Metal-lithium composite belt and preparation method thereof

Abstract

The invention provides a metal-lithium composite belt and a preparation method thereof. The preparation method comprises the following steps: preparing lithium metal composite slurry; and coating two side surfaces of a metal foil with the lithium metal composite slurry, and drying to obtain the metal-lithium composite belt. The lithium metal composite slurry is used for coating the surfaces of the two sides of the metal foil, the process is simple, the cost is reduced, the interface bonding strength of the lithium film and the metal foil is improved, and therefore the problem that the thin lithium film in the metal-lithium composite belt is prone to breakage is solved while the thin lithium film with the thickness smaller than 10 micrometers is formed. In addition, the metal-lithium composite belt prepared based on the preparation method can effectively improve the charge and discharge efficiency of the battery, enhance the cycle stability of the battery, and significantly improve the safety performance of the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a metal-lithium composite belt and a preparation method thereof. Background Art

[0002] Nowadays, lithium-ion batteries are widely used in many fields such as portable electronic products, electric vehicles, energy storage systems, etc. With the continuous improvement of the performance requirements of lithium batteries in various application scenarios, such as higher energy density, longer cycle life, better safety, etc., the continuous innovation of lithium battery materials and technologies has been promoted.

[0003] Currently, the commonly used negative electrode material for lithium batteries is graphite material. The specific capacity of graphite negative electrode is 372mAh / g. The energy density of traditional graphite negative electrode system has not much room for improvement. As a negative electrode material, metallic lithium has the advantages of high capacity (theoretical capacity 3860mAh / g) and low potential (-3.040Vvs. standard hydrogen electrode). Therefore, metallic lithium is considered by the industry to be one of the best negative electrode solutions for high energy density batteries. However, metallic lithium itself has low density, soft texture, and easy adhesion. Without an auxiliary substrate, it is difficult to achieve continuous rolling of ultra-thin plates on the rolling mill, and subsequent use is also difficult. In addition, problems such as dendrite growth and large volume changes in lithium metal also limit its application.

[0004] The metal-lithium composite belt combines the high capacity of lithium and the conductivity of metal, which conforms to the trend of thinner and lighter batteries and higher performance. Therefore, the use of metal-lithium composite belt as the negative electrode is an unstoppable trend, among which the research on copper-lithium composite belt is the most in-depth. The traditional copper-lithium composite belt is prepared by physical method. For example, CN119252841A discloses an easy-to-make lithium-copper composite belt and its preparation method and equipment, wherein the lithium-copper composite belt comprises: a copper foil having a thickness of 2-6 μm, divided into a perforated area and an unperforated area, wherein the perforated area has a plurality of pores, the pore spacing is 0.5-2 mm, the pore diameter is 0.05-0.5 mm, and the edges of the pores have copper foil retained in the form of spikes or protrusions; and a lithium foil compounded to at least one surface of the copper foil and at least covering at least a portion of the perforated area, wherein the spikes or protrusions are embedded in the lithium foil. The preparation method includes: preparing a lithium foil with a thickness of 20-50 μm and a copper foil with a thickness of 2-6 μm; punching holes in the copper foil; and compounding the lithium foil and the copper foil together by mechanical rolling. In the prior art, an overly thick lithium foil will seriously affect the charging and discharging efficiency of the battery, shorten the battery cycle life, and even cause safety problems. However, when the thickness of the lithium foil is reduced to less than 10 μm, the strength of the lithium foil is low and the overly thin lithium foil is easy to break, so it is difficult to prepare.

[0005] Therefore, there is an urgent need to provide a method for preparing a metal-lithium composite tape to solve the problem that the thin lithium film is easily broken in the prior art. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a metal-lithium composite belt and a preparation method thereof. The present invention uses lithium metal composite slurry to coat the surfaces of both sides of the metal foil, which not only simplifies the process and reduces the cost, but also improves the interface bonding strength between the lithium film and the metal foil, thereby forming a thin lithium film with a thickness of less than 10μm, while solving the problem that the thin lithium film in the metal-lithium composite belt is easy to break. In addition, the metal-lithium composite belt prepared based on the preparation method can effectively improve the charge and discharge efficiency of the battery, enhance the cycle stability of the battery, and significantly improve the safety performance of the battery.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a metal-lithium composite tape, the preparation method comprising the following steps:

[0009] Prepare lithium metal composite slurry.

[0010] The lithium metal composite slurry is coated on both side surfaces of the metal foil, and the metal-lithium composite tape is obtained after drying.

[0011] The present invention uses lithium metal composite slurry to coat the surfaces of both sides of the metal foil, which not only simplifies the process and reduces the cost, but also improves the interface bonding strength between the lithium film and the metal foil, thereby forming a thin lithium film with a thickness of less than 10 μm, while solving the problem that the thin lithium film in the metal-lithium composite belt is easy to break. In addition, the metal-lithium composite belt prepared based on the preparation method can effectively improve the charge and discharge efficiency of the battery, enhance the cycle stability of the battery, and significantly improve the safety performance of the battery.

[0012] In the present invention, lithium metal composite slurry coating has the following advantages over lithium metal molten liquid coating: 1) Slurry coating can be used with lithium metal and other materials that are easy to decompose, volatilize or difficult to form a stable molten state at high temperature. For example, some functional materials that are sensitive to temperature can better maintain their performance and characteristics through slurry coating, while molten liquid coating is limited to materials that can form a stable molten state at a certain temperature, which is often not applicable to such special materials; 2) Slurry coating does not require high temperature to be converted into a molten state, which not only reduces energy consumption, but also avoids the influence of high temperature on the performance of the base material. At the same time, the lower process temperature is also conducive to improving the safety of the production process and reducing the risks of fire and explosion caused by high temperature; 3) Slurry coating can accurately control the thickness of the coating by adjusting the viscosity, solid content and coating process parameters of the slurry, and can realize the preparation of thin coatings with good coating thickness uniformity, while molten liquid coating is relatively difficult to accurately control the coating thickness due to the influence of factors such as molten liquid fluidity and surface tension, especially for the preparation of ultra-thin coatings, the advantages of slurry coating are more obvious.

[0013] It should be noted that the present invention does not specifically limit the type of metal foil, and illustratively, it may be copper foil or aluminum foil.

[0014] Preferably, the lithium metal composite slurry comprises lithium powder, a dispersant, a conductive agent and an organic solvent.

[0015] Preferably, the mass ratio of the lithium powder, the dispersant and the conductive agent is 1:(0.02-0.1):(0.05-0.5), wherein the selection range of the dispersant "0.02-0.1" can be, for example, 0.02, 0.04, 0.06, 0.08 or 0.1, etc., and the selection range of the conductive agent "0.05-0.5" can be, for example, 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5, etc.

[0016] In the present invention, the mixing of lithium powder and dispersant in an appropriate proportion helps to improve the dispersibility of the slurry, prevent lithium powder particles from aggregating with each other, ensure that the lithium powder maintains a good dispersion state in the slurry, and improve the stability of the slurry; the mixing of lithium powder and conductive agent in an appropriate proportion helps to form a conductive bridge between lithium powder particles, thereby promoting electron transmission and improving the conductive properties of the slurry. In short, the mixing of lithium powder, dispersant and conductive agent in an appropriate proportion not only makes the slurry have good fluidity and thixotropy, so that it can better adapt to different coating processes and equipment during the coating process, thereby forming a lithium film with uniform thickness and good quality, and the formed lithium film has a low breaking rate, and has excellent density, adhesion and conductive properties, which has an important influence on improving the charge and discharge efficiency, cycle stability and service life of the battery.

[0017] Preferably, the solid content of the lithium metal composite slurry is 10-90%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 82%, 84%, 86%, 88% or 90%, etc.

[0018] Preferably, the particle size D50 of the lithium powder is 40-100 nm, for example, 40 nm, 60 nm, 80 nm or 100 nm.

[0019] In the present invention, the particle size D50 of the lithium powder is 40-100nm. The nano-scale lithium powder particles are conducive to the slurry being spread more easily on the surface of the aluminum foil during the coating process, reducing thickness deviation and coating defects, improving the thickness uniformity of the lithium film, and can also avoid the agglomeration phenomenon caused by excessively large or small particles, facilitating the coating operation. In addition, the lithium powder particles with appropriate particle sizes have high interface bonding strength with the aluminum foil. This good bonding force can prevent the lithium film from peeling off and peeling during the use of the battery, thereby improving the service life and reliability of the battery.

[0020] Preferably, the dispersant includes an inorganic dispersant and / or an organic dispersant.

[0021] Preferably, the inorganic dispersant includes sodium hexametaphosphate and / or sodium silicate.

[0022] Preferably, the organic dispersant includes any one of sodium polyacrylate, polyvinyl pyrrolidone or sodium dodecylbenzene sulfonate, or a combination of at least two thereof.

[0023] Preferably, the conductive agent includes any one of graphite, conductive carbon black, carbon fiber or graphene, or a combination of at least two of them.

[0024] It should be noted that the present invention does not limit the type of the organic solvent, and illustratively, it may be N-methylpyrrolidone or the like.

[0025] Preferably, the viscosity of the lithium metal composite slurry is 500-2000 mPa·s, for example, 500 mPa·s, 1000 mPa·s, 1500 mPa·s or 2000 mPa·s, etc., preferably 800-1500 mPa·s.

[0026] In the present invention, the lithium metal composite slurry with suitable viscosity can improve the uniformity of coating thickness and achieve high-precision coating on the one hand, and can make the slurry shrink evenly during the drying process, reduce surface defects, and improve the mechanical properties of the lithium film on the other hand.

[0027] Preferably, the lithium metal composite slurry further contains a modifier; the modifier includes any one of a surfactant and / or a nano-metal oxide or a combination of at least two thereof.

[0028] In the present invention, the surfactant can reduce the surface tension of the lithium metal composite slurry, improve the wettability of the lithium metal composite slurry to the aluminum foil, enable the lithium metal composite slurry to better adhere to the surface of the aluminum foil, and improve the interface bonding strength. At the same time, the surfactant can also prevent the lithium powder particles in the lithium metal composite slurry from agglomerating to a certain extent, and improve the stability of the lithium metal composite slurry.

[0029] In the present invention, nano metal oxides can not only improve the conductivity and stability of lithium metal composite slurry, but also enhance the adhesion between lithium metal composite slurry and aluminum foil, improve the overall performance of metal-lithium composite tape, and at the same time can also inhibit the growth of lithium dendrites to a certain extent, thereby improving the safety performance of the battery.

[0030] Preferably, the surfactant comprises sodium lauryl sulfate and / or polyethylene glycol octylphenyl ether.

[0031] Preferably, the nano metal oxide includes nano aluminum oxide and / or nano titanium oxide.

[0032] Preferably, based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 1-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0033] In the present invention, a suitable modifier is added to the lithium metal composite slurry, which can not only further enhance the stability and coating quality of the lithium metal composite slurry, but also has an excellent effect on improving the electrical performance of the battery, and helps to improve the charge and discharge efficiency, cycle stability and service life of the battery.

[0034] Preferably, the coating method includes any one of slit coating, extrusion coating or gravure coating, or a combination of at least two of them.

[0035] In the present invention, the slit coating method can achieve high-precision control of the thickness of the lithium film, and can also accurately control the width of the lithium film, thereby achieving flexible adjustment of the width of the lithium film. In addition, the slit coating method can achieve very good lateral coating uniformity, reducing the thickness difference and performance fluctuation of the lithium film in the width direction.

[0036] Preferably, the slot coating method includes the following parameters:

[0037] The slit width is 10-90μm, for example, it can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm or 90μm, etc. The coating speed is 15-35m / min, for example, it can be 15m / min, 20m / min, 25m / min or 30m / min, etc. The coating temperature is 30-120℃, for example, it can be 30℃, 50℃, 70℃, 90℃, 100℃ or 120℃, etc.

[0038] The present invention only needs to use a temperature of 30-120°C to achieve the coating of lithium metal composite slurry. Compared with molten liquid coating, the process temperature is greatly reduced, which helps to reduce energy consumption in the production process, achieve energy conservation and emission reduction, and reduce production costs. In addition, the coating material can be prevented from being damaged by heat, thereby better maintaining the original characteristics and performance of the material. The coating process at a temperature of 30-120°C makes it easier to control the flow and spread of the slurry, and can achieve more accurate control of the coating thickness and coating range.

[0039] Preferably, the thickness of the metal foil is 1-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0040] Preferably, before the lithium metal composite slurry is coated on both side surfaces of the metal foil, the metal foil is pretreated.

[0041] Preferably, the pretreatment method includes a corona method or a physical embossing method.

[0042] In the present invention, the metal foil is pretreated by a corona method or a physical embossing method, which can effectively increase the adhesion of the metal foil surface and enhance the stability of the lithium film on the metal foil. Secondly, the surface energy distribution of the metal foil surface after the adhesion improvement treatment is more uniform, which enables the lithium metal composite slurry to be spread more evenly on the metal foil surface during coating, avoiding the slurry agglomeration or local accumulation caused by surface energy differences, thereby obtaining a lithium film with uniform thickness and stable performance.

[0043] Preferably, in the corona method, the corona power is 5-10kW, for example, 5kW, 6kW, 7kW, 8kW, 9kW or 10kW, the corona time is 5-7s, for example, 5s, 6s or 7s, and the discharge frequency is 1-10kHz, for example, 1kHz, 2kHz, 3kHz, 4kHz, 5kHz, 6kHz, 7kHz, 8kHz, 9kHz or 10kHz, etc.

[0044] Preferably, the drying temperature is 80-120°C, for example, 80°C, 90°C, 100°C, 110°C or 120°C.

[0045] Preferably, the preparation method comprises the following steps:

[0046] (1) A dispersant, a conductive agent and an organic solvent are stirred and mixed, and then lithium powder with a particle size D50 of 40-100 nm and a modifier are added and stirred and mixed to obtain a lithium metal composite slurry with a viscosity of 500-2000 mPa·s and a solid content of 80-90%.

[0047] Among them, the mass ratio of lithium powder, dispersant and conductive agent is 1: (0.02-0.1): (0.05-0.5); based on the mass of solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 1-10%.

[0048] (2) Pre-treating both side surfaces of a copper foil having a thickness of 1-10 μm by a corona method or a physical embossing method, and then coating the lithium metal composite slurry on both side surfaces of the copper foil by a slit coating method, followed by drying at 80-120° C. to obtain a metal-lithium composite tape.

[0049] The slit coating method includes the following parameters: slit width is 10-90 μm, coating speed is 15-35 m / min, and coating temperature is 30-120°C.

[0050] In a second aspect, the present invention provides a metal-lithium composite belt, wherein the metal-lithium composite belt is prepared by the method for preparing the metal-lithium composite belt as described in the first aspect.

[0051] The metal-lithium composite strip comprises a metal foil and a lithium film coated on both side surfaces of the metal foil.

[0052] The thickness of the lithium film is less than 10 μm, for example, 8 μm, 6 μm, 5 μm, 3 μm, 1 μm, 0.5 μm or 0.1 μm, etc. The density of the lithium film is greater than 95%, for example, 96%, 97% or 98%, etc.

[0053] Preferably, the width of the metal foil is greater than or equal to the width of the lithium film.

[0054] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The present invention uses lithium metal composite slurry to coat the surfaces of both sides of the metal foil, which not only simplifies the process and reduces the cost, but also improves the interface bonding strength between the lithium film and the metal foil, thereby forming a thin lithium film with a thickness of less than 10 μm and solving the problem that the thin lithium film in the metal-lithium composite tape is easy to break. In addition, the metal-lithium composite tape prepared based on this preparation method can effectively improve the charge and discharge efficiency of the battery, enhance the cycle stability of the battery, and significantly improve the safety performance of the battery.

[0057] (2) For the metal-lithium composite belt prepared based on the preparation method provided by the present invention, its belt breakage rate is less than 1%, which has good industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a schematic diagram of the cross-sectional structure of the metal-lithium composite belt provided in Example 1 of the present invention.

[0059] Among them, 1-aluminum foil; 2-lithium film. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0061] Example 1

[0062] This embodiment provides a method for preparing a metal-lithium composite tape, the preparation method comprising the following steps:

[0063] (1) A dispersant, a conductive agent and an organic solvent are stirred and mixed, and then lithium powder with a particle size D50 of 70 nm is added and stirred and mixed to obtain a lithium metal composite slurry with a viscosity of 1200 mPa·s and a solid content of 50%.

[0064] Among them, the mass ratio of lithium powder, dispersant and conductive agent is 1:0.06:0.25; the dispersant is sodium hexametaphosphate, the conductive agent is conductive carbon black, and the organic solvent is N-methylpyrrolidone.

[0065] (2) The surfaces of both sides of a copper foil having a thickness of 6 μm were pretreated by a corona method, and then the lithium metal composite slurry was coated on the surfaces of both sides of the copper foil by a slit coating method, and then dried at 100° C. to obtain a metal-lithium composite tape.

[0066] The slit coating method includes the following parameters: slit width of 50 μm, coating speed of 20 m / min, and coating temperature of 80° C. The corona method includes the following parameters: corona power of 7 kW, corona time of 6 s, and discharge frequency of 5 kHz.

[0067] This embodiment also provides a metal-lithium composite belt, which is prepared by the preparation method described above.

[0068] The metal-lithium composite belt comprises a copper foil and a lithium film coated on both sides of the copper foil, wherein the density of the lithium film is 98%, and the width of the copper foil is greater than that of the lithium film.

[0069] Example 2

[0070] This embodiment provides a method for preparing a metal-lithium composite tape, the preparation method comprising the following steps:

[0071] (1) A dispersant, a conductive agent and an organic solvent are stirred and mixed, and then lithium powder with a particle size D50 of 40 nm is added and stirred and mixed to obtain a lithium metal composite slurry with a viscosity of 500 mPa·s and a solid content of 10%.

[0072] Among them, the mass ratio of lithium powder, dispersant and conductive agent is 1:0.2:0.5; the dispersant is sodium polyacrylate, the conductive agent is graphite, and the organic solvent is N-methylpyrrolidone.

[0073] (2) The surfaces of both sides of a copper foil with a thickness of 2 μm were pretreated by a corona method, and then the lithium metal composite slurry was coated on the surfaces of both sides of the copper foil by a slit coating method, and then dried at 80° C. to obtain a metal-lithium composite tape.

[0074] The slit coating method includes the following parameters: slit width is 10 μm, coating speed is 15 m / min, and coating temperature is 30° C. The corona method includes the following parameters: corona power is 5 kW, corona time is 5 s, and discharge frequency is 1 kHz.

[0075] This embodiment also provides a metal-lithium composite belt, which is prepared by the preparation method described above.

[0076] The schematic diagram of the cross-sectional structure of the metal-lithium composite belt is as follows Figure 1 As shown, it includes a copper foil 1 and a lithium film 2 coated on both sides of the copper foil 1 , wherein the density of the lithium film 2 is 97%, and the width of the copper foil 1 is greater than that of the lithium film 2 .

[0077] Example 3

[0078] This embodiment provides a method for preparing a metal-lithium composite tape, the preparation method comprising the following steps:

[0079] (1) A dispersant, a conductive agent and an organic solvent are stirred and mixed, and then lithium powder with a particle size D50 of 100 nm is added and stirred and mixed to obtain a lithium metal composite slurry with a viscosity of 2000 mPa·s and a solid content of 90%.

[0080] Among them, the mass ratio of lithium powder, dispersant and conductive agent is 1:0.1:0.05; the dispersant is sodium dodecylbenzene sulfonate, the conductive agent is carbon fiber, and the organic solvent is N-methylpyrrolidone.

[0081] (2) The surfaces of both sides of a copper foil having a thickness of 10 μm were pretreated by a corona method, and then the lithium metal composite slurry was coated on the surfaces of both sides of the copper foil by a slit coating method, and then dried at 120° C. to obtain a metal-lithium composite tape.

[0082] The slit coating method includes the following parameters: slit width is 90 μm, coating speed is 35 m / min, and coating temperature is 120° C. The corona method includes the following parameters: corona power is 10 kW, corona time is 7 s, and discharge frequency is 10 kHz.

[0083] This embodiment also provides a metal-lithium composite belt, which is prepared by the preparation method described above.

[0084] The metal-lithium composite belt comprises a copper foil and a lithium film coated on both sides of the copper foil, wherein the density of the lithium film is 97%, and the width of the copper foil is greater than that of the lithium film.

[0085] Example 4

[0086] The difference between this embodiment and embodiment 1 is that a modifier is further added to the lithium metal composite slurry in step (1), and the modifier is polyethylene glycol octylphenyl ether; based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 5%.

[0087] The rest of the preparation methods and parameters were the same as those in Example 1.

[0088] Example 5

[0089] The difference between this embodiment and embodiment 1 is that a modifier is further added to the lithium metal composite slurry in step (1), and the modifier is nano-alumina with a particle size D50 of 50 nm; based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 5%.

[0090] The rest of the preparation methods and parameters were the same as those in Example 1.

[0091] Example 6

[0092] The difference between this embodiment and embodiment 4 is that, based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 1%.

[0093] The rest of the preparation methods and parameters were the same as those in Example 4.

[0094] Example 7

[0095] The difference between this embodiment and embodiment 4 is that, based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 10%.

[0096] The rest of the preparation methods and parameters were the same as those in Example 4.

[0097] Example 8

[0098] The difference between this embodiment and embodiment 1 is that the corona method in step (2) is replaced by a physical embossing method.

[0099] The rest of the preparation methods and parameters were the same as those in Example 1.

[0100] Example 9

[0101] The difference between this embodiment and embodiment 1 is that no dispersant is added in step (1).

[0102] The rest of the preparation methods and parameters were the same as those in Example 1.

[0103] Example 10

[0104] The difference between this embodiment and embodiment 1 is that no conductive agent is added in step (1).

[0105] The rest of the preparation methods and parameters were the same as those in Example 1.

[0106] Embodiment 11

[0107] The difference between this embodiment and embodiment 1 is that the viscosity of the lithium metal composite slurry in step (1) is 300 mPa·s.

[0108] The rest of the preparation methods and parameters were the same as those in Example 1.

[0109] Example 12

[0110] The difference between this embodiment and embodiment 1 is that the viscosity of the lithium metal composite slurry in step (1) is 2500 mPa·s.

[0111] The rest of the preparation methods and parameters were the same as those in Example 1.

[0112] Example 13

[0113] The difference between this embodiment and embodiment 4 is that, based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 15%.

[0114] The rest of the preparation methods and parameters were the same as those in Example 4.

[0115] Comparative Example 1

[0116] The difference between this comparative example and Example 1 is that step (1) is not performed, but lithium powder is directly evaporated onto the surface of the aluminum foil in the form of thermal evaporation.

[0117] The rest of the preparation methods and parameters were the same as those in Example 1.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 1 is that step (1) is not performed, but the lithium powder is directly coated on the surface of the aluminum foil in the form of a molten liquid.

[0120] The rest of the preparation methods and parameters were the same as those in Example 1.

[0121] Performance Testing

[0122] 1. Take 3 metal-lithium composite tapes from each of the above embodiments and comparative examples, use a radiographic thickness gauge to detect the thickness of the lithium film on one side, and take the average value. In addition, the metal-lithium composite tapes provided in the above embodiments and comparative examples are subjected to peel strength measurement using a tensile testing machine, that is, firstly cut the lithium-copper composite tape sample into 10 mm × 10 mm blocks, and then fix the two sides of the metal-lithium composite tape on the two fixtures of the peel strength tester to perform a 180-degree peel test.

[0123] The above test results are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] analyze:

[0128] The present invention uses lithium metal composite slurry to coat the surfaces of both sides of the metal foil, which not only simplifies the process and reduces the cost, but also improves the interface bonding strength between the lithium film and the metal foil, thereby forming a thin lithium film with a thickness of less than 10 μm and solving the problem that the thin lithium film in the metal-lithium composite belt is easy to break. For the metal-lithium composite belt prepared by the preparation method provided by the present invention, its breaking rate is less than 1%, which has good industrial application potential.

[0129] It can be seen from Example 1 and Examples 4-7 that adding a suitable modifier to the lithium metal composite slurry can further enhance the stability and coating quality of the lithium metal composite slurry, thereby enhancing the peel strength of the lithium film and achieving precise control of the thickness.

[0130] It can be seen from Examples 1 and 9-10 that if no dispersant is added, the dispersion effect of the slurry is poor, the lithium powder is unevenly dispersed, and the coating quality deteriorates; if no conductive agent is added, although it has little effect on the peel strength and thickness control of the lithium film, it will increase the internal resistance of the battery, which is not conducive to improving the battery's charge and discharge performance and cycle performance.

[0131] It can be seen from Examples 1 and 11-12 that if the viscosity of the lithium metal composite slurry is too low, the slurry is not evenly coated and the lithium film thickness is difficult to accurately control; if the viscosity of the lithium metal composite slurry is too high, coating is difficult and it is difficult to obtain a precise lithium film thickness.

[0132] It can be seen from Example 1 and Example 13 that if the mass proportion of the modifier is too high, the stability and coating quality of the lithium metal composite slurry will decrease, and the peel strength of the lithium film will deteriorate.

[0133] It can be seen from Example 1 and Comparative Example 1 that if lithium powder is directly evaporated on the surface of aluminum foil in the form of thermal evaporation, the lithium powder and the aluminum foil surface are mainly bonded through physical adsorption and weak chemical bonds, the bonding force is weak, and the lithium film is easy to fall off the aluminum foil surface. In addition, during the thermal evaporation process, the deposition rate and distribution of the lithium powder are difficult to accurately control, and the local thickness is prone to being too thick or too thin, and even agglomeration may occur, resulting in increased surface roughness.

[0134] It can be seen from Example 1 and Comparative Example 2 that if lithium powder is directly coated on the surface of aluminum foil in the form of a molten liquid, due to the poor wettability of the molten liquid and the surface of the aluminum foil, it is easy to cause the molten liquid to not be evenly spread on the aluminum foil, and it is easy to form droplets or local accumulation, resulting in poor flatness and uniformity of the coating. Secondly, lithium is very easy to react with oxygen, water vapor, etc. in the air in a molten state to generate compounds such as lithium oxide, which will not only change the chemical composition of lithium and affect the performance of the battery, but also the oxidation product may form an uneven film on the surface of the aluminum foil, hindering the good combination of lithium and aluminum foil and reducing the coating quality. Finally, although the molten liquid will solidify after cooling, this solidification process may cause the bonding force formed between lithium and aluminum foil to be not strong enough, which easily causes the lithium layer to fall off from the aluminum foil, and due to the large fluidity of the molten liquid, it is easy to cause uneven coating thickness during the coating process, making it difficult to achieve accurate control of a specific thickness, and the thickness uniformity is poor.

[0135] It should be noted that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a metal-lithium composite belt, characterized in that: The preparation method comprises the following steps: Prepare lithium metal composite slurry; The lithium metal composite slurry is coated on both side surfaces of the metal foil, and the metal-lithium composite tape is obtained after drying.

2. The method for preparing the metal-lithium composite tape according to claim 1, characterized in that: The lithium metal composite slurry includes lithium powder, dispersant, conductive agent and organic solvent; Preferably, the mass ratio of the lithium powder, the dispersant and the conductive agent is 1:(0.02-0.1):(0.05-0.5); Preferably, the solid content of the lithium metal composite slurry is 10-90%.

3. The method for preparing the metal-lithium composite tape according to claim 2, characterized in that: The particle size D50 of the lithium powder is 40-100 nm; Preferably, the dispersant comprises an inorganic dispersant and / or an organic dispersant; Preferably, the inorganic dispersant includes sodium hexametaphosphate and / or sodium silicate; Preferably, the organic dispersant includes any one or a combination of at least two of sodium polyacrylate, polyvinyl pyrrolidone or sodium dodecylbenzene sulfonate; Preferably, the conductive agent includes any one of graphite, conductive carbon black, carbon fiber or graphene, or a combination of at least two of them.

4. The method for preparing the metal-lithium composite tape according to any one of claims 1 to 3, characterized in that: The viscosity of the lithium metal composite slurry is 500-2000 mPa·s, preferably 800-1500 mPa·s.

5. The method for preparing the metal-lithium composite tape according to any one of claims 2 to 4, characterized in that: The lithium metal composite slurry also contains a modifier; The modifier includes any one of surfactant and / or nano metal oxide or a combination of at least two thereof; Preferably, the surfactant comprises sodium lauryl sulfate and / or polyethylene glycol octylphenyl ether; Preferably, the nano metal oxide includes nano aluminum oxide and / or nano titanium oxide.

6. The method for preparing the metal-lithium composite tape according to claim 5, characterized in that: Based on the mass of the solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 1-10%.

7. The method for preparing the metal-lithium composite tape according to any one of claims 1 to 6, characterized in that: The coating method includes any one of slit coating, extrusion coating or gravure coating, or a combination of at least two thereof; Preferably, the slot coating method includes the following parameters: The slit width is 10-90 μm, the coating speed is 15-35 m / min, and the coating temperature is 30-120°C.

8. The method for preparing the metal-lithium composite tape according to any one of claims 1 to 7, characterized in that: The thickness of the metal foil is 1-10 μm; Preferably, before the lithium metal composite slurry is coated on both sides of the metal foil, the metal foil is pretreated; Preferably, the pretreatment method includes a corona method or a physical embossing method; Preferably, in the corona method, the corona power is 5-10 kW, the corona time is 5-7 s, and the discharge frequency is 1-10 kHz.

9. The method for preparing the metal-lithium composite tape according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) mixing a dispersant, a conductive agent and an organic solvent, and then adding lithium powder with a particle size D50 of 40-100 nm and a modifier, and mixing them to obtain a lithium metal composite slurry with a viscosity of 500-2000 mPa·s and a solid content of 80-90%; The mass ratio of lithium powder, dispersant and conductive agent is 1:(0.02-0.1):(0.05-0.5); based on the mass of solid matter in the lithium metal composite slurry, the mass proportion of the modifier is 1-10%; (2) pre-treating both sides of a copper foil having a thickness of 1-10 μm by a corona method or a physical embossing method, and then coating the lithium metal composite slurry on both sides of the copper foil by a slit coating method, and then drying at 80-120° C. to obtain a metal-lithium composite tape; The slit coating method includes the following parameters: slit width is 10-90 μm, coating speed is 15-35 m / min, and coating temperature is 30-120°C.

10. A metal-lithium composite belt, characterized in that The metal-lithium composite belt is prepared by the method for preparing the metal-lithium composite belt according to any one of claims 1 to 9; The metal-lithium composite strip comprises a metal foil and a lithium film coated on both sides of the metal foil; The thickness of the lithium film is less than 10 μm, and the density of the lithium film is greater than 95%.

Images