An electrode tab, a method of manufacturing the same, a secondary battery, and an electric device

Abstract

The application discloses an electrode pole piece and a preparation method thereof, a secondary battery and an electric device. The electrode pole piece comprises a current collector and an active material layer which is compounded on the surface of the current collector. The raw material for preparing the active material layer comprises a sublimation agent, the sublimation agent is composed of water and a sublimation aid, the mass of the sublimation aid accounts for 10-30% of the mass of the sublimation agent, and the sublimation aid is iodine and / or an alcohol with a melting point between-10 DEG C and 10 DEG C. The application can overcome the defect that the above-mentioned sublimation pore-forming process cannot be carried out under conventional conditions, is favorable for reducing energy consumption and cost, saving resources, and has the advantages of being green, environment-friendly and excellent in pore-forming effect.

Description

Technical Field

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

[0002] Electrode sheets are a crucial component of a battery, primarily composed of current collectors and an active material layer attached to the surface of the current collectors. Poor kinetic performance of electrode sheets is a significant factor limiting improvements in battery cycle performance. Research has found that increasing the porosity of electrode sheets can enhance their kinetic performance, thereby improving battery cycle performance.

[0003] However, the process of improving the porosity of electrode sheets needs to be carried out under low pressure conditions, which is quite difficult and requires specific low-pressure equipment to operate. This results in high costs for creating pores using this method, which is not conducive to industrial promotion and large-scale production. Summary of the Invention

[0004] This invention discloses an electrode sheet and its preparation method, a secondary battery, and an electrical device. This solution can overcome the defect that the above-mentioned sublimation pore-forming process cannot be carried out under conventional conditions, which is conducive to reducing energy consumption and cost, saving resources, and has the advantages of being green and environmentally friendly with excellent pore-forming effect.

[0005] Firstly, this application discloses an electrode sheet.

[0006] The electrode sheet includes a current collector and an active material layer composited on the surface of the current collector. The raw materials for preparing the active material layer include a sublimation agent, which is composed of water and a sublimation co-sublimation agent. The mass of the sublimation co-sublimation agent accounts for 10% to 30% of the mass of the sublimation agent. The sublimation co-sublimation agent is iodine and / or an alcohol with a melting point between -10°C and 10°C.

[0007] As an optional implementation, in an embodiment of the present invention, the porosity of the electrode sheet is 25% to 40%.

[0008] As an optional implementation, in embodiments of the present invention, the sublimation aid includes one or both of tert-butanol and 2-methyl-2-butanol.

[0009] As an optional implementation, in an embodiment of the present invention, the raw materials for preparing the active material layer further include unsublimated raw materials, and the mass ratio of the sublimation agent to the mass of the unsublimated raw materials is (1-1.2):1.

[0010] As an optional implementation, in an embodiment of the present invention, the unsublimated raw material consists of 94% to 97% by mass of active electrode material and 1% to 2% by mass of conductive agent and 1% to 2.5% by mass of binder.

[0011] As an optional implementation, in an embodiment of the present invention, the active material layer is composed of 94% to 97% by mass of active electrode material and 1% to 2% by mass of conductive agent and 1% to 2.5% by mass of binder.

[0012] As an optional implementation, in the embodiments of the present invention, the electrode sheet is a positive electrode sheet or a negative electrode sheet.

[0013] Secondly, this application discloses a method for preparing an electrode sheet.

[0014] The method for preparing the electrode sheet includes the following steps:

[0015] Preparation of active electrode slurry: Unsublimed raw materials and sublimation agent are mixed and dispersed to obtain active electrode slurry. The sublimation agent is composed of water and a sublimation co-sublimation agent, and the sublimation co-sublimation agent accounts for 10% to 30% of the mass of the sublimation agent. The sublimation co-sublimation agent is iodine and / or an alcohol with a melting point between -10°C and 10°C.

[0016] Preparation of electrode sheets: Active electrode slurry is coated on the current collector, then frozen to solidify the active electrode slurry on the surface of the current collector, and heated at 100kPa to 110kPa to sublimate the sublimation agent and water to form an active electrode layer, and then rolled to obtain the electrode sheet.

[0017] As an optional implementation, in an embodiment of the present invention, in the step of preparing the electrode sheet, the freezing temperature is 0℃~10℃ and the freezing time is 15min~30min; and / or, the heating temperature is 90℃~150℃ and the heating time is 30min~60min.

[0018] Thirdly, this application discloses a secondary battery.

[0019] The secondary battery includes:

[0020] Electrolyte

[0021] A positive electrode sheet, wherein the positive electrode sheet is at least partially immersed in the electrolyte;

[0022] A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte;

[0023] And a negative electrode sheet, wherein the negative electrode sheet is an electrode sheet prepared as described in the first aspect or the second aspect, and the negative electrode sheet is disposed on the side of the diaphragm opposite to the positive electrode sheet and is at least partially immersed in the electrolyte;

[0024] or

[0025] Electrolyte

[0026] A positive electrode sheet, wherein the positive electrode sheet is an electrode sheet prepared as described in the first aspect or the second aspect, and the positive electrode sheet is at least partially immersed in the electrolyte;

[0027] A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte;

[0028] And a negative electrode plate, which is disposed on the side of the diaphragm opposite to the positive electrode plate and is at least partially immersed in the electrolyte.

[0029] As an optional implementation, in an embodiment of the present invention, the secondary battery has a liquid retention coefficient of 1.2 to 1.5, a DC resistance of 100 mΩ to 200 mΩ, and a 3C capacity retention rate of 90 to 95%.

[0030] Fourthly, this application provides an electrical device. The electrical device includes the secondary battery described in the third aspect.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] An electrode sheet provided in this embodiment of the invention utilizes iodine and / or alcohols with melting points between -10°C and 10°C as a sublimation aid due to the good solubility of iodine and / or alcohols with melting points between -10°C and 10°C. When this sublimation aid is combined with water in the aforementioned proportions to form a sublimation agent, the freezing point of the sublimation agent is between 0°C and 10°C. Therefore, the refrigeration energy required for the sublimation agent to change from a liquid to a solid state before sublimation is reduced. The triple point pressure of this sublimation agent is 100 kPa to 110 kPa. Figure 1 , Figure 1 The position of the black dot is the triple point of the sublimation agent. Under normal pressure, the sublimation agent sublimates directly from the solid to the gaseous state without going through a melting state, and forms a pressure difference, which generates a large number of pores in the electrode and increases the porosity of the electrode.

[0033] Since the proposed solution generates a large number of pores simply by heating under normal pressure, the use of the sublimation agent does not affect the stability of the components in the active material layer. During subsequent rolling processing, the electrode sheets are less prone to powder sticking to the rollers or other desorption phenomena, effectively avoiding the increased cracks in the electrode sheets that can easily occur under negative pressure heating, which could damage the structural stability of the electrode sheets, leading to increased resistance or even significant desorption. Therefore, this solution offers superior pore control, which is beneficial for increasing the liquid retention coefficient, reducing DC resistance, and improving 3C capacity retention in secondary batteries.

[0034] When the amount of sublimation aid added is too small, the sublimation aid in the electrode sheet is prone to sublimation and dissolution simultaneously, which is not conducive to the direct transformation of the sublimation aid from solid to gaseous state under normal pressure, resulting in a significant reduction in the porosity of the electrode sheet. When the amount of sublimation aid added is too large, it can easily cause the electrode sheet to crack, destroying the structural stability of the electrode sheet. Furthermore, during the rolling process, the powder of the active electrode sheet is prone to sticking to the roller, and the electrical performance of the electrode sheet decreases. If the melting point of the alcohol is too high or too low, mixing alcohol as a sublimation aid with water will not achieve sublimation under normal pressure, and the sublimation pore formation of the electrode sheet still cannot be carried out under conventional conditions.

[0035] Therefore, this application uses iodine and / or alcohols with specific melting points and water in the above-mentioned proportions as sublimation agents. This allows the electrode sheet to complete pore formation under low energy consumption and normal pressure, thereby reducing the difficulty of the electrode sheet pore formation process. It can improve the liquid retention coefficient of the electrode sheet while saving production costs, and reduce the limitations on improving the dynamic performance of the electrode sheet caused by excessively difficult and costly electrode sheet pore formation processes. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram illustrating the triple point of water and the triple point of water mixed with a sublimation aid, as disclosed in an embodiment of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0039] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0040] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0041] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0042] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0043] Sublimation pore-forming using a sublimation agent is one method to improve the porosity of electrode sheets. The process is as follows: During electrode sheet preparation, water is first mixed with active electrode material, conductive agent, and binder to prepare an electrode slurry. The electrode slurry is then coated onto the surface of the current collector and directly frozen below 0°C to solidify the electrode slurry on the current collector surface. Sublimation treatment is then performed to increase the porosity of the electrode layer on the current collector surface. (Refer to...) Figure 1 , Figure 1The intersection of the three lines shown is the triple point of water. Since the pressure corresponding to the triple point of water is 0.61 kPa, specific pressure-reducing equipment is required to strictly control the pressure below 0.61 kPa. Heating is then performed at this pressure to allow water to sublimate directly from a solid state to a gaseous state. During sublimation, the internal pressure of the electrode increases, creating a pressure difference with the outside. The gas escapes outwards while simultaneously forming numerous pores inside the electrode, thereby increasing the porosity of the electrode. Therefore, in the above-described sublimation pore-forming process, water not only acts as a solvent to disperse the active electrode material, conductive agent, and binder, but also as a sublimation agent. Through sublimation drying, the porosity of the electrode is increased, offering multiple advantages. However, the above-mentioned sublimation pore-forming process requires the temperature to be lowered to below 0°C and the pressure during the sublimation process must be strictly controlled to below 0.61 kPa. Otherwise, water sublimation becomes difficult and the pore-forming effect of the electrode sheet will be significantly reduced. Therefore, this sublimation pore-forming process cannot be carried out under normal conditions, and the process has high energy consumption and high cost, making it difficult to further apply in industrial production.

[0044] Therefore, this application provides an electrode sheet and its preparation method, which uses water and iodine or alcohol with a specific melting point range in a specific ratio as a sublimation agent. The freezing point of this sublimation agent is between 0°C and 10°C, and the energy consumption for freezing to form a solid is low. More importantly, the triple point of this sublimation agent is significantly changed, and it can sublimate under normal pressure without controlling the pressure of the sublimation process to be below 0.61 kPa. This overcomes the shortcomings of the above-mentioned sublimation pore-forming process, which is difficult to carry out under normal conditions. It is beneficial to reduce energy consumption and cost, save resources, and has the advantages of being green and environmentally friendly and having excellent pore-forming effect.

[0045] The technical solution of the present invention will be further described below with reference to the embodiments and accompanying drawings.

[0046] In a first aspect, embodiments of this application provide an electrode sheet.

[0047] The electrode includes a current collector and an active material layer composited on the surface of the current collector. The raw materials for preparing the active material layer include a sublimation agent, which is composed of water and a co-sublimation agent. The mass of the co-sublimation agent accounts for 10% to 30% of the mass of the sublimation agent. The co-sublimation agent is iodine and / or an alcohol with a melting point between -10°C and 10°C.

[0048] This application discovers that iodine and / or alcohols with the aforementioned melting points have better solubility in water. When iodine and / or alcohols with melting points between -10°C and 10°C are used as sublimation aids, and when these aids are combined with water in the aforementioned proportions to form a sublimation agent, the freezing point of the sublimation agent is between 0°C and 10°C. Therefore, the refrigeration energy required for the sublimation agent to change from a liquid to a solid state before sublimation is reduced. The triple point pressure of this sublimation agent is 100 kPa to 110 kPa, as referenced... Figure 1, Figure 1 The position of the black dot is the triple point of the sublimation agent. Under normal pressure, the sublimation agent sublimates directly from the solid to the gaseous state without going through a melting state, and forms a pressure difference, which generates a large number of pores in the electrode and increases the porosity of the electrode.

[0049] Since the proposed solution generates a large number of pores simply by heating under normal pressure, the use of the sublimation agent does not affect the stability of the components in the active material layer. During subsequent rolling processing, the electrode sheets are less prone to powder sticking to the rollers or other desorption phenomena, effectively avoiding the increased cracks in the electrode sheets that can easily occur under negative pressure heating, which could damage the structural stability of the electrode sheets, leading to increased resistance or even significant desorption. Therefore, this solution offers superior pore control, which is beneficial for increasing the liquid retention coefficient, reducing DC resistance, and improving 3C capacity retention in secondary batteries.

[0050] When the amount of sublimation aid added is too small, the sublimation aid in the electrode sheet is prone to sublimation and dissolution simultaneously, which is not conducive to the direct transformation of the sublimation aid from solid to gaseous state under normal pressure, resulting in a significant reduction in the porosity of the electrode sheet. When the amount of sublimation aid added is too large, it can easily cause the electrode sheet to crack, destroying the structural stability of the electrode sheet. Furthermore, during the rolling process, the powder of the active electrode sheet is prone to sticking to the roller, and the electrical performance of the electrode sheet decreases. If the melting point of the alcohol is too high or too low, mixing alcohol as a sublimation aid with water will not achieve sublimation under normal pressure, and the sublimation pore formation of the electrode sheet still cannot be carried out under conventional conditions.

[0051] Therefore, this application uses iodine and / or alcohols with specific melting points and water in the above-mentioned proportions as sublimation agents. This allows the electrode sheet to complete pore formation under low energy consumption and normal pressure, thereby reducing the difficulty of the electrode sheet pore formation process. It can improve the liquid retention coefficient of the electrode sheet while saving production costs, and reduce the limitations on improving the dynamic performance of the electrode sheet caused by excessively difficult and costly electrode sheet pore formation processes.

[0052] The sublimation aid can be an alcohol with a melting point between -10°C and 10°C. For example, the sublimation aid can be an alcohol with a melting point of -10°C, -5°C, 0°C, 5°C and 10°C, including one or both of tert-butanol and 2-methyl-2-butanol.

[0053] It should be noted that the solution proposed in this application is universally applicable to electrode sheets, and is suitable for both positive and negative electrode sheets. It can improve the porosity of either positive or negative electrode sheets, while reducing the process difficulty and cost of improving the porosity of electrode sheets, which is very beneficial for improving the dynamic performance of the battery.

[0054] In some embodiments, the porosity of the electrode sheet is 25% to 40%.

[0055] By using iodine and / or alcohols with specific melting points and water in the aforementioned proportions as sublimation agents, the electrode sheet exhibits a superior pore structure, with a porosity reaching up to 40%. This demonstrates that the aforementioned sublimation agent can significantly improve the electrical performance of the electrode sheet. Examples of such sublimation agents include porosities of 25%, 28%, 30%, 32%, 35%, 38%, and 40%.

[0056] In some embodiments, the raw materials for preparing the active material layer also include unsublimated raw materials, and the mass ratio of the sublimation agent to the unsublimated raw materials is (1-1.2):1.

[0057] The active material layer mainly consists of unsublimated raw materials such as active electrode materials, conductive agents, and binders. During the preparation of the electrode sheet, the sublimation agent and these unsublimated raw materials are mixed in the aforementioned mass ratio to ensure uniform dispersion of water, sublimation aid, and unsublimated raw materials. After the water and sublimation aid in the aforementioned mass ratio sublimate, an electrode sheet with a better pore structure and higher porosity is obtained. For example, the mass ratio of sublimation agent to unsublimated raw materials is 1:1, 1.1:1, and 1.2:1, etc.

[0058] Specifically, the unsublimated raw material consists of 94% to 97% active electrode material by mass and 1% to 2% conductive agent and 1% to 2.5% binder by mass.

[0059] When the electrode sheet is a positive electrode sheet, the active electrode material of the active material layer is a positive active material such as layered lithium cobalt oxide, olivine-structured lithium iron phosphate, spinel-structured lithium manganese oxide, and layered nickel-cobalt-manganese ternary materials. When the electrode sheet is a negative electrode sheet, the active electrode material of the active material layer is a negative active material such as graphite and hard carbon. The conductive agent can be carbon nanotubes and conductive carbon black, and the binder can be styrene-butadiene rubber, polyacrylic acid, and carboxymethyl cellulose.

[0060] Secondly, embodiments of this application provide a method for preparing an electrode sheet.

[0061] The preparation method of this electrode sheet includes the following steps:

[0062] Preparation of active electrode slurry: Unsublimed raw materials and sublimation agent are mixed and dispersed to obtain active electrode slurry. The sublimation agent is composed of water and a sublimation co-sublimation agent, which accounts for 10% to 30% of the mass of the sublimation agent. The sublimation co-sublimation agent is iodine and / or alcohol with a melting point between -10℃ and 10℃.

[0063] Preparation of electrode sheets: Active electrode slurry is coated on the current collector, then frozen to solidify the active electrode slurry on the surface of the current collector, and heated at 100kPa to 110kPa to sublimate the sublimation agent and water to form an active electrode layer, and then rolled to obtain the electrode sheet.

[0064] In the preparation of active electrode slurry, a specific proportion of the above-mentioned sublimation aid is added in combination with water as a sublimation agent. After the active electrode slurry is coated onto the surface of the current collector, it is subjected to freezing treatment to allow the active electrode slurry to condense and form a solid. Since the above-mentioned sublimation agent can sublimate at 100kPa to 110kPa, when heated at normal pressure, the sublimation agent can directly sublimate from solid to gas without melting, resulting in an unrolled electrode sheet with high porosity.

[0065] The raw materials for the active electrode layer mainly include active electrode material, conductive agent and binder. After solidification and normal pressure drying, the adhesion stability between the active electrode layer and the current collector is improved, the binder is not easy to float, and in the subsequent rolling process, the active electrode material and conductive agent powder are less likely to stick to the roller.

[0066] In summary, the electrode sheet of this application can achieve a significant increase in porosity under normal pressure, without the need for specific equipment to control the sublimation of the electrode sheet at lower pressures. This reduces the difficulty of creating pores in the electrode sheet, which is beneficial for saving resources and reducing manufacturing costs. Simultaneously, it can improve the adhesion stability between the active electrode layer and the current collector layer, solving the problem of adhesive floating during rolling.

[0067] In some embodiments, during the preparation of the electrode sheet, the freezing temperature is 0°C to 10°C and the freezing time is 15 min to 30 min; and / or, the heating temperature is 90°C to 150°C and the heating time is 30 min to 60 min.

[0068] By using a sublimation aid and water in the above proportions, the solidification point of the active electrode slurry is increased. Therefore, the electrode slurry does not need to be reduced to below 0°C and can be solidified at 0°C to 10°C. At this temperature, the electrode slurry is easier to freeze into a solid and the freezing energy consumption is lower.

[0069] Furthermore, in the step of preparing the electrode sheet, the unrolled electrode sheet is rolled at 25°C with a rolling pressure of 1×10⁻⁶. 6 kg / m 2 ~3×10 6 kg / m 2 The electrodes are then rolled to obtain electrode sheets.

[0070] Under the above rolling conditions, the compaction density of the active electrode layer is increased, and the adhesion between the active electrode layer and the current collector is improved. During the rolling process, the active electrode layer with larger porosity maintains better stability and is less prone to powder detachment and sticking to the roller.

[0071] Thirdly, embodiments of this application provide a secondary battery.

[0072] The secondary battery includes:

[0073] Electrolyte

[0074] The positive electrode sheet is at least partially immersed in the electrolyte;

[0075] A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte;

[0076] And a negative electrode sheet, wherein the negative electrode sheet is an electrode sheet prepared in the first aspect or the second aspect, and the negative electrode sheet is disposed on the side of the diaphragm away from the positive electrode sheet and is at least partially immersed in the electrolyte;

[0077] or

[0078] Electrolyte

[0079] Positive electrode sheet, wherein the positive electrode sheet is an electrode sheet prepared in the first aspect or the second aspect, and the positive electrode sheet is at least partially immersed in the electrolyte;

[0080] A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte;

[0081] And a negative electrode plate, which is disposed on the side of the diaphragm away from the positive electrode plate and is at least partially immersed in the electrolyte;

[0082] In some embodiments, the secondary battery has a liquid retention factor of 1.2 to 1.5, a DC resistance of 100 mΩ to 200 mΩ, and a 3C capacity retention rate of 90 to 95%.

[0083] By using the aforementioned electrode sheets with higher porosity in secondary batteries, the liquid retention coefficient and 3C capacity retention rate of secondary batteries are improved, while the DC resistance is reduced.

[0084] Fourthly, embodiments of this application provide an electrical device. This electrical device includes the secondary battery mentioned in the third aspect.

[0085] Example 1

[0086] This application provides an electrode sheet, which consists of a current collector and an active material layer composited on the current collector. The current collector is aluminum foil, and the active material layer is composed of hard carbon, carbon nanotubes, conductive carbon black SP, and styrene-butadiene rubber in a mass ratio of 96.5%:0.8%:0.7%:2%.

[0087] The preparation method of the above-mentioned electrode sheet includes the following steps:

[0088] Preparation of active electrode slurry: Hard carbon, carbon nanotubes, conductive carbon black SP, and styrene-butadiene rubber are mixed in a mass ratio of 96.5%:0.8%:0.7%:2%. Then, a sublimation agent is added and mixed and dispersed. The mass ratio of the sublimation agent to the total mass of the hard carbon, carbon nanotubes, conductive carbon black SP, and styrene-butadiene rubber is 100:100. The sublimation agent is composed of water and a co-sublimation agent in a mass ratio of 80%:20%. The co-sublimation agent is tert-butanol.

[0089] Preparation of electrode sheets: The above-mentioned active electrode paste is coated onto a current collector, which is an aluminum foil. The foil is then frozen at -5°C for 15 minutes to allow the active electrode paste on the aluminum foil surface to solidify. Next, it is placed in an oven and heated to 100°C under normal pressure (101 kPa) to sublimate the sublimation agent and water, forming an active electrode layer. Finally, the layer is rolled at 25°C with a pressure of 2 × 10⁻⁶ kPa. 6 kg / m 2 Below, the unrolled electrode sheets are passed through a rolling mill to obtain electrode sheets.

[0090] Example 2

[0091] This application provides an electrode sheet, which differs from Example 1 in that the sublimation agent is 2-methyl-2-butanol, while the rest is the same as Example 1.

[0092] Example 3

[0093] This application provides an electrode sheet, which differs from Example 1 in that the sublimation agent is iodine, while the rest is the same as Example 1.

[0094] Example 4

[0095] This application provides an electrode sheet, which differs from Example 1 in that the sublimation agent is composed of water and a co-sublimation agent in a mass ratio of 70%:30%, while the rest remains the same as in Example 1.

[0096] Example 5

[0097] This application provides an electrode sheet, which differs from Example 1 in that the sublimation agent is composed of water and a co-sublimation agent in a mass ratio of 90%:10%, while the rest remains the same as in Example 1.

[0098] Comparative Example 1

[0099] This application provides an electrode sheet as a comparative example, which differs from Example 1 in that the sublimation agent is water, and no co-sublimation agent is added. Specifically, the preparation method of the electrode sheet is as follows:

[0100] Preparation of active electrode slurry: Hard carbon, carbon nanotubes, conductive carbon black SP, and styrene-butadiene rubber are mixed in a mass ratio of 96.5%:0.8%:0.7%:2%, and then water is added to mix and disperse. The mass ratio of water to the total mass of active electrode material, conductive agent and binder is 100:100.

[0101] Preparation of electrode sheets: The above-mentioned active electrode paste is coated onto a current collector, which is an aluminum foil. The foil is then frozen at -5°C for 15 minutes to solidify the active electrode paste on the aluminum foil surface. Next, it is placed in an oven and heated to 100°C at 0.61 kPa to form the active electrode layer. Finally, the foil is rolled at 25°C with a pressure of 2 × 10⁻⁶ kPa. 6 kg / m 2 Below, the unrolled electrode sheet is passed through a rolling mill to obtain the electrode sheet.

[0102] Comparative Example 2

[0103] This application provides an electrode sheet as a comparative example, which differs from Example 1 in that the sublimation agent is composed of water and a co-sublimation agent in a mass ratio of 92%:8%, while the rest remains the same as in Example 1.

[0104] Comparative Example 3

[0105] This application provides an electrode sheet as a comparative example, which differs from Example 1 in that the sublimation agent is composed of water and a co-sublimation agent in a mass ratio of 65%:35%, while the rest remains the same as in Example 1.

[0106] Experiment 1

[0107] Porosity testing of electrode sheets: Using the electrode sheets prepared in the above examples and comparative examples as test materials, the porosity of the electrode sheets was tested. A PoreMaster 60 mercury porosimeter (Quantachrome Instruments, USA) was used in the experiment. The pressure applied in the low-pressure station (LP) was approximately 0.6 to 50 PSI, and the pressure applied in the high-pressure station (HP) was 20 to 60,000 PSI. A certain amount of liquid mercury was poured into the test material, the pressure of the liquid mercury was measured using a pressure gauge, the volume of the liquid mercury was calculated, and finally, the porosity was determined using the ratio of the volume of the liquid mercury to the volume of the test material.

[0108] Experiment 2

[0109] Using the electrode sheets prepared in the above embodiments and comparative examples as negative electrodes, secondary batteries were fabricated respectively. The liquid retention coefficient, DC resistance, and 3C capacity retention rate of the secondary batteries were tested. The preparation method of the secondary batteries is as follows:

[0110] Weigh out the corresponding amounts of lithium iron phosphate, conductive carbon black, and sodium carboxymethyl cellulose in a mixing tank at a mass percentage of 95%:2.5%:2.5%. Add deionized water and stir for 6 hours to obtain the positive electrode slurry. Coat the positive electrode slurry onto aluminum foil and place it in a vacuum oven to dry at 150°C for 20 hours. The roller pressing pressure is 2×10⁻⁶. 6 kg / m 2 The positive electrode sheet is obtained by forming an active electrode layer through a roller press.

[0111] Take the negative electrode sheets to be tested prepared in the above embodiments and comparative examples respectively, and use a cutting tool to cut the positive electrode sheet and the negative electrode sheet to be tested to a certain size respectively. After cutting, the positive electrode sheet and the negative electrode sheet to be tested are wound with a polyethylene separator, and then the positive and negative electrode tabs are welded. After drying, they are then packaged with aluminum-plastic film to form a battery cell.

[0112] 1 mol / L lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1. The resulting solution is injected into the battery cell as the electrolyte, and finally packaged to form a secondary battery.

[0113] Test of electrolyte retention coefficient for secondary batteries: 1. Measure and calculate the porosity AKS of the separator. 2. Obtain the porosities AKC and AKA of the positive and negative electrodes. 3. Based on the length LC, width WC, and thickness HC of the positive electrode, the length LA, width WA, and thickness HA of the negative electrode, and the length LS, width WS, and thickness HS of the separator, calculate the total pore volume Vtotal using the porosities AKS, AKC, and AKA of the separator, positive and negative electrodes: Vtotal = (AKC × LC × WC × HC) + (AKA × LA × WA × HA) + (AKS × LS × WS × HS). 4. Calculate the electrolyte retention capacity mE: mE = ρE × Vtotal, where ρE is the density of the electrolyte. 5. Multiply the calculated electrolyte retention capacity by the injection coefficient to obtain the injection volume, and divide the injection volume by the battery capacity to obtain the electrolyte retention coefficient.

[0114] DC resistance test of secondary battery: The DC resistance is calculated using the following formula, R = (U 0.1C -U 1C ) / (I 1C -I0. 1C ), where R is the DC resistance, I 1C For a battery with a discharge rate of 1C, I 0.1C U is the battery current at a discharge rate of 0.1C. 1C U is the terminal voltage of the battery after discharging at a rate of 1C for 1 second.0.1C This is the terminal voltage of the battery after discharging at a rate of 0.1C for 10 seconds. DC resistance test procedure: After fully charging the battery as described in the following example, discharge it at a constant current of 0.1C for 10 seconds, and record the current I. 0.1C and terminal voltage U 0.1C Then, discharge at a constant current of 1C for 1 second and record the current I. 1C and terminal voltage U 1C Four batteries were tested in each group, and the average DC resistance of the batteries was calculated.

[0115] 3C capacity retention test of secondary batteries: The secondary battery to be tested is placed in the test chamber and allowed to stand for 5 minutes. Then, it is discharged to 2.5V at different rates, and the discharge capacity is recorded. After standing for 10 minutes, it is charged to 3.65V at a constant current of 0.5C, and then held at a constant voltage of 3.65V until the current drops to 0.05C (cutoff). Then, it is charged to 3.65V at constant current rates of 1C, 2C, and 3C, and held at a constant voltage of 3.65V until the current drops to 0.05C (cutoff), and the discharge capacity at each rate is recorded. The capacity retention rate at each rate = discharge capacity at each rate / 0.5C discharge capacity.

[0116] The test procedure for different rate charge and discharge is as follows: Place the secondary battery to be tested into the test box, let it stand for 5 minutes, then discharge it to 3.0V at a constant current at different rates, let it stand for 10 minutes, and then charge it to 4.2V at the same rate (current), and keep it at a constant voltage of 4.2V until the current drops to 0.05C to cut off.

[0117] Table 1

[0118]

[0119] As can be seen from the data in Table 1, compared with Comparative Example 1, the porosity, liquid retention coefficient, and 3C capacity retention rate of Example 1 are significantly improved, and the DC resistance is significantly reduced. This proves that compared with Comparative Example 1, which uses sublimation under vacuum conditions, the sublimation treatment of Example 1 under normal pressure conditions produces electrode sheets with higher porosity and higher liquid retention coefficient. Moreover, the components of the active material layer can be stably attached to the current collector layer, and the DC resistance and 3C capacity retention rate are also correspondingly improved.

[0120] Furthermore, a comparison of the data from Examples 1, 4, and 5 with Comparative Examples 2 and 3 reveals that the porosity and liquid retention coefficient of Examples 1, 4, and 5 are greater than those of Comparative Example 2, but smaller than those of Comparative Example 3. However, the 3C capacity retention rate of Examples 1, 4, and 5 is significantly higher than that of Comparative Examples 2 and 3, and the DC resistance is lower. This demonstrates that the mass ratio of sublimation aid to water has a significant impact on the porosity of the electrode sheet, as well as the DC resistance and 3C capacity retention rate of the battery. When the mass ratio of sublimation aid to water is within a specific range, the porosity of the electrode sheet, the liquid retention coefficient of the secondary battery, and the 3C capacity retention rate are all significantly improved, and the DC resistance is significantly reduced. When the mass ratio of water to sublimation aid is too low, the battery electrode sheet undergoes both sublimation and dissolution, which is not conducive to the direct transformation of water from solid to gaseous state under normal pressure. This results in a significant decrease in the porosity of the electrode sheet in Comparative Example 2, a significant decrease in the liquid retention coefficient and 3C capacity retention rate of the secondary battery, and an increase in the DC resistance. In Comparative Example 3, the mass ratio of water to sublimation agent was too high, which made the electrode sheet prone to cracking. Although the porosity and liquid retention coefficient were improved by testing, the large cracks in the electrode sheet made the powder in the active electrode layer prone to desorption during the rolling process, which led to a decrease in the structural stability of the electrode sheet, an increase in the DC resistance of the secondary battery, and a decrease in the 3C capacity retention rate.

[0121] A comparison of Example 1 with Examples 2 and 3 shows that using tert-butanol, 2-methyl-2-butanol, and iodine as sublimation aids can all increase the porosity of the electrode sheet under normal pressure, while maintaining good structural stability of the electrode sheet and preventing desorption during the rolling process.

[0122] The electrode plates, their preparation methods, secondary batteries, and electrical devices disclosed in the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the electrode plates, their preparation methods, secondary batteries, electrical devices, and their core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An active electrode paste, characterized in that: The electrode slurry includes unsublimed raw materials and a sublimation agent. The sublimation agent is composed of water and a sublimation co-agent. The mass of the sublimation co-agent accounts for 10% to 30% of the mass of the sublimation agent. The sublimation co-agent is iodine and / or an alcohol with a melting point between -10°C and 10°C. The freezing point of the sublimation agent is between 0°C and 10°C, and the triple point of the sublimation agent is between 100 kPa and 110 kPa.

2. The active electrode slurry according to claim 1, characterized in that: The sublimation aid includes one or both of tert-butanol and 2-methyl-2-butanol.

3. The active electrode paste according to claim 1, characterized in that: The mass ratio of the sublimation agent to the mass of the unsublimated raw material is (1~1.2):

1.

4. The active electrode slurry according to claim 1, characterized in that: The unsublimated raw material consists of 94% to 97% active electrode material by mass, 1% to 2% conductive agent, and 1% to 2.5% binder by mass, and the total mass percentage of each component in the active electrode slurry is 100%.

5. A method for preparing an electrode sheet, characterized in that: Includes the following steps: Preparation of active electrode slurry as described in any one of claims 1-4: The unsublimated raw material and the sublimation agent are mixed and dispersed to obtain the active electrode slurry, wherein the sublimation agent is composed of water and a sublimation co-agent, the sublimation co-agent accounts for 10% to 30% of the mass of the sublimation agent, the sublimation co-agent is iodine and / or an alcohol with a melting point between -10°C and 10°C, the freezing point of the sublimation agent is between 0°C and 10°C, and the triple point of the sublimation agent is between 100 kPa and 110 kPa; Preparation of electrode sheets: Active electrode slurry is coated on the current collector, then frozen to transform the active electrode slurry on the surface of the current collector into a solid. The active electrode layer is formed by sublimation of the co-sublimation agent and water at 100 kPa to 110 kPa. After rolling, the electrode sheet is obtained.

6. The method for preparing the electrode sheet according to claim 5, characterized in that: In the step of preparing the electrode sheet, the freezing temperature is 0℃~10℃ and the freezing time is 15 min~30 min; and / or, the heating temperature is 90℃~150℃ and the heating time is 30 min~60 min.

7. The method for preparing the electrode sheet according to claim 5, characterized in that: The porosity of the electrode sheet is 25%~40%.

8. A secondary battery, characterized in that: include: Electrolyte A positive electrode sheet, wherein the positive electrode sheet is at least partially immersed in the electrolyte; A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte; And a negative electrode sheet, wherein the negative electrode sheet is an electrode sheet prepared by the preparation method according to any one of claims 5-7, wherein the negative electrode sheet is disposed on the side of the diaphragm opposite to the positive electrode sheet and is at least partially immersed in the electrolyte; or Electrolyte A positive electrode sheet, wherein the positive electrode sheet is an electrode sheet prepared by the preparation method according to any one of claims 5-7, and the positive electrode sheet is at least partially immersed in the electrolyte; A diaphragm is located on one side of the positive electrode and is at least partially immersed in the electrolyte; And a negative electrode plate, which is disposed on the side of the diaphragm opposite to the positive electrode plate and is at least partially immersed in the electrolyte.

9. The secondary battery according to claim 8, characterized in that: The secondary battery has a liquid retention coefficient of 1.2 to 1.5, a DC resistance of 100 mΩ to 200 mΩ, and a 3C capacity retention rate of 90 to 95%.

10. An electrical appliance, characterized in that: Includes the secondary battery as described in claim 9.

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