An electric core, a preparation method thereof and a lithium ion battery

Abstract

The application discloses a kind of battery and its preparation method and lithium ion battery, the battery includes positive sheet, negative sheet and diaphragm, diaphragm is arranged between positive sheet and negative sheet, and the outer edge of positive sheet and negative sheet is flush;Positive sheet and negative sheet each independently include current collector, active material layer and insulating buffer layer, active material layer and insulating buffer layer are arranged on the surface of current collector;Insulating buffer layer is attached to at least two sides of active material layer, and is configured to be fixedly bonded with positive and negative sheet and diaphragm.By the above, by the same width design of positive and negative sheet and the setting of insulating buffer layer on positive and negative sheet, the risk of internal short circuit after falling can be effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrode core, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high voltage, high energy density and long service life, and are widely used in consumer electronics. With the increasing demand for energy density year by year, and the capacity and weight of battery monomers becoming higher and higher, specific performance requirements such as fast charging and fast discharging also need to be considered, and the safety performance of the battery during the drop of the whole machine is also required to be higher.

[0003] The battery in the whole machine is usually fixed by bonding the electrode core aluminum plastic film outer surface with adhesive paper, but there is usually no bonding between the aluminum plastic film inside and the bare electrode core. Due to the presence of electrolyte, when the whole machine drops, the bare electrode core and the aluminum plastic film will slide, the bare electrode core will impact the top packaging area, and even indirectly impact the top protection plate and the host battery compartment, causing the electrode core electrolyte to leak, short circuit, and even thermal runaway fire. To solve this problem, currently, a hot melt adhesive tape is usually added between the bare electrode core and the outer packaging aluminum plastic film to enhance the bonding between the bare electrode core and the aluminum plastic film, so as to improve the sliding displacement problem of the internal bare electrode core during the drop. However, the hot melt adhesive only bonds the outermost electrode tab of the electrode core, and there is still a sliding displacement phenomenon between the inner layer electrode tabs during the drop. The electrode tab far from the hot melt adhesive bonding layer is still prone to displacement and impact on the protection plate and the battery compartment. In addition, due to the Overhang of the positive and negative electrodes of the lithium ion battery, that is, the size of the negative electrode is larger than that of the positive electrode, which is to ensure that the negative electrode completely wraps the positive electrode and prevent lithium precipitation at the edge. However, the above setting makes the Overhang region of the negative electrode tab beyond the edge of the positive electrode tab prone to bending and generating debris, thereby causing internal short circuit and drop failure. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes an electrode core, a preparation method thereof and a lithium ion battery.

[0005] In a first aspect of the present application, an electrode core is provided, comprising a positive electrode tab, a negative electrode tab and a separator, the separator being arranged between the positive electrode tab and the negative electrode tab, and the outer edges of the positive electrode tab and the negative electrode tab being flush; the positive electrode tab and the negative electrode tab each independently comprise a current collector, an active material layer and an insulating buffer layer, the active material layer and the insulating buffer layer being arranged on the surface of the current collector; the insulating buffer layer is arranged on at least two side edges of the active material layer and is configured to fix and bond the positive electrode tab and the negative electrode tab with the separator. Preferably, the insulating buffer layer is arranged on at least two opposite side edges of the active material layer.

[0006] According to the embodiment of the application, the battery cell has at least the following beneficial effects: the battery cell comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the outer edges of the positive electrode sheet and the negative electrode sheet are flush; the positive electrode sheet and the negative electrode sheet each independently comprise a current collector, an active material layer and an insulating buffer layer, the active material layer and the insulating buffer layer are arranged on the surface of the current collector; the insulating buffer layer is arranged on at least two side edges of the active material layer and is configured to fix and bond the positive electrode sheet and the negative electrode sheet to the separator. Through the above arrangement, the positive electrode sheet and the negative electrode sheet have the same width in the direction parallel to the separator; the insulating buffer layer is arranged on the surface of the current collector of the positive electrode sheet and the negative electrode sheet and on at least two side edges of the active material layer, and the insulating buffer layer is configured to fix and bond the positive electrode sheet and the negative electrode sheet to the separator, so that the bonding between the positive electrode sheet and the negative electrode sheet and the separator is strengthened, the overall rigidity of the battery cell is improved, and when the battery cell is assembled into a battery and falls, if displacement occurs, the positive electrode sheet and the negative electrode sheet are displaced as a whole (i.e., the displacement amount of the positive electrode sheet is similar to that of the negative electrode sheet), and when the positive electrode sheet and the negative electrode sheet impact the battery compartment or the protection plate, the insulating buffer layer on the edge of the positive electrode sheet and the negative electrode sheet can serve as a buffer zone to jointly and simultaneously withstand the impact, so that the problem that the design that the size of the negative electrode sheet is greater than that of the positive electrode sheet easily causes the active material layer to bend and generate debris or the interface to be damaged, resulting in internal short circuit or power drop, can be effectively avoided, and the risk of internal short circuit after falling is reduced.

[0007] In the above battery cell, the size of the outer edge of the active material layer on the negative electrode sheet is generally greater than that of the active material layer on the positive electrode sheet; since the positive electrode sheet and the negative electrode sheet are arranged opposite to each other and the outer edges of the positive electrode sheet and the negative electrode sheet are flush, and the insulating buffer layer is arranged on the side edges of the active material layer on the surface of the current collector of the positive electrode sheet and the negative electrode sheet, and the size of the outer edge of the active material layer on the negative electrode sheet is greater than that of the active material layer on the positive electrode sheet, the area of the negative active material layer can completely cover the area of the positive active material layer, so that the problem of insufficient overhang causing lithium precipitation is not caused. Preferably, the width difference between the active material layers on the positive electrode sheet and the negative electrode sheet is greater than 0.4 mm, so as to avoid misalignment between the layers during winding or sheet assembly, which causes the edge of the positive electrode sheet to exceed the edge of the negative electrode sheet and causes lithium precipitation. The width difference between the active material layers on the positive electrode sheet and the negative electrode sheet can be designed according to the sheet width tolerance, the winding / stacking equipment capacity or the number of winding / stacking layers, etc.

[0008] In addition, in the above battery cell, the outer edge of the insulating buffer layer on the positive electrode sheet and the negative electrode sheet is generally flush with the outer edge of the current collector; in the direction parallel to the separator, the size of the separator is generally greater than that of the positive electrode sheet and the negative electrode sheet, so as to avoid direct contact between the positive electrode sheet and the negative electrode sheet to cause short circuit.

[0009] Specifically, the positive electrode sheet and the negative electrode sheet are provided with an active material layer and an insulating buffer layer on at least one side surface of the current collector, the insulating buffer layer is arranged on at least two side edges of the active material layer, and is configured to fix and bond the positive electrode sheet and the negative electrode sheet with the separator. For example, the positive electrode sheet and / or the negative electrode sheet is provided with the active material layer and the insulating buffer layer on one side surface of the current collector according to the above structure; or, the positive electrode sheet and / or the negative electrode sheet is provided with the active material layer and the insulating buffer layer on both side surfaces of the current collector according to the above structure. Alternatively, the positive electrode sheet and the negative electrode sheet each independently has a first region and a second region, the active material layer and the insulating buffer layer are arranged on one side surface of the current collector according to the above structure on the first region, and the active material layer and the insulating buffer layer are arranged on both side surfaces of the current collector according to the above structure on the second region. Generally, the insulating buffer layer and the active material layer are arranged on the same side of the current collector, and the insulating buffer layer is arranged on at least two side edges of the active material layer. The insulating buffer layer is generally arranged on at least two opposite side edges of the active material layer.

[0010] In some embodiments of the present application, the single-edge width of the insulating buffer layer in the positive electrode sheet is greater than the single-edge width of the insulating buffer layer in the negative electrode sheet; preferably, the single-edge width of the insulating buffer layer in the negative electrode sheet is greater than or equal to 0.5 mm; preferably, the single-edge width of the insulating buffer layer on the positive electrode sheet is at least 0.2 mm greater than the single-edge width of the insulating buffer layer on the negative electrode sheet; further preferably, the single-edge width of the insulating buffer layer in the positive electrode sheet is greater than or equal to 1.5 mm. The above single-edge width is the single-edge width in the direction parallel to the current collector. By controlling the single-edge width of the insulating buffer layer on the positive electrode sheet and the negative electrode sheet within the above range, and by making the single-edge width of the insulating buffer layer on the positive electrode sheet greater than the single-edge width of the insulating buffer layer on the negative electrode sheet, the region of the active material layer on the positive electrode sheet beyond the edge of the negative active material layer can be avoided, thereby preventing lithium precipitation. The insulating buffer layer on the positive electrode sheet and the insulating buffer layer on the negative electrode sheet are generally arranged on the same side of the current collector and are located on at least two side edges of the active material layer on the current collector; and on the same side, the single-edge width of the insulating buffer layer in the positive electrode sheet is greater than the single-edge width of the insulating buffer layer in the negative electrode sheet. The width of one side of the insulating buffer layer on the positive electrode sheet and the negative electrode sheet can be equal to or different from the width of the insulating buffer layer on the opposite side.

[0011] In some embodiments of the present application, the thickness of the insulating buffer layer is less than or equal to the thickness of the active material layer. Generally, the thickness of the insulating buffer layer is controlled to be as close as possible to the thickness of the active material layer but not more than the thickness of the active material layer, so as to effectively play the role of the insulating buffer layer region in protecting the edge of the electrode sheet from damage when falling, and to effectively avoid the influence of the over-thick insulating buffer layer on the interface between the positive electrode sheet and the negative electrode sheet and the influence on the electrical performance. Specifically, the thickness of the insulating buffer layer can be designed to be greater than 50% of the thickness of the active material layer and less than the thickness of the active material layer; for example, the thickness of the insulating buffer layer can be designed to be 70-85% of the thickness of the active material layer.

[0012] In some embodiments of the present application, the insulating buffer layer is an insulating ceramic layer.

[0013] In some embodiments of the present application, the material of the insulating ceramic layer comprises a first ceramic powder and a first binder, and the amount of the first binder accounts for 10-30% of the total weight of the insulating ceramic layer, for example, 10%, 12%, 15%, 20%, 25%, 28%, or 30%. By controlling the content of the first binder in the insulating ceramic layer within the above range, the content of the first binder is much higher than the conventional amount of the binder in the active material layer of the positive or negative electrode sheet (usually less than 5%), so that after the electrolyte is injected in the subsequent battery preparation process, the first binder in the insulating ceramic layer will swell after absorbing the electrolyte, increasing the thickness of the insulating ceramic layer. After processes such as formation and aging, the first binder in the insulating ceramic layer can permeate into the porous structure of the separator in large amounts, so that the adhesion between the positive and negative electrode sheets and the separator is strengthened, achieving the fixation and adhesion of the positive and negative electrode sheets and the separator. In addition, the area of the negative electrode sheet edge beyond the active material layer on the positive electrode sheet does not participate in the storage of lithium ions in the charging and discharging process, and the negative electrode sheet edge surface will not deposit lithium.

[0014] Preferably, the first binder is polyvinylidene fluoride (PVDF), because it is chemically stable and will not react with the electrolyte to affect the performance of the battery cell. In addition, the binder in the active material layer of the positive and negative electrode sheets is also preferably PVDF. The use of PVDF as the first binder in the insulating ceramic layer and the binder in the active material layer facilitates the fusion and stability of the junction area between the insulating ceramic layer and the active material layer.

[0015] In some embodiments of the present application, the separator comprises a separator substrate and a ceramic layer, and the ceramic layer is arranged on the surface of the separator substrate. The material of the ceramic layer comprises a second ceramic powder and a second binder. Preferably, the material of the ceramic layer comprises 70-99 wt% of the second ceramic powder and 1-30 wt% of the binder. The second binder can be the same as the first binder in the insulating ceramic layer to facilitate the fusion and stability of the junction area between the insulating ceramic layer and the separator, and is preferably polyvinylidene fluoride (PVDF).

[0016] In some embodiments of the present application, the battery cell is a jelly-roll type battery cell or a stacked type battery cell.

[0017] In some embodiments of the present application, the battery cell is a jelly-roll type battery cell, and the insulating buffer layer is arranged on both sides of the active material layer in the direction of winding of the battery cell.

[0018] In some embodiments of the present application, the battery cell is a stacked battery cell, and the insulating buffer layer is attached to the outer edge of the active material layer. That is, the insulating buffer layer is attached to each side edge of the active material layer. In this way, the insulating buffer layer can effectively prevent the battery cell from being damaged in all directions. In some embodiments of the present application, when the battery cell is a stacked battery cell, the insulating buffer layer can be attached to only two opposite side edges of the active material layer, which correspond to the side of the assembled battery cell where the tab is led out and the opposite side, i.e., the head and tail of the electrode plate. Based on the above structure, the gap between the side edge of the electrode plate and the outer packaging aluminum plastic film is smaller than the gap between the head and tail of the electrode plate and the outer packaging. Therefore, the side edge of the electrode plate is less likely to be damaged during the drop test. In addition, if the stacked battery cell is formed by stacking in the "Z" shape along the direction perpendicular to the tab leading-out side, the side edge of the electrode plate can be completely covered by the separator, and even if it is damaged, it is also covered by the separator and is less likely to come into contact with the electrode plate to form a short circuit.

[0019] In a second aspect of the present application, a method for preparing any of the battery cells according to the first aspect of the present application is provided, which comprises the following steps:

[0020] S1, preparing an insulating buffer layer preparation slurry;

[0021] S2, preparing a positive electrode plate and a negative electrode plate, comprising: preparing an active material slurry, then coating the active material slurry on the surface of a current collector to form an active material coating layer, and then attaching and coating the insulating buffer layer preparation slurry on at least two side edges of the active material coating layer, followed by drying and rolling;

[0022] S3, assembling the positive electrode plate and the negative electrode plate with a separator to prepare a battery cell;

[0023] The order of preparing the insulating buffer layer preparation slurry in step S1 and preparing the active material slurry in step S2 is not limited.

[0024] In step S1, the insulating buffer layer preparation slurry can be prepared by mixing ceramic powder, a binder and a solvent. The mass ratio of the ceramic powder, the binder and the solvent can be controlled to be (7-9):(1-3):10. The ceramic powder can be alumina or boehmite, and the binder is preferably polyvinylidene fluoride (PVDF). The solvent is generally an organic solvent, such as N-methyl pyrrolidone (NMP).

[0025] In addition, in step S2, the preparation process of the positive electrode plate and the negative electrode plate, the corresponding current collector is selected according to the requirements, and the corresponding active material slurry is prepared. After rolling, further slitting and edge cutting can be performed, and the width of the final negative electrode plate is ensured to be the same as that of the positive electrode plate (i.e., the outer edges of the electrode plates are flush). In addition, the width of the insulating buffer layer on the positive electrode plate is greater than that on the negative electrode plate.

[0026] The step S3 can include: arranging the diaphragm between the positive electrode sheet and the negative electrode sheet, and adopting the winding or laminating mode to make the battery cell.

[0027] In a third aspect of the present application, a lithium ion battery is provided, which comprises any one of the battery cells provided in the first aspect of the present application. The lithium ion battery can specifically comprise the above battery cell, electrolyte and shell, and the battery cell and the electrolyte are sealed in the shell. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the drawings and examples, in which:

[0029] Figure 1 A schematic diagram of the coating process of the positive electrode sheet in Example 1 is shown in the figure;

[0030] Figure 2 A schematic diagram of the structure of the positive electrode sheet prepared in Example 1 is shown in the figure;

[0031] Figure 3 A schematic diagram of the structure of the negative electrode sheet prepared in Example 1 is shown in the figure;

[0032] Figure 4 A schematic diagram of the structure of the battery cell prepared in Example 1 is shown in the figure;

[0033] Figure 5 A schematic diagram of the structure of the battery cell prepared in Example 1 is shown in the figure; Figure 4 A schematic diagram of the structure of a laminated unit in the battery cell is shown in the figure;

[0034] Figure 6 A schematic diagram of the structure of the lithium ion battery prepared in Example 1 is shown in the figure. DETAILED DESCRIPTION

[0035] The concept and technical effects of the present application will be described below in conjunction with the examples, so as to fully understand the purposes, features and effects of the present application. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples of the present application, other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0036] Example 1

[0037] In this example, a lithium ion battery is prepared, and the preparation method comprises the following steps:

[0038] S1, preparation of the insulating ceramic slurry, comprising: mixing alumina ceramic powder, binder polyvinylidene fluoride (PVDF) and N-methyl pyrrolidone (NMP) to form an insulating ceramic slurry by stirring, wherein the mass ratio of the alumina ceramic powder, PVDF and NMP is 8:2:10 (i.e. 4:1:5);

[0039] S2. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, conductive carbon, binder polyvinylidene fluoride (PVDF), and solvent N-methylpyrrolidone (NMP) are mixed and stirred at a mass ratio of 97:1.4:1.6:82 to prepare a positive electrode active slurry; then... Figure 1 As shown, an aluminum foil with a thickness of 10 μm is used as the positive electrode current collector 11a. The positive electrode current collector 11a travels along the coating belt direction M. Positive electrode active slurry is coated on both surfaces of the positive electrode current collector 11a to form a positive electrode active slurry layer 12a. While coating the positive electrode active slurry layer 12a, an insulating ceramic slurry is simultaneously coated on the edge of the positive electrode active slurry layer 12a to form an insulating ceramic slurry layer 13a located at the edge of the positive electrode active slurry layer 12a. Then, through drying, rolling, slitting, and edge trimming processes, a positive electrode sheet is obtained.

[0040] The positive electrode sheet produced is as follows Figure 2 As shown, the positive electrode 10 includes a positive current collector 11, a positive active material layer 12, and a first insulating ceramic layer 13. The positive active material layer 12 is disposed on both surfaces of the positive current collector 11. The first insulating ceramic layer 13 is disposed on both surfaces of the positive current collector 11 in the same layer as the positive active material layer 12. The first insulating ceramic layer 13 is attached to the outer edge of the positive active material layer 12, and the outer edge of the first insulating ceramic layer 13 is flush with the outer edge of the positive current collector 11. The thicknesses of the positive active material layer 12 and the first insulating ceramic layer 13 are 48 μm and 35 μm, respectively. Along the direction perpendicular to the coating tape, the width of one side of the first insulating ceramic layer 13 is 1.5 mm, the width of the positive active material layer 12 is 100 mm, and thus the total width of the positive electrode 10 is 103 mm.

[0041] S3. Prepare the negative electrode sheet according to a similar operation to step S2, including: mixing and stirring the negative electrode active material graphite, conductive carbon, binder PVDF, and solvent N-methylpyrrolidone (NMP) in a mass ratio of 97.3:1.1:1.6:100 to prepare a negative electrode active slurry; taking a copper foil with a thickness of 6μm as the negative electrode current collector, coating the negative electrode active slurry on both surfaces of the negative electrode current collector with an area size larger than the area size of the positive electrode active slurry layer, and simultaneously coating the edge of the negative electrode active slurry layer with an insulating ceramic slurry to form an insulating ceramic slurry layer at the edge of the negative electrode active slurry layer, and then performing drying, rolling, slitting, and edge trimming processes to obtain the negative electrode sheet.

[0042] The resulting negative electrode sheet is as follows Figure 3As shown, the negative electrode sheet 20 includes a negative electrode current collector 21, a negative electrode active material layer 22, and a second insulating ceramic layer 23. The negative electrode active material layer 22 is arranged on both surfaces of the negative electrode current collector 21, and the size (length and width) of the negative electrode active material layer 22 in the direction parallel to the negative electrode current collector 21 is greater than the size of the positive electrode active material layer 12 in the direction parallel to the positive electrode current collector 11. The second insulating ceramic layer 23 is arranged on both surfaces of the negative electrode current collector 21 together with the negative electrode active material layer 22 and on the edges of the negative electrode active material layer 22. The outer edge of the second insulating ceramic layer 23 is flush with the outer edge of the negative electrode current collector 21. The thicknesses of the negative electrode active material layer 22 and the second insulating ceramic layer 23 are 61 μm and 48 μm, respectively. In the direction perpendicular to the coating running direction, the single-side width of the second insulating ceramic layer 23 is 0.5 mm, the width of the negative electrode active material layer 22 is 102 mm, and thus the total width of the negative electrode sheet is 103 mm. The overall size (length and width) of the negative electrode sheet 20 in the direction parallel to the negative electrode current collector 21 is the same as the overall size of the positive electrode sheet 10 in the direction parallel to the positive electrode current collector 11.

[0043] S4, Preparation of the battery cell: Take the separator film (the substrate is PE, and the surface is coated with a mixed coating layer of 95 wt% ceramic powder and 5 wt% PVDF), and then stack the positive electrode sheet, the separator film, and the negative electrode sheet in sequence to prepare the battery cell 40. The structure of the battery cell 40 is shown in Figure 4 and Figure 5 As shown, Figure 4 is a schematic structural diagram of the battery cell 40 prepared in this embodiment, Figure 5 is Figure 4 a schematic structural diagram of a stack unit in the battery cell 40. The stack unit includes the positive electrode sheet 10, the separator film 30, and the negative electrode sheet 20 arranged in sequence. The battery cell includes a plurality of stack units arranged in sequence. The positive electrode sheet 10 in each stack unit is arranged opposite to the negative electrode sheet 20 in the adjacent stack unit, and the separator film 30 is arranged between the positive electrode sheet 10 and the negative electrode sheet 20. The negative electrode sheet 20 in each stack unit is arranged opposite to the positive electrode sheet 10 in the adjacent stack unit, and the separator film 30 is arranged between the negative electrode sheet 20 and the positive electrode sheet 10.

[0044] S5, Package the battery cell prepared in step S4 with an aluminum plastic film, inject electrolyte, and then prepare the finished lithium ion battery through formation and capacity grading. The structure of the finished lithium ion battery is shown in Figure 5 The finished lithium ion battery includes the aluminum plastic film shell 50 and the battery cell 40.

[0045] Comparative Example 1

[0046] A lithium ion battery was prepared in the present comparative example, and the preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that the second insulating ceramic layer was not provided on the negative electrode sheet in step S3 of the present comparative example, and the negative electrode active material layer was used instead. Specifically, during the preparation process of coating the negative electrode active paste on the negative electrode current collector, the second insulating ceramic layer setting region in Example 1 was coated with the negative electrode active paste, and other operations were similar to those in Example 1. The prepared negative electrode sheet included the negative electrode current collector and the negative electrode active material layer, the negative electrode active material layer was arranged on both surfaces of the negative electrode current collector, the outer edge of the negative electrode active material layer was flush with the outer edge of the negative electrode current collector, the thickness of the negative electrode active material layer was 61 μm, the width of the negative electrode active material layer along the direction perpendicular to the coating running direction was 103 mm, the size of the negative electrode active material layer along the direction parallel to the negative electrode current collector was greater than the size of the positive electrode active material layer along the direction parallel to the positive electrode current collector, and the overall size of the negative electrode sheet along the direction parallel to the negative electrode current collector was the same as the overall size of the positive electrode sheet along the direction parallel to the positive electrode current collector. Other operations of the present comparative example were the same as those in Example 1.

[0047] Comparative Example 2

[0048] A lithium ion battery was prepared in the present comparative example, and the preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that the first insulating ceramic layer was not provided on the positive electrode sheet in step S2 of the present comparative example, and the positive electrode active material layer was not used instead. Specifically, after the positive electrode active paste layer was prepared on the positive electrode current collector according to the operation in step S2 in Example 1, the positive electrode current collector was prepared by directly performing the drying, rolling, slitting, and edge cutting processes. The positive electrode sheet included the positive electrode current collector and the positive electrode active material layer, and the positive electrode active material layer was arranged on both surfaces of the positive electrode current collector. The outer edge of the positive electrode active material layer was flush with the outer edge of the negative electrode current collector, the thickness of the positive electrode active material layer was 48 μm, and the width of the positive electrode active material layer along the direction perpendicular to the coating running direction was 100 mm. Then, the negative electrode sheet was prepared according to the operation in step S3 in Example 1, and the width size of the negative electrode sheet along the coating running direction was greater than the width size of the positive electrode sheet along the coating running direction. Other operations were the same as those in Example 1.

[0049] Comparative Example 3

[0050] A lithium ion battery was prepared in the present comparative example. The preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that: in the present comparative example, the preparation of the positive electrode sheet in step S2 and the preparation of the negative electrode sheet in step S3 were both cancelled, and the area of the current collector where the insulating ceramic slurry was originally coated was cut off when the electrode sheet was cut, and other operations were the same as in Example 1. The size of the negative active material layer in the parallel direction of the negative current collector was greater than the size of the positive active material layer in the parallel direction of the positive current collector. In the present comparative example, the edges of the current collectors on the positive and negative electrode sheets were not provided with an insulating ceramic layer, and the overall size of the negative electrode sheet in the parallel direction of the negative current collector was greater than the overall size of the positive electrode sheet in the parallel direction of the positive current collector.

[0051] Comparative Example 4

[0052] A lithium ion battery was prepared in the present comparative example. The preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that: in the present comparative example, the mass ratio of the alumina ceramic powder, PVDF and NMP in step S1 was adjusted to 93:7:100 from 4:1:5 in Example 1. The content of the binder PVDF in the insulating ceramic slurry in the present comparative example was less than 10% and higher than the proportion of the binder PVDF in the active material slurry on the electrode sheet. Other operations were the same as in Example 1.

[0053] Comparative Example 5

[0054] A lithium ion battery was prepared in the present comparative example. The preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that: in the present comparative example, the mass ratio of the alumina ceramic powder, PVDF and NMP in step S1 was adjusted to 98.6:1.4:100 from 4:1:5 in Example 1. The content of the binder PVDF in the insulating ceramic slurry in the present comparative example was less than 10% and similar to the proportion of the binder PVDF in the active material slurry on the electrode sheet. Other operations were the same as in Example 1.

[0055] Comparative Example 6

[0056] A lithium ion battery was prepared in the present comparative example. The preparation method of the lithium ion battery in the present comparative example was different from that in Example 1 in that: in the present comparative example, the width of the active material layer in the positive electrode sheet prepared in step S2 was changed to 101.6 mm, and the single-side width of the first insulating ceramic layer was changed to 0.4 mm. In step S3, the single-side width of the second insulating ceramic layer in the negative electrode sheet prepared after cutting was changed to 0.2 mm. Other operations were the same as in Example 1. In the parallel direction of the current collector, the size of the negative active material layer on the negative electrode sheet was greater than the size of the positive active material layer on the positive electrode sheet. The overall size of the negative electrode sheet was the same as the overall size of the positive electrode sheet.

[0057] Comparative Example 7

[0058] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the width of the active material layer in the positive electrode sheet prepared in step S2 of this comparative example was changed to 101.8 mm, and the single-side width of the first insulating ceramic layer was changed to 0.6 mm. Other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than the size of the positive electrode active material layer on the positive electrode sheet. The overall size of the negative electrode sheet was the same as the overall size of the positive electrode sheet.

[0059] Example 2

[0060] A lithium ion battery was prepared in this example. The preparation method of the lithium ion battery in this example was different from that in Example 1 in that the width of the active material layer in the positive electrode sheet prepared in step S2 of this comparative example was changed to 101.6 mm, and the single-side width of the first insulating ceramic layer was changed to 1.2 mm. The single-side width of the second insulating ceramic layer in the negative electrode sheet prepared after cutting in step S3 was changed to 1.0 mm. Other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than the size of the positive electrode active material layer on the positive electrode sheet. The overall size of the negative electrode sheet was the same as the overall size of the positive electrode sheet.

[0061] Example 3

[0062] A lithium ion battery was prepared in this example. The preparation method of the lithium ion battery in this example was different from that in Example 1 in that the mass ratio of the aluminum oxide ceramic powder, PVDF and NMP in step S1 of this comparative example was changed to 85:15:100. Other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than the size of the positive electrode active material layer on the positive electrode sheet. The overall size of the negative electrode sheet was the same as the overall size of the positive electrode sheet.

[0063] Example 4

[0064] A lithium ion battery was prepared in this example. The preparation method of the lithium ion battery in this example was different from that in Example 1 in that the mass ratio of the aluminum oxide ceramic powder, PVDF and NMP in step S1 of this comparative example was changed to 75:25:100. Other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than the size of the positive electrode active material layer on the positive electrode sheet. The overall size of the negative electrode sheet was the same as the overall size of the positive electrode sheet.

[0065] Comparative Example 8

[0066] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the thickness of the first insulating ceramic layer in step S2 of this comparative example was 12 μm. The thickness of the second insulating ceramic layer in S3 was 24 μm, respectively; other operations were the same as in Example 1; wherein in the direction parallel to the current collector, the size of the negative active material layer on the negative electrode sheet was larger than that of the positive active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet was the same as that of the positive electrode sheet.

[0067] Comparative Example 9

[0068] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the thickness of the first insulating ceramic layer in step S2 of this comparative example was 24 μm. The thickness of the second insulating ceramic layer in S3 was 36 μm, respectively; other operations were the same as in Example 1; wherein in the direction parallel to the current collector, the size of the negative active material layer on the negative electrode sheet was larger than that of the positive active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet was the same as that of the positive electrode sheet.

[0069] Comparative Example 10

[0070] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the single-side width of the first insulating ceramic layer in the positive electrode sheet prepared in step S2 of this comparative example was 1.5 mm, the width of the positive active material layer was 98 mm, and the total width of the positive electrode sheet was 101 mm. The single-side width of the second insulating ceramic layer in the negative electrode sheet prepared in step S3 was 1.5 mm, the width of the negative active material layer was 100 mm, and the total width of the negative electrode sheet was 103 mm; other operations were the same as in Example 1; wherein in the direction parallel to the current collector, the size of the negative active material layer on the negative electrode sheet was larger than that of the positive active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet was the same as that of the positive electrode sheet.

[0071] Comparative Example 11

[0072] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the single-side width of the first insulating ceramic layer in the positive electrode sheet prepared in step S2 of this comparative example was 3.5 mm, the width of the positive electrode active material layer was 96 mm, and thus the total width of the positive electrode sheet was 103 mm. The single-side width of the second insulating ceramic layer in the negative electrode sheet prepared in step S3 was 1.5 mm, the width of the negative electrode active material layer was 98 mm, and thus the total width of the negative electrode sheet was 101 mm; other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than that of the positive electrode active material layer on the positive electrode sheet, and the overall size of the negative electrode sheet was the same as that of the positive electrode sheet.

[0073] Comparative Example 12

[0074] A lithium ion battery was prepared in this comparative example. The preparation method of the lithium ion battery in this comparative example was different from that in Example 1 in that the single-side width of the second insulating ceramic layer in the negative electrode sheet prepared in step S3 of this comparative example was 0.9 mm, the width of the negative electrode active material layer was 101 mm, and thus the total width of the negative electrode sheet was 102.8 mm; other operations were the same as in Example 1. In the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet was greater than that of the positive electrode active material layer on the positive electrode sheet, and the overall size of the negative electrode sheet was the same as that of the positive electrode sheet.

[0075] For ease of comparison, the general settings of the above examples and comparative examples are listed in Table 1 as follows. In the last column (whether the positive and negative electrode sheets are equal in width) of Table 1, Y represents YES and N represents NO.

[0076] Table 1

[0077]

[0078] Performance Test

[0079] The lithium ion batteries prepared in the above examples and comparative examples were respectively subjected to performance tests, which specifically included:

[0080] (1) Drop test

[0081] The specific test method was as follows: the lithium ion battery was placed in a test fixture, dropped from a height of 1 m in the order of six faces and four corners in turn downward, and a total of 40 drops were tested in 4 rounds.

[0082] Short circuit judgment: 48 h before the drop test, the cell voltage U1 was tested; 1 h before the start of the drop test, the cell voltage U2 was tested after the test; 48 h after the drop test, the cell voltage U3 was tested; if U3-U2> U2-U1, it was determined that an internal short circuit occurred in the cell.

[0083] Visual inspection: check the aluminum plastic film for damage and liquid leakage before and after the drop test.

[0084] Pole piece damage inspection: for the battery pack without short circuit, further disassemble the lithium ion battery after the drop test to confirm whether the pole piece of the battery cell is damaged.

[0085] (2) Lithium precipitation detection

[0086] The specific test method is: the ambient temperature is 25±3℃. 1) Charging: first charge at 0.5C to 4.4V, and then charge at constant voltage to 0.02C cut-off, and stand for 5min; 2) Discharge: 0.5C constant voltage charging to 3.0V cut-off, and stand for 5min; 3) Repeat steps 1)~2) 10 times; 4) After 10 times of charging and discharging, fully charge the battery cell again, then disassemble the battery cell, and visually inspect whether there is lithium precipitation at the edge area of the pole piece.

[0087] The lithium ion batteries prepared in each example and comparative example are subjected to drop and full charge lithium precipitation tests according to the above method, and the results are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] From the above, by comparing the performance test results of the lithium ion batteries of Example 1 and Comparative Examples 1~3, it can be seen that in Example 1, by designing the positive and negative pole pieces to have the same width, and by setting the insulating ceramic layer on the surface of the current collector of the positive and negative pole pieces and on the two opposite side edges of the active material layer, the risk of internal short circuit after the battery drop can be reduced; in Comparative Example 1, although the positive and negative pole pieces are designed to have the same width, the insulating ceramic layer is not set on the two side edges of the active material layer on the surface of the current collector of the negative pole piece, so the battery still has the risk of internal short circuit after drop; in Comparative Example 2, while ensuring that the size of the negative active material layer is greater than that of the positive active material layer, the insulating ceramic layer is not set on the two side edges of the active material layer on the surface of the current collector of the positive pole piece, and then the size of the negative pole piece is greater than that of the positive pole piece, so the battery has a high risk of internal short circuit after drop; and in Comparative Example 3, the design of the conventional lithium ion battery is adopted, the insulating ceramic layer is not set on the two side edges of the active material layer on the surface of the current collector of the positive and negative pole pieces, and the size of the negative pole piece is greater than that of the positive pole piece, so the lithium ion battery has a very high risk of internal short circuit after drop. Moreover, in the lithium ion batteries of Comparative Examples 1~3, the width of the active material layer on the negative pole piece is greater than that on the positive pole piece by more than 2mm, and the active material layer area on the positive pole piece is less likely to exceed the active material layer area on the negative pole piece, which can effectively avoid lithium precipitation at the edge of the negative pole piece.

[0092] Comparative Example 1 and Comparative Examples 4, 5 can be seen, the content of the binder PVDF in the insulating ceramic layer in Comparative Example 4 is 7%, which is lower than 10% and higher than the content of the binder PVDF in the active material layer of the positive and negative electrode sheets, and the content of the binder PVDF in the insulating ceramic layer in Comparative Example 5 is 1.4%, which is lower than 10% and similar to the content of the binder PVDF in the active material layer of the positive and negative electrode sheets. The content of the binder in Comparative Examples 4, 5 is too low, and the binder cannot fully penetrate into the porous structure of the separator during the preparation of the lithium ion battery to strengthen the adhesion between the positive and negative electrode sheets and the separator, and thus the adhesion between the positive and negative electrode sheets and the separator is still limited, and the battery still has a high risk of short circuit after falling.

[0093] Further comparing Example 1, 8 and Comparative Examples 6-7, the positive and negative electrode sheets in the lithium ion battery of Comparative Example 6 are set to the same width, but the single-side width of the insulating ceramic layer on the negative electrode sheet is 0.2 mm, and the single-side width of the insulating ceramic layer on the positive electrode sheet is 0.4 mm, the width of the insulating ceramic layer is insufficient, and the adhesion of the edge of the electrode sheet is not enough, which cannot well play the role of preventing the electrode sheet from being damaged and short-circuited, and the lithium ion battery has a high risk of short circuit after falling; the positive and negative electrode sheets in the lithium ion battery of Comparative Example 7 are set to the same width, and the single-side width of the insulating ceramic layer on the negative electrode sheet is 0.5 mm, and the single-side width on the positive electrode sheet is 0.6 mm, that is, the single-side width of the insulating ceramic layer on the positive and negative electrode sheets is more than 0.5 mm, which has a good protection for the edge of the electrode sheet, and can effectively prevent the edge from short-circuiting due to falling, but the width of the active material layer on the negative electrode sheet is only 0.2 mm larger than that on the positive electrode sheet. Due to the tolerance of coating, winding alignment, the above design of the active material layer of the positive and negative electrode sheets cannot effectively avoid the above tolerance, resulting in that the negative active material layer in some areas cannot completely exceed the positive active material layer, and thus lithium precipitation exists at the edge of the negative electrode. On the basis of Comparative Example 6, the single-side width of the insulating ceramic layer on the positive electrode sheet in the lithium ion battery of Example 2 is increased to 1.2 mm, and the single-side width of the insulating ceramic layer on the negative electrode sheet is increased to 1.0 mm, and the width difference of the active material layer on the positive and negative electrode sheets is 0.4 mm, which neither short-circuits nor precipitates lithium.

[0094] Comparing the lithium ion batteries of Example 3 and Example 4 with Example 1, the content of the binder PVDF in the insulating ceramic layer is adjusted to 10% and 25% respectively, which can effectively reduce the risk of internal short circuit of the battery after falling.

[0095] Comparing the lithium ion batteries of Comparative Example 8 and Comparative Example 9 with Example 1, the thickness of the ceramic insulating layer is reduced, the adhesion between the electrode sheet and the separator is poor, and thus the edge of the electrode sheet is damaged and short-circuited.

[0096] Compared with the lithium ion battery of Example 1, the positive and negative electrode sheets of Comparative Example 10 and Comparative Example 11 adopt unequal width design. Although the tests show that the lithium ion batteries of Comparative Example 10 and Comparative Example 11 do not short circuit and do not lithiumize, it is found that the edges of the electrode sheets of the lithium ion batteries of Comparative Example 10 and Comparative Example 11 are damaged after the short circuit test, so there is a risk of short circuit, while the edges of the electrode sheets of the lithium ion battery of Example 1 are not damaged. In addition, the energy density of the lithium ion batteries of Example 1, Comparative Example 10 and Comparative Example 11 is tested respectively, and it is found that the energy density of the lithium ion batteries of Comparative Example 10 and Comparative Example 11 is reduced by 2.0% and 4.0% respectively compared with Example 1. Compared with Example 1, the positive and negative electrodes of Comparative Example 12 adopt unequal width design. The test shows that the lithium ion battery of Comparative Example 12 does not short circuit and does not lithiumize, and the energy density of the lithium ion batteries of Example 1 and Comparative Example 12 is equal, but the edges of the electrode sheets of the lithium ion battery of Comparative Example 12 are also damaged after the short circuit test, so there is a risk of short circuit. Therefore, in order to effectively reduce the risk of internal short circuit after the battery falls and ensure the energy density of the battery, the positive and negative electrode sheets are preferably designed with equal width (i.e. the outer edges are flush).

[0097] From the above, the positive and negative electrode sheets of the present application adopt the same width design in the direction parallel to the separator; and the insulating buffer layer is arranged on the surface of the current collector of the positive and negative electrode sheets and at least two side edges of the active material layer, and the insulating buffer layer is configured to fix and bond the positive and negative electrode sheets and the separator, which can strengthen the bonding of the positive and negative electrode sheets and the separator and improve the overall rigidity of the battery cell. After being assembled into a battery, if displacement occurs when falling, the overall displacement of the battery cell (i.e. the overall displacement amount of the positive and negative electrode sheets is similar) occurs, and the edges of the positive and negative electrode sheets impact the battery compartment or the protection plate, the insulating buffer layer at the edges of the positive and negative electrode sheets can act as a buffer zone to bear the impact together and simultaneously, thereby effectively avoiding the problem that the design of the negative electrode sheet size being larger than the positive electrode sheet size easily leads to the bending of the internal active material layer to generate debris or the interface to be damaged, causing internal short circuit or electric energy drop, thereby reducing the risk of internal short circuit after falling. In addition, by controlling the insulating ceramic layer on the positive and negative electrode sheets within a certain range, the generation of lithiumization phenomenon can be avoided.

[0098] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application.

Claims

1. An electric cell, characterized by, The application relates to a battery cell, comprising: a positive electrode sheet, a negative electrode sheet and a separator, the separator being arranged between the positive electrode sheet and the negative electrode sheet, and the outer edges of the positive electrode sheet and the negative electrode sheet being flush; the positive electrode sheet and the negative electrode sheet each independently comprising a current collector, an active material layer and an insulating buffer layer, the active material layer and the insulating buffer layer being arranged on the surface of the current collector; the insulating buffer layer being arranged on at least two side edges of the active material layer and being configured to fix and bond the positive electrode sheet and the negative electrode sheet to the separator; the single-edge width of the insulating buffer layer in the positive electrode sheet is greater than the single-edge width of the insulating buffer layer in the negative electrode sheet; the single-edge width of the insulating buffer layer in the negative electrode sheet is greater than or equal to 0.5 mm; the width difference between the active material layer on the negative electrode sheet and the active material layer on the positive electrode sheet is greater than 0.4 mm; the insulating buffer layer is an insulating ceramic layer, the material of the insulating ceramic layer comprising a first ceramic powder and a first binder, the mass of the first binder accounting for 10-30% of the total mass of the insulating ceramic layer; the thickness of the insulating buffer layer is less than or equal to the thickness of the active material layer; the separator comprises a separator base and a ceramic layer, the ceramic layer being arranged on the surface of the separator base, the material of the ceramic layer comprising a second ceramic powder and a second binder; the battery cell is a winding type battery cell or a stacking type battery cell; the battery cell is a winding type battery cell, and the insulating buffer layer is arranged on two opposite side edges of the active material layer in the winding direction of the battery cell; the battery cell is a stacking type battery cell, and the insulating buffer layer is arranged on the outer edge of the active material layer; the application further relates to a preparation method of the battery cell, comprising the following steps: S1, preparing an insulating buffer layer preparation slurry; S2, preparing a positive electrode sheet and a negative electrode sheet, each independently comprising the following steps: preparing an active material slurry, then coating the active material slurry on the surface of a current collector to form an active material coating layer, and then coating an insulating buffer layer preparation slurry on at least two side edges of the active material coating layer, and then drying and rolling; S3, assembling a battery cell by using a separator and the positive electrode sheet and the negative electrode sheet; wherein the order of preparing the insulating buffer layer preparation slurry in step S1 and preparing the active material slurry in step S2 is not limited; the application further relates to a battery cell comprising any one of the battery cells in claims 1-6. ​ ​ ​ 2. The electric cell of claim 1, wherein, ​ 3. The electric cell of claim 1, wherein, ​ 4. The electric cell of any one of claims 1 to 3, wherein, ​ 5. The electric cell of claim 4, wherein, ​ 6. The electric cell of claim 4, wherein, ​ 7. The method of producing an electric cell according to any one of claims 1 to 6, characterized by, ​ ​ ​ ​ ​ 8. A lithium-ion battery, characterized by, ​

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