Pole piece, method for manufacturing the same, and secondary battery

Abstract

The application provides an electrode sheet, a preparation method of the electrode sheet and a secondary battery. The preparation method of the electrode sheet comprises the following steps: step S1, adding a pore-forming material to an electrode sheet slurry to obtain a coating slurry; step S2, coating the coating slurry on at least one side surface of the electrode sheet, once heating, making the pore-forming material expand to form vesicles, coating solidification, twice heating, vesicle breakage and shrinkage into particles, and forming holes on the surface of the coating; and step S3, removing the particles in the holes, and then the preparation of the electrode sheet is completed. The preparation method of the electrode sheet can increase the contact surface area of the electrode sheet and electrolyte, reduce impedance, improve kinetic performance, and improve the cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, specifically to an electrode sheet, its preparation method, and a secondary battery. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used as power sources for various portable electronic devices due to their numerous advantages, including high energy density, high operating voltage, long cycle life, no memory effect, environmental friendliness, and flexible size and shape design to meet specific needs. These broad applications and diverse practical requirements, in turn, have greatly promoted the development of lithium-ion batteries.

[0003] The rapid development of mobile electronic devices demands higher capacity (i.e., volumetric energy density) for lithium-ion batteries that power these lightweight, portable, and powerful devices. However, existing manufacturing processes typically only achieve 300Wh / L to 500Wh / L, which is insufficient to meet the needs of electronic devices.

[0004] Existing gap coating or bonding coating cannot meet the high energy density requirements of 800-830Wh / L and fast charging and discharging functions. Therefore, a technical solution is urgently needed to solve the above problems. Summary of the Invention

[0005] One of the objectives of this invention is to provide an electrode preparation method that addresses the shortcomings of existing technologies, thereby increasing the contact surface area between the electrode and the electrolyte, reducing impedance, improving kinetic performance, and increasing battery cycle life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing an electrode includes the following steps:

[0008] Step S1: Add the pore-forming material to the electrode slurry and stir to obtain the coating slurry;

[0009] Step S2: Apply the coating slurry to at least one side of the electrode surface, heat it once to make the pore-forming material expand to form vesicles, the coating is cured, and heat it a second time to make the vesicles rupture and shrink into particles, forming pores on the coating surface.

[0010] Step S3: Remove the particles inside the pores, and the electrode preparation is complete.

[0011] Currently, the coating area obtained by electrode preparation methods depends on the current collector area supporting the coating. Therefore, the contact area between the electrolyte and the electrode is limited by the current collector area, and even intermittent or continuous coating cannot meet the high energy density requirements of 3C battery cells. The electrode preparation method of this invention adds a pore-forming material to the electrode slurry, greatly increasing the surface area of ​​the electrode coating and improving the contact area between the electrode and the electrolyte, thereby increasing the energy density and meeting the high energy density requirements of 800-830 Wh / L for battery cells, as well as fast charging and discharging capabilities. Specifically, the pore-forming material has a core-shell structure. When heated, the shell softens, the core vaporizes, and the internal pressure increases, causing the pore-forming material to expand. Simultaneously, under buoyancy, the pore-forming material floats and accumulates on the surface of the electrode coating, creating pre-set pores. Continuous heating of the electrode and the pore-forming material constitute overheating, causing the pore-forming material to thin. Due to external forces, the microcapsules shrink, subsequently creating the pre-set pores and increasing the electrode surface area. Finally, the particles within the pores are removed to obtain the electrode. The electrode slurry is a conventional electrode active material slurry, including active materials, conductive agents, binders, and solvents. Depending on the electrode polarity, positive electrode active materials such as lithium cobalt oxide and lithium nickel cobalt manganese oxide are added, while negative electrode active materials such as carbon, graphite, and mesophase carbon microspheres are added. Also depending on the electrode polarity, aluminum foil is used as the current collector for the positive electrode, and copper foil is used for the negative electrode.

[0012] The pore-forming material consists of hydrocarbon particles encapsulated in a polymer material. Employing a core-shell structure, the shell initially protects the core material. During heating, the shell softens and expands, while the gaseous core material, also heated, provides pressure to the shell, causing it to expand further and thus forming pores.

[0013] The pore-forming material comprises a shell and a core within the shell. The shell has a thickness of 2–15 μm, and the outer diameter of the pore-forming material particles is 5 μm–50 μm. The pore-forming material employs a core-shell structure. After coating, the shell softens under heating conditions, while the core material vaporizes to form gas, increasing the pressure within the shell and causing it to expand and form vesicles. Preferably, the shell thickness is 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 14 μm, or 15 μm. The outer diameter of the pore-forming material particles is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 20 μm, 24 μm, 27 μm, 30 μm, 34 μm, 37 μm, 40 μm, 43 μm, 45 μm, 48 μm, or 50 μm.

[0014] The shell material is one or a mixture of several of the following: polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyphenylene ether, and polysulfone. The shell material softens easily at certain temperatures, making it more prone to expansion and deformation to form vesicles. The core material is an alkane, olefin, alkyne, alicyclic hydrocarbon, aromatic hydrocarbon, or a liquid hydrocarbon synthesized from it and an organic solvent. The core material is located within the shell and sublimates and vaporizes at certain temperatures, increasing the pressure within the shell and causing it to expand and form a vesicle.

[0015] The amount of the pore-forming material added is 0.5 wt% to 2 wt% of the coating slurry. Setting the amount of the pore-forming material within a certain range allows the prepared electrode to have a larger surface area, lower impedance, better kinetic and cycling performance, while also possessing a certain degree of mechanical strength. The amounts of the pore-forming material added are 0.5 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, and 2 wt% of the coating slurry by mass.

[0016] In step S2, the duration of the primary and secondary heating is 10s to 180s, and the heating temperature is 60℃ to 150℃. Setting the primary and secondary heating times within a certain range ensures that the pore-forming material can expand and vaporize, as well as expand, crack, and contract to form particles. The heating time and temperature need to be controlled within a specific timeframe to prevent premature curing of the coating. Premature curing would make it difficult to form pores even if the core gas in the pore-forming material generates expansion pressure. Premature expansion and contraction of the pore-forming material would also prevent the coating slurry from remaining in a fluid state, continuing to refill the cracked pores, and ultimately preventing pore formation. Preferably, the heating time is 10s, 12s, 14s, 15s, 20s, 25s, 30s, 50s, 60s, 80s, 90s, 100s, 120s, 140s, 160s, or 180s, and the heating temperature is 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃.

[0017] The spacing between two adjacent holes ranges from 0.1 μm to 1500 μm, the diameter of the hole is ≤100 μm, and the depth is ≤50 μm. Setting specific hole spacing, hole size, and depth ensures the electrode maintains certain performance characteristics. Preferably, the hole spacing is 0.1 μm, 4 μm, 8 μm, 10 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, or 1500 μm. The diameters of the pores are 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, and 100μm, and the depths of the pores are 10μm, 20μm, 30μm, 40μm, 45μm, and 50μm.

[0018] In step S2, the coating method is one or more of single-layer extrusion coating, double-layer extrusion coating, transfer coating, gravure coating, and microgravure coating; in step S3, the removal method is adsorption or brush sweeping.

[0019] The second objective of this invention is to provide an electrode with low impedance, high electromechanical performance and cycle performance, good wettability with electrolyte, and short standing time.

[0020] To achieve the above objectives, the present invention adopts the following technical solution:

[0021] An electrode sheet is prepared by the electrode sheet preparation method described above.

[0022] A third objective of this invention is to provide a secondary battery comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the negative electrode is an electrode prepared by the above method.

[0023] To achieve the above objectives, the present invention adopts the following technical solution:

[0024] A secondary battery includes the aforementioned electrode. The secondary battery of the present invention has high ionic conductivity, thus exhibiting fast charging capability, and also has low impedance and good electrochemical performance. The secondary battery can be one of a sodium-ion battery, a lithium-ion battery, a potassium-ion battery, or a calcium-ion battery. Preferably, taking a lithium-ion battery as an example, the lithium-ion battery includes a positive electrode, a separator, a negative electrode, an electrolyte, and a casing. The separator separates the positive electrode and the negative electrode, and the casing is used to encapsulate the positive electrode, the separator, the negative electrode, and the electrolyte.

[0025] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, which may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more of Mn and Al, and N is selected from one or more of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more selected from O4, LiCoPO4, LiMnPO4, LiFePO4, and LiNiPO4. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W, including but not limited to. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil, among others.

[0026] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which may be one or more of the following: graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion batteries, for example, it may be, but is not limited to, metal foil, and more specifically, copper foil.

[0027] The electrolyte comprises an organic solvent, a lithium electrolyte salt, and additives. The lithium electrolyte salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0028] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0029] The casing can be made of stainless steel, aluminum-plastic film, or aluminum plate.

[0030] Compared to existing technologies, the advantages of this invention are as follows: The electrode preparation method of this invention involves adding a pore-forming material with a core-shell structure to the electrode slurry. Upon heating, the shell material softens while the core material vaporizes, causing the pore-forming material to expand and form vesicles. These vesicles float to the surface of the electrode coating under buoyancy. Continued heating solidifies the coating, causing the vesicles to expand, rupture, and shrink to form particles. The particles are then removed to obtain the electrode. This pore-forming material creates a porous structure on the electrode coating surface, significantly increasing the electrode's surface area by 50% to 350%. This accelerates ion mobility, shortens charge / discharge time, improves battery dynamics, reduces impedance, and enhances fast charging speed. It also improves the wettability between the electrolyte and the electrode, reduces electrolyte settling time, and increases inter-process efficiency. Furthermore, it effectively suppresses lithium dendrite formation, improving battery cycle life. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the electrode obtained by the electrode preparation method of the present invention.

[0032] Figure 2 This is a side view of the electrode obtained by the electrode preparation method of the present invention.

[0033] Figure 3 This is a temperature-expansion ratio curve of the pore-forming material of the present invention.

[0034] Figure 4 This is a comparison diagram of the impedance curves of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0035] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0036] Example 1

[0037] The preparation of the negative electrode includes the following steps: Step S1, adding the pore-forming material to the electrode slurry at a mass ratio of 1.5 wt% and stirring evenly to obtain a coating slurry; wherein, the electrode slurry is made by mixing graphite with conductive agent superconducting carbon (Super-P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) at a mass ratio of 96:2.0:1.0:1.0; wherein, the shell of the pore-forming material is made of polyethylene material with a thickness of 10 μm, and the core is made of cyclopentane;

[0038] Step S2: Apply the coating slurry to at least one side surface of the copper foil current collector, and combine it with... Figure 3 As shown in the temperature-expansion ratio curve of the pore-forming material, the coating was first heated for 60 seconds at a temperature of 80°C, causing the pore-forming material to expand and form vesicles, after which the coating solidified. A second heating for 20 seconds at a temperature of 110°C caused the vesicles to rupture and shrink into particles, forming pores in the coating. The measured pore diameter was 60 μm and the depth was 45 μm. The spacing between two adjacent pores was 1200 μm.

[0039] Step S3: Remove the particles from the pores. (Electrode such as...) Figure 1 and Figure 2 As shown. After removing particles, the material is cold-pressed, then trimmed, cut into sheets, and slit. After slitting, the material is dried at 110°C for 4 hours under vacuum, and then the tabs are welded to obtain the negative electrode sheet.

[0040] Preparation of positive electrode:

[0041] Lithium cobalt oxide, superconducting carbon (Super-P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed evenly at a mass ratio of 97:1.5:1.5 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The slurry is coated on a current collector aluminum foil, dried at 85°C, and then cold-pressed. Then, it is trimmed, cut into sheets, and slit. After slitting, it is dried at 110°C for 4 hours under vacuum conditions. The tabs are then welded to form the positive electrode sheet.

[0042] Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (mass ratio of 1:2:1) to obtain an electrolyte with a concentration of 1 mol / L.

[0043] Preparation of lithium-ion batteries: The above-mentioned negative electrode sheet, separator and positive electrode sheet are wound into a cell. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode is led out by spot welding with aluminum tabs and the negative electrode is led out by spot welding with nickel tabs. Then the cell is placed in an aluminum-plastic packaging bag, the above-mentioned electrolyte is injected, and after encapsulation, formation and capacity testing, a lithium-ion battery is made.

[0044] Example 2

[0045] The difference from Example 1 is that the amount of pore-forming material added in step S1 is 0.5 wt%.

[0046] The rest is the same as in Example 1, and will not be repeated here.

[0047] Example 3

[0048] The difference from Example 1 is that the amount of pore-forming material added in step S1 is 0.8 wt%.

[0049] The rest is the same as in Example 1, and will not be repeated here.

[0050] Example 4

[0051] The difference from Example 1 is that the amount of pore-forming material added in step S1 is 1 wt%.

[0052] The rest is the same as in Example 1, and will not be repeated here.

[0053] Example 5

[0054] The difference from Example 1 is that the amount of pore-forming material added in step S1 is 2 wt%.

[0055] The rest is the same as in Example 1, and will not be repeated here.

[0056] Example 6

[0057] The difference from Example 1 is that in step S2, the first heating time is 60s and the first heating temperature is 80℃, the second heating time is 50s and the second heating temperature is 140℃.

[0058] The rest is the same as in Example 1, and will not be repeated here.

[0059] Example 7

[0060] The difference from Example 1 is that in step S2, the first heating time is 30s, the first heating temperature is 60℃, the second heating time is 80s, and the second heating temperature is 140℃.

[0061] The rest is the same as in Example 1, and will not be repeated here.

[0062] Example 8

[0063] The difference from Example 1 is that in step S2, the first heating time is 80s, the first heating temperature is 90℃, the second heating time is 10s, and the second heating temperature is 100℃.

[0064] The rest is the same as in Example 1, and will not be repeated here.

[0065] Comparative Example 1

[0066] An electrode is prepared by the following steps: coating the electrode slurry onto both sides of the current collector and heating to cure the coating to obtain the electrode.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the amount of pore-forming material added in step S1 is 8 wt%. The rest is the same as in Example 1, and will not be repeated here.

[0069] The electrodes obtained from Examples 1-8 and Comparative Examples 1 and 2 were used to prepare secondary batteries, and performance tests were conducted. The test results are recorded in Table 1.

[0070] Cyclic performance test: At 25℃, the lithium-ion secondary battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to 1000 charge-discharge cycles using the above method, and the discharge capacity of each cycle was recorded. Cycle capacity retention (%) = Discharge capacity of the 1000th cycle / Discharge capacity of the first cycle × 100%.

[0071] Table 1

[0072]

[0073] Combination Figure 4As shown in Table 1, compared to traditional electrodes, the electrode prepared by this invention has a larger surface area, which can be increased by about 3 times. This accelerates ion flow, shortens charge and discharge time, thereby improving the battery's kinetic performance, reducing impedance, and increasing fast charging speed. When the electrode of this invention is applied to a secondary battery, it exhibits lower impedance and higher capacity retention. The impedance is between 0.04 and 0.06 mΩ, which is half the impedance of conventional electrodes. After 1000 charge and discharge cycles, the capacity retention is above 86%, compared to the 71% capacity retention of Comparative Example 1, demonstrating better cycle performance.

[0074] Comparing Examples 1-5 and Comparative Example 2, it was found that when the amount of pore-forming material added is within a certain range, the prepared electrode exhibits better performance when applied to a battery. When the amount of pore-forming material added exceeds a certain range, the pores overlap and contact each other, partially reducing the surface area and thus affecting battery performance. When the amount of pore-forming material added is 1.5 wt%, the prepared electrode exhibits better performance when applied to a battery. This is because excessive addition of pore-forming material increases the number of pores, affecting the mechanical properties of the electrode and thus battery performance.

[0075] Comparing Examples 1 and 6-8, it is found that when the initial heating time in step S2 is set to 60s, the initial heating temperature to 80℃, the secondary heating time to 20s, and the secondary heating temperature to 110℃, the prepared secondary battery exhibits better performance. This is because appropriate initial heating temperature and heating time can form suitable pores, resulting in better electrode performance.

[0076] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method of manufacturing a pole piece, characterized by, Includes the following steps: Step S1: Add the pore-forming material to the electrode slurry and stir to obtain a coating slurry; the pore-forming material is a particle of hydrocarbon encapsulated by a polymer material; the pore-forming material includes a shell and a core located within the shell; the material of the shell is one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyphenylene ether, and polysulfone; the material of the core is alkanes, alkenes, alkynes, alicyclic hydrocarbons, aromatic hydrocarbons, and liquid hydrocarbons synthesized from them with organic solvents; the amount of the pore-forming material added is 0.5wt%~2wt% of the coating slurry by mass. Step S2: Apply the coating slurry to at least one side of the electrode surface, heat it once to make the pore-forming material expand to form vesicles, and the coating solidifies. Heat it a second time to make the vesicles rupture and shrink into particles, and pores are formed on the coating surface. The time for the first heating and the second heating is 10s~180s, and the heating temperature is 60℃~150℃. Step S3: Remove the particles inside the pores, and the electrode preparation is complete.

2. The pole piece manufacturing method according to claim 1, wherein The shell layer has a thickness of 2~15μm, and the outer diameter of the pore-forming material particles is 5μm~50μm.

3. The electrode preparation method according to claim 1, characterized in that, The spacing between two adjacent holes ranges from 0.1μm to 1500μm, the diameter of the hole is ≤100μm, and the depth is ≤50μm.

4. The electrode preparation method according to claim 1, characterized in that, The coating method in step S2 is one or more of single-layer extrusion coating, double-layer extrusion coating, transfer coating, gravure coating, and microgravure coating; the removal method in step S3 is adsorption or brush sweeping.

5. An electrode sheet, characterized in that, It is prepared by the electrode preparation method described in any one of claims 1 to 4.

6. A secondary battery, characterized in that, Includes the electrode sheet as described in claim 5.

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