LiFSI. The pore formers for the first layer to the third layer are LiFSI alone, a combination of LiFSI and VC, and VC alone, respectively.

[0099] The layer closest to the current collector is the first layer, and the layers away from the current collector are the second layer and the third layer in sequence.

[0100] ① Positive electrode: The mass ratio of the solid substances in the slurry of the first layer: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of the pore former (LiFSI) to lithium iron phosphate is 1:20, and the solid content of the slurry is 62%;

[0101] The mass ratio of the solid substances in the slurry of the second layer: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of the pore former (LiFSI:VC = 1:1, volume ratio) to lithium iron phosphate is 1:20, and the solid content of the slurry is 62%;

[0102] The mass ratio of the solid substances in the slurry of the third layer: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of the pore former (VC) to lithium iron phosphate is 1:20, and the solid content of the slurry is 62%;

[0103] Since the pore-forming volume of VC is greater than that of LiFSI, this design can achieve that the total pore volume in the coating gradually increases from the inside to the outside in the vertical direction of the electrode tab, and the overall porosity of the electrode tab will also increase.

[0104] Negative electrode: Conventional electrode tab

[0105] ③Dry-mix the above solid substances and pore-forming agents in proportion. After mixing evenly, add NMP solvent, with the solid content of the slurry being 62%.

[0106] ④Then coat and roll the slurry in a conventional manner until it is infiltrated by the injected liquid, and infiltrate at 45 °C for 48 h.

[0107] At 45 °C, after infiltrating for 48 h, the pore-forming agent dissolves in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1 - 2 mol / L.

[0108] ⑤The battery cell from which the pore-forming agent has been removed is transferred to the subsequent process in a conventional manner to make a battery.

[0109] Example 2 Multilayer coating with different pore-forming agent particle sizes

[0110] In this example, between the electrolyte additives of each active material coating, the particle sizes of the electrolyte additives are different. The particle sizes of the pore-forming agents from the first layer to the second layer are D50: 15 ± 5 μm and D50: 30 ± 5 μm respectively.

[0111] The layer closest to the current collector is the first layer, and the layer far from the current collector is the second layer, with a thickness ratio of 1:1

[0112] ①Negative electrode: The mass ratio of the solid substances in the first layer of slurry: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore-forming agent (LiCl D50: 15 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%.

[0113] The mass ratio of the solid substances in the second layer of slurry: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore-forming agent (LiCl D50: 30 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%.

[0114] This design can achieve that the total pore volume of the coating gradually increases from the inside to the outside in the vertical direction of the electrode sheet, and the overall porosity of the electrode sheet will also increase.

[0115] Positive electrode: Conventional electrode sheet

[0116] ③Dry-mix the above solid substances and pore-forming agents in proportion. After mixing evenly, add water solvent, with the solid content of the slurry being 55%.

[0117] ④Then coat and roll the slurry in a conventional manner until it is infiltrated by the injected liquid. At 25 °C, after infiltrating for 72 h, the pore-forming agent dissolves in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1 - 2 mol / L.

[0118] ⑤ The cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0119] Example 3 Multilayer coating with different pore-forming agent ratios

[0120] In this embodiment, the electrolyte additives in each active material coating have different volume proportions in the electrode material of the coating in which they are located. The volume ratios of the pore former (LiTFSI) to lithium iron phosphate in the first layer and the second layer are 1:25 and 1:15 respectively.

[0121] The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer.

[0122] ① Positive electrode: The solid mass ratio of the first layer slurry is: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (LiTFSI) to lithium iron phosphate is 1:25, and the solid content of the slurry is 62%;

[0123] The second layer slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (LiTFSI) to lithium iron phosphate is 1:15, and the slurry solid content is 62%;

[0124] This design can realize that the total pore volume of the coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0125] Negative electrode: conventional electrode

[0126] ③ Dry-mix the above solid substances and pore-forming agent in proportion, add NMP solvent after mixing evenly, wherein the solid content of the slurry is 62%;

[0127] ④ Then, the slurry is coated and rolled in a conventional manner until the liquid is infiltrated. After infiltration for 2 hours at 90°C, the pore-forming agent is dissolved in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1-2 mol / L.

[0128] ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0129] Example 4

[0130] In this embodiment, the electrolyte additives of each active material coating have different particle sizes. The particle sizes of the pore-forming agent in the first layer and the second layer are D50: 0.1±5μm and D50: 10±5μm, respectively.

[0131] The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1.

[0132] ① Negative electrode: The mass ratio of solid substances in the first layer of slurry: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore former (LiCl D50: 0.1 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%;

[0133] ② Second layer of slurry: The mass ratio of solid substances: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore former (LiCl D50: 10 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%;

[0134] This design can achieve that the total volume of pores in the coating gradually increases from the inside to the outside in the vertical direction of the electrode plate, and the overall porosity of the electrode plate also increases.

[0135] Positive electrode: Conventional electrode plate

[0136] ③ Dry-mix the above solid substances and pore formers in proportion. After mixing evenly, add water solvent, and the solid content of the slurry is 55%;

[0137] ④ Then coat and roll the slurry in a conventional manner until it is infiltrated by the injection liquid. At 25 °C, after 72 h of infiltration, the pore former dissolves in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1 - 2 mol / L.

[0138] ⑤ The battery cell after removing the pore former is transferred to the subsequent process in a conventional manner to make a battery.

[0139] Example 5

[0140] In this example, the particle sizes of the electrolyte additives are different between each active material coating. The particle sizes of the pore formers from the first layer to the second layer are D50: 30 ± 5 μm and D50: 50 ± 5 μm respectively.

[0141] The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1

[0142] ① Negative electrode: The mass ratio of solid substances in the first layer of slurry: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore former (LiCl D50: 30 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%;

[0143] ② Second layer of slurry: The mass ratio of solid substances: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of the pore former (LiCl D50: 50 ± 5 μm) to graphite is 1:20, and the solid content of the slurry is 55%;

[0144] This design can realize that the total pore volume of the coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0145] Positive electrode: conventional electrode

[0146] ③ Dry-mix the above solid substances and pore-forming agent in proportion, add water solvent after mixing evenly, wherein the slurry solid content is 55%;

[0147] ④ Then, the slurry is coated and rolled in a conventional manner until the liquid is infiltrated. After infiltration for 72 hours at 25°C, the pore-forming agent is dissolved in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1-2 mol / L.

[0148] ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0149] Example 6

[0150] In this embodiment, the electrolyte additives in each active material coating have different volume proportions in the electrode material of the coating in which they are located. The volume ratios of the pore former (LiCl) to graphite in the first layer and the second layer are 1:10 and 1:1 respectively.

[0151] The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1.

[0152] ① Negative electrode: The first layer of slurry solid matter mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore former (LiCl D50: 30 ± 5 μm) to graphite is 1:10, and the slurry solid content is 55%;

[0153] The second layer slurry solid matter mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore former (LiClD50: 30 ± 5μm) and graphite is 1:1, and the slurry solid content is 55%;

[0154] This design can realize that the total pore volume of the coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0155] Positive electrode: conventional electrode

[0156] ③ Dry-mix the above solid substances and pore-forming agent in proportion, add water solvent after mixing evenly, wherein the slurry solid content is 55%;

[0157] ④ Then, the slurry is coated and rolled in a conventional manner until the liquid is infiltrated. After infiltration for 72 hours at 25°C, the pore-forming agent is dissolved in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1-2 mol / L.

[0158] ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0159] Example 7

[0160] In this embodiment, the electrolyte additives in each active material coating have different volume proportions in the electrode material of the coating in which they are located. The volume ratios of the pore former (LiTFSI) to lithium iron phosphate in the first layer and the second layer are 1:25 and 1:20 respectively.

[0161] The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer.

[0162] ① Positive electrode: The solid mass ratio of the first layer slurry is: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (LiTFSI) to lithium iron phosphate is 1:25, and the solid content of the slurry is 62%;

[0163] The second layer slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (LiTFSI) to lithium iron phosphate is 1:20, and the slurry solid content is 62%;

[0164] This design can realize that the total pore volume of the coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0165] Negative electrode: conventional electrode

[0166] ③ Dry-mix the above solid substances and pore-forming agent in proportion, add NMP solvent after mixing evenly, wherein the solid content of the slurry is 62%;

[0167] ④ Then, the slurry is coated and rolled in a conventional manner until the liquid is infiltrated. After infiltration for 2 hours at 90°C, the pore-forming agent is dissolved in the electrolyte. At this time, the concentration range of the lithium salt in the electrolyte is 0.1-2 mol / L.

[0168] ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0169] Comparative Example 1

[0170] ① Positive electrode: conventional electrode, slurry solid material mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, slurry solid content 62%;

[0171] ② Negative electrode: Conventional electrode sheet, mass ratio of solid substances in the slurry: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, solid content of the slurry is 55%;

[0172] ③ Transfer to the subsequent process in a conventional manner to fabricate the battery.

[0173] Electrochemical Performance Test

[0174] Perform electrochemical tests on the batteries prepared in Examples 1 - 3 and Comparative Example 1. The test results of the total pore volume ratio and rate performance of the overall battery are shown in Table 1. At 25°C, the 0.5C cycle energy retention rate is shown in Figure 5 .

[0175] Table 1 Test results of the batteries in the examples and comparative examples

[0176]

[0177]

[0178] From Table 1 and Figure 5 the provided data, it can be seen that in the case of making holes in the positive electrode, the positive electrode sheet structure with three coatings in Example 1 shows more excellent performance advantages compared to the two - coating structure used in Example 3. The battery prepared by the multi - coating hole - making method of the present invention exceeds the performance of the conventional battery (Comparative Example 1).

[0179] For making holes in the negative electrode, the negative electrode sheet shown in Example 2 also shows excellent performance advantages and exceeds the performance of the conventional battery (Comparative Example 1).

[0180] The present invention uses a multi - layer coating technology to construct a multi - layer pore structure, resulting in a gradient difference in the total pore volume of the electrode sheet, that is, the total pore volume of the upper coating is greater than that of the lower coating. This is the core of improving the battery performance. This method can significantly improve the rate performance of the battery. The pore distribution and structure stability constructed by this specific preparation method are good, enabling the battery to perform excellently during long - term use and ensuring its excellent performance in terms of stability and reliability.

[0181] Microstructure Characterization Test

[0182] The present invention conducted microstructure characterization tests on the reference positive electrode of Comparative Example 1 and the positive electrode sheet coated with three layers of slurry in Example 1 to obtain the microscopic morphology of the material cross-section on the positive current collector. Through the observation of this microscopic morphology, various microscopic geometric shape information of the positive electrode material cross-section can be understood. To obtain more accurate microscopic morphology data, the present invention adopted the argon ion polishing technique, also known as the CP cross-section polishing technique. This technique bombards the cross-section of the material sample to obtain a flat polished cross-section. Subsequently, in combination with a scanning electron microscope (SEM), the observation and analysis of the microscopic characteristics of the internal structure of the sample were completed.

[0183] In the CP-SEM characterization results of the reference positive electrode of Comparative Example 1, it can be seen that Figure 6 the presented microscopic morphology. While the CP-SEM characterization results of the positive electrode sheet in Example 1 are presented in Figure 7 it. By carefully observing these cross-sectional morphologies, it can be found that the number of pores in the electrode sheet constructed in the present invention has increased significantly. When the total volume of the upper-layer pores in the vertical direction of the electrode sheet is greater than that of the lower layer, the liquid-phase diffusion of the pore-forming agent in the electrode sheet is first fast and then slow. When the vertical pore distribution of the electrode sheet is consistent or the total volume of the upper-layer pores is less than that of the lower layer, the liquid-phase diffusion rate of the electrode sheet is stable or first slow and then fast. This design of the gradient total pore volume not only optimizes the infiltration and penetration process of the electrolyte but also significantly reduces the difference in the pore volume distribution in the vertical direction of the electrode sheet. The battery in Example 1 shows significant advantages in terms of cycle stability and rate performance. The acquisition of these excellent performances is precisely due to the ingenious design of the gradient pore structure and its optimization effect on the infiltration and penetration process of the electrolyte.

[0184] Disassembly and Observation after Full Charge of the Battery

[0185] For the batteries in Example 1, Example 2, Example 3, and Comparative Example 1, after 400 cycles of charge and discharge, these batteries were fully charged and then disassembled and analyzed.

[0186] Observing the interface state of the electrode can determine the charge-discharge mechanism of the battery and the advantages and disadvantages of the battery. After analysis, it is concluded that the state of the electrode corresponds to the total pore volume of the coating, cycling, and rate performance. The present invention effectively improves the pore distribution of the electrode in the vertical direction by constructing coatings with multiple different pore-forming states on the electrode. This improvement not only significantly enhances the performance of the battery under high-rate discharge conditions but also endows the battery with cycling stability. Specifically, the structure of the present invention starts from the surface layer of the current collector and is constructed layer by layer upward, forming a highly stable layered structure. Although more pores are introduced in this process, the overall structural stability is ensured through the gradient pore structure. This gradient pore structure not only optimizes the penetration of the electrolyte and the ion transport path but also effectively alleviates the volume change and stress concentration generated during the charge-discharge cycle, thereby further improving the cycling life and overall performance of the battery.

[0187] The present invention adopts a multi-layer coating technology and adds a specific pore-forming agent during the preparation of the slurry. After the battery cell is prepared and infiltrated with the electrolyte, the pore-forming agent dissolves in the electrolyte to form pores. No additional equipment is added during the entire process.

[0188] The pore distribution design of the present invention significantly promotes the liquid-phase transport efficiency of lithium ions in the electrode, realizes the optimized layout of the lithium ion diffusion path, and effectively reduces the resistance during the transport process. This improvement not only enhances the rate performance of the battery, that is, the charge-discharge ability of the battery under high current density, but also significantly improves the cycling performance of the battery, that is, the capacity retention rate and stability of the battery after multiple charge-discharge cycles. Therefore, the present invention has important application value and market potential in improving battery performance.

[0189] It should be noted that although the above embodiments describe the various steps in a specific order, those skilled in the art can understand that in order to achieve the effects of the present invention, the different steps do not necessarily have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the protection scope of the present invention.

[0190] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. An electrode sheet for an alkali metal ion liquid battery, characterized in that, include: current collector; In a direction away from the current collector, a plurality of active material coatings are sequentially applied on the same side of the current collector; The active material coating includes an electrolyte additive, and the electrolyte additive in each active material coating can be dissolved in the electrolyte of the alkali metal ion liquid battery to form pores in each active material layer, and the total volume of the pores of the coating gradually increases in a direction away from the current collector.

2. The electrode tab according to claim 1, wherein, The electrolyte additives for each active material coating differ in at least one of the following: The type of electrolyte additive, the particle size of the electrolyte additive and the volume proportion of the electrolyte additive in the electrode material of the coating in which it is located are so that the electrolyte additive can form the pores in the corresponding coating after being dissolved in the electrolyte, and the total volume of the pores in the coating gradually increases along the direction away from the current collector.

3. The pole piece according to claim 2, characterized in that, The active material coating further comprises: an active material, a binder and a conductive agent; and / or The types of electrolyte additives include: One or more of lithium salt crystals, organic electrolyte solvent crystals and functional additive crystals.

4. The pole piece according to claim 3, characterized in that, The lithium salt crystals include: one or more of lithium chloride, lithium bis(fluorosulfonyl)imide salt and lithium bis(trifluoromethanesulfonyl)imide; The organic electrolyte solvent crystals include vinylene carbonate or vinyl ethylene carbonate; The functional additive crystals include 1,3-propane sultone.

5. The pole piece according to claim 1, wherein, In each active material coating, the electrolyte additive D50 has a particle size in the range of 0.1-50 μm.

6. The pole piece according to claim 2, characterized in that, In the case where the types of electrolyte additives between the active material coatings are different, the average single pore-forming volume of the electrolyte additives of the coatings gradually increases in a direction away from the current collector.

7. The pole piece according to claim 2, wherein In the case where the particle sizes of the electrolyte additives are different between the active material coatings, the particle sizes of the electrolyte additives of the coatings gradually increase in a direction away from the current collector.

8. The pole piece according to claim 2, wherein When the volume proportions of the electrolyte additives between the active material coatings in the electrode materials of the coatings are different, the volume proportions in the coatings gradually increase in the direction away from the current collector.

9. A method for manufacturing an electrode sheet for an alkali metal ion battery, characterized in that, include: Wet mixing the electrode material and the electrolyte additive multiple times to form a slurry of multiple active material coatings; wherein the electrolyte additive in each wet mixing is different in at least one of the following: the type of the electrolyte additive, the particle size of the electrolyte additive, and the volume proportion of the electrolyte additive in the electrode material of the coating in which it is located; The slurries of the plurality of coating layers are sequentially coated on a current collector.

10. A method for preparing an electrode assembly, characterized in that, include: An electrode sheet according to any one of claims 1 to 8 or an electrode sheet prepared by the preparation method according to claim 9; Roll-pressing the pole piece at room temperature; Winding or stacking the rolled pole pieces to obtain the battery cells to be wetted; The battery cell is infiltrated with an electrolyte.

11. The method according to claim 10, wherein The step of using an electrolyte to infiltrate the battery core comprises: At 25° C.-90° C., the electrolyte is injected into the battery cell and soaked for 2-72 hours.

12. A lithium-ion battery, characterized in that, The invention comprises a battery cell obtained by the preparation method according to claim 10 or 11.

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