A method for preparing a lightweight lithium metal anode and a secondary battery
The battery's specific energy and safety were improved by increasing the tensile strength of the polymer membrane material. The density of the copper foil was 8.93 g/cm³, the density of the polymer membrane was 0.7–1.4 g/cm³, and the density of the polymer membrane material itself was 0.7–1.4 g/cm³.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA ENERGY LITHIUM
- Filing Date
- 2022-01-27
- Publication Date
- 2026-05-26
AI Technical Summary
In existing lithium batteries, the metallic lithium anode is easily stretched and broken, resulting in an uneven surface that affects the battery's specific energy and safety. Furthermore, the tensile strength of the polymer film is insufficient, making mass production difficult.
A pre-frozen polymer film is used, combined with a step-by-step cold rolling process, on which a copper layer is deposited and a lithium/lithium alloy strip is laminated. Low-temperature hardening and low-pressure lamination are used to ensure a smooth surface.
Mass production of lightweight lithium metal anodes has been achieved, which improves battery specific energy and enhances safety. The proportion of copper foil in battery mass has been reduced, and battery specific energy has been increased by 10%. The polymer film plays an insulating role in the event of a short circuit.
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Figure CN116565148B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of energy storage technology, and in particular to a method for preparing a lightweight metallic lithium anode that can be used in secondary batteries. Background Technology
[0002] Lithium-ion batteries are widely used in aerospace, computers, mobile communication devices, and electric vehicles due to their high energy density, long cycle life, and wide operating temperature range. With societal development and technological advancements, the demands on the energy density and cycle life of lithium-ion batteries are increasing. Currently, lithium-ion batteries using graphite as the anode are insufficient to meet these demands, necessitating the development of novel anode and cathode materials with higher specific capacity. For anode materials, lithium metal possesses a high specific capacity (3860 mAh / g, 10 times that of graphite anodes) and the lowest redox potential (-3.04 V vs. standard hydrogen potential), effectively improving the battery's specific energy.
[0003] Currently, in manufactured batteries, the positive electrode material uses lithium iron phosphate, lithium cobalt oxide, or high-nickel ternary materials, which already contain lithium. The negative electrode uses very little metallic lithium (the metallic lithium thickness is less than 50µm). Because metallic lithium is very soft, it is easily stretched and broken without additional support when the metallic lithium thickness is less than 50µm. Therefore, the lightweight metallic lithium negative electrode currently used generally employs a lithium-copper composite strip, where copper acts as both a current collector and an auxiliary material. Currently, the copper foil thickness used in secondary batteries is 6-8µm, accounting for about 13% of the total battery mass. The battery's specific energy needs further improvement. Summary of the Invention
[0004] To improve battery specific energy, the inventors discovered that a thin layer of copper deposited on a lightweight polymer film can replace thick copper foil as the current collector. Directly laminating lithium metal / lithium alloy strips onto this polymer film significantly reduces the specific gravity of the lithium metal anode, thus increasing battery specific energy. However, because the polymer film is relatively soft and has low tensile strength, and the copper layer deposited on it is relatively thin (20nm-3um), the improvement in tensile strength is minimal. When pressure laminating lithium metal / lithium alloy strips onto this polymer-assisted film, the high lamination pressure causes varying degrees of stretching. This stretched polymer-assisted film may shrink back after the lamination pressure is removed, resulting in an uneven surface and wrinkles on the lightweight lithium metal anode. To obtain a smooth lightweight lithium metal anode, the inventors adopted a process of pre-freezing followed by step-by-step low-pressure cold rolling, avoiding the shrinkage of the stretched polymer-assisted film and thus successfully achieving mass production of lightweight lithium metal anodes.
[0005] One aspect of the present invention provides a method for preparing a lightweight lithium metal anode, comprising:
[0006] (1) A copper layer is vapor-deposited on at least one surface of a polymer membrane to obtain a polymer-assisted membrane;
[0007] (2) Place the polymer-assisted membrane in a freezing device and freeze it;
[0008] (3) The lithium metal / lithium alloy strip and the frozen polymer auxiliary film are fed into the step-by-step cold rolling unit with the lithium metal / lithium alloy facing the copper metal layer. The primary lithium metal anode is obtained by pressure bonding through the first cooling roller of the step-by-step cold rolling unit, and the lightweight lithium metal anode is obtained by pressure bonding through the second cooling roller.
[0009] The pressure of the first cooling roller pressure bonding and the pressure of the second cooling roller pressure bonding are 1-20 MPa.
[0010] In this invention, the polymer-assisted film is hardened by low temperature, which increases its tensile strength. Combined with two-step cooling roller low-pressure lamination, it is beneficial to laminate the lithium metal / lithium alloy strip onto the polymer-assisted film to obtain a lithium metal anode with a smooth surface.
[0011] Optionally, the polymer membrane material includes at least one of polyethylene terephthalate, polypropylene, polyethylene, polybutylene terephthalate, polycarbonate, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyimide, polystyrene, polypropylene, poly(p-phenylene terephthalamide), poly(diphenylene dicarboxylate), acrylonitrile-butadiene-styrene copolymer, aramid, epoxy resin, polyoxymethylene, phenolic resin, silicone rubber, starch and its derivatives, cellulose and its derivatives, protein and its derivatives, polyethylene glycol and its crosslinks, and polyvinyl alcohol and its crosslinks.
[0012] Optionally, the vapor deposition method includes: vacuum evaporation, magnetron sputtering, and ion plating.
[0013] Optionally, the thickness of the polymer membrane is 3-10 μm.
[0014] Optionally, the thickness of the copper layer is 20nm-3um, preferably 100nm-2um, and more preferably 0.5-2um.
[0015] Optionally, the thickness of the lithium metal strip / lithium alloy strip is 1-100 μm, preferably 3-50 μm, more preferably 3-20 μm, and optionally, the lithium metal / lithium alloy strip has a protective film.
[0016] Optionally, the protective film material is a polyester or polyolefin, such as polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, or polypropylene. An anti-stick material, such as white oil or silicone oil, may be applied to the surface of the protective film near the lithium / lithium alloy metal.
[0017] Optionally, the lithium alloy is an alloy formed by metallic lithium with one or more of Ag, Al, Au, Ba, Be, Bi, C, Ca, Cd, Co, Cr, Cs, Fe, Ga, Ge, Hf, Hg, In, Ir, K, Mg, Mn, Mo, N, Na, Nb, Ni, Pt, Pu, Rb, Rh, S, Se, Si, Sn, Sr, Ta, Te, Ti, Y, V, Zn, Zr, Pb, Pd, Sb, and Cu; the content of metallic lithium in the lithium alloy is typically 10-99.9% by weight.
[0018] Alternatively, the freezing equipment can be a freezer-like device, with a temperature set from -10°C to -18°C, and a freezing time of at least 2 hours before it can be taken out and used directly as a composite lithium metal / lithium alloy strip.
[0019] Alternatively, the cold rolling roll is cooled by circulating a coolant inside the roll, and the surface temperature of the roll is -15°C to -5°C.
[0020] Optionally, the pressure of the cooling roller pressure compounding is 1-20 MPa, preferably 1-10 MPa, more preferably 1-5 MPa, and preferably, the pressure of the second roller pressure compounding is greater than the pressure of the first roller pressure compounding.
[0021] In a specific example, step-by-step cold rolling includes the following steps:
[0022] Unwind the first protective film and the second protective film, unwind the first lithium metal / lithium alloy strip and the second lithium metal / lithium alloy strip, unwind the polymer auxiliary film, and place the polymer auxiliary film in the middle position. The lithium layer / lithium alloy layer of the first lithium metal / lithium alloy strip and the second lithium metal / lithium alloy strip are arranged opposite to the polymer film. The first protective film and the polymer auxiliary film are arranged opposite to each other with the first lithium metal / lithium alloy strip as the center, and the second protective film and the polymer auxiliary film are arranged opposite to each other with the second lithium metal / lithium alloy strip as the center. The five layers are unwound simultaneously, and after being combined with small pressure by the first cooling roller, a primary lithium metal anode is obtained. After being combined with small pressure by the second cooling roller, a lightweight lithium metal anode is obtained by winding.
[0023] For the first lithium metal / lithium alloy strip and / or the second lithium metal / lithium alloy strip with their own protective films, the first and / or second protective films in the above steps can be omitted. Unwind the first lithium metal / lithium alloy strip and the second lithium metal / lithium alloy strip, unwind the polymer auxiliary film, and place the polymer auxiliary film in the middle position, with the lithium layer / lithium alloy layer of the first lithium metal / lithium alloy strip and the polymer film facing each other. Unwind all three layers simultaneously, and after passing through the first cooling roller under low pressure to form a primary lithium metal anode, pass through the second cooling roller under low pressure to form a secondary lithium metal anode, and then rewind to obtain a lightweight lithium metal anode.
[0024] Another aspect of the present invention provides a secondary battery comprising a lightweight lithium metal anode prepared by the above method, and a positive electrode / separator / electrolyte or a positive electrode / solid electrolyte.
[0025] Optionally, the lightweight lithium metal anode can be used directly as the anode of a secondary battery, and can be assembled with a positive electrode / electrolyte / separator to form a liquid secondary battery; it can also be assembled with a positive electrode / solid electrolyte (with or without electrolyte) to form a semi-solid or solid secondary battery.
[0026] Optionally, the positive electrode active material can be selected from lithium iron phosphate, lithium cobalt oxide, high-nickel ternary materials (NCM nickel-cobalt-manganese ternary or NCA nickel-cobalt-aluminum ternary), etc.
[0027] Optionally, the diaphragm can be selected from polypropylene (PP) membrane or polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite membrane, and the diaphragm can be coated with ceramic or PVDF (polyvinylidene fluoride).
[0028] Optionally, the solid electrolyte may be selected from sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes (e.g., composed of polyethylene oxide, PVDF, polyacrylonitrile, etc. and lithium salts), sulfide solid electrolytes and polymer mixed electrolytes, oxide solid electrolytes and polymer mixed electrolytes.
[0029] Optionally, the electrolyte may be an ester-based electrolyte or an ether-based electrolyte.
[0030] Alternatively, the secondary battery is assembled using a stacking or winding process.
[0031] The technical solution of the present invention achieves at least one of the following beneficial effects:
[0032] 1. Lightweight lithium metal anodes with smooth surfaces can be mass-produced through three mature processes: vapor deposition, freezing, and rolling, which can be used for industrial production and application.
[0033] 2. By replacing part of the copper foil with a polymer film, the battery's specific energy can be increased by approximately 10% (the density of copper foil is 8.93 g / cm³). 3 The density of the polymer membrane material is 0.7–1.4 g / cm³. 3 ).
[0034] 3. High safety: When a short circuit occurs in the battery, the polymer film in the lightweight lithium metal anode material acts as an insulating barrier between the positive and negative electrodes. Attached Figure Description
[0035] Figure 1 This is a process flow diagram for preparing a lightweight lithium metal anode according to the present invention.
[0036] Figure 2 This is another process flow diagram for preparing a lightweight lithium metal anode according to the present invention.
[0037] Figure 3 This is a schematic diagram of the lightweight lithium metal anode prepared according to the present invention.
[0038] Figure 4 This is a photograph of the lightweight lithium metal anode product from Example 1.
[0039] Figure 5 Photograph of the lightweight metallic lithium anode product for Comparative Example 1. Detailed Implementation
[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0041] Preparation of polymer-assisted films: These films were prepared using a vacuum evaporation apparatus at a high vacuum of 10... -3 At a temperature of 800℃, a 1µm thick copper layer is deposited on both surfaces of a BOPP (biaxially oriented polypropylene) film to obtain a polymer auxiliary film. The polymer auxiliary film is then packaged in a dried aluminum-plastic bag and stored in a freezer for at least two hours before it can be used in products.
[0042] Step-by-step cold rolling apparatus and process: The step-by-step cold rolling apparatus includes an unwinding end 10, a cryogenic roll composite end 20, and a winding end 30, such as Figure 1 and 2 As shown.
[0043] For unsupported lithium metal / lithium alloy strips, the following is adopted: Figure 1The process produces lightweight lithium metal anodes. The lithium metal / lithium alloy strip requires a protective film. At the unwinding end 10, a first protective film (101), a second protective film (102), a first lithium metal / lithium alloy strip (103), a second lithium metal / lithium alloy strip (104), and a polymer auxiliary film (105) frozen for more than 2 hours are simultaneously unwound. The strips are then transferred through a support roller (106), and a web alignment sensor (107) aligns the first and second lithium / lithium alloy strips and the polymer auxiliary film. Driven by a tension sensor (108), and then through the support roller again, the strips enter the frozen roll composite end 20. Cooling oil (203) is introduced into the cooling roller to... The primary lithium metal anode is obtained by low-pressure lamination of the first cooling roller (201) at a pressure of 1-5 MPa. Due to the low pressure during lamination, the primary lithium metal anode has some problems with poor adhesion between lithium and the polymer auxiliary film. After passing through the support roller, the primary lithium metal anode product is lamination of the second cooling roller (202) at a pressure of 1-10 MPa. After passing through the support roller, it enters the winding end 30. After correction by the correction detection sensor 107, it is wound up to obtain a lightweight lithium metal anode (301). The first protective film (101) and the second protective film (102) are wound up at the same time. The wound protective film can be reused.
[0044] For lithium metal / lithium alloy strips that already have a protective film, the following methods are adopted: Figure 2 The process involves unwinding a first lithium / lithium alloy strip (103') with a protective film and a second lithium / lithium alloy strip (104') with a protective film, along with a polymer auxiliary film (105) that has been frozen for more than 2 hours. The strips are then passed through a support roller (106), and aligned by a web-correction sensor (107). Following the transmission of the tension sensor (108), the strips are passed through the support roller again. Cooling oil (203) is introduced into the cooling roller for cooling. The strips are then combined under low pressure using the first cooling roller (201). The pressure is set... At 1-5 MPa, a primary lithium metal anode is obtained. Due to the low pressure during the composite process, the primary lithium metal anode has some issues with the adhesion between lithium and the polymer auxiliary film. After being transferred by the support roller, the primary lithium metal anode product is composited under low pressure by the second cooling roller (202), with the pressure set at 1-10 MPa. After being transferred by the support roller and corrected by the correction detection sensor 107, it is wound up to obtain a lightweight lithium metal anode (301). At the same time, the first protective film (302) and the second protective film (303) are also wound up. The wound protective film can be reused.
[0045] Protective films 101, 102, 302, and 303 can be made of the same material or different materials.
[0046] Figure 3 This is a schematic diagram of the lightweight lithium metal anode prepared according to the present invention, wherein a copper layer 2 is provided on two surfaces of a polymer film 1, and a lithium metal / lithium alloy strip 3 is provided on the side of the copper layer 2 facing away from the polymer film 1. The lightweight lithium metal anode of the present invention has a smooth surface without wrinkles.
[0047] Example 1:
[0048] Lightweight lithium anode preparation: A rolled BOPP (biaxially oriented polypropylene) film with a thickness of 4 μm was used as the substrate. The rolled BOPP film was first dried in a vacuum oven at 60°C for 24 hours, and then deposited using a vacuum evaporation device (vacuum degree 10). -3 Copper layers with a thickness of 1 μm are deposited on both the top and bottom surfaces of a rolled BOPP film at a temperature of 800°C (Pa) to obtain a current collector with a metallic copper layer. The current collector is then packaged in a dried aluminum-plastic bag and stored in a freezer at -10°C to -18°C for at least two hours before it can be used in products.
[0049] Using a winding and unwinding system and two roller presses placed at the front and rear, two rolls of lithium metal strip (20µm thick) are unwound, with a current collector unwound in the middle. The strips are first laminated using the first roller press at a pressure of 1 MPa, and then laminated again using the second roller press at a pressure of 2 MPa, resulting in a tightly bonded three-layer lithium metal anode. The surface temperature of the rolls in the first and second roller presses is -10℃. A photograph of the resulting lightweight lithium metal anode product is shown below. Figure 4 As shown, the surface of lithium metal is flat.
[0050] Comparative Example 1:
[0051] Preparation of lithium metal anode: A rolled BOPP (biaxially oriented polypropylene) film with a thickness of 4 μm was used as the substrate. The rolled BOPP film was first dried in a vacuum oven at 60°C for 24 hours, and then subjected to vacuum evaporation (vacuum degree 10). -3 Copper layers with a thickness of 1 μm are deposited on the top and bottom surfaces of a rolled BOPP film within a range of Pa (temperature 800℃) to obtain a current collector.
[0052] Using a winding and unwinding system and two roller presses placed at the front and rear, two rolls of lithium metal strip (20µm thick) are unwound, and a current collector is unwound in the middle. The layers are then laminated using a roller press at room temperature with a pressure set to 2 MPa, resulting in a three-layer, tightly bonded lithium metal anode. Figure 5 As shown, the surface of lithium metal has many wrinkles, making it unsuitable for battery use.
Claims
1. A method for preparing a lightweight lithium metal anode, characterized in that, The method includes: (1) A copper layer is vapor-deposited on at least one surface of a polymer membrane to obtain a polymer-assisted membrane; (2) Place the polymer-assisted membrane in a freezing device and freeze it; (3) The lithium metal / lithium alloy strip and the frozen polymer auxiliary film are fed into the step-by-step cold rolling device with the lithium metal / lithium alloy facing the copper metal layer. The primary lithium metal anode is obtained by pressure bonding through the first cooling roller of the step-by-step cold rolling device, and the lightweight lithium metal anode is obtained by pressure bonding through the second cooling roller. The pressure of the first cooling roller pressure bonding and the pressure of the second cooling roller pressure bonding are 1-20 MPa.
2. The method according to claim 1, characterized in that, The thickness of the lithium metal / lithium alloy strip is 1-100 μm, and optionally, the lithium metal / lithium alloy strip has a protective film.
3. The method according to claim 1, characterized in that, The thickness of the polymer film is 3-10 μm; and / or the thickness of the copper layer is 20 nm-3 μm.
4. The method according to claim 1, characterized in that, The polymer membrane material includes at least one of the following: polyethylene terephthalate, polypropylene, polyethylene, polybutylene terephthalate, polycarbonate, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyimide, polystyrene, polypropylene, poly(p-phenylene terephthalamide), poly(diphenylene dicarboxylate), acrylonitrile-butadiene-styrene copolymer, aramid, epoxy resin, polyoxymethylene, phenolic resin, silicone rubber, starch and its derivatives, cellulose and its derivatives, protein and its derivatives, polyethylene glycol and its crosslinks, and polyvinyl alcohol and its crosslinks.
5. The method according to claim 1, characterized in that, Vapor deposition methods include: vacuum evaporation, magnetron sputtering, and ion plating.
6. The method according to claim 1, characterized in that, The freezing equipment is set to a temperature of -10°C to -18°C, and the freezing time is at least 2 hours.
7. The method according to claim 1, characterized in that, The cooling roller is cooled by circulating coolant inside the roller, and the surface temperature of the roller is -15°C to -5°C.
8. The method according to claim 1, characterized in that, The pressure of the first cooling roller pressure bonding and the second cooling roller pressure bonding is 1-10 MPa.
9. The method according to claim 2, characterized in that, The lithium metal / lithium alloy strip has a protective film, which is made of polyester or polyolefin.
10. The method according to claim 9, characterized in that, The polyesters or polyolefins include polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polypropylene.
11. The method according to claim 9, characterized in that, The protective film has an anti-sticking material, white oil or silicone oil, on the surface near the lithium / lithium alloy metal.
12. A secondary battery comprising a lightweight lithium metal anode prepared by the method of any one of claims 1-11, and further comprising a positive electrode / separator / electrolyte or a positive electrode / solid electrolyte.