Jelly-roll cell and electrochemical device

Abstract

The present disclosure relates to the technical field of lithium ion batteries. Provided are a jelly-roll cell and an electrochemical device. The jelly-roll cell is formed by rolling a positive electrode sheet, a separator and a negative electrode sheet, which are sequentially stacked, wherein a polymer layer is provided on at least one surface of a carrier layer of the separator, and first coating regions and second coating regions are alternately spaced apart on the polymer layer in the direction of the length of the separator, each first coating region comprising several first protrusions, and each second coating region comprising several second protrusions; and in the direction of the thickness of the separator, the maximum height of each first protrusion from the carrier layer is H1, the maximum height of each second protrusion from the carrier layer is H2, and the relationship therebetween satisfies: H1:H2=(0.3-1):1. The jelly-roll cell can reserve an expansion space, thereby avoiding the problem of hole blockage caused by extrusion due to the inability to release the expansion stress of the battery cell, preventing the hindrance of lithium ion transmission, and significantly ameliorating the problems of black spots and lithium plating of the battery cell.

Description

A wound battery cell and electrochemical device Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a wound battery cell and an electrochemical device. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, low self-discharge, and no memory effect, making them widely used. Currently, batteries primarily consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is typically provided with a glue layer, which primarily serves to prevent it from falling off and secures it between the positive and negative electrodes, making it a crucial barrier between the positive and negative electrode materials. Furthermore, the separator provides a transport channel for ions in the electrolyte.

[0003] With the advent of the 5G era and the rapid development of lithium-ion battery technology, people are placing higher demands on the energy density, fast charging capabilities, and charge and discharge rates of lithium-ion batteries. Fast-charging lithium batteries are also a development trend in consumer lithium-ion batteries. The development of fast-charging technology has also brought about safety issues for lithium-ion batteries. As the number of battery charge and discharge cycles increases, fast charging conditions can easily cause black spots and lithium precipitation on the arcs on both sides of the lithium battery. This can lead to problems such as lithium battery cycle derating, corrugation at the arcs, and expansion failure, which greatly shortens the service life of lithium batteries.

[0004] Therefore, it is of great significance to develop a lithium battery that can solve the problem of black spot lithium precipitation.

[0005] Summary of the Invention

[0006] The present disclosure found that as the lithium battery cycle progresses, the positive and negative electrodes of the lithium-ion battery continue to expand. On the horizontal surface of the wound lithium battery (including the wound cell) (the unbent area), its expansion is unconstrained and can expand freely. There is no stress accumulation between the positive and negative electrode sheets, and between the separator and the electrode sheets. However, at the arc of the wound lithium battery (the bent area), due to the constraints of the aluminum-plastic film and the characteristics of the cell itself at the arc, it cannot expand freely in the width direction of the cell, which ultimately leads to stress accumulation at the arc. Since the stress is concentrated at the arc, as the cycle progresses, the expansion of the negative electrode sheet causes the space between the positive and negative electrodes to be continuously squeezed, and the electrolyte transmission space becomes smaller and smaller, making the electrolyte transmission at the arc the most seriously hindered. The arc is prone to untimely electrolyte replenishment, resulting in electrolyte bridge breakage. At the same time, due to the internal stress squeezing the separator at the arc, the glue layer is prone to pore blockage, resulting in lithium ion transmission obstruction, insufficient lithium insertion and black spot lithium precipitation at the arc.

[0007] The present disclosure aims to overcome the above-mentioned problems existing in the prior art and to provide a wound battery cell and an electrochemical device. In the wound battery cell, the polymer layer distributed at intervals in the separator is shaped as a convex shape, and the height difference of the polymer layer in different coating areas (e.g., the flat area and the arc area) is controlled, which can solve the problem of lithium deposition in the battery. Furthermore, when the different coating areas correspond to the flat area and the arc area of ​​the wound battery cell, expansion space can be reserved for the arc area, thereby increasing the lithium insertion energy of the negative electrode sheet in the arc area and increasing the electrolyte storage capacity in the arc area, significantly improving the problem of black spot lithium deposition in the arc area.

[0008] The purpose of this disclosure is achieved through the following technical solutions:

[0009] A first aspect of the present disclosure provides a wound battery cell, which is formed by winding a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; the separator includes a carrier layer, a polymer layer is provided on at least one surface of the carrier layer, and the polymer layer has a first coating area and a second coating area cyclically distributed along the length direction of the separator, the first coating area includes a plurality of first protrusions, and the second coating area includes a plurality of second protrusions; along the thickness direction of the separator, the maximum height of the first protrusion from the carrier layer is H1, and the maximum height of the second protrusion from the carrier layer is H2, and the relationship between H1 and H2 satisfies: H1:H2=(0.3~1):1.

[0010] A second aspect of the present invention provides an electrochemical device, comprising the wound battery cell according to the first aspect of the present invention and a casing, wherein the wound battery cell is accommodated in the casing.

[0011] Beneficial effects of the present disclosure:

[0012] The wound battery cell provided by the present disclosure can reserve expansion space, thereby avoiding the problem of blockage caused by the expansion stress of the battery cell due to extrusion and the obstruction of lithium ion transmission, and significantly improving the problem of black spots and lithium precipitation in the battery cell.

[0013] Furthermore, the wound battery cell can reserve expansion space for the arc area, avoiding the problem of hole blockage in the arc area, improving the lithium insertion energy of the negative electrode sheet in the arc area, and significantly improving the problem of black spots and lithium precipitation in the arc area.

[0014] Furthermore, the expansion space reserved in the wound battery cell can increase the storage capacity of the electrolyte in the arc area, increase the wettability of the arc area, and improve the capacity retention rate of the battery.

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, unless otherwise specified, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a SEM image (electron microscope image) of a diaphragm in one embodiment of the present disclosure;

[0017] FIG2 is a SEM image of a diaphragm in one embodiment of the present disclosure;

[0018] FIG3 is a SEM image of a diaphragm in one embodiment of the present disclosure;

[0019] FIG4 is a SEM image of the second coating area in the diaphragm in one embodiment of the present disclosure;

[0020] FIG5 is a SEM image of the second coating area in the diaphragm in one embodiment of the present disclosure;

[0021] FIG6 is a SEM image of the first coating area in the diaphragm in one embodiment of the present disclosure;

[0022] FIG7 is a SEM image of the first coating area in the diaphragm according to one embodiment of the present disclosure;

[0023] FIG8 is a SEM image of primary particles in one embodiment of the present disclosure;

[0024] FIG9 is a SEM image of secondary particles in one embodiment of the present disclosure;

[0025] FIG10 is a schematic diagram showing a cross-sectional structure of a battery cell in one embodiment of the present disclosure;

[0026] FIG11 is a graph showing the results of testing the battery cycle life in Example 1 and Comparative Example 1 of the present disclosure.

[0027] FIG12 is a graph showing the results of testing the battery expansion rate in Example 1 and Comparative Example 1 of the present disclosure.

[0028] FIG13 is a picture showing the lithium deposition in Example 1 and Comparative Example 1 of the present disclosure.

[0029] Reference numerals: 1: positive electrode sheet; 2: negative electrode sheet; 3: first separator; 31: first extension portion; 32: second extension portion; 4: second separator; 41: third extension portion; 42: fourth extension portion. DETAILED DESCRIPTION

[0030] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0031] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0032] A first aspect of the present disclosure provides a wound battery cell, which is formed by winding a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; the separator includes a carrier layer, a polymer layer is provided on at least one surface of the carrier layer, and the polymer layer has a first coating area and a second coating area cyclically distributed along the length direction of the separator, the first coating area includes a plurality of first protrusions, and the second coating area includes a plurality of second protrusions; along the thickness direction of the separator, the maximum height of the first protrusion from the carrier layer is H1, and the maximum height of the second protrusion from the carrier layer is H2, and the relationship between H1 and H2 satisfies: H1:H2=(0.3~1):1.

[0033] According to an embodiment of the present disclosure, the wound battery cell includes an unbent planar area and a bent arc area; the first coating area is located in the planar area; and / or the second coating area is located in the arc area. The positional relationship between the first and second coating areas relative to the planar and arc areas of the wound battery cell is defined so that the height of the polymer layer in the planar area is smaller than that in the arc area, leaving more room for expansion in the arc area and significantly improving the problem of black speckle lithium deposition in the arc area.

[0034] The present disclosure research found that in the wound battery cell, a first coating area and a second coating area are arranged in a cyclically spaced distribution in the diaphragm, and a plurality of first protrusions are arranged in the first coating area, and a plurality of second protrusions are arranged in the second coating area, and the maximum height ratio (H1:H2) of the first protrusion to the second protrusion is limited to the range of (0.3~1):1. Even if the height of the first protrusion in the plane area of ​​the diaphragm is smaller than the height of the second protrusion in the arc area, expansion space can be reserved for the arc area, thereby avoiding the problem that the expansion stress of the arc area cannot be released to squeeze the polymer layer and cause pore blockage, avoiding the obstruction of lithium ion transmission, improving the lithium insertion energy of the negative electrode sheet in the arc area, and significantly improving the problem of black spots and lithium precipitation in the arc area.

[0035] Furthermore, the polymer layers are distributed at intervals, which can form stable coating gaps, and promote the heat dissipation during repeated charging and discharging. The reduction in battery temperature rise is conducive to reducing the risk of lithium plating and improving the problem of black spot lithium plating.

[0036] According to the embodiments of the present disclosure, the first coating area can be located on the entire planar area or on a portion of the planar area. Preferably, the entire planar area is the first coating area. Preferably, a plurality of first protrusions are provided in the entire planar area, so that the polymer layer is distributed throughout the planar area, leaving a certain expansion space for the planar area to expand, and improving the bonding strength between the diaphragm and the electrode piece.

[0037] According to the embodiments of the present disclosure, the second coating area can be located in the entire arc area or a portion of the arc area. Preferably, the entire arc area is the second coating area. Preferably, a plurality of second protrusions are provided in the entire arc area, so that the polymer layer is distributed throughout the arc area. The relatively high height of the second protrusions can reserve more expansion space for the arc area, significantly alleviating the problem of black spots and lithium deposition in the arc area of ​​wound battery cells.

[0038] According to an embodiment of the present disclosure, the separator includes a carrier layer, which may be a substrate, and a polymer layer is provided on at least one surface of the substrate. The substrate includes at least one of polyethylene, polypropylene, polyethylene, polypropylene, polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and aramid.

[0039] In the present disclosure, the “cyclic interval distribution” can be interpreted as multiple identical or different protruding polymer layers cyclically distributed on the surface of the carrier layer at identical or different intervals.

[0040] In the present disclosure, the “first protrusion and the second protrusion” may be in any protrusion shape, such as an island shape, a column shape, a cup shape, or other regular or irregular protrusion shapes.

[0041] In the present disclosure, “the maximum height of the protrusion from the carrier layer” can be interpreted as the maximum distance between the highest point of the first protrusion or the second protrusion away from the carrier layer and the surface of the carrier layer, which can be understood as the maximum thickness of the polymer layer.

[0042] According to embodiments of the present disclosure, a plurality of polymer layers of equal or different sizes are provided on one or both surfaces of the carrier layer in a cyclically spaced arrangement. To simplify the manufacturing process, it is preferred that the plurality of identical or similar polymer layers are provided on the entire surface of the substrate in a cyclically spaced arrangement. For example, the plurality of identical or similar polymer layers are provided in an island-like arrangement, i.e., the first and second protrusions are both island-shaped, thereby forming the island-shaped polymer layers.

[0043] According to an embodiment of the present disclosure, a plurality of island-shaped first protrusions and second protrusions arranged evenly at intervals (or arranged in a matrix) are provided on both surfaces of the carrier layer.

[0044] According to an embodiment of the present disclosure, the relationship between H1 and H2 satisfies: H1:H2=(0.3-1):1. For example, the ratio of H1 to H2 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any point value in the range of any two of the above point values.

[0045] In some preferred embodiments, the relationship between H1 and H2 satisfies: H1:H2=(0.4-0.8):1.

[0046] When the ratio of H1 to H2 is within the above range, the expansion space reserved in the arc area can be of appropriate size, avoiding the problem of blockage in the arc area caused by too small expansion space, and also avoiding the effect of too large expansion space on the adhesion of the diaphragm, thereby comprehensively improving the lithium insertion energy of the negative electrode sheet in the arc area and significantly improving the problem of black spots and lithium precipitation in the arc area.

[0047] In order to more significantly improve the problem of black spot lithium deposition in the arc area, the present disclosure further defines the value range of the maximum height H1 of the first protrusion from the carrier layer and the maximum height H2 of the second protrusion from the carrier layer.

[0048] According to an embodiment of the present disclosure, H1 and H2 are each independently 0.15μm to 5μm. For example, H1 and H2 can each independently be 0.15μm, 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.5μm, 4μm, 4μm, 4.5μm, 5μm or any point value in the range consisting of any two of the above point values.

[0049] According to an embodiment of the present disclosure, H1 and H2 are each independently 0.5μm to 3μm. For example, H1 and H2 can each independently be 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 2.3μm, 2.5μm, 2.8μm, or 3μm, and more preferably 0.5μm to 1μm or any point value in the range composed of any two of the above point values.

[0050] When the maximum height H1 of the first protrusion from the carrier layer and the maximum height H2 of the second protrusion from the carrier layer are within the above range, the gap between the electrode and the diaphragm substrate can be increased to store electrolyte and provide electrolyte for later cycles (during the cycle, the electrode expands and squeezes the diaphragm polymer layer, and the polymer layer has elasticity and releases diluted electrolyte to supplement the electrolyte needed during the cycle). It can also reserve space for the expansion of the electrode and improve the problem of black spots and lithium precipitation in the arc area.

[0051] According to an embodiment of the present disclosure, the first protrusion includes a first polymer; the first protrusion is formed by fusion bonding of the first polymer, and the first polymer satisfies at least one of the following conditions:

[0052] i) the first polymer includes a non-granular polymer, a granular polymer, or a partially melted granular polymer;

[0053] ii) the first polymer comprises first polymer particles, and the first polymer particles are fully and / or partially fused;

[0054] iii) The first polymer particles include a plurality of primary particles and / or a plurality of secondary particles.

[0055] In i), the first polymer can exist in three states: a non-granular polymer, a granular polymer, or a partially melted granular polymer (i.e., a combination of granular and non-granular polymers). The first polymer in the first protrusions can exist in one, two, or all three of these states.

[0056] The state of the first polymer affects the function of the first protrusions in the polymer layer. When the first polymer is non-granular, it improves adhesion between the separator and the electrode. When the first polymer is granular, it provides more space for battery expansion, increasing electrolyte storage and providing sufficient electrolyte for later battery cycles. When the first polymer is a combination of granular and non-granular forms, it not only increases adhesion between the separator and the electrode, but also provides adequate expansion space and electrolyte storage, thereby improving the overall performance of the battery.

[0057] In ii), the first polymer includes first polymer particles and may also contain other components, such as a binder. In the wound battery cell, the first polymer particles are fully and / or partially fused. Complete fusion of the first polymer particles renders the first polymer non-granular; partial fusion of the first polymer particles renders the first polymer both non-granular and granular.

[0058] In iii), the first polymer particles include a plurality of primary particles and / or a plurality of secondary particles.

[0059] In this disclosure, the terms "primary particles" and "secondary particles" have the conventional meanings in the art. The term "primary particle" refers to a single active particle; the term "secondary particle" refers to a particle formed by the agglomeration of several primary particles. For example, the secondary particle may be formed by the agglomeration of two primary particles, five primary particles, ten primary particles, fifty primary particles, or one hundred primary particles. Primary and secondary particles may have regular or irregular shapes, such as spherical or elliptical.

[0060] According to an embodiment of the present disclosure, the first protrusion is formed by fusion bonding of a plurality of primary particles, or by fusion bonding of a plurality of secondary particles, or by fusion bonding of a plurality of primary particles and secondary particles.

[0061] According to an embodiment of the present disclosure, the second protrusions include second polymer particles and may also contain other components, such as a binder.

[0062] According to an embodiment of the present disclosure, the second polymer particles are granular and / or partially fused. In a wound battery cell, the second polymer particles are not fused and are all granular, or partially fused and have both granular and non-granular forms. The state of the second polymer affects the effect of the second protrusion in the polymer layer. When the second polymer is granular, it can increase the gap between the pole piece and the diaphragm substrate, provide more space for battery expansion, increase the storage capacity of the electrolyte, and provide sufficient electrolyte for the later cycle of the battery; when the second polymer is both granular and non-granular, it can provide both expansion space and electrolyte storage, thereby improving the overall performance of the battery.

[0063] Furthermore, when the first polymer is in a non-granular state and the second polymer is in a granular state, the adhesion between the diaphragm and the electrode can be enhanced at the same time, and the lithium plating caused by the separation of the diaphragm and the electrode due to the expansion stress of the electrode can be weakened, and at the same time, the black spot lithium plating in the arc area caused by stress expansion can be improved.

[0064] According to an embodiment of the present disclosure, the second polymer particles include a plurality of primary particles and / or a plurality of secondary particles.

[0065] According to an embodiment of the present disclosure, the second protrusion is formed by fusion bonding of a plurality of primary particles, or by fusion bonding of a plurality of secondary particles, or by fusion bonding of a plurality of primary particles and secondary particles.

[0066] According to the embodiment of the present disclosure, when the first protrusion and the second protrusion are composed of secondary particles, the secondary particles are spread out on the carrier layer in a disordered manner. Multiple secondary spherical particles can be stacked together, or a single secondary spherical particle can be spread out on the carrier layer alone. The specific setting state can be freely adjusted.

[0067] According to an embodiment of the present disclosure, the first protrusions in the plane area (first coating area) are non-granular, as shown in Figures 6 and 7. Multiple particles are dissolved and connected together, without distinct particle size features, and the secondary particles do not have good sphericity.

[0068] According to an embodiment of the present disclosure, the second protrusions in the arc area (second coating area) are granular, as shown in Figures 4 and 5. The primary spherical particles have uniform particle size, with an average particle size of 0.2 to 2.5 μm, and the secondary particles do not have good sphericity.

[0069] According to an embodiment of the present disclosure, the average particle size of the primary particles is 0.1 μm to 2.5 μm, for example, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm or any point value in the range of two points above, more preferably 0.4 μm to 1.1 μm. As shown in Figure 8, the particle size of the primary particles (spherical) can be uniform, with a particle size of 0.2 μm to 1.2 μm, preferably 0.2 μm to 0.5 μm. The particle size of the primary spherical particles may not be distinct particles, but may be multiple particles connected together, but with obvious boundary lines between them.

[0070] According to embodiments of the present disclosure, the average particle size of the secondary particles is 2 μm to 8 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value within a range consisting of any two of these values, more preferably 2 μm to 5 μm. As shown in FIG7 , the particle size of the secondary particles can be non-uniform, i.e., multiple secondary particles are dissolved and connected together, without distinct particle size characteristics.

[0071] According to the embodiment of the present disclosure, the interior of the secondary particles may be hollow or solid, with a hollow structure being preferred.

[0072] According to an embodiment of the present disclosure, the primary particles and / or the secondary particles are independently one or more of spherical, regular polygonal or irregular polygonal.

[0073] According to an embodiment of the present disclosure, the circumscribed sphere diameter of each secondary particle (spherical) is between 2 μm and 8 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or any point value in the range consisting of two points above, preferably 2 μm to 5 μm, and each secondary spherical particle is composed of 80 to 730 primary particles, for example, it can be 80, 100, 200, 300, 400, 500, 600, 730 or any point value in the range consisting of two points above. The primary particle diameter is between 0.1 μm and 1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm or any point value in the range composed of any two of the above point values, preferably 0.1 μm to 0.3 μm, as shown in Figure 9.

[0074] According to an embodiment of the present disclosure, the expansion rate of the primary particles and / or the secondary particles is 27% to 63%, for example, 27%, 35%, 45%, 55%, 63%, or any value within a range of two of the above values, preferably 35% to 45%. When the expansion rate is within the above range, the first polymer particles and / or the second polymer particles can swell and absorb and store a large amount of electrolyte, providing electrolyte for later battery cycles, improving the problem of electrolyte starvation during battery cycles, reducing the occurrence of lithium ion transmission bridge failure, and improving the problem of black spots and lithium precipitation in the arc area.

[0075] The test method for the expansion rate is as follows: the average particle size of the polymer particles before absorbing the electrolyte and the average particle size after absorbing the electrolyte at 25°C are recorded, and the expansion rate is calculated by the particle size change ratio. The expansion rate = (particle size of the polymer particles after absorbing the electrolyte - particle size of the polymer particles before absorbing the electrolyte) / particle size of the polymer particles before absorbing the electrolyte.

[0076] According to an embodiment of the present disclosure, the polymer particles include one or more of PMMA, PMMA-HFP, PVDF, and PVDF-HFP. Preferably, PVDF and PVDF-HFP are water-based nano-scale PVDF and water-based nano-scale PVDF-HFP.

[0077] According to an embodiment of the present disclosure, the first protrusions or the second protrusions include granular polymers with distinct boundaries. As shown in FIG1 , the first polymer particles and the second polymer particles are spherical particles.

[0078] According to the embodiments of the present disclosure, the first polymer particles and the second polymer particles are not limited to spherical particles, and polymer particles of quasi-spherical, other regular or irregular shapes are all within the protection scope of the present disclosure.

[0079] According to an embodiment of the present disclosure, the average particle size of the first polymer particles is 0.1 μm-8 μm, for example, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any point value in the range consisting of any two of the above points, preferably 0.4 μm-2.5 μm. When the first polymer particles are composed only of primary particles, the average particle size of the first polymer particles is the average particle size of the primary particles; when the first polymer particles are composed only of secondary particles, the average particle size of the first polymer particles is the average particle size of the secondary particles; when the first polymer particles are composed of both primary and secondary particles, the average particle size of the first polymer particles is the sum of the average particle size of the primary particles and the average particle size of the secondary particles.

[0080] According to an embodiment of the present disclosure, the average particle size of the second polymer particles is 0.1 μm-8 μm, for example, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any point value in the range consisting of any two of the above points, preferably 0.4 μm-2.5 μm. When the second polymer particles are composed only of primary particles, the average particle size of the second polymer particles is the average particle size of the primary particles; when the second polymer particles are composed only of secondary particles, the average particle size of the second polymer particles is the average particle size of the secondary particles; when the second polymer particles are composed of both primary and secondary particles, the average particle size of the second polymer particles is the sum of the average particle size of the primary particles and the average particle size of the secondary particles.

[0081] In the present disclosure, the “average particle size” refers to the diameter of the largest circumscribed sphere of primary particles, secondary particles, first polymer particles, and second polymer particles of spherical, other regular, or irregular shapes.

[0082] When the average particle size of the first polymer particles and the second polymer particles is within the above range, the voids in the polymer layer can be further increased, leaving more room for expansion, thereby avoiding pore blockage in the arc region that affects lithium ion transmission and significantly improving the problem of black spots and lithium precipitation in the arc region.

[0083] The present invention selects polymer particles with suitable average particle size and expansion rate when preparing the diaphragm, which can adjust the gap between the diaphragm and the electrode, reserve expansion space for the arc area, avoid pore blockage in the arc area that affects lithium ion transmission, and significantly improve the problem of black spots and lithium precipitation in the arc area.

[0084] According to an embodiment of the present disclosure, in any 50μm*50μm area of ​​the first protrusion and / or the second protrusion, the number of secondary particles with an circumscribed sphere diameter greater than 2μm is 90 to 300, for example, 90, 100, 150, 200, 250, 300 or any point value in the range composed of the above two point values. The number of secondary particles with an circumscribed sphere diameter greater than 4μm is 20 to 80, for example, 20, 30, 40, 50, 60, 70, 80 or any point value in the range composed of the above two point values. As shown in Figure 8. When the number of secondary particles and the circumscribed sphere diameter in the first protrusion and / or the second protrusion are within the above range, the adhesion between the polymer layer and the diaphragm carrier layer and the adhesion between the polymer layer and the pole piece can be increased. When it is less than this numerical range, the adhesion between the polymer layer and the diaphragm carrier layer and the polymer layer and the pole piece is weak, and delamination is prone to occur.

[0085] After the wound battery cell is injected with electrolyte, the polymer particles (first polymer particles and second polymer particles) in the polymer layer will swell and become larger. During battery formation, in the thickness direction of the battery cell, that is, the upper and lower parts of the plane area will be directly subjected to pressure. After the plane area is subjected to greater pressure, the first polymer particles in the plane area are squeezed to a high degree. Setting a first protrusion with a small height in this area can relieve the squeezing force on the diaphragm and relieve the pressure on the diaphragm. The arc area is subjected to a smaller force. Setting a second protrusion with a large height in this area can further relieve the pressure on the plane area diaphragm, prevent the plane area diaphragm from being compressed and deformed, and better maintain the performance of the plane area diaphragm. Therefore, the maximum thickness of the polymer in the plane area is less than the maximum thickness of the polymer in the arc area. The granular polymer layer and the higher protrusion height in the arc area reserve space for the expansion of the pole piece, avoiding the problem of pore blockage caused by excessive squeezing of the polymer layer, and significantly improving the problem of black spot lithium precipitation.

[0086] According to an embodiment of the present disclosure, the first protrusion and / or the second protrusion are in the shape of one or more of an island, a column, a cup, a dot, a regular polygon, or an irregular polygon. The shapes of the first and second protrusions can be the same or different, and the specific shapes can be freely adjusted through the manufacturing process. In some preferred embodiments, the first protrusion and / or the second protrusion are in the shape of an island.

[0087] According to an embodiment of the present disclosure, the density of the first polymer particles and / or the second polymer particles decreases from the edge region to the center region of the first protrusion and / or the second protrusion, while the average particle size of the first polymer particles and / or the second polymer particles increases. When the number of particles and the average particle size in the polymer layer are within the above ranges, the adhesion between the polymer layer and the diaphragm carrier layer and the electrode layer can be improved. If the number of polymer particles in the outermost region is too small, the adhesion between the polymer layer and the electrode layer is weak, and delamination is likely to occur, affecting the cycle performance and safety performance of the battery.

[0088] According to an embodiment of the present disclosure, the diaphragm satisfies at least one of the following characteristics:

[0089] a) the plurality of first protrusions and / or the plurality of second protrusions are independently arranged at intervals;

[0090] b) the plurality of first protrusions and / or the plurality of second protrusions are independently arranged in a matrix;

[0091] c) the maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is 200 μm to 430 μm;

[0092] d) the distance between the centers of the largest circumscribed circles of two adjacent first protrusions and / or second protrusions is 200 μm to 800 μm;

[0093] e) a plurality of gaps are present between the first protrusion and / or the second protrusion;

[0094] f) a plurality of gaps are present between the first protrusion and / or the second protrusion; the gaps account for 10% to 30%, preferably 10% to 25%, of the total area of ​​the protrusion;

[0095] g) a plurality of gap regions are spaced between the first protrusions and / or the second protrusions; the number of gap regions in each of the first protrusions and / or each of the second protrusions is 3 to 15; and / or the maximum circumscribed circle diameter of the gap region is 5 μm to 80 μm;

[0096] h) The air permeability of the separator is 20,000 s / 100 mL to 50,000 s / 100 mL, preferably 35,000 s / 100 mL to 48,000 s / 100 mL.

[0097] According to the embodiments of the present disclosure, in a), the plurality of first protrusions and / or the plurality of second protrusions are independently spaced apart, and may be spaced at equal or varying distances. The spaced-apart polymer layers can form stable coating gaps, facilitating heat dissipation, reducing battery temperature rise, and mitigating the risk of lithium plating.

[0098] According to the embodiment of the present disclosure, in b), as shown in Figures 1 and 2, the multiple first protrusions and / or the multiple second protrusions are independently arranged in a matrix, and the spacing between the matrix can be freely adjusted. The matrix arrangement ensures uniform distribution of the polymer layer and more uniform expansion space, providing sufficient and uniform space for the electrode to expand, significantly solving the problem of arc lithium deposition. In addition, the matrix arrangement facilitates processing and improves the processing efficiency of the separator.

[0099] According to an embodiment of the present disclosure, in c), the maximum circumscribed sphere diameter of the first and / or second protrusions is between 200 μm and 430 μm, for example, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 430 μm, or any value within a range consisting of any two of these values; preferably, it is between 220 μm and 370 μm. When the maximum circumscribed circle diameter of the first and / or second protrusions is within this range, the polymer layer has better adhesion to the electrode and the separator carrier layer, thereby improving the safety and service life of the battery.

[0100] According to an embodiment of the present disclosure, the first polymer particles and / or the second polymer particles are arranged on at least one surface of the carrier layer, which can be a single layer or multiple layers. The layers can be completely covered or not completely covered, and usually not more than 10 layers. In each first protrusion and / or second protrusion, there are approximately 270 to 650 first polymer particles and / or second polymer particles in each layer (based on the average particle size of the above-mentioned first polymer particles and / or second polymer particles, and the diameter of the largest circumscribed circle of the first protrusion and / or second protrusion). The farther away from the carrier layer, the fewer polymer particles (first polymer particles and / or second polymer particles), and there are no less than 270 polymer particles away from the outermost layer of the carrier layer. In each first protrusion and / or second protrusion, controlling the number of polymer particles can improve the adhesion between the polymer layer and the diaphragm carrier layer and the adhesion to the pole piece.

[0101] According to an embodiment of the present disclosure, in d), the distance between the centers of the largest circumscribed circles of two adjacent first and / or second protrusions is between 200 μm and 800 μm, for example, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, or any value within a range of any two of these values; preferably, it is between 300 μm and 500 μm. The distance between the centers of the largest circumscribed circles of adjacent first and / or second protrusions can be recorded as the distance between the two adjacent first and / or second protrusions. When this distance is within the above range, the separator and the electrode sheet have good adhesion, and the battery has good cycling stability. When the center-to-center distance is less than 200 μm, the polymer layer is prone to swelling, adhesion, and pore blocking, deteriorating electrical performance. When the center-to-center distance is greater than 800 μm, the contact area between the polymer layer and the electrode sheet is too small, which can easily lead to delamination between the positive and negative electrode sheets and the separator, creating gaps and affecting ion transmission efficiency.

[0102] According to an embodiment of the present disclosure, in e), a plurality of void regions are spaced between the first protrusion and / or the second protrusion. During the drying process after the polymer layer slurry is applied, due to the surface tension of the polymer layer, a plurality of void regions are formed in the polymer layer (the first protrusion and / or the second protrusion) that do not completely cover the carrier layer. The void regions allow lithium ions to pass through the polymer layer, increasing the lithium ion insertion and extraction speed and improving the fast charging performance of the battery.

[0103] According to an embodiment of the present disclosure, in f), a plurality of void regions are spaced between the first protrusions, and the void regions account for 10% to 30% of the total area of ​​the first protrusions, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any value within a range consisting of two of the above values; preferably, 10% to 25%. A plurality of void regions are spaced between the second protrusions, and the void regions account for 10% to 30% of the total area of ​​the second protrusions, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any value within a range consisting of two of the above values; preferably, 10% to 25%. The area ratio of the void regions in the first protrusions and the area ratio of the void regions in the second protrusions can be the same or different. When the area ratio of the gap region between the first protrusion and the second protrusion is within the above range, more lithium ions can pass through the polymer layer, thereby improving the fast charging performance of the battery; and better adhesion between the diaphragm and the electrode can be achieved, thereby improving the cycle stability of the battery.

[0104] According to an embodiment of the present disclosure, in g), there are several gap areas between the first protrusion and / or the second protrusion; the number of gap areas in each first protrusion and / or each second protrusion is 3 to 15, for example, it can be 3, 5, 7, 9, 11, 13, 15 or any point value in the range composed of any two of the above point values, preferably 8 to 12.

[0105] According to an embodiment of the present disclosure, there are several void areas between the first protrusion and / or the second protrusion; the maximum circumscribed circle diameter of the void area is 5μm to 80μm, for example, it can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 40μm, 50μm, 60μm, 75μm, 80μm or any point value in the range composed of two of the above point values, preferably 10μm to 60μm. The maximum circumscribed circle diameter of the void area is related to the size of the void area. The larger the diameter, the larger the void area (or the larger the area). The void area allows lithium ions to pass through the polymer layer. Controlling the number and size of the void areas can increase the lithium ion deintercalation speed and improve the fast charging performance of the battery.

[0106] According to an embodiment of the present disclosure, the air permeability of the separator is 20,000 s / 100 mL to 50,000 s / 100 mL, for example, 20,000 s / 100 mL, 25,000 s / 100 mL, 30,000 s / 100 mL, 35,000 s / 100 mL, 40,000 s / 100 mL, 45,000 s / 100 mL, or 50,000 s / 100 mL, preferably 35,000 s / 100 mL to 48,000 s / 100 mL, or any value within a range consisting of any two of the above values.

[0107] The test method for the air permeability of the diaphragm is as follows: take a 30cm long diaphragm to be tested and place it on the air permeability tester, perform three horizontal point tests (at least one of the three points of the diaphragm corresponds to the position of the arc area), and take the average value to obtain the air permeability of the diaphragm.

[0108] After the diaphragm is soaked in electrolyte and formed, part of the polymer layer will swell and penetrate into the gap of the carrier layer (including substrate) to cause pore plugging. In addition, the solvent in the electrolyte will also occupy the substrate pores, resulting in a decrease in the porosity of the diaphragm and an increase in air permeability. The air permeability directly reflects the porosity of the diaphragm. During the use of the diaphragm after being soaked in electrolyte and formed, the smaller the air permeability, the better. However, the air permeability tends to increase, and arc lithium precipitation is prone to occur when the air permeability is higher than 50000s / 100mL. The reason is that the diaphragm has more pore plugging and the air permeability becomes larger, which can cause ion transport to be blocked and induce lithium precipitation. The air permeability of the diaphragm disclosed herein is in the above range, which can significantly solve or improve the problem of black spot lithium precipitation in the arc area of ​​the diaphragm.

[0109] According to an embodiment of the present disclosure, the first protrusions include first polymer particles, a first binder, a first dispersant, a first thickener, and a first surfactant.

[0110] According to an embodiment of the present disclosure, the second protrusions include second polymer particles, a second binder, a second dispersant, a second thickener, and a second surfactant.

[0111] According to an embodiment of the present disclosure, the first adhesive and the second adhesive independently include at least one of styrene-butadiene latex, styrene-acrylic latex, pure styrene latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate and polyurethane.

[0112] According to an embodiment of the present disclosure, the first dispersant and the second dispersant independently include at least one of sodium acrylate, ammonium polyacrylate, n-butanol, and cyclohexanol.

[0113] According to an embodiment of the present disclosure, the first thickener and the second thickener independently include one or both of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0114] According to an embodiment of the present disclosure, the first surfactant and the second surfactant independently include at least one of ethylene oxide polymers and polyether polymers, for example, they may include at least one of fluoroalkyl methoxy ether alcohols, fluoroalkyl ethoxy ether alcohols, polyoxyethylene alkyl amides, and fatty alcohol polyoxyethylene ethers.

[0115] The first protrusion and the second protrusion further include a solvent, and the specific type of the solvent is not limited. For example, the solvent can be at least one of deionized water, acetone, and NMP, or a mixture of the three.

[0116] According to an embodiment of the present disclosure, in the first protrusion, the mass ratio of the first polymer particles, the first adhesive, the first dispersant, the first thickener and the first surfactant is (6-30):(2-12):(0.1-1.5):(1-10):(0.1-0.4).

[0117] According to an embodiment of the present disclosure, in the second protrusion, the mass ratio of the second polymer particles, the second adhesive, the second dispersant, the second thickener and the second surfactant is (6-30):(2-12):(0.1-1.5):(1-10):(0.1-0.4).

[0118] When the mass ratio of the components in the first protrusions and the second protrusions is within the above range, the polymer layer has good adhesion and appropriate porosity.

[0119] The present disclosure provides a diaphragm suitable for a wound lithium-ion battery that can absorb liquid and relieve stress, so that the expansion stress at the arc of the lithium-ion battery is smoothly released, and space for electrolyte transmission is reserved, thereby improving the situation where electrolyte transmission is hindered at the arc, avoiding electrolyte bridge breakage caused by untimely electrolyte replenishment at the arc, and avoiding diaphragm blockage at the arc, thereby improving the lithium insertion speed at the arc and avoiding the problem of black spot lithium precipitation.

[0120] According to an embodiment of the present disclosure, a heat-resistant layer is provided on at least one surface of the carrier layer, and the polymer layer is provided on the surface of the carrier layer and / or the surface of the heat-resistant layer.

[0121] According to an embodiment of the present disclosure, a heat-resistant layer is provided on one surface of the carrier layer, and a polymer layer is provided on the other, opposing surface of the carrier layer. Alternatively, a heat-resistant layer is provided on one surface of the carrier layer, a polymer layer is provided on the heat-resistant layer, and a polymer layer is also provided on the other, opposing surface of the carrier layer. Alternatively, heat-resistant layers are provided on two opposing surfaces of the carrier layer, and polymer layers are provided on both sides of the heat-resistant layers. The specific arrangement of the heat-resistant layers and the polymer layers can be adjusted as needed.

[0122] According to an embodiment of the present disclosure, the heat-resistant layer includes inorganic particles, a third adhesive, and a third thickener. The inorganic particles include one or more of aluminum oxide, boehmite, magnesium oxide, boron nitride, and magnesium hydroxide. The third adhesive includes at least one of styrene-butadiene latex, styrene-acrylic latex, pure benzene latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, and polyurethane. The third thickener includes one or both of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0123] According to an embodiment of the present disclosure, the mass ratio of the inorganic particles, the third binder, and the third thickener is (70-95):(2-35):(2-35). In the heat-resistant layer, when the mass ratio of the three components is within the above range, the adhesion between the heat-resistant layer and the carrier layer and the polymer layer can be increased, thereby increasing the stability of the separator.

[0124] According to an embodiment of the present disclosure, a first separator is provided on a surface of the positive electrode sheet away from the negative electrode sheet, and a second separator is provided on a surface of the positive electrode sheet close to the negative electrode sheet.

[0125] According to embodiments of the present disclosure, the first and second diaphragms may be the same or different, preferably the same. When the first and second diaphragms are the same, the diaphragms are divided into a first side and a second side, which may or may not be the same, preferably different. That is, the first side of the diaphragm is a polymer layer, and the other side may be a polymer layer or a heat-resistant layer plus a polymer layer.

[0126] According to an embodiment of the present disclosure, as shown in Figure 10, a battery cell is formed by winding a positive electrode sheet 1, a first separator 3, a negative electrode sheet 2, and a second separator 4, which are stacked in sequence. The first separator 3 and the second separator 4 are the same or different. According to an embodiment of the present disclosure, the first separator and the second separator are the same. Unless otherwise specified, the separator in the present disclosure can represent either the first separator or the second separator.

[0127] According to an embodiment of the present disclosure, as shown in FIG10 , in the winding direction of the battery cell, the lengths of both the first separator 3 and the second separator 4 are greater than the length of the negative electrode sheet 2, and the first separator 3 and the second separator 4 completely cover the negative electrode sheet 2. The first separator 3 includes a first main portion facing the negative electrode sheet, and a first extension 31 and a second extension 32 connected to the first main portion and extending beyond the negative electrode sheet. The second separator 4 includes a second main portion facing the negative electrode sheet, and a third extension 41 and a fourth extension 42 connected to the second main portion and extending beyond the negative electrode sheet. The first extension 31 and the third extension 41 are located at the winding start, while the second extension 32 and the fourth extension 42 are located at the winding end. The first extension 31 and the third extension 41 contact each other at the winding start to form a first bonding area, while the second extension 32 and the fourth extension 42 contact each other at the winding end to form a second bonding area. Preferably, the first and second separators are flush at both the winding start and winding end. Preferably, the lengths of the first diaphragm and the second diaphragm are equal or differ by ±2 mm.

[0128] According to an embodiment of the present disclosure, the lengths of the first extension portion and the third extension portion are independently 10 mm to 30 mm, for example, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm or any value in the range consisting of any two of the above values.

[0129] According to an embodiment of the present disclosure, the lengths of the second extension portion and the fourth extension portion are independently 3 mm to 10 mm, for example, 3 mm, 5 mm, 6 mm, 8 mm, 9 mm, 10 mm or any point value in the range consisting of any two of the above point values.

[0130] The lengths of the first extension and the third extension at the starting end of the winding are greater than the lengths of the second extension and the fourth extension at the end of the winding. The shorter end of the winding can prevent the diaphragm from overlapping with other components of the battery cell, thereby increasing the thickness of the battery cell.

[0131] According to an embodiment of the present disclosure, the bonding strength of the first bonding area is 4 N / m to 12 N / m, for example, it can be 4 N / m, 6 N / m, 8 N / m, 10 N / m, 12 N / m or any point value in the range consisting of any two of the above point values.

[0132] According to an embodiment of the present disclosure, the bonding strength of the second bonding area is 1 N / m to 6 N / m, for example, it can be 1 N / m, 2 N / m, 3 N / m, 4 N / m, 5 N / m, 6 N / m or any point value in the range consisting of any two of the above point values.

[0133] The bonding strength of the first bonding area at the starting end of the winding is greater than the bonding strength of the second bonding area at the end of the winding, which can increase the bonding force inside the wound battery and avoid delamination of the inner ring of the winding core, which may cause deformation of the battery cell.

[0134] According to an embodiment of the present disclosure, the length of the planar region is greater than the diameter of the arc region. Preferably, the length of the planar region is greater than 2*the diameter of the arc region. Limiting the length of the planar region to be greater than the diameter of the arc region can reduce stress accumulation in the planar region, better relieve expansion stress, alleviate pore blockage caused by force squeezing the diaphragm in the planar region, and improve lithium deposition.

[0135] According to an embodiment of the present disclosure, the ratio of the thickness of the negative electrode sheet to the total thickness of the first or second separator is (8-15):1, for example, 8:1, 9:1, 10:1, 12:1, 14:1, 15:1, or any value within a range consisting of any two of these values. When the ratio of the thickness of the negative electrode sheet to the thickness of the separator is within this range, the separator can absorb sufficient electrolyte to meet the consumption and lithium ion transmission requirements of negative electrode sheets of different thicknesses during cycling, while also ensuring the energy density of the lithium battery.

[0136] In the present disclosure, the lithium-ion battery has a winding structure, which may be a lug-centered winding structure, a conventional winding structure, or a multi-lug winding structure.

[0137] In the present disclosure, the electrolyte may be any commonly used electrolyte in the art and is not specifically limited herein.

[0138] A second aspect of the present disclosure provides an electrochemical device, comprising the wound battery cell according to the first aspect of the present disclosure and a shell, wherein the wound battery cell is accommodated in the shell.

[0139] According to an embodiment of the present disclosure, the electrochemical device includes a lithium-ion secondary battery, such as a wound lithium-ion secondary battery.

[0140] There is no limitation on the type of the housing, and it may be, for example, an aluminum-plastic film or other similar or dissimilar materials.

[0141] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0142] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0143] The present invention will be described in detail below with reference to specific embodiments. These embodiments are intended to help you understand the present invention but are not intended to limit it.

[0144] Group A Examples and Group A Comparative Examples

[0145] The lithium-ion batteries of the examples and comparative examples in Group A below were all prepared according to the following method, with the only difference being the battery separators. The specific differences in the battery separators are shown in Tables 1 to 3.

[0146] (1) Diaphragm preparation

[0147] S1: Preparation of polymer coating slurry: Weigh PMMA powder (first polymer particles / second polymer particles): styrene-butadiene latex (binder), n-butanol (dispersant), sodium carboxymethyl cellulose (thickener), and ethylene oxide polymer (surfactant) in a ratio of 30:3:1:2:0.2 (mass ratio), add deionized water, stir for 10 minutes, heat to 50°C to form a mixture, and filter through a 400-mesh stainless steel sieve to obtain a polymer slurry with a viscosity of 3 Pa·s and a solids content of 31%.

[0148] S2: Preparation of heat-resistant layer slurry: boehmite: styrene-butadiene latex (binder): sodium carboxymethyl cellulose (thickener) = 85:6:9 (mass ratio), add deionized water and stir for 10 minutes, heat to 50°C to form a mixture, and filter through a 400-mesh stainless steel screen to obtain a heat-resistant layer slurry with a slurry viscosity of 5 Pa·s and a solid content of 37%.

[0149] S3: The heat-resistant layer slurry was coated on one side of a polyethylene substrate film with a thickness of 5 μm and a porosity of 38% using a gravure coating method at a coating rate of 20 m / min. The film was then dried in a three-stage oven at temperatures of 55°C, 70°C, and 60°C, respectively. After drying, a separator containing a heat-resistant layer was obtained, and the heat-resistant ceramic coating had a thickness of 2 μm.

[0150] S4: Using island-shaped gravure coating method, the polymer coating slurry is respectively coated on the first coating area and the second coating area on both sides of the diaphragm containing the heat-resistant layer. The coating thickness of the first coating area is H1, the coating thickness of the second coating area is H2, and the coating rate is 20m / min; a three-stage oven is used for drying, and the oven temperatures are 55℃, 70℃, and 60℃ respectively. After drying, the diaphragm is obtained.

[0151] (2) Preparation of positive electrode sheet

[0152] Take lithium cobalt oxide: conductive carbon black: polyvinylidene fluoride in a mass ratio of 97.2:1.5:1.3 and add them to a stirring tank. Add NMP solvent and fully stir according to a known batching process. Pass through a 200-mesh sieve to prepare a positive electrode slurry with a solid content of 73%. Subsequently, use a coater to coat the positive electrode slurry on an aluminum foil current collector with a single-layer coating thickness of 35 μm ± 2 and a coating length of 1241 mm ± 1.

[0153] (3) Negative electrode preparation

[0154] Artificial graphite: conductive agent: styrene-butadiene rubber: lithium carboxymethyl cellulose are taken in a mass ratio of 96%: 1.5%: 1.5%; 1%; deionized water is then added as a solvent to prepare a negative electrode slurry with a solid content of 45.5%. The negative electrode active slurry is evenly coated on both surfaces of the copper foil, and the prepared negative electrode sheet is dried at 100°C to obtain a negative electrode sheet; the coating length is 1243mm±1mm, and the single-layer coating thickness is 45μm±2.

[0155] (4) Preparation of batteries: The positive electrode sheet, the negative electrode sheet and the separator are wound to form a roll core, which is then wrapped with aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a weight ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by hot pressing process.

[0156] Table 1

[0157] In Examples 1 to 3, as well as Examples 4-1 and 4-3, the first polymer particles and the second polymer particles each consisted of a plurality of primary particles. In Example 4, the first polymer particles and the second polymer particles in Examples 4, 4-2, and 4-4 each consisted of a plurality of secondary particles.

[0158] Table 2

[0159] In Example 5, the characteristics of the gap region were changed, wherein the area ratio of the gap region was the average of the area ratio of the gap region to the total area of ​​the first protrusion and the second protrusion.

[0160] Group B Examples

[0161] Table 3

[0162] Among them, the test method for the bonding strength of the first bonding area and the second bonding strength includes: charging the batteries of Example 1 and Example 6 groups at a constant current of 0.7C, with a cut-off current of 0.05C, and leaving the batteries for 5 minutes after they are fully charged. The fully charged batteries are dissected, and a diaphragm sample with a length of 8mm and a width of 8mm is selected. A 3M single-sided tape is attached to the diaphragm sample, and the 3M single-sided tape is placed at an angle of 180 degrees to the diaphragm on a universal tensile machine at a speed of 100mm / min and a test displacement of 50mm. The test results are recorded as the bonding strength between the diaphragms (unit: N / m).

[0163] Comparative Example 1

[0164] The same procedure was followed as in Example 1, except that no polymer coating was provided.

[0165] The relevant performance tests of the battery separators and batteries in the above examples and comparative examples are recorded in Tables 4 and 5. The test methods are described as follows:

[0166] (1) Cycle life test

[0167] At 25°C, the charge and discharge regime is 1.8C constant current constant voltage charging to 4.48V and then 0.05C / 4C discharging to 3.0V for 200 cycles. Capacity retention is calculated as follows: Nth discharge capacity / first discharge capacity*100%.

[0168] (2) Battery expansion rate test

[0169] At an ambient temperature of 25°C, the charge and discharge regime is 1.8C constant current constant voltage charging to 4.48V and then 0.05C / 4C discharging to 3.0V for 200 cycles. The expansion rate is calculated as (Nth full charge thickness / first full charge thickness-1)*100%.

[0170] (3) Battery lithium deposition detection

[0171] At 25°C, the charge and discharge profile was 1.8C constant current and constant voltage, charging to 4.48V, and discharging to 3.0V at 0.05C / 4C for 200 cycles. Afterwards, the battery was fully charged, the cell was disassembled in a dry environment, and lithium deposition on the negative electrode surface was observed. The degree of lithium deposition was ranked as very severe, severe, slight, and no (in descending order).

[0172] Table 4

[0173] The results in Table 4 show that the wound battery cell of the present invention allows for expansion space, reducing the battery's expansion rate and effectively alleviating the problem of black speckle lithium deposition in the cell. Furthermore, the reserved expansion space in the wound battery cell increases the electrolyte storage capacity in the arc region, improving the wettability of the arc region and enhancing the battery's capacity retention.

[0174] Table 5

[0175] It can be seen from the results in Table 5 that changing the length of the extensions at both ends of the wound battery cell separator and the bonding strength of the bonding area has a slight effect on the battery capacity retention rate, lithium plating and expansion rate, and can be used in conjunction with the separator of the present invention to jointly improve the battery capacity retention rate, reduce lithium plating and reduce the expansion rate.

[0176] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0177] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wound cell, characterized in that, The battery cell is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet that are sequentially stacked. The separator includes a carrier layer, and a polymer layer is provided on at least one surface of the carrier layer. The polymer layer is cyclically and spacedly distributed with a first coating area and a second coating area along the length direction of the separator. The first coating area includes a plurality of first protrusions, and the second coating area includes a plurality of second protrusions. Along the thickness direction of the separator, the maximum height of the first protrusion from the carrier layer is H1, and the maximum height of the second protrusion from the carrier layer is H2. The relationship between H1 and H2 satisfies: H1:H2 = (0.3 - 1):

1.

2. The battery cell according to claim 1, wherein, The wound battery cell includes an unbent planar area and a bent arc area. The first coating area is located in the planar area; and / or The second coating area is located in the arc area.

3. The battery cell according to claim 1 or 2, characterized in that, The relationship between H1 and H2 satisfies: H1:H2 = (0.4 - 0.8):

1.

4. The battery cell according to any one of claims 1 to 3, characterized in that, H1 and H2 are each independently 0.15 μm to 5 μm; Preferably, H1 and H2 are each independently 0.5 μm to 3 μm.

5. The battery cell according to any one of claims 1 to 4, characterized in that The first protrusion includes a first polymer; the first protrusion is formed by fusing the first polymer, and the first polymer satisfies at least one of the following conditions: i) The first polymer includes a non-granular polymer, a granular polymer, and a partially molten granular polymer; ii) The first polymer includes first polymer particles, and all and / or part of the first polymer particles are fused; iii) The first polymer particles include a plurality of primary particles and / or a plurality of secondary particles.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The second protrusion includes second polymer particles; the second polymer particles are in a granular shape and / or are partially fused; Preferably, the second polymer particles include a plurality of primary particles and / or a plurality of secondary particles.

7. The battery cell according to claim 5 or 6, characterized in that, The primary particles and the secondary particles independently include one or more of PMMA, PMMA-HFP, PVDF, and PVDF-HFP.

8. The battery cell according to any one of claims 5 to 7, wherein the average particle size of the primary particles is 0.1 μm to 2.5 μm, preferably 0.4 μm to 1.1 μm; The average particle size of the secondary particles is 2 μm to 8 μm, preferably 2 μm to 5 μm.

9. The battery cell according to any one of claims 5 to 8, wherein the swelling ratio of the primary particles and / or the secondary particles is independently 27 to 63%, preferably 35 to 45%; Preferably, the primary particles and / or the secondary particles are independently one or more of a spherical shape, a regular polygon, and an irregular polygon.

10. The battery cell according to any one of claims 5 to 9, characterized in that, The average particle size of the first polymer particles is 0.1 μm to 8 μm, preferably 0.4 μm to 2.5 μm; and / or, the average particle size of the second polymer particles is 0.1 μm to 8 μm, preferably 0.4 μm to 2.5 μm; and / or, in any 50 μm * 50 μm area of the first protrusion and / or the second protrusion, the number of secondary particles with an outer circumscribed sphere diameter > 2 μm is 90 to 300, and the number of secondary particles with an outer circumscribed sphere diameter > 4 μm is 20 to 80.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The first protrusion and / or the second protrusion is / are one or more of an island shape, a column shape, a cup shape, a dot shape, a regular polygon, or an irregular polygon; Preferably, the density of the first polymer particles and / or the second polymer particles from the edge region to the center region of the first protrusion and / or the second protrusion shows a decreasing trend, and the average particle size of the first polymer particles and / or the second polymer particles shows an increasing trend.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The separator satisfies at least one of the following characteristics: a) The multiple first protrusions and / or the multiple second protrusions are independently arranged at intervals; b) The multiple first protrusions and / or the multiple second protrusions are independently arranged in a matrix; c) The maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is 200 μm to 430 μm; d) The distance between the centers of the maximum circumscribed circles of two adjacent first protrusions and / or second protrusions is 200 μm to 800 μm; e) There are several void areas spaced between the first protrusion and / or the second protrusion; f) There are several void areas spaced between the first protrusion and / or the second protrusion; the void areas account for 10% to 30% of the total area of the first protrusion and / or the second protrusion; preferably 10% to 25%; g) There are several void areas spaced between the first protrusion and / or the second protrusion; the number of void areas in each first protrusion and / or each second protrusion is 3 to 15; and / or, the maximum circumscribed circle diameter of the void areas is 5 μm to 80 μm; h) The air permeability of the separator is 20000 s / 100 mL to 50000 s / 100 mL, preferably 35000 s / 100 mL to 48000 s / 100 mL.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The first protrusion includes first polymer particles, a first binder, a first dispersant, a first thickener, and a first surfactant; and / or, the second protrusion includes second polymer particles, a second binder, a second dispersant, a second thickener, and a second surfactant.

14. The battery cell according to claim 13, characterized in that, In the first protrusion, the mass ratio of the first polymer particles, the first binder, the first dispersant, the first thickener, and the first surfactant is (6 - 30):(2 - 12):(0.1 - 1.5):(1 - 10):(0.1 - 0.4); and / or, in the second protrusion, the mass ratio of the second polymer particles, the second binder, the second dispersant, the second thickener, and the second surfactant is (6 - 30):(2 - 12):(0.1 - 1.5):(1 - 10):(0.1 - 0.4).

15. The battery cell according to any one of claims 1 to 14, characterized in that, A heat-resistant layer is provided on at least one surface of the carrier layer, and the polymer layer is disposed on the surface of the carrier layer and / or the surface of the heat-resistant layer; Preferably, the heat-resistant layer includes inorganic particles, a third binder, and a third thickener.

16. The battery cell according to any one of claims 1 to 15, characterized in that, The separator includes a first separator and a second separator, and the positive electrode sheet, the first separator, the negative electrode sheet, and the second separator are stacked in the thickness direction of the battery; in the winding direction of the battery core, the lengths of the first separator and the second separator are both greater than the length of the negative electrode sheet.

17. The battery cell according to claim 16, wherein The first separator includes a first main body facing the negative electrode sheet, and a first extension portion and a second extension portion connected to the first main body and extending beyond the negative electrode sheet. The second separator includes a second main body facing the negative electrode sheet, and a third extension portion and a fourth extension portion connected to the second main body and extending beyond the negative electrode sheet. The first extension portion and the third extension portion are located at the winding starting end, and the second extension portion and the fourth extension portion are located at the winding ending end. The first extension portion and the third extension portion are in contact with each other at the winding starting end to form a first bonding area, and the second extension portion and the fourth extension portion are in contact with each other at the winding ending end to form a second bonding area.

18. The battery cell according to claim 17, wherein The lengths of the first extension portion and the third extension portion are independently 10 mm to 30 mm; and / or, the lengths of the second extension portion and the fourth extension portion are independently 3 mm to 10 mm. Preferably, the bonding strength of the first bonding area is 4 N / m to 12 N / m; and / or, the bonding strength of the second bonding area is 1 N / m to 6 N / m.

19. The battery cell according to any one of claims 2 to 18, characterized in that, The length of the planar area is greater than the diameter of the arc area. Preferably, the length of the planar area > 2 * the diameter of the arc area. Preferably, the ratio of the thickness of the negative electrode sheet to the total thickness of the first separator or the second separator is (8 to 15):

1.

20. An electrochemical device, characterized in that, Comprising the wound cell according to any one of claims 1 to 19 and a housing, and the wound cell is accommodated in the housing.

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