Cushion bag and lithium battery preparation method for improving pole piece deformation through cushion bag

Abstract

The invention provides a cushion bag and a lithium battery preparation method for improving pole piece deformation through the cushion bag. The lithium battery preparation method for improving pole piece deformation through the cushion bag comprises the following steps: preparing a positive plate, and compacting the positive plate; preparing a negative plate, and compacting the negative plate; when the positive plate, the diaphragm and the negative plate are wound to a preset position, an inflated cushion bag is placed between the positive plate or the negative plate and the diaphragm, and then winding is continued; exhausting the cushion bag so as to draw out the cushion bag after the thickness of the cushion bag is changed; and filling the roll core into a shell, and performing liquid injection, formation and packaging to obtain the lithium battery. The cushion bag supports the roll core in the winding process to form a reserved shrinkage space, so that distortion caused by non-concentrated internal stress of the pole piece is avoided, short-circuit lithium precipitation of the lithium ion battery is avoided, and deformation of the lithium battery is reduced; and after winding is completed, exhausting is performed through the cushion bag, so that the cushion bag shrinks and is separated from the surface of the pole piece, friction between the cushion bag and the pole piece is reduced, and powder falling of the pole piece is avoided.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a pad and a method for preparing a lithium battery by using the pad to improve deformation of a pole piece. Background Art

[0002] Lithium-ion batteries are widely used in daily life due to their high energy density, long cycle life, and environmental protection. The preparation process of lithium-ion batteries mainly includes pulping, coating, rolling, slitting, sheeting, winding, liquid injection, and formation.

[0003] The production process of the battery cell mainly includes winding and lamination processes. The battery prepared by the lamination process has a higher capacity, but the production process and equipment requirements are more precise. The winding process has high production efficiency and low equipment requirements. However, excessive tension fluctuations in the winding process may cause the diaphragm to be stretched during the winding process, resulting in the shrinkage of the diaphragm after the winding is completed. In addition, the interlayer spacing at the corners inside the core after the core is pressed is small. During the charging process, the pole piece expands, resulting in stress concentration in the width direction of the core, generating a bending moment, causing the pole piece to twist, and causing the prepared lithium battery to have an "S" deformation. When inserting the core into the form of an insert to improve the deformation of the pole piece, due to the close contact between the insert and the pole piece of the core, the insert rubs against the pole piece when it is pulled out, which is prone to the problem of pole piece powder falling off.

[0004] For example, a lithium battery and its winding method disclosed in the comparative document CN202011085889.X, the positive electrode sheet, the first diaphragm, the negative electrode sheet, and the second diaphragm are stacked in sequence to form a to-be-wound object; the to-be-wound object is wound, and during the winding process, inserts are respectively inserted at at least two different predetermined positions, and the inserts and the to-be-wound object are wound together; the inserts are pulled out to obtain a winding core, and the inserts are staggered along the width direction of the winding core. This scheme achieves the effect of reducing the tension of the diaphragm by staggering two inserts, and creates a certain gap between each turn of the winding core, thereby reducing the probability of main body deformation after the battery cell is divided. However, the inserts of this scheme cannot be adjusted, which will cause the friction between the electrode sheet and the insert to cause powder loss. Summary of the invention

[0005] The purpose of the present disclosure is to overcome the deficiencies in the prior art and to provide a lithium battery preparation method that prevents pole piece deformation after battery charging, reduces powder loss caused by friction with the pole piece, and improves pole piece deformation through the pad.

[0006] The purpose of this disclosure is achieved through the following technical solutions:

[0007] A cushion bag includes a contact layer and an inflatable layer, wherein the contact layer is provided with a accommodating space, the inflatable layer is arranged in the accommodating space, the inflatable layer is integrally connected with the contact layer and is used to support the contact layer, the inflatable layer is provided with a plurality of inflatable channels at intervals, the inflatable channels are used to control the deformation of the inflatable layer, and an inflatable connection port is provided at one end of each of the inflatable channels, and each of the inflatable connection ports is respectively connected to a corresponding air source.

[0008] A method for preparing a lithium battery by using a cushion capsule to improve the deformation of a pole piece, using the cushion capsule described above for preparation, the method for preparing a lithium battery by using a cushion capsule to improve the deformation of a pole piece comprises the following steps:

[0009] preparing a positive electrode sheet, and compacting the positive electrode sheet;

[0010] preparing a negative electrode sheet, and compacting the negative electrode sheet;

[0011] Winding the positive electrode sheet, the separator and the negative electrode sheet, when the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, placing an inflated cushion bag between the positive electrode sheet or the negative electrode sheet and the separator, and continuing to wind to form a reserved shrinkage space to obtain a winding core with the cushion bag inserted;

[0012] venting the cushion bag of the winding core to change the thickness of the cushion bag, and then pulling out the cushion bag;

[0013] After the coil core is encased, liquid injection, formation and packaging are performed to obtain a lithium battery.

[0014] In one embodiment, the thickness of the pad varies from 0.5mm to 2mm.

[0015] In one embodiment, the compaction pressure of the positive electrode sheet is 5Mpa-20Mpa, and the compaction pressure of the negative electrode sheet is 5Mpa-20Mpa.

[0016] In one embodiment, after the positive electrode sheet and the negative electrode sheet are respectively compacted, and before the positive electrode sheet, the separator and the negative electrode sheet are wound, the following steps are also included:

[0017] The positive electrode sheet and the negative electrode sheet are cut.

[0018] In one embodiment, the positive electrode sheet, the separator and the negative electrode sheet are wound. When the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, an inflated cushion bag is placed between the positive electrode sheet or the negative electrode sheet and the separator, and the winding is continued to form a reserved shrinkage space. After obtaining a winding core for inserting the cushion bag, the cushion bag of the winding core is exhausted to change the thickness of the cushion bag. Before the cushion bag is extracted, the following steps are also included:

[0019] The air pressure of the multiple inflation channels of the cushion bag is adjusted to make the cushion bag adapt to the stress change of the winding core.

[0020] In one embodiment, a cushion bag is sequentially added at different winding positions during the winding process of the winding core.

[0021] In one embodiment, when the positive electrode sheet, the separator and the negative electrode sheet are wound, the winding tension is 00.5Mpa-0.18Mpa.

[0022] In one embodiment, preparing the positive electrode sheet comprises the following steps:

[0023] Preparing positive electrode material slurry;

[0024] The positive electrode material slurry is coated on aluminum foil, and the surface density of the positive electrode material slurry coating is 20 mg / cm 2 -50mg / cm 2 , to obtain the positive electrode sheet;

[0025] The positive electrode sheet is placed in an oven for baking, and the baking temperature is 90°C-120°C.

[0026] In one embodiment, preparing the negative electrode sheet comprises the following steps:

[0027] Preparing negative electrode material slurry;

[0028] The negative electrode material slurry is coated on the copper foil, and the surface density of the negative electrode material slurry coating is 10.5 mg / cm 2 -20mg / cm 2 ;

[0029] The negative electrode sheet is placed in an oven for baking, and the baking temperature is 80°C-110°C.

[0030] Compared with the prior art, the present invention has at least the following advantages:

[0031] The above-mentioned lithium battery preparation method using a cushion bag to improve the deformation of the pole piece is to place an inflated cushion bag during the winding process, so that the inflated cushion bag supports the pole piece of the winding core to form a reserved shrinkage space, avoid the bending moment caused by the non-concentration of stress inside the winding core, and cause the pole piece to be twisted, avoid the lithium-ion battery short circuit lithium precipitation and other problems, and reduce the deformation of the lithium battery; after the winding is completed, the cushion bag is vented, so that the cushion bag shrinks and separates from the pole piece surface, reducing the friction between the cushion bag and the pole piece, thereby avoiding the problem of powder loss of the pole piece, reducing the impact of the withdrawal of the cushion bag on the winding core, and avoiding the deformation of the winding core during the winding process. The air pressure of the cushion bag is adjusted so that the cushion bag adapts to the stress change of the winding core to reduce the shrinkage space. The shrinkage space is adjusted by the cushion bag to effectively utilize the space in the winding core, thereby improving the energy density of the lithium battery, and then improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a schematic diagram of the structure of a cushion bag according to an embodiment;

[0034] Figure 2 for Figure 1 a cross-sectional view of the bladder shown;

[0035] Figure 3 for Figure 1 The schematic diagram of the structure of the cushion bag in different inflation states shown;

[0036] Figure 4 A flowchart of a method for preparing a lithium battery by improving deformation of a pole piece through a pad according to an embodiment;

[0037] Figure 5 0.5C cycle performance curves of lithium batteries prepared in Examples 1-3 and Comparative Example 1;

[0038] Figure 6 1C cycle performance curve of the lithium batteries prepared in Examples 1-3 and Comparative Example 1. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present disclosure are given in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thoroughly and comprehensively understood.

[0040] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present disclosure. The terms used herein in the specification of the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0042] In order to better understand the technical solutions and beneficial effects of the present invention, the present invention is further described in detail below in conjunction with specific embodiments:

[0043] like Figures 1 to 3As shown, it is a cushion bag 10 of an embodiment of the present invention, including a contact layer 100 and an inflatable layer 200. The contact layer 100 is provided with a receiving space 101. The inflatable layer 200 is arranged in the receiving space 101. The inflatable layer 200 is connected to the contact layer 100 and used to support the contact layer 100. The inflatable layer 200 is provided with a plurality of inflatable channels 201 at intervals. The inflatable channels 201 are used to control the deformation of the inflatable layer 200. One end of each inflatable channel 201 is provided with an inflatable connection port 202, and each inflatable connection port 202 is connected to a corresponding air source. In this embodiment, the inflatable layer 200 can be made of thermoplastic elastomer materials such as TPU and TPE, which are soft, have good tensile strength and high and low temperature resistance. The contact layer 100 is made of modified PP, which has good heat resistance. The hardness of the contact layer 100 is higher than that of the inflatable layer 200, so that the contact layer 100 has better support for the surface of the pole piece. The air source is used to inhale and inflate the air channel 201, so that the air-filled layer 200 is deformed, so that the height of the position where the air-filled layer 200 supports the contact layer 100 changes, thereby controlling the thickness change of the cushion 10. When the positive electrode sheet, the separator and the negative electrode sheet are wound, the inflated cushion 10 is placed, so that the inflated cushion 10 forms a reserved shrinkage space in the winding core. When the winding is completed, the winding core with the cushion 10 inserted is obtained. After the cushion 10 is exhausted, the thickness becomes thinner, which facilitates the removal of the cushion 10 from the winding core, so that the friction between the cushion 10 and the electrode sheet material of the winding core is reduced, thereby reducing the powder loss of the electrode sheet material of the winding core.

[0044] like Figure 4 As shown, a method for preparing a lithium battery by improving the deformation of a pole piece by using a pad bag according to an embodiment of the present invention comprises the following steps:

[0045] S101 prepares a positive electrode sheet and compacts the positive electrode sheet. In this embodiment, the positive electrode sheet is compacted so that the particles of the positive electrode material of the positive electrode sheet are more closely connected, the thickness of the positive electrode sheet is reduced, and the density of the positive electrode sheet is increased, thereby increasing the energy density of the battery and improving the conductivity and ion transport performance inside the positive electrode sheet. After compaction, the thickness of the positive electrode sheet is also made more uniform, thereby improving the cycle stability and safety of the battery.

[0046] S103 prepares a negative electrode sheet and compacts the negative electrode sheet. In this embodiment, the negative electrode sheet is compacted so that the particles of the negative electrode material of the negative electrode sheet are more closely connected, the thickness of the negative electrode sheet is reduced, and the density of the negative electrode sheet is increased. By compacting the negative electrode sheet, the density of the negative electrode sheet is increased and the thickness of the negative electrode sheet is made more uniform.

[0047] S105: Winding the positive electrode sheet, the separator and the negative electrode sheet. When the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, an inflated cushion bag is placed between the positive electrode sheet or the negative electrode sheet and the separator, and the winding is continued to form a reserved shrinkage space to obtain a winding core with the cushion bag inserted. In this embodiment, the volume and thickness of the cushion bag increase after inflation, so that the cushion bag can support the positive electrode sheet, the separator and the negative electrode sheet, so that the inflated cushion bag forms a reserved shrinkage space during the winding process. After the battery is charged, the material of the electrode sheet of the winding core expands and generates a problem of internal stress non-concentration. The reserved shrinkage space can alleviate the problem of electrode sheet distortion caused by the internal stress non-concentration of the winding core.

[0048] S107 vents the cushion bag of the winding core after shaping, so that the cushion bag shrinks and the cushion bag is pulled out. In this embodiment, after the cushion bag is vented, the cushion bag shrinks, so that the cushion bag is separated from the surface material of the electrode, thereby reducing the friction between the cushion bag and the surface material of the electrode, avoiding the problem of lithium deposition caused by short circuit of lithium-ion battery, and further reducing the powder loss of the electrode.

[0049] S109: After the core is encased, liquid is injected, formed and packaged to obtain a lithium battery. In this embodiment, a reserved shrinkage space is formed in the core of the lithium battery, which relieves the stress between the diaphragm, the positive electrode sheet and the negative electrode sheet, thereby reducing the distortion of the electrode sheet after the lithium battery cycle, thereby improving the cycle stability of the battery.

[0050] The above-mentioned method for preparing a lithium battery by improving the deformation of the pole piece through a cushion bag, places an inflated cushion bag during the winding process, so that the inflated cushion bag supports the pole piece of the winding core to form a reserved shrinkage space, avoids the bending moment caused by the non-concentrated stress inside the winding core to cause the pole piece to twist, avoids the problems of lithium-ion battery short circuit and lithium deposition, and reduces the deformation of the lithium battery; after the winding is completed, the cushion bag is vented, so that the cushion bag shrinks and separates from the surface of the pole piece, reducing the friction between the cushion bag and the pole piece, thereby avoiding the problem of powder loss of the pole piece, reducing the influence of pulling out the cushion bag on the winding core, and avoiding the deformation of the winding core during the winding process.

[0051] In one embodiment, the length of the cushion is 5mm-100mm, and the thickness of the cushion is 1mm-3mm. In this embodiment, when the thickness of the cushion is too thick, the space occupied by the battery is large, and when the cushion is too thin, the thickness of the cushion changes little, and the thickness of the cushion needs to be controlled within 1mm-3mm. The specifications of lithium batteries are different, and the corresponding pad sizes are different. When the length of the pad is less than 5mm, the corresponding size of the pad is small, the inflation channel of the pad is small, and it is difficult for the air source to evacuate and inflate the inflation channel; when the length of the pad is greater than 100mm, the pad is longer, and the reserved shrinkage space formed by the pad in the winding core is longer, and the reserved shrinkage space is prone to deformation, which leads to a decrease in the effect of the reserved shrinkage space in relieving the stress of the positive electrode, negative electrode and diaphragm; the length of the pad is 5mm-100mm, and the specifications of the lithium battery match the pad of the corresponding size, so that the reserved shrinkage space formed by the winding core has better stability, and the reserved shrinkage space effectively relieves the stress of the electrode. After the lithium battery is charged, the electrode is not easily deformed after expansion, which makes the lithium battery more stable.

[0052] In one embodiment, the thickness of the cushion bag changes by 0.5mm-2mm. In this embodiment, when the inflation channel of the cushion bag is inflated, the thickness of the cushion bag increases, and when the inflation channel of the cushion bag is evacuated, the thickness of the cushion bag decreases, thereby causing the reserved shrinkage space formed to change. When the thickness change of the cushion bag is less than 0.5mm, the cushion bag still has a large area of ​​contact with the surface of the positive electrode sheet or the negative electrode sheet, and it is easy to rub against the material of the positive electrode sheet or the negative electrode sheet when the cushion bag is pulled out, thereby causing the positive electrode sheet or the negative electrode sheet to produce powder loss; because the cushion bag is thin, when the pressure is too high when the inflation channel of the cushion bag is evacuated, it is easy to cause the inflation channel of the cushion bag to be damaged and the thickness of the cushion bag is too thin to produce a large change; therefore, the change of the thickness of the cushion bag is controlled within 0.5mm-2mm, ensuring that the cushion bag is separated from the surface of the positive electrode sheet or the negative electrode sheet, thereby reducing the friction with the material of the positive electrode sheet or the negative electrode sheet to produce powder loss, and avoiding damage caused by excessive evacuation pressure of the inflation channel of the cushion bag.

[0053] In one of the embodiments, the compaction pressure of the positive electrode sheet is 5Mpa-20Mpa, and the compaction pressure of the negative electrode sheet is 5Mpa-20Mpa. In this embodiment, when the compaction pressure is less than 5Mpa, the compaction density is low, and the core energy density of the positive electrode sheet and the negative electrode sheet is small, so that the discharge specific capacity of the prepared battery cell decreases rapidly after the same number of cycles, and the capacity retention rate is poor. When the compaction pressure is greater than 20Mpa, when the compaction density is too large, the porosity in the electrode material is reduced, so that the electrolyte infiltration effect is not good, and then the material structure and the distribution of the conductive agent are destroyed. When winding, the material of the electrode sheet is easily deformed or broken by external force, thereby affecting the structural integrity of the battery. Therefore, the compaction pressure of the positive electrode sheet and the negative electrode sheet is controlled at 5Mpa-20Mpa, so that the thickness of the obtained positive electrode sheet and the negative electrode sheet is thin and a certain porosity is maintained, so that the electrolyte infiltration effect is better.

[0054] Furthermore, since the materials of the positive electrode sheet are aluminum foil, conductive agent, binder and LiCoO2, LiMn2O4, LiFePO4, Li(Ni x Co y Mn z )O2, the material of the negative electrode sheet is copper foil, conductive carbon black SP, styrene-butadiene rubber SBR, carboxymethyl cellulose CMC, graphite and silicon carbon, so that the compaction density of the positive electrode sheet and the negative electrode sheet after compaction changes differently, the material of the positive electrode sheet has high hardness and stable crystal structure, and a large pressure is required during the compaction process of the material of the positive electrode sheet to achieve a close arrangement, and the material of the negative electrode sheet, such as graphite, has high compressibility and toughness, and a relatively low pressure is required during the compaction process to achieve a close arrangement, thereby controlling the porosity of the positive electrode sheet and the negative electrode sheet and maintaining consistency as well as the close arrangement structure. Therefore, when compacting the positive electrode sheet, a preset positive electrode compaction pressure is set, a preset positive electrode compaction time is set, and the positive electrode sheet is hot pressed; when compacting the negative electrode sheet, a preset negative electrode compaction pressure is set, and the preset negative electrode compaction pressure is reduced by 0.5Mpa-1Mpa than the preset positive electrode compaction pressure, and the negative electrode compaction time is set, and the negative electrode compaction time is reduced by 10s than the positive electrode compaction time, and the negative electrode sheet is hot pressed.

[0055] In this embodiment, the preset positive electrode compaction pressure and the preset negative electrode compaction pressure are both within the range of 5Mpa-20Mpa, and the preset negative electrode compaction pressure is reduced to reduce the compression amount of the negative electrode sheet material. The preset positive electrode compaction time is 20s-30s. By reducing the compaction time of the negative electrode sheet, the compression amount of the negative electrode sheet material is further reduced, so that the porosity and the close arrangement structure of the positive electrode sheet and the negative electrode sheet maintain a certain stability and consistency, thereby making the winding core obtained after the positive electrode sheet, the diaphragm and the negative electrode sheet are wound better. After the positive electrode sheet is hot pressed, the conductive agent and the binder in the positive electrode material will form a uniform network structure during the hot pressing process, enhance the strength and connectivity of the positive electrode material, reduce the internal resistance of the battery, and thus improve the energy density and power density. After the negative electrode sheet is hot pressed, the physical properties of the negative electrode sheet are more uniform and stable, and defects such as cracks and delamination are reduced, thereby improving the cycle performance and safety of the battery.

[0056] In one embodiment, after the positive electrode sheet and the negative electrode sheet are respectively compacted, and before the positive electrode sheet, the separator and the negative electrode sheet are wound, the following steps are also included:

[0057] The positive electrode sheet and the negative electrode sheet are cut. In this embodiment, when the positive electrode sheet and the negative electrode sheet are cut, the positive electrode sheet and the negative electrode sheet are made into fixed sizes by cutting, thereby ensuring the stability of the structure of the positive electrode sheet and the negative electrode sheet; wherein the width of the negative electrode sheet is wider than that of the positive electrode sheet, and when the diaphragm at the edge of the negative electrode sheet is damaged, the positive electrode sheet and the negative electrode sheet are prevented from directly contacting each other to cause a short circuit.

[0058] like Figure 3 As shown, in one embodiment, the positive electrode sheet, the separator and the negative electrode sheet are wound. When the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, an inflated cushion bag is placed between the positive electrode sheet or the negative electrode sheet and the separator, and the winding is continued to form a reserved shrinkage space. After obtaining a winding core for inserting the cushion bag, the cushion bag of the winding core is exhausted to change the thickness of the cushion bag. Before the cushion bag is extracted, the following steps are also included:

[0059] The air pressure of the multiple inflation channels of the cushion bag is adjusted to make the cushion bag adapt to the stress change of the core. In this embodiment, when the core is wound, the positive electrode sheet or the negative electrode sheet is bent, and multiple points of the positive electrode sheet or the negative electrode sheet are selected with an interval of 3mm-5mm. When the inclination angle between the tangents of the multiple points is greater than 90°, an internal corner is generated in the obtained core. After the core is pressed, the interlayer spacing at the internal corner of the core is small, the stress change at the internal corner of the core is large, and more relief space is required at the internal corner of the core. Specifically, the amount of air rushed into the inflation channel of the cushion bladder near the corner of the core is larger, so that the thickness of the cushion bladder near the corner of the core is thicker, and more shrinkage space is formed near the corner of the core, which is conducive to relieving the stress generated at the corner of the core; the amount of air rushed into the inflation channel of the cushion bladder away from the corner of the core is smaller, so that the thickness of the cushion bladder near the corner of the core is thinner, and less stress is generated away from the corner of the core, reducing the size of the shrinkage space formed away from the corner of the core, thereby saving the space of the core. The shrinkage space at any core position is adjusted by the cushion bladder adapting to effectively utilize the space in the core, thereby improving the energy density of the lithium battery and further improving the cycle performance of the battery.

[0060] Furthermore, in one embodiment, after the air pressure of the cushion bag is adjusted, the cushion bag of the winding core is exhausted to change the thickness of the cushion bag, and before the cushion bag is withdrawn, the following steps are also included:

[0061] The roll core inserted into the pad bag is heat-pressed and shaped.

[0062] In this embodiment, the inserted cushion capsule core is hot pressed to form a fixed shape of the cushion capsule core, which facilitates the packaging of the core into the shell. During the hot pressing process, the stress between the diaphragm, the positive electrode sheet and the negative electrode sheet is relieved and fixed into shape, thereby improving the stability of the reserved shrinkage space formed by the cushion capsule.

[0063] It can be understood that after the core is wound to form a reserved shrinkage space, the core is pressurized during the hot pressing process, which increases the pressure between the pole piece and the cushion bag, which easily causes the cushion bag to deform and shrink, thereby affecting the reserved shrinkage space formed. Therefore, before the core inserted into the cushion bag is hot-pressed and finalized, the following steps are also included:

[0064] The cushion is inflated and pressurized to increase the pressure between the cushion and the positive electrode sheet, the separator and the negative electrode sheet, and then the winding core inserted with the cushion is hot-pressed and formed. In this embodiment, since the reserved shrinkage space is fixed in volume after winding, pressurizing the cushion will not expand the reserved shrinkage space, which increases the supporting pressure of the cushion on the positive electrode sheet, the negative electrode sheet and the separator, thereby avoiding the cushion being compressed by force during hot-pressing. After the cushion is inflated and pressurized, the pressure between the positive electrode sheet, the separator, the negative electrode sheet and the cushion is also increased, so that the positive electrode sheet, the separator and the negative electrode sheet are more closely attached, thereby improving the stability of the winding core.

[0065] In one of the embodiments, a cushion bag is sequentially placed at different winding positions during the winding process of the core. In this embodiment, when the core is wound to a preset position, a cushion bag is placed on one side of the core, and the winding is continued to form a reserved shrinkage space in the core, thereby relieving the stress on one side of the core; another cushion bag is placed on the other side of the core, or another cushion bag is placed on the other side of the core after the core is wound several times, so that a reserved shrinkage space is formed on the other side of the core, thereby relieving the stress on the other side of the core, and then the winding is continued. The cushion bag forms a reserved shrinkage space on both sides of the core, so that the stress on both sides of the core is relieved, further reducing the deformation problem of the pole piece, and making the prepared lithium battery structure more stable.

[0066] In one embodiment, a lithium battery preparation method using a pad to improve the deformation of the pole piece has a winding tension of 0.05Mpa-0.18Mpa. The winding tension affects the flatness and fit of the positive pole piece, the negative pole piece and the diaphragm, thereby affecting the internal resistance and the shell penetration rate. When the winding tension is too large, it is easy to cause a short circuit or a broken piece risk.

[0067] Furthermore, after the cushion bag is added during the winding process, the cushion bag increases the porosity of the winding core, thereby affecting the shell-entry rate of the winding core. When the positive electrode sheet, the separator and the negative electrode sheet are wound, the winding is performed at a preset winding pressure. When the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, the inflated cushion bag is placed between the positive electrode sheet or the negative electrode sheet and the separator, and the following steps are also included:

[0068] The preset winding tension of the winding increases by 0.001Mpa-0.005Mpa, and the total number of winding turns decreases by 0.8-0.9 turns. In this embodiment, the preset winding tension after the winding tension is increased is controlled within 0.05Mpa-0.18Mpa. When the winding tension increases, the shrinkage rate of the diaphragm is relatively large. The reserved shrinkage space formed by the cushion bag in the winding core can eliminate part of the influence of the diaphragm shrinkage, so that the winding tension that can be set during the winding process becomes larger. By increasing the winding tension, the positive electrode sheet, the negative electrode sheet and the diaphragm are more closely attached, thereby increasing the density of the winding core. By reducing the number of winding turns, the volume change increment of the winding core is further controlled, so that the winding core can be smoothly put into the shell for packaging.

[0069] In one embodiment, preparing the positive electrode sheet comprises the following steps:

[0070] Preparing positive electrode material slurry;

[0071] The positive electrode material slurry is coated on aluminum foil, and the surface density of the positive electrode material slurry coating is 20 mg / cm 2 -50mg / cm 2 , to obtain the positive electrode sheet;

[0072] The positive electrode sheet is placed in an oven for baking at a temperature of 80°C to 110°C. In this embodiment, the surface density of the positive electrode material slurry coating is less than 20 mg / cm 2 When the positive electrode material slurry is coated with a thinner thickness, the positive electrode material is less, which makes the battery energy density lower. When the surface density of the positive electrode material slurry is greater than 50 mg / cm 2 When the positive electrode material slurry is coated with a thicker thickness, the positive electrode material is prone to breakage during the winding process. By baking in an oven at 80℃-110℃, the moisture of the positive electrode material of the positive electrode sheet is dried, which can also help release the stress generated by the positive electrode material during the pressing process, thereby reducing the deformation of the winding core after winding.

[0073] In one embodiment, the positive electrode material slurry includes a positive electrode material, a conductive agent and a binder. The positive electrode material includes LiCoO2, LiMn2O4, LiFePO4, Li(Ni x Co y Mn z )O2 and the like. In this embodiment, the adhesive binds the positive electrode material and the conductive agent together, so that the positive electrode material slurry coated on the positive electrode sheet has good lithium ion conductivity.

[0074] Furthermore, in one embodiment, the thickness of the aluminum foil of the positive electrode sheet is 10 μm-13 μm. In this embodiment, when the thickness of the aluminum foil of the positive electrode sheet is less than 10 μm, the strength of the aluminum foil is low and it is easy to break when winding. When the thickness of the aluminum foil is greater than 13 μm, the thickness of the positive electrode sheet is too thick, so that the energy density of the lithium battery made of the positive electrode sheet decreases.

[0075] In one embodiment, preparing the negative electrode sheet comprises the following steps:

[0076] Preparing negative electrode material slurry;

[0077] The negative electrode material slurry is coated on the copper foil, and the surface density of the negative electrode material slurry coating is 10.5 mg / cm 2 -20mg / cm 2 ;

[0078] The negative electrode sheet is placed in an oven for baking at a temperature of 80°C to 110°C. In this embodiment, the surface density of the negative electrode material slurry coating is less than 10.5 mg / cm 2 When the negative electrode material slurry is coated with a thinner thickness, the negative electrode material is less, which makes the battery energy density lower. When the surface density of the negative electrode material slurry is greater than 20 mg / cm 2 When the negative electrode material slurry is coated with a thicker thickness, the negative electrode material is prone to breakage during the winding process. By baking in an oven at 80℃-110℃, the moisture of the negative electrode material of the positive electrode sheet is dried, and the stress generated by the negative electrode material during the pressing process can be released, thereby reducing the deformation of the winding core after winding.

[0079] Furthermore, in one of the embodiments, the thickness of the copper foil of the negative electrode sheet is 6μm-8μm. In this embodiment, when the thickness of the copper foil of the negative electrode sheet is less than 6μm, the strength of the copper foil is low, and it is easy to break when winding. When the thickness of the copper foil is greater than 8μm, the thickness of the negative electrode sheet is too thick, so that the energy density of the lithium battery made of the negative electrode sheet decreases; the copper foil provides the tensile strength of the negative electrode sheet, and the thickness of the copper foil is reduced.

[0080] In one embodiment, the negative electrode material slurry includes negative electrode material, conductive carbon black SP, styrene butadiene rubber SBR and carboxymethyl cellulose CMC, and the negative electrode material is at least one of graphite and silicon carbon. In this embodiment, the graphite or silicon carbon of the negative electrode material has good charge and discharge performance and good cycle life; the conductive carbon black SP can enhance the conductivity of the negative electrode material, reduce the internal resistance of the battery, and improve the charge and discharge performance of the battery; styrene butadiene rubber SBR is used as a binder to make the negative electrode material particles closely bonded to prevent the negative electrode material from falling off and pulverizing during the charge and discharge process; carboxymethyl cellulose CMC has excellent dispersibility and water retention, and improves the uniformity and stability of the negative electrode material slurry; after mixing the negative electrode material, conductive carbon black SP, styrene butadiene rubber SBR and carboxymethyl cellulose CMC, a negative electrode material slurry with excellent performance can be prepared.

[0081] Compared with the prior art, the present invention has at least the following advantages:

[0082] The above-mentioned lithium battery preparation method using a cushion bag to improve the deformation of the pole piece is to place an inflated cushion bag during the winding process, so that the inflated cushion bag supports the pole piece of the winding core to form a reserved shrinkage space, avoid the bending moment caused by the non-concentration of stress inside the winding core, and cause the pole piece to be twisted, avoid the lithium-ion battery short circuit lithium precipitation and other problems, and reduce the deformation of the lithium battery; after the winding is completed, the cushion bag is vented, so that the cushion bag shrinks and separates from the pole piece surface, reducing the friction between the cushion bag and the pole piece, thereby avoiding the problem of powder loss of the pole piece, reducing the impact of the withdrawal of the cushion bag on the winding core, and avoiding the deformation of the winding core during the winding process. The air pressure of the cushion bag is adjusted so that the cushion bag adapts to the stress change of the winding core to reduce the shrinkage space. The shrinkage space is adjusted by the cushion bag to effectively utilize the space in the winding core, thereby improving the energy density of the lithium battery, and then improving the cycle performance of the battery.

[0083] Some specific examples are listed below, and if % is mentioned, it means percentage by weight. It should be noted that the following examples do not exhaust all possible situations, and the materials used in the following examples can be obtained from commercial sources unless otherwise specified.

[0084] Example 1

[0085] First, prepare the slurry. The positive electrode slurry is composed of one or more of LiCoO2, LiMn2O4, LiFePO4, Li(NixCoyMnz)O2, etc., conductive agent SP and CNT, and a binder. The slurry ratio is positive electrode material: conductive agent: binder = 97.4%: 1.2%: 1.4%.

[0086] The prepared positive electrode material slurry was coated on a 10 or 13 μm aluminum foil with a coating surface density of 20 mg / cm 2 -50mg / cm 2The positive electrode is baked at 90℃-120℃.

[0087] The positive electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0088] The negative electrode slurry is prepared. The negative electrode is a mixture of one or two of graphite and silicon carbon. The slurry formula ratio is negative electrode material: SP: SBR: CMC = 92.76: 1.1: 2: 1.3.

[0089] The prepared negative electrode slurry was coated on a 6 or 8 μm copper foil with a coating surface density of 10.5 mg / cm 2 -20mg / cm 2 , and then baked at a temperature of 80℃-110℃ to form the positive electrode sheet.

[0090] The negative electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0091] The prepared pole piece is cut into required sizes and wound.

[0092] The separator is first rolled halfway, and the negative electrode sheet is inserted, and then rolled halfway again, and the positive electrode sheet is inserted. When the positive electrode sheet, separator and negative electrode sheet are wound to 10 turns, an inflated 1mm×15mm cushion bag is placed on one side of the winding core, and another inflated 1mm×15mm cushion bag is placed on the other side of the winding core, and the winding is continued to obtain a winding core; the winding core is hot-pressed and shaped; the cushion bag of the winding core is exhausted, the cushion bag is extracted, and the winding core is shelled, and liquid is injected, formed and packaged to obtain the lithium battery of Example 1. The specification of the lithium battery is 603759-1500mAh, and the lithium battery of Example 1 is tested.

[0093] Example 2

[0094] First, prepare the slurry. The positive electrode slurry is composed of one or more of LiCoO2, LiMn2O4, LiFePO4, Li(NixCoyMnz)O2, etc., conductive agent SP and CNT, and a binder. The slurry ratio is positive electrode material: conductive agent: binder = 97.4%: 1.2%: 1.4%.

[0095] The prepared positive electrode material slurry was coated on a 10 or 13 μm aluminum foil with a coating surface density of 20 mg / cm 2 -50mg / cm 2 The positive electrode is baked at 90℃-120℃.

[0096] The positive electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0097] The negative electrode slurry is prepared. The negative electrode is a mixture of one or two of graphite and silicon carbon. The slurry formula ratio is negative electrode material: SP: SBR: CMC = 92.76: 1.1: 2: 1.3.

[0098] The prepared negative electrode slurry was coated on a 6 or 8 μm copper foil with a coating surface density of 10.5 mg / cm 2 -20mg / cm 2 , and then baked at a temperature of 80℃-110℃ to form the positive electrode sheet.

[0099] The negative electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0100] The prepared pole piece is cut into required sizes and wound.

[0101] The separator is first rolled halfway, and the negative electrode sheet is inserted, and then rolled halfway again, and the positive electrode sheet is inserted. When the positive electrode sheet, separator and negative electrode sheet are wound to 10 turns, an inflated 1mm×15mm cushion bag is placed on one side of the winding core, and the winding is continued to obtain a winding core; the winding core is hot-pressed and shaped; the cushion bag of the winding core is exhausted, the cushion bag is extracted, and the winding core is shelled, and then liquid is injected, formed and packaged to obtain the lithium battery of Example 2. The specification of the lithium battery is 603759-1500mAh. The lithium battery of Example 2 is tested.

[0102] Example 3

[0103] First, prepare the slurry. The positive electrode slurry is composed of one or more of LiCoO2, LiMn2O4, LiFePO4, Li(NixCoyMnz)O2, etc., conductive agent SP and CNT, and a binder. The slurry ratio is positive electrode material: conductive agent: binder = 97.4%: 1.2%: 1.4%.

[0104] The prepared positive electrode material slurry was coated on a 10 or 13 μm aluminum foil with a coating surface density of 20 mg / cm 2 -50mg / cm 2 The positive electrode is baked at 90℃-120℃.

[0105] The positive electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0106] The negative electrode slurry is prepared. The negative electrode is a mixture of one or two of graphite and silicon carbon. The slurry formula ratio is negative electrode material: SP: SBR: CMC = 92.76: 1.1: 2: 1.3.

[0107] The prepared negative electrode slurry was coated on a 6 or 8 μm copper foil with a coating surface density of 10.5 mg / cm 2 -20mg / cm 2, and then baked at a temperature of 80℃-110℃ to form the positive electrode sheet.

[0108] The negative electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0109] The prepared pole piece is cut into required sizes and wound.

[0110] The separator is first rolled halfway, and the negative electrode sheet is inserted, and then rolled halfway again, and the positive electrode sheet is inserted. When the positive electrode sheet, separator and negative electrode sheet are wound to 10 turns, an inflated 1mm×5mm cushion bag is placed on one side of the winding core, and another inflated 5mm cushion bag is placed on the other side of the winding core, and the winding is continued. The cushion bag of the winding core is exhausted, and the cushion bag is pulled out. After the winding core is shelled, liquid is injected, formed and packaged to obtain the lithium battery of Example 3. The specification of the lithium battery is 603759-1500mAh. The lithium battery of Example 3 is tested.

[0111] Comparative Example 1

[0112] First, prepare the slurry. The positive slurry is composed of one or more of LiCoO2, LiMn2O4, LiFePO4, Li(NixCoyMnz)O2, etc., conductive agent SP and CNT, and a binder. The slurry ratio is positive electrode material: conductive agent: binder = 97.4%: 1.2%: 1.4%.

[0113] The prepared positive electrode material slurry was coated on a 10 or 13 μm aluminum foil with a coating surface density of 20 mg / cm 2 -50mg / cm 2 The positive electrode is baked at 90℃-120℃.

[0114] The positive electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0115] The negative electrode slurry is prepared. The negative electrode is a mixture of one or two of graphite and silicon carbon. The slurry formula ratio is negative electrode material: SP: SBR: CMC = 92.76: 1.1: 2: 1.3.

[0116] The prepared negative electrode slurry was coated on a 6 or 8 μm copper foil with a coating surface density of 10.5 mg / cm 2 -20mg / cm 2 The positive electrode is baked at a temperature of 80°C-110°C.

[0117] The negative electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0118] The prepared pole piece is cut into required sizes and wound.

[0119] No padding bag is inserted during the winding process. After winding, a core is obtained; the core is heat-pressed and shaped; after the core is shelled, liquid is injected, formed and packaged to obtain a lithium battery of comparative example 1, the specification of the lithium battery is 603759-1500mAh, and the lithium battery of comparative example 1 is tested.

[0120] Comparative Example 2

[0121] First, prepare the slurry. The positive electrode slurry is composed of one or more of LiCoO2, LiMn2O4, LiFePO4, Li(NixCoyMnz)O2, etc., conductive agent SP and CNT, and a binder. The slurry ratio is positive electrode material: conductive agent: binder = 97.4%: 1.2%: 1.4%.

[0122] The prepared positive electrode material slurry was coated on a 10 or 13 μm aluminum foil with a coating surface density of 20 mg / cm 2 -50mg / cm 2 The positive electrode is baked at 90℃-120℃.

[0123] The positive electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0124] The negative electrode slurry is prepared. The negative electrode is a mixture of one or two of graphite and silicon carbon. The slurry formula ratio is negative electrode material: SP: SBR: CMC = 92.76: 1.1: 2: 1.3.

[0125] The prepared negative electrode slurry was coated on a 6 or 8 μm copper foil with a coating surface density of 10.5 mg / cm 2 -20mg / cm 2 , and then baked at a temperature of 80℃-110℃ to form the positive electrode sheet.

[0126] The negative electrode sheet is compacted under a pressure of 5Mpa-20Mpa.

[0127] The prepared pole piece is cut into required sizes and wound.

[0128] The separator is first rolled halfway, and the negative electrode is inserted, and then rolled halfway again, and the positive electrode is inserted. When the positive electrode, separator and negative electrode are wound to 10 turns, an inflated 1mm×15mm PVC gasket is placed on one side of the winding core, and another inflated 1mm×15mm PVC gasket is placed on the other side of the winding core, and the winding is continued to obtain a winding core; the winding core is hot-pressed and shaped; the gasket of the winding core is vented, the gasket is extracted, and the winding core is shelled, and liquid is injected, formed and packaged to obtain the lithium battery of Example 1. The specification of the lithium battery is 603759-1500mAh. The lithium battery of Example 1 is tested.

[0129] Table 1 Battery performance test table of Examples 1-3 and Comparative Example 1

[0130]

[0131] Table 2 Results of residual battery powder in Examples 1-3 and Comparative Example 2

[0132]

[0133] from Figure 5 and Figure 6 As can be seen from Table 1, compared with Comparative Example 1, the capacity retention rates of Examples 1-3 after 300 cycles of 0.5C charge and discharge are improved, and the number of times that the 1C charge and discharge capacity retention rates of Examples 1-3 are lower than 80% is increased. The resistance of the battery is low, indicating that the battery is less deformed, and the reserved shrinkage space formed by the pad can effectively alleviate the expansion problem caused by battery charging.

[0134] The specifications of the 603759-1500mAh lithium battery are 60×37×59mm. The inserted pads in Examples 1 and 2 are both 1mm×15mm. Example 1 inserts pads on both sides, and Example 2 inserts pads on one side. Example 1 has more reserved shrinkage space, and the capacity retention rate is higher after 300 cycles of 0.5C charge and discharge, and the number of times the 1C charge and discharge capacity retention rate is lower than 80% is more. The pad in Example 1 is more compatible with the 603759-1500mAh lithium battery, indicating that the larger reserved shrinkage space formed by the pad can effectively alleviate the expansion problem caused by battery charging; Example 3 has expansion deformation. The inserted pad in Example 3 is 1mm×5mm, and the shrinkage space formed is smaller. After the battery is charged and expanded, the reserved shrinkage space that is too small cannot alleviate the deformation of the electrode.

[0135] As can be seen from Table 2, in Examples 1-3, compared with Comparative Example 2, the PVC gasket is wound into a core, and when the PVC is pulled out of the core, it is easy to rub against the electrode and cause powder loss; the electrode is placed in a cushion bag and wound into a core. After the cushion bag is exhausted, it is pulled out, and there is no problem of powder loss due to friction with the electrode, thereby reducing the impact of pulling out the cushion bag on the core.

[0136] The above-mentioned embodiments only express several implementation methods of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the disclosed patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present disclosure, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the disclosed patent shall be subject to the attached claims.

Claims

1. A cushion bag, characterized in that: It includes a contact layer and an inflatable layer, the contact layer is provided with a accommodating space, the inflatable layer is arranged in the accommodating space, the inflatable layer is connected to the contact layer as a whole and is used to support the contact layer, the inflatable layer is provided with a plurality of inflatable channels at intervals, the inflatable channels are used to control the deformation of the inflatable layer, one end of each of the inflatable channels is provided with an inflatable connection port, and each of the inflatable connection ports is respectively connected to a corresponding air source.

2. A method for preparing a lithium battery by improving the deformation of a pole piece through a pad, characterized in that: The preparation method of a lithium battery by using the cushion bag as claimed in claim 1 to improve the deformation of the pole piece comprises the following steps: preparing a positive electrode sheet, and compacting the positive electrode sheet; preparing a negative electrode sheet, and compacting the negative electrode sheet; Winding the positive electrode sheet, the separator and the negative electrode sheet, when the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, placing an inflated cushion bag between the positive electrode sheet or the negative electrode sheet and the separator, and continuing to wind to form a reserved shrinkage space to obtain a winding core with the cushion bag inserted; venting the cushion bag of the winding core to change the thickness of the cushion bag, and then pulling out the cushion bag; After the coil core is encased, liquid injection, formation and packaging are performed to obtain a lithium battery.

3. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: The thickness of the pad varies from 0.5mm to 2mm.

4. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: The compaction pressure of the positive electrode sheet is 5Mpa-20Mpa, and the compaction pressure of the negative electrode sheet is 5Mpa-20Mpa.

5. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: After the positive electrode sheet and the negative electrode sheet are respectively compacted, and before the positive electrode sheet, the separator and the negative electrode sheet are wound, the following steps are also included: The positive electrode sheet and the negative electrode sheet are cut.

6. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: The positive electrode sheet, the separator and the negative electrode sheet are wound. When the positive electrode sheet, the separator and the negative electrode sheet are wound to a preset position, an inflated cushion bag is placed between the positive electrode sheet or the negative electrode sheet and the separator, and the winding is continued to form a reserved shrinkage space. After obtaining a winding core for inserting the cushion bag, the cushion bag of the winding core is exhausted to change the thickness of the cushion bag. Before the cushion bag is extracted, the following steps are also included: The air pressure of the multiple inflation channels of the cushion bag is adjusted to make the cushion bag adapt to the stress change of the winding core.

7. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: During the winding process of the winding core, the cushion bag is added in sequence at different winding positions.

8. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: When the positive electrode sheet, the separator and the negative electrode sheet are wound, the winding tension is 0.05Mpa-0.18Mpa.

9. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: The preparation of the positive electrode sheet comprises the following steps: Preparing positive electrode material slurry; The positive electrode material slurry is coated on aluminum foil, and the surface density of the positive electrode material slurry coating is 20 mg / cm 2 -50mg / cm 2 , to obtain the positive electrode sheet; The positive electrode sheet is placed in an oven for baking, and the baking temperature is 90°C-120°C.

10. The method for preparing a lithium battery by improving pole piece deformation by using a pad according to claim 2, characterized in that: The preparation of the negative electrode sheet comprises the following steps: Preparing negative electrode material slurry; The negative electrode material slurry is coated on the copper foil, and the surface density of the negative electrode material slurry coating is 10.5 mg / cm 2 -20mg / cm 2 ; The negative electrode sheet is placed in an oven for baking, and the baking temperature is 80°C-110°C.

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