A method for inhibiting lithium precipitation in a lithium-ion battery

Abstract

The present application relates to a method for inhibiting lithium precipitation in a lithium-ion battery, comprising the following steps: a) heating the lithium-ion battery to a temperature of 40-80°C; and b) aging the lithium-ion battery at the temperature of step a) for 10-100 hours. The method disclosed in the present application can significantly reduce the precipitation and / or growth of lithium dendrites in the lithium-ion battery, thereby improving the discharge capacity of the lithium-ion battery and enhancing the safety of the lithium-ion battery.

Description

Technical Field

[0001] This application relates to a method for suppressing lithium plating in lithium-ion batteries, comprising heating the lithium-ion battery to a temperature of 40°C to 80°C, and subsequently aging the lithium-ion battery at that temperature for 10 to 100 hours. Background Technology

[0002] Lithium-ion batteries have become the most popular energy storage system due to their low cost, long lifespan, and high safety, and are now widely used in pure electric vehicles, hybrid electric vehicles, and smart grids. However, lithium-ion batteries pose a risk of lithium deposition during charging. Especially during high-current fast charging or low-temperature charging, the rate at which lithium ions insert into the negative electrode is slower than the rate at which they conduct to the negative electrode active material, leading to the deposition of metallic lithium on the surface of the negative electrode. This deposition typically forms dendritic lithium crystals, or lithium dendrites. Lithium dendrites readily react with the electrolyte in various ways, generating large amounts of gas and heat. Furthermore, lithium dendrites can potentially puncture the separator, causing a short circuit or even combustion and explosion in the lithium battery. Therefore, there is a widespread need to suppress lithium dendrite growth and improve battery safety.

[0003] Existing technologies primarily aim to improve the performance of the separator through electrical or mechanical modification, or to minimize lithium deposition by adding additives to the electrolyte. However, lithium dendrite deposition is almost unavoidable during the lifecycle of commercial lithium-ion batteries. Therefore, there is a need in the art for a method that can suppress lithium dendrite deposition and / or growth throughout the entire lifecycle of a lithium-ion battery. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for suppressing lithium plating in lithium-ion batteries, which can effectively suppress the precipitation and / or growth of lithium dendrites throughout the entire life cycle of lithium-ion batteries, thereby solving the technical problem that the unavoidable growth of lithium dendrites in the prior art leads to a decrease in the capacity of lithium-ion batteries and an increase in safety risks.

[0005] To achieve the above objectives, the first aspect of this application provides a method for suppressing lithium plating in lithium-ion batteries, comprising the following steps:

[0006] a) Heating the lithium-ion battery to a temperature of 40°C to 80°C; and

[0007] b) Age the lithium-ion battery at the temperature in step a) for 10 to 100 hours.

[0008] By heating a lithium-ion battery to a specific temperature higher than room temperature and aging it at that temperature for a period of time, some lithium dendrites are thermally "melted" and the surface of the formed lithium dendrites is passivated, effectively reducing the reactivity of lithium dendrites and inhibiting their continued growth.

[0009] The reactions that may occur during this process include, but are not limited to, the following reaction equations:

[0010] C3H4O3(EC)+2Li→Li2CO3+C2H4;

[0011] C4H8O3(EMC)+2Li→Li2CO3+C3H8.

[0012] In any embodiment, the method includes, in step a), heating the lithium-ion battery to a temperature of 45°C to 70°C, optionally to a temperature of 55°C to 65°C. By selecting a specific temperature range for aging, a better passivation effect can be achieved, thereby further improving the technical effect of suppressing lithium plating.

[0013] In any embodiment, the method includes, in step b), aging the lithium-ion battery at the temperature of step a) for 40 to 70 hours. By specifically selecting the aging time, the effect of suppressing lithium dendrite growth can be further optimized. In some embodiments, the aging in step b) is completed by allowing the battery to stand at the aforementioned temperature.

[0014] In any embodiment, in step b), the aging temperature remains constant over time, or varies in a gradient over time. An adjustable temperature gradient allows for more effective regulation of the inhibition of lithium plating.

[0015] In any embodiment, the method further includes the following step: determining the amount of lithium plating on the negative electrode of the lithium-ion battery by disassembling and reassembling the lithium-ion battery and measuring its discharge capacity before heating. In any embodiment, the method further includes the following step: adjusting the heating temperature and aging time according to the amount of lithium plating on the negative electrode of the lithium-ion battery. By setting the aging program according to the specific amount of lithium plating in the lithium battery, the efficiency of suppressing lithium plating can be improved, energy consumption reduced, and the risk of thermal runaway decreased.

[0016] In any embodiment, the lithium-ion battery is a battery that has been returned to the factory for maintenance after use. In some embodiments, the lithium plating is the precipitation and growth of lithium dendrites. After the aging treatment, the surface of the lithium dendrites is passivated.

[0017] In any embodiment, the method further includes charging the lithium-ion battery and allowing it to stand before heating until its internal resistance value remains stable.

[0018] In any embodiment, the lithium-ion battery is not charged or discharged during steps a) and b) of the method. In any embodiment, steps a) and b) are performed at atmospheric pressure. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0020] Figure 1 This is a side view of a specially designed directional lithium-ion battery used for detecting short-circuit resistance in an embodiment of this application, wherein the internal resistance meter connecting the negative electrode and the copper foil electrode is not shown.

[0021] Figure 2 This is a graph showing the change in resistance value measured by an internal resistance meter in an embodiment of this application as the temperature increases from 25°C to 60°C and is left to stand for different periods of time.

[0022] Explanation of reference numerals in the attached figures

[0023] 1 Copper foil electrode

[0024] 2 negative electrode plates

[0025] 3 Positive electrode sheet

[0026] 4. Separating membrane

[0027] 5 Insulation Part

[0028] 6. Insulating adhesive Detailed Implementation

[0029] For the sake of brevity, this application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0030] After multiple charge-discharge cycles during use, lithium-ion batteries inevitably experience lithium plating. This is primarily because the rate at which lithium ions embed into the negative electrode is slower than the rate at which they migrate to the active material of the negative electrode. This results in the remaining lithium ions, unable to embed into the negative electrode, depositing as metallic lithium on the surface of the negative electrode. This metallic lithium typically manifests as dendritic crystals, known as lithium dendrites. Lithium dendrites have a high specific surface area, making them prone to various side reactions with the electrolyte, increasing gas production and reducing battery capacity. When lithium dendrites grow excessively, they can puncture the separator, leading to short circuits or even combustion and explosion. Existing technologies have developed methods to suppress lithium dendrite growth, mainly including modifying the electrode sheets and separator, and adding specific additives to the electrolyte. However, these methods are costly or complex to operate and cannot specifically suppress lithium plating throughout the entire lifespan of the lithium-ion battery.

[0031] Through research, the inventors have discovered that by aging lithium-ion batteries at a temperature within a specific range above room temperature for a specific period of time, the precipitation and / or growth of lithium dendrites in lithium-ion batteries can be effectively suppressed or even reduced.

[0032] Specifically, the first aspect of this application provides a method for suppressing lithium plating in lithium-ion batteries, comprising the following steps:

[0033] a) Heating the lithium-ion battery to a temperature of 40°C to 80°C; and

[0034] b) Age the lithium-ion battery at the temperature in step a) for 10 to 100 hours.

[0035] Lithium-ion batteries can be in any state, especially those returned for maintenance after use. They can be heated to temperatures between 40°C and 80°C using any suitable method, such as an oven or constant-temperature oven. Below 40°C, the effect of inhibiting lithium dendrite growth is not significant; above 80°C, a chain reaction of exothermic heat can easily occur inside the battery, causing thermal runaway. Excessively high heating temperatures must be avoided; therefore, it is advantageous to control the heating rate at 10°C per hour or less, optionally 5°C per hour or less. After the lithium-ion battery is heated to the predetermined temperature or range, it can be maintained at that temperature or range using a constant-temperature device and aged for 10 to 100 hours. The aging time can be adjusted specifically according to the actual condition of the lithium-ion battery. When the aging time is less than 10 hours, the effect of inhibiting lithium dendrite growth is insufficient; when the aging time is greater than 100 hours, the improvement in inhibiting lithium dendrite growth is significantly reduced, therefore, excessively long aging times are uneconomical.

[0036] Unbound by any particular theory, the inventors believe that during the high-temperature aging of lithium-ion batteries using the aforementioned method, the inevitably precipitated lithium dendrites react more readily with the electrolyte at elevated temperatures, causing some of the formed lithium dendrites to thermally "melt." Simultaneously, as the lithium dendrites undergo complex and varied reactions with the electrolyte, a passivation layer gradually forms on the surface of the precipitated lithium dendrites. The low specific surface area of ​​the passivation layer, in turn, reduces the reaction rate between the lithium dendrites and the electrolyte, preventing a chain reaction of exothermic reactions within the battery and effectively preventing thermal runaway. As the aging process continues, the passivation layer gradually thickens, making it difficult for lithium ions to deposit as metallic lithium on the surface of the passivation layer, thereby inhibiting further growth of lithium dendrites.

[0037] In some implementations, the method includes heating the lithium-ion battery to a temperature of 45°C to 70°C, optionally to 55°C to 65°C, in step a). It has been found that optimal suppression of lithium dendrite growth can be achieved by further selecting a specific heating temperature range. A higher suppression effect can be achieved in the temperature range of 55°C to 65°C compared to lower temperatures. The risk of thermal runaway can be further reduced in the temperature range of 55°C to 65°C compared to higher temperatures, such as above 70°C. The technical effect of suppressing lithium plating can be further improved by selecting a specific temperature range for aging. The technical effect of suppressing lithium plating can be determined, for example, by measuring the short-circuit resistance of a specially designed oriented lithium plating cell device, the details of which will be described in detail in the embodiments below.

[0038] In some embodiments, the method includes aging the lithium-ion battery at the temperature of step a) for 40 to 70 hours in step b). As mentioned above, the choice of aging time has a substantial impact on the technical effectiveness of suppressing lithium plating. When the aging time is less than 40 hours, the technical effect of the method in suppressing lithium plating is not fully realized; when the aging time is greater than 70 hours, the subsequent improvement in suppressing lithium plating gradually saturates. Although the effect of suppressing lithium plating continues, considering the costs of high-temperature energy consumption, time, and processing throughput, longer aging times are generally uneconomical. By specifically selecting the aging time, the effect of suppressing lithium dendrite growth can be further optimized. In some embodiments, the aging in step b) is completed by standing at the above-mentioned temperature. Obviously, the aging process can also be carried out by other means besides standing, such as rotating it at a constant speed in a heating device to ensure uniform heating.

[0039] In some implementations, in step b), the aging temperature remains constant over time or varies in a gradient over time. An adjustable temperature gradient allows for more effective regulation of the lithium plating suppression effect. For example, in a practical heating process, the lithium-ion battery to be treated can be uniformly heated to 60°C at a heating rate of 5°C per hour and aged at that temperature for 60 hours. Alternatively, the lithium-ion battery to be treated can be rapidly heated to 50°C at a heating rate of 10°C per hour and aged for 20 hours, then the lithium-ion battery can be heated from 50°C to 60°C at a heating rate of 5°C per hour and aged at this temperature for 20 hours, and finally the lithium-ion battery can be heated from 60°C to 70°C at a heating rate of 5°C per hour and aged at this temperature for 20 hours. This gradient heating method provides more flexible processing options to accommodate lithium-ion batteries in different lithium plating states.

[0040] In some embodiments, the method further includes the following steps: determining the amount of lithium plating on the negative electrode of the lithium-ion battery by disassembling, reassembling, and measuring the discharge capacity before heating. In some embodiments, the method further includes the following steps: adjusting the heating temperature and aging time based on the amount of lithium plating on the negative electrode of the lithium-ion battery. By setting the aging program according to the specific amount of lithium plating in the lithium battery, the efficiency of suppressing lithium plating can be improved, energy consumption reduced, and the risk of thermal runaway decreased. In some embodiments, the lithium-ion battery is a battery that has been returned to the factory for maintenance after use. The lithium-ion battery in this application has different lithium plating states at different stages. The method of this invention can produce a substantial technical effect of suppressing lithium dendrite growth for all lithium-ion battery states throughout its lifespan. However, for lithium-ion batteries with different lithium plating states, the actual amount of lithium plating can be analyzed and determined before high-temperature aging treatment, and then the aging temperature and time can be set specifically to more accurately control the growth of lithium dendrites in the lithium-ion battery. The analysis and judgment of lithium plating amount in lithium-ion batteries can be carried out as follows: The battery is left to stand at room temperature, then subjected to charge-discharge cycles, and the final discharge capacity C1 is recorded. The battery is then left to stand at a low temperature and subjected to high-rate discharge. Afterward, the battery is left to stand at room temperature, disassembled, and the positive electrode, electrolyte, and separator are removed. The positive electrode, electrolyte, separator, and lithium-filled negative electrode are then assembled into a new battery. The new battery is left to stand at room temperature and then discharged, and the discharge capacity C2 is recorded. The ratio of the two discharge capacities, C2 / C1, is calculated as the lithium plating amount of the lithium-ion battery. By setting different high-temperature aging parameters for lithium-ion batteries with different lithium plating amounts, such as heating temperature, aging time, gradient heating, etc., a more accurate suppression of lithium plating can be achieved.

[0041] In some implementations, lithium plating refers to the deposition and growth of lithium dendrites. After aging treatment, the surface of the lithium dendrites is passivated. The passivated surface of the lithium dendrites has a passivation layer that hinders further reaction between the lithium dendrites and the electrolyte, and also makes it difficult for subsequent lithium ions to continuously deposit on the surface of the already formed lithium dendrites, thereby inhibiting the growth of lithium dendrites.

[0042] In some embodiments, the method of the present invention further includes charging the lithium-ion battery and allowing it to stand before heating until its internal resistance value remains stable. This step determines the starting point of the heating aging process, and the resistance value at this point is also a benchmark for evaluating the effectiveness of the technique in suppressing lithium dendrite growth.

[0043] In some embodiments, the lithium-ion battery is not charged or discharged in steps a) and b). In some embodiments, steps a) and b) are performed at atmospheric pressure. The method of the present invention differs from the formation treatment performed on lithium-ion batteries after assembly, therefore eliminating the need for charging and discharging operations. In particular, the method of the present invention does not require high pressure or vacuum conditions, nor does it require protection under an inert atmosphere such as nitrogen. Because the method of the present invention does not require special operating conditions, it offers advantages such as ease of operation and low cost.

[0044] The composition and structure of lithium-ion batteries will be described in detail below.

[0045] Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0046] Electrolyte

[0047] The detection device according to this application includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte includes an electrolyte salt and a solvent.

[0048] In this application, the electrolyte salt can be a commonly used electrolyte salt in lithium-ion batteries, such as a lithium salt, including lithium salts that can be used as high thermal stability salts, lithium salts that can be used as low impedance additives, or lithium salts that can inhibit aluminum foil corrosion. As an example, the electrolyte salt can be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), LiSO3F (lithium fluorosulfonate), NDFOP (difluorodioxalate), Li2F(SO2N)2SO2F, KFSI, CsFSI, Ba(FSI)2, and LiFSO2NSO2CH2CH2CF3.

[0049] There are no particular restrictions on the type of solvent, which can be selected according to actual needs. In some embodiments, the solvent is a non-aqueous solvent. Optionally, the solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylic acid esters. In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), tetrahydrofuran, sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0050] In some embodiments, the electrolyte may optionally include other additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance, such as additives improving battery overcharge performance, additives improving battery high-temperature performance, and additives improving battery low-temperature performance. As an example, the additives are selected from at least one of the following: cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate ester compounds, and carboxylic acid ester compounds.

[0051] [Positive electrode plate]

[0052] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a conductive agent.

[0053] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0054] The positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (e.g., aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0055] The positive electrode active material layer disposed on the surface of the positive electrode current collector includes a positive electrode active material. The positive electrode active material used in this application can be any conventional positive electrode active material used in secondary batteries. In some embodiments, the positive electrode active material may comprise one or more selected from lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides include, but are not limited to, one or more selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of olivine-structured lithium-containing phosphates include, but are not limited to, one or more selected from lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These materials are all commercially available. Carbon may be coated on the surface of the positive electrode active material.

[0056] The positive electrode active material layer may optionally include a conductive agent. However, there is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] The positive electrode active material layer may optionally include a binder. As an example, the binder may be one or more of styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0058] In this application, the positive electrode sheet can be prepared according to methods known in the art. As an example, a carbon-coated positive electrode active material, a conductive agent, and a binder can be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, a positive electrode sheet is obtained.

[0059] [Negative electrode plate]

[0060] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer including a negative electrode active material.

[0061] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0062] In the electrode assembly of this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (e.g., copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0063] In the electrode assembly of this application, the negative electrode material layer typically comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0064] The specific type of negative electrode active material is not limited; any active material known in the art that can be used as the negative electrode of a lithium-ion secondary battery can be used. Those skilled in the art can select according to actual needs. As an example, the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon oxides, silicon-carbon composites, and lithium titanate.

[0065] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] As an example, the adhesive may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0067] Other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0068] [Isolation membrane]

[0069] The electrode assembly using an electrolyte also includes a separator membrane. The separator membrane is disposed between the positive and negative electrode plates, serving as a separator. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected. In some embodiments, the material of the separator membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0070] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0071] In some embodiments, the electrode assembly may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and the electrolyte.

[0072] In some embodiments, the outer packaging of the electrode assembly can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the electrode assembly can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0073] This application does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.

[0074] Figure 1 This is a side view of a specially designed directional lithium-ion battery used for detecting short-circuit resistance according to an embodiment of this application, wherein the internal resistance meter connecting the negative electrode and the copper foil electrode is not shown. It includes a negative electrode 2, a positive electrode 3, a copper foil electrode 1, a separator 4, an insulating portion 5, and an insulating adhesive 6. Electrolyte is filled between the negative and positive electrodes, unless otherwise specified.

[0075] Example

[0076] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. Unless otherwise specified, all experimental steps are performed under normal pressure.

[0077] Fabrication of a specially designed lithium-ion battery with directional lithium plating:

[0078] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95.5:2.5:2. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode. Artificial graphite (anode material), conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were thoroughly mixed in a deionized water solvent system at a mass ratio of 96.5:1.5:1:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode. A conventional 1 mol / L LiPF6 (ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + dimethyl carbonate (DMC) = 1:1:1 (V / V / V)) was used as the electrolyte. The thickness of the copper foil electrode was approximately the same as that of the negative electrode. A polypropylene film was used as the separator.

[0079] The manufacturing process of lithium-ion batteries is carried out entirely in a drying room. The non-end faces of the copper foil electrode are insulated with a 20μm thick PET insulating adhesive. The copper foil electrode is clamped on both sides using a 200μm thick Mylar film (i.e., PET polyester film) as insulation, fixing it in a position horizontally opposite the negative electrode. The distance between the end face of the copper foil electrode and the end face of the negative electrode is 1.2mm. The negative electrode is 0.8mm longer than the positive electrode on one side of the copper foil electrode. The negative electrode, separator, positive electrode, and copper foil electrode are then assembled... Figure 1 The electrodes are arranged in the order shown and then wound to obtain the electrode assembly. The electrode assembly is placed in the battery casing, dried, and then injected with electrolyte. The copper foil electrode and the tab of the negative electrode are connected to the battery using a HT3562 internal resistance meter installed in situ.

[0080] Detection Mechanism: During the charging process of the specially designed directional lithium-ion battery, the negative electrode is slightly longer than the positive electrode on one side, causing lithium ions to concentrate on the end face of the negative electrode and precipitate as lithium dendrites during charging. As charging continues, the lithium dendrites grow and extend from the side of the negative electrode towards the end face of the copper foil electrode, which is positioned roughly horizontally and opposite to it. An internal resistance meter is connected to the copper foil electrode and the negative electrode, continuously collecting the resistance value between them. As the lithium dendrites continue to grow and extend, the resistance value collected by the internal resistance meter will theoretically decrease as the tip of the dendrite approaches the end face of the copper foil electrode. When the lithium dendrite finally reaches and overlaps the end face of the copper foil electrode, a short circuit is formed between them. At this point, the resistance value collected by the internal resistance meter will show a sharp decrease, theoretically even approaching zero. Of course, during actual charging, lithium dendrites undergo various side reactions with the electrolyte, resulting in a passivation layer of a certain thickness on their surface. This passivation layer causes the resistance value between the copper foil electrode and the negative electrode, as measured by an internal resistance meter, to be in a relatively low resistance range above zero. When left to stand at room temperature for an extended period under these conditions, the resistance value will eventually stabilize at a lower value.

[0081] By measuring the resistance between the copper foil electrode and the negative electrode using an internal resistance meter, the deposition of lithium ions on the end face of the negative electrode facing the copper foil electrode can be detected in real time, which is the process of lithium dendrite growth. The more the lithium dendrites grow, the closer their tips get to the end face of the copper foil electrode opposite the negative electrode, and the resistance value between the copper foil electrode and the negative electrode, as measured by the internal resistance meter, decreases. By plotting the resistance value between the copper foil electrode and the negative electrode against the corresponding time, a functional relationship between the resistance value and time can be obtained, reflecting the state of lithium dendrite deposition, growth, and passivation over time.

[0082] However, it should be emphasized that the specially designed lithium-ion battery with directional lithium plating is only intended to visually demonstrate the effect of temperature and time on suppressing lithium plating during the aging process, and is presented in the form of short-circuit internal resistance values ​​for qualitative and quantitative analysis. It is understood that the method of this invention is applicable to other conventional lithium-ion batteries, which also have similar effects in suppressing lithium plating.

[0083] Example 1

[0084] The specially prepared directional lithium-ion battery, as described above, was formed using a 0.1C charging rate. After formation, it was charged at a constant current rate of 0.33C to 4.25V. Once the cutoff voltage was reached, it was then charged at a constant voltage, with the apparatus at room temperature (25℃). After the internal resistance of the lithium-ion battery stabilized, it was transferred to an oven at 45℃ and allowed to stand. The change in resistance between the copper foil electrode and the negative electrode was observed using an internal resistance meter.

[0085] Examples 2-10 and the comparative examples are also specific embodiments by changing the standing temperature and time. Except for the parameters in Table 1, the other methods and detection procedures are the same as in Example 1. The specific experimental conditions are shown in Table 1.

[0086] Table 1: Method parameters of Examples 1-10 and Comparative Examples 1-3

[0087] Example 1 45℃ 12h Example 2 45℃ 24h Example 3 45℃ 36h Example 4 45℃ 48h Example 5 60℃ 12h Example 6 60℃ 24h Example 7 60℃ 36h Example 8 60℃ 48h Example 9 70℃ 24h Example 10 70℃ 48h Comparative Example 1 25℃ 0h Comparative Example 2 25℃ 0h Comparative Example 3 25℃ 0h

[0088] Short-circuit internal resistance tests were performed on the lithium-ion batteries of Examples 1-10 and Comparative Examples 1-3, and the test results are shown in Table 2. Comparative Example 1 used the same lithium-ion battery 1 in the testing process as Examples 1-4; Comparative Example 2 used the same lithium-ion battery 2 in the testing process as Examples 5-8; and Comparative Example 3 used the same lithium-ion battery 3 in the testing process as Examples 9-10. The components of lithium-ion batteries 1-3 are identical; the differences in stable internal resistance detected at 25°C are due only to deviations in the actual operation process (e.g., differences in lithium plating conditions between different batteries, such as different length differences between the positive and negative electrodes or different distances between the negative electrode end and the copper foil electrode, resulting in different initial resting times required to reach stable resistance). For example, for lithium-ion battery 1, after undergoing the above charging process, its stable internal resistance value was measured at 25°C, which is the short-circuit internal resistance of Comparative Example 1. Device 1 was then heated to 45°C and left to stand at this temperature for 12h, 24h, 36h, and 48h, respectively, after which its internal resistance was measured. These values ​​represent the short-circuit internal resistances of Examples 1, 2, 3, and 4, respectively. The internal resistance measurements were performed in real time; that is, the temperature at which the measurements were taken was the same as the temperature at which the device was left to stand. The same principle applies to other examples and lithium-ion battery types. Table 2 below summarizes the short-circuit internal resistance test results for Examples 1-10 and Comparative Examples 1-3.

[0089] Table 2: Short-circuit internal resistance test results of Examples 1-10 and Comparative Examples 1-3

[0090] Example 1 186 5.6 Example 2 550 16.7 Example 3 584 17.7 Example 4 606 18.4 Example 5 400 16.7 Example 6 650 27.1 Example 7 720 30 Example 8 780 32.5 Example 9 510 51 Example 10 740 74 Comparative Example 1 33 / Comparative Example 2 24 / Comparative Example 3 10 /

[0091] As shown in Table 2, the high-temperature static aging method of the present invention has a significant inhibitory effect on lithium dendrite growth in lithium-ion batteries. For example, Comparative Example 2 and Examples 5-8 used the same lithium-ion battery. The stable internal resistance measured at 25°C and t (time) of 0h is the resistance value of Comparative Example 2, which is 24Ω. When the temperature is increased from 25°C to 60°C, the internal resistance measured after 12h is 400Ω, which is 16.7 times higher than the original value before high-temperature aging; the internal resistance measured after 24h at this temperature is 650Ω, which is 27.1 times higher than the original value before high-temperature aging; the internal resistance measured after 36h at this temperature is 720Ω, which is 30 times higher than the original value before high-temperature aging; and the internal resistance measured after 48h at this temperature is 780Ω, which is 32.5 times higher than the original value before high-temperature aging. Specific changes can also be found in this application. Figure 2The curves shown demonstrate that both increased temperature and extended aging time significantly increased the short-circuit resistance, indicating that lithium dendrite growth was significantly suppressed and the surface was largely passivated. Furthermore, it can be observed that the rate of increase in resistance gradually decreases with further increases in aging time, suggesting that the improvement achieved by significantly extending the aging time will also gradually diminish.

[0092] For other embodiments, similar effects to aging at 60°C were observed at 45°C and 70°C. Of course, the higher the temperature, the greater the increase in internal resistance over the same time period, meaning a more significant effect in suppressing lithium dendrite growth. However, higher temperatures also mean a higher risk of thermal runaway within the battery at high temperatures.

[0093] Although this application has been described with reference to embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for suppressing lithium plating in a lithium-ion battery, wherein the electrode assembly of the lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a copper foil electrode, wherein the end face of the copper foil electrode is horizontally opposite to the end face of the negative electrode; the positive electrode is longer than the negative electrode on the side closest to the copper foil electrode; the non-end face side of the copper foil electrode is covered with insulating adhesive; both sides of the copper foil electrode are clamped and fixed by Mylar film; the end face of the copper foil electrode is spaced apart from the end face of the negative electrode; during charging, lithium dendrites grow and extend from the side of the negative electrode toward the end face of the copper foil electrode; the method includes: Charge the lithium-ion battery to the cutoff voltage and let it rest until its internal resistance remains stable before proceeding to the following steps: a) Heating the lithium-ion battery to a temperature of 55°C to 65°C; and b) Age the lithium-ion battery at the temperature in step a) for 40 to 70 hours; In steps a) and b), the lithium-ion battery is not charged or discharged. The lithium deposition refers to the deposition and growth of lithium dendrites; the internal resistance value is the resistance value between the copper foil electrode and the negative electrode sheet.

2. The method of claim 1, wherein the aging in step b) is accomplished by standing at the stated temperature.

3. The method according to claim 1, wherein the aging temperature in step b) remains constant over time, or varies in a gradient over time.

4. The method according to any one of claims 1 to 3, further comprising the following step: Before heating, the amount of lithium plating on the negative electrode of the lithium-ion battery is determined by disassembling and reassembling the battery and measuring its discharge capacity.

5. The method according to claim 3, further comprising the following step: The heating temperature and aging time are adjusted according to the amount of lithium plating on the negative electrode of the lithium-ion battery.

6. The method of claim 1, wherein the surface of the lithium dendrites is passivated after the aging treatment.

7. The method according to any one of claims 1 to 3, wherein steps a) and b) are performed at atmospheric pressure.

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