Preparation method of all-solid-state battery composite negative plate and prepared negative plate

Abstract

The invention belongs to the field of all-solid-state batteries, and relates to a preparation method of an all-solid-state battery composite negative electrode plate, the prepared negative electrode plate and the preparation method, and the preparation method comprises the following steps: placing a lithium alloy foil between a first copper foil and a second copper foil, and carrying out rolling treatment to obtain a lithium-containing composite current collector; coating one side, deviating from the lithium alloy foil, of the first copper foil with a carbon-coated layer, and forming through holes in the first copper foil and the carbon-coated layer to obtain a porous carbon-coated composite current collector; and coating negative electrode slurry on one side, deviating from the first copper foil, of the carbon coating layer by a wet method to obtain the all-solid-state battery composite negative electrode plate. The lithium alloy foil is arranged between the first copper foil and the second copper foil for rolling treatment, the lithium source is pre-buried in the lithium-containing composite current collector, the lithium source is more slowly and uniformly pre-lithiated after being coated with negative electrode slurry through the through holes, and the carbon coating layer can reduce the possibility of side reaction caused by direct contact between sulfide electrolyte and the first copper foil and the second copper foil. And the surface and the interior of the pole piece are not easily damaged in the pre-lithiation process, so that the first efficiency of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the field of all-solid-state batteries, and relates to a preparation method of a composite negative electrode sheet for an all-solid-state battery and the obtained negative electrode sheet. Background Art

[0002] An all-solid-state battery is a lithium battery that uses solid electrode materials and solid electrolyte materials and does not contain any liquid. Due to its high energy density and high safety, the all-solid-state battery has become the most promising next-generation battery technology, but it still faces many basic scientific problems and engineering scale-up technology problems to be solved.

[0003] Taking the sulfide all-solid-state battery as an example, after replacing the organic liquid electrolyte with an inorganic sulfide solid electrolyte, due to the relatively narrow thermodynamic stable electrochemical window of the sulfide electrolyte itself (1.7 - 2.5V), serious side reactions occur between it and the high-voltage positive electrode and the low-potential negative electrode.

[0004] On the positive electrode side, there is a space charge layer between the sulfide electrolyte and the uncoated oxide positive electrode. The formation of the space charge layer will lead to an increase in the migration barrier of lithium ions at the interface and an increase in the interface impedance, thereby resulting in a capacity decay of the battery. Currently, the suppression of the space charge layer is mainly achieved by coating the positive electrode material. The coating materials are mainly materials such as LiNbO3, LiZrO2, and dielectric materials such as BaTiO3. After assembling a half-cell with the positive electrode material coated by the above method and testing, the initial efficiency can often reach more than 90%. For the positive electrode with uniform coating and matching a sulfide electrolyte with strong antioxidant properties, the initial efficiency even reaches 95%. Therefore, the initial efficiency of the positive electrode of the sulfide all-solid-state battery is currently relatively high and does not significantly restrict the improvement of the initial efficiency of the full battery.

[0005] On the negative electrode side, the side reaction between the sulfide electrolyte and the negative electrode material is relatively serious at low potentials. The lithium intercalation platform potential of graphite is relatively low (0.1V (vs. Li / Li + ))), and the high electronic conductivity of graphite will exacerbate the decomposition reaction of the sulfide electrolyte at this low potential. For example, the sulfide electrolyte Li3PS4 undergoes a side reaction at this low potential: Li3PS4 + 8Li + + 8e - = 4Li2S + Li3P, where the by-products Li2S and Li3P generated have poor ionic and electronic conductivities, resulting in an increase in the interface impedance of the negative electrode material, a decrease in the initial efficiency, and a deterioration of the rate performance. As a high specific capacity and silicon negative electrode material, it will also undergo the above electrolyte reduction decomposition reaction with the sulfide electrolyte at a low lithium intercalation potential. In addition, due to the volume expansion and contraction of silicon particles themselves, particle fragmentation occurs, and the newly generated interface will further react with the sulfide electrolyte. Therefore, the initial efficiency and cycle performance of the negative electrode are often poor.

[0006] From the above problems, we can find that in sulfide all-solid-state batteries, the side reactions on the positive electrode side can be solved by coating and a higher first efficiency has been achieved. In comparison, the side reactions on the negative electrode side are more serious and the first efficiency is often lower than that of the positive electrode. Therefore, the low first efficiency of the negative electrode has become the key reason restricting the improvement of the first efficiency of all-solid-state batteries, which is not conducive to the performance and industrial application of all-solid-state batteries. Therefore, pre-lithiation of the negative electrode to improve the first efficiency of half-cells and full cells is an effective way to solve the problem.

[0007] However, there are currently few pre-lithiation technologies based on all-solid-state negative electrode plates. Traditional calendering pre-lithiation technology is relatively dangerous and has certain requirements on the peeling strength and surface density of the electrode plates. The solvents used in chemical pre-lithiation themselves have a certain polarity and will produce side reactions with the electrodes containing sulfide electrolytes. These are all unfavorable for all-solid-state negative electrode plates. Summary of the invention

[0008] The present invention aims to provide a method for preparing a composite negative electrode sheet for an all-solid-state battery and the prepared negative electrode sheet, wherein a lithium alloy foil is placed between a first copper foil and a second copper foil for roll-rolling, a lithium source is pre-embedded in a lithium-containing composite current collector, and a through hole is opened so that the lithium source can be pre-lithiated more slowly and evenly through the through hole after the negative electrode slurry is coated. The carbon coating layer can reduce the possibility of side reactions caused by direct contact between the sulfide electrolyte in the negative electrode slurry and the first copper foil and the second copper foil. The whole process is safe and efficient, does not require additional operations, and is not prone to damage to the surface and interior of the electrode sheet during the pre-lithiation process, thereby improving the initial efficiency of the battery.

[0009] In a first aspect, the present invention provides a method for preparing a composite negative electrode sheet for an all-solid-state battery, comprising the following steps:

[0010] Step 1, preparing a lithium-containing composite current collector: placing a lithium alloy foil between a first copper foil and a second copper foil, and performing a rolling process to obtain a lithium-containing composite current collector;

[0011] Step 2, preparing a porous carbon-coated composite current collector: coating a carbon-coated layer on the side of the first copper foil away from the lithium alloy foil, and opening through holes on the first copper foil and the carbon-coated layer to obtain a porous carbon-coated composite current collector;

[0012] Step 3, wet coating of negative electrode slurry: wet coating of the negative electrode slurry on the side of the carbon coating layer away from the first copper foil to obtain a composite negative electrode sheet for an all-solid-state battery.

[0013] By placing a lithium alloy foil between a first copper foil and a second copper foil and performing a rolling process, the resulting lithium-containing composite current collector contains a lithium source. A carbon-coated layer is coated on the side of the first copper foil facing away from the lithium alloy foil, and then a negative electrode slurry is coated by a wet process, which can reduce the possibility of side reactions and corrosion caused by direct contact between the sulfide electrolyte in the negative electrode slurry and the first copper foil and the second copper foil. Through holes are formed in the first copper foil and the carbon-coated layer, so that the lithium source in the lithium alloy foil can be pre-lithiated through the through holes after the negative electrode slurry is coated. The pre-lithiation process is slower and more uniform, the whole process is safe and efficient, no additional operations are required, and it is not easy to cause damage to the surface and interior of the electrode during the pre-lithiation process, thereby improving the initial efficiency of the battery.

[0014] In some embodiments, the rolling process includes preliminary rolling and secondary rolling. The preliminary rolling is performed after the lithium alloy foil overlaps with the first copper foil and the second copper foil. After the preliminary rolling, a composite copper foil is obtained. The secondary rolling is performed on the composite copper foil, and after the secondary rolling, a lithium-containing composite current collector is obtained.

[0015] In some embodiments, the pressure of the preliminary rolling is 300 N to 500 N, the temperature is 22 °C to 28 °C, the temperature of the secondary rolling is 40 °C to 50 °C, and the pressure is 800 N to 1000 N.

[0016] For example, the pressure of the preliminary rolling is 300 N, 330 N, 350 N, 400 N, 450 N, 500 N, etc., the temperature is 22 °C, 23 °C, 25 °C, 26 °C, 28 °C, etc., the temperature of the secondary rolling is 40 °C, 42 °C, 43 °C, 45 °C, 46 °C, 48 °C, 50 °C, etc., and the pressure is 800 N, 850 N, 900 N, 950 N, 1000 N, etc.

[0017] The two rolling processes are to better press the first copper foil, the second copper foil, and the lithium-silver alloy foil to obtain a lithium-containing composite current collector with the required thickness. The preliminary rolling at low temperature and low pressure plays a role of pre-pressing, pre-pressing the first copper foil, the second copper foil, and the lithium-silver alloy foil into a thicker composite copper foil. The high temperature and high pressure during the secondary rolling can enhance the pressing effect, continuously and uniformly thinning the composite copper foil to the required thickness. Only performing the preliminary rolling cannot make the three-layer foil adhere and reach the final thickness. Only performing the secondary rolling will directly cause the foil to wrinkle or deform severely. After pre-pressing by the preliminary rolling, high-pressure thinning during the secondary rolling can obtain a flatter lithium-containing composite current collector.

[0018] In some embodiments, the thickness of the first copper foil and the second copper foil is 6 μm to 12 μm, the thickness of the lithium alloy foil is 5 μm to 12 μm, and the thickness of the lithium-containing composite current collector is 10 μm to 20 μm.

[0019] For example, the thicknesses of the first copper foil and the second copper foil are 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, etc., the thicknesses of the lithium alloy foil are 5μm, 8μm, 10μm, 11μm, 12μm, etc., and the thicknesses of the lithium-containing composite current collector are 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, etc.

[0020] In some embodiments, the thickness of the first copper foil and the second copper foil is 8μm to 10μm, the thickness of the lithium alloy foil is 6μm to 8μm, and the thickness of the lithium-containing composite current collector is 12μm to 18μm.

[0021] The thicknesses of the first copper foil, the second copper foil, and the lithium alloy foil affect the thickness of the lithium-containing composite current collector. The thicker the lithium-containing composite current collector, the heavier its mass, and the lower the mass energy density of the battery. When the thickness of the lithium-containing composite current collector is 10μm to 20μm, a higher energy density can be obtained, and the initial efficiency of the battery can be improved.

[0022] In some embodiments, the thickness of the carbon-coated layer is 200nm to 1000nm.

[0023] In some embodiments, the thickness of the carbon-coated layer is 400nm to 600nm.

[0024] For example, the thicknesses of the carbon-coated layer are 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.

[0025] If the carbon-coated layer is too thin, the separation effect on the negative electrode slurry and the copper foil is poor. If the carbon-coated layer is too thick, the energy density of the battery will decrease. Within the above range of thickness, it can not only reduce the possibility of side reactions between the copper foil and the sulfide electrolyte, but also minimize the impact on the energy density of the battery.

[0026] In some embodiments, the carbon-coated layer includes one or more of nano-conductive graphite or carbon-coated particles.

[0027] Nano-conductive graphite and carbon-coated particles can maintain the stability of structure and performance during the battery cycle, reduce the polarization phenomenon inside the battery, and lower the energy loss during the charge and discharge process of the battery, thereby improving the cycle life of the battery.

[0028] In some embodiments, the diameter of the through holes is 0.1μm to 2μm, and the interval between the through holes is 0.05cm to 0.5cm.

[0029] In some embodiments, the diameter of the through holes is 1μm to 1.5μm, and the interval between the through holes is 0.1cm to 0.4cm.

[0030] For example, the diameter of the through holes is 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 1.8 μm, 2 μm, etc., and the intervals between the through holes are 0.05 cm, 0.1 cm, 0.15 cm, 0.2 cm, 0.25 cm, 0.3 cm, 0.35 cm, 0.4 cm, 0.45 cm, 0.5 cm, etc.

[0031] During wet coating, the negative electrode slurry will enter the through holes. The negative electrode slurry remaining in the through holes with the through hole diameters within the above ranges is very little, and due to the blockage of the second copper foil, the negative electrode slurry will not spread downward either, further reducing the possibility of side reactions.

[0032] In some embodiments, the lithium alloy is at least one of a lithium-indium alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-tin alloy, and a lithium-silver alloy.

[0033] Indium metal has a high lithium affinity, can promote the lateral growth of lithium, effectively inhibit dendrite formation, thereby improving the cycle life and energy density of lithium batteries. Aluminum-lithium alloys can reduce the specific gravity of the alloy, increase stiffness, while still maintaining high strength, good corrosion resistance and fatigue resistance, as well as appropriate ductility, which enables them to improve the comprehensive performance of the battery to a certain extent when used as a prelithiation material. Magnesium-lithium alloys are currently the lightest metal structural materials, with the characteristics of ultra-light weight, high specific strength, and high specific modulus, and may help reduce the battery weight and improve the structural performance during the prelithiation process. Lithium-tin alloys have a high theoretical specific capacity, can compensate for lithium loss during the cycle, and greatly improve the energy density of tin foil in the use of full batteries. Lithium-silver alloys have a certain degree of electrochemical inertness after delithiation, which is beneficial to achieving high lithium utilization rate and lossless lithium replenishment.

[0034] In some embodiments, the atomic proportion of metallic lithium in the lithium alloy foil is 10% to 98%.

[0035] In some embodiments, the atomic proportion of metallic lithium in the lithium alloy foil is 40% to 60%.

[0036] For example, the atomic proportion of metallic lithium in the lithium alloy foil is 10%, 15%, 23%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90%, 98%, etc.

[0037] The atomic proportion of metallic lithium in the lithium alloy foil represents the lithium content in the lithium alloy foil. The higher the lithium content, the lower the mass of the lithium alloy foil that needs to be added. The lower the lithium content, the higher the mass of the lithium alloy foil that needs to be added. When the atomic proportion of metallic lithium in the lithium alloy foil is within the above range, the thickness of the lithium alloy foil to be added can not only meet the sufficient lithium source but also not be too thick to cause a reduction in the battery energy density.

[0038] In some embodiments, the negative electrode paste includes negative electrode active particles, a sulfide electrolyte, and a binder, and the sulfide electrolyte is at least one of lithium germanium phosphorus sulfur, lithium silicon phosphorus sulfur chlorine, and lithium boron sulfur electrolyte.

[0039] The crystal structure of the sulfide electrolyte usually has a relatively open framework, which can provide a fast migration channel for lithium ions, resulting in a relatively high ionic conductivity. In the lithium silicon phosphorus sulfur chlorine electrolyte, the introduction of chlorine atoms can further optimize the crystal structure and increase the migration sites of lithium ions, thereby improving the ionic conductivity. The boron element in the lithium boron sulfur electrolyte can enhance the structural stability of the electrolyte, so that when it contacts with the electrode material, it is not easy to undergo a chemical reaction and cause performance degradation. The lithium silicon phosphorus sulfur chlorine electrolyte can adapt to the surface morphology of the electrode when contacting the electrode, further reducing the interface resistance, which is beneficial to improving the charge-discharge efficiency of the battery. The presence of boron element in the lithium boron sulfur electrolyte helps to form a strong three-dimensional structure, making it have a relatively high hardness and compressive strength, and can maintain structural integrity during battery assembly and use.

[0040] In some embodiments, the particle size D50 of the sulfide electrolyte is 0.1 μm to 6 μm.

[0041] When the particle size D50 of the sulfide electrolyte is within the above range, it can provide more ion transport channels, making it easier for lithium ions, etc. to migrate in the electrolyte, thereby improving the ionic conductivity. It can also reduce the side reactions between the sulfide electrolyte and the electrode material, making the contact between the electrolyte and the electrode more uniform, and avoiding the aggravation of side reactions caused by a locally excessive reaction interface, which helps to improve the cycle life and safety of the battery.

[0042] In some embodiments, the binder is one or more of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene rubber, nitrile rubber, chloroprene rubber, and ethylene-propylene rubber.

[0043] The binder is an organic ester solvent rather than water, reducing the possibility of the binder entering the through holes and reacting with the lithium-silver alloy.

[0044] In some embodiments, the percentage of the binder is 0.5% to 6%. For example, the percentages of the binder are 0.5%, 1%, 1.5%, 2.5%, 3.5%, 4.5%, 5.5%, 6%.

[0045] The percentage of the binder within the range of 0.5% to 6% can effectively bond the electrode material and the sulfide electrolyte particles together, form a stable electrode structure, prevent the active material from falling off during charge and discharge, and improve the cycle stability of the electrode.

[0046] In some embodiments, the negative electrode active particles are one or more of silicon, silicon-carbon material, silicon-oxygen material, and graphite material.

[0047] Using silicon as the negative electrode material can enable the battery to store more electric charge under the same mass, thereby improving the energy density of the battery. The silicon-carbon material obtained by compounding silicon and carbon can effectively alleviate the volume expansion problem of silicon during charge and discharge. The carbon material can act as a buffer medium to limit the volume change of silicon particles, reduce the pulverization and shedding of the electrode material, thereby improving the cycle performance of the battery and extending the service life of the battery. During charge and discharge, the silicon-oxygen material has a relatively small volume change because the introduction of oxygen atoms changes the crystal structure of the material, making the material have better flexibility and structural stability, and can withstand a certain degree of volume change while reducing the possibility of damaging the electrode structure, thereby improving the cycle stability and safety of the battery. Graphite has a typical layered structure, which can provide a stable channel for the insertion and extraction of lithium ions. During charge and discharge, lithium ions can reversibly insert and extract between the layers without causing obvious damage to the graphite structure, thereby ensuring the cycle stability of the battery.

[0048] In a second aspect of the present invention, there is provided a composite negative electrode sheet for an all-solid-state battery prepared by any one of the above preparation methods, including a negative electrode slurry layer, a carbon-coated layer, a first copper foil, a lithium alloy layer, and a second copper foil which are sequentially overlapped. Through holes are formed in the carbon-coated layer and the first copper foil, the diameter of the through holes is 0.1 μm to 2 μm, and the interval between the through holes is 0.05 cm to 0.5 cm.

[0049] The lithium alloy foil is placed between the first copper foil and the second copper foil to provide a lithium source. The carbon-coated layer can reduce the possibility of side reactions and corrosion caused by direct contact between the sulfide electrolyte in the negative electrode slurry and the first copper foil and the second copper foil during wet coating of the negative electrode slurry. The through holes formed in the first copper foil and the carbon-coated layer enable the lithium source to be pre-lithiated after the negative electrode slurry is coated. The pre-lithiation process is slower and more uniform, the whole process is safe and efficient, and it is not easy to cause damage to the surface and inside of the electrode during the pre-lithiation process, thereby improving the first efficiency of the battery.

[0050] In summary, the present application includes at least one of the following beneficial technical effects:

[0051] By placing a lithium alloy foil between a first copper foil and a second copper foil and performing a rolling process, a lithium source is pre-embedded in the lithium-containing composite current collector. The carbon coating layer can reduce the possibility of side reactions occurring due to direct contact between the sulfide electrolyte in the negative electrode paste and the first copper foil and the second copper foil. Through holes are opened so that the lithium source can undergo slower and more uniform prelithiation through the through holes after the negative electrode paste is coated. The whole process is safe and efficient, without the need for additional operations and is not likely to cause damage to the surface and interior of the electrode during the prelithiation process, thereby improving the initial efficiency of the battery. Description of the Drawings

[0052] Figure 1 This is a schematic structural diagram of the composite negative electrode sheet of the all-solid-state battery in Embodiment 4 of the present invention.

[0053] Reference numerals: 01, negative electrode paste layer; 02, carbon coating layer; 03, first copper foil; 04, lithium alloy layer; 05, second copper foil. Detailed Embodiments

[0054] The technical solutions of the present invention are further described below through specific embodiments. The specific embodiments do not represent limitations on the protection scope of the present invention. Some non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the protection scope of the present invention.

[0055] The materials and reagents used in this application are all commercially available.

[0056] Embodiment 1

[0057] A method for preparing a composite negative electrode sheet of an all-solid-state battery, comprising the following steps:

[0058] Step 1, preparing a lithium-containing composite current collector

[0059] Stack a first copper foil, a second copper foil, and an ultra-thin lithium-silver alloy foil together. The thickness of the first copper foil and the second copper foil is 8 μm, and the thickness of the lithium-silver alloy foil is 5 μm. The lithium-silver alloy foil is located between the two copper foils, and the atomic ratio of metallic lithium in the lithium-silver alloy foil is 15%. The original composite copper foil is obtained through preliminary rolling by a rolling mill. The pressure for preliminary rolling is 300 N, and it is carried out at room temperature (about 25°C). Then, the original composite copper foil is subjected to secondary rolling by a hot rolling mill. The temperature for secondary rolling is 45°C, and the pressure is 800 N, to obtain a lithium-containing composite current collector with a thickness of 16 μm.

[0060] Step 2, preparing a porous carbon-coated composite current collector

[0061] Coat a 500-nm-thick nano-conductive graphite layer on the surface of the first copper foil of the lithium-containing composite current collector as the carbon coating layer. Through holes are opened in the first copper foil and the carbon coating layer for slow prelithiation. The distance between adjacent through holes is 0.5 cm, and the diameter of the through holes is 10 μm, to obtain a porous carbon-coated composite current collector with a thickness of 16.5 μm.

[0062] Step 3: Wet-coating the negative electrode slurry

[0063] Mix graphite, sulfide electrolyte Li6PS5Cl with D50 of 0.1 μm, and binder SBS in a mass ratio of 80:17:3. Then add anisole to adjust the solid content to 51%. Use a ball mill to ball-mill at a speed of 350 r / min for 1 h to obtain the negative electrode slurry. Place a scraper on the surface of the carbon-coated layer of the above porous carbon-coated composite current collector, pour in the negative electrode slurry for scraper coating, and place it in an oven at 90 °C for baking for 12 h to obtain a composite negative electrode sheet for a all-solid-state battery that can undergo negative electrode prelithiation.

[0064] Example 2

[0065] A method for preparing a composite negative electrode sheet for a all-solid-state battery, comprising the following steps:

[0066] Step 1: Prepare a lithium-containing composite current collector

[0067] Stack the first copper foil, the second copper foil, and a thin ultra-thin lithium-silver alloy foil together. The thicknesses of the first copper foil and the second copper foil are 8 μm, and the thickness of the lithium-silver alloy foil is 5 μm. The atomic ratio of metallic lithium in the lithium-silver alloy foil is 15%. The lithium-silver alloy foil is located between the two copper foils. After preliminary rolling by a rolling mill, the original composite copper foil is obtained. The pressure for preliminary rolling is 300 N, and it is carried out at room temperature (about 25 °C). Then the original composite copper foil is subjected to secondary rolling by a hot rolling mill. The temperature for secondary rolling is 45 °C, and the pressure is 800 N to obtain a lithium-containing composite current collector with a thickness of 16 μm.

[0068] Step 2: Prepare a porous carbon-coated composite current collector

[0069] Coat a 500-nm-thick nano-conductive graphite layer on the surface of the first copper foil of the lithium-containing composite current collector as the carbon-coated layer. Through holes are opened in the first copper foil and the carbon-coated layer for slow prelithiation. The distance between adjacent through holes is 0.1 cm, and the diameter of the through holes is 10 μm to obtain a porous carbon-coated composite current collector with a thickness of 16.5 μm.

[0070] Step 3: Wet-coating the negative electrode slurry

[0071] Mix graphite, sulfide electrolyte Li6PS5Cl with D50 of 0.1 μm, and binder SBS in a mass ratio of 80:17:3. Then add anisole to adjust the solid content to 51%. Use a ball mill to ball-mill at a speed of 350 r / min for 1 h to obtain the negative electrode slurry. Place a scraper on the surface of the carbon-coated layer of the above porous carbon-coated composite current collector, pour in the negative electrode slurry for scraper coating, and place it in an oven at 90 °C for baking for 12 h to obtain a composite negative electrode sheet for a all-solid-state battery that can undergo negative electrode prelithiation.

[0072] Example 3

[0073] A preparation method of a composite negative electrode sheet for an all-solid-state battery, comprising the following steps:

[0074] Step 1: Prepare a lithium-containing composite current collector

[0075] Stack a first copper foil, a second copper foil, and a thin ultra-thin lithium-silver alloy foil together. The thickness of the first copper foil and the second copper foil is 8 μm, and the thickness of the lithium-silver alloy foil is 5 μm. The atomic proportion of metallic lithium in the lithium-silver alloy foil is 15%. The lithium-silver alloy foil is located between the two copper foils. After preliminary rolling by a rolling mill, a raw composite copper foil is obtained. The pressure of the preliminary rolling is 300 N, and it is carried out at room temperature (about 25 °C). Then, the raw composite copper foil is subjected to secondary rolling by a hot rolling mill. The temperature of the secondary rolling is 45 °C, and the pressure is 800 N, obtaining a lithium-containing composite current collector with a thickness of 16 μm.

[0076] Step 2: Prepare a porous carbon-coated composite current collector

[0077] Coat a 500-nm-thick nano-conductive graphite layer on the surface of the first copper foil of the lithium-containing composite current collector as a carbon-coated layer. Through holes penetrating through the first copper foil and the carbon-coated layer are formed for slow prelithiation. The distance between adjacent through holes is 0.05 cm, and the diameter of the through holes is 10 μm, obtaining a porous carbon-coated composite current collector with a thickness of 16.5 μm.

[0078] Step 3: Wet-coat the negative electrode slurry

[0079] Mix graphite, the sulfide electrolyte Li6PS5Cl with a D50 of 0.1 μm, and the binder SBS in a mass ratio of 80:17:3. Then, add anisole to adjust the solid content to 51%. Use a ball mill to ball mill at a speed of 350 r / min for 1 h to obtain the negative electrode slurry. Place a doctor blade on the surface of the carbon-coated layer of the above-mentioned porous carbon-coated composite current collector, pour in the negative electrode slurry for doctor blade coating, and place it in an oven at 90 °C for baking for 12 h, obtaining a composite negative electrode sheet for an all-solid-state battery that can be subjected to negative electrode prelithiation.

[0080] Example 4

[0081] As Figure 1 shown, a composite negative electrode sheet for an all-solid-state battery includes: a negative electrode slurry layer 01, a carbon-coated layer 02, a first copper foil 03, a lithium alloy layer 04, and a second copper foil 05 that are sequentially overlapped. Through holes penetrating through the carbon-coated layer 02 and the first copper foil 03 are formed. The interval between the through holes is 0.5 cm, and the diameter of the through holes is 10 μm.

[0082] Comparative Example 1

[0083] A preparation method of a composite negative electrode sheet for an all-solid-state battery, comprising the following steps:

[0084] Graphite, sulfide electrolyte Li6PS5Cl with a D50 of 0.1 μm, and binder SBS are mixed in a mass ratio of 80:17:3. Then, anisole is added to adjust the solid content to 51%. The mixture is ball-milled at a speed of 350 r / min for 1 h using a ball mill to obtain a negative electrode slurry. A doctor blade is placed on the surface of a common 6-μm-thick copper foil, and the negative electrode slurry is poured in for doctor blade coating. It is placed in an oven at 90 °C and baked for 12 h to obtain a negative electrode sheet for a all-solid-state battery.

[0085] Comparative Example 2

[0086] A method for preparing a composite negative electrode sheet for an all-solid-state battery, comprising the following steps:

[0087] Graphite, sulfide electrolyte Li6PS5Cl with a D50 of 0.1 μm, and binder SBS are mixed in a mass ratio of 80:17:3. Then, anisole is added to adjust the solid content to 51%. The mixture is ball-milled at a speed of 350 r / min for 1 h using a ball mill to obtain a negative electrode slurry. A doctor blade is placed on the surface of an 8-μm-thick carbon-coated copper foil, and the negative electrode slurry is poured in for doctor blade coating. It is placed in an oven at 90 °C and baked for 12 h to obtain a negative electrode sheet for a all-solid-state battery.

[0088] Comparative Example 3

[0089] Step 1: Prepare a lithium-containing composite current collector

[0090] A first copper foil, a second copper foil, and a thin ultra-thin lithium-silver alloy foil are stacked together. The first copper foil and the second copper foil have a thickness of 8 μm, and the lithium-silver alloy foil has a thickness of 5 μm. The atomic ratio of metallic lithium in the lithium-silver alloy foil is 15%. The lithium-silver alloy foil is located between the two copper foils. The original composite copper foil is obtained through preliminary rolling by a rolling mill. The pressure for preliminary rolling is 300 N, and it is carried out at room temperature (about 25 °C). Then, the original composite copper foil is subjected to secondary rolling by a hot rolling mill. The temperature for secondary rolling is 45 °C, and the pressure is 800 N to obtain a lithium-containing composite current collector with a thickness of 16 μm.

[0091] Step 2: Prepare a porous composite current collector

[0092] Through holes are opened in the first copper foil for slow prelithiation. The distance between adjacent through holes is 0.5 cm, and the diameter of the through holes is 10 μm to obtain a porous composite current collector with a thickness of 16.5 μm.

[0093] Step 3: Wet-coat the negative electrode slurry

[0094] Graphite, sulfide electrolyte Li6PS5Cl with a D50 of 0.1 μm, and binder SBS were mixed at a mass ratio of 80:17:3. Then, anisole was added to adjust the solid content to 51%. The mixture was ball-milled at a speed of 350 r / min for 1 h to obtain the negative electrode slurry. A doctor blade was placed on the surface of the first copper foil of the above-mentioned porous composite current collector, and the negative electrode slurry was poured in for doctor blade coating. It was then baked in an oven at 90 °C for 12 h to obtain a composite negative electrode sheet of a all-solid-state battery capable of negative electrode prelithiation.

[0095] Performance Test

[0096] The negative electrode sheets prepared in the above-mentioned examples and comparative examples were assembled into half-cells and full-cells. The specific assembly methods are as follows:

[0097] Half-cell:

[0098] Weigh 100 mg of Li6PS5Cl electrolyte into a PEEK material container with a diameter of 10 mm, apply a pressure of 1 t and keep the pressure for 1 minute. Then weigh 13 mg of the above-mentioned all-solid-state battery composite negative electrode sheet (cut into a disc with a diameter of 10 mm) and place it on one side of the electrolyte, apply a pressure of 3.6 t and keep the pressure for 3 minutes. Then, an indium foil with a diameter of 9 mm and a thickness of 100 μm and a lithium foil with a diameter of 8 mm and a thickness of 50 μm were sequentially placed on the other side of the electrolyte as the lithium-indium negative electrode. Finally, the whole was pressurized at 2 t and kept the pressure for 3 minutes. After tightening the screws and applying a test pressure of 15 NM, the electrochemical performance test was carried out.

[0099] Full-cell:

[0100] The above-mentioned all-solid-state battery composite negative electrode sheet was used to coat a ternary electrode sheet as the composite positive electrode, and an electrolyte membrane was used as the separator. The three were prepared into a small soft-pack battery with an area of 9 square centimeters through lamination and assembly. A pressure of 10 NM was applied to the small soft-pack battery. After completion of assembly, the electrochemical performance test was carried out.

[0101] The above-mentioned half-cells and full-cells were placed on a Neware battery performance cabinet and subjected to the first-cycle charge-discharge test under the condition of 328 ± 1 K. The test method is as follows:

[0102] Half-cell: Leave it for 10 min to stabilize the battery state; then discharge at a constant voltage to -0.61 V (vs. Li-In), and the discharge rate is set to 0.05 C until cutoff; leave it for 10 min again; then charge in a constant current mode to 1 V (vs. Li-In), and the charge rate is 0.05 C. Cycle 1 time, and record the first-cycle charge specific capacity and first efficiency.

[0103] Full cell: Left standing for 10 min; then charged to 4.25 V in constant voltage mode at a charge rate of 0.1 C until cutoff; left standing for 10 min; discharged to 2.0 V in constant current mode at a discharge rate of 0.1 C, cycled once, and the first-cycle discharge specific capacity and first efficiency were recorded.

[0104] The results are shown in Table 1 and Table 2:

[0105] Table 1. First-cycle lithium deintercalation specific capacity and first efficiency of half cells assembled with negative electrode sheets in the examples and comparative examples

[0106]

[0107] Table 2. First-cycle lithium deintercalation specific capacity and first efficiency of full cells assembled with negative electrode sheets in the examples and comparative examples

[0108]

[0109] As can be seen from Table 1 and Table 2, for the half cell assembled with the composite negative electrode sheet of the all-solid-state battery in Example 1, the first-cycle lithium deintercalation amount at 0.05 C was 352 mAh / g, the first-cycle lithium intercalation amount was 401 mAh / g, and the first efficiency was 88%. For the half cell assembled with the composite negative electrode sheet of the all-solid-state battery in Example 2, the first-cycle lithium deintercalation amount at 0.05 C was 367 mAh / g, the first-cycle lithium intercalation amount was 408 mAh / g, and the first efficiency was 90%. For Example 3, the first-cycle lithium deintercalation amount at 0.05 C was 349 mAh / g, the first-cycle lithium intercalation amount was 410 mAh / g, and the first efficiency was 85%. For the full cell assembled with the composite negative electrode sheet of the all-solid-state battery in Example 1, the first-cycle discharge specific capacity at 0.1 C was 195 mAh / g, the first-cycle charge specific capacity was 238 mAh / g, and the first efficiency was 82%. For the full cell assembled with the composite negative electrode sheet of the all-solid-state battery in Example 2, the first-cycle discharge specific capacity at 0.1 C was 206 mAh / g, the first-cycle charge specific capacity was 237 mAh / g, and the first efficiency was 87%. For the full cell assembled with the composite negative electrode sheet of the all-solid-state battery in Example 3, the first-cycle discharge specific capacity at 0.1 C was 186 mAh / g, the first-cycle charge specific capacity was 233 mAh / g, and the first efficiency was 80%.

[0110] In Examples 1-3, the current collector is pre-lithiated using a lithium-silver alloy foil and modified with a carbon-coated layer. The lithium-containing composite current collector contains a lithium source. By means of opening through-holes on the surface of the first copper foil and the carbon-coated layer, the lithium source in the lithium-silver alloy can slowly enter the negative electrode to complete pre-lithiation and ensure the lithium supplementation effect. This method of slowly and uniformly pre-lithiating after coating the negative electrode slurry is safe and efficient, without the need for additional operations and without worrying about the damage to the surface and interior of the electrode sheet during the pre-lithiation process. In addition, since the negative electrode sheet of the present application is prepared by wet-coating the negative electrode slurry, when the all-solid electrode sheet is baked in a dry room with trace amounts of moisture present, the copper foil will undergo a side reaction with the sulfide electrolyte and thus corrode the copper foil, which is disadvantageous to the performance of the electrode sheet and the subsequent battery assembly and manufacturing. By setting a carbon-coated layer on the surface of the composite current collector in the present application, the peel strength of the electrode sheet can be effectively increased and the possibility of the copper foil being corroded can be reduced. Therefore, the half-cell assembled from the all-solid battery composite negative electrode sheet of Examples 1-3 can obtain a relatively excellent initial efficiency, which is significantly improved compared to Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0111] Specifically comparing Example 1, Example 2, and Example 3, the distance between adjacent through-holes of the first copper foil and the carbon-coated layer in Example 1 is relatively larger than that in Example 2, and the number of openings is relatively smaller, which may lead to insufficient pre-lithiation of the negative electrode and thus a slightly lower initial efficiency. In Example 3, the distance between adjacent through-holes of the first copper foil and the carbon-coated layer is relatively smaller than that in Example 2, and the number of openings is larger, which may lead to excessive contact between the electrolyte and the copper foil, resulting in slight corrosion and thus affecting the initial efficiency. The number of openings in Example 2 can better balance the pre-lithiation effect and the contact between the electrolyte and the copper foil, maintaining sufficient pre-lithiation while reducing the contact corrosion between the electrolyte and the copper foil.

[0112] The amount of lithium deintercalation in the first cycle of the half-cell assembled from the negative electrode sheet of Comparative Example 1 at 0.05C is 295 mAh / g, the amount of lithium intercalation in the first cycle is 399 mAh / g, and the initial efficiency is 74%. The discharge specific capacity in the first cycle of the full cell assembled from the negative electrode sheet of Comparative Example 1 at 0.1C is 168 mAh / g, the charge specific capacity in the first cycle is 235 mAh / g, and the initial efficiency is 71%. In Comparative Example 1, the negative electrode slurry is directly coated on a common copper foil to prepare the negative electrode sheet, and it is impossible to slowly and uniformly pre-lithiate after coating the negative electrode slurry as in Examples 1-3. Therefore, the initial efficiency of Comparative Example 1 is lower than that of Examples 1-3.

[0113] The first-cycle de-lithiation capacity of the half-cell assembled with the negative electrode sheet of Comparative Example 2 is 300 mAh / g at 0.05C, the first-cycle lithium intercalation capacity is 395 mAh / g, and the first efficiency is 76%. The first-cycle discharge specific capacity of the full cell assembled with the negative electrode sheet of Comparative Example 2 is 174 mAh / g at 0.1C, the first-cycle charge specific capacity is 238 mAh / g, and the first efficiency is 73%. Comparative Example 2 prepares the negative electrode sheet by directly coating the negative electrode slurry on the existing carbon-coated copper foil. It can be found that the first efficiency of Comparative Example 2 is significantly improved compared with that of Comparative Example 1, indicating that the existing carbon-coated copper foil can inhibit the reaction between the copper foil and the sulfide electrolyte in the negative electrode to a certain extent. However, since it is impossible to slowly and uniformly pre-lithiate after coating the negative electrode slurry, the first efficiency of Comparative Example 2 is also lower than that of Examples 1-3.

[0114] The first-cycle de-lithiation capacity of the half-cell assembled with the negative electrode sheet of Comparative Example 3 is 316 mAh / g at 0.05C, the first-cycle lithium intercalation capacity is 400 mAh / g, and the first efficiency is 79%. The first-cycle discharge specific capacity of the full cell assembled with the negative electrode sheet of Comparative Example 3 is 184 mAh / g at 0.1C, the first-cycle charge specific capacity is 239 mAh / g, and the first efficiency is 77%. Although lithium-silver alloy is introduced into the copper foil for lithium compensation in Comparative Example 3, the carbon-coated layer is not coated. Although the first efficiency of the negative electrode is improved compared with that of Comparative Example 1, due to excessive contact between the electrolyte and the copper foil, relatively serious corrosion occurs, which affects the first efficiency, making the first efficiency of Comparative Example 3 lower than that of Examples 1-3.

[0115] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that, without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. In addition, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for preparing a composite negative electrode sheet for an all-solid-state battery, characterized in that: The following steps are involved: Step 1, preparing a lithium-containing composite current collector: placing a lithium alloy foil between a first copper foil and a second copper foil, and performing a rolling process to obtain a lithium-containing composite current collector; Step 2, preparing a porous carbon-coated composite current collector: coating a carbon-coated layer on the side of the first copper foil away from the lithium alloy foil, and opening through holes on the first copper foil and the carbon-coated layer to obtain a porous carbon-coated composite current collector; Step 3, wet coating of negative electrode slurry: wet coating of negative electrode slurry on the side of the carbon coating layer away from the first copper foil to obtain a composite negative electrode sheet for an all-solid-state battery.

2. The preparation method according to claim 1, characterized in that The rolling process includes primary rolling and secondary rolling, wherein the primary rolling is applied to the lithium alloy foil after it overlaps with the first copper foil and the second copper foil, and a composite copper foil is obtained after the primary rolling, and the secondary rolling is applied to the composite copper foil, and a lithium-containing composite current collector is obtained after the secondary rolling; Preferably, the pressure of the preliminary rolling is 300N to 500N, the temperature is 22°C to 28°C, and the temperature of the secondary rolling is 40°C to 50°C, and the pressure is 800N to 1000N.

3. The preparation method according to claim 1, characterized in that: The thickness of the first copper foil and the second copper foil is 6 μm to 12 μm, the thickness of the lithium alloy foil is 5 μm to 12 μm, and the thickness of the lithium-containing composite current collector is 10 μm to 20 μm; Preferably, the thickness of the first copper foil and the second copper foil is 8 μm to 10 μm, the thickness of the lithium alloy foil is 6 μm to 8 μm, and the thickness of the lithium-containing composite current collector is 12 μm to 18 μm.

4. The preparation method according to claim 1, characterized in that: The thickness of the carbon coating layer is 200nm to 1000nm; Preferably, the carbon coating layer has a thickness of 400nm to 600nm; Preferably, the carbon coating layer comprises one or more of nano-conductive graphite or carbon-coated particles.

5. The preparation method according to claim 1, characterized in that: The diameter of the through holes is 0.1 μm to 2 μm, and the interval between the through holes is 0.05 cm to 0.5 cm; Preferably, the diameter of the through holes is 1 μm to 1.5 μm, and the interval between the through holes is 0.1 cm to 0.4 cm.

6. The preparation method according to claim 1, characterized in that: The lithium alloy is at least one of lithium indium alloy, lithium aluminum alloy, lithium magnesium alloy, lithium tin alloy and lithium silver alloy; Preferably, the atomic percentage of metallic lithium in the lithium alloy foil is 10% to 98%; Preferably, the atomic percentage of metallic lithium in the lithium alloy foil is 40% to 60%.

7. The preparation method according to claim 1, characterized in that: The negative electrode slurry comprises negative electrode active particles, a sulfide electrolyte and a binder, wherein the sulfide electrolyte is at least one of lithium germanium phosphorus sulfur, lithium silicon phosphorus sulfur chlorine and lithium boron sulfur electrolyte; Preferably, the particle size D50 of the sulfide electrolyte is 0.1 μm to 6 μm.

8. The preparation method according to claim 7, characterized in that: The binder is one or more of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene type block copolymer (SEPS), styrene-butadiene rubber, nitrile rubber, chloroprene rubber and ethylene-propylene rubber; Preferably, the percentage of the binder is 0.5% to 6%.

9. The preparation method according to claim 7, characterized in that: The negative electrode active particles are one or more of silicon, silicon-carbon material, silicon-oxygen material and graphite material.

10. An all-solid-state battery composite negative electrode sheet prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The invention comprises a negative electrode slurry layer (01), a carbon coating layer (02), a first copper foil (03), a lithium alloy layer (04) and a second copper foil (05) which are overlapped in sequence, wherein the carbon coating layer (02) and the first copper foil (03) are provided with through holes, the diameter of the through holes is 0.1 μm to 2 μm, and the intervals between the through holes are 0.05 cm to 0.5 cm.

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