Substrate, method of preparing substrate, battery cell, and method of preparing same

Abstract

The application discloses a kind of substrates, including: current collector;Active material layer, which is coated on the surface of current collector, and the edge of current collector has blank area not covered by active material layer;And polymer layer, which is coated at the junction of blank area and active material layer.This application forms a special substrate by coating polymer layer at the junction of blank area and active material layer at the edge of current collector, and the substrate is die-cut to obtain integrally connected pole piece body and pole lug, and then the above-mentioned pole piece body is formed into an electric core by winding or stacking.The polymer is melted at 100-190 DEG C, and solidified at room temperature, so that the inner pole lug and the junction position of the packaging shell are sealed by the polymer, without additional welding of the outer pole lug.For the same size of pole piece, without the pole lug welding structure, the internal utilization of the packaging shell is higher, the overall length of the electric core is smaller, and the energy density is higher;At the same time, the problem of electric core short circuit caused by the metal hard bristles of welding site piercing the diaphragm is also avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a substrate, a method for preparing the substrate, a battery cell and a method for preparing the battery cell. BACKGROUND

[0002] At present, the domestic soft package lithium ion battery often adopts winding and laminating as the assembly process. With the rapid development of the market, the demand for fast charging and high energy density is increasing. The use of multi-tab winding process or laminating process can effectively increase the fast charging performance of the battery cell, but at the same time, the energy density (ED) of the process is reduced.

[0003] Due to the conventional multi-tab winding structure or laminating structure of the battery cell, the outer tab inside the packaging shell needs to be welded with the inner tab of the foil. The welding point is formed at the welding position, which not only increases the welding resistance between the tab and the metal shell, making the battery resistance increase, but also increases the battery mass, reduces the battery energy density, and in the welding process, metal burrs are inevitably generated at the welding position, which can easily pierce the separator, increasing the risk of short circuit of the battery cell. SUMMARY

[0004] One of the purposes of the present application is to provide a substrate to solve the problem of reduced battery energy density and short circuit of the battery cell caused by welding the outer tab. In order to achieve the above purpose, the following technical solutions are adopted in the present application:

[0005] a current collector;

[0006] an active material layer coated on the surface of the current collector, and the edge of the current collector has a blank area not covered by the active material layer; and

[0007] a polymer layer coated at the junction of the blank area and the active material layer.

[0008] The second purpose of the present application is to provide a battery cell, which includes a tab, the tab includes a tab body and a tab, and the tab body and the tab are integrally cut and formed from the above-mentioned substrate. After cutting, the tab body and the tab are integrally connected, and the polymer layer is covered at the connection between the tab body and the tab.

[0009] Further, the battery cell is a winding battery cell, and a plurality of tabs are connected to the tab body at equal intervals. After packaging, the polymer layer is sealed between the tab and the packaging shell.

[0010] Further, the battery cell is a laminated battery cell, and one tab is connected to one tab body. After packaging, the polymer layer is sealed between the tab and the packaging shell.

[0011] The third purpose of the present application is to provide a method for preparing the above-mentioned substrate, which includes the following steps:

[0012] The active material slurry is coated on the surface of the current collector to form an active material layer, and the edge of the current collector has a blank area not covered by the active material layer;

[0013] The polymer slurry is coated on the surface of the current collector and covers the blank area and the junction of the active material layer.

[0014] Further, the active material is coated on the surface of the current collector, which further comprises:

[0015] The active material slurry and the polymer slurry are obtained respectively.

[0016] Further, obtaining the polymer slurry comprises the following sub-steps:

[0017] Mixing polypropylene, modified polypropylene, polyethylene terephthalate powder and deionized water;

[0018] After uniform mixing and stirring, the polymer slurry is obtained.

[0019] The fourth object of the present application is to provide a method for preparing the above-mentioned battery cell, comprising the following steps:

[0020] The substrate is obtained by using any of the above-mentioned methods for preparing the substrate;

[0021] After drying, the substrate is die-cut to obtain an integrally connected tab body and tab, and the polymer layer covers the connection between the tab body and the tab;

[0022] The battery cell is prepared.

[0023] Further, the battery cell is prepared, comprising the following sub-steps:

[0024] The tab body obtained after die-cutting is made into a wound battery cell by winding;

[0025] The wound battery cell is placed in a packaging shell for heat sealing, and the heat sealing temperature is greater than the melting point of the polymer;

[0026] After the heat-sealed battery cell cools to room temperature, the polymer solidifies, and the interface position between the tab and the packaging shell is sealed by the polymer.

[0027] Further, the battery cell is prepared, comprising the following sub-steps:

[0028] The tab body obtained after die-cutting is made into a stacked battery cell by stacking;

[0029] The wound battery cell is placed in a packaging shell for heat sealing, and the heat sealing temperature is greater than the melting point of the polymer;

[0030] After the heat-sealed battery cell cools to room temperature, the polymer solidifies, and the interface position between the tab and the packaging shell is sealed by the polymer.

[0031] The beneficial effects of the present application are: compared with the prior art, the present application forms a special substrate by coating a polymer layer at the junction of the blank area of the current collector edge and the active material layer, the pole piece is cut from the substrate, the pole piece includes an integral pole piece body and a pole lug, at this time the polymer layer covers the connection between the pole piece body and the pole lug, and then the electric core is formed by winding or stacking, the physical properties of the polymer, i.e. melting at 100-190℃ and solidifying at room temperature, can make the inner pole lug and the sealing shell interface position be sealed by the polymer, without the need for additional welding of the outer pole lug, for the same size of the pole piece, without the pole lug welding structure, the internal utilization rate of the sealing shell is higher, the overall length of the electric core is smaller, and the energy density is higher; at the same time, the problem of metal burr produced by the welding position easily piercing the separator to cause short circuit of the electric core is also avoided. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0033] Figure 1 It is a schematic diagram of the substrate structure;

[0034] Figure 2 It is a process flow diagram for preparing the substrate;

[0035] Figure 3 It is a schematic diagram of the substrate cutting for preparing the wound electric core;

[0036] Figure 4 It is a schematic diagram of the substrate cutting for preparing the stacked electric core;

[0037] Figure 5 It is a process flow diagram for preparing the electric core;

[0038] Wherein: 1, substrate; 11, current collector; 12, active material layer; 13, blank area; 14, polymer layer; 15, pole lug; 16, pole piece body. DETAILED DESCRIPTION

[0039] In the following, the embodiments of the present application will be disclosed with drawings, and many practical details will be described in the following description for the purpose of clear illustration. However, it should be understood that these practical details are not used to limit the present application. That is, in some embodiments of the present application, these practical details are unnecessary.

[0040] In addition, the technical solutions among various embodiments can be combined with each other, but it must be based on that a person skilled in the art can realize, when the combination of the technical solutions appears contradictory or unachievable, it should be considered that the combination of the technical solutions does not exist, and is not within the protection scope required by the present application.

[0041] Embodiment one

[0042] Please refer to Figure 1 , Figure 1 The figure is a schematic diagram of a substrate structure. In order to solve the problems of energy density reduction and short circuit of the battery cell caused by the welding of the outer tab, the present embodiment provides a substrate 1, which comprises a current collector 11, an active material layer 12, a blank area 13 and a polymer layer 14; the active material layer 12 is coated on the surface of the current collector 11, the blank area 13 is at the edge of the current collector 11 and is not covered by the active material layer 12; and the polymer layer 14 is coated at the junction of the blank area 13 and the active material layer 12.

[0043] The current collector 11 can be a copper foil or an aluminum foil; the active material layer 12 can adopt the existing positive active material layer or negative active material layer, wherein the positive active material layer can be composed of lithium cobalt oxide, and the negative active material layer can be composed of graphite and silicon-carbon material or graphite and carbon-tin material, which will not be described here; and the polymer layer 14 is formed by mixing and stirring polypropylene, graft-modified polypropylene, polyethylene terephthalate powder and deionized water and then coating on the surface of the current collector 11.

[0044] Preferably, as shown in Figure 1 , a current collector surface has two active material layers 12, the two active material layers 12 are arranged at intervals, and the interval area between the two active material layers 12 forms a blank area 13, and then two polymer layers 14 are coated at the junction of the two blank areas 13 and the active material layers 12. In this way, the active material layer 12 coated on the surface of the current collector 11 is symmetrical about the central axis of the current collector 11, and the central axis of the current collector 11 has a blank area 13 on both sides which is not covered by the active material layer 12; and the polymer layer 14 is coated at the junction of the blank area 13 and the active material layer 12. Such design facilitates batch die cutting in the later stage and improves work efficiency.

[0045] Embodiment two

[0046] Please refer to Figure 2 , Figure 2 The figure is a process flow chart for preparing a substrate. The method for preparing the above-mentioned substrate comprises the following steps:

[0047] The active material slurry is prepared by the method of the prior art, which will not be described here.

[0048] The polymer slurry is prepared by mixing polypropylene, grafted modified polypropylene and polyethylene terephthalate powder in a ratio of 1:(1-4):1 to obtain a mixture, and then adding the mixture into deionized water in a solid-liquid ratio (1 g:40-100 ml) to form a mixed and uniform polymer slurry;

[0049] The active material slurry is coated on the surface of the current collector 11 to form the active material layer 12, and the edge of the current collector 11 has a blank area 13 not covered by the active material layer 12;

[0050] The polymer slurry is coated on the surface of the current collector 11 to form a polymer layer, which covers the blank area 13 and the junction of the active material layer 12, and the overlap width d1 of the polymer layer and the active material layer is in the range of 0.5-2 mm.

[0051] Example Three

[0052] Please refer to Figure 3 , Figure 3 A schematic diagram of the base material used to prepare the wound battery cell. This embodiment provides a battery cell, which includes a tab, and the tab includes a tab ear 15 and a tab body 16, and the tab ear 15 and the tab body 16 are integrally cut and formed from the above-mentioned base material 1; after cutting, a plurality of tab ears 15 are integrally connected to the tab body 16 at equal intervals, and the polymer layer 14 covers the connection between the tab ear 15 and the tab body 16. The above-mentioned cut tab body 16 is wound into a wound battery cell, and after packaging, the polymer layer 14 is sealed between the tab ear 15 and the packaging shell, and the packaging shell is specifically an aluminum plastic film. In preparation, the separator, the packaging shell, and the electrolyte can use the existing ones, which will not be described here.

[0053] Example Four

[0054] Please refer to Figure 4 , Figure 4 A schematic diagram of the base material used to prepare the stacked battery cell. This embodiment provides a battery cell, which is different from example three in that after cutting, one tab ear 15 is integrally connected to one tab body 16. The above-mentioned cut tab body 16 is stacked into a stacked battery cell.

[0055] Example Five

[0056] Please refer to Figure 5 , Figure 5 A process flow chart for preparing a battery cell. The method for preparing the above-mentioned battery cell includes the following steps:

[0057] The base material 1 in example one is obtained by using the method for preparing the base material in example two;

[0058] After drying, the above-mentioned base material 1 is cut to obtain integrally connected tab ears 15 and tab bodies 16, and the polymer layer 14 covers the connection between the tab ear 15 and the tab body 16.

[0059] The die-cut polar piece body 16 is prepared into an electric core in a winding or stacking manner, the winding or stacking formed electric core is placed into a packaging shell for heat packaging, and then cooled to room temperature for polymer sealing.

[0060] In order to further illustrate the technical effects of the present application, the following four groups of experiments are carried out according to the above steps, and the experimental data of the following samples are used for detailed description.

[0061] Experiment one: according to the prior art, an active material slurry is prepared; a polymer slurry is prepared, polypropylene, grafted modified polypropylene and polyethylene terephthalate powder are mixed in a ratio of 1:1:1 to obtain a mixture; the mixture is added to deionized water with PH6 and a temperature of 20℃ in a solid-liquid ratio (1g:40ml), stirred to form a mixed uniform polymer slurry, the stirring revolution speed is 10rpm and the rotation speed is 1000rpm, the whole process is sealed and the vacuum degree is-85kPa; at this time, the viscosity of the polymer slurry is 9000mPa.s, the fineness is ≤30μm, and the solid content is ≤15%; the active material slurry is coated on the surface of the current collector to form an active material layer, and the edge of the current collector has a blank area not covered by the active material layer; the polymer slurry is coated on the surface of the current collector to form a polymer layer, covering the blank area and the junction of the active material layer, wherein the overlapping width d1 of the polymer layer and the active material layer is 0.5mm; the above substrate is dried, the water content of the dried substrate is <150ppm, and the polymer melting point is 190℃ at this time; the above polar piece is die-cut to obtain a polar piece, the polar piece includes a polar piece body and a tab, a plurality of tabs are integrally connected to the polar piece body at equal intervals, and the polar piece body is wound to form an electric core; the electric core is placed into a packaging shell for heat packaging, the heat packaging temperature is controlled at 200℃, and the polymer layer is melted; after the heat packaged electric core is cooled to room temperature, the polymer layer is solidified, and the tab and the packaging shell interface position are sealed by the polymer layer. Finally, the electric core is shaped and corrected, and the top side is packaged to obtain a sample electric core A1.

[0062] Experiment two: the difference from experiment one is that when preparing the polymer slurry, polypropylene, copolymerized polypropylene and polyethylene terephthalate powder are mixed in a ratio of 1:4:1 to obtain a mixture; the mixture is added to deionized water with PH8 and a temperature of 50℃ in a solid-liquid ratio (1g:100ml), stirred to form a mixed uniform polymer slurry, the stirring revolution speed is 50rpm and the rotation speed is 2000rpm, the whole process is sealed and the vacuum degree is-90kPa; at this time, the viscosity of the polymer slurry is 6000mPa.s, the fineness is ≤30μm, and the solid content is ≤15%;

[0063] In addition, the width d1 of the polymer layer overlapping the active material layer is 2 mm; when the wound cell is put into the packaging shell for heat sealing, the heat sealing temperature is controlled at 110°C. The sample cell A2 is obtained.

[0064] Experiment three: The difference between experiment one and experiment two is that when preparing the polymer slurry, the polypropylene, cross-linked polypropylene and polyethylene terephthalate powder are mixed in a ratio of 1:2:1 to obtain a mixture; the mixture is added to deionized water with PH 7 and a temperature of 40°C in a solid-liquid ratio (1 g:200 ml), and stirred to form a uniformly mixed polymer slurry, at this time the stirring revolution speed is 30 rpm and the rotation speed is 1500 rpm, the whole process is sealed and the vacuum degree is -95 kPa; at this time the viscosity of the polymer slurry is 3000 mPa.s, the fineness is ≤30 μm, and the solid content is ≤15%;

[0065] In addition, the width d1 of the polymer layer overlapping the active material layer is 1 mm; when the stacked cell is put into the packaging shell for heat sealing, the heat sealing temperature is controlled at 160°C. The sample cell A3 is obtained.

[0066] Experiment four: The difference between experiment one, experiment two and experiment three is that when preparing the polymer slurry, the polypropylene, cross-linked polypropylene and polyethylene terephthalate powder are mixed in a ratio of 1:3:1 to obtain a mixture; the mixture is added to deionized water with PH 7 and a temperature of 30°C in a solid-liquid ratio (1 g:150 ml), and stirred to form a uniformly mixed polymer slurry, at this time the stirring revolution speed is 40 rpm and the rotation speed is 1000 rpm, the whole process is sealed and the vacuum degree is -80 kPa; at this time the viscosity of the polymer slurry is 4000 mPa.s, the fineness is ≤30 μm, and the solid content is ≤15%; the width d1 of the polymer layer overlapping the active material layer is 1.5 mm; when the stacked cell is put into the packaging shell for heat sealing, the heat sealing temperature is controlled at 140°C. The sample cell A4 is obtained.

[0067] The wound cell B1 is prepared by using the traditional technology, i.e. the outer tab welding method, and other conditions are the same as experiment one.

[0068] The stacked cell B2 is prepared by using the traditional technology, i.e. the outer tab welding method, and other conditions are the same as experiment four.

[0069] The above-mentioned lithium battery preparation method of the traditional technology comprises the following steps:

[0070] A substrate is prepared, and an active material layer is coated on the current collector, wherein the active material slurry is the same as the preparation method of experiment one and is a prior art, which will not be described here.

[0071] The above-mentioned substrate is die-cut according to product specifications to obtain a tab body.

[0072] Welding multiple tabs on the preset region of the tab body;

[0073] The tab body with the welded tabs is made into an electric cell by winding or stacking;

[0074] The electric cell formed by winding or stacking is put into a packaging shell for heat packaging;

[0075] After the electric cell after heat packaging is cooled to room temperature, shaping correction and top side packaging are performed to obtain a finished product.

[0076] The experimental comparison data of the electrical performance of the lithium ion battery prepared in the application and the lithium ion battery prepared by the conventional technology are as follows:

[0077]

[0078] The above experimental results show that the cycle number, energy density, discharge capacity, tab temperature rise and internal resistance of the electric cell prepared in the application are all superior to those of the existing lithium battery with welded external tabs.

[0079] Polypropylene is a thermoplastic synthetic resin with excellent performance, is a colorless translucent thermoplastic lightweight general-purpose plastic, has chemical resistance, heat resistance, electrical insulation, high strength mechanical properties and good high wear resistance processing performance, etc., but the large forming shrinkage of polypropylene limits its application in the battery field; polyethylene terephthalate has good creep resistance, fatigue resistance, wear resistance, heat resistance and dimensional stability, and the composite material prepared by compounding polypropylene and polyethylene terephthalate has good physical and mechanical properties in a wide temperature range and good bending fatigue resistance, and has excellent electrical insulation, friction resistance, fatigue resistance and dimensional stability. However, polypropylene is a non-polar material, and polyethylene terephthalate is a polar material, and the compatibility of the two is poor, so the application adds modified polypropylene to the polypropylene and polyethylene terephthalate powder to obtain a mixture, so that the mixture has good compatibility and does not decompose under the condition of electrolyte infiltration, and has good insulation performance.

[0080] The application mixes polypropylene, modified polypropylene and polyethylene terephthalate powder to obtain a mixture; and adds the above mixture to deionized water, stirs to form a mixed uniform polymer slurry; the polymer slurry is coated on the inner tabs of the negative and positive tabs, and the characteristics of the polymer melting at 100-190℃ and solidifying at room temperature make the inner tab and the sealing shell interface position sealed by the polymer, without the need for additional welding of external tabs. For tabs of the same size, the internal utilization of the packaging shell is higher, the overall length of the electric cell is smaller, and the energy density is higher; at the same time, the problem of metal burrs easily piercing the separator to cause short circuit of the electric cell due to the welding site is also avoided.

[0081] The above merely illustrates the embodiments of the present application, but should not be taken as limitations. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the scope of claims of the present application.

Claims

1. An electric cell, characterized by, The pole piece comprises a tab (15) and a pole piece body (16), and the tab (15) and the pole piece body (16) are integrally die-cut from a base material (1); after die-cutting, the tab (15) and the pole piece body (16) are integrally connected, and a polymer layer (14) covers the connection between the tab (15) and the pole piece body (16); The base material (1) comprises: a current collector (11); an active material layer (12) coated on the surface of the current collector (11), and the edge of the current collector (11) has a blank area (13) not covered by the active material layer (12); and a polymer layer (14) coated at the junction of the blank area (13) and the active material layer (12); The base material preparation method comprises the following steps: active material slurry and polymer slurry are obtained respectively, wherein polypropylene, grafted modified polypropylene and polyethylene terephthalate powder are mixed in a ratio of 1:(1-4):1 to obtain a mixture, and the mixture is added to deionized water in a solid-liquid ratio of 1g:40-100ml, and the polymer slurry is obtained after uniform mixing and stirring; the active material slurry is coated on the surface of the current collector to form an active material layer, and the edge of the current collector has a blank area not covered by the active material layer; the polymer slurry is coated on the surface of the current collector to form a polymer layer, which covers the junction of the blank area and the active material layer, and the overlap width d1 of the polymer layer and the active material layer ranges from 0.5 to 2mm; The electric core preparation method comprises the following steps: After drying the base material, die-cutting is performed to obtain integrally connected tabs and pole piece bodies, and the polymer layer covers the connection between the tabs and the pole piece bodies; The pole piece body obtained after die-cutting is made into a wound core by winding or a stacked core by stacking; The wound core or stacked core is placed in a packaging shell for heat sealing, and the heat sealing temperature is greater than the melting point of the polymer; After the heat-sealed core cools to room temperature, the polymer solidifies, and the tab and the packaging shell interface position are sealed by the polymer.

2. The electric cell of claim 1, wherein, When the wound core is made by winding, a plurality of tabs (15) are connected to the pole piece body (16) in sequence at equal intervals.

3. The electric cell of claim 1, wherein, When the stacked core is made by stacking, one tab (15) is connected to one pole piece body (16).

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