Negative plate, battery and electric device

Abstract

The embodiment of the invention provides a negative plate, a battery and a power utilization device, the negative plate comprises a negative current collector, a carbon layer and a negative active material layer, and the carbon layer is arranged on at least one side of the negative current collector; the negative electrode active material layer is arranged on one side, deviating from the negative electrode current collector, of the carbon layer and comprises metal lithium or lithium alloy; the carbon layer comprises conductive carbon and a binder, and the conductive carbon comprises dot-shaped conductive carbon, one-dimensional conductive carbon and two-dimensional conductive carbon. The carbon layer is arranged between the negative electrode current collector and the negative electrode active material layer, the carbon layer formed by dotted conductive carbon, one-dimensional conductive carbon and two-dimensional conductive carbon has a three-dimensional structure and lithium affinity, and when the carbon layer is compounded with the negative electrode active material containing lithium through a rolling method, the rolling pressure can be reduced compared with that of a conventional current collector; and the stripping force between the negative electrode current collector and the negative electrode active material layer is obviously improved, so that the condition that the negative electrode current collector is separated from the lithium-containing negative electrode active material layer is further avoided, and the electrochemical performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode, a battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries have become the preferred choice for consumer electronics batteries and new energy vehicle power batteries due to their advantages such as high energy density, long cycle life, and no memory effect. However, the low specific capacity of the graphite or silicon-doped anode used in existing lithium-ion batteries limits the further improvement of their energy density.

[0003] Lithium metal anodes have a specific capacity of 3860 mAh / g, and their use will significantly improve the energy density of lithium batteries. Existing lithium metal anodes generally use copper foil as the current collector. However, the interfacial affinity between copper foil and lithium metal is insufficient. To achieve mechanical bonding between the lithium layer and copper foil, ultra-high rolling pressure is required. During long-term storage or operation, the lithium-copper composite strip obtained by rolling is prone to interfacial delamination between the lithium layer and copper foil due to the difference in thermal expansion coefficients between lithium metal and copper foil and the lack of interfacial chemical bonding. This leads to a significant increase in interfacial contact resistance, causing electrochemical performance degradation problems such as battery capacity decay and reduced cycle life. Summary of the Invention

[0004] This application provides a negative electrode sheet, a battery, and an electrical device, aiming to solve the problem that the existing lithium layer is prone to peeling off from the copper foil.

[0005] In a first aspect, this application provides a negative electrode sheet, including a negative electrode current collector, a carbon layer and a negative electrode active material layer, wherein the carbon layer is disposed on at least one side of the negative electrode current collector; the negative electrode active material layer is disposed on the side of the carbon layer opposite to the negative electrode current collector, and the negative electrode active material layer comprises metallic lithium or a lithium alloy. The carbon layer includes conductive carbon and a binder, and the conductive carbon includes dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon.

[0006] In this application, a carbon layer is disposed between the negative electrode current collector and the negative electrode active material layer. The carbon layer formed by dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon has a three-dimensional structure and lithium affinity. When combined with the lithium-containing negative electrode active material by the rolling method, the rolling pressure can be reduced compared with conventional current collectors, and the peeling force between the negative electrode current collector and the negative electrode active material layer is greater than 80 N / m. The peeling force is significantly improved, which further avoids the separation of the current collector and the lithium-containing negative electrode active material layer during storage or operation, and improves the electrochemical performance of the battery.

[0007] Specifically, dot-shaped conductive carbon provides short-range conductive pathways in the carbon layer, while one-dimensional and two-dimensional conductive carbons provide long-range conductive pathways in the carbon layer. The combination of these three types of conductive carbons provides multi-dimensional high conductivity for the negative electrode, and the one-dimensional and two-dimensional conductive carbons construct a three-dimensional framework in the carbon layer, further improving the mechanical strength and overall stability of the negative electrode sheet.

[0008] Optionally, the mass ratio of the dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon is 6-9:2-3:1. By limiting the mass ratio of the dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon to the above range, the carbon layer forms a complementary "point-line-surface" conductive pathway, improving the conductivity of the negative electrode. Within this mass ratio range, the dot-shaped conductive carbon is dispersed between the one-dimensional and two-dimensional conductive carbons, serving as the basic framework of the conductive network. The one-dimensional and two-dimensional conductive carbons further reduce the transport resistance of electrons at the macroscopic scale and interface. Simultaneously, the dot-shaped conductive carbon has a microporous structure, providing storage sites for lithium ions. The one-dimensional conductive carbon within this range can form mesopores in the carbon layer, giving the carbon layer a porous structure, improving its lithiophilicity, and increasing the bonding strength between the carbon layer and the lithium-containing negative electrode active material layer. The layered structure of the two-dimensional conductive carbon gives the carbon layer a high porosity, further improving its lithiophilicity.

[0009] Optionally, the dotted conductive carbon includes at least one of Super P, furnace black, and acetylene black; And / or, the one-dimensional conductive carbon includes at least one of whisker carbon nanotubes, single-walled carbon nanotubes, multi-walled carbon nanotubes, and VGCF. And / or, the two-dimensional conductive carbon includes graphene.

[0010] By selecting the aforementioned conductive carbon to form a conductive network in the carbon layer, the conductivity of the carbon layer is improved while its lithium affinity is also enhanced, thus increasing the bonding strength between the carbon layer and the negative electrode active material layer and reducing the rolling pressure when the lithium-containing negative electrode active material layer and the carbon layer are combined.

[0011] Optionally, the conductive carbon surface is loaded with a lithium-philic metal and / or a lithium-philic compound. By loading a lithium-philic metal or a lithium-philic compound onto the conductive carbon surface, lithium is chemically bonded to guide uniform deposition.

[0012] Optionally, with the carbon layer content being 100%, the mass content of the conductive carbon is 10%-60%, and the mass content of the binder is 40%-90%. By limiting the content of conductive carbon and binder within the above ranges, the conductivity of the carbon layer meets the requirements, while ensuring the bonding strength between the carbon layer and the negative electrode current collector and the negative electrode active material layer.

[0013] Optionally, the thickness of the carbon layer is 0.75-3 μm. By limiting the thickness of the carbon layer within this range, a strong bond is ensured between the carbon layer and the negative electrode active material layer, while simultaneously guaranteeing the energy density of the battery and improving its electrochemical performance.

[0014] Optionally, the negative electrode further includes a lithium-loving modified layer, which is located between the negative electrode current collector and the carbon layer; The lithiophilic modification layer comprises a lithiophilic metal and / or a metal oxide, wherein the lithiophilic metal comprises at least one selected from Au, Ag, Zn, Sn, Mg, Al, In, Ti, Nb, and Mo; and the metal oxide comprises ZnO or SnO. x Al2O3, MoO x TiO x At least one of the following. By setting a lithiophilic modification layer, the lithium nucleation overpotential is reduced, and uniform lithium nucleation is promoted. This ensures that even after the active material in the negative electrode active material layer is consumed in the later stages of cycling, the lithiophilic modification layer can still guarantee uniform deposition and stripping of lithium metal during charge and discharge.

[0015] Optionally, the negative electrode further includes an SEI layer, which is disposed on the side of the negative electrode active material layer opposite to the carbon layer. The SEI layer includes at least one of lithium-containing fluorides, oxides, nitrides, and halides. The aforementioned SEI layer has high ionic conductivity. By setting an SEI layer as an interface layer on the negative electrode active material layer, uniform lithium-ion transport can be promoted, and lithium dendrite formation can be avoided.

[0016] Secondly, this application provides a battery including the aforementioned negative electrode. By selecting the aforementioned negative electrode, the battery exhibits better cycle performance. It should be noted that the battery can be a stacked, wound, or cylindrical battery.

[0017] Thirdly, this application provides an electrical device including the battery described above. By using the battery with good cycle stability, the battery life of the electrical device is improved. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of a negative electrode sheet provided in another embodiment of this application; Figure 3 These are cross-sectional electron microscope (SEM) images and EDS images of the negative electrode sheet provided in Embodiment 1 of this application; Figure 4 These are cross-sectional electron microscope (SEM) images and EDS images of the negative electrode sheet provided in Embodiment 2 of this application; Figure 5These are cross-sectional electron microscope (TEM) images and EDS images of the negative electrode sheet provided in Comparative Example 1 of this application; Figure 6 This is the negative electrode sheet provided in Comparative Example 2 of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Negative electrode current collector; 11. Base film; 12. Conductive layer; 2. Carbon layer; 3. Negative electrode active material layer; 4. Lithophilic modification layer; 5. SEI layer. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] like Figure 1 and Figure 2 As shown, one embodiment of this application provides a negative electrode sheet, including a negative electrode current collector 1, a carbon layer 2 and a negative electrode active material layer 3. The carbon layer 2 is disposed on at least one side of the negative electrode current collector 1; the negative electrode active material layer 3 is disposed on the side of the carbon layer 2 opposite to the negative electrode current collector 1, and the negative electrode active material layer 3 includes metallic lithium or a lithium alloy. The carbon layer 2 includes conductive carbon and a binder, and the conductive carbon includes dot-shaped conductive carbon, one-dimensional conductive carbon and two-dimensional conductive carbon.

[0022] In this application, a carbon layer 2 is disposed between the negative electrode current collector 1 and the negative electrode active material layer 3. The carbon layer 2, formed by dotted conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon, has a three-dimensional structure and lithium affinity. When combined with the lithium-containing negative electrode active material by the rolling method, the rolling pressure can be reduced compared with conventional current collectors, and the peeling force between the negative electrode current collector 1 and the negative electrode active material layer 3 is greater than 80 N / m. The peeling force is significantly improved, which further avoids the separation of the current collector and the lithium-containing negative electrode active material layer 3 during storage or operation, thereby improving the electrochemical performance of the battery.

[0023] Specifically, dot-shaped conductive carbon provides short-range conductive pathways in carbon layer 2, while one-dimensional and two-dimensional conductive carbon provide long-range conductive pathways in carbon layer 2. The combination of the above three types of conductive carbon provides multi-dimensional high conductivity for the negative electrode, and the one-dimensional and two-dimensional conductive carbon construct a three-dimensional framework in carbon layer 2, further improving the mechanical strength and overall stability of the negative electrode sheet.

[0024] In one embodiment, the mass ratio of the dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon is 6-9:2-3:1. By limiting the mass ratio of the dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon to the above range, the carbon layer 2 forms a complementary "point-line-surface" conductive pathway, improving the conductivity of the negative electrode. Within this mass ratio range, the dot-shaped conductive carbon is dispersed between the one-dimensional and two-dimensional conductive carbons, serving as the basic framework of the conductive network. The one-dimensional and two-dimensional conductive carbons further reduce the transport resistance of electrons at the macroscopic scale and interface. Simultaneously, the dot-shaped conductive carbon has a microporous structure, providing storage sites for lithium ions. The one-dimensional conductive carbon within this range can form mesopores in the carbon layer 2, giving the carbon layer 2 a porous structure, improving its lithiophilicity, and increasing the bonding strength between the carbon layer 2 and the lithium-containing negative electrode active material layer 3. The layered structure of the two-dimensional conductive carbon gives the carbon layer 2 a high porosity, further improving its lithiophilicity.

[0025] Specifically, the mass ratio of dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon includes, but is not limited to, 6:2:1, 6:3:1, 7:2:1, 7:3:1, 8:2:1, 8:3:1, 9:2:1, or 9:3:1.

[0026] The mass of dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon can be obtained by thermogravimetric analysis (TGA). Specifically, the weight loss curve of the carbon layer after removing the binder is tested in an air atmosphere, and the mass ratio of the three types of conductive carbon is obtained by backfitting the weight loss rates of dot-shaped, one-dimensional, and two-dimensional conductive carbon.

[0027] In one embodiment, the dotted conductive carbon includes at least one of Super P, furnace black, and acetylene black; And / or, the one-dimensional conductive carbon includes at least one of whisker carbon nanotubes, single-walled carbon nanotubes, multi-walled carbon nanotubes, and VGCF. And / or, the two-dimensional conductive carbon includes graphene.

[0028] By selecting the aforementioned conductive carbon to form a conductive network in the carbon layer 2, the conductivity of the carbon layer 2 is improved, while the lithium affinity of the carbon layer 2 is also improved, the bonding strength between the carbon layer 2 and the negative electrode active material layer 3 is increased, and the rolling pressure when the lithium-containing negative electrode active material layer 3 and the carbon layer 2 are combined is reduced.

[0029] The specific types of dotted conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon in carbon layer 2 are not limited, and can be any combination of the above types. Preferably, the conductive carbon is furnace black, carbon nanotubes, and graphene.

[0030] In one embodiment, the conductive carbon surface is loaded with a lithiophilic metal and / or a lithiophilic compound. By loading a lithiophilic metal or a lithiophilic compound onto the conductive carbon surface, lithium is chemically bonded to guide uniform deposition. Specifically, the lithiophilic metal includes, but is not limited to, silver (Ag), gold (Au), tin (Zn), or indium (In). The lithiophilic compound includes, but is not limited to, LiF or Li3N.

[0031] Furthermore, the mass content of the lithium-loving metal and / or lithium-loving compound in the carbon layer 2 is 0.1%-10%. By limiting the content of the lithium-loving metal and / or lithium-loving compound within the above range, lithium can be uniformly deposited on the carbon layer 2.

[0032] Specifically, the mass content of the lithium-loving metal and / or lithium-loving compound in carbon layer 2 includes, but is not limited to, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0033] In one embodiment, with the carbon layer 2 content being 100%, the mass content of the conductive carbon is 10%-60%, and the mass content of the binder is 40%-90%. By limiting the content of conductive carbon and binder within the above ranges, the conductivity of the carbon layer 2 is ensured to meet the requirements, while also guaranteeing the bonding strength between the carbon layer 2 and the negative electrode current collector 1 and the negative electrode active material layer 3.

[0034] Specifically, the mass content of conductive carbon includes, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. The mass content of the binder includes, but is not limited to, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%. Preferably, the mass content of conductive carbon is 20%-40%, and the mass content of the binder is 60%-80%.

[0035] Further, the binder includes at least one of polyacrylate (PAA), ethylene-acrylic acid copolymer (EAA), polyvinylidene fluoride (PVDF), and hydrogenated nitrile butadiene rubber (HNBR). Preferably, the binder includes polyacrylate.

[0036] In one embodiment, the thickness of the carbon layer 2 is 0.75-3 μm. By limiting the thickness of the carbon layer 2 to this range, a strong bond is ensured between the carbon layer 2 and the negative electrode active material layer 3, while simultaneously guaranteeing the energy density of the battery and improving its electrochemical performance.

[0037] Specifically, the thickness of carbon layer 2 includes, but is not limited to, 0.75 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Preferably, the thickness of carbon layer 2 is 0.75-1.5 μm. The thickness of carbon layer 2 can be obtained by interfacial scanning electron microscopy.

[0038] In one embodiment, the negative electrode further includes a lithium-loving modified layer 4, which is located between the negative electrode current collector 1 and the carbon layer 2; The lithiophilic modification layer 4 comprises a lithiophilic metal and / or a metal oxide, wherein the lithiophilic metal comprises at least one selected from Au, Ag, Zn, Sn, Mg, Al, In, Ti, Nb, and Mo; and the metal oxide comprises ZnO or SnO. x Al2O3, MoO x TiO x At least one of the following. By setting the lithiophilic modification layer 4, the lithium nucleation overpotential is reduced, and uniform nucleation of metallic lithium is promoted. This ensures that even after the active material in the negative electrode active material layer 3 is consumed in the later stages of cycling, the lithiophilic modification layer 4 can still ensure uniform deposition and stripping of metallic lithium during charging and discharging.

[0039] The lithiophilic modified layer 4 can be prepared on at least a portion of the surface of the negative electrode current collector 1 by electroplating, magnetron sputtering and / or vacuum evaporation.

[0040] Furthermore, the thickness of the lithiophilic modified layer 4 is 0-500 nm. Specifically, the thickness of the lithiophilic modified layer 4 includes, but is not limited to, 1-10 nm, 10-50 nm, 50-100 nm, 100-150 nm, 150-200 nm, 200-250 nm, 250-300 nm, 300-350 nm, 350-400 nm, 400-450 nm, or 450-500 nm.

[0041] In one embodiment, the negative electrode further includes an SEI layer 5, which is disposed on the side of the negative electrode active material layer 3 opposite to the carbon layer 2. The SEI layer 5 includes at least one of lithium-containing fluorides, oxides, nitrides, and halides. The SEI layer 5 has high ionic conductivity. By providing the SEI layer 5 as an interface layer on the negative electrode active material layer 3, uniform lithium ion transport can be promoted, and lithium dendrite formation can be avoided.

[0042] Furthermore, the thickness of the SEI layer 5 is 0-2 μm, specifically, the thickness of the SEI layer 5 includes, but is not limited to, 0.5 μm, 1 μm, 1.5 μm, or 2 μm. The SEI layer 5 can be generated on the surface of the negative electrode active material layer 3 through in-situ reaction to produce an artificial SEI rich in F, S, and N. For example, a compound containing an aminosulfonyl fluoride structure can be dissolved in an organic solvent to form a solution, and the lithium metal negative electrode can be immersed in the solution to generate an SEI layer 5 rich in F, S, and N in situ on the surface of the negative electrode active material layer 3. Alternatively, the SEI layer 5 can be prepared on the surface of the negative electrode active material layer 3 by physical vapor deposition.

[0043] In one embodiment, the negative electrode current collector 1 is a metal foil or a composite current collector. When the negative electrode current collector 1 is a metal foil, its thickness is 2.5-9 μm. The material of the metal foil includes, but is not limited to, copper, nickel, tin, or stainless steel.

[0044] When the negative electrode current collector 1 is a composite current collector, its thickness is 4-50 μm. Preferably, the thickness of the composite current collector is 3.5-17 μm. The composite current collector includes a base film 11 and a conductive layer 12. The base film 11 is made of at least one of polyethylene (PE), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), polyethylene (PE), polyamide (PA), polyphenylene sulfide (PPS), and polyacrylonitrile (PAN), and the thickness of the base film 11 is 1-20 μm.

[0045] The conductive layer 12 includes, but is not limited to, copper, nickel, or tin.

[0046] Furthermore, the composite current collector also includes a substrate layer for increasing the bonding force between the base film 11 and the conductive layer 12. The substrate layer is located between the base film 11 and the conductive layer 12 and has a thickness of 5-1000 nm. The substrate layer is made of at least one of nickel (Ni), chromium (Cr), titanium (Ti), zinc (Zn), aluminum (Al), and silicon (Si).

[0047] In the composite current collector structure, the elastic modulus and elongation of the base film 11 are significantly higher than those of the conductive layer 12. When lithium metal / lithium alloy strips are rolled onto the surface of the composite current collector, which is not lithium-affinity, wrinkles easily appear on the surface of the composite current collector, and the conductive layer 12 does not make complete contact with the lithium metal. In this application, the presence of the carbon layer 2 can effectively reduce the pressure required for rolling, prevent the base film 11 from undergoing plastic elongation, and allow the lithium metal / lithium alloy strip to be effectively laminated onto the surface of the composite current collector, resulting in a smooth lithium-copper composite strip surface.

[0048] One embodiment of this application provides a battery including the negative electrode sheet as described above. By selecting the aforementioned negative electrode sheet, the battery exhibits better cycle performance. It should be noted that the battery can be a pouch cell, cylindrical cell, or prismatic cell. Specifically, the battery can be a liquid battery, a semi-solid cell, or a solid cell.

[0049] The battery also includes a positive electrode, a separator, and an electrolyte.

[0050] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer, the positive active material layer being disposed on at least one side of the positive current collector, and the positive active material layer including a positive active material, such as lithium nickel cobalt manganese oxide (LiNi). x Mn y Co zAt least one of the following: O2, x+y+z=1), lithium iron manganese phosphate (LiFexMnyPO4, x+y=1), lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium-rich manganese-based, lithium nickel manganese oxide (LMNO), and lithium vanadium oxide phosphate (Li3V2(PO4)3, LiVOPO4).

[0051] In some embodiments, the electrolyte includes a liquid electrolyte, a semi-solid electrolyte, and an all-solid electrolyte, wherein the semi-solid electrolyte is obtained by mixing liquid electrolyte and solid electrolyte in any proportion.

[0052] Solid electrolytes include, but are not limited to, oxide electrolytes, sulfide electrolytes, halide electrolytes, polymer electrolytes, and polymer-inorganic composite solid electrolytes. The oxide solid electrolytes include, but are not limited to, NASICON (sodium fast ion conductor) structural materials, perovskite structural materials, anti-perovskite structural materials, LISICON (lithium fast ion conductor) structural materials, and garnet structural materials.

[0053] The electrolyte includes organic solvents, lithium salts, and additives. Organic solvents include, but are not limited to, PC (propylene carbonate), EC (ethylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), DEC (diethyl carbonate), DME (ethylene glycol dimethyl ether), or DOL (1,3-dioxolane). Lithium salts include, but are not limited to, lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroantimonyate (LiSbF6), and lithium bis(trifluoromethanesulfonate imine) (LiT). Lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiFSI or LiN(SO2CF3)2), lithium perchlorate (LiClO4), lithium iodide (LiI), lithium magnesium bis(fluorosulfonyl)imide (Li2Mg(N(SO2CF3)2)2), lithium trifluoromethanesulfonyl-perfluorobutylsulfonylimide (LiTNFSI), lithium fluorosulfonyl-perfluorobutylsulfonylimide (LiFNFSI), and lithium bis(oxalatoborate) (LiBOB).

[0054] In some embodiments, the separator includes, but is not limited to, PE separators, PP separators, nonwoven separators, and PI separators. Further, at least one side of the separator is provided with a coating, the coating comprising at least one of: an oxide solid electrolyte, an alkaline oxide, and a polymer binder; the oxide solid electrolyte comprises at least one of: NASICON (sodium fast ion conductor) type solid electrolyte, garnet type solid electrolyte, and perovskite type solid electrolyte. The alkaline oxide comprises at least one of: alumina, silicon oxide, zirconium oxide, titanium oxide, and boehmite; the polymer binder comprises at least one of: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), and aramid fiber.

[0055] One embodiment of this application provides an electrical device including the battery described above. By using the battery with good cycle stability, the battery life of the electrical device is improved. Exemplary examples include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, aircraft, and robots.

[0056] The present application will be further illustrated by the following examples.

[0057] Example 1 This embodiment illustrates the negative electrode sheet and battery disclosed in this application, and includes the following operating steps: 1. Negative electrode sheet The negative electrode current collector 1 is a 3.5μm copper current collector, and the negative electrode active material layer 3 is lithium metal with a thickness of 20μm; Carbon layer 2: Conductive carbon (acetylene black, single-walled carbon nanotubes, graphene = 7:2:1), binder polyacrylic acid and dispersant polyvinylpyrrolidone (PVP) are dispersed in water to form a slurry. The slurry is coated on both sides of the copper current collector and dried to form carbon layer 2 on the copper current collector.

[0058] The carbon layer 2 has a thickness of 1 μm, a conductive carbon content of 30%, and an adhesive content of 70%.

[0059] A copper current collector containing carbon layer 2 was placed between two 20μm lithium metal strips, and rolled using a 400mm diameter, 400mm width roller press at 200MPa pressure and 15m / min speed to obtain a lithium-copper composite strip.

[0060] 2. Positive electrode plate NCM811, conductive carbon black, and PTFE binder were added to NMP at a mass ratio of 96:2:2 to obtain a mixed slurry. The mixed slurry was coated onto a composite aluminum current collector, dried, and rolled to obtain a positive electrode sheet.

[0061] The composite aluminum current collector was obtained by vapor-depositing a 1μm aluminum coating on both sides of a 6μm PET base film 11.

[0062] 3. Electrolyte DOL and DME were mixed in a mass ratio of 1:1, dispersed, and then lithium salt LiTFSI was added with a concentration of 1 mol / L.

[0063] 4. Battery A separator is placed between the negative electrode sheets prepared above, and then the sandwich structure consisting of the negative electrode sheets, the negative electrode sheets and the separator is stacked, encapsulated with an aluminum-plastic film, and the battery is obtained after liquid injection and formation.

[0064] Example 2 Example 2 is used to illustrate the negative electrode and battery disclosed in this application, including most of the operation steps in Example 1 above, except that: the current collector is a 6.5μm composite copper current collector, including a 4.5μm PET base film 11 and a 1μm copper plating layer prepared on both sides of the base film 11.

[0065] A composite copper current collector containing carbon layer 2 was placed between two 20μm lithium metal strips and rolled using a 400mm diameter, 400mm width roller press at 120MPa pressure and 10 m / min speed to obtain a lithium copper composite strip.

[0066] Example 3 Example 3 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operation steps in Example 1 above, except that: the carbon layer 2 contains metallic silver nanoparticles, and the silver content is 5%.

[0067] Carbon layer 2: Conductive carbon (acetylene black, single-walled carbon nanotubes, graphene = 7:2:1), metallic silver nanoparticles, binder polyacrylic acid and dispersant polyvinylpyrrolidone (PVP) are dispersed in water to form a slurry. The slurry is coated on both sides of the copper current collector and dried to form carbon layer 2 on the copper current collector.

[0068] Example 4 Example 4 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operation steps in Example 1 above, except that: the carbon layer 2 contains metallic silver nanoparticles, and the silver content is 10%.

[0069] Carbon layer 2: Conductive carbon (acetylene black, single-walled carbon nanotubes, graphene = 7:2:1), metallic silver nanoparticles, binder polyacrylic acid and dispersant polyvinylpyrrolidone (PVP) are dispersed in water to form a slurry. The slurry is coated on both sides of the copper current collector and dried to form carbon layer 2 on the copper current collector.

[0070] Example 5 Example 5 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operation steps in Example 1 above, except that: the carbon layer 2 contains metallic silver nanoparticles, and the silver content is 0.01%.

[0071] Carbon layer 2: Conductive carbon (acetylene black, single-walled carbon nanotubes, graphene = 7:2:1), metallic silver nanoparticles, binder polyacrylic acid and dispersant polyvinylpyrrolidone (PVP) are dispersed in water to form a slurry. The slurry is coated on both sides of the copper current collector and dried to form carbon layer 2 on the copper current collector.

[0072] Example 6 Example 6 illustrates the negative electrode and battery disclosed in this application, including most of the operating steps in Example 1 above, except that a lithium-affinity modified layer 4, i.e., a Zn layer, with a thickness of 100 nm is provided between the copper current collector and the carbon layer 2.

[0073] Example 7 Example 7 illustrates the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1 above, except that an SEI layer 5 is provided on the surface of the lithium metal in the negative electrode active material layer 3.

[0074] The SEI layer on the surface of lithium metal is formed by physical vapor deposition (PVD). The main component of the SEI layer is Li2S, and its thickness is 70 nm.

[0075] Examples 8-20 Examples 8-20 are used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1 above, except that the formulation in Table 1 is used.

[0076] Table 1 Comparative Example 1 Comparative Example 1 is used to illustrate the negative electrode and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 is not provided.

[0077] Comparative Example 2 Comparative Example 2 is used to illustrate the negative electrode and battery disclosed in this application, including most of the operating steps in Example 2, except that the carbon layer 2 is not provided.

[0078] Comparative Example 3 Comparative Example 3 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 does not contain dotted conductive carbon acetylene black.

[0079] Comparative Example 4 Comparative Example 4 is used to illustrate the negative electrode and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 does not contain one-dimensional conductive carbon single-walled carbon nanotubes.

[0080] Comparative Example 5 Comparative Example 5 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 does not contain two-dimensional conductive carbon graphene.

[0081] Comparative Example 6 Comparative Example 6 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 contains only dotted conductive carbon acetylene black.

[0082] Comparative Example 7 Comparative Example 7 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 contains only one-dimensional conductive carbon single-walled carbon nanotubes.

[0083] Comparative Example 8 Comparative Example 8 is used to illustrate the negative electrode sheet and battery disclosed in this application, including most of the operating steps in Example 1, except that the carbon layer 2 contains only two-dimensional conductive carbon graphene.

[0084] Performance testing I. The following performance tests were performed on the negative electrode sheets and batteries prepared in the above embodiments and comparative examples: 1. Peel strength test: First, cut the electrode into strips 20mm wide, then place them in a constant temperature and humidity environment (temperature not exceeding 25°C, dew point not exceeding -30°C) for at least 8 hours. Select high-strength double-sided adhesive tape with an adhesion strength ≥150N / m and apply the tape smoothly to the surface of the active material layer of the electrode, ensuring no air bubbles.

[0085] For the sample with the tape applied, pre-separate the coating and current collector interface by about 20-30mm at the edge of the clamp. Fix one end of the current collector to the upper clamp of the universal testing machine, and fix the peeled clamp (tape + coating) to the lower clamp. Ensure the sample is perpendicular to the clamp. Set the peel angle to 180°, the peel speed to 50 mm / min, and the peel distance to 100mm, and take the average force value within this distance as the result. For a single embodiment or comparative example, multiple samples need to be tested (e.g., n≥3), and the average value is taken.

[0086] 2. Cyclic test: Charge to 4.3V at 0.33C at 25℃; discharge at 1C; discharge to 2.8V, record the specific capacity of the first discharge in mAh / g, and then cycle until the capacity retention rate is 80%, and record the number of cycles at this time.

[0087] The test results are shown in Table 2.

[0088] Table 2 Depend on Figure 3 It can be seen that the negative electrode has a five-layer structure, with pure copper in the middle, carbon layers 2 on both sides of the pure copper, and lithium metal (not shown in the EDS spectrum) in the carbon layers 2 furthest from the pure copper. The carbon layers 2 and the lithium metal bands are partially fused together. Figure 4 It can be seen that the negative electrode has a seven-layer structure. The middle layer is a PP polymer base film 11, and copper plating layers are applied to both sides of the PP polymer base film 11. A carbon layer 2 is located on the surface of the copper plating layers away from the base film 11. The material of the carbon layer 2 away from the pure copper is lithium metal, and the carbon layer 2 and the lithium metal strip are partially fused together. Figure 5 As can be seen, the negative electrode has a three-layer structure, with pure copper in the middle and lithium metal on both sides. Figure 6 As can be seen, the negative electrode sheet has wrinkles and cannot be used.

[0089] The test results of Examples 1 and 2 and Comparative Examples 1 and 2 show that the introduction of carbon layer 2 improves the peel strength and cycle performance between the lithium metal anode active material and the current collector. The test results of Examples 1 and 2 and Examples 3, 4, and 5 show that introducing the lithiophilic element Ag into carbon layer 2 slightly improves the peel strength and significantly enhances the cycle performance. Examples 8-11 show that when the conductive carbon content in carbon layer 2 is 10%-60%, the anode sheet exhibits high peel strength while the battery also has good cycle performance. As the conductive carbon content in carbon layer 2 increases, the peel strength decreases while the cycle performance improves; however, when the conductive carbon content is too high, reaching 70%, both peel strength and cycle performance show a significant downward trend. The test results of Examples 1 and 2 and Comparative Examples 3-8 show that when the conductive carbon composition of carbon layer 2 changes, the absence of dot-like conductive carbon significantly reduces cycle performance, while the absence of one-dimensional and two-dimensional conductive carbon reduces the surface roughness of carbon layer 2, thereby reducing peel strength. Furthermore, the test results of Examples 1 and 12-16 show that when the mass ratio of dotted conductive carbon: one-dimensional conductive carbon: two-dimensional conductive carbon is in the range of 6-9:2-3:1, the negative electrode sheet has high peel strength and the battery also has good cycle performance.

[0090] The test results of Examples 1 and 17-20 show that when the thickness of the carbon layer is in the range of 0.75-3 μm, the lithium metal anode active material and the current collector have high peel strength, while ensuring the energy density of the battery and improving the electrochemical performance of the battery.

[0091] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0092] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector, a carbon layer, and a negative electrode active material layer. The carbon layer is disposed on at least one side of the negative electrode current collector. The negative electrode active material layer is disposed on the side of the carbon layer opposite to the negative electrode current collector. The negative electrode active material layer includes metallic lithium or a lithium alloy. The carbon layer includes conductive carbon and a binder, and the conductive carbon includes dot-shaped conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon.

2. The negative electrode sheet according to claim 1, characterized in that, The mass ratio of the dotted conductive carbon, one-dimensional conductive carbon, and two-dimensional conductive carbon is 6-9:2-3:

1.

3. The negative electrode sheet according to claim 1, characterized in that, The dotted conductive carbon includes at least one of Super P, furnace black and acetylene black; And / or, the one-dimensional conductive carbon includes at least one of whisker carbon nanotubes, single-walled carbon nanotubes, multi-walled carbon nanotubes, and VGCF. And / or, the two-dimensional conductive carbon includes graphene.

4. The negative electrode sheet according to claim 1, characterized in that, The conductive carbon surface is loaded with a lithium-loving metal and / or a lithium-loving compound.

5. The negative electrode sheet according to claim 1, characterized in that, With the carbon layer content being 100%, the mass content of the conductive carbon is 10%-60%, and the mass content of the binder is 40%-90%.

6. The negative electrode sheet according to claim 1, characterized in that, The thickness of the carbon layer is 0.75-3 μm.

7. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet further includes a lithium-loving modified layer, which is located between the negative electrode current collector and the carbon layer; The lithiophilic modification layer comprises a lithiophilic metal and / or a metal oxide, wherein the lithiophilic metal comprises at least one selected from Au, Ag, Zn, Sn, Mg, Al, In, Ti, Nb, and Mo; and the metal oxide comprises ZnO or SnO. x Al2O3, MoO x TiO x At least one of them.

8. The negative electrode sheet according to claim 1, characterized in that, The negative electrode also includes an SEI layer, which is disposed on the side of the negative electrode active material layer away from the carbon layer. The SEI layer includes at least one of lithium-containing fluorides, oxides, nitrides, and halides.

9. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-8.

10. An electrical device, characterized in that, Includes the battery as described in claim 9.

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