CN116315509A - A kind of electric core and preparation method thereof and lithium ion battery - Google Patents

Abstract

The invention discloses an electric core, a preparation method thereof and a lithium ion battery, wherein the electric core comprises a positive plate, a negative plate and a diaphragm, the diaphragm is clamped between the positive plate and the negative plate, and the outer edges of the positive plate and the negative plate are flush; the positive electrode plate and the negative electrode plate respectively and independently comprise a current collector, an active material layer and an insulating buffer layer, wherein the active material layer and the insulating buffer layer are arranged on the surface of the current collector; the insulating buffer layer is attached to at least two sides of the active material layer and is configured to fixedly bond the positive and negative plates and the diaphragm. By the design of the same width of the positive and negative plates and the arrangement of the insulating buffer layer on the positive and negative plates, the risk of internal short circuit after falling can be effectively reduced.

Description

A kind of electric core and its preparation method and lithium ion battery

technical field

The invention relates to the technical field of batteries, in particular to a battery cell, a preparation method thereof and a lithium ion battery.

Background technique

Lithium-ion batteries have the advantages of high voltage, high energy density, and long life, and are widely used in consumer electronics. As the demand for energy density increases year by year, and the capacity of battery cells is getting higher and higher, and the weight is getting heavier, it is also necessary to take into account specific performance requirements such as fast charging and fast discharging, and the safety performance of the whole machine when the battery is dropped higher requirements.

The battery of the whole machine is usually fixed by adhesive paper bonding the outer surface of the aluminum-plastic film of the battery cell, but there is usually no adhesion between the inside of the aluminum-plastic film and the bare battery cell, and due to the presence of electrolyte, when the whole machine falls , There will be sliding between the bare cell and the aluminum-plastic film, and the bare cell impacts the top packaging area, or even indirectly hits the top protection plate and the battery compartment of the host, causing electrolyte leakage, short circuit, or even thermal runaway and fire. In order to solve this problem, hot-melt tape is often used between the bare cells of the battery and the outer packaging aluminum-plastic film to enhance the bonding between the bare cells and the aluminum-plastic film, so as to improve the stability of the internal bare cells. The problem of sliding displacement when falling. However, the hot melt adhesive only bonds the outermost pole piece of the battery core, and there is still a phenomenon of sliding displacement between the inner pole piece when it is dropped, and the pole piece far away from the hot melt adhesive layer is still prone to displacement when it is dropped, resulting in Hitting the protective plate and 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, the purpose is to ensure that the negative electrode completely wraps the positive electrode and prevents lithium from being separated at the edge. The area is very easy to bend and generate debris, which will cause internal short circuit and cause drop failure.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the present invention proposes a battery cell, a preparation method thereof, and a lithium ion battery.

According to the first aspect of the present invention, a battery cell is proposed, including a positive electrode sheet, a negative electrode sheet, and a separator, the separator is interposed between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet and the negative electrode sheet are The outer edges of the sheet are flush; the positive electrode sheet and the negative electrode sheet each independently include a current collector, an active material layer and an insulating buffer layer, and the active material layer and the insulating buffer layer are arranged on the surface of the current collector The insulating buffer layer is attached to at least two sides of the active material layer, and is configured to fix and bond the positive electrode sheet and the negative electrode sheet to the separator. Wherein, the insulating buffer layer is preferably attached to at least two opposite sides of the active material layer.

According to the embodiment of the present invention, the electric core has at least the following beneficial effects: the electric core includes a positive electrode sheet, a negative electrode sheet, and a diaphragm, and the diaphragm is sandwiched between the positive electrode sheet and the negative electrode sheet, and the outer edges of the positive and negative electrode sheets are even; The sheet and the negative electrode sheet independently include a current collector, an active material layer and an insulating buffer layer, and the active material layer and the insulating buffer layer are arranged on the surface of the current collector; the insulating buffer layer is attached to at least two sides of the active material layer, and It is configured to fixedly bond the positive electrode sheet and the negative electrode sheet to the separator. Through the above settings, the positive and negative electrodes are designed with the same width in the direction parallel to the diaphragm; and an insulating buffer layer is attached to the surface of the positive and negative electrode collectors and at least both sides of the active material layer, and the insulating buffer layer It is configured to fix and bond the positive and negative electrodes and the separator, which can strengthen the bonding between the positive and negative electrodes and the separator, and improve the overall rigidity of the battery; after subsequent assembly into a battery, if it is dropped, the battery will be damaged. When the overall displacement occurs (that is, the overall displacement of the positive and negative electrodes is similar), when it hits the battery compartment or the protective plate, the insulating buffer layer on the edge of the positive and negative electrodes can be used as a buffer to withstand the impact at the same time, thereby effectively avoiding the size of the negative electrode. A design larger than the size of the positive electrode sheet is likely to cause the internal active material layer to bend and generate debris or the interface is damaged to cause internal short circuit or power drop, thereby reducing the risk of internal short circuit after falling.

In the above electric cores, the outer edge size of the active material layer on the negative electrode sheet is generally larger than the outer edge size of the active material layer on the positive electrode sheet; since the positive electrode sheet and the negative electrode sheet are arranged oppositely, and the outer edges of the two are flush, the positive and negative electrode sheets The side of the active material layer on the surface of the current collector is fitted with an insulating buffer layer, and the outer edge size of the active material layer on the negative electrode sheet is larger than the outer edge size of the active material layer on the positive electrode sheet, which can ensure that the negative electrode active material layer area completely covers the positive electrode active material layer area, and thus will not cause the problem of lithium precipitation due to insufficient overhang. Preferably, the difference in width of the active material layer on the positive and negative electrodes is more than 0.4mm, so as to avoid misalignment between layers during winding or slicing assembly, which will cause the edge of the positive electrode to exceed the edge of the negative electrode and lead to lithium precipitation. The width difference of the active material layer on the positive and negative electrodes can be designed according to the specific conditions such as the width tolerance of the electrode, the capacity of the winding/stacking equipment, or the number of layers of winding/stacking.

In addition, in the above cells, the outer edge of the insulating buffer layer on the positive and negative electrodes is generally flush with the outer edge of the current collector; in the direction parallel to the diaphragm, the size of the diaphragm is generally larger than the size of the positive and negative electrodes to avoid positive and negative electrodes. The negative electrode is in direct contact with the short circuit.

Specifically, the positive electrode sheet and the negative electrode sheet are provided with an active material layer and an insulating buffer layer at least on one side of the current collector, and the insulating buffer layer is attached to at least two sides of the active material layer, and is configured to connect the positive electrode sheet and the negative electrode sheet. The negative electrode sheet is fixedly bonded to the separator. For example, on the positive electrode sheet and/or the negative electrode sheet, an active material layer and an insulating buffer layer are arranged on one side of the current collector according to the above structure; material layer and insulating buffer layer. Alternatively, the positive electrode sheet and the negative electrode sheet each independently have a first area section and a second area section, and the active material layer and the insulating buffer layer on the first area section are arranged on one side surface of the current collector according to the above structure, and the second area section The active material layer and insulating buffer layer on the segment are arranged on both sides of the current collector according to the above structure. Generally speaking, the insulating buffer layer and the active material layer are disposed on the same side of the current collector, and the insulating buffer layer is attached to at least two sides of the active material layer. The insulating buffer layer is generally attached to at least two opposite sides of the active material layer.

In some embodiments of the present invention, the unilateral width of the insulating buffer layer in the positive electrode sheet is greater than the unilateral width of the insulating buffer layer in the negative electrode sheet; preferably, the unilateral width of the insulating buffer layer in the negative electrode sheet Greater than or equal to 0.5mm; preferably, the unilateral width of the insulating buffer layer on the positive electrode sheet is at least 0.2mm greater than the unilateral width of the insulating buffer layer on the negative electrode sheet; further preferably, the unilateral width of the insulating buffer layer in the positive electrode sheet is greater than or equal to 1.5mm. The above unilateral width is the unilateral width along the direction parallel to the current collector. By controlling the unilateral width of the insulating buffer layer on the positive and negative electrodes within the above range, wherein the unilateral width of the insulating buffer layer on the positive electrode is greater than the unilateral width of the insulating buffer layer on the negative electrode, it can be avoided that the active material layer area on the positive electrode exceeds the negative electrode The edge of the active material layer leads to 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 and at least two sides of the active material layer on the current collector; and on the same side, the unilateral width of the insulating buffer layer in the positive electrode sheet is greater than that of the negative electrode The single side width of the insulating buffer layer in the chip. The width of one side of the insulating buffer layer on the positive and negative electrode sheets and the width of the insulating buffer layer on the opposite side can be equal or different.

In some embodiments of the present invention, 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 exceeding the thickness of the active material layer, so as to effectively exert the effect of protecting the edge of the pole piece from the insulating buffer layer area when it is dropped, and can effectively avoid the insulating buffer layer. Excessive thickness will affect the interface between the positive and negative electrodes of the battery and affect 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 smaller 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.

In some embodiments of the present invention, the insulating buffer layer is an insulating ceramic layer.

In some embodiments of the present invention, the material of the insulating ceramic layer includes 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 , eg 10%, 12%, 15%, 20%, 25%, 28%, 30%. By controlling the content of the first binder in the insulating ceramic layer to the above range, the proportion of the first binder content is much higher than the conventional amount of the binder in the active material layer of the positive and negative plates (usually lower than 5%), and then in the subsequent battery preparation process, after the electrolyte is injected, the first binder in the insulating ceramic layer will swell after absorbing the electrolyte, so that the thickness of the insulating ceramic layer will increase, and after chemical formation, aging, etc. In the process, the first binder in the insulating ceramic layer can penetrate into the porous structure of the separator in a large amount, so that the bonding between the positive and negative electrodes and the separator is strengthened, and the positive and negative electrodes are fixedly bonded to the separator. In addition, because the area where the edge of the negative electrode exceeds the active material layer on the positive electrode does not participate in the storage of lithium ions during the charging and discharging process, lithium will not be deposited on the edge of the negative electrode.

Among them, the first binder is preferably polyvinylidene fluoride (PVDF), because its chemical properties are stable, and it will not react with the electrolyte to affect the performance of the battery cell; in addition, the binder in the active material layer on the positive and negative electrodes is also Preferably, PVDF is used, and the first binder in the insulating ceramic layer and the binder in the active material layer of the pole piece are both made of PVDF, which is beneficial to the fusion and stability of the boundary area between the insulating ceramic layer and the active material layer.

In some embodiments of the present invention, the diaphragm includes a diaphragm base and a ceramic layer, the ceramic layer is arranged on the surface of the diaphragm base, and the material of the ceramic layer includes a second ceramic powder and a second binder . Preferably, the material of the ceramic layer includes 70-99wt% of the second ceramic powder and 1-30wt% of the binder. Wherein, the second binder may be the same as the first binder in the insulating ceramic layer, so as to facilitate the fusion and stability of the junction area between the insulating ceramic layer and the diaphragm, and specifically, polyvinylidene fluoride (PVDF) is preferably used.

In some embodiments of the present invention, the cell is a wound cell or a stacked cell.

In some embodiments of the present invention, the electric core is a winding electric core, and the insulating buffer layer is attached to two sides of the active material layer facing the winding direction of the electric core.

In some embodiments of the present invention, the cell is a laminated cell, and the insulating buffer layer is attached and wound around the outer edge of the active material layer. That is, the insulating buffer layer is attached to each side of the active material layer. From the above, the insulating buffer layer is used to surround the active material layer, which can play a role of buffering and bonding in all directions, and effectively prevent drop failure. In some embodiments of the present invention, when the electric core is a laminated electric core, the insulating buffer layer can also only adhere to the two opposite sides arranged on the active material layer, and the two opposite sides correspond to the poles of the assembled electric core. The ear lead-out side and its opposite side, that is, the head and tail of the pole piece. Based on the above structural settings, the gap between the side of the pole piece and the aluminum-plastic film of the outer packaging is smaller than the gap between the head and tail of the pole piece and the outer packaging. During the drop test, the pole piece The side is not easy to be broken; in addition, if the laminated cell is composed of "Z" laminated sheets along the direction perpendicular to the lead-out side of the tab, the side of the pole piece can be completely wrapped by the diaphragm, and even if it is damaged, it will not be damaged. Wrapped by the diaphragm, it is not easy to contact the opposite electrode to form a short circuit.

In the second aspect of the present invention, a method for preparing any battery cell proposed in the first aspect of the present invention is proposed, including the following steps:

S1, preparation of insulating buffer layer to prepare slurry;

S2. Prepare the positive electrode sheet and the negative electrode sheet, including: preparing active material slurry, and then coating it on the surface of the current collector to form an active slurry coating, and attaching and coating an insulating buffer layer on at least two sides of the active slurry coating Preparation of slurry, followed by drying and rolling;

S3, preparing a battery cell by assembling the separator with 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.

In step S1, ceramic powder, binder and solvent can be mixed to prepare an insulating buffer layer to prepare slurry; the mass ratio of ceramic powder, binder and solvent can be controlled at (7~9):(1~3) :10. Among them, the ceramic powder can be alumina, boehmite, etc.; the binder is preferably polyvinylidene fluoride (PVDF); the solvent is generally an organic solvent, such as N-methylpyrrolidone (NMP).

In addition, in step S2, in the preparation process of the positive electrode sheet and the negative electrode sheet, select the corresponding current collector and prepare the corresponding active material slurry according to the requirements; Finally, the final negative electrode sheet is as wide as the positive electrode sheet (that is, the outer edge of the electrode sheet is flush); and the width of the insulating buffer layer on the positive electrode sheet is greater than the width of the insulating buffer layer on the negative electrode sheet.

Step S3 may include: sandwiching the separator between the positive electrode sheet and the negative electrode sheet, and making a cell by winding or stacking.

The third aspect of the present invention provides a lithium-ion battery, which includes any battery cell proposed in the first aspect of the present invention. The lithium-ion battery may specifically include the above electric core, electrolyte and casing, and the electric core and electrolyte are sealed in the casing.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, wherein:

Fig. 1 is the coating process schematic diagram of anode sheet in embodiment 1;

Fig. 2 is the structural representation of the positive electrode sheet that makes in embodiment 1;

Fig. 3 is the structural representation of the negative electrode sheet that makes in embodiment 1;

Fig. 4 is the structural representation of the battery cell that makes in embodiment 1;

Fig. 5 is a structural schematic diagram of a laminated unit in the cell shown in Fig. 4;

FIG. 6 is a schematic structural view of the lithium-ion battery prepared in Example 1.

Detailed ways

The conception and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments, so as to fully understand the purpose, features and effects of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts belong to The protection scope of the present invention.

Example 1

This embodiment has prepared a kind of lithium ion battery, and its preparation method comprises the following steps:

S1. Preparation of insulating ceramic slurry, including: mixing and dissolving alumina ceramic powder and binder vinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to form insulating ceramic slurry, wherein, The mass ratio of aluminum ceramic powder, PVDF and NMP is 8:2:10 (ie 4:1:5);

S2. Preparation of the positive electrode sheet: mix the positive electrode active material lithium cobaltate, conductive carbon, binder polyvinylidene fluoride (PVDF) and solvent N-methylpyrrolidone (NMP) according to the mass ratio of 97:1.4:1.6:82 Stir to make a positive electrode active slurry; then as shown in Figure 1, take an aluminum foil with a thickness of 10um as the positive electrode current collector 11a, and the positive electrode current collector 11a advances along the coating direction M, and coat the two surfaces of the positive electrode current collector 11a Positive pole active slurry, forms positive pole active slurry layer 12a; When coating positive pole active slurry layer 12a, insulator ceramic slurry is coated on the edge of positive pole active slurry layer 12a synchronously, forms and is located at positive pole active slurry layer 12a The insulating ceramic slurry layer 13a on the edge is then dried, rolled, slit, and trimmed to obtain a positive electrode sheet.

The prepared positive electrode sheet is shown in Figure 2, the positive electrode sheet 10 includes a positive electrode current collector 11, a positive electrode active material layer 12 and a first insulating ceramic layer 13, the positive electrode active material layer 12 is separately arranged on both surfaces of the positive electrode current collector 11, the second An insulating ceramic layer 13 is arranged on both surfaces of the positive electrode current collector 11 in the same layer as the positive electrode active material layer 12, and the first insulating ceramic layer 13 is attached to the outer edge of the positive electrode active material layer 12, and the first insulating ceramic layer 13 The outer edge is flush with the outer edge of the positive electrode current collector 11; the thicknesses of the positive electrode active material layer 12 and the first insulating ceramic layer 13 are 48 μm and 35 μm respectively; The width of one side is 1.5 mm, the width of the positive electrode active material layer 12 is 100 mm, and the total width of the positive electrode sheet 10 is 103 mm.

S3. Prepare the negative electrode sheet according to the operation similar to step S2, including: mixing the negative electrode active material graphite, conductive carbon, binder PVDF, and solvent N-methylpyrrolidone (NMP) according to the mass ratio of 97.3:1.1:1.6:100 Stir to make the negative electrode active slurry; take the copper foil with a thickness of 6 μm as the negative electrode current collector, and coat the negative electrode active slurry with the area size greater than the positive electrode active slurry layer area size on the two surfaces of the negative electrode current collector. The edge of the material layer is coated with insulating ceramic slurry to form an insulating ceramic slurry layer on the edge of the negative electrode active slurry layer, and then drying, rolling, slitting, and edge trimming are performed to obtain a negative electrode sheet.

The prepared negative electrode sheet is shown in Figure 3, 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 separately 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 on the direction parallel to the negative electrode current collector 21 is greater than the size of the positive electrode active material layer 12 on the direction parallel to the positive electrode current collector 11, the second insulating ceramic layer 23 and the negative electrode active material layer 22 are arranged on both surfaces of the negative electrode current collector 21 in the same layer and on the edge of the negative electrode active material layer 22, and the outer edge of the second insulating ceramic layer 23 is flush with the outer edge of the negative electrode current collector 21; the negative electrode active material layer 22 and the first negative electrode active material layer The thickness of the two insulating ceramic layers 23 is 61 μm and 48 μm respectively; The total width of the 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;

S4, the preparation of electric core: take isolation film (base material is PE, and the surface is coated with 95wt% ceramic powder and 5wt% PVDF to form the mixture coating), then stack positive electrode sheet, diaphragm, negative electrode sheet successively Sheet made battery cell 40, its structure is shown in Fig. 4 and Fig. 5, and Fig. 4 is the structural representation of the cell 40 that this embodiment makes, and Fig. 5 is the structure of a laminated unit in the cell 40 shown in Fig. 4 Schematic diagram; the laminated unit includes a stacked positive electrode sheet 10, a separator 30 and a negative electrode sheet 20, and the battery cell includes a plurality of stacked laminated units; the positive electrode sheet 10 in each laminated unit and the adjacent laminated unit The negative electrode sheet 20 in the stack is arranged oppositely, and a separator 30 is sandwiched between the two; the negative electrode sheet 20 in each laminated unit is opposite to the positive electrode sheet 10 in the adjacent laminated unit, and the two are sandwiched between them. a diaphragm 30 is provided;

S5, using aluminum-plastic film to encapsulate the battery cell obtained in step S4, then injecting electrolyte, and then forming and dividing the volume to obtain a finished lithium-ion battery. The resulting structure is shown in Figure 5, which includes an aluminum-plastic film housing 50 And cell 40.

Comparative example 1

This comparative example prepares a kind of lithium-ion battery, and the difference between the preparation method of this comparative example lithium-ion battery and embodiment 1 is: in the step S3 of this comparative example, cancel setting the second insulating ceramic layer on the negative electrode sheet, and use negative electrode active material layer instead; specifically, when the negative electrode active slurry is coated on the negative electrode current collector in the preparation process, the second insulating ceramic layer setting area in embodiment 1 is coated with the negative electrode active slurry together, and other operations are similar to the implementation Example 1, the prepared negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is separately arranged on both surfaces of the negative electrode current collector, and the outer edge of the negative electrode active material layer is flush with the outer edge of the negative electrode current collector, and The width along the direction perpendicular to the coating tape is 103mm, the thickness of the negative electrode active material layer is 61 μm, and the size of the negative electrode active material layer in the direction parallel to the negative electrode current collector is larger than that of the positive electrode active material layer in parallel to the direction of the positive electrode current collector The overall size of the negative electrode sheet in the direction parallel to the negative electrode current collector is the same as the overall size of the positive electrode sheet in the direction parallel to the positive electrode current collector. Other operations of this comparative example are the same as in Example 1.

Comparative example 2

This comparative example prepares a kind of lithium-ion battery, the difference between the preparation method of this comparative example lithium-ion battery and embodiment 1 is: in the step S2 of this comparative example, cancel setting the first insulating ceramic layer on the positive electrode sheet, and do not use positive electrode active The material layer is replaced; after the positive electrode active slurry layer is obtained on the positive electrode current collector according to the operation in step S2 in Example 1, the positive electrode current collector is obtained directly by drying, rolling, slitting, and edge trimming; the positive electrode The sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is separately arranged on both surfaces of the positive electrode current collector; the outer edge of the positive electrode active material layer is flush with the outer edge of the negative electrode current collector, and the thickness of the positive electrode active material layer is 48 μm. And be 100mm along the width perpendicular to the direction of coating travel; then make negative electrode sheet by the operation of step S3 in embodiment 1, the width dimension of negative electrode sheet on the coating travel direction is greater than that of positive electrode sheet in coating travel The width dimension in the tape direction. Other operations are the same as in Example 1.

Comparative example 3

This comparative example prepares a kind of lithium-ion battery, the difference between the preparation method of this comparative example lithium-ion battery and Example 1 is: the preparation of the positive electrode sheet in the step S2 of this comparative example and the preparation of the negative electrode sheet in the step S3 all cancel the insulating ceramics Layer setting, and when cutting the electrode piece, cut off the current collector area reserved for coating the insulating ceramic slurry, other operations are the same as in Example 1, and the size of the negative electrode active material layer in the direction parallel to the negative electrode current collector is larger than The size of the positive electrode active material layer in the direction parallel to the positive electrode current collector; and in this comparative example, the edge of the current collector on the positive and negative electrode sheets is not provided with an insulating ceramic layer, and the overall size of the negative electrode sheet in the direction parallel to the negative electrode current collector is greater than that of the positive electrode sheet The overall dimension in the direction parallel to the positive current collector.

Comparative example 4

This comparative example has prepared a kind of lithium-ion battery, and the difference between the preparation method of this comparative example lithium-ion battery and embodiment 1 is: in this comparative example, the mass ratio of alumina ceramic powder, PVDF and NMP in step S1 is determined by the embodiment. 4:1:5 in 1 is adjusted to 93:7:100, the content of binder PVDF in the insulating ceramic slurry of this comparative example is lower than 10% and higher than that of binder PVDF in the active material slurry on the pole piece Proportion, other operations are identical with embodiment 1.

Comparative example 5

This comparative example has prepared a kind of lithium-ion battery, and the difference between the preparation method of this comparative example lithium-ion battery and embodiment 1 is: in this comparative example, the mass ratio of alumina ceramic powder, PVDF and NMP in step S1 is determined by the embodiment. 4:1:5 in 1 is adjusted to 98.6:1.4:100, the content of binder PVDF in the insulating ceramic slurry of this comparative example is less than 10% and is the same as the proportion of binder PVDF in the active material slurry on the pole piece. Ratio is close, other operations are identical with embodiment 1.

Comparative example 6

This comparative example prepared a lithium ion battery, the difference between the preparation method of the lithium ion battery of this comparative example and Example 1 is that: the width of the active material layer in the positive electrode sheet prepared in step S2 of this comparative example becomes 101.6mm, The unilateral width of the first insulating ceramic layer becomes 0.4mm; the unilateral width of the second insulating ceramic layer in the negative plate obtained after cutting in step S3 becomes 0.2mm, and other operations are the same as in Example 1; wherein Parallel to the direction of the current collector, the size of the negative electrode active material layer on the negative electrode sheet is larger than the size of the positive electrode active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Comparative example 7

This comparative example prepared a lithium ion battery, the difference between the preparation method of the lithium ion battery of this comparative example and Example 1 is that: the width of the active material layer in the positive electrode sheet prepared in step S2 of this comparative example becomes 101.8mm, The unilateral width of the first insulating ceramic layer becomes 0.6mm, and other operations are the same as in embodiment 1; wherein in the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet is greater than the size of the positive electrode active material layer on the positive electrode sheet; and The overall size of the negative electrode sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Example 2

This example prepared a lithium-ion battery. The difference between the preparation method of the lithium-ion battery in this example and Example 1 is that the width of the active material layer in the positive electrode sheet prepared in step S2 of this comparative example becomes 101.6mm, The unilateral width of the first insulating ceramic layer becomes 1.2 mm; the unilateral width of the second insulating ceramic layer in the negative electrode sheet obtained after cutting in step S3 becomes 1.0 mm, and other operations are the same as in Example 1; wherein Parallel to the direction of the current collector, the size of the negative electrode active material layer on the negative electrode sheet is larger than the size of the positive electrode active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Example 3

This example prepared a lithium-ion battery. The difference between the preparation method of the lithium-ion battery in this example and Example 1 is that the mass ratio of alumina ceramic powder, PVDF and NMP in step S1 of this comparative example becomes 85: 15:100; other operations are 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 sheet is greater than the size of the positive active material layer on the positive sheet; and the overall size of the negative sheet is the same as that of the positive electrode of the positive sheet The overall dimensions of the slices are the same.

Example 4

This example prepared a lithium-ion battery. The difference between the preparation method of the lithium-ion battery in this example and Example 1 is that the mass ratio of alumina ceramic powder, PVDF and NMP in step S1 of this comparative example is changed to 75: 25:100; other operations are 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 sheet is greater than the size of the positive active material layer on the positive sheet; and the overall size of the negative sheet is the same as that of the positive electrode of the positive sheet The overall dimensions of the slices are the same.

Comparative example 8

In this comparative example, a lithium-ion battery was prepared. The difference between the preparation method of the lithium-ion battery in this comparative example and Example 1 is that the thickness of the first insulating ceramic layer in step S2 of this comparative example is 12 μm. The thickness of the second insulating ceramic layer in S3 is respectively 24 μm; Other operations are identical with embodiment 1; Wherein in the direction parallel to current collector, the size of the negative electrode active material layer on the negative electrode sheet is greater than the size of the positive electrode active material layer on the positive electrode sheet; and the negative electrode The overall size of the sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Comparative example 9

A lithium-ion battery was prepared in this comparative example. The difference between the preparation method of the lithium-ion battery in this comparative example and Example 1 is that the thickness of the first insulating ceramic layer in step S2 of this comparative example is 24 μm. The thickness of the second insulating ceramic layer in S3 is respectively 36 μm; Other operations are identical with embodiment 1; Wherein in the direction parallel to current collector, the size of the negative electrode active material layer on the negative electrode sheet is greater than the size of the positive electrode active material layer on the positive electrode sheet; and the negative electrode The overall size of the sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Comparative example 10

This comparative example prepares a kind of lithium-ion battery, the difference between the preparation method of this comparative example lithium-ion battery and Example 1 is that: the unilateral width of the first insulating ceramic layer in the positive electrode sheet made in step S2 of this comparative example is 1.5 mm, the width of the positive electrode active material layer is 98 mm, and the total width of the positive electrode sheet is 101 mm. The unilateral width of the second insulating ceramic layer in the negative electrode sheet obtained in step S3 is 1.5mm, the width of the negative electrode active material layer is 100mm, and then the total width of the negative electrode sheet is 103mm; other operations are the same as in Example 1; In the current collector direction, the size of the negative electrode active material layer on the negative electrode sheet is larger than the size of the positive electrode active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Comparative example 11

This comparative example prepares a kind of lithium-ion battery, the difference between the preparation method of this comparative example lithium-ion battery and embodiment 1 is: the unilateral width of the first insulating ceramic layer in the positive electrode piece that this comparative example step S2 makes is 3.5 mm, the width of the positive electrode active material layer is 96 mm, and the total width of the positive electrode sheet is 103 mm. The unilateral width of the second insulating ceramic layer in the negative electrode sheet obtained in step S3 is 1.5mm, the width of the negative electrode active material layer is 98mm, and then the total width of the negative electrode sheet is 101mm; other operations are the same as in Example 1; In the current collector direction, the size of the negative electrode active material layer on the negative electrode sheet is larger than the size of the positive electrode active material layer on the positive electrode sheet; and the overall size of the negative electrode sheet is the same as that of the positive electrode sheet of the positive electrode sheet.

Comparative example 12

This comparative example prepares a kind of lithium-ion battery, the difference between the preparation method of this comparative example lithium-ion battery and Example 1 is: the unilateral width of the second insulating ceramic layer in the negative electrode sheet made in step S3 of this comparative example is 0.9 mm, the width of the negative electrode active material layer is 101mm, and then the total width of the negative electrode sheet is 102.8mm; other operations are the same as in Example 1; wherein in the direction parallel to the current collector, the size of the negative electrode active material layer on the negative electrode sheet is greater than that of the positive electrode on the positive electrode sheet The size of the active material layer; and the overall size of the negative electrode sheet is the same as the overall size of the positive electrode sheet of the positive electrode sheet.

For the convenience of comparison, the general settings of the above embodiments and comparative examples are listed in Table 1 below. In the last column of Table 1 (whether the positive and negative plates are equal in width), Y means yes (YES), and N means no ( NO).

Table 1

Performance Testing

The lithium-ion batteries made by each of the above examples and comparative examples were tested for performance, specifically including:

(1) Drop test

The specific test method is: put the lithium-ion battery into the test fixture at a height of 1m, and drop it in the order of six faces and four corners facing downwards. A total of 4 rounds of tests were performed for a total of 40 drops.

Short circuit judgment: 48 hours before the drop test, test the cell voltage U ₁ ; test the cell voltage U ₂ 1 hour before the drop test, test the cell voltage U ₃ after 48 hours after the drop test; if U ₃ -U ₂ >U ₂ -U ₁ , it is determined that the battery cell has an internal short circuit.

Appearance inspection: Visually check whether the aluminum-plastic film is damaged or leaked before and after the drop test.

Pole piece damage inspection: For battery packs without short circuit, further disassemble the lithium-ion battery after the drop test to confirm whether the battery pole piece is damaged.

(2) Lithium analysis detection

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

According to the above method, the lithium-ion batteries prepared in each embodiment and comparative example were dropped and fully charged to analyze lithium, and the obtained results are shown in Table 2.

Table 2

From the above, by comparing the performance test results of Example 1 and Comparative Examples 1 to 3 lithium-ion batteries, it can be seen that in Example 1, the positive and negative electrodes are designed with the same width, and on the surface of the positive and negative electrode collectors, the active The two opposite sides of the material layer are fitted with an insulating ceramic layer, which can reduce the risk of internal short circuit after the battery is dropped; although the positive and negative plates in Comparative Example 1 are set with the same width, the two sides of the current collector surface active material layer are not placed on the negative plate. An insulating ceramic layer is arranged on the side, and the battery still has the risk of internal short circuit after falling; while in Comparative Example 2, while ensuring that the size of the negative active material layer is larger than the size of the positive active material layer, the active material layer on the surface of the current collector on the positive electrode sheet is not Insulating ceramic layers are provided on both sides, and the size of the negative electrode sheet is larger than that of the positive electrode sheet, so the battery has a high risk of internal short circuit after falling; while comparative example 3 adopts the design of a conventional lithium-ion battery, the surface of the current collector on the positive and negative electrode sheets If no insulating ceramic layer is provided on both sides of the active material layer, and the size of the negative electrode sheet is larger than that of the positive electrode sheet, the risk of internal short circuit after the lithium-ion battery is dropped is extremely high. And, in comparative example 1～3 lithium-ion battery, the width of the active material layer on the negative electrode sheet is larger than the width of the active material layer on the positive electrode sheet by more than 2mm, and the active material layer area on the positive electrode sheet is less likely to exceed the active material layer area on the negative electrode sheet, which can Effectively avoid lithium deposition at the edge of the negative electrode.

Comparing Example 1 and Comparative Examples 4 and 5, it can be seen that the content of binder PVDF in the insulating ceramic layer in Comparative Example 4 is 7%, which is lower than 10% and higher than that of the active material layer of the positive and negative plates. The content of the binder PVDF, while the content of the binder PVDF in the insulating ceramic layer in Comparative Example 5 is 1.4%, which is lower than 10% and is similar to the content of the binder PVDF in the active material layer of the positive and negative plates. The binder content in the insulating ceramic layers of ratios 4 and 5 is too low, and the binder cannot fully penetrate into the porous structure of the separator during the preparation process of the lithium-ion battery to strengthen the bonding between the positive and negative electrodes and the separator, and then The bonding force between the positive and negative electrode sheets and the separator is still relatively limited, and the battery still has a high risk of short circuit after falling.

Further comparing Examples 1 and 8 with Comparative Examples 6 to 7, although the positive and negative plates in the lithium-ion battery of Comparative Example 6 are set with the same width, the single side width of the insulating ceramic layer on the negative plate is 0.2 mm, and the single side width of the insulating ceramic layer on the positive plate is 0.2 mm. The side width is 0.4mm, the width of the insulating ceramic layer is insufficient, and the adhesion to the edge of the pole piece is not enough, so it cannot play a good role in preventing the pole piece from being damaged and short-circuited. Lithium-ion batteries have a high risk of short-circuit after falling; comparative examples 7. The positive and negative plates in the lithium-ion battery are set at the same width, and the unilateral width of the insulating ceramic layer on the negative plate is 0.5mm, and the unilateral width on the positive plate is 0.6mm, that is, the unilateral width of the insulating ceramic layer on the positive and negative plates is 0.5mm. More than mm, it has better protection for the edge of the electrode sheet, which can effectively prevent edge short circuit caused by falling, but the width of the active material layer on the negative electrode sheet is only 0.2mm larger than the width of the active material layer on the positive electrode sheet, due to coating, winding alignment There are tolerances, and the design of the active material layers of the positive and negative electrodes above cannot effectively avoid the above tolerances, resulting in the negative active material layer not completely exceeding the positive active material layer in some areas, and lithium precipitation occurs at the edge of the negative electrode. Example 2 Lithium-ion battery On the basis of comparative example 6, the unilateral width of the insulating ceramic layer on the positive electrode sheet is increased to 1.2mm, the unilateral width of the insulating ceramic layer on the negative electrode sheet is increased to 1.0mm, and the active material layer on the positive and negative electrode sheets The difference in width is 0.4mm, neither short circuit nor lithium precipitation; in the actual mass production process, in order to avoid the risk of lithium precipitation caused by unstable coating/slitting/winding process, generally the active material layer on the positive and negative electrodes The width difference control is greater than 0.4mm.

In Example 3 and Example 4, compared with Example 1, the content of the binder PVDF in the insulating ceramic layer was adjusted to 10% and 25%, respectively, which can effectively reduce the risk of internal short circuit after the battery is dropped.

Compared with Example 1, the lithium-ion batteries of Comparative Example 8 and Comparative Example 9 reduced the thickness of the ceramic insulating layer, and the adhesion between the pole piece and the separator became worse, and then the edge of the pole piece was damaged and short-circuited.

Compared with Example 1, the lithium-ion batteries of Comparative Example 10 and Comparative Example 11 adopted unequal width designs for the positive and negative electrodes. Although the test showed that the lithium-ion batteries of Comparative Example 10 and Comparative Example 11 did not have a short circuit and did not decompose lithium, but After the short-circuit test, the lithium-ion batteries of Comparative Example 10 and Comparative Example 11 were disassembled and found that the edge of the pole piece was damaged, so there was a risk of short circuit, while the lithium-ion battery of Example 1 was disassembled and no damage was found on the edge of the pole piece. In addition, the energy densities of the lithium-ion batteries of Example 1, Comparative Example 10 and Comparative Example 11 were tested respectively, and it was found that the energy densities of the lithium-ion batteries of Comparative Example 10 and Comparative Example 11 were respectively reduced by 2.0%, 4.0%. Comparative Example 12 Compared with Example 1, the positive and negative electrodes are designed with unequal widths. After testing, the lithium-ion battery of Comparative Example 12 has no short circuit and does not decompose lithium, and the energy density of the lithium-ion batteries of Example 1 and Comparative Example 12 However, after the short-circuit test, the Li-ion battery of Comparative Example 12 was disassembled and found that the edge of the pole piece was damaged, so there was 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, it is preferable to adopt a design of equal width (that is, the outer edges are flush) of the positive and negative electrodes.

From the above, the application adopts the same width design for the positive and negative electrodes in the direction parallel to the diaphragm; and on the surface of the positive and negative electrode collectors, at least two edges of the active material layer are attached to the insulating buffer layer, and the insulating buffer The layer is configured to fix and bond the positive and negative electrode sheets and the separator, which can strengthen the bonding between the positive and negative electrode sheets and the separator, and improve the overall rigidity of the battery cell; When the overall displacement of the core occurs (that is, the overall displacement of the positive and negative electrodes is similar), when it hits the battery compartment or the protective plate, the insulating buffer layer on the edge of the positive and negative electrodes can be used as a buffer to jointly and simultaneously withstand the impact, thereby effectively preventing the negative electrode from being damaged. The design of the size larger than the size of the positive electrode sheet is likely to cause the internal active material layer to bend and generate debris or the interface is damaged to cause internal short circuit or power drop, thereby reducing the risk of internal short circuit after falling. In addition, the occurrence of lithium precipitation can be avoided by controlling the insulating ceramic layer on the positive and negative electrodes within a specific range.

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims (10)

1. A cell, characterized in that it comprises: a positive electrode sheet, a negative electrode sheet and a diaphragm, the diaphragm is sandwiched between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet and the negative electrode sheet The outer edges are flush; the positive electrode sheet and the negative electrode sheet each independently include a current collector, an active material layer and an insulating buffer layer, and the active material layer and the insulating buffer layer are arranged on the surface of the current collector; The insulating buffer layer is attached to at least two sides of the active material layer, and is configured to fix and bond the positive electrode sheet and the negative electrode sheet to the separator. 2. The cell according to claim 1, characterized in that, the unilateral width of the insulating buffer layer in the positive electrode sheet is greater than the unilateral width of the insulating buffer layer in the negative electrode sheet; preferably, in the negative electrode sheet The width of one side of the insulating buffer layer is greater than or equal to 0.5 mm. 3. The battery cell according to claim 1, wherein the thickness of the insulating buffer layer is less than or equal to the thickness of the active material layer. 4. The electric core according to claim 1, wherein the insulating buffer layer is an insulating ceramic layer; preferably, the material of the insulating ceramic layer includes a first ceramic powder and a first binder, and the second A mass of the binder accounts for 10-30% of the total weight of the insulating ceramic layer. 5. The electric core according to claim 4, wherein the diaphragm comprises a diaphragm matrix and a ceramic layer, the ceramic layer is arranged on the surface of the diaphragm matrix, and the material of the ceramic layer comprises a second ceramic powder material and a second binder. 6. The battery cell according to any one of claims 1 to 5, characterized in that, the battery cell is a wound-type battery cell or a laminated battery cell. 7. The battery cell according to claim 6, wherein the battery cell is a wound-type battery cell, and the insulating buffer layer is attached to the active material layer along the winding direction of the battery cell two opposite sides of . 8 . The battery cell according to claim 6 , wherein the battery cell is a laminated battery cell, and the insulating buffer layer is attached and wound around the outer edge of the active material layer. 9. The preparation method of the electric core described in any one of claims 1 to 8, is characterized in that, comprises the following steps: S1, preparation of insulating buffer layer to prepare slurry; S2. Prepare the positive electrode sheet and the negative electrode sheet, each independently comprising: preparing the active material slurry, then coating it on the surface of the current collector to form an active slurry coating, and laminating coating on at least two sides of the active slurry coating Preparation of slurry for the insulating buffer layer, followed by drying and rolling; S3, preparing a battery cell by assembling the separator with 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. 10. A lithium ion battery, characterized in that it comprises the battery cell according to any one of claims 1 to 8.

Images