Negative electrode material, negative electrode plate, and secondary battery and device comprising negative electrode material and negative electrode plate

Abstract

The invention provides a negative electrode material, a negative electrode plate, a secondary battery containing the negative electrode plate and a device. The negative electrode material comprises a lithium metal layer and a first protective layer, and the first protective layer comprises at least one of LiF, LiC6 and Li3N. The first protective layer is arranged on the surface of the lithium metal layer, and the first protective layer comprises at least one of LiF, LiC6 and Li3N. LiF, LiC6 or Li3N has good electronic insulativity and strength, and can relieve continuous decomposition of the electrolyte at the same time. More importantly, LiF, LiC6 or Li3N has relatively high interface energy for the lithium metal negative electrode, and diffusion of lithium ions on an electrolyte / lithium metal negative electrode interface is promoted by reducing an activation energy barrier, so that the lithium metal negative electrode is stabilized. Therefore, the first protective layer can control the deposition rate of lithium in the charge-discharge process, reduce the consumption of active lithium during the first charge, and improve the cycle performance of the lithium battery.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically relates to a negative electrode material, a negative electrode sheet, a secondary battery and a device including the same. Background Art

[0002] Among all metal elements, lithium metal has the smallest relative atomic mass (6.94) and the lowest standard electrode potential (3.045V). Its theoretical specific capacity can reach 3860 mAh / g. Therefore, using lithium metal as the negative electrode of a battery and cooperating with some high energy density positive electrode materials can significantly improve the energy density and working voltage of the battery.

[0003] However, lithium metal has extremely high activity. It easily reacts with the electrolyte, resulting in the consumption of lithium and the electrolyte. In addition, during the charge and discharge process, the difference in the deposition rate of lithium will form lithium dendrites, which may cause a safety risk of short circuit between the positive and negative electrodes in severe cases. At the same time, during the charge and discharge process, lithium metal will undergo severe expansion and contraction, resulting in an increase in the interfacial impedance. These problems lead to extremely poor cycle performance of lithium metal batteries.

[0004] Existing technologies for improving the cycle performance of lithium metal batteries usually rely on lithium-aluminum alloys or composite negative electrode coatings to avoid direct contact between lithium metal and the electrolyte, so as to reduce the consumption of active lithium. However, the commonly used organolithium compounds in composite negative electrode coatings often have poor stability and strength. With the continuous charge and discharge of the battery, its huge volume expansion will lead to the consumption of the composite coating and expose a new active lithium interface, further exacerbating the consumption of active lithium.

[0005] Therefore, there is an urgent need to develop a lithium metal negative electrode material with improved cycle performance. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present application provides a negative electrode material, a negative electrode sheet, a secondary battery and a device including the same. The present application provides a first protective layer on the surface of the lithium metal layer of the negative electrode material. The first protective layer includes at least one of LiF, LiC6, and Li3N. LiF, LiC6, or Li3N has good electron insulation and strength, and at the same time can alleviate the continuous decomposition of the electrolyte. More importantly, LiF, LiC6, or Li3N has a relatively high interfacial energy with the lithium metal negative electrode, and promotes the diffusion of lithium ions at the electrolyte / lithium metal negative electrode interface by reducing the activation energy barrier, thereby stabilizing the lithium metal negative electrode.

[0007] The first aspect of the present application provides a negative electrode material, which includes a lithium metal layer and a first protective layer, wherein the first protective layer includes at least one of LiF, LiC6, and Li3N.

[0008] The second aspect of the present application provides a negative electrode sheet, which includes the aforementioned negative electrode material.

[0009] The third aspect of the present application provides a secondary battery, which includes the aforementioned negative electrode sheet.

[0010] The fourth aspect of the present application provides a device, which includes the aforementioned secondary battery.

[0011] The technical solution of the present application can achieve the following beneficial effects:

[0012] In the present application, a first protective layer is provided on the surface of the lithium metal layer of the negative electrode material. Among them, the first protective layer includes at least one of LiF, LiC6, and Li3N. LiF, LiC6, or Li3N has good electron insulation and strength, and at the same time can alleviate the continuous decomposition of the electrolyte. More importantly, LiF, LiC6, or Li3N has a relatively high interfacial energy with the lithium metal negative electrode. By reducing the activation energy barrier, it promotes the diffusion of lithium ions at the electrolyte / lithium metal negative electrode interface, thereby stabilizing the lithium metal negative electrode. Therefore, the first protective layer can control the deposition rate of lithium during charge and discharge, reduce the consumption of active lithium during the first charge, and improve its cycling performance. Detailed Embodiments

[0013] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0014] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0015] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0016] A list of items joined by the term "at least one of", "at least one", "at least one kind of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single component or multiple components. Item B may include a single component or multiple components. Item C may include a single component or multiple components.

[0017] Negative electrode material

[0018] One or more embodiments of the present application provide a negative electrode material, which includes a lithium metal layer and a first protective layer, wherein the first protective layer includes at least one of LiF, LiC6, and Li3N.

[0019] In the present application, by providing a first protective layer on the surface of the lithium metal layer, wherein the first protective layer includes at least one of LiF, LiC6, and Li3N. LiF, LiC6, or Li3N has good electron insulation and strength, and at the same time can alleviate the continuous decomposition of the electrolyte. More importantly, LiF, LiC6, or Li3N has a relatively high interfacial energy with the lithium metal negative electrode. By reducing the activation energy barrier, it promotes the diffusion of lithium ions at the electrolyte / lithium metal negative electrode interface, thereby stabilizing the lithium metal negative electrode. Therefore, the first protective layer can control the deposition rate of lithium during charge and discharge, reduce the consumption of active lithium during the first charge, and improve its cycle performance.

[0020] In some embodiments, the first protective layer preferably includes LiF and LiC6.

[0021] In some embodiments, in the first protective layer, the mass ratio of LiC6 to LiF is from 0.5 to 6.5. If the mass ratio of LiC6 to LiF in the first protective layer is too high, the thickness of the protective coating is relatively thin and cannot accommodate the deposited lithium. Part of the lithium metal is deposited on the surface of the coating, resulting in the inability to limit the volume expansion, and the exposed new interface will continuously consume active lithium, leading to an accelerated cycle decay; if the mass ratio of LiC6 to LiF is too low, the lithium ion diffusion impedance is large, the lithium deposition rate is uneven, resulting in an accelerated side reaction, a larger volume expansion, and a poorer cycle stability; therefore, it is necessary to control the mass ratio of LiC6 to LiF within the above range. In some embodiments, the mass ratio of LiC6 to LiF is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 or a range composed of any two of the above values. In some embodiments, the mass ratio of LiC6 to LiF is from 3.2 to 4.5.

[0022] In some embodiments, the negative electrode material further includes a second protective layer, and the second protective layer includes a ceramic compound. The ceramic compound in the second protective layer can prevent lithium dendrites from piercing the separator. The combined action of the first protective layer and the second protective layer can overcome the volume expansion of lithium metal during charge and discharge, ensure the interface stability during the cycling process of the lithium metal battery, and further improve its cycling performance.

[0023] In some embodiments, the ceramic compound includes at least one of MgO, γ-AlOOH, CaO, Al2O3, SiO2, TiO2, ZrO2, and Y2O3.

[0024] In some embodiments, based on the mass of the second protective layer, the mass percentage of the ceramic compound is 43% to 70%. In the second protective layer, if the mass percentage of the ceramic compound is too high, it will lead to an increase in the ion transport impedance and uneven deposition of lithium ions; if the mass percentage of the ceramic compound is too low, the second protective layer cannot effectively inhibit the growth of lithium dendrites during cycling, and in severe cases, it will cause short circuit between the positive and negative electrodes, resulting in safety problems. Therefore, it is necessary to control the mass percentage of the ceramic compound within the above range. In some embodiments, the mass percentage of the ceramic compound is 43%, 45%, 50%, 55%, 60%, 65%, 70%, or a range composed of any two of the above values. In some embodiments, based on the mass of the second protective layer, the mass percentage of the ceramic compound is 47% to 60%.

[0025] In some embodiments, the second protective layer further includes a solid electrolyte. The introduction of the solid electrolyte in the second protective layer can effectively control the lithium ion transport path and ensure the kinetic performance of the negative electrode sheet.

[0026] In some embodiments, the solid electrolyte includes at least one of polyethylene oxide (PEO), lithium aluminum titanium phosphate (LATP), and lithium lanthanum zirconate (LLZO).

[0027] In some embodiments, based on the mass of the second protective layer, the mass percentage of the solid electrolyte is 27% to 54%. Limiting the mass percentage of the solid electrolyte within the above range can ensure that the second protective layer has appropriate ion transport ability.

[0028] In some embodiments, the second protective layer further includes a binder. The binder in the second protective layer can overcome the volume expansion of lithium metal during charge and discharge and effectively ensure the interface stability during cycling.

[0029] In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. In some embodiments, the binder is preferably polyvinylidene fluoride.

[0030] In some embodiments, based on the mass of the second protective layer, the mass percentage of the binder is 1.2% to 3.5%.

[0031] In some embodiments, the ionic conductivity of the first protective layer is 5 mS / cm to 11 mS / cm. It can be understood that in the first protective layer, if the ionic conductivity is too high, the thickness of the protective coating is relatively thin and cannot accommodate the deposited lithium. Part of the lithium metal is deposited on the surface of the coating, resulting in the inability to limit the volume expansion, and the exposed new interface will continuously consume the active lithium, leading to an accelerated cycle decay; if the ionic conductivity is too low, the diffusion impedance of lithium ions is large, and the lithium deposition rate is uneven, resulting in an accelerated side reaction, a larger volume expansion, and a worse cycle stability. Therefore, it is necessary to control the ionic conductivity within the above range. In some embodiments, the ionic conductivity of the first protective layer is 5 mS / cm, 6 mS / cm, 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, or a range composed of any two of the above values. In some embodiments, the ionic conductivity of the first protective layer is 6 mS / cm to 10 mS / cm.

[0032] In some embodiments, the insulation resistance value of the second protective layer is 13 MΩ to 85 MΩ. In the second protective layer, if the insulation resistance value is too high, the ionic transport impedance increases, resulting in uneven deposition of lithium ions; if the insulation resistance value is too low, the second protective layer cannot effectively inhibit the growth of lithium dendrites during the cycle, and in severe cases, it may cause a short circuit between the positive and negative electrodes, resulting in safety problems. Therefore, it is necessary to control the insulation resistance value within the above range. In some embodiments, the insulation resistance value of the second protective layer is 13 MΩ, 23 MΩ, 33 MΩ, 43 MΩ, 53 MΩ, 63 MΩ, 73 MΩ, 85 MΩ, or a range composed of any two of the above values. In some embodiments, the insulation resistance value of the second protective layer is 16 MΩ to 81 MΩ.

[0033] In some embodiments, the thickness of the first protective layer is from 2 μm to 30 μm. If the thickness of the first protective layer is too low, the thickness of the protective coating is relatively thin and cannot accommodate the deposited lithium. Part of the lithium metal is deposited on the surface of the coating, resulting in the inability to limit volume expansion. The exposed new interface will continuously consume active lithium, leading to an accelerated cycle decay. If the thickness of the first protective layer is too high, the lithium-ion diffusion impedance is large, and the lithium deposition rate is uneven, resulting in an accelerated side reaction, a larger volume expansion, and a worse cycle stability. In some embodiments, the thickness of the first protective layer is 2 μm, 6 μm, 10 μm, 14 μm, 18 μm, 22 μm, 26 μm, 30 μm, or a range composed of any two of the above values. In some embodiments, the thickness of the first protective layer is from 13 μm to 24 μm.

[0034] In some embodiments, the thickness of the second protective layer is from 1 μm to 32 μm. In some embodiments, if the thickness of the second protective layer is too high, it will lead to an increase in ion transport impedance and uneven deposition of lithium ions. If the thickness of the second protective layer is too low, the second protective layer cannot effectively inhibit the growth of lithium dendrites during the cycling process, and in severe cases, it will cause a short circuit between the positive and negative electrodes, resulting in safety problems. In some embodiments, the thickness of the second protective layer is 1 μm, 2 μm, 6 μm, 10 μm, 14 μm, 18 μm, 22 μm, 26 μm, 30 μm, 32 μm, or a range composed of any two of the above values. In some embodiments, the thickness of the second protective layer is from 15 μm to 25 μm.

[0035] In some embodiments, the second protective layer contains pores, and the porosity of the second protective layer is between 37% and 60%. If the pores of the second protective layer are too few, it will lead to an increase in ion transport impedance and uneven deposition of lithium ions. If the pores of the second protective layer are too many, the second protective layer cannot effectively inhibit the growth of lithium dendrites during the cycling process, and in severe cases, it will cause a short circuit between the positive and negative electrodes, resulting in safety problems.

[0036] In some embodiments, the second protective layer contains pores, and the average pore diameter of the pores is between 0.1 μm and 3 μm. If the average pore diameter of the second protective layer is too small, it will lead to an increase in ion transport impedance and uneven deposition of lithium ions. If the average pore diameter of the second protective layer is too large, the second protective layer cannot effectively inhibit the growth of lithium dendrites during the cycling process, and in severe cases, it will cause a short circuit between the positive and negative electrodes, resulting in safety problems.

[0037] Negative electrode sheet

[0038] One or more embodiments of the present application provide a negative electrode sheet, which includes the aforementioned negative electrode material.

[0039] The negative electrode sheet further includes a negative electrode current collector, and the negative electrode current collector includes at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0040] The negative current collector is optionally coated with an undercoat material. The undercoat material optionally includes a binder and a conductive agent. The binder includes, but is not limited to: at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. The conductive agent includes, but is not limited to: at least one of carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials include metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer includes polyphenylene derivatives.

[0041] Secondary battery

[0042] One or more embodiments of the present application provide a secondary battery, which includes a positive electrode sheet, an electrolyte, a separator, and the aforementioned negative electrode sheet.

[0043] Positive electrode sheet

[0044] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes at least one of lithium iron phosphate-based materials, lithium cobaltate-based materials, and nickel-cobalt-based ternary materials. In some embodiments, the lithium iron phosphate-based materials include at least one of Li x Fe y R (1-y) PO4 materials, where R includes at least one of Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B, Nb elements, 0.05 ≤ x ≤ 1.2, 0 < y ≤ 1. In some embodiments, the lithium cobaltate-based materials include Li 1+z Co 1-j-k Ma j Mb k O2 materials, where Ma is at least one of Al, Ga, Hf, Mg, Sn, Zn, Zr; Mb is at least one of Ni, Mn, V, Mo, Nb, Cu, Fe, In, W, Cr, 0 ≤ j ≤ 0.01, 0 ≤ k ≤ 0.01, -0.05 ≤ z ≤ 0.08. In some embodiments, the nickel-cobalt-based ternary materials include Li a Ni m Co n A (1-m-n)At least one of the O2 materials, wherein A includes at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.9 ≤ a ≤ 1.2, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1.

[0045] In some embodiments, the positive electrode active material is preferably LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0046] In some embodiments, the positive electrode active material layer further includes a binder and optionally includes a conductive material. The binder improves the binding between the positive electrode active material particles and also improves the binding between the positive electrode active material and the current collector.

[0047] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0048] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based materials are selected from metal powders, metal fibers, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0049] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0050] Electrolyte

[0051] In some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent.

[0052] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate) borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0053] In some embodiments, the concentration of the lithium salt is from 0.7 mol / L to 1.7 mol / L.

[0054] In some embodiments, the non-aqueous solvent includes at least one of a chain carbonate compound, a cyclic carbonate compound, and a carboxylic acid ester compound.

[0055] In some embodiments, the chain carbonate compound includes, but is not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC).

[0056] In some embodiments, the cyclic carbonate compound includes, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene carbonate (VEC).

[0057] In some embodiments, the carboxylic acid ester compound includes, but is not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone.

[0058] Separator

[0059] In some embodiments, a separator is provided between the positive electrode plate and the negative electrode plate to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application.

[0060] In some embodiments, the separator includes a base film and a coating provided on the base film. The base film includes at least one of a polyethylene film, a polypropylene film, a PP / PE / PP composite film, a polyimide film, an aramid film, a polyethylene terephthalate film, or a non-woven fabric. In some embodiments, the coating includes at least one of a polymer layer, an inorganic ceramic layer, or a mixed layer of a polymer and an inorganic ceramic layer.

[0061] In some embodiments, the inorganic ceramic layer includes inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0062] The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride - hexafluoropropylene).

[0063] In the secondary battery of the present application, the adhesion between the aforementioned negative electrode sheet and the separator is controlled within the range of 15 N / m to 80 N / m. Controlling the adhesion within this range is beneficial to suppressing the expansion of the negative electrode, ensuring the flatness of the interface, reducing the lithium - ion transfer impedance, thereby improving the cycle performance and at the same time reducing the expansion rate of the battery cell during the cycle.

[0064] In some embodiments, the secondary battery may include an outer package, and the outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch - type soft package. The material of the soft package can be a plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0065] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other arbitrary shape.

[0066] In some embodiments, the present application also provides a battery module. The battery module includes the above - mentioned secondary battery. Since the battery module of the present application adopts the above - mentioned secondary battery, it has at least the same advantages as the secondary battery. The number of secondary batteries included in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0067] In some embodiments, the present application also provides a battery pack, which includes the above - mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0068] Device

[0069] One or more embodiments of the present application provide a device, and the device includes at least one of the above - mentioned secondary battery, battery module, or battery pack.

[0070] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug - in hybrid electric vehicles, energy storage systems, etc. In order to meet the high - power and high - energy - density requirements of the device for the secondary battery, a battery pack or a battery module can be adopted.

[0071] In other embodiments, the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0072] In the following, the secondary battery of the present application will be further elaborated in combination with specific examples and comparative examples.

[0073] Examples and Comparative Examples

[0074] Hereinafter, examples and comparative examples are given to further specifically illustrate the present application, but the present application is not limited to these examples as long as it does not deviate from its gist.

[0075] The materials, solvents, etc. used in the following examples were all obtained commercially.

[0076] Example 1

[0077] Preparation of the positive electrode sheet: The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, the conductive agent acetylene black, multi-walled carbon nanotubes, and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 95:2:1:2, and after being fully homogenized and mixed evenly, a positive electrode slurry was obtained; the positive electrode slurry was evenly coated on both side surfaces of the positive electrode current collector aluminum (Al) foil, and then after baking, cold pressing, and die cutting, a positive electrode sheet was obtained.

[0078] Preparation of the negative electrode sheet: The lithium foil and the copper foil coated with the undercoat material were cold pressed together. The undercoat material was carbon black and PVDF, and the mass percentage content of PVDF in the undercoat material was 3%, and the thickness of the undercoat material was 2 μm; the compacted composite lithium foil and copper foil were hot pressed at 60 °C for 3 min to obtain a composite negative electrode. The mixed LiC6 and LiF were plated on the composite negative electrode using a CVD tool, and the mass ratio of LiC6 to LiF was 2, and the thickness of the first protective layer was 10 μm; first, PVDF was dissolved in NMP, and then mixed with γ-AlOOH (hydrated alumina) and LLZO (lithium lanthanum zirconate). Among them, the mass percentage content of γ-AlOOH was 48%, the mass percentage content of LLZO was 49.9%, and the mass percentage content of PVDF was 2.1%. An appropriate amount of NMP was added to adjust the viscosity, and the discharge viscosity was controlled to be 1000 - 4000 cp. The slurry was coated on the first protective layer by transfer coating, the thickness of the second protective layer was 20 μm, the porosity of the second protective layer was 42%, and the average pore diameter was 480 nm.

[0079] Preparation of the electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 2:1:3, and then lithium hexafluorophosphate with a final concentration of 1.2 mol / L was added to prepare the electrolyte.

[0080] Preparation of the separator: A polyethylene (PE) porous polymer film was used as the separator.

[0081] Preparation of lithium metal battery: The negative electrode sheet, separator, and positive electrode sheet are stacked in sequence. The separator is located between the positive and negative electrode sheets to play an electron insulation role. The laminated core is obtained by laminating. After baking, the aluminum-plastic film is punched and the core is placed into the pit. After encapsulation and liquid injection, the lithium metal battery is obtained.

[0082] Examples 2-18 and Comparative Examples 1-3

[0083] Examples 2-18 and Comparative Examples 1-3 are based on Example 1, and are achieved by adjusting the mass ratio of LiC6 to LiF in the first protective layer, the type and mass percentage of ceramic compounds in the second protective layer, the type and mass percentage of solid electrolytes in the second protective layer, the mass percentage of binders in the second protective layer, the porosity of the second protective layer, the average pore diameter of the second protective layer, the ionic conductivity of the first protective layer, the insulation resistance of the second protective layer, the thickness of the first protective layer, the thickness of the second protective layer, etc. The specific adjustment methods and test data are shown in Table 1. Other preparation methods are the same as those in Example 1.

[0084] Testing methods

[0085] 1. Ionic conductivity test

[0086] The electrode sheet to be tested is made into a symmetric battery for EIS testing. During the test, the pressure is 0.2 MPa, the perturbation is 5 mV, and the test frequency is 5 mHz to 10 6 Hz.

[0087] 2. Insulation resistance test

[0088] Use a Hi-pot tester for testing. The test voltage is 100 V, the test time is 2 s, and the test pressure is 0.4 MPa.

[0089] 3. Thickness test

[0090] Take the upper, middle, and lower positions of the electrode sheet respectively. The position close to the tab side is defined as the upper. The distance from the test position of the upper to the edge of the film area on the tab side is >10 mm. Use a micrometer for thickness measurement, and take the average value after measuring 3 times.

[0091] 4. Porosity test

[0092] 1) Prepare mercury liquid and a pressure gauge, and pour a certain amount of mercury liquid into the material.

[0093] 2) Use the pressure gauge to measure the pressure of the mercury liquid. Calculate the volume of the mercury liquid, and use the density of mercury and the pressure measured by the pressure gauge

[0094] to obtain the volume of the mercury liquid.

[0095] 3) Calculate the porosity, and use the ratio of the volume of the mercury liquid to the volume of the material to calculate the porosity.

[0096] 5. Pore Size Test

[0097] The total pore volume V can be calculated from the thickness and porosity of the electrode. V = sampling area * electrode thickness * electrode porosity. The BET test is generally carried out by the gas adsorption method, usually using nitrogen, which is a common test in the industry. The measured specific surface area is denoted as S, with the unit m 2 / g.

[0098] Average pore size = V / (S * M), where M is the mass of the sampled sample.

[0099] 6. Swelling Rate Test

[0100] Use a micrometer to measure the thickness of the negative electrode of the fully charged battery before and after cycling, and the thicknesses are denoted as THK1 and THK2 respectively. The swelling rate during cycling = THK2 / THK1 - 100%.

[0101] 7. Cycling Test:

[0102] Under the condition of 25 °C, the lithium metal batteries of Examples 1-18 and Comparative Examples 1-3 are charged at a constant current of 0.7C to the upper limit voltage of 4.30V, and then transferred to constant voltage charging. The cut-off current for charging is 0.05C. After the battery is left standing for 10 minutes, it is discharged at a constant current of 1.2C to the lower limit voltage of 3V. The lithium metal batteries are subjected to 200 charge-discharge tests in the above manner, and the discharge capacity of the 200th cycle is obtained. The capacity retention rate of 200 cycles = the discharge capacity of the 200th cycle / the discharge capacity of the 1st cycle.

[0103] The test results are shown in Table 1 below.

[0104] Table 1

[0105]

[0106]

[0107] It can be seen from Examples 1-18 that the lithium metal batteries with the composite coating of the present application show good cycling stability and low negative electrode swelling rate during the cycling test. This indicates that under the synergistic effect of the first protective layer and the second protective layer, uniform deposition of lithium can be achieved, side reactions can be inhibited, and volume expansion can be reduced. At the same time, the beneficial component LiF in the first protective layer enhances the stability of the SEI and effectively inhibits the growth of lithium dendrites. In addition, the ceramic material in the second protective layer can well inhibit the growth of uneven lithium deposition during cycling, avoid the lithium dendrites piercing the separator and causing internal short circuit, thereby improving the safety performance of the battery.

[0108] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some modifications and changes can be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A negative electrode material, which comprises a lithium metal layer and a first protective layer, wherein, The first protective layer includes at least one of LiF, LiC6, and Li3N.

2. The negative electrode material according to claim 1, wherein, The negative electrode material further includes a second protective layer, and the second protective layer includes a ceramic compound.

3. The negative electrode material according to claim 1, wherein, The mass ratio of LiC6 to LiF is 0.5 to 6.

5.

4. The negative electrode material according to claim 2, wherein, The negative electrode material satisfies at least one of the following conditions: (1) The ceramic compound includes at least one of MgO, γ-AlOOH, CaO, Al2O3, SiO2, TiO2, ZrO2, and Y2O3; (2) Based on the mass of the second protective layer, the mass percentage of the ceramic compound is 43% to 70%; (3) The second protective layer further includes a binder; (4) The second protective layer further includes a solid electrolyte; (5) The ionic conductivity of the first protective layer is 5 mS / cm to 11 mS / cm; (6) The insulation resistance value of the second protective layer is 13 MΩ to 85 MΩ.

5. The negative electrode material according to claim 4, wherein, The negative electrode material satisfies at least one of the following conditions: (1) Based on the mass of the second protective layer, the mass percentage of the ceramic compound is 47% to 60%; (2) The binder includes at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene; (3) Based on the mass of the second protective layer, the mass percentage of the binder is 1.2% to 3.5%; (4) The solid electrolyte includes at least one of poly(ethylene oxide), lithium titanium aluminum phosphate, and lithium lanthanum zirconate; (5) Based on the mass of the second protective layer, the mass percentage of the solid electrolyte is 27% to 54%; (7) The ionic conductivity of the first protective layer is 6 mS / cm to 10 mS / cm; (8) The insulation resistance value of the second protective layer is 16 MΩ to 81 MΩ.

6. The negative electrode material according to any one of claims 2, 4 or 5, wherein, The negative electrode material satisfies at least one of the following conditions: (1) The thickness of the first protective layer is 2 μm to 30 μm; (2) The thickness of the second protective layer is 1 μm to 32 μm; (3) The thickness of the lithium metal layer is 1 μm to 120 μm; (4) The second protective layer contains pores, and the porosity of the second protective layer is between 37% and 60%; (5) The second protective layer contains pores, and the average pore diameter of the pores is between 100 nm and 3000 nm.

7. A negative electrode tab, wherein, The negative electrode sheet includes the negative electrode material according to any one of claims 1 to 6.

8. A secondary battery, wherein, The secondary battery includes a positive electrode sheet, an electrolyte, a separator, and the negative electrode sheet according to claim 7.

9. A device, wherein, The device includes the secondary battery according to claim 8.

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