Rolling device as well as electrode and battery prepared by adopting rolling device

Abstract

The utility model relates to the technical field of batteries, in particular to a rolling device as well as an electrode and a battery prepared by adopting the rolling device, the rolling device comprises an unwinding device used for unwinding a gluing current collector; the preheating device is arranged at the downstream of the unwinding device and is used for preheating the glued current collector; the first rolling mechanism comprises a first compression roller and a second compression roller which are oppositely arranged, a powder feeding port is formed between the first compression roller and the second compression roller, and the first compression roller and the second compression roller are used for rolling powder to form an electrode layer; the second rolling structure comprises a third compression roller and a fourth compression roller which are oppositely arranged, and the third compression roller and the fourth compression roller are used for rolling the electrode layer and the preheated gluing current collector; and the winding device is used for winding the electrode. According to the rolling device provided by the utility model, the problem that the stripping force between the current collector and the dry-method diaphragm is reduced after speed increase in the dry-method electrode preparation process can be solved.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a rolling device, an electrode and a battery prepared by using the same. Background Art

[0002] Lithium-ion batteries are widely used in the fields of consumption, energy storage, electric vehicles and the like due to their many advantages. The electrode processing technology of lithium-ion batteries can be divided into a wet process and a dry process according to whether a solvent is used. The wet process is a common coating process for preparing lithium-ion battery electrodes. In order to ensure the fluidity of the battery slurry, the solvent content of the battery slurry is generally between 30% and 60%. Therefore, solvent volatilization usually occurs during the wet process, which will cause environmental pollution. Moreover, the drying energy consumption of the solvent will increase the manufacturing cost of the battery, and the finally remaining solvent impurities will cause side reactions inside the battery and affect the battery performance.

[0003] The dry electrode technology is a technology in which electrode active materials, conductive agents, and dry binders are mixed evenly, and then without adding a solvent, the obtained powder mixture is directly rolled into a self-supporting membrane, and then the membrane is thermally pressed and compounded with a current collector to prepare a battery electrode. The electrode film of the dry electrode mainly relies on the fibrosis of the dry binder to form a network structure, and the electrode active materials and the conductive agents are fixed in the binder fiber grid to form an electrode film with a self-supporting structure; while the wet coating technology for preparing the electrode needs to rely on the support of the current collector to coat the slurry on the current collector, which is the most direct difference between the dry electrode preparation process and the traditional coating process.

[0004] Since lithium batteries require metal foil to collect electrons, and the adhesion between the dry electrode membrane and the surface of the current collector foil is not good, a layer of hot melt adhesive needs to be coated on the current collector foil. The melting point of the hot melt adhesive is generally between 90°C and 130°C. After hot pressing, the hot melt adhesive melts, and the current collector foil and the dry membrane are firmly bonded together to form a dry electrode. At present, the common process is to bond the coated current collector foil and the dry membrane by continuous hot roll rolling, and the rolling temperature is 130°C - 150°C. However, this process has a drawback: as the production speed increases, the contact time between the current collector and the hot roll shortens, and the hot melt adhesive on the surface cannot be fully melted, and the adhesion of the membrane decreases significantly (such as Figure 3 ), which affects the mechanical properties of the electrode and leads to problems such as poor powder dropping during the manufacturing process and battery cycle degradation.

[0005] The above problems limit the speed increase and mass production application of the dry electrode process and need to be solved urgently. Summary of the Utility Model

[0006] According to one aspect of the present utility model, a rolling device and an electrode and a battery prepared by using the same are provided. The rolling device of the present utility model can solve the problem that the peeling force between the current collector and the dry film decreases after the speed is increased during the preparation of the dry electrode.

[0007] To achieve the above object, the present utility model adopts the following technical solutions:

[0008] In a first aspect, the present utility model provides a rolling device, and the rolling device includes:

[0009] A unwinding device for unwinding a coated current collector, and the coated current collector includes a current collector substrate and an adhesive layer provided on at least one surface of the current collector substrate;

[0010] A preheating device is provided downstream of the unwinding device for preheating the coated current collector;

[0011] A first rolling mechanism includes a first pressure roller and a second pressure roller arranged oppositely, and a powder feeding port is arranged between the first pressure roller and the second pressure roller, and the first pressure roller and the second pressure roller are used for rolling the powder to form an electrode layer;

[0012] A second rolling structure includes a third pressure roller and a fourth pressure roller arranged oppositely, and the third pressure roller and the fourth pressure roller are used for rolling the electrode layer and the preheated coated current collector so that the electrode layer adheres to the surface of the coated current collector;

[0013] A winding device for winding the electrode.

[0014] In the present utility model, by rolling the powder to form an electrode layer, no solvent is used during the preparation process, and the prepared electrode layer is also called a dry film, and the obtained electrode is a dry electrode.

[0015] The present utility model provides a preheating device downstream of the unwinding device for preheating the coated current collector, which can enable the heated current collector substrate to transfer heat to the adhesive layer to promote the adhesive layer to reach or partially reach the molten state in advance, and then enter the second rolling mechanism to bond with the dry film (i.e., the electrode layer formed by rolling the powder), avoiding the problem that the adhesive layer of the coated current collector is not sufficiently heated during high-speed rolling, resulting in poor hot melt bonding effect, realizing the improvement of the adhesion of the electrode sheet, and being beneficial to improving the cycle performance of the battery.

[0016] The rolling device of the present utility model can be well compatible with the existing dry electrode preparation system, which is beneficial to realizing the high-speed preparation of dry electrodes.

[0017] Preferably, the preheating device is an electromagnetic heater. The current collector substrate is generally a metal foil. In the present invention, when the metal foil passes through a high-frequency electromagnetic field, eddy currents are generated on the surface, and relying on the principle of self-resistance heating, the current collector can be rapidly heated, so that the hot melt adhesive on the surface of the current collector substrate is fully melted. After being rolled by the second rolling structure, the problem of the decrease in the peeling force between the current collector and the dry film during the preparation of the dry electrode can be improved.

[0018] In the present invention, the electromagnetic heater can indirectly preheat the current collector substrate in the coated current collector, which belongs to a non-contact heating method. Compared with the traditional contact heating with a hot roller and hot air oven heating, the present invention has the advantages of high heating efficiency, small floor area, simple control, etc., and has better mass production prospects.

[0019] Preferably, the rolling device further includes a temperature measuring device for detecting the surface temperature of the coated current collector after being processed by the preheating device. By setting the temperature measuring device, the working parameters (such as power and startup time) of the preheating device can be adjusted more conveniently, thereby improving the peeling force between the current collector and the electrode layer in the electrode.

[0020] Preferably, the first pressing roller, the second pressing roller, the third pressing roller and the fourth pressing roller are arranged in the horizontal direction.

[0021] Preferably, the first pressing roller, the second pressing roller, the third pressing roller and the fourth pressing roller are heating rollers.

[0022] Preferably, a roll gap is provided between the third pressing roller and the fourth pressing roller for the preheated coated current collector to pass through, and the preheating device is arranged above the roll gap.

[0023] Preferably, the rolling device further includes a first transfer roller for adjusting the vertical passing of the current collector through the roll gap.

[0024] Preferably, the rolling device further includes a surface density measuring instrument, and the surface density measuring instrument is arranged downstream of the second rolling mechanism.

[0025] Preferably, a thinning mechanism is further arranged between the first rolling mechanism and the second rolling structure, and the thinning mechanism is used for thinning the thickness of the electrode layer.

[0026] Preferably, the thinning mechanism includes at least one pair of calender rolls.

[0027] Preferably, the calender roll is a heating roll.

[0028] The present invention also provides a method for preparing an electrode by using the above rolling device, including the following steps:

[0029] (1) Uniformly mix the active material, conductive agent, and hot-melt adhesive in a mixer to obtain powder material;

[0030] (2) Feed the powder material through the powder feeding port. The first pressing roller and the second pressing roller roll the powder material to form an electrode layer. The electrode layer runs towards the second rolling mechanism and optionally passes through the rolling of a thinning structure during the running process to thin the thickness of the electrode layer, obtaining an electrode layer for compounding with the current collector;

[0031] (3) After the coated current collector is unrolled, it is preheated by an electromagnetic heater. The preheated coated current collector is rolled by the relatively arranged third pressing roller and fourth pressing roller, and the electrode layer is bonded to the coated current collector under a certain temperature and pressure to obtain an electrode;

[0032] (4) The electrode runs towards the winding device, and the winding device winds the electrode.

[0033] In the present utility model, the production speed refers to the unwinding speed or the winding speed. The unwinding speed and the winding speed are the same.

[0034] In the present utility model, the power of the preheating device (such as the electromagnetic heater) can be adjusted according to the production speed. Generally speaking, if the production speed is relatively fast, the power can be appropriately increased; if the production speed is relatively slow, the power can be appropriately decreased.

[0035] In the present utility model, by adjusting the power of the preheating device, the temperature of the coated current collector during hot pressing can be well controlled, solving the problem that the peel force decreases as the production speed increases, and having a high industrial application prospect.

[0036] In one embodiment, based on the total mass of the active material, conductive agent, and hot-melt adhesive being 100%, the mass content of the active material is 95% - 99%, for example, it can be 95%, 95.5%, 96%, 96.5%, 97%, 98%, or 99%, etc.; the mass content of the conductive agent is 0.5% - 3%, for example, it can be 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6%, or 3%, etc.; the mass content of the hot-melt adhesive is 0.5% - 3%, for example, it can be 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6%, or 3%, etc.

[0037] The adhesive layer on the surface of the coated current collector is generally a hot-melt adhesive, and its softening temperature is generally 100 - 200°C. Depending on the type of the adhesive, its softening temperature is also different. Accordingly, the preheating temperature and the certain temperature in step (3) can be adjusted adaptively.

[0038] In one embodiment, the preheating temperature is 100°C - 200°C, for example, it can be 100°C, 120°C, 140°C, 150°C, 160°C, 180°C or 200°C, etc.

[0039] In one embodiment, the certain temperature in step (3) is 100°C - 200°C, for example, it can be 100°C, 120°C, 140°C, 150°C, 160°C, 180°C or 200°C, etc.

[0040] In one embodiment, the pressure in step (3) is 5 - 30T, for example, it can be 5T, 8T, 10T, 12T, 15T, 17T, 20T, 22T, 24T, 26T, 28T or 30T, etc. According to the types of active materials, the pressure here can be appropriately adjusted. For example, for the negative electrode active material graphite, the pressure is preferably 5T - 20T; for the positive electrode active materials lithium iron phosphate or lithium nickel cobalt manganese oxide, the pressure is preferably 10T - 30T.

[0041] In one embodiment, before winding, the areal density of the electrode is measured using an areal density measuring instrument.

[0042] In one embodiment, for the negative electrode active material graphite, the areal density of the prepared graphite electrode is 5mg / cm 2 -20mg / cm 2 , for example, it can be 5mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 10mg / cm 2 , 12mg / cm 2 , 15mg / cm 2 , 16mg / cm 2 , 18mg / cm 2 or 20mg / cm 2 etc.

[0043] In the present utility model, the first pressing roller and the second pressing roller form a differential roller. While rolling the dry powder material into a film-shaped positive electrode layer, the positive electrode layer is made to run towards the direction of the third pressing roller and the fourth pressing roller.

[0044] In the present utility model, the third pressing roller and the fourth pressing roller form a differential roller. While compounding the positive electrode layer and the coated current collector to form a positive electrode, the positive electrode is made to run towards the direction of the winding device.

[0045] In a second aspect, the present utility model provides an electrode, which is prepared by the rolling device described in the first aspect.

[0046] The electrode in the present utility model can be a positive electrode or a negative electrode. The active material in the positive electrode is the positive electrode active material, and the active material in the negative electrode is the negative electrode active material. The present utility model does not specifically limit the types of the positive electrode active material and the negative electrode active material, and those skilled in the art can select according to needs.

[0047] Preferably, the electrode includes a current collector and an electrode layer, and the current collector and the electrode layer are connected by glue.

[0048] Preferably, the glue is a conductive glue.

[0049] In one embodiment, the conductive glue is a mixture formed by dispersing a conductive agent in a hot melt adhesive.

[0050] In one embodiment, the mass ratio of the conductive agent in the conductive glue is 20%-50%, for example, it can be 20%, 22%, 25%, 28%, 30%, 33%, 36%, 40%, 45% or 50%, etc.

[0051] Since the hot melt adhesive will increase the impedance, generally a conductive agent is added to the hot melt adhesive to form a conductive glue for use.

[0052] In one embodiment, the total thickness of the conductive glue is controlled within 3 μm. The purpose of such setting is to avoid increasing the impedance.

[0053] In a third aspect, the present utility model provides a battery, and the battery includes the electrode described in the second aspect.

[0054] The present utility model has the following beneficial effects:

[0055] By arranging a preheating device downstream of the unwinding device in the present utility model to preheat the coated current collector, the heated current collector substrate can transfer heat to the glue layer to prompt the glue layer to reach or partially reach the molten state in advance, and then enter the second rolling mechanism to bond with the dry film (i.e., the electrode layer formed by rolling the powder), avoiding the problem of poor hot melt bonding effect caused by insufficient heating of the glue layer of the coated current collector during high-speed rolling, realizing the improvement of the adhesive force of the pole piece, and being beneficial to improving the cycle performance of the battery. Description of the Drawings

[0056] Figure 1 is a schematic structural diagram of the rolling device in the present utility model;

[0057] Figure 2 is a diagram showing the change of the peeling force of the pole piece with the production speed in Example 2;

[0058] Figure 3 is a diagram showing the change of the peeling force of the pole piece with the production speed in Comparative Example 1. Detailed Embodiments

[0059] The technical solution of the present utility model will be further described below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present utility model, rather than limiting the present utility model. In addition, it should be noted that for the convenience of description, only the parts related to the present utility model are shown in the drawings, rather than all of them.

[0060] In the description of the present utility model, unless otherwise clearly defined and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0061] In the present utility model, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features therebetween. Moreover, the first feature being "above", "above", and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "below", and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0062] In the description of the embodiments of the present disclosure, the orientation or positional relationships such as "above", "below", "left", "right", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present utility model. In addition, the terms "first" and "second" are only used for distinction in description and do not have special meanings.

[0063] In one embodiment of the present utility model, a rolling device is provided, and for its structural schematic diagram, see Figure 1 , and the rolling device includes:

[0064] A unwinding device 1 for unwinding the glue-coated current collector, and the glue-coated current collector includes a current collector substrate and a glue layer provided on at least one surface of the current collector substrate;

[0065] A preheating device 2 provided downstream of the unwinding device for preheating the glue-coated current collector;

[0066] The first rolling mechanism 3 includes a first pressing roller 31 and a second pressing roller 32 which are arranged oppositely. A powder feeding port 33 is arranged between the first pressing roller 31 and the second pressing roller 32. The first pressing roller 31 and the second pressing roller 32 are used for rolling the powder to form an electrode layer.

[0067] The second rolling structure 4 includes a third pressing roller 41 and a fourth pressing roller 42 which are arranged oppositely. The third pressing roller 41 and the fourth pressing roller 42 are used for rolling the electrode layer and the preheated glue-coated current collector, so that the electrode layer adheres to the surface of the glue-coated current collector.

[0068] The winding device 5 is used for winding the electrode.

[0069] Further, the preheating device 2 is an electromagnetic heater.

[0070] Further, the rolling device further includes a temperature measuring device 6, which is used for detecting the surface temperature of the glue-coated current collector after being processed by the preheating device.

[0071] In one embodiment, the temperature measuring device 6 is a temperature measuring gun.

[0072] Further, the first pressing roller 31, the second pressing roller 32, the third pressing roller 41 and the fourth pressing roller 42 are arranged horizontally.

[0073] Further, the first pressing roller 31, the second pressing roller 32, the third pressing roller 41 and the fourth pressing roller 42 are heating rollers; a roll gap is arranged between the third pressing roller 41 and the fourth pressing roller 42, and the roll gap is used for allowing the preheated glue-coated current collector to pass through. The preheating device 2 is arranged above the roll gap.

[0074] Further, the rolling device further includes a first transfer roller 7, and the first transfer roller 8 is used for adjusting the current collector to vertically pass through the roll gap.

[0075] In one embodiment, the rolling device further includes a surface density measuring instrument 8, and the surface density measuring instrument 8 is arranged downstream of the second rolling mechanism 4.

[0076] Further, a thinning mechanism 9 is further arranged between the first rolling mechanism 3 and the second rolling structure 4, and the thinning mechanism 9 is used for thinning the thickness of the electrode layer.

[0077] Further, the thinning mechanism 9 includes at least one pair of calender rollers 91.

[0078] Further, the calender roller 91 is a heating roller.

[0079] In another embodiment of the present utility model, an electrode is provided, and the electrode is prepared by the above-mentioned rolling device.

[0080] In one embodiment, the electrode includes a current collector and an electrode layer, and the current collector and the electrode layer are connected by glue.

[0081] In one embodiment, the glue is a conductive glue.

[0082] In another embodiment of the present utility model, a battery is provided, and the battery includes the above-mentioned electrode.

[0083] Example 1

[0084] This example provides a rolling device. Based on the above embodiments, as Figure 1 shown, wherein the temperature measuring device 6 is a temperature measuring gun; the adjacent first pressing roller 31 and the second pressing roller 32 form a pair of differential rollers, and the number of pairs of differential rollers in the rolling device is 2 pairs, and the number of powder feeding ports 33 is 2, which are used to form electrode layers on both side surfaces of the current collector; the number of calendering rollers 91 is 8. Among them, 4 calendering rollers 91 are arranged between the third pressing roller 41 and the first rolling structure, and 4 calendering rollers 91 are arranged between the fourth pressing roller 42 and the first rolling structure.

[0085] Example 2

[0086] This example provides a method for preparing an electrode by using the rolling device of Example 1, including the following steps:

[0087] (1) Graphite, conductive agent SP and polytetrafluoroethylene PTFE are added to a mixer in a mass ratio of 96:2:2 and mixed evenly. The mixed powder is subjected to air flow pulverization to fully fibrillate the polytetrafluoroethylene PTFE, and the fibrillated dry electrode powder is obtained.

[0088] The dry electrode powder is fed through the powder feeding port. After the feeding starts, it is rolled by the first pressing roller 31 and the second pressing roller 32, and the powder forms a dry film and sequentially passes through the calendering rollers 91 in the direction of the arrow in Figure 1 to be thinned to the surface density of the electrode of 10 mg / cm 2 . The first pressing roller 31, the second pressing roller 32, the third pressing roller 41, the fourth pressing roller 42 and the calendering rollers 91 are preheated to 120 °C. The coated current collector (copper foil coated with hot melt adhesive, and the hot melt adhesive contains 25 wt% of SP) is unrolled from the unrolling device 1. The temperature of the electromagnetic heater is set to 130 °C, and the power output is automatically adjusted according to the temperature value feedback by the temperature measuring gun on the coating surface. The coated current collector heated by the electromagnetic heater passes through the roll gap between the third pressing roller 41 and the fourth pressing roller 42 and is thermally bonded with the dry film to form a pole piece, that is, a dry pole piece.

[0089] Among them, the automatic adjustment method can be: controlling the power output by adjusting the input current of the electromagnetic heater. By changing the magnitude of the current, the power of the heater can be adjusted. Generally speaking, increasing the current can increase the power output, and decreasing the current can decrease the power output.

[0090] In this embodiment, the production speeds are changed to 5 m / min, 10 m / min, and 20 m / min in sequence, and the measured peeling forces of the pole pieces obtained are 37.2 N / m, 35.5 N / m, and 34.7 N / m respectively, as Figure 2 shown.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 2 is that the rolling device used in the preparation method does not contain an electromagnetic heater.

[0093] In this comparative example, the production speeds are changed to 5 m / min, 10 m / min, and 20 m / min in sequence, and the measured peeling forces of the pole pieces obtained are 36.5 N / m, 28.7 N / m, and 16.3 N / m respectively, as Figure 3 shown.

[0094] From Examples 1 - 2 and Comparative Example 1, it can be seen that the rolling device provided by the present utility model can solve the problem of the decrease in the peeling force between the current collector and the dry film during the dry electrode preparation process when the speed is increased.

[0095] Obviously, the above-mentioned embodiments of the present utility model are only examples for clearly explaining the present utility model, and are not intended to limit the implementation manners of the present utility model. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present utility model shall be included in the protection scope of the claims of the present utility model.

Claims

1. A roller pressing device, characterized in that, The roll pressing device includes: An unwinding device for unwinding the glue-coated current collector, where the glue-coated current collector includes a current collector substrate and a glue layer provided on at least one surface of the current collector substrate; A preheating device disposed downstream of the unwinding device for preheating the glue-coated current collector; A first roll pressing mechanism including a first press roll and a second press roll disposed opposite to each other, with a powder feeding port provided between the first press roll and the second press roll, and the first press roll and the second press roll are used for roll pressing the powder to form an electrode layer; A second roll pressing structure including a third press roll and a fourth press roll disposed opposite to each other, and the third press roll and the fourth press roll are used for roll pressing the electrode layer and the preheated glue-coated current collector so that the electrode layer adheres to the surface of the glue-coated current collector; A winding device for winding the electrode.

2. The roll pressing device according to claim 1, characterized in that The preheating device is an electromagnetic heater.

3. The roll pressing device according to claim 1, wherein The roll pressing device further includes a temperature measuring device for detecting the surface temperature of the glue-coated current collector after being processed by the preheating device.

4. The roll pressing device according to claim 1, characterized in that, The first press roll, the second press roll, the third press roll, and the fourth press roll are arranged in the horizontal direction; The first press roll, the second press roll, the third press roll, and the fourth press roll are heating rolls.

5. The roll pressing device according to claim 1, wherein: A roll gap is provided between the third press roll and the fourth press roll, and the roll gap is used for the preheated glue-coated current collector to pass through, and the preheating device is disposed above the roll gap.

6. The roll pressing device according to claim 5, characterized in that, The roll pressing device further includes a first transfer roll, and the first transfer roll is used for adjusting the vertical passing of the current collector through the roll gap.

7. The rolling device according to claim 1, characterized in that, The roll pressing device further includes a surface density measuring instrument, and the surface density measuring instrument is disposed downstream of the second roll pressing structure.

8. The roll pressing device according to claim 1, characterized in that, A thickness reducing mechanism is further provided between the first roll pressing mechanism and the second roll pressing structure, and the thickness reducing mechanism is used for reducing the thickness of the electrode layer; The thickness reducing mechanism includes at least one pair of calender rolls; The calender roll is a heating roll.

9. An electrode, characterized in that, The electrode is prepared by the roll pressing device according to any one of claims 1-8; The electrode includes a current collector and an electrode layer, and the current collector and the electrode layer are connected by glue.

10. A battery, characterized in that, The battery includes the electrode according to claim 9.

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