Heat treatment process for electrode sheet, aluminum foil, positive electrode sheet and heat treatment device

Abstract

A heat treatment process for an electrode sheet, an aluminum foil, a positive electrode sheet and a heat treatment device. The present invention aims to solve the problems that existing electrode sheet baking methods results in a high water content of baked electrode sheets and poor consistency in the drying degrees of the electrode sheets and requires a long time period for baking, and that positive electrode sheets have low elongation, high tensile strength and poor flexibility. In order to achieve the aim, the provided heat treatment process for an electrode sheet comprises the following steps: putting an electrode sheet into the heat treatment device for heat treatment. By means of the heat treatment of the electrode sheet, the elongation of the electrode sheet can be efficiently improved, the tensile strength of the electrode sheet is reduced, and the aim of improving the flexibility of the electrode sheet is achieved, thereby meeting the requirements on the elongation of positive electrode sheets during the winding manufacturing process of a high-energy-density-system lithium-ion battery, the cycling process of a battery and safety tests such as an extrusion test; moreover, moisture in the electrode sheet is removed, and the electrode sheet is thus made to keep dry.

Description

Pole heat treatment process, aluminum foil, positive electrode and heat treatment equipment

[0001] This application claims priority to Chinese patent application No. 202310879923.8 filed on July 17, 2023, entitled “Heat treatment process of positive electrode sheet and aluminum foil, positive electrode sheet”. The entire contents of the above Chinese patent application are incorporated into this application by reference.

[0002] This application claims priority to Chinese patent application No. 202311717096.9 filed on December 13, 2023, with the invention name “Pole baking process and baking equipment”. The entire contents of the above Chinese patent application are incorporated into this application by reference. Technical Field

[0003] The present invention relates to the technical field of batteries, and specifically provides a heat treatment process for a pole piece, aluminum foil, a positive pole piece, and heat treatment equipment. Background Art

[0004] Residual moisture in lithium battery pole pieces has a serious impact on the active materials and electrolyte in the battery, leading to reduced battery cycle life, increased safety risks, and other issues. It also affects the processing performance of the pole pieces. Therefore, in order to ensure the electrochemical performance of lithium batteries, the moisture requirements of the pole pieces are very strict.

[0005] Heat treatment of lithium-ion battery pole pieces can effectively reduce the water content and has a significant impact on battery performance. Currently, the commonly used pole piece heat treatment methods include pole coil baking and bare cell baking. Pole coil baking is to bake the pole coil in a vacuum / nitrogen high-temperature environment to remove moisture. However, due to the large thickness of the pole coil, the inner and outer pole pieces of the pole coil are heated unevenly during the baking process, resulting in different degrees of stress release and thickness rebound of the pole pieces at different positions, poor consistency of pole piece thickness and internal stress, and also different moisture removal effects between the inner and outer layers of the pole coil. In addition, there are also problems of long baking time and high cost. Bare cell baking is to bake the wound, unfilled battery cell at high temperature to remove residual moisture in the positive and negative pole pieces and diaphragms. However, due to the safety risks of closed pores and thermal shrinkage of the diaphragm at high temperatures, too high a baking temperature (generally not exceeding 100°C) cannot be used, the baking efficiency is low, and it is difficult to effectively remove adsorbed water and crystallized water in the pole pieces. There are also problems of long baking time and high cost.

[0006] Furthermore, aluminum foil, as the current collector for the positive electrode of lithium-ion batteries, has different mechanical property requirements at different stages of the manufacturing process. The rolling process requires the aluminum foil to have high tensile strength, high hardness, and moderate elongation; the winding and forming processes require high elongation, moderate tensile strength, and increased flexibility of the electrode sheet. Existing aluminum foil, to meet the requirements of the rolling process, has a high hardness. This results in low elongation, poor flexibility, and high tensile strength for the aluminum foil and the rolled positive electrode sheet. This makes it difficult to meet the elongation requirements of the positive electrode sheet during the winding manufacturing process and battery cycling of high-energy-density lithium-ion batteries. Furthermore, it is difficult to ensure that the positive electrode sheet will not break and cause internal short circuits under abusive conditions such as extrusion.

[0007] Accordingly, this field requires a new technical solution to solve the above technical problems.

[0008] Summary of the Invention

[0009] The present invention aims to solve the above technical problems, namely, to solve the problems of high moisture content of the pole pieces after baking, poor consistency of pole piece drying and long baking time in the existing pole piece baking method, as well as the problems of low elongation, high tensile strength and poor flexibility of the positive pole pieces.

[0010] In a first aspect, the present invention provides a heat treatment process for a pole piece, the heat treatment process comprising the following steps: placing the pole piece in a heat treatment device for heat treatment.

[0011] In the preferred technical solution of the heat treatment process of the above-mentioned electrode, the heat treatment time is 0.5 to 20 seconds, and the heat treatment temperature is 150 to 250°C.

[0012] When the above technical solution is adopted, the electrode undergoes a rapid heat treatment of 0.5 to 20 seconds at a heat treatment temperature of 150 to 250°C, which can efficiently improve the elongation of the electrode, reduce the tensile strength of the electrode, and achieve the purpose of increasing the flexibility of the electrode. After the flexibility of the electrode is greatly improved, it can effectively meet the requirements for the elongation of the positive electrode in the winding manufacturing process of high-energy density lithium-ion batteries, battery cycling process and extrusion and other safety tests, and can also ensure that the internal short circuit problem caused by the breakage of the positive electrode will not occur under abuse conditions such as extrusion; at the same time, the heat treatment can effectively remove the residual NMP solvent and residual moisture in the positive electrode, thereby achieving the goal of high-efficiency electrode drying.

[0013] In the preferred technical solution of the above-mentioned heat treatment process for the pole piece, the heat treatment equipment is a hot roller heating equipment, and the heat treatment time is 5 to 20 seconds.

[0014] When adopting the above technical solution, since the tensile strength will decrease sharply with the increase of temperature, the temperature needs to be controlled within a certain range; using hot roller heating equipment, since hot roller heating equipment is relatively mature, the cost of using hot oil to heat the roller is low, and the control is also simple. The hot roller heating equipment can heat the roller quickly and accurately, and the temperature distribution on the roller surface is uniform. The heat conduction speed is significantly better than hot air convection heating, and the electrode temperature is also very uniform. In addition, the hot roller heating equipment is easy to adjust and control, can meet various production needs, has high durability, and saves costs.

[0015] In the preferred technical solution of the heat treatment process of the above-mentioned electrode, the heat treatment equipment is an induction heating equipment, the heat treatment temperature is 180-250° C., and the heat treatment time is 0.5-2 s.

[0016] When adopting the above technical solution, an induction heating device is used. The heating device is a device that heats an electrical conductor through electromagnetic induction. The electromagnetic induction heating device uses the alternating electromagnetic field generated by alternating current to generate eddy currents in the metal conductor, and through the eddy currents, the electrons, lattices, magnetic domains, etc. inside the metal move, so that the metal is quickly heated. It has the characteristics of fast and uniform heating. The induction heating device is used to first heat the aluminum foil of the pole piece, and then the heat is transferred from the aluminum foil to the composite material layer coated on the aluminum foil. This heat transfer method can heat the aluminum foil very quickly, realize the brittle-to-ductile transition of the aluminum foil, and at the same time avoid making the temperature of the composite material layer coated on the aluminum foil too high, reducing the thermal impact on the binder and active material.

[0017] In the preferred technical solution of the heat treatment process of the above-mentioned electrode, the heat treatment equipment is an infrared heating equipment, the heat treatment temperature is 180-250° C., and the heat treatment time is 2-10 seconds.

[0018] When adopting the above technical solution, infrared heating equipment is used. Since the infrared heating equipment transmits the waveform heat radiation emitted by the infrared radiation lamp to the electrode, and since infrared rays do not require an additional transmission medium, they can directly transfer energy to the electrode. The heat transfer loss is very small and the heat conversion efficiency is very high. Therefore, the energy consumption cost of using infrared heating equipment is low and the heating speed is fast. In addition, infrared heating does not require the use of hot air and will not produce secondary pollution. Infrared heating can accurately control the heating intensity and time to achieve precise control of heating. In addition, the infrared heating equipment has a very short on-off response time, and can reach the set power in about 1 second after powering on. The power can be adjusted quickly, and the intensity of infrared radiation is relatively uniform. These factors make the consistency and adjustability of the infrared heating equipment very good.

[0019] In the preferred technical solution of the heat treatment process of the above-mentioned electrode, the electrode is a positive electrode, and the positive electrode includes aluminum foil, and the weight ratio of the components of the aluminum foil is: Si: 0.1 to 0.7 parts; Fe: 1.1 to 1.4 parts; Sr: 0.01 to 0.03 parts; Al: 97.8 to 98.8 parts.

[0020] The aluminum foil obtained by adopting this composition ratio has higher elongation and flexibility than the existing aluminum foil. The positive electrode sheet containing this aluminum foil also has high elongation and flexibility. On this basis, a heat treatment process is further carried out to more effectively meet the requirements for the elongation of the positive electrode sheet in the winding manufacturing process of high-energy density lithium-ion batteries, the battery cycle process, and extrusion and other safety tests.

[0021] In the preferred technical solution of the above-mentioned heat treatment process for the electrode, the thickness of the aluminum foil is 4 to 15 μm.

[0022] In the preferred technical solution of the above-mentioned heat treatment process for the pole piece, the elongation of the aluminum foil is greater than 2.5%.

[0023] When the above technical solution is adopted, the elongation and flexibility of the aluminum foil are both high.

[0024] In the preferred technical solution of the above-mentioned heat treatment process of the electrode, the heat treatment process includes a electrode baking process, and the electrode baking process is used to remove residual moisture on the electrode when the electrode passes through the heat treatment equipment in a belt-walking manner.

[0025] In the preferred technical solution of the above-mentioned electrode heat treatment process, the heat treatment equipment includes an oven, and the electrode baking process includes: filling the oven with protective gas and the volume of the protective gas accounts for not less than 98%; controlling the air pressure in the oven to be higher than the external atmospheric pressure.

[0026] When the above technical solution is adopted, the electrode baking process of the present invention allows the electrode to pass through an oven during the tape conveying process to remove the residual moisture on the electrode. By introducing protective gas into the oven to form a protective gas atmosphere, the high-temperature protective gas can quickly adsorb the moisture on the electrode, so that the moisture on the electrode is quickly converted into moisture in the protective gas, thereby accelerating the drying efficiency of the electrode and shortening the baking time of the electrode. In addition, the air pressure in the oven is higher than the external atmospheric pressure and the volume proportion of the protective gas is not less than 98%, which can prevent external air from entering the oven, reduce the proportion of air in the oven and thus reduce the oxygen content, and can reduce the probability of oxidation of the electrode tab area during high-temperature baking, so as to improve the performance of the electrode; thus, the electrode baking process of the present invention realizes unwinding baking of the electrode. Compared with other baking processes, baking the electrode of the same length can effectively shorten the baking time, improve the baking efficiency and improve the baking quality; in addition, the electrode baked by the baking process of the present invention has low water content, uniform thickness distribution and good flatness, thereby also improving the battery performance of the lithium battery made therefrom.

[0027] In the preferred technical solution of the above-mentioned electrode heat treatment process, the difference between the air pressure in the oven and the external atmospheric pressure ranges from 5Pa to 100Pa; and / or the protective gas is a combination of one or more of nitrogen, argon and helium.

[0028] When the above technical solution is adopted, the difference between the air pressure in the oven and the external atmospheric pressure is maintained in the range of 5Pa to 100Pa, so that the oven is in a slightly positive pressure environment. This can not only prevent outside air from entering the oven to reduce the oxygen content in the oven, but also reduce the leakage amount of protective gas and the leakage rate, thereby effectively reducing the amount of protective gas used and reducing costs.

[0029] In the preferred technical solution of the above-mentioned heat treatment process for the electrode, the baking temperature in the oven is not lower than 160°C.

[0030] In the preferred technical solution of the above-mentioned heat treatment process for the electrode, the baking temperature in the oven ranges from 160°C to 220°C.

[0031] When adopting the above technical solution, the baking temperature in the oven is not lower than 160°C. Firstly, the high temperature can quickly evaporate the moisture on the electrode. Secondly, the saturated water content of the protective gas is high in a high temperature environment, which can increase the adsorption capacity of the protective gas, thereby improving the drying efficiency and reducing the amount of protective gas used.

[0032] In the preferred technical solution of the above-mentioned heat treatment process of the pole piece, the conveying speed of the pole piece is not less than 60m / min.

[0033] When the above technical solution is adopted, the conveying speed of the electrode is set to be no less than 60 m / min, which can achieve rapid baking and shorten the baking time.

[0034] In the preferred technical solution of the above-mentioned heat treatment process for the electrode, the baking time of the electrode is in the range of 0.5s to 30s, and the baking time of the electrode is negatively correlated with the baking temperature in the oven.

[0035] When the above technical solution is adopted, the baking time of the electrode is 0.5s to 30s, and the baking speed is fast and the efficiency is high.

[0036] In the preferred technical solution of the above-mentioned heat treatment process for the electrode, the water content of the protective gas in the oven is not higher than 500g / m 3 .

[0037] When the above technical solution is adopted, the water content of the protective gas in the oven is not higher than 500g / m 3 , which can ensure that the protective gas in the oven can continuously absorb moisture and avoid the saturation of the water content of the protective gas, thereby ensuring that the moisture on the electrode can be quickly removed and the baking quality is guaranteed.

[0038] In the preferred technical solution of the above-mentioned heat treatment process of the electrode, the water content of the protective gas in the oven is in the range of 50g / m 3 ~500g / m 3 .

[0039] When the above technical solution is adopted, the water content of the protective gas in the oven is controlled at 50g / m 3 ~500g / m 3 , which can make the protective gas in the oven have a strong enough ability to absorb moisture to ensure the baking quality. In addition, filling a small amount of absolute dry protective gas can keep the protective gas in the oven in circulation, which can save the amount of protective gas, avoid excessive consumption of protective gas and reduce costs.

[0040] In the preferred technical solution of the above-mentioned electrode heat treatment process, the electrode baking process also includes: real-time detection of the water content of the protective gas at the outlet of the oven; determining the protective gas flow rate based on the water content of the protective gas; and filling the protective gas into the oven according to the protective gas flow rate.

[0041] When the above technical solution is adopted, the water content of the shielding gas at the outlet of the oven is detected in real time, and the shielding gas flow rate is determined so that the shielding gas can be filled into the oven according to the shielding gas flow rate, and the water content of the shielding gas in the oven is regulated to control the water content of the shielding gas within the set range. This control method can eliminate the influence of the water content fluctuation in the incoming electrode on the humidity of the shielding gas in the oven, thereby ensuring the consistency of the dryness of the discharged electrode, and at the same time can reduce the amount of shielding gas used and reduce costs.

[0042] In a second aspect, the present invention further provides a heat treatment device, comprising an oven and a controller, wherein the controller is configured to be able to perform the pole piece baking process according to any one of claims 10 to 18.

[0043] In a third aspect, the present invention further provides an aluminum foil, which is the aluminum foil contained in the positive electrode plate obtained by the heat treatment process of the electrode plate.

[0044] In a fourth aspect, the present invention further provides a positive electrode plate, wherein the positive electrode plate is a positive electrode plate obtained by a heat treatment process of the plate.

[0045] In the preferred technical solution of the above-mentioned positive electrode plate, the positive electrode plate includes the aluminum foil and a composite material layer coated on the aluminum foil.

[0046] When the above technical solution is adopted, the positive electrode sheet adopts the aluminum foil obtained by the component ratio disclosed in the present invention, and its elongation and flexibility are relatively high; the positive electrode sheet obtained by coating the composite material layer on the aluminum foil has a reduced tensile strength; the positive electrode sheet after rolling is subjected to heat treatment, which can efficiently improve the elongation of the sheet, reduce the tensile strength of the sheet, and achieve the purpose of increasing the flexibility of the sheet. After the flexibility of the sheet is greatly improved, it can effectively meet the requirements for the elongation of the positive electrode sheet in the winding manufacturing process of high-energy density lithium-ion batteries, the battery cycle process and extrusion and other safety tests, and can also ensure that internal short circuit problems caused by breakage of the positive electrode sheet will not occur under abuse conditions such as extrusion.

[0047] In the preferred technical solution of the above-mentioned positive electrode plate, the composite material layer is any one of a nickel-cobalt-manganese ternary material layer, a nickel-cobalt-aluminum ternary material layer, a lithium iron phosphate material layer, and a lithium manganese oxide material layer.

[0048] When the above technical solutions are adopted, the nickel-cobalt-manganese ternary material and the nickel-cobalt-aluminum ternary material have high energy density and good high-temperature resistance, and the lithium iron phosphate material and the lithium manganese oxide material have high safety and low cost, which can effectively improve the use effect of the positive electrode. DETAILED DESCRIPTION

[0049] The following describes some embodiments of the present invention. It should be understood by those skilled in the art that these embodiments are merely intended to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art may adjust them as needed to suit specific applications.

[0050] It should be noted that, in the description of the present invention, the ordinal numbers "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0051] On the first aspect, based on the first problem pointed out in the background technology, that is, the problem that the positive electrode plate in the prior art has low elongation, high tensile strength and poor flexibility, the present invention provides a heat treatment process for the plate, aluminum foil, and a positive electrode plate, aiming to achieve efficient improvement of the elongation of the positive electrode plate, reduction of the tensile strength, and increase of the flexibility of the positive electrode plate by improving the elemental composition and structure of the aluminum foil in combination with the heat treatment process of the positive electrode plate.

[0052] Specifically, the aluminum foil of the present invention comprises the following components by weight: Si: 0.1-0.7 parts; Fe: 1.1-1.4 parts; Sr: 0.01-0.03 parts; Al: 97.8-98.8 parts; and the total content of other elements is less than or equal to 0.1 parts. Preferably, the aluminum foil has a thickness of 4-15 μm, a tensile strength of 230 MPa or greater, and an elongation of greater than 2.5%. This aluminum foil exhibits both high elongation and flexibility, while its tensile strength is lower than that of existing aluminum foils, but remains high.

[0053] The positive electrode plate of the present invention comprises an aluminum foil and a composite material layer coated on the aluminum foil.

[0054] After coating the aluminum foil with the composite material layer, the aluminum foil is rolled to enhance the bonding strength between the composite material layer and the aluminum foil, while also compressing the battery cell volume and increasing the cell energy density. The resulting positive electrode sheet has a density of 3.1 to 3.8 g / cc, and its tensile strength decreases somewhat after rolling. Heat treatment of the positive electrode sheet during or after rolling can efficiently increase its elongation, reduce its tensile strength, and increase its flexibility. This significant improvement in flexibility effectively meets the elongation requirements of high-energy-density lithium-ion batteries during winding manufacturing, battery cycling, and safety testing such as extrusion. It also prevents internal short circuits caused by positive electrode sheet breakage under abusive conditions such as extrusion.

[0055] Preferably, the composite material layer is a nickel-cobalt-manganese ternary material layer or a nickel-cobalt-aluminum ternary material layer. These two materials have a high energy density, which can increase the surface density of the positive electrode sheet, thereby effectively improving the battery's endurance; they also have a high cycle life, reduce the frequency of battery replacement, and reduce the cost of use; in addition, they also have a low discharge rate, which can reduce the energy loss of the battery during long-term storage and non-use, thereby improving the reliability and stability of the battery; at the same time, they have excellent high-temperature mechanical properties and good high-temperature fatigue resistance, making it less likely to undergo plastic deformation and fracture under high temperature and high pressure, thereby improving the safety of the positive electrode sheet. In addition, these two materials do not contain harmful substances such as heavy metals, are environmentally friendly, and meet environmental protection requirements. It should be noted that the composite material layer can also be a lithium iron phosphate material layer, a lithium manganese oxide material layer, a lithium cobalt oxide material layer, a lithium manganese oxide material layer, etc. Those skilled in the art can make adjustments as needed, all of which fall within the scope of protection of the present invention.

[0056] At the same time, the present invention discloses a heat treatment process for a pole piece, which comprises the following steps: placing the pole piece in a heat treatment device for heat treatment, wherein the heat treatment time is 0.5 to 20 seconds and the heat treatment temperature is 150 to 250°C. Since the drying temperature after coating and before rolling is 80 to 100°C, which cannot reach the heat treatment temperature, only heat treatment at a heat treatment temperature of 150 to 250°C can effectively improve the flexibility of the aluminum foil and the positive pole piece; the heat treatment time is controlled within the range of 0.5 to 20 seconds because too long a heat treatment time will affect the active material, causing problems such as cracking and oxidation of the positive pole piece. After a rapid heat treatment of 0.5 to 20 seconds and a heat treatment temperature of 150 to 250° C., the elongation of the electrode sheet can be efficiently improved, the tensile strength of the electrode sheet can be reduced, and the flexibility of the electrode sheet can be increased. After the flexibility of the electrode sheet is greatly improved, it can effectively meet the elongation requirements of the positive electrode sheet in the winding manufacturing process of high-energy density lithium-ion batteries, the battery cycle process, and safety tests such as extrusion. It can also ensure that the internal short circuit problem caused by the breakage of the positive electrode sheet will not occur under abuse conditions such as extrusion; in addition, during the manufacturing process of lithium-ion batteries, due to the influence of various factors, some electrode sheets cannot be completely dried, thereby affecting their electrochemical performance and may also cause problems such as battery flatulence. Therefore, a baking process is required to remove residual moisture. The heat treatment process of the present invention integrates the baking removal of moisture with the need to adjust the mechanical properties of the aluminum foil and the electrode sheet through heat treatment, thereby achieving the purpose of effectively removing residual NMP solvent and residual moisture in the positive electrode sheet while improving the flexibility and elongation of the aluminum foil and the electrode sheet and reducing the tensile strength of the aluminum foil and the electrode sheet, thereby achieving the purpose of high-efficiency electrode sheet drying.

[0057] It should be noted that the heat treatment equipment may be a hot roller heating equipment, an induction heating equipment, an infrared heating equipment, or other heat treatment equipment, all of which are within the scope of protection of the present invention.

[0058] Specifically, when the heat treatment equipment is a hot roller heating equipment, the heat treatment temperature is 150-250°C, and the heat treatment time is 5-20s. The hot roller heating equipment is used. Since the hot roller heating equipment is relatively mature, the cost of using hot oil to heat the roller is low, and the control is also simple. The hot roller heating equipment can heat the roller quickly and accurately, and the temperature distribution on the roller surface is uniform. The heat conduction speed is significantly better than hot air convection heating, and the electrode temperature is also very uniform. In addition, the hot roller heating equipment is easy to adjust and control, can meet various production needs, has high durability, and saves costs.

[0059] When the heat treatment equipment is an induction heating equipment, the heat treatment temperature is 180-250°C and the heat treatment time is 0.5-2s; the induction heating equipment is a device that heats electrical conductors through electromagnetic induction. The electromagnetic induction heating equipment uses the alternating electromagnetic field generated by alternating current to generate eddy currents in the metal conductor, and through the eddy currents, the electrons, lattices, magnetic domains, etc. inside the metal move, so that the metal is quickly heated. It has the characteristics of fast and uniform heating. The induction heating equipment is used to first heat the aluminum foil of the pole piece, and then the heat is transferred from the aluminum foil to the composite material layer coated on the aluminum foil. This heat transfer method can heat the aluminum foil very quickly, realize the brittle-tough transition of the aluminum foil, and at the same time avoid making the temperature of the composite material layer coated on the aluminum foil too high, reducing the thermal impact on the binder and active material.

[0060] When the heat treatment equipment is an infrared heating equipment, the heat treatment temperature is 180-250°C, and the heat treatment time is 2-10s. When using infrared heating equipment, since the infrared heating equipment transmits the waveform heat radiation emitted by the infrared radiation lamp to the electrode, and since infrared rays do not require an additional transmission medium, they can directly transfer energy to the electrode, with very little heat transfer loss and very high heat conversion efficiency. Therefore, the energy consumption cost of using infrared heating equipment is low and the heating speed is fast. In addition, infrared heating does not require the use of hot air and will not produce secondary pollution. Infrared heating can accurately control the heating intensity and time to achieve precise control of heating. In addition, the on-off response time of the infrared heating equipment is very short, and the set power can be reached in about 1s after powering on, and the power can be adjusted quickly. The intensity of the infrared radiation is relatively uniform. These factors make the consistency and adjustability of the infrared heating equipment very good.

[0061] In addition, the heat treatment process can be a separate process, specifically including the following steps: unwinding the electrode roll; placing the electrode into a heat treatment device for heat treatment; and winding the electrode after the heat treatment is completed.

[0062] When heat treating the positive electrode sheet, the heat treatment process can also be combined with rolling, which specifically includes the following steps: unwinding the aluminum foil roll; rolling the aluminum foil; heat treating the positive electrode sheet obtained after rolling; and rolling up the positive electrode sheet after the heat treatment.

[0063] In addition, the heat treatment process can also be combined with the electrode slitting. Taking the heat treatment of the positive electrode sheet as an example, the heat treatment process specifically includes the following steps: unwinding the rolled positive electrode sheet; placing the positive electrode sheet into the heat treatment equipment for heat treatment; slitting the positive electrode sheet after the heat treatment is completed; and winding the slit positive electrode sheet into sections.

[0064] It should be noted that the above heat treatment process is not restrictive and those skilled in the art can adjust it according to actual needs, which falls within the scope of protection of the present invention.

[0065] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the following uses the positive electrode sheet as an example to explain the technical solutions of the present invention in detail through several specific embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0066] Example 1:

[0067] The weight ratio of each component of the aluminum foil is: Si: 0.45 parts; Fe: 1.1 parts; Sr: 0.02 parts; Al: 98.3 parts; other elements: 0.13 parts.

[0068] Parameters of the aluminum foil: thickness 15um, tensile strength 245MPa, elongation 3.5%.

[0069] The heat treatment equipment is a hot roller heating equipment, the heat treatment temperature is 200°C, and the heat treatment time is 10s.

[0070] Example 2:

[0071] The weight ratio of each component of the aluminum foil is: Si: 0.45 parts; Fe: 1.1 parts; Sr: 0.02 parts; Al: 98.3 parts; and other elements: 0.13 parts.

[0072] Parameters of the aluminum foil: thickness 15um, tensile strength 245MPa, elongation 3.5%.

[0073] The heat treatment equipment is an infrared heating equipment, the filament temperature is 1600℃, and the average radiation power density of the pole piece is 10W / cm 2 , the heat treatment time is 5s.

[0074] Example 3:

[0075] The weight ratio of each component of the aluminum foil is: Si: 0.58 parts; Fe: 1.2 parts; Sr: 0.03 parts; Al: 98.1 parts; and other elements 0.09 parts.

[0076] Parameters of the aluminum foil: thickness 12um, tensile strength 232MPa, elongation 4.2%.

[0077] The heat treatment equipment is electromagnetic heating equipment with a heating power of 40W / cm 2 , the heat treatment time is 1s.

[0078] Example 4:

[0079] The weight ratio of each component of the aluminum foil is: Si: 0.58 parts; Fe: 1.2 parts; Sr: 0.03 parts; Al: 98.1 parts; and other elements 0.09 parts.

[0080] Parameters of the aluminum foil: thickness 12um, tensile strength 232MPa, elongation 4.2%.

[0081] The heat treatment equipment is an infrared heating equipment with a filament temperature of 1400°C and an average radiation power density of 7W / cm 2 , the heat treatment time is 5s.

[0082] Comparative Example 1:

[0083] The weight ratio of each component of the aluminum foil is: Si: 0.45 parts; Fe: 1.1 parts; Sr: 0.02 parts; Al: 98.3 parts; other elements: 0.13 parts.

[0084] Parameters of the aluminum foil: thickness 15um, tensile strength 245MPa, elongation 3.5%.

[0085] No heat treatment is performed.

[0086] Comparative Example 2:

[0087] The weight ratio of each component of the aluminum foil is: Si: 0.3 parts; Fe: 0.3 parts; Sr: 0.02 parts; Al: 99.28 parts; other elements: 0.1 parts.

[0088] Parameters of the aluminum foil: thickness 15um, tensile strength 260MPa, elongation 2.5%.

[0089] No heat treatment is performed.

[0090] In order to further demonstrate the effect of the present invention, the following test method is provided:

[0091] The method for measuring the elongation and tensile strength of the electrode is: using a universal tensile testing machine to perform a tensile test, taking a straight spline of the positive electrode, with an intercept of 50mm and a tensile rate of 5mm / min. The method for testing the flexibility of the electrode is: testing the bending resistance of the electrode through a semicircular bending test, making a 25mm long electrode into a semicircle, using a universal tensile testing machine to perform a bending test, and recording the spacing when the pressure suddenly changes, which is recorded as the bending allowance. The smaller the bending allowance, the better the flexibility of the electrode. Among them, the universal tensile testing machine is a device used to test the pressure, elastic modulus, yield point, elongation, stress strain and other indicators of various materials or components under different mechanical properties such as tension, compression, bending, and shear. It has high-precision load sensors and displacement sensors, which can achieve high-precision testing and data acquisition, and the test results are highly reliable.

[0092] The test results of each embodiment and comparative example are shown in Table 1.

[0093] Table 1 Test values ​​of positive electrode sheets of Examples 1-4 and Comparative Examples 1-2

[0094] Comparing the test values ​​of Comparative Example 1 and Comparative Example 2, the aluminum foil component ratio used in Comparative Example 1 is the aluminum foil component ratio disclosed in the present invention, and the aluminum foil component ratio used in Comparative Example 2 is the aluminum foil component ratio of the prior art. Neither Comparative Example 1 nor Comparative Example 2 is heat treated. By comparing the test values ​​of Comparative Example 1 and Comparative Example 2, it can be seen that the elongation of Comparative Example 1 is higher than that of Comparative Example 2, and the bending allowance, tensile strength, moisture content and NMP content of Comparative Example 1 are lower than those of Comparative Example 2. It can be concluded that the elongation and flexibility of the electrode made of the aluminum foil obtained by adopting the aluminum foil component ratio of the present invention are higher than those of the existing electrode, and the tensile strength is lower than that of the existing electrode, but it is still slightly higher.

[0095] Comparing the test values ​​of Example 1 and Comparative Example 1, the aluminum foil component ratios used in Example 1 and Comparative Example 1 are the aluminum foil component ratios disclosed in the invention and the specific ratio values ​​are the same. Example 1 is heat-treated, and Comparative Example 1 is not heat-treated. By comparing the test values ​​of Example 1 and Comparative Example 1, it can be seen that the elongation of Example 1 is significantly higher than that of Comparative Example 1, and the bending allowance, tensile strength, moisture content, and NMP content of Example 1 are significantly lower than those of Comparative Example 1. It can be concluded that when the components and parameters of the aluminum foil materials are the same, the electrode pieces that have been heat-treated are better than those that have not been heat-treated. The elongation of the overheated electrode is significantly improved, and the bending allowance, tensile strength, moisture content and NMP content of the electrode are significantly reduced. The reduction in bending allowance indicates that the flexibility of the electrode is improved. It can be concluded that the electrode can be effectively improved by the heat treatment process, the tensile strength can be reduced, and the flexibility can be increased, thereby meeting the elongation requirements of the positive electrode in the winding manufacturing process of high-energy-density lithium-ion batteries, the battery cycle process, and extrusion and other safety tests. In addition, the heat treatment effectively removes the residual NMP solvent and residual moisture in the positive electrode, achieving the purpose of high-efficiency electrode drying.

[0096] Comprehensively comparing the test values ​​of Examples 1-4 with those of Comparative Example 1, it can be seen that the aluminum foil component ratios used in Examples 1-4 and Comparative Example 1 are the aluminum foil component ratios disclosed in the invention, Examples 1-4 are heat-treated, and Comparative Example 1 is not heat-treated. By comparing the test values ​​of Examples 1-4 with those of Comparative Example 1, it can be seen that the elongation of Examples 1-4 is significantly higher than that of Comparative Example 1, and the bending allowance, tensile strength, moisture content, and NMP content of Examples 1-4 are significantly lower than those of Comparative Example 1. It can be concluded that when the components and parameters of the aluminum foil materials are the same, the electrode pieces that have been heat-treated are better than those that have not been heat-treated. The elongation of the electrode that has been heat treated is significantly improved, and the bending allowance, tensile strength, moisture content, and NMP content of the electrode are significantly reduced. The reduction in bending allowance indicates that the flexibility of the electrode is improved. From this, it can be further concluded that the electrode can be effectively improved by the heat treatment process. The elongation, reduction of tensile strength, and increase of flexibility can meet the requirements of the positive electrode elongation in the winding manufacturing process of high-energy-density lithium-ion batteries, battery cycling process, and extrusion and other safety tests. In addition, the heat treatment effectively removes the residual NMP solvent and residual moisture in the positive electrode, achieving the purpose of high-efficiency electrode drying.

[0097] Comparing the test values ​​of Example 3 and Example 4, the aluminum foil component ratios used in Example 3 and Example 4 are both the aluminum foil component ratios disclosed in the invention and the specific ratio values ​​are the same. Example 3 is heat treated and uses electromagnetic heating equipment, and Example 4 is heat treated and uses infrared heating equipment. By comparing the test values ​​of Example 3 and Example 4, it can be seen that the elongation of Example 4 is higher than that of Example 3, and the bending allowance, tensile strength, moisture content, and NMP content of Example 4 are all lower than those of Example 3. It can be concluded that, when the components and parameters of the aluminum foil materials are the same, the electrode piece heat-treated with the infrared heating equipment has higher elongation and flexibility, and lower tensile strength than the electrode piece heat-treated with the electromagnetic heating equipment. Therefore, when other conditions are the same, the use of infrared heating equipment is better than the use of electromagnetic heating equipment.

[0098] In summary, since rolling generally requires the aluminum foil to have high tensile strength, high hardness and moderate elongation, heat treatment after or during rolling can be performed to increase the elongation of the aluminum foil and the positive electrode sheet, reduce the tensile strength of the aluminum foil and the positive electrode sheet, and increase the flexibility of the aluminum foil and the positive electrode sheet, so that the sheet can meet the requirements of the winding and formation stages for high elongation, moderate tensile strength and high flexibility of the aluminum foil, and can also ensure that internal short circuit problems caused by breakage of the positive electrode sheet will not occur under abuse conditions such as extrusion.

[0099] It should be noted that the above-mentioned embodiments are only used to illustrate the principles of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the principles of the present invention, those skilled in the art can adjust the above-mentioned embodiments so that the present invention can be applied to more specific application scenarios.

[0100] On the second aspect, based on the second problem pointed out in the background technology, that is, the baking processes such as electrode coil baking and bare cell baking in the existing technology have high moisture content of the electrode, poor consistency of the electrode drying degree and long baking time.

[0101] The present invention provides another heat treatment process for an electrode, which includes a electrode baking process. The electrode baking process forms a protective gas atmosphere by introducing protective gas into an oven. The high-temperature protective gas can quickly adsorb moisture on the electrode, so that the moisture on the electrode is quickly converted into the water content of the protective gas, thereby accelerating the drying efficiency of the electrode and shortening the baking time of the electrode; the air pressure in the oven is higher than the external atmospheric pressure and the volume proportion of the protective gas is not less than 98%, which can prevent external air from entering the oven, reduce the proportion of air in the oven and thus reduce the oxygen content, and can reduce the probability of oxidation in the electrode ear area during high-temperature baking, so as to improve the performance of the electrode.

[0102] The electrode baking process of the present invention realizes unwinding baking of the electrode, which can effectively shorten the baking time, improve the baking efficiency and enhance the baking quality for electrode pieces of the same length; in addition, the electrode pieces baked using the baking process of the present invention have low water content, uniform thickness distribution and good flatness, thereby also improving the battery performance of the lithium battery prepared thereby.

[0103] Specifically, the electrode baking process of the present invention is used to remove residual moisture on the electrode when the electrode passes through the oven in a belt-feed manner. The electrode baking process includes: filling the oven with protective gas and the volume of the protective gas in the oven accounts for not less than 98%; controlling the air pressure in the oven to be higher than the external atmospheric pressure.

[0104] The electrode baking process of the present invention forms a protective gas atmosphere by introducing protective gas into the oven. The high-temperature protective gas can quickly adsorb moisture on the electrode, so that the moisture on the electrode is quickly converted into moisture in the protective gas, thereby accelerating the drying efficiency of the electrode and shortening the baking time of the electrode.

[0105] The electrode baking process of the present invention makes the air pressure in the oven higher than the external atmospheric pressure and the volume proportion of the protective gas is not less than 98%, thereby making the oven a positive pressure environment, which can prevent external air from entering the oven, reduce the proportion of air in the oven, and thus reduce the oxygen content, and further reduce the probability of oxidation of the electrode tab area during high-temperature baking, thereby improving the performance of the electrode.

[0106] It should be noted that the present invention does not impose any restrictions on the specific type of shielding gas, as long as the shielding gas is not oxygen and can be used safely at high temperatures. In actual applications, those skilled in the art can select the type of shielding gas according to actual needs. For example, the shielding gas can be nitrogen, or the shielding gas can be an inert gas, or the shielding gas can be a mixture of nitrogen and inert gases, etc. Any adjustments and changes to the specific type of shielding gas do not deviate from the basic principles of the present invention and should be limited within the scope of the present invention.

[0107] Preferably, the protective gas is a combination of one or more of nitrogen, argon and helium.

[0108] In one embodiment, the shielding gas is nitrogen.

[0109] In another embodiment, the shielding gas is a mixture of nitrogen and helium in any proportion.

[0110] In another embodiment, the shielding gas is a mixture of helium and argon in any proportion.

[0111] It should also be noted that the present invention does not impose any restrictions on the specific structure of the oven. As long as the oven can meet the requirements of the electrode conveying and can bake the electrode conveyed into the oven, in actual applications, technical personnel in this field can set the structure of the oven according to actual needs.

[0112] Exemplarily, the oven includes a box body and a heating device arranged in the box body. The box body is provided with a pole piece inlet and a pole piece outlet. The pole piece can enter the box body from the pole piece inlet and then be output from the box body from the pole piece outlet. The heating device can heat the pole piece in the box body to remove moisture on the pole piece.

[0113] Exemplarily, the heating device is a hot roller, and the electrode is heated by the hot roller while it is moving along the hot roller, which can quickly dry out the moisture on the electrode.

[0114] Exemplarily, the heating device is an infrared heating device, which can quickly dry the moisture on the electrode during the tape traveling.

[0115] In a preferred embodiment, the difference between the air pressure in the oven and the external atmospheric pressure is in the range of 5 Pa to 100 Pa.

[0116] When the air pressure in the oven is higher than the external atmospheric pressure, the protective gas in the oven is kept output outward, thereby preventing the outside air from entering the oven, reducing the oxygen content in the oven, and further reducing the probability of the pole piece's tab area being oxidized at high temperatures. If the pressure difference between the air pressure in the oven and the external atmospheric pressure is too large, a large amount of protective gas will leak out, and it will be necessary to continuously fill more protective gas into the oven, resulting in a waste of protective gas and high costs. In the present invention, the difference (pressure difference) between the air pressure in the oven and the external atmospheric pressure is maintained between 5Pa and 100Pa, so that the oven is in a slightly positive pressure environment, which can not only prevent the outside air from entering the oven, but also reduce the amount and rate of leakage of protective gas in the oven, reduce the consumption of protective gas, and reduce costs.

[0117] Although the pressure difference between the oven pressure and the outside atmospheric pressure is set between 5 Pa and 100 Pa in the preferred embodiment described above, this does not limit the scope of protection of the present invention. In actual applications, the pressure difference between the oven pressure and the outside atmospheric pressure may be set to 110 Pa or 3 Pa. Such adjustments and changes to the pressure difference between the oven pressure and the outside atmospheric pressure do not deviate from the basic principles of the present invention and are intended to be within the scope of protection of the present invention.

[0118] Of course, it is preferred that the difference between the air pressure in the oven and the external atmospheric pressure is in the range of 5Pa to 100Pa. This setting can not only maintain a slightly positive pressure environment in the oven, reduce the oxygen content in the oven, and avoid oxidation of the pole piece's tab part in the oven, but also reduce the amount of protective gas used and reduce costs.

[0119] Preferably, the baking temperature in the oven is not less than 160°C. Keeping the baking temperature in the oven not less than 160°C, that is, maintaining a relatively high baking temperature in the oven, can quickly evaporate the water in the electrode, thereby improving the baking efficiency. In addition, the saturated water content of the shielding gas increases with increasing temperature. Keeping the baking temperature in the oven not less than 160°C can ensure that the shielding gas in the oven has a sufficiently strong ability to absorb moisture, thereby improving the drying efficiency and reducing the amount of shielding gas used.

[0120] Although the oven temperature is set to no less than 160°C in the preferred embodiment described above, this should not limit the scope of protection of the present invention. In actual applications, the oven temperature can be set to less than 160°C, for example, to 150°C or 140°C. Such adjustments and changes to the oven temperature do not deviate from the basic principles of the present invention and should be within the scope of protection of the present invention. Of course, it is preferred that the oven temperature be set to no less than 160°C to reduce costs and improve baking efficiency.

[0121] More preferably, the baking temperature in the oven is in the range of 160°C to 220°C.

[0122] The baking temperature in the oven is set between 160°C and 220°C, so that the baking temperature in the oven is not higher than 220°C. This can maintain a sufficiently high electrode drying speed, reduce energy waste, and lower the requirements for the oven's heating device.

[0123] Preferably, the electrode tape speed is not less than 60 m / min. Ensuring that the electrode tape speed is not less than 60 m / min enables rapid baking, shortens baking time, and reduces the size of the oven, thereby reducing costs.

[0124] Preferably, the baking time of the electrode is in the range of 0.5s to 30s, and the baking time of the electrode is negatively correlated with the baking temperature in the oven. It should be noted that the baking time of the electrode here specifically refers to the time required for one point of the electrode to pass through the oven.

[0125] The baking time of the electrode is between 0.5s and 30s, which is short, fast and efficient. For example, when the electrode tape speed is 60m / min and the baking temperature in the oven is 160°C, the baking time of the electrode is 15s. For example, when the electrode tape speed is 80m / min and the baking temperature in the oven is 220°C, the baking time of the electrode is 5s.

[0126] More preferably, the baking time of the electrode is in the range of 3s to 15s. This baking time range corresponds to a moderate electrode tape speed, stable electrode tape movement, short baking time, and high efficiency.

[0127] Preferably, the water content of the protective gas in the oven is not higher than 500g / m 3 .

[0128] The higher the water content of the protective gas, the lower its ability to absorb moisture. The water content of the protective gas in the oven should not exceed 500g / m 3 When the baking temperature is not lower than 160°C, the protective gas can have a strong ability to absorb moisture, thereby ensuring that the moisture on the electrode can be effectively removed and the baking quality can be guaranteed.

[0129] Preferably, the moisture content of the protective gas in the oven is in the range of 50 g / m 3 ~500g / m 3 .

[0130] The moisture content of the protective gas in the oven is controlled at 50g / m 3 ~500g / m 3 That is, the water content of the protective gas in the oven is not less than 50g / m 3 , which can not only make the protective gas in the oven have a strong enough ability to absorb moisture to ensure the baking quality and baking efficiency, but also save the amount of protective gas. That is, by filling a small amount of absolute dry protective gas (keeping a small protective gas flow rate), the protective gas in the oven can be kept in circulation, avoiding excessive consumption of protective gas and reducing costs.

[0131] Preferably, the electrode baking process of the present invention further comprises:

[0132] Real-time detection of the moisture content of the protective gas at the outlet of the oven.

[0133] Specifically, a high-temperature humidity sensor is provided at the pole piece outlet of the oven, and the high-temperature humidity sensor is used to detect the moisture content of the protective gas.

[0134] Determine the shielding gas flow rate based on the water content of the shielding gas.

[0135] Specifically, in actual applications, the controller stores a "Comparison Table of Moisture Content and Shielding Gas Flow Rate of Shielding Gas". After obtaining the moisture content of the shielding gas, the "Comparison Table of Moisture Content and Shielding Gas Flow Rate of Shielding Gas" can be used to directly query the shielding gas flow rate corresponding to the moisture content of the shielding gas, so that the shielding gas can be filled into the oven according to the determined shielding gas flow rate.

[0136] Among them, by baking the electrode at different baking temperatures, moisture content of the shielding gas and shielding gas flow rate, and testing the baked electrode, the appropriate baking temperature range and the correspondence between the shielding gas flow rate and the moisture content of the shielding gas in the baking temperature range are finally obtained, and the correspondence is made into a "Shielding Gas Moisture Content and Shielding Gas Flow Rate Comparison Table" and stored in the controller so that the shielding gas flow rate can be determined according to the moisture content of the shielding gas and the "Shielding Gas Moisture Content and Shielding Gas Flow Rate Comparison Table".

[0137] Fill the oven with protective gas according to the protective gas flow rate.

[0138] By real-time detection of the moisture content of the shielding gas at the outlet of the oven, the shielding gas flow rate is determined so that the shielding gas can be filled into the oven according to the shielding gas flow rate, thereby regulating the moisture content of the shielding gas in the oven to control the moisture content of the shielding gas within the set range. This control method can eliminate the impact of moisture content fluctuations in the incoming electrode on the humidity of the shielding gas in the oven, thereby ensuring the consistency of the dryness of the discharged electrode, and at the same time can reduce the amount of shielding gas used and reduce costs.

[0139] In addition, the present invention also provides a heat treatment device, which includes an oven and a controller, and the controller is configured to be able to perform the above-mentioned electrode baking process.

[0140] The following describes in detail the beneficial effects of the electrode baking process of the present invention through several specific embodiments. The surface density, rolling thickness, electrode width and electrode length of the following embodiments and comparative examples are the same.

[0141] It should be noted that although the following embodiments and comparative examples are described using negative electrode sheets as an example, this does not limit the scope of application of the electrode sheet baking process of the present invention. The electrode sheet baking process of the present invention is also applicable to baking positive electrode sheets.

[0142] Example 5:

[0143] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0144] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0145] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 50m 3 / h.

[0146] Example 6:

[0147] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0148] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 180°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 10s.

[0149] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 50m 3 / h.

[0150] Example 7:

[0151] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0152] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 220°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 3s.

[0153] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 50m 3 / h.

[0154] Example 8:

[0155] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0156] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 50g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0157] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 45m 3 / h.

[0158] Example 9:

[0159] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0160] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 300g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0161] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 52m 3 / h.

[0162] Example 10:

[0163] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0164] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 500g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0165] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 60m 3 / h.

[0166] Example 11:

[0167] The graphite negative electrode sheet is passed through an oven during the conveying process, so that the residual moisture on the graphite negative electrode sheet is removed during the process of passing through the oven, and the graphite negative electrode sheet is heated by infrared heating during the baking process.

[0168] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 99%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 7s.

[0169] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 55m 3 / h.

[0170] Example 12:

[0171] The graphite negative electrode sheet is passed through an oven during the conveying process, so that the residual moisture on the graphite negative electrode sheet is removed during the process of passing through the oven, and the graphite negative electrode sheet is heated by infrared heating during the baking process.

[0172] During the baking process, the protective gas filled in the oven is argon and helium, where argon and helium are mixed in a ratio of 10:1, and the volume proportion of the protective gas in the oven is 99%, and the water content of the protective gas in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 7s.

[0173] The difference between the pressure in the oven and the outside atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the amount of protective gas is 50m 3 / h.

[0174] Example 13:

[0175] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0176] During the baking process, the protective gas filled in the oven is argon, and the volume of argon in the oven accounts for 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0177] The difference between the pressure in the oven and the outside atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the amount of argon gas used is 49m 3 / h.

[0178] Example 14:

[0179] The graphite + silicon (10%) negative electrode sheet is passed through an oven during the conveying process, so that the residual moisture on the graphite + silicon (10%) negative electrode sheet is removed during the process of passing through the oven, and the graphite + silicon (10%) negative electrode sheet is heated by a hot roller during the baking process.

[0180] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of argon in the oven is 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite + silicon (10%) negative electrode sheet is 15s.

[0181] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 60m 3 / h.

[0182] Comparative Example 3:

[0183] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0184] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 95%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0185] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 48m 3 / h.

[0186] Comparative Example 4:

[0187] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0188] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 1000g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0189] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 40m 3 / h.

[0190] Comparative Example 5:

[0191] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0192] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 1000g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0193] The difference between the pressure in the oven and the outside atmospheric pressure is controlled at 150-200 Pa. Through testing and calculation, it is known that the nitrogen consumption is 300m 3 / h.

[0194] Comparative Example 6:

[0195] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0196] During the baking process, the oven is not filled with protective gas, the gas in the oven is air, and the water content of the air in the oven is 20g / m 3 The baking temperature in the oven is 160°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0197] Through testing and calculation, it is known that the air consumption is 500m 3 / h.

[0198] Comparative Example 7:

[0199] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0200] During the baking process, the oven is not filled with protective gas, the gas in the oven is air, and the water content of the air in the oven is 10g / m 3 The baking temperature in the oven is 130°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0201] Comparative Example 8:

[0202] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0203] During the baking process, the oven is not filled with protective gas, the gas in the oven is air, and the water content of the air in the oven is 10g / m 3 The baking temperature in the oven is 130°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 60s.

[0204] Comparative Example 9:

[0205] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0206] During the baking process, the oven is not filled with protective gas, the gas in the oven is air, and the water content of the air in the oven is 10g / m 3 The baking temperature in the oven is 100°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 600s.

[0207] Comparative Example 10:

[0208] The graphite negative electrode sheet is passed through an oven during the conveying process to remove the residual moisture on the graphite negative electrode sheet during the process of passing through the oven. The graphite negative electrode sheet is heated by a hot roller during the baking process.

[0209] During the baking process, the protective gas filled in the oven is nitrogen, and the volume proportion of nitrogen in the oven is 98%, and the water content of nitrogen in the oven is 100g / m 3 The baking temperature in the oven is 130°C (hot roller temperature), and the baking time of the graphite negative electrode sheet is 15s.

[0210] The difference between the pressure in the oven and the external atmospheric pressure is controlled at 5-100 Pa. Through testing and calculation, it is known that the nitrogen consumption is 50m 3 / h.

[0211] Test Example 1

[0212] The electrodes obtained after baking in the above-mentioned Examples 5-14 and Comparative Examples 3-10 were tested and observed to detect the moisture content of the electrodes and whether there was oxidation in the tab area of ​​the electrodes. The test results are shown in Table 2.

[0213] Table 2 Pole performance test data

[0214] It can be seen from the experimental data in Table 2 that the moisture content of the negative electrode plates prepared in Examples 5 to 14 is less than 110 ppm, which is much lower than the 200 ppm required for the plates of lithium batteries, and there is no oxidation in the tab area. Therefore, the moisture content of the plates obtained by baking using the pole plate baking process of the present invention is low, which is convenient for controlling the baking effect, and the protective gas can protect the tabs from oxidation during the baking process.

[0215] By comparing Examples 5 to 7, Example 11 and Comparative Example 3, it can be seen that only the tab area of ​​the negative electrode of Comparative Example 3 has a slight oxidation phenomenon. It can be seen that when the proportion of protective gas is 95% and the electrode is baked at a temperature of 160°C, oxidation of the tab area will be caused, thereby affecting the performance of the lithium battery. Only when the proportion of protective gas in the oven is not less than 98% can the tab be better protected from oxidation. Therefore, the present invention preferably makes the proportion of protective gas in the oven not less than 98%.

[0216] By comparing Examples 5 to 7 with Comparative Example 10, it can be seen that the water content of the negative electrode sheet of Comparative Example 10 is much higher than that of the negative electrode sheets of Examples 5 to 7, and does not meet the standards of lithium batteries. Therefore, it can be seen that only when the baking temperature is controlled above 160°C can the electrode sheet be dried relatively quickly, the baking quality of the electrode sheet be better controlled, and the baking effect of the electrode sheet be ensured while improving the baking efficiency. Therefore, the present invention preferably makes the baking temperature not less than 160°C.

[0217] Comparing Examples 5, 8 to 10 and Comparative Example 4, it can be seen that the water content of the negative electrode sheet of Comparative Example 4 is much higher than that of the negative electrode sheets of Examples 5, 8 to 10, and slightly higher than the water content requirement of the lithium battery for the electrode sheet. Therefore, it can be seen that only by controlling the humidity of the protective gas in the oven at 500g / m 3 The following is the best way to better control the baking quality of the electrode. Therefore, the present invention preferably makes the water content of the protective gas in the oven no higher than 500g / m 3 In addition, the humidity in the oven is controlled at 50g / m 3 ~500g / m 3 The use of absolute dry shielding gas can be reduced, thereby reducing costs.

[0218] Comparing Examples 5 to 14 with Comparative Example 5, it can be seen that the amount of protective gas used in Comparative Example 5 is 300m 3 / h, which is much higher than the dosage in the embodiment, while the dosage in the embodiment is basically maintained at 40-60m 3 / h. It can be seen that when the pressure difference between the air pressure in the oven and the external atmospheric pressure is too large, the amount of protective gas used will be greatly increased. Therefore, the present invention preferably makes the air pressure in the oven 5 to 100 Pa higher than the external atmospheric pressure in order to reduce costs.

[0219] By comparing Examples 5 to 14 with Comparative Examples 6 to 9, it can be seen that the tab areas of the negative electrode plates of Comparative Examples 6 to 9 all have oxidation phenomena. This shows that direct drying in air can easily cause oxidation, and thus protective gas must be used to protect the plate to enable the plate to maintain good performance.

[0220] Test Example 2

[0221] The negative electrode sheets obtained in the above Examples 5-14 and Comparative Examples 3-10 were respectively wound with the same positive electrode sheets to make lithium batteries, and the battery performance of the prepared lithium batteries was tested. The test results are shown in Table 3.

[0222] Among them, the battery first efficiency = discharge capacity in the second step of capacity division ÷ (formation charge capacity + charge capacity in the first step of capacity division), battery capacity = formation charge capacity + charge capacity in the first step of capacity division.

[0223] Table 3 Battery performance test data

[0224] It can be seen from the experimental data in Table 3 that the first efficiency of the lithium batteries prepared using the negative electrode sheets obtained by baking in Examples 5 to 14 is maintained at 89% to 90%, and the battery capacity is between 2980 and 3050 mAh, and the battery performance is stable and good; while the first efficiency of the lithium batteries prepared using the negative electrode sheets obtained in the comparative examples is lower than that of the lithium batteries prepared using the negative electrode sheets of the examples, and the battery capacity is also lower than that of the lithium batteries prepared using the negative electrode sheets of the examples.

[0225] Furthermore, the performance of the pole piece baked by the pole piece baking process of the present invention is stable, and the performance of the lithium battery produced therefrom is stable and easy to control. In addition, during the baking process, it is preferred that the volume proportion of the protective gas in the oven is ≥98%, the baking temperature in the oven is preferably ≥160°C, and most preferably the baking temperature in the oven is 160-220°C to save energy; it is preferred that the water content of the protective gas in the oven is ≤500g / m 3 It is most preferred to make the water content of the protective gas in the oven 50-500g / m 3 , in order to reduce the amount of protective gas used and reduce costs.

[0226] In summary, the heat treatment method of the electrode of the present invention realizes the uncoiling baking of the electrode, which can effectively shorten the baking time of the electrode, improve the baking efficiency and enhance the baking quality; in addition, the electrode baked by the heat treatment method of the present invention has a low water content, the water content of different electrode areas is close, and the performance is good, and the lithium battery produced thereby has good battery performance.

[0227] Thus far, the technical solutions of the present invention have been described in conjunction with preferred embodiments. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is clearly not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A heat treatment process for a pole piece, characterized in that: The heat treatment process comprises the following steps: The pole piece is placed in a heat treatment device for heat treatment.

2. The heat treatment process of the pole piece according to claim 1, characterized in that: The heat treatment time is 0.5 to 20 seconds, and the heat treatment temperature is 150 to 250°C.

3. The heat treatment process of the pole piece according to claim 2, characterized in that: The heat treatment equipment is a hot roller heating equipment, and the heat treatment time is 5 to 20 seconds.

4. The heat treatment process of the pole piece according to claim 2, characterized in that: The heat treatment equipment is an induction heating equipment, the heat treatment temperature is 180-250° C., and the heat treatment time is 0.5-2 s.

5. The heat treatment process of the pole piece according to claim 2, characterized in that: The heat treatment equipment is an infrared heating equipment, the heat treatment temperature is 180-250° C., and the heat treatment time is 2-10 seconds.

6. The heat treatment process of the pole piece according to claim 1, characterized in that: The electrode sheet is a positive electrode sheet, and the positive electrode sheet includes aluminum foil, and the weight ratio of each component of the aluminum foil is: Si: 0.1-0.7 parts; Fe: 1.1-1.4 parts; Sr: 0.01-0.03 parts; A1: 97.8 to 98.8 parts.

7. The heat treatment process of the pole piece according to claim 6, characterized in that: The thickness of the aluminum foil is 4-15 um.

8. The heat treatment process of the pole piece according to claim 6, characterized in that: The elongation of the aluminum foil is greater than 2.5%.

9. The heat treatment process of the pole piece according to claim 1, characterized in that: The heat treatment process includes a pole piece baking process, and the pole piece baking process is used to remove residual moisture on the pole piece when the pole piece passes through the heat treatment equipment in a belt-walking manner.

10. The heat treatment process of the pole piece according to claim 9, characterized in that: The heat treatment equipment includes an oven, and the pole piece baking process includes: Filling the oven with protective gas and the volume proportion of the protective gas is not less than 98%; The gas pressure in the oven is controlled to be higher than the external atmospheric pressure.

11. The heat treatment process of the pole piece according to claim 10, characterized in that: The difference between the air pressure in the oven and the external atmospheric pressure is in the range of 5 Pa to 100 Pa; And / or, the protective gas is a combination of one or more of nitrogen, argon and helium.

12. The heat treatment process of the pole piece according to claim 10, characterized in that: The baking temperature in the oven is not less than 160°C.

13. The heat treatment process of the pole piece according to claim 12, characterized in that: The baking temperature in the oven ranges from 160°C to 220°C.

14. The heat treatment process of the pole piece according to claim 13, characterized in that: The pole piece's tape running speed is no less than 60 m / min.

15. The heat treatment process of the pole piece according to claim 14, characterized in that: The baking time of the pole piece is in the range of 0.5s to 30s, and the baking time of the pole piece is negatively correlated with the baking temperature in the oven.

16. The heat treatment process of the pole piece according to claim 10, characterized in that: The water content of the protective gas in the oven is not higher than 500g / m 3 .

17. The thermal treatment process of the pole piece according to claim 16, characterized in that: The moisture content of the protective gas in the oven is in the range of 50 g / m 3 ~500g / m 3 .

18. The heat treatment process of a pole piece according to any one of claims 10 to 17, characterized in that: The pole piece baking process also includes: Real-time detection of the water content of the protective gas at the outlet of the oven; Determining the flow rate of the protective gas according to the water content of the protective gas; The protective gas is filled into the oven according to the protective gas flow rate.

19. A heat treatment device, characterized in that: The heat treatment equipment comprises an oven and a controller, and the controller is configured to be able to perform the pole piece baking process according to any one of claims 10 to 18.

20. An aluminum foil, characterized in that: The aluminum foil is the aluminum foil contained in the pole piece obtained by the heat treatment process of the pole piece according to any one of claims 1 to 8.

21. A positive electrode sheet, characterized in that: The positive electrode plate is a positive electrode plate obtained by the heat treatment process of the electrode plate according to any one of claims 1 to 8.

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