Negative plate assembly and method for storing lithium supplement negative plate

Abstract

The invention discloses a negative pole piece assembly and a method for storing a lithium supplement negative pole piece, the negative pole piece assembly comprises the lithium supplement negative pole piece and a heat absorption film layer, the heat absorption film layer and the lithium supplement negative pole piece are stacked and then are wound and formed, the heat absorption film layer is internally provided with a phase change material, the phase change material can generate phase change heat absorption, and the lithium supplement negative pole piece can be stored in the heat absorption film layer. Pits are formed in at least part of the surface of the heat absorption film layer.

Description

Negative electrode assembly and method for storing lithium-supplemented negative electrode Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a negative electrode sheet assembly and a method for storing lithium-supplemented negative electrode sheets. Background Art

[0002] Lithium-ion batteries, with their advantages of high voltage, high energy density, and long cycle life, have become one of the most promising secondary batteries for application and development. The initial coulombic efficiency (CEE) of a lithium-ion battery is a key factor affecting its performance. For the negative electrode, the solid electrolyte film (SEI) formed on its surface during the initial charge consumes some of the lithium from the positive electrode, resulting in lithium loss in the positive electrode material and reducing the battery's initial efficiency, thereby affecting its capacity and energy density.

[0003] To address the problem of low initial charge and discharge efficiency in batteries, replenishing the negative electrode sheet with excess lithium to compensate for lithium loss during the initial charge is an effective solution. However, the refilled negative electrode sheet can pose safety risks such as combustion during storage. Furthermore, the refilled negative electrode sheet coil will nitride and turn black, resulting in lithium loss.

[0004] Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a negative electrode sheet assembly, which aims to make the lithium-supplementing negative electrode sheet have both good lithium-supplementing performance and safety performance.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a negative electrode sheet assembly, which includes: a lithium-supplemented negative electrode sheet and a heat-absorbing film layer, wherein the heat-absorbing film layer and the lithium-supplemented negative electrode sheet are stacked and then wound into a shape, the heat-absorbing film layer contains a phase change material, the phase change material can undergo phase change and absorb heat, and pits are formed on at least part of the surface of the heat-absorbing film layer.

[0007] Compared with the prior art, the present application has at least the following beneficial effects: the negative electrode sheet assembly of the present application includes a lithium-supplemented negative electrode sheet and a heat-absorbing film layer. The heat-absorbing film layer and the lithium-supplemented negative electrode sheet are stacked and then wound into a shape. The heat-absorbing film layer contains a phase change material, which can undergo phase change and absorb heat. The lithium-supplemented negative electrode sheet coil generates a large amount of heat due to the intense lithium insertion reaction. The phase change material in the heat-absorbing film layer undergoes phase change and absorbs heat under the action of this exothermic action, thereby absorbing the heat generated by the lithium-supplemented negative electrode sheet and improving the safety performance of the lithium-supplemented negative electrode sheet. At the same time, the metallic lithium in the lithium-supplemented negative electrode sheet reacts with the oxygen between the coil layers. After the oxygen between the layers is exhausted, the pits on the surface of the heat-absorbing film layer can replenish oxygen, thereby solving the problem of low lithium-supplementing performance of the lithium-supplemented negative electrode sheet and blackening of the lithium-supplemented negative electrode sheet caused by the reaction of metallic lithium with nitrogen after the oxygen between the layers of the lithium-supplemented negative electrode sheet is exhausted. As a result, the lithium-supplemented negative electrode sheet in the negative electrode sheet assembly of the present application has both good lithium-supplementing performance and safety performance.

[0008] In any embodiment of the present application, a cavity is formed in the heat-absorbing film layer, and a phase change material is provided in the cavity, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0009] In any embodiment of the present application, the temperature at which the phase change material undergoes phase change and absorbs heat is 30° C.-40° C. Thus, the safety performance of the lithium-supplemented negative electrode sheet can be improved.

[0010] In any embodiment of the present application, the enthalpy value of the phase change material is not less than 90 J / g, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0011] In any embodiment of the present application, the phase change material includes at least one of paraffin wax, crystalline hydrated salt phase change material, and molten salt phase change material, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0012] In any embodiment of the present application, the phase change material accounts for 50% to 80% of the total mass of the heat absorption film layer, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0013] In any embodiment of the present application, the thickness of the heat absorption film layer is 30 μm-100 μm, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0014] In any embodiment of the present application, the thickness of the heat absorption film layer is 50 μm-70 μm, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0015] In any embodiment of the present application, the heat-absorbing film layer includes: a first substrate, a second substrate, and a heat-absorbing layer; the first substrate and the second substrate are spaced apart and form a closed cavity, and the first substrate and / or the second substrate have the recess formed on the surface of the first substrate and / or the second substrate; the heat-absorbing layer is disposed in the cavity and includes the phase change material. This improves the safety of the lithium-supplemented negative electrode sheet.

[0016] In any embodiment of the present application, the thickness of the first substrate and / or the second substrate is 7 μm to 9 μm, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0017] In any embodiment of the present application, the area of ​​a single pit is 1 mm 2 -100mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0018] In any embodiment of the present application, the area of ​​a single pit is 20 mm 2 -50mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0019] In any embodiment of the present application, the depth of a single pit is 1 μm to 5 μm, thereby solving the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet.

[0020] In any embodiment of the present application, the distribution density of the pits on the first substrate and / or the second substrate is 1 ea / mm 2 -500ea / mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0021] In any embodiment of the present application, the distribution density of the pits on the first substrate and / or the second substrate is 20 ea / mm 2 -50ea / mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0022] In any embodiment of the present application, the thickness of the heat absorption layer is 30 μm-80 μm, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0023] In any embodiment of the present application, the thickness of the heat absorption layer is 30 μm-50 μm, thereby improving the safety performance of the lithium-supplemented negative electrode sheet.

[0024] In any embodiment of the present application, the heat absorption layer further includes an adhesive.

[0025] In any embodiment of the present application, based on the total mass of the heat absorption film layer, the adhesive accounts for 5%-10%.

[0026] In any embodiment of the present application, the heat absorption layer further includes an auxiliary agent.

[0027] In any embodiment of the present application, based on the total mass of the heat absorption film layer, the auxiliary agent accounts for 15%-40%.

[0028] A second aspect of the present application provides a storage method for a lithium-replenished negative electrode sheet, comprising: stacking a heat-absorbing film layer and the lithium-replenished negative electrode sheet, followed by winding. The heat-absorbing film layer has a recess formed on at least a portion of its surface, and a cavity is formed within the heat-absorbing film layer. A phase-change material is disposed within the cavity, and the phase-change material is capable of absorbing heat through a phase change. This method enables the lithium-replenished negative electrode sheet to achieve both a good lithium replenishment rate and safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0030] FIG1 is a schematic structural diagram of the negative electrode assembly of the present application.

[0031] FIG2 is a schematic diagram of the longitudinal cross-sectional structure of the heat-absorbing film layer on the negative electrode assembly of the present application.

[0032] Description of the drawings:

[0033] 100: negative electrode assembly; 10: lithium-supplemented negative electrode; 20: heat-absorbing film layer; 21: first substrate; 22: second substrate; 23: heat-absorbing layer; 201: cavity; 202: pit. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0035] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0036] In the description herein, unless otherwise indicated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0037] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0038] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0039] Currently, market developments indicate that lithium-ion secondary batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As the application of power batteries continues to expand, market demand is also growing.

[0040] The first coulombic efficiency of lithium-ion secondary batteries is an important factor affecting the performance of lithium-ion batteries. For the negative electrode, the solid electrolyte film (SEI film) formed on the surface of the negative electrode during the first charging process will consume part of the lithium from the positive electrode, causing the loss of lithium in the positive electrode material, reducing the first efficiency of the battery, and thus affecting the battery capacity and energy density.

[0041] The inventors of this application have noted that although the problem of low initial charge and discharge efficiency of the battery can be solved by replenishing the negative electrode sheet with lithium, the intense lithium insertion reaction during the storage of the refilled negative electrode sheet after winding will generate a large amount of heat, which may cause safety risks such as combustion. At the same time, the lithium in the refilled negative electrode sheet coil reacts with nitrogen to undergo a nitridation reaction, causing the refilled negative electrode sheet to turn black. Moreover, the lithium ions in the nitrided product cannot be used in subsequent cycles, resulting in lithium loss.

[0042] Therefore, in a first aspect, the present application provides a negative electrode sheet assembly. Referring to FIG1 , the negative electrode sheet assembly 100 includes a lithium-supplemented negative electrode sheet 10 and a heat-absorbing film layer 20 . The heat-absorbing film layer 20 is stacked and wound with the lithium-supplemented negative electrode sheet 10 . The heat-absorbing film layer 20 contains a phase change material capable of undergoing a phase change and absorbing heat. Pits are formed on at least a portion of the surface of the heat-absorbing film layer 20 .

[0043] After extensive research, the inventors discovered that the lithium-supplemented negative electrode sheet 10 coil generates a large amount of heat due to the intense lithium insertion reaction. By stacking the lithium-supplemented negative electrode sheet 10 with a heat-absorbing film layer 20 containing a phase change material and then winding it into a coil, the phase change material in the heat-absorbing film layer 20 undergoes a phase change under the heat released by the lithium-supplemented negative electrode sheet 10 coil, absorbing the heat generated by the lithium-supplemented negative electrode sheet 10, thereby reducing the coil temperature and improving the safety performance of the lithium-supplemented negative electrode sheet 10. Simultaneously, the metallic lithium in the lithium-supplemented negative electrode sheet 10 first reacts with oxygen in the air, producing a product that can be used in subsequent lithium ion cycles. However, once the oxygen in the coil is depleted, the metallic lithium in the lithium-supplemented negative electrode sheet 10 undergoes a nitridation reaction with nitrogen. The lithium ions in the nitridation product cannot be used in subsequent cycles, resulting in lithium loss in the lithium-supplemented negative electrode sheet 10. Furthermore, the lithium-supplemented negative electrode sheet 10 turns black due to the nitridation reaction. The present application utilizes a heat-absorbing film layer 20 with surface pits that can store oxygen, allowing oxygen to be replenished after oxygen is depleted between layers of the coil. This solves the problem of lithium loss and blackening caused by the reaction between metallic lithium and nitrogen after oxygen is depleted between layers of the lithium-replenished negative electrode sheet 10. As a result, the lithium-replenished negative electrode sheet 10 in the negative electrode sheet assembly 100 of the present application achieves both excellent lithium replenishment performance and safety.

[0044] After in-depth research, the inventors of this application have found that when the negative electrode sheet assembly 100 of this application satisfies the above conditions and optionally satisfies one or more of the following conditions, the lithium replenishment performance and safety performance of the lithium replenishment negative electrode sheet 10 can be further improved.

[0045] In some embodiments, the lithium-replenished negative electrode sheet 10 of the present application can be obtained by applying lithium powder or lithium sheet to the negative electrode sheet. As an example, the lithium-replenished negative electrode sheet using lithium powder can be obtained by the following steps: S1: mixing lithium powder, a binder, and a solvent into a slurry, and then applying the slurry to the surface of the negative electrode sheet; S2: heating the negative electrode sheet to evaporate and remove the solvent, thereby completing the lithium powder replenishment and obtaining the lithium-replenished negative electrode sheet. In still other embodiments, the lithium-replenished negative electrode sheet using lithium sheet can be obtained by the following steps: stacking a metal lithium sheet and a negative electrode sheet, placing the sheet in a sealed box, heating the sealed box, and adjusting the vacuum level; step S2: standing at a constant pressure to obtain the lithium-replenished negative electrode sheet.

[0046] In a lithium-ion secondary battery, the negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0047] The negative electrode current collector may be made of conventional metal foil, carbon-coated metal foil, porous metal plate, etc. For example, the negative electrode current collector may be made of copper foil.

[0048] There is no limitation on the specific type of the negative electrode active material. Active materials known in the art that can be used for the negative electrode of lithium-ion secondary batteries can be used, and those skilled in the art can select them according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of carbon-based materials, silicon-based materials, and carbon-silicon composite materials. Specifically, the carbon-based material may be selected from one or more of hard carbon, soft carbon, amorphous carbon, and graphite; the silicon-based material may be selected from one or more of Si, SiO, and SiO2; the carbon-silicon composite material may include, but is not limited to, composite materials of carbon-based materials and silicon-based materials. These materials can all be obtained commercially.

[0049] The negative electrode film layer typically also optionally includes a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the adhesive is used to firmly bond the negative electrode active material and the adhesive to the negative electrode current collector. This application does not specifically limit the types of conductive and adhesive agents, and they can be selected based on actual needs.

[0050] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0051] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0052] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, the present application is not limited thereto, and other materials that can be used as thickeners for negative electrode sheets of lithium-ion secondary batteries may also be used in the present application.

[0053] In some embodiments, the phase change material may be in a powder, gel, or film state, and the temperature at which the phase change material undergoes phase change and absorbs heat is 30°C-40°C, for example, 30°C-39°C, 31°C-40°C, 32°C-38°C, 33°C-38°C, 34°C-37°C, 35°C-37°C, or 36°C-37°C. Specifically, upon reaching the phase change temperature, the phase change material undergoes phase change and absorbs heat, thereby maintaining the temperature of the lithium-supplemented negative electrode sheet at no more than 40°C, thereby improving the safety of the lithium-supplemented negative electrode sheet.

[0054] In some embodiments, the enthalpy value of the phase change material is not less than 90 J / g, thereby being able to timely absorb a large amount of heat released by the lithium-supplemented negative electrode sheet coil, reduce the temperature of the lithium-supplemented negative electrode sheet, and improve the safety performance of the lithium-supplemented negative electrode sheet.

[0055] In some embodiments, the phase change material includes at least one of paraffin, crystalline hydrated salt phase change material and molten salt phase change material. As an example, the crystalline hydrated salt phase change material includes but is not limited to at least one of alkali metal or alkaline earth metal halides, sulfates, phosphates, nitrates and carbonates; the molten salt phase change material includes but is not limited to at least one of fluoride salts, chloride salts, nitrates, sulfates and Glauber's salt.

[0056] In some embodiments, based on the total mass of the heat-absorbing film layer, the phase-change material accounts for 50%-80%, for example, 52%-80%, 55%-80%, 55%-78%, 55%-75%, 58%-72%, 60%-70%, 62%-68%, 64%-66%, or 62%-65%. Thus, the aforementioned content of phase-change material in the heat-absorbing film layer can promptly absorb the large amount of heat released by the lithium-replenished negative electrode sheet coil, thereby reducing the temperature of the lithium-replenished negative electrode sheet and improving the safety performance of the lithium-replenished negative electrode sheet.

[0057] In some embodiments, the heat-absorbing film layer has a thickness of 30 μm to 100 μm, for example, 35 μm to 95 μm, 40 μm to 90 μm, 45 μm to 85 μm, 50 μm to 80 μm, 50 μm to 75 μm, or 55 μm to 70 μm. This allows for timely absorption of the large amount of heat released by the lithium-supplemented negative electrode sheet coil, improving the safety performance of the lithium-supplemented negative electrode sheet. In other embodiments, the heat-absorbing film layer has a thickness of 50 μm to 70 μm. This improves the safety performance of the lithium-supplemented negative electrode sheet.

[0058] In some embodiments, the width of the heat-absorbing film layer can be selected based on the width of the lithium-supplemented negative electrode sheet. For example, the width of the heat-absorbing film layer can be the same as the width of the lithium-supplemented negative electrode sheet. That is, after the heat-absorbing film layer and the lithium-supplemented negative electrode sheet are stacked and wound together, the heat-absorbing film layer can fully contact the lithium-supplemented negative electrode sheet, thereby promptly absorbing heat released by the lithium-supplemented negative electrode sheet and improving the safety performance of the lithium-supplemented negative electrode sheet. For example, the width of the heat-absorbing film layer is 50 μm to 200 μm, such as 50 μm to 190 μm, 60 μm to 180 μm, 70 μm to 170 μm, 80 μm to 160 μm, 90 μm to 150 μm, 100 μm to 150 μm, 110 μm to 140 μm, or 120 μm to 130 μm.

[0059] In some embodiments, a cavity is formed in the heat-absorbing film layer, and a phase change material is provided in the cavity. When the lithium-replenished negative electrode sheet roll releases a large amount of heat due to the violent lithium insertion reaction, the phase change material undergoes phase change and absorbs heat, thereby absorbing the heat generated by the lithium-replenished negative electrode sheet. The phase change material undergoes phase change and absorbs heat and becomes liquid. By arranging the phase change material in the cavity in the heat-absorbing film layer, the phase change material can be prevented from undergoing phase change and absorbing heat to become liquid and leaking.

[0060] In some embodiments, referring to FIG2 , the heat-absorbing film layer 20 includes a first substrate 21, a second substrate 22, and a heat-absorbing layer 23. The first substrate 21 and the second substrate 22 are spaced apart and form a closed cavity 201. The heat-absorbing layer 23 is disposed within the cavity 201 and includes the phase-change material. Specifically, the first substrate 21 and the second substrate 22 cooperate to form the closed cavity 201, and the heat-absorbing layer 23 including the phase-change material is disposed within the cavity 201. When the lithium-supplemented negative electrode sheet coil releases a large amount of heat due to the lithium insertion reaction, the phase-change material in the heat-absorbing layer 23 undergoes a phase change and absorbs heat, becoming liquid. By disposing the heat-absorbing layer 23 including the phase-change material within the cavity 201 formed by the first substrate 21 and the second substrate 22, leakage of the phase-change material due to the phase change and absorption of heat can be prevented.

[0061] In some embodiments, the material of the first substrate 21 and / or the second substrate 22 may include, but is not limited to, one or more resins such as polyethylene terephthalate, polyvinyl chloride, polyethylene, and polypropylene.

[0062] In some embodiments, the thickness of the first substrate 21 and / or the second substrate 22 is 7 μm-9 μm, for example, 7.2 μm-9 μm, 7.4 μm-9 μm, 7.6 μm-9 μm, 7.8 μm-9 μm, 8 μm-9 μm, 7.2 μm-9 μm, 7.4 μm-9 μm, 7.6 μm-9 μm, 7.8 μm-9 μm, 8 μm-9 μm. Thus, the closed cavity 201 formed by the first substrate 21 and the second substrate 22 within this thickness range can prevent the phase change material in the closed space 201 from absorbing heat and becoming liquid and leaking.

[0063] In some embodiments, referring to FIG2 , pits 202 are formed on the surface of the first substrate 21 and / or the second substrate 22. For example, pits 202 are formed on the surface of both the first substrate 21 and the second substrate 22, and the area of ​​a single pit 202 is 1 mm. 2 -100mm 2 , for example 5mm 2 -95mm 2 , 10mm 2 -90mm 2 , 15mm 2 -85mm 2 , 20mm 2 -80mm 2 , 25mm 2 -75mm 2 , 30mm 2 -70mm 2 , 35mm2 -65mm 2 , 40mm 2 -60mm 2 , 45mm 2 -55mm 2 or 45mm 2 -50mm 2 Thus, the pit 202 can store more oxygen, so that oxygen can be replenished after the oxygen between the layers of the lithium-supplemented negative electrode sheet is exhausted, solving the problem of lithium loss and blackening caused by the reaction of metal lithium with nitrogen after the oxygen between the layers of the lithium-supplemented negative electrode sheet is exhausted. In other embodiments, the area of ​​a single pit 202 is 20mm 2 -50mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0064] In some embodiments, the depth of a single pit 202 is 1 μm-5 μm, for example, 1 μm-4 μm, 1 μm-3 μm, 2 μm-3 μm, 2 μm-4 μm or 4 μm-5 μm. In this way, more oxygen can be stored, so that oxygen can be replenished after the oxygen between the layers of the lithium-supplemented negative electrode sheet is exhausted, solving the problem of lithium loss and blackening of the lithium-supplemented negative electrode sheet. In some embodiments, the distribution density of the pits 202 on the first substrate 21 and / or the second substrate 22 is 1 ea / mm 2 -500ea / mm 2 , for example 10ea / mm 2 -450ea / mm 2 , 50ea / mm 2 -400ea / mm 2 , 100ea / mm 2 -350ea / mm 2 , 150ea / mm 2 -300ea / mm 2 or 200ea / mm 2 -250ea / mm 2 As a result, the heat-absorbing film layer 20 can store more oxygen, so that oxygen can be replenished after the oxygen between the layers of the lithium-supplemented negative electrode sheet is exhausted. In other embodiments, the distribution density of the pits 202 on the first substrate 21 and / or the second substrate 22 is 20 ea / mm 2 -50ea / mm 2 Thus, the problems of lithium loss and blackening of the lithium-supplemented negative electrode sheet can be solved.

[0065] In some embodiments, the heat absorption layer 23 in the heat absorption film layer 20 has a thickness of 30 μm to 80 μm, such as 30 μm to 75 μm, 30 μm to 70 μm, 35 μm to 65 μm, 40 μm to 60 μm, 45 μm to 55 μm, or 45 μm to 50 μm. In other embodiments, the heat absorption layer 23 has a thickness of 30 μm to 50 μm. This allows the heat released by the lithium-replenished negative electrode sheet to be fully absorbed, reducing the temperature of the lithium-replenished negative electrode sheet and improving the safety performance of the lithium-replenished negative electrode sheet.

[0066] In some embodiments, the heat absorption layer 23 further includes an adhesive. For example, the adhesive may be one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC). In some embodiments, the adhesive accounts for 5%-10% of the total mass of the heat absorption film layer 20, such as 6%-10%, 6%-9%, 7%-9%, or 7%-8%. This ensures that the heat absorption layer 23 is bonded to the cavity 201, improving the stability of the heat absorption film layer 20.

[0067] In some embodiments, the heat absorption layer 23 further includes additives, such as curing agents and plasticizers. For example, the curing agent may include one or more of hydrochloric acid, phosphoric acid, p-toluenesulfonic acid, phenolsulfonic acid, ethylenediamine, m-phenylenediamine, triethylenetetramine, diethylenetriamine, diaminodiphenylmethane, and ethylenetriamine; the plasticizer may include one or more of glycerol, triacetin, carboxymethyl cellulose, and sodium alginate. In some embodiments, the additives account for 15%-40% of the total mass of the heat absorption film layer 20, such as 6%-10%, 6%-9%, 7%-9%, or 7%-8%. In other embodiments, the heat absorption layer 23 may further include a fluxing agent. For example, the fluxing agent may include one or more of Li2CO3, Na2CO3, K2CO3, NH4Cl, NH4F, NaCl, LiCl, KCl, CaF2, BaF2, B2O3, and H3BO3.

[0068] In some embodiments, the heat absorption film layer 20 can be prepared by the following method: a phase change material, an adhesive, and an additive are mixed and heated to a molten state; then, one side of the first substrate 21 and the second substrate 22 are heated to 80° C. to 120° C., and then, an embossing roller is used to press the one side of the first substrate 21 and the second substrate 22 to form pits 202 on one side of the first substrate 21 and the second substrate 22; after cooling, the molten mixed slurry is formed on the surface of one of the first substrate 21 and the second substrate 22 where the pits 202 are not formed; a heat absorption layer 23 is formed on one surface of the first substrate 21 and the second substrate 22; then, the first substrate 21 and the second substrate 22 are covered on the heat absorption layer 23 (the heat absorption layer 23 contacts the surface of the other of the first substrate 21 and the second substrate 22 where the pits 202 are not formed); and the edges and ends of the first substrate 21 and the second substrate 22 are sealed with an adhesive, thereby enclosing the heat absorption layer 23 in the closed cavity 201 formed by the first substrate 21 and the second substrate 22. As an example, the heat absorption layer 23 can be formed by extrusion molding, coating molding, cold pressing molding, etc., and the depth, area and distribution density of the pits 202 on the first substrate 21 and the second substrate 22 can be controlled by using embossing rollers with different protrusion heights, protrusion areas and protrusion distribution densities.

[0069] The second aspect of the present application provides a storage method for lithium-supplemented negative electrode sheets, comprising: stacking a heat-absorbing film layer and a lithium-supplemented negative electrode sheet and then winding them into a shape, wherein pits are formed on at least part of the surface of the heat-absorbing film layer, and a phase change material is provided in the heat-absorbing film layer, and the phase change material can undergo phase change and absorb heat.

[0070] The lithium-replenishing negative electrode sheet coil generates a large amount of heat due to the intense lithium insertion reaction. By stacking the heat-absorbing film layer with the lithium-replenishing negative electrode sheet and then winding it into shape, the phase change material in the heat-absorbing film layer undergoes phase change and absorbs heat under the heat release of the lithium-replenishing negative electrode sheet coil, thereby absorbing the heat generated by the lithium-replenishing negative electrode sheet and improving the safety performance of the lithium-replenishing negative electrode sheet. At the same time, the metallic lithium in the lithium-replenishing negative electrode sheet will first react with oxygen in the air, and the generated product can be used for subsequent lithium ion cycles. When the oxygen in the coil is exhausted, the metallic lithium on the lithium-replenishing negative electrode sheet will undergo a nitridation reaction with nitrogen. The lithium ions in the nitrided product cannot be used in subsequent cycles, resulting in lithium loss on the lithium-replenishing negative electrode sheet. The present application uses a heat-absorbing film layer with pits formed on the surface. The pits can store oxygen, that is, oxygen can be replenished after the oxygen between the coil layers is exhausted, thereby solving the problem of lithium loss and blackening caused by the reaction of metallic lithium with nitrogen after the oxygen between the layers of the lithium-replenishing negative electrode sheet is exhausted. Therefore, the storage method of the present application can achieve high lithium replenishment performance and safety performance of the lithium-replenishing negative electrode sheet.

[0071] In some embodiments, the heat-absorbing film layer and the lithium-replenished negative electrode sheet are wound synchronously with the same winding tension and speed. This prevents the negative electrode sheet from becoming darker and hotter after lithium replenishment, ensuring full contact between the heat-absorbing film layer and the lithium-replenished negative electrode sheet, thereby improving the safety and lithium replenishment performance of the lithium-replenished negative electrode sheet. Furthermore, the heat-absorbing film layer of this application is reusable and can be recycled after the lithium-replenished negative electrode sheet is wound into a battery cell, with a maximum reuse frequency of 50 or more.

[0072] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0073] Example 1

[0074] The method for preparing a lithium-supplemented negative electrode sheet includes:

[0075] (1) Adding the negative electrode active material hard carbon, the conductive agent carbon nanotube material and the adhesive sodium carboxymethyl cellulose to water and stirring to form a uniform negative electrode slurry (the mass ratio of the negative electrode active material hard carbon to the conductive agent carbon nanotube and the adhesive sodium carboxymethyl cellulose is 94.4:4:1.6), coating the negative electrode slurry on the surface of the negative electrode current collector copper foil, and then transferring it to a vacuum drying oven for complete drying, and finally punching it to obtain a negative electrode sheet;

[0076] (2) The metal lithium sheet and the negative electrode sheet are stacked and placed in a sealed box, the sealed box is heated, and the vacuum degree is adjusted; then the box is allowed to stand at a constant pressure to obtain a lithium-supplemented negative electrode sheet.

[0077] Methods for storing lithium-supplemented negative electrode sheets include:

[0078] (a) mixing phase change material paraffin, polyvinylidene fluoride, and glycerol to prepare mixed resin particles;

[0079] (b) The first PET substrate (7 μm thick) and the second PET substrate (7 μm thick) were heated to 100°C, and then the convex height was 5 μm and the single convex area was 50 mm. 2 And the distribution density is 100ea / mm 2 The embossing roller presses one side of the first PET substrate and the second PET substrate to form pits on the surfaces of the first PET substrate and the second PET substrate, wherein the area of ​​a single pit on the first PET substrate and the second PET substrate is 50 mm 2, the pit depth is 5μm, and the distribution density of the pit is 100ea / mm 2 The mixed resin particles obtained in step (a) are heated to a molten state, and the molten mixed slurry is applied to the side of the first PET substrate where no pits are formed by roller pressing, and then solidified to form a heat absorption layer (50 μm) on the first PET substrate;

[0080] (c) Covering the heat-absorbing layer with a second PET substrate (the surface of the second PET substrate without the recesses is in contact with the heat-absorbing layer), sealing the edges and ends of the first and second PET substrates with polyvinylidene fluoride adhesive, thereby enclosing the heat-absorbing layer in the closed cavity formed by the first and second PET substrates to obtain a heat-absorbing film layer (64 μm thick, with a phase change material content of 50 wt%), which is then rolled.

[0081] (d) The lithium-supplemented negative electrode sheet and the heat-absorbing film layer are synchronously rolled up to obtain a negative electrode sheet assembly.

[0082] The preparation method of the lithium-replenishing negative electrode sheet of Examples 2-38 is the same as that of Example 1. The method of storing the lithium-replenishing negative electrode sheet refers to Example 1, and the relevant parameters of the heat absorption film layer are shown in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] Note: The proportion of phase change material is the total mass of phase change material / total mass of heat absorption film layer.

[0087] Comparative Example

[0088] The method for preparing the lithium-supplemented negative electrode sheet is the same as that in Example 1, and the lithium-supplemented negative electrode sheet is directly rolled up.

[0089] The negative electrode sheet assembly coils obtained in Examples 1-38 and the lithium-supplemented negative electrode sheet coils of the comparative example were stored at an ambient temperature of 25°C for 24 hours, and their temperatures were measured at 0 min, 20 min, 40 min, 1 h, 5 h, and 10 h, respectively. After storage for 24 hours, the coils were disassembled and the surfaces of the lithium-supplemented negative electrode sheets were observed. The temperatures during storage and the surface colors after storage for 24 hours are shown in Table 2.

[0090] Table 2

[0091]

[0092]

[0093] Note: If the surface of the lithium-supplemented negative electrode does not turn black, it means that no nitriding reaction has occurred (metallic lithium is white).

[0094] Conclusion: The data in Table 2 show that the heat generated by the lithium intercalation reaction in the lithium-replenished negative electrode sheet coil primarily occurs within 0-1 hour after lithium refilling, and the temperature gradually decreases after 1 hour due to the completion of the reaction. However, the lithium-replenished negative electrode sheets of Examples 1-38, due to being stacked with the heat-absorbing film layer before winding, maintained a temperature never exceeding 40°C within 0-1 hour, while the temperature of the lithium-replenished negative electrode sheet of the comparative example exceeded 40°C. This indicates that stacking the lithium-replenished negative electrode sheet with the heat-absorbing film layer containing phase change material before winding can effectively reduce the temperature of the lithium-replenished negative electrode sheet and improve its storage safety. Furthermore, the lithium-replenished negative electrode sheets of Examples 1-38 showed no blackening after 24 hours of storage, while the lithium-replenished negative electrode sheet of the comparative example had blackened stripes and circular areas on its surface, indicating that the heat-absorbing film layer with pits on the surface can solve the problem of nitridation blackening during storage of the lithium-replenished negative electrode sheet coil.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode sheet assembly, wherein: include: Lithium-supplemented negative electrode sheet; The heat-absorbing film layer is wound after being stacked with the lithium-supplementing negative electrode sheet. The heat-absorbing film layer contains a phase change material that can undergo phase change and absorb heat. Pits are formed on at least part of the surface of the heat-absorbing film layer.

2. The negative electrode sheet assembly according to claim 1, wherein: A cavity is formed in the heat absorption film layer, and a phase change material is arranged in the cavity.

3. The negative electrode sheet assembly according to claim 1 or 2, wherein: The temperature at which the phase change material undergoes phase change and absorbs heat is 30°C-40°C.

4. The negative electrode sheet assembly according to any one of claims 1 to 3, wherein: The enthalpy value of the phase change material is not less than 90 J / g.

5. The negative electrode sheet assembly according to any one of claims 1 to 4, wherein: The phase change material includes at least one of paraffin, crystalline hydrated salt phase change material and molten salt phase change material.

6. The negative electrode sheet assembly according to any one of claims 1 to 5, wherein: Based on the total mass of the heat absorption film layer, the phase change material accounts for 50%-80%.

7. The negative electrode sheet assembly according to any one of claims 1 to 6, wherein: The thickness of the heat absorption film layer is 30 μm-100 μm, and can be optionally 50 μm-70 μm.

8. The negative electrode sheet assembly according to any one of claims 1 to 7, wherein: The heat absorbing film layer comprises: a first substrate; a second substrate, wherein the first substrate and the second substrate are spaced apart and form a closed cavity, and the pit is formed on the surface of the first substrate and / or the second substrate; A heat absorption layer is provided in the cavity, and the heat absorption layer comprises the phase change material.

9. The negative electrode sheet assembly according to any one of claims 1 to 8, wherein: The thickness of the first substrate and / or the second substrate is 7 μm-9 μm.

10. The negative electrode sheet assembly according to any one of claims 1 to 9, wherein: The area of ​​a single pit is 1 mm 2 -100mm 2 , 20mm optional 2 -50mm 2 .

11. The negative electrode sheet assembly according to any one of claims 1 to 10, wherein: The depth of a single pit is 1 μm-5 μm.

12. The negative electrode sheet assembly according to any one of claims 1 to 11, wherein: The distribution density of the pits on the first substrate and / or the second substrate is 1 ea / mm 2 -500ea / mm 2 , optional 20ea / mm 2 -50ea / mm 2 .

13. The negative electrode sheet assembly according to any one of claims 1 to 12, wherein: The thickness of the heat absorption layer is 30 μm-80 μm, and can be optionally 30 μm-50 μm.

14. The negative electrode sheet assembly according to any one of claims 1 to 13, wherein: The heat absorption layer further includes an adhesive.

15. The negative electrode sheet assembly according to any one of claims 1 to 14, wherein: Based on the total mass of the heat absorption film layer, the adhesive accounts for 5%-10%.

16. The negative electrode sheet assembly according to any one of claims 1 to 15, wherein: The heat absorption layer further comprises an auxiliary agent.

17. The negative electrode sheet assembly according to any one of claims 1 to 16, wherein: Based on the total mass of the heat-absorbing film layer, the auxiliary agent accounts for 15%-40%.

18. A storage method for lithium-supplemented negative electrode sheets, wherein: include: The heat-absorbing film layer and the lithium-supplementing negative electrode sheet are stacked and wound into a shape, wherein pits are formed on at least a portion of the surface of the heat-absorbing film layer, and a phase change material is provided in the heat-absorbing film layer, and the phase change material can undergo phase change and absorb heat.

Images