Electrode sheet preparation method, electrode sheet, battery, and electric device

Abstract

The present application relates to the technical field of batteries, and in particular to an electrode sheet preparation method, an electrode sheet, a battery, and an electric device. The electrode sheet preparation method comprises: preparing on at least one side of a current collector an active layer containing an active substance and a binder; heating the active layer to heat the surface layer of the active layer to a heating temperature; and performing heat preservation on the active layer to enable the surface layer of the active layer to be at a heat preservation temperature, wherein the heating temperature and the heat preservation temperature are each independently greater than or equal to a melting point or softening point of the binder, and less than a decomposition temperature of the binder. By using the method of the present application to prepare an electrode sheet, a battery using the electrode sheet can have good cycle performance.

Description

Preparation method of pole piece, pole piece, battery, and electrical device Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a method for preparing a pole piece, a pole piece, a battery, and an electrical device. Background Art

[0002] As batteries are used in more and more scenarios, the market is placing increasingly higher demands on various battery performances. Battery life is one of the key performance indicators that affects the user experience of various electrical devices. Therefore, extending battery life is the key to promoting further development of batteries.

[0003] Electrodes, as crucial components of batteries, have a critical impact on battery life. Therefore, battery life can be improved by improving electrodes. However, during battery cycling, electrodes often degrade, leading to poor cycling performance and, in turn, shortened battery life.

[0004] Summary of the Invention

[0005] In view of the above problems, the present application provides a method for preparing a pole piece, a pole piece, a battery, and an electrical device, which can solve the problem of poor battery cycle performance.

[0006] In a first aspect, the present application provides a method for preparing a pole piece, comprising:

[0007] preparing an active layer comprising an active material and a binder on at least one side of the current collector;

[0008] Heating the active layer to raise the surface temperature of the active layer to a heating temperature;

[0009] Performing heat preservation treatment on the active layer so that the surface of the active layer is at a heat preservation temperature;

[0010] The heating temperature and the holding temperature are independently greater than or equal to the melting point or softening point of the binder, and less than the decomposition temperature of the binder.

[0011] The use of the method of the embodiment of the present application to prepare the electrode sheet can make the battery using the electrode sheet have good cycle performance, which is mainly due to:

[0012] (1) In the preparation method of the embodiment of the present application, the active layer is subjected to a heat treatment to raise the surface temperature of the active layer to or above the melting point or softening point of the binder, thereby causing the binder to become molten or softened. At the same time, heat preservation treatment is carried out at a temperature within the same range, which can promote the re-mobilization of the binder molecular chains in the molten or softened state, thereby facilitating the uniform distribution of the binder in the active layer, facilitating the release of stress within the electrode, and increasing the cohesion and adhesion of the electrode, ultimately improving the cycle performance of the battery.

[0013] (2) The redistribution of the binder includes the infiltration of the binder on the surface of the active layer into the interior of the active layer, which is beneficial to reducing the binder on the surface of the active layer, thereby helping to increase the porosity of the surface of the active layer, accelerating the absorption rate of the electrode for the electrolyte, and making the electrode fully contact with the electrolyte, thereby effectively participating in the electrochemical reaction, reducing the internal resistance of the battery during the charge and discharge cycle, and thus improving the cycle performance of the battery.

[0014] (3) The temperature during heating and heat preservation is lower than the decomposition temperature of the binder. The binder will not decompose (ablate) during heating and heat preservation, which is beneficial to maintaining the total amount of binder in the active layer and improving the cohesion and adhesion of the electrode. At the same time, the active material will not be affected by the decomposition products of the binder during heating and heat preservation, which is further beneficial to improving the cycle performance of the battery.

[0015] (4) During the heating and insulation process, the moisture and residual impurities adsorbed in the active layer volatilize, which helps to reduce the reaction between the moisture in the electrode and the lithium salt in the electrolyte, thereby improving the interface stability of the electrode and improving the battery cycle performance.

[0016] In some embodiments, the heating temperature and the holding temperature are independently less than or equal to the average of the melting point or softening point of the binder and the decomposition temperature of the binder. This prevents the binder from decomposing (ablating) during both the heating and holding processes, which helps maintain the total amount of binder in the active layer, improves the cohesion and adhesion of the electrode, and prevents binder decomposition residues from affecting the active material. Furthermore, at this temperature, the binder can maintain a high viscosity and a moderate flow rate, which helps maintain the stability of the electrode structure.

[0017] In some embodiments, the heat preservation treatment time is greater than or equal to 0.1s, and optionally 0.1 to 2.5s. After a certain period of heat preservation, the adhesive in a molten or softened state on the surface has enough time to penetrate into the interior of the active layer, thereby balancing the distribution of the adhesive in the active layer.

[0018] In some embodiments, the holding temperature is less than or equal to the heating temperature. The holding temperature is equal to or lower than the heating temperature, which not only maintains the binder in a melted or softened state, making the binder in a flowable state with a high viscosity, but also prevents the binder from flowing too much, thereby maintaining the stability of the electrode structure and preventing powder loss.

[0019] In some embodiments, the melting point or softening point of the binder is 140-180°C, and the decomposition temperature of the binder is 300-350°C. The heating temperature and the holding temperature are independently 170-230°C, and optionally 190-230°C. The heating temperature and holding temperature can be set within an appropriate range for different binders. Within the above heating and holding temperature ranges, the binder melts or softens without decomposition, and the active material is free of binder residue interference, which is beneficial for maintaining the structural and performance stability of the active material.

[0020] In some embodiments, the active material includes lithium nickel cobalt manganese oxide; optionally, the molar ratio of Ni, Co, and Mn in the lithium nickel cobalt manganese oxide is (1-8):(1-2):(1-3). The method of the embodiment of the present application can be used to prepare different lithium nickel cobalt manganese oxide positive electrode sheets. The stability of the lithium nickel cobalt manganese oxide can be maintained during the preparation process, and the resulting battery has excellent cycle performance.

[0021] In some embodiments, the number average molecular weight of the binder is (35-150)×10 4 , optionally (45~150)×10 4 Generally, the melting point or softening point of the binder is generally related to its molecular weight. Within this number average molecular weight range, the binder has a lower melting point or softening point, which helps to implement the heating and heat preservation steps of the embodiment of the present application at low temperatures.

[0022] In some embodiments, the heating treatment and the heat preservation treatment each independently include laser irradiation. Laser as a heating source offers high energy density and heating efficiency within a short time, enabling rapid heating of the active layer to the desired temperature. Laser irradiation also features controllable power, wavelength, and stability, effectively controlling the active layer temperature within a desired range.

[0023] In some embodiments, the laser comprises one or more of an infrared laser and a near-infrared laser. Optionally, the laser has a wavelength of 1000 nm to 15 μm. The pole piece has strong absorption of infrared and near-infrared light. Irradiation with laser light in this wavelength range has high photothermal conversion efficiency, allowing the active layer to be heated to the desired temperature in a short period of time.

[0024] In some embodiments, the laser power in the heat treatment step is 2000-4500 W, and optionally 2000-4000 W. Heating under high-power laser is beneficial for rapidly increasing the temperature of the active layer.

[0025] In some embodiments, the laser power in the heat preservation step is 80-200 W, optionally 100-150 W. Heat preservation treatment under low-power laser can maintain the surface temperature of the active layer within a desired temperature range without overheating.

[0026] In some embodiments, the electrode sheet preparation method further includes a step of compacting the electrode sheet after the insulation treatment. During the heating and insulation steps, the binder in the active layer is redistributed, and the moisture and impurities absorbed in the active layer evaporate, which may cause the electrode sheet thickness to change. Therefore, performing a compaction process after the insulation treatment facilitates control of the electrode sheet thickness, for example, ensuring that the electrode sheet thickness is consistent before and after the heating and insulation treatments.

[0027] In a second aspect, the present application provides a pole piece, which is obtained according to the preparation method of the first aspect.

[0028] In the electrode of the embodiment of the present application, the binder is evenly distributed, so that the electrode has high bonding strength, high porosity, and low water content. It can still maintain good structural stability after long-term charge and discharge cycles, which is beneficial to improving the cycle performance of the battery using the electrode.

[0029] In a third aspect, the present application provides a battery, comprising the electrode described in the second aspect.

[0030] The above-mentioned pole piece has high bonding force, high porosity, low water content, and good structural stability. The battery containing the pole piece will also show good cycle performance and long battery life.

[0031] In a fourth aspect, the present application provides an electrical device, which includes the battery described in the third aspect.

[0032] The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as power sources, or in various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The battery exhibits advantages such as good cycle performance and long lifespan. Therefore, its application in various electrical devices can improve the user experience of these devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0035] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0036] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0037] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0038] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0039] FIG6 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application;

[0040] FIG7 shows the cycle performance test results of the lithium-ion batteries in Example 1 and Comparative Example 1 of the present application;

[0041] FIG8 is an XRD pattern of the lithium nickel cobalt manganese oxide positive electrode sheet of Example 1 of the present application before and after heating treatment and heat preservation treatment;

[0042] FIG9 is an SEM image of the lithium nickel cobalt manganese oxide positive electrode sheet of Example 1 of the present application before and after heating treatment and heat preservation treatment;

[0043] In FIG8 and FIG9, "before treatment" refers to before the heating treatment and the heat-keeping treatment, and "after treatment" refers to after the heating treatment and the heat-keeping treatment.

[0044] Reference numerals:

[0045] 01-shell, 02-cover, 03-electrode assembly, 04-battery cell, 05-battery module, 06-upper box, 07-lower box. DETAILED DESCRIPTION

[0046] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0048] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0049] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0050] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0051] In the description of the embodiments of the present application, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0052] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0053] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0054] Electrodes, as an important component of batteries, have a critical impact on battery life. However, during battery cycling, electrodes often experience performance degradation, resulting in poor battery cycle performance.

[0055] Important components of the electrode include active materials, binders, etc., which have an important influence on the performance of the electrode. For example, lithium nickel cobalt manganese oxide, as a relatively excellent lithium-ion battery positive electrode active material, has been widely used in passenger cars, commercial vehicles and other power fields in recent years. Compared with lithium iron phosphate materials, lithium-ion batteries using lithium nickel cobalt manganese oxide as the positive electrode have greater energy density and better fast charging and low-temperature performance. However, in practice, it is found that due to the influence of the synthesis process, for example, in the process of synthesizing lithium nickel cobalt manganese oxide, an excess of lithium source is usually used, resulting in lithium nickel cobalt manganese oxide containing a lot of residual alkali, such as lithium oxide, lithium carbonate, etc. The presence of residual alkali makes lithium nickel cobalt manganese oxide easy to absorb moisture in the air. After being assembled into a secondary battery, this moisture reacts with the lithium salt in the electrolyte, causing the battery to produce gas and deteriorate the battery cycle performance.

[0056] At the same time, after the active material and binder are made into the active layer of the electrode, there are often phenomena such as poor binder distribution, uneven porosity distribution or too low porosity, which also affect the battery cycle performance.

[0057] In order to improve the cycle performance of batteries, related technologies have studied a variety of technical means. For example, by forming a coating layer on the surface of the active material, the interfacial interaction of the active material during the battery cycle is improved, thereby improving the battery cycle performance. However, the presence of the coating layer may be detrimental to the electronic or ion conductivity of the electrode, thereby causing the internal resistance of the battery to be high and reducing the battery cycle performance. For another example, by preparing the electrode by means of radiation irradiation, the aging problem of the binder in the electrode is reduced, the stability of the electrode is improved, and the effect of improving the battery cycle performance is achieved. However, radiation irradiation will cause the crystal form of the active material to be distorted, and the organic matter in the electrode will react to form residual free radicals during the irradiation process, thereby deteriorating the electrode capacity and making it difficult to effectively improve the battery cycle performance.

[0058] To solve the above problems, the embodiments of the present application heat and keep the electrode insulated during the electrode preparation process, and control the heating temperature and the insulation temperature within a certain range, thereby improving the structure of the electrode, including balancing the distribution of the binder in the electrode, improving the porosity of the electrode, reducing the moisture content of the electrode, etc., and maintaining the stability of the active material, thereby improving the battery cycle performance.

[0059] The electrodes processed by the above method can be used to make batteries, and then used in various electrical devices, including but not limited to mobile phones, tablets, laptops, electric toys, electric tools, electric vehicles, electric cars, ships, spacecraft, etc.

[0060] The present application will be further described below with reference to the following examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0061]

Pole piece preparation method

[0062] A first aspect of an embodiment of the present application provides a method for preparing a pole piece, comprising:

[0063] preparing an active layer comprising an active material and a binder on at least one side of the current collector;

[0064] The active layer is subjected to a heating treatment so that the surface temperature of the active layer is raised to a heating temperature;

[0065] Performing insulation treatment on the active layer to keep the surface of the active layer at an insulation temperature;

[0066] The heating temperature and the holding temperature are independently greater than or equal to the melting point or softening point of the binder, and less than the decomposition temperature of the binder.

[0067] In the electrode preparation method of the present embodiment, the surface layer of the active layer refers to the outermost layer of the active layer that contacts the outside world. Typically, an electrode comprises a current collector and an active layer disposed on at least one side of the current collector. Therefore, the surface layer of the active layer is typically also the surface layer of the electrode. Generally, the area within 40% of the electrode thickness along the thickness of the electrode, from the outside inward, can be considered the surface layer of the electrode.

[0068] The softening point is the temperature at which the three-dimensional long-range order of the macromolecular chain structure of an amorphous polymer transitions to a disordered viscous flow state. The melting point is the temperature at which the three-dimensional long-range order of the macromolecular chain structure of a crystalline polymer transitions to a disordered viscous flow state, and is the lower limit of the molding and processing temperature for crystalline polymers. Generally, the melting point range is relatively narrow, while the softening point range is relatively wide. The decomposition temperature refers to the temperature at which, when the temperature of a polymer in a viscous flow state is further increased, the degradation of the polymer chain will be accelerated, and even significant degradation of the polymer chain will occur.

[0069] The use of the method of the embodiment of the present application to prepare the electrode sheet can make the battery using the electrode sheet have good cycle performance, which is mainly due to:

[0070] (1) In the preparation method of the embodiment of the present application, the active layer is subjected to a heat treatment to raise the surface temperature of the active layer to or above the melting point or softening point of the binder, thereby causing the binder to become molten or softened. At the same time, heat preservation treatment is carried out at a temperature within the same range, which can promote the re-mobilization of the binder molecular chains in the molten or softened state, thereby facilitating the uniform distribution of the binder in the active layer, facilitating the release of stress within the electrode, and increasing the cohesion and adhesion of the electrode, ultimately improving the cycle performance of the battery.

[0071] (2) The redistribution of the binder includes the infiltration of the binder on the surface of the active layer into the interior of the active layer, which is beneficial to reducing the binder on the surface of the active layer, thereby helping to increase the porosity of the surface of the active layer, accelerating the absorption rate of the electrode for the electrolyte, and making the electrode fully contact with the electrolyte, thereby effectively participating in the electrochemical reaction, reducing the internal resistance of the battery during the charge and discharge cycle, and thus improving the cycle performance of the battery.

[0072] (3) The temperature during heating and heat preservation is lower than the decomposition temperature of the binder. The binder will not decompose (ablate) during heating and heat preservation, which is beneficial to maintaining the total amount of binder in the active layer and improving the cohesion and adhesion of the electrode. At the same time, the active material will not be affected by the decomposition products of the binder during heating and heat preservation, which is further beneficial to improving the cycle performance of the battery.

[0073] (4) During the heating and insulation process, the moisture and residual impurities adsorbed in the active layer volatilize, which helps to reduce the reaction between the moisture in the electrode and the lithium salt in the electrolyte, thereby improving the interface stability of the electrode and improving the battery cycle performance.

[0074] In some embodiments, the heating temperature and the holding temperature are independently less than or equal to the average of the melting point or softening point of the binder and the decomposition temperature of the binder. This prevents the binder from decomposing (ablating) during both the heating and holding processes, which helps maintain the total amount of binder in the active layer, improves the cohesion and adhesion of the electrode, and prevents binder decomposition residues from affecting the active material. Furthermore, at this temperature, the binder can maintain a high viscosity and a moderate flow rate, which helps maintain the stability of the electrode structure.

[0075] In some embodiments, the holding time is greater than or equal to 0.1s, and may optionally be 0.1-2.5s, for example, any of 0.1s, 0.2s, 0.4s, 0.6s, 0.8s, 1s, 1.2s, 1.4s, 1.6s, 1.8s, 2s, 2.2s, and 2.5s, or a range therebetween. The holding time allows the molten or softened binder on the surface sufficient time to penetrate into the active layer, thereby balancing the distribution of the binder within the active layer.

[0076] In some embodiments, the heating treatment time is 0.05 to 0.3 s, for example, any one of 0.05 s, 0.1 s, 0.15 s, 0.2 s, 0.25 s, and 0.3 s, or a range of values ​​between any two of them. The heating treatment time is the time it takes for the surface layer of the active layer to heat up to the heating temperature. The heating rate affects the uniformity of the material. The embodiment of the present application can rapidly heat up to quickly transform the binder on the surface of the active layer from a solid state to a molten or softened state; at the same time, it is also beneficial for heat to be quickly transferred to the interior of the active layer, causing the binder inside the active layer to quickly melt or soften, thereby forming a whole with the binder on the surface, and promoting uniform distribution of the binder in the active layer.

[0077] In some embodiments, the holding temperature is less than or equal to the heating temperature. Optionally, the holding temperature is less than the heating temperature. The holding temperature being equal to or lower than the heating temperature not only maintains the binder in a melted or softened state, allowing the binder to be in a flowable state with a relatively high viscosity, but also prevents the binder from flowing excessively, thereby facilitating the stability of the electrode structure and preventing powder loss.

[0078] In some embodiments, the melting point or softening point of the binder is 140-180°C, and the decomposition temperature of the binder is 300-350°C. The heating temperature and the holding temperature are independently 170-230°C, and optionally 190-230°C, for example, any one of 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, and 230°C, or any range therebetween. Alternatively, the heating temperature can be set at 180-230°C, and the holding temperature can be set at 180-200°C.

[0079] The heating and holding temperatures can be measured using an infrared thermometer or other temperature measuring instrument. The heating and holding temperatures can be set within appropriate ranges for different binders. Within these ranges, the binder melts or softens without decomposing, eliminating any binder residue from interfering with the active material and maintaining the structural and performance stability of the active material.

[0080] In some embodiments, the active material includes lithium nickel cobalt manganese oxide; optionally, the molar ratio of Ni, Co, and Mn in the lithium nickel cobalt manganese oxide is (1-8): (1-2): (1-3), for example, any one of 8:1:1, 8:1.5:0.5, 6:2:2, 5:2:3, 5:3:2, and 1:1:1, or a range between any two thereof. The method of the embodiment of the present application can be used to prepare different lithium nickel cobalt manganese oxide positive electrode sheets, and the stability of the lithium nickel cobalt manganese oxide can be maintained during the preparation process, and the resulting battery has excellent cycle performance.

[0081] In some embodiments, the melting point or softening point of the binder is 140-180°C, optionally 150-180°C, for example, any one of 140°C, 150°C, 160°C, 170°C, and 180°C, or a range therebetween. By using a binder with a low melting point or low softening point, the binder can be melted or softened by heating and holding the active layer at a relatively low temperature, thereby achieving redistribution of the binder. This helps lower the temperature during the heating and holding process, thereby reducing the probability of structural damage to the lithium nickel cobalt manganese oxide, and thereby improving the cycling stability of the electrode.

[0082] In some embodiments, the decomposition temperature of the binder is 300-350°C, optionally 300-320°C, for example, any one of 3000°C, 310°C, 320°C, 330°C, 340°C, and 350°C, or a range therebetween. Both the heating and holding temperatures are lower than the decomposition temperature of the binder. Heating and holding the active layer below the decomposition temperature can melt or soften the binder, thereby redistributing the binder, and can also reduce the probability of structural damage to the lithium nickel cobalt manganese oxide, thereby improving the cycling stability of the electrode.

[0083] In some embodiments, the number average molecular weight of the binder can be set to (35-150)×10 4 , optionally (45~150)×10 4 , for example 35×10 4 , 40×10 4 , 45×10 4 , 50×10 4 , 60×10 4 , 70×10 4 ,80×10 4 ,90×10 4 , 100×10 4 , 120×10 4 , 140×10 4 , 150×10 4Any point value in or the range value between any two of them. The number average molecular weight is a way to characterize molecular size, which is the total weight of all molecules in a polymer sample divided by the total number of molecules. Gel chromatography (GPC) can be used to test the number average molecular weight of the binder using polystyrene (PS) as a standard. Generally, the melting point or softening point of the binder usually has a certain relationship with its molecular weight. Within this number average molecular weight range, the binder has a lower melting point or softening point, which helps to implement the heating and insulation steps of the embodiments of the present application at low temperatures.

[0084] As an example, the binder may include one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, and optionally polyvinylidene fluoride.

[0085] In some embodiments, the active layer further includes a conductive agent, which includes one or more of conductive carbon black, carbon nanotubes, and graphene. This conductive agent can transfer heat from the surface of the active layer to the interior of the active layer via electrons, thereby uniformly heating the positive electrode sheet and promoting uniform distribution of the binder throughout the active layer.

[0086] The mass content of each substance in the active layer can be set as needed.

[0087] For example, the mass content of the active substance in the active layer may include but is not limited to 90% to 98%, such as 95% to 98%, for example, any one of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or a range between any two of them.

[0088] The mass content of the binder and the conductive agent in the active layer can independently include but are not limited to 0.5% to 5%, such as 1% to 5%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of them.

[0089] In some embodiments, the heating treatment and the heat preservation treatment each independently include laser irradiation treatment.

[0090] Laser irradiation uses a laser to generate and irradiate a laser beam. Laser heating offers high energy density and efficiency within a short timeframe, rapidly heating the active layer to the desired temperature. Laser irradiation also features controllable power and wavelength, along with high stability, effectively maintaining the active layer temperature within the desired range.

[0091] Both the heating treatment and the heat preservation treatment are performed by laser irradiation. In actual operation, at least one set of lasers can be used to heat the active layer, and at least another set of lasers can be used to hold the active layer. During the heating treatment or the heat preservation treatment, lasers can be provided on one or both sides of the pole piece, optionally on both sides of the pole piece, to heat and hold the two surface layers of the active layer.

[0092] In some embodiments, the laser comprises one or more of an infrared wavelength laser and a near-infrared wavelength laser. Optionally, the wavelength of the laser is 1000 nm to 15 μm, optionally 1000 to 3000 nm, for example, any one of 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, 2200 nm, 2400 nm, 2600 nm, 2800 nm, 3000 nm, 5000 nm, 1 μm, 5 μm, 10 μm, and 15 μm, or a range of values ​​between any two of them. The laser wavelength is mainly related to the type of laser excitation medium, so different laser wavelengths can be obtained by selecting different laser excitation media. Infrared wavelength laser refers to a laser with a wavelength of 0.76 to 100 μm, and near-infrared wavelength laser refers to a laser with a wavelength of 780 to 3000 nm. The electrode has strong absorption of infrared light and near-infrared light. When irradiated with laser in this wavelength range, it has high photothermal conversion efficiency and can heat the active layer to the required temperature in a short time.

[0093] In some embodiments, the laser generating the laser includes one or more of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, an ytterbium-doped yttrium aluminum garnet (Yb:YAG) laser, a fiber laser, a CO2 laser, and an antimony arsenide laser. These lasers can generate infrared or near-infrared wavelength lasers. For example, an Nd:YAG laser can emit a laser with a wavelength of 1064 nm, a Yb:YAG laser can emit a laser with a wavelength of 1030 nm, and a fiber laser can emit a laser with a wavelength of 1080 nm.

[0094] In some embodiments, the laser power during the heat treatment step is 2000-4500 W, optionally 2000-4000 W, for example, any one of 2000 W, 2200 W, 2400 W, 2600 W, 2800 W, 3000 W, 3200 W, 3400 W, 3600 W, 3800 W, 4000 W, 4200 W, or 4500 W, or any range therebetween. The laser power can be set directly in the laser. Heating under high-power laser light facilitates rapid heating of the active layer.

[0095] In some embodiments, the laser power during the heat preservation step is 80-200 W, optionally 100-150 W, for example, any one of 80 W, 100 W, 120 W, 140 W, 150 W, 160 W, 180 W, and 200 W, or any range therebetween. Heat preservation at low laser power can maintain the surface temperature of the active layer within a desired temperature range without overheating.

[0096] In some embodiments, the heating treatment step and the heat preservation treatment step each independently include a step of moving the pole piece relative to the laser. Optionally, the movement speed is 20 to 200 m / min, and more optionally 20 to 60 m / min, for example, it can be any point value of 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, 70 m / min, 80 m / min, 90 m / min, 100 m / min, 120 m / min, 140 m / min, 160 m / min, 180 m / min, 200 m / min or a range value between any two of them. In the preparation method of the embodiment of the present application, the heating treatment and the heat preservation treatment can be in dynamic state, the pole piece moves relative to the laser, and the laser performs a short heating treatment and a short heat preservation treatment on the pole piece, which can increase the temperature of the active layer, reduce heat accumulation, and reduce unnecessary side reactions.

[0097] In some embodiments, the laser irradiation treatment includes one or both of pulsed laser irradiation and continuous laser irradiation. Pulsed laser refers to a single light pulse emitted by a laser operating in a pulsed mode, with a certain interval between two adjacent light pulses. Continuous laser, on the other hand, is continuous, uninterrupted laser light emitted by a continuous laser. Whether pulsed or continuous laser irradiation is used, the active layer can reach the desired temperature in a short period of time and be maintained at the desired temperature.

[0098] In some embodiments, the method for preparing the electrode further includes the step of compacting the electrode after the insulation treatment. During the heating treatment step and the insulation treatment step, the binder in the active layer is redistributed, and at the same time, the moisture and impurities absorbed in the active layer are volatilized, which may cause the thickness of the electrode to change. Therefore, after the insulation treatment, compaction treatment is carried out to achieve control of the thickness of the electrode, for example, the thickness of the electrode can be made consistent before and after the heating and insulation treatment. The compaction treatment can be carried out at room temperature or at a high temperature. For example, the temperature of the compaction treatment can be 25 to 130°C, such as any one of 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 130°C, or any range between two of them.

[0099] In addition, in the preparation method of the electrode, the preparation method of the active layer containing active material and binder can be carried out according to the following steps: mixing the active material, binder and solvent to obtain slurry; coating the slurry on at least one surface of the current collector, drying and compacting to obtain the active layer.

[0100]

Pole piece

[0101] A second aspect of an embodiment of the present application provides a pole piece, which is obtained according to the preparation method of the first aspect mentioned above.

[0102] In the electrode of the embodiment of the present application, the binder is evenly distributed, so that the electrode has high bonding strength, high porosity, and low water content. It can still maintain good structural stability after long-term charge and discharge cycles, which is beneficial to improving the cycle performance of the battery using the electrode.

[0103] It is understood that, structurally, the pole piece may include a current collector and an active layer disposed on at least one surface of the current collector, the active layer comprising an active material and a binder. Simultaneously, the pole piece may be prepared by the preparation method of the first aspect.

[0104] In some embodiments, the bonding force of the electrode sheet is greater than or equal to 25 N / m, and optionally is 25 to 28 N / m, for example, any one of 25 N / m, 26 N / m, 27 N / m, and 28 N / m, or a range of values ​​therebetween. The bonding force of the electrode sheet can be measured using a high-speed rail tensile testing machine. The electrode sheet of the embodiment of the present application has high bonding force, which is beneficial for maintaining the stability of the electrode sheet during battery cycling, thereby improving the cycling performance of the battery.

[0105] In some embodiments, the water content of the electrode is ≤60 ppm, and can optionally be 25 to 60 ppm, such as any one of 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, and 60 ppm, or any range therebetween. The water content of the electrode refers to the mass content of water in the electrode and can be measured using a moisture meter. Low water content helps reduce the reaction between water in the electrode and lithium salts in the electrolyte, thereby improving the interfacial stability of the electrode and enhancing battery cycling performance.

[0106]

Battery

[0107] A third aspect of an embodiment of the present application provides a battery, which includes the electrode according to the second aspect.

[0108] The above-mentioned pole piece has high bonding force, high porosity, low water content, and good structural stability. The battery containing the pole piece will also show good cycle performance and long battery life.

[0109] The active material in the above-mentioned electrode piece may include a positive electrode material of lithium nickel cobalt manganese oxide, so the electrode piece can be used as a positive electrode of a battery.

[0110] Typically, a battery may further include a negative electrode sheet, an electrolyte, a separator, an outer packaging, etc. Meanwhile, the battery of the embodiment of the present application may include one or more of a battery cell, a battery module, and a battery pack.

[0111] 1. Negative electrode

[0112] The negative electrode sheet may include a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector and comprising a negative electrode active material, a binder, and a conductive agent.

[0113] Among them, the negative electrode current collector may include but is not limited to a metal current collector, a carbon current collector, a conductive resin current collector, a composite current collector of metal and resin, etc., more specifically copper, nickel, titanium, iron and their respective alloys, stainless steel, carbon fiber, carbon nanotubes (CNT), graphite, etc.

[0114] The negative electrode active material may include one or more of graphite, hard carbon, soft carbon, mesophase carbon microbeads, graphene, silicon, and silicon dioxide. The mass content of the negative electrode active material in the negative electrode active layer may include, but is not limited to, 90% to 98%, such as 95% to 98%, for example, any one of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 98%, or a range therebetween.

[0115] The conductive agent in the negative electrode plate may include, but is not limited to, acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, graphene, etc. The mass content of the conductive agent contained in the negative electrode plate in the active layer may include, but is not limited to, 0.5% to 10%, such as 1% to 5%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%, or any range therebetween.

[0116] The negative electrode active layer may further optionally include a thickener, such as carboxymethyl cellulose (CMC). The mass content of the thickener in the active layer includes, but is not limited to, 0.5% to 5%, such as 1% to 5%, including but not limited to any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, or any range therebetween.

[0117] 2. Electrolytes

[0118] An electrolyte can serve as a carrier for ion transport within a battery. In the batteries of the present application, the electrolyte employed can be a solid electrolyte, such as a polymer electrolyte or an inorganic solid electrolyte, but is not limited thereto. Alternatively, the electrolyte can be an electrolyte solution. The electrolyte solution includes a solvent and a lithium salt dissolved in the solvent.

[0119] The solvent may be a non-aqueous organic solvent, for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB), preferably two or more.

[0120] The lithium salt may include one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium bis(oxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate), for example, one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiBOB (lithium bis(oxalatoborate), LiDFOB (lithium difluorooxalatoborate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide).

[0121] The electrolyte may also optionally contain other additives, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1,3-PS), vinyl sulfate (DTD), methylene disulfonate (MMDS), 1-propylene-1,3-sultone (PST), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sultone (1,4-BS), ethylene sulfite (DTO), dimethyl sulfite (DMS), diethyl sulfite (DES), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB), but are not limited thereto.

[0122] 3. Isolation film

[0123] The battery also includes an isolation membrane stacked between the positive electrode sheet and the negative electrode sheet, which is used to separate the positive electrode sheet and the negative electrode sheet, so that the electrons in the battery cannot pass freely, preventing the two poles from contacting and short-circuiting, while allowing the ions in the electrolyte to pass freely between the positive and negative electrodes.

[0124] The isolation membrane can be any porous structure isolation membrane with electrochemical stability and mechanical stability, such as a single layer or multilayer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0125] 4. Outer packaging

[0126] The battery may include an outer packaging that can be used to encapsulate an electrode assembly including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0127] The battery outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell; or a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] The outer package shape can be cylindrical, square or any other shape. For example, FIG1 is an example of a battery cell with an outer package shape of a square structure.

[0129] Referring to Figure 2 , the outer packaging may include a housing 01 and a cover plate 02 . Housing 01 may include a base plate and side plates connected thereto, which together form a housing cavity. Housing 01 has an opening communicating with the housing cavity, and cover plate 02 can be positioned over the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet, and separator may be wound or laminated to form an electrode assembly 03 . One or more electrode assemblies 03 are encapsulated within the housing cavity. Electrolyte is impregnated within electrode assembly 03 .

[0130] 5.Battery cells, battery modules, and battery packs

[0131] The battery of the embodiment of the present application may be at least one of a battery cell, a battery module, and a battery pack. According to different packaging forms, batteries are divided into battery cells, battery modules, and battery packs. Among them, the battery cell is the most basic unit of a secondary battery, including an electrode assembly and an electrolyte. The electrode assembly is usually composed of a positive electrode sheet, a negative electrode sheet, and an isolating member. The positive electrode sheets and the negative electrode sheets are alternately stacked, and an isolating film is provided between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining a bare cell, or a bare cell after winding. The cell is placed in a casing, an electrolyte is injected, and the casing is sealed to obtain a battery cell. The battery cell mainly relies on the movement of metal ions in the electrolyte between the positive electrode sheet and the negative electrode sheet to work.

[0132] In some battery packaging technologies, one or more battery cells can be first integrated into a battery module, and then one or more battery modules can be assembled into a battery pack. In other battery packaging technologies, one or more battery cells can be directly installed in a box to form a battery pack, eliminating the intermediate state of the battery module, thereby reducing the weight of the battery pack and improving the energy density of the battery.

[0133] Referring to Figure 3, an example battery module is shown. In the battery module, multiple battery cells 04 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 04 can be secured using fasteners.

[0134] Optionally, the battery module may further include a housing having a receiving space, and the plurality of battery cells 04 are received in the receiving space.

[0135] Refer to Figures 4 and 5, which illustrate an example battery pack. The battery pack may include a battery box and multiple battery modules 05 disposed within the battery box. The battery box comprises an upper box body 06 and a lower box body 07. The upper box body 06 can be placed over the lower box body 07 to form an enclosed space for accommodating the battery modules 05. The multiple battery modules 05 can be arranged in any manner within the battery box.

[0136]

Electrical devices

[0137] An embodiment of the present application further provides an electrical device, which includes the battery of the third aspect described above.

[0138] The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as power sources, or in various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The battery exhibits advantages such as good cycle performance and long lifespan. Therefore, its application in various electrical devices can improve the user experience of these devices.

[0139] Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, and the like. Electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft. The electrical devices may be selected from batteries consisting of single cells, battery modules, or battery packs based on their intended use.

[0140] Figure 6 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0141] The following embodiments of the present application are described in detail. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0142] [Example]

[0143] Example 1

[0144] 1) Lithium nickel cobalt manganese oxide positive electrode sheet

[0145] This embodiment provides a lithium nickel cobalt manganese oxide positive electrode sheet and a preparation method thereof. The lithium nickel cobalt manganese oxide positive electrode sheet includes an aluminum foil and a positive electrode active layer arranged on both surfaces of the aluminum foil. The positive electrode active layer contains lithium nickel cobalt manganese oxide, conductive carbon black, carbon nanotubes and PVDF.

[0146] The preparation method of lithium nickel cobalt manganese oxide positive electrode sheet comprises the following steps:

[0147] 96 wt% lithium nickel cobalt manganese oxide (molar ratio Ni:Co:Mn=8:1:1), 1.0 wt% conductive carbon black, 0.5 wt% carbon nanotubes, 2.5 wt% PVDF (number average molecular weight 600,000, i.e. 60×10 4 ; melting point 172 ° C, decomposition temperature 310 ° C) were mixed, and then N-methyl pyrrolidone was added and stirred to disperse to prepare a positive electrode slurry containing lithium nickel cobalt manganese oxide. The positive electrode slurry was coated on aluminum foil, dried, and cold pressed to obtain a double-sided loading of 0.6g / 1540.25mm 2 , compacted density is 3.5g / cm 3 Nickel cobalt manganese oxide lithium positive electrode sheet.

[0148] The cold pressed products are subjected to heating treatment and heat preservation treatment in sequence.

[0149] Heat treatment: The lithium nickel cobalt manganese oxide cathode sheet is moved at a constant speed of 20m / min under a laser. A 2000W Nd:YAG laser is placed on each side of the lithium nickel cobalt manganese oxide cathode sheet. The laser heats the surface temperature of the active layer of the lithium nickel cobalt manganese oxide cathode sheet to 200°C (heating temperature).

[0150] Insulation treatment: Then, under the irradiation of two other 100W fiber lasers arranged along the movement direction of the lithium nickel cobalt manganese oxide positive electrode sheet and set on both sides of the lithium nickel cobalt manganese oxide positive electrode sheet, the surface layer of the active layer contained in the lithium nickel cobalt manganese oxide positive electrode sheet was kept at 190°C (insulation temperature) for 1 second (insulation time).

[0151] Then, the mixture was cooled to 25°C and rolled.

[0152] 2) Lithium-ion batteries

[0153] This embodiment also provides a lithium-ion battery comprising an electrode assembly (bare cell) consisting of the aforementioned lithium nickel cobalt manganese oxide positive electrode sheet, a graphite negative electrode sheet, and a separator, as well as an electrolyte and an outer packaging. The bare cell is placed in the outer packaging and the electrolyte soaks into the bare cell.

[0154] Lithium-ion batteries can be assembled as follows:

[0155] 95wt% artificial graphite, 1.0wt% conductive carbon black, 2.0wt% styrene-butadiene rubber (SBR), and 2.0wt% sodium carboxymethyl cellulose (CMC) were mixed and stirred with deionized water to form a negative electrode slurry. The negative electrode slurry was then coated on Cu foil. After both sides were finished, the foil was dried, cold-pressed, slit, and sheeted to produce a graphite negative electrode sheet.

[0156] The graphite negative electrode sheet, separator, and nickel-cobalt-manganese oxide positive electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, and then wound to form a bare cell. The bare cell is then placed in an outer package, injected with the prepared electrolyte, and subjected to steps such as encapsulation, electrolyte injection, formation, and venting to obtain a lithium-ion battery (cell).

[0157] Example 2

[0158] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the electrode sheet movement speed is 60 m / min, the heating laser power is 3000 W, the heating temperature is 190° C., and the holding time is 0.33 s. Other steps are the same as those in embodiment 1.

[0159] Example 3

[0160] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the electrode sheet movement speed is 200 m / min, the heating laser power is 4000 W, the heating temperature is 180° C., and the holding time is 0.1 s. Other steps are the same as those in embodiment 1.

[0161] Example 4

[0162] The only difference between this embodiment and embodiment 3 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the holding time is 0.5 s. Other aspects are the same as those of embodiment 3.

[0163] Example 5

[0164] The only difference between this embodiment and embodiment 3 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the holding time is 2 seconds. Other aspects are the same as those of embodiment 3.

[0165] Example 6

[0166] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molar ratio of Ni:Co:Mn in the lithium nickel cobalt manganese oxide is 6:2:2, the heating laser power is 3500W, and the heating temperature is 210° C. Other aspects are the same as embodiment 1.

[0167] Example 7

[0168] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molar ratio of Ni:Co:Mn in the lithium nickel cobalt manganese oxide is 5:2:3, the heating laser power is 4000 W, and the heating temperature is 220° C. Other steps are the same as those in embodiment 1.

[0169] Example 8

[0170] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molar ratio of Ni:Co:Mn in the lithium nickel cobalt manganese oxide is 1:1:1, the heating laser power is 4500W, and the heating temperature is 230° C. Other steps are the same as those in embodiment 1.

[0171] Example 9

[0172] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molecular weight of PVDF is 1 million and the melting point of PVDF is 175° C. Other aspects are the same as those of embodiment 1.

[0173] Example 10

[0174] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molecular weight of PVDF is 1.5 million and the melting point of PVDF is 180° C. Other aspects are the same as those of embodiment 1.

[0175] Example 11

[0176] The only difference between this embodiment and embodiment 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the molecular weight of PVDF is 450,000 and the melting point of PVDF is 150° C. Other aspects are the same as those of embodiment 1.

[0177] Example 12

[0178] The only difference between this embodiment and embodiment 1 is that in the method for preparing the lithium nickel cobalt manganese oxide positive electrode sheet, the laser used in the laser heating step is a Yb:YAG laser, and the laser used in the laser heat preservation step is a CO2 laser. Other aspects are the same as those of embodiment 1.

[0179] Example 13

[0180] The only difference between this embodiment and embodiment 1 is that in the method for preparing the lithium nickel cobalt manganese oxide positive electrode sheet, the laser in the laser heating step is a fiber laser, and the laser in the laser heat preservation step is an antimony arsenide laser. Other aspects are the same as those of embodiment 1.

[0181] [Comparative Example]

[0182] Comparative Example 1

[0183] The only difference between this comparative example and Example 1 is that the heating treatment and heat preservation treatment are not performed in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet. Other steps are the same as in Example 1.

[0184] Comparative Example 2

[0185] The only difference between this comparative example and Example 1 is that the heat preservation treatment is not performed in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet. Other steps are the same as in Example 1.

[0186] Comparative Example 3

[0187] The only difference between this comparative example and Example 1 is that in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet, the heating temperature is 320° C. and the heating laser power is 5500 W. Other steps are the same as in Example 1.

[0188] Comparative Example 4

[0189] The only difference between this comparative example and Example 6 is that the heating treatment and heat preservation treatment are not performed in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet. Other steps are the same as those in Example 6.

[0190] Comparative Example 5

[0191] The only difference between this comparative example and Example 7 is that the heating treatment and heat preservation treatment are not performed in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet. Other steps are the same as Example 7.

[0192] Comparative Example 6

[0193] The only difference between this comparative example and Example 8 is that the heating treatment and heat preservation treatment are not performed in the preparation method of the lithium nickel cobalt manganese oxide positive electrode sheet. Other aspects are the same as Example 8.

[0194]

Electrochemical performance and structure test

[0195] The positive electrode sheets and lithium-ion batteries of the embodiments and comparative examples were tested to obtain relevant test results.

[0196] 1. Heating temperature, holding temperature and holding time

[0197] Table 1. Test results of battery electrochemical performance of Examples 1 to 5 and Comparative Examples 1 to 3

[0198] (PVDF melting point 172°C, decomposition temperature 310°C; Ni:Co:Mn=8:1:1)

[0199] Table 2. Performance test results of positive electrode sheets of Examples 1 to 5 and Comparative Examples 1 to 3

[0200] The test results in Table 1 show that when the positive electrode sheet was applied to a battery without heat treatment or insulation treatment (Comparative Example 1), the battery's capacity retention rate after 500 cycles at 1C was 96.63%. Furthermore, adding a heat treatment step without insulation treatment (Comparative Example 2) showed less improvement in the battery's cycling performance, with a capacity retention rate of 96.97% after 500 cycles at 1C. Analysis combined with the test results in Table 2 suggests that simply heating the electrode sheet may not improve the electrode sheet enough, resulting in little change in the bonding strength of the positive electrode sheet and little improvement in cycling performance.

[0201] In contrast, in Examples 1 to 5, by sequentially performing heating treatment and heat preservation treatment during the preparation of the positive electrode sheet, the capacity retention rate of the corresponding battery after 500 cycles at 1C can be increased to 97.2% or above, as shown in FIG7 , and the cycle performance is improved. This is mainly because after the heating treatment and the heat preservation treatment, the binder is fully balanced, so that the bonding force of the positive electrode sheet is increased, and the water evaporates during the heat preservation process, and the porosity of the positive electrode sheet is improved (the increase in the liquid absorption rate reflects the increase in the porosity of the positive electrode sheet, which can improve the wettability of the positive electrode sheet); and during the heating treatment and the heat preservation treatment, the heating temperature and the heat preservation temperature are both lower than the decomposition temperature of the binder, and the nickel cobalt manganese oxide can remain stable and is not affected by the impurities generated by the decomposition of the binder during the heating process, as shown in the XRD pattern of the positive electrode sheet of Example 1 before and after the heating treatment and the heat preservation treatment in Figure 8, and the SEM image of the positive electrode sheet of Example 1 before and after the heating treatment and the heat preservation treatment in Figure 9. After the heating treatment and the heat preservation treatment, the crystal form, structure, and degree of crystallization of the nickel cobalt manganese oxide do not change significantly. Under the combined effect of these phenomena, the interface performance of the positive electrode sheet is greatly improved, and the impedance of the positive electrode sheet is reduced, thereby improving the battery cycle performance.

[0202] During the heating and insulation treatment processes, the heating temperature and the insulation temperature can be set in a temperature range greater than or equal to the melting point of the binder and less than the decomposition temperature of the binder. More specifically, they can be set in the first 50% of the interval between the melting point of the binder and the decomposition temperature of the binder (i.e., set to be greater than or equal to the melting point of the binder and less than or equal to the average value of the melting point of the binder and the decomposition temperature of the binder). The heating temperature and the insulation temperature can be the same or different (the insulation temperature can be higher or lower than the heating temperature). As a result, the battery cycle performance can be improved, as shown in Examples 1 to 3. Among them, when the insulation temperature is lower than the heating temperature, the battery exhibits better cycle performance. If either the heating temperature or the insulation temperature is too high, for example, in Comparative Example 3, setting the heating temperature to 320°C will reduce the battery cycle performance. According to the test results in Table 2, this is mainly due to the decomposition of the binder caused by excessively high temperature, which reduced the bonding strength of the positive electrode sheet. In addition, the decomposition products of the binder reacted with the active material lithium nickel cobalt manganese oxide, and the decomposition residues remained in the electrode sheet without being removed, which increased the side reactions between the positive electrode sheet and the electrolyte, causing the interface performance of the positive electrode sheet to deteriorate.

[0203] At the same time, the battery's cycling performance is related to the holding time. As shown in Examples 3-5, within the holding time range of 0.1-2s, the battery's 500-cycle capacity retention at 1C initially increases and then decreases with increasing holding time. Therefore, selecting an appropriate holding time can help achieve optimal battery cycling performance.

[0204] In addition, the test results also show that compared with comparative examples 1 to 3, the positive electrode sheets of Examples 1 to 5 have higher gram capacity and better rate performance (higher 3C capacity retention rate), which shows that heating treatment and heat preservation treatment can not only improve the battery cycle performance, but also improve the gram capacity and rate performance.

[0205] 2.Ni:Co:Mn molar ratio

[0206] Table 3. Electrochemical performance test results of batteries at different Ni:Co:Mn molar ratios

[0207] (PVDF melting point 172°C, decomposition temperature 310°C)

[0208] Table 4. Performance test results of positive electrode sheets at different Ni:Co:Mn molar ratios

[0209] According to the test results in Table 3, it can be seen that the method of sequentially performing heating treatment and heat preservation treatment during the preparation process is suitable for preparing positive electrode sheets with different Ni:Co:Mn molar ratios, and can improve the cycle performance of the battery. For example, the capacity retention rate of Example 6 after 500 cycles at 1C is higher than that of Comparative Example 4 using the same Ni:Co:Mn molar ratio but without heating treatment and heat preservation treatment; the capacity retention rate of Example 7 after 500 cycles at 1C is higher than that of Comparative Example 5 using the same Ni:Co:Mn molar ratio but without heating treatment and heat preservation treatment; and the capacity retention rate of Example 8 after 500 cycles at 1C is higher than that of Comparative Example 6 using the same Ni:Co:Mn molar ratio but without heating treatment and heat preservation treatment. Similarly, this is mainly because after the heating treatment and heat preservation treatment, the binder is fully balanced, which increases the bonding strength of the positive electrode sheet, and the water evaporates during the heat preservation process, which increases the porosity of the positive electrode sheet, thereby greatly improving the interface performance of the positive electrode sheet, while reducing the impedance of the positive electrode sheet, and ultimately improving the cycle performance of the battery.

[0210] Similar to Examples 1 to 5, for positive electrode sheets with different Ni:Co:Mn molar ratios, after heating treatment and heat preservation treatment, in addition to having excellent battery cycle performance, they also exhibit high positive electrode sheet specific capacity and rate performance.

[0211] 3. Binder molecular weight and melting point

[0212] Table 5. Battery electrochemical performance test results under different binders

[0213] (PVDF decomposition temperature 310°C; Ni:Co:Mn=8:1:1)

[0214] The test results in Table 5 show that when using PVDF with different molecular weights and melting points, the batteries have good cycle performance and rate performance after the positive electrode sheets are heated and kept warm.

[0215] 4. Laser

[0216] Table 6. Battery electrochemical performance test results under different lasers

[0217] (PVDF melting point 172°C, decomposition temperature 310°C; Ni:Co:Mn=8:1:1)

[0218] According to Table 6, using a laser that can emit infrared wavelength laser or near-infrared wavelength laser to perform heating treatment and heat preservation treatment on the positive electrode sheet can improve the cycle performance and rate performance of the battery.

[0219]

Performance test method

[0220] (1) Adhesion strength of positive electrode sheet

[0221] Cut the positive electrode sheet into 20*100mm 2 The test specimens of the required size are kept aside; the double-sided tape is used to adhere the side of the specimen to be tested, and is compacted with a pressure roller to ensure that the double-sided tape is completely adhered to the specimen; the other side of the double-sided tape of the specimen is adhered to the stainless steel surface, and one end of the specimen is bent in the opposite direction with a bending angle of 180°; a high-speed rail tensile testing machine is used for testing, one end of the stainless steel is fixed to the lower fixture of the tensile testing machine, and the bent end of the specimen is fixed to the upper fixture, and the angle of the specimen is adjusted to ensure that the upper and lower ends are in a vertical position, and then the specimen is stretched at a speed of 50 mm / min until the specimen is completely peeled off from the substrate, and the displacement and force in the process are recorded. It is generally believed that the force when the forces are balanced is the bonding force of the positive electrode.

[0222] (2) Liquid absorption rate of positive electrode

[0223] Fix the positive electrode on a clean glass plate, and draw electrolyte (1 mol·L -1 After the electrolyte is dissolved in water (LiPF6, EC:DMC:EMC mass ratio = 1:1:1), it is placed in vertical contact with the positive electrode to allow the electrode to absorb the electrolyte. The time it takes to completely absorb the electrolyte is measured, and the electrolyte absorption rate is obtained by conversion.

[0224] (3) Positive electrode gram capacity and 1C capacity retention rate

[0225] After cleaning one side of the positive electrode sheet with N-methylpyrrolidone or deionized water, punch out a single-sided circular electrode sheet with a diameter of 14 mm and weigh it. Simultaneously, weigh the corresponding current collector substrate under the 14 mm diameter circular sheet to obtain the total loading. Calculate the active material loading based on the electrode sheet formulation.

[0226] The 2032 button cell was equipped with a negative electrode shell, nickel foam, a 16 mm diameter lithium sheet, an 18 mm diameter Celgard2325 separator, and 0.1 g 1 mol L -1 A 2032 button cell was assembled using a LiPF6 electrolyte solution of EC:DMC:EMC (mass ratio 1:1:1), a 14mm diameter single-sided circular electrode (active material side facing the separator), and a 2032 button cell positive electrode casing. The assembled button cell was left to rest for 12 hours before testing: at 25°C, it was charged at a current of 0.1C to the upper voltage limit of the positive electrode active material. Then, it was charged at a constant voltage at the upper voltage limit until the current dropped below 0.05C. After a 5-minute rest, it was discharged at a current of 0.1C to the lower voltage limit of the positive electrode active material. The discharge capacity (i.e., the initial discharge capacity, C0) was recorded. The initial discharge capacity was divided by the positive electrode active material loading to obtain the positive electrode capacity in grams.

[0227] The button cell was charged at 25°C with a current of 1C to the upper limit of the voltage of the positive electrode active material, then charged at a constant voltage at the upper limit voltage until the current was less than 0.05C, and then stopped charging. After standing for 5 minutes, it was discharged with a current of 1C to the lower limit of the voltage of the positive electrode active material. The discharge capacity at this time was recorded as C1. This test method was repeated 500 times, and the discharge capacity at this time was recorded as C1. 500 According to C 500 The capacity retention rate @500cls under 1C is calculated by C1 = (C1-C 500 ) / C1*100%.

[0228] (4) Moisture content of the positive electrode

[0229] Cut the cathode sheet to be tested into pieces less than 5mm in length and width. Place 0.6-1g of the cut pieces in a dry vial. Add Karl Fischer anolyte and catholyte to the titration cell at a ratio of 20:1 by volume. Connect the generator electrode, indicator electrode, and air tube in the titration cell to the Karl Fischer moisture meter. Set the test temperature to 170°C, the actual electrode weight, the air flow rate to 40mL / min, the start drift to 10μg / min, the stop drift to 20μg / min, and the stabilization time to 20s to determine the moisture content of the cathode sheet.

[0230] (5) Discharge rate (3C capacity retention rate)

[0231] The battery cell was allowed to rest at 25°C for 30 minutes; discharged at a constant current of 0.33C to 2.8V, and then discharged at a constant current of 0.33C to 2.8V; allowed to rest at 25°C for 1 hour; charged at a constant current of 0.33C to a cut-off voltage (the charging cut-off voltage of Examples 6 to 8 and Comparative Examples 4 to 6 was 4.35V, and the charging cut-off voltage of other Examples and Comparative Examples was 4.25V); then charged at a constant voltage at the cut-off voltage with a cut-off current of 0.05C.

[0232] Repeat the above steps and record the discharge capacity C at 0.33C. 0.33 .

[0233] Let it stand at 25℃ for 30min; discharge it to 2.8V at 3C, let it stand at 25℃ for 1 hour, and record the discharge capacity C3 at 3C. 0.33 and C3 to obtain 3C capacity retention rate = (C 0.33 -C3) / C 0.33 *100%.

[0234] (6) DC resistance (25℃DCR@50%SOC)

[0235] The battery cell was left to stand at 25°C for 30 min, charged at a constant current of 0.33C to a cut-off voltage (the charging cut-off voltage of Examples 6 to 8 and Comparative Examples 4 to 6 was 4.35V, and the charging cut-off voltage of other Examples and Comparative Examples was 4.25V), and then charged at a constant voltage at the cut-off voltage with a cut-off current of 0.05C. At this time, the state of charge (SOC) of the battery was 100%.

[0236] After standing at 25°C for 5 minutes, discharge at 0.33C with a cutoff current of 0.5C to adjust the SOC to 50%. After standing at 25°C for 1 hour, record the voltage V1.

[0237] Discharge at 5C for 30s, record the voltage V2 and the current I of 5C constant current discharge.

[0238] Allow the battery to rest at 25°C for 40 seconds, then charge at a constant current of 3.75C for 30 seconds. Allow the battery to rest at 25°C for 1 hour, then charge at a constant current of 0.33C to the cutoff voltage (4.35V for Examples 6-8 and Comparative Examples 4-6, and 4.25V for the other Examples and Comparative Examples). Continue charging at the cutoff voltage with a constant voltage of 0.05C at the cutoff current. Allow the battery to rest at 25°C for 5 minutes, and record the voltage V1'.

[0239] Then discharge at 0.33C, cut-off current 0.9C, adjust SOC to 50%, let stand at 25℃ for 1 hour, discharge at 5C for 30 seconds, record voltage V2' and current I' of 5C constant current discharge.

[0240] Let it rest for 40 seconds at 25°C, charge at 3.75C constant current for 30 seconds, and let it rest for 5 minutes at 25°C. You can repeat the above steps multiple times.

[0241] The DC resistance of the battery cell at 25°C, 50% SOC, and 5C constant current discharge for 30s, that is, 25°C DCR@50% SOC = (V2-V1) / I = (V2'-V1') / I'.

[0242] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for preparing a pole piece, characterized in that: include: An active layer comprising an active material and a binder is prepared on at least one side of the current collector; Performing a heating treatment on the active layer to raise the surface temperature of the active layer to a heating temperature; Performing heat preservation treatment on the active layer so that the surface of the active layer is at a heat preservation temperature; The heating temperature and the insulation temperature are independently greater than or equal to the melting point or softening point of the binder, and less than the decomposition temperature of the binder.

2. The method for preparing a pole piece according to claim 1, characterized in that: The heating temperature and the insulation temperature are independently less than or equal to an average value of a melting point or a softening point of the binder and a decomposition temperature of the binder.

3. The method for preparing a pole piece according to claim 1 or 2, characterized in that: The heat preservation treatment time is greater than or equal to 0.1 s, and can be optionally 0.1 to 2.5 s.

4. The method for preparing a pole piece according to any one of claims 1 to 3, characterized in that: The insulation temperature is less than or equal to the heating temperature.

5. The method for preparing a pole piece according to any one of claims 1 to 4, characterized in that: The melting point or softening point of the binder is 140-180°C, and the decomposition temperature of the binder is 300-350°C; the heating temperature and the insulation temperature are independently 170-230°C, and optionally 190-230°C.

6. The method for preparing a pole piece according to claims 1 to 5, characterized in that: The active material includes lithium nickel cobalt manganese oxide; optionally, in the lithium nickel cobalt manganese oxide, the molar ratio of Ni, Co and Mn is (1-8): (1-2): (1-3).

7. The method for preparing a pole piece according to claims 1 to 6, characterized in that: The number average molecular weight of the binder is (35-150)×10 4 , optionally (45~150)×10 4 .

8. The method for preparing a pole piece according to any one of claims 1 to 7, characterized in that: The heating treatment and the heat-retaining treatment each independently include laser irradiation treatment.

9. The method for preparing a pole piece according to claim 8, characterized in that: The laser includes one or more of an infrared wavelength laser and a near-infrared wavelength laser. Optionally, the wavelength of the laser is 1000nm to 15μm.

10. The method for preparing a pole piece according to claim 8 or 9, characterized in that: The laser power in the heating treatment step is 2000-4500W, optionally 2000-4000W.

11. The method for preparing a pole piece according to any one of claims 8 to 10, characterized in that: The laser power in the heat preservation step is 80-200W, and optionally 100-150W.

12. The method for preparing a pole piece according to any one of claims 1 to 11, characterized in that: The method for preparing the pole piece further comprises the step of compacting the pole piece after the heat preservation treatment.

13. A pole piece, characterized in that: The pole piece is obtained according to the preparation method according to any one of claims 1 to 12.

14. A battery, characterized in that: The battery comprises the electrode sheet according to claim 13.

15. An electrical device, characterized in that: The electrical device comprises the battery according to claim 14.

Images