Negative electrode composition, negative electrode plate, preparation method of negative electrode plate, battery and electric device

Abstract

The invention belongs to the technical field of batteries, and provides a negative electrode composition, a negative electrode plate, a preparation method of the negative electrode plate, a battery and an electric device. The negative electrode piece comprises a negative electrode current collector and a negative electrode modification layer located on the surface of the negative electrode current collector, the negative electrode modification layer comprises lithium sulfide, lithium alloy formed by lithium and lithium-loving metal and lithium-phobic metal, and the atom molar ratio of the lithium-loving metal to the lithium-phobic metal in the lithium alloy is (1-30): 1. The negative pole piece can improve the safety and cycling stability of the battery.

Description

Technical Field

[0001] This application belongs to the technical field of batteries. Specifically, it relates to a negative electrode composition, a negative electrode sheet, a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries have been widely used in electronic devices such as electric vehicles, mobile phones, and laptop computers due to their high energy density, long discharge life, and low self-discharge. With the development of technology and market demand, higher requirements have been put forward for the capacity, cycle performance, and safety performance of batteries. As the main material in lithium-ion batteries, the negative electrode material is the carrier of lithium ions and electrons during the charging process of the battery, playing the role of energy storage and release. Currently, the commercially available negative electrode materials for lithium-ion batteries mainly include carbon negative electrodes (such as natural graphite, disordered carbon), silicon negative electrodes, etc. However, these negative electrode materials have problems such as low capacity and short cycle life. Lithium metal, due to its high theoretical capacity and the lowest reduction potential, can be used as a new battery negative electrode. However, it easily causes problems such as safety hazards, too high impedance, and poor stability in the battery.

[0003] Therefore, it is necessary to further improve the negative electrode sheet. Summary of the Invention

[0004] Aiming at the above-mentioned problems, the purpose of this application is to provide a negative electrode composition, a negative electrode sheet, a preparation method thereof, a battery, and an electrical device. By introducing a negative electrode modification layer formed by the negative electrode composition into the negative electrode sheet, the growth of metal dendrites can be inhibited, and the safety and cycle stability of the battery can be improved.

[0005] In a first aspect, this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode modification layer located on the surface of the negative electrode current collector. Among them, the negative electrode modification layer contains lithium sulfide, a lithium alloy formed by lithium and a lithiumophilic metal, and a lithium-phobic metal, and the atomic molar ratio of the lithiumophilic metal to the lithium-phobic metal in the lithium alloy is (1 to 30):1.

[0006] In the negative electrode sheet of the present application, introducing the negative electrode modification layer on the surface of the current collector can endow the negative electrode with high conductivity / lithium conductivity / lithiophilic properties, and to a certain extent form a barrier protection for the lithium metal in the negative electrode sheet, improving the cycle performance, rate performance and safety performance of the battery. Specifically, lithium sulfide (Li2S) has the ability to conduct lithium ions and stabilize the interface, and the lithium alloy has lithiophilic properties, which can effectively reduce the initial nucleation overpotential of the lithium metal in the negative electrode, promote the uniform nucleation of the subsequent lithium metal on the surface of the negative electrode, inhibit the formation of dendrites, and the lithium-phobic metal has high stability and conductivity, which helps to uniform the electric field on the electrode surface. The growth behavior without dendrites itself can also avoid the side reaction of the direct contact between the lithium metal in the negative electrode and the electrolyte to a certain extent, improving the cycle life of the battery; moreover, by controlling the relative content of the lithiophilic metal and the lithium-phobic metal, while inhibiting the formation of dendrites, the resistance can be avoided from being too high. In this way, while ensuring safety, the battery has high rate performance.

[0007] In some embodiments of the present application, the atomic molar ratio of the lithiophilic metal to the lithium-phobic metal in the lithium alloy is (2-10):1. Thereby, while the battery has high safety and cycle stability, the rate performance of the battery can be improved.

[0008] In some embodiments of the present application, the ratio of the total mass of the lithiophilic metal and the lithium-phobic metal in the lithium alloy to the mass of lithium sulfide is (4-60):1.

[0009] Optionally, the ratio of the total mass of the lithiophilic metal and the lithium-phobic metal in the lithium alloy to the mass of lithium sulfide is (10-50):1.

[0010] In some embodiments of the present application, the lithiophilic metal includes at least one of zinc, indium, aluminum, magnesium, silver, tin, gallium, antimony, bismuth or germanium. Optionally, the lithiophilic metal includes indium. Thereby, the lithium-indium alloy formed by indium and lithium has a higher affinity for lithium, improving the migration of ions.

[0011] In some embodiments of the present application, the resistivity of the lithium-phobic metal at 20 °C is lower than 15 μΩ·cm. Optionally, the lithium-phobic metal includes at least one of copper, iron, nickel, cobalt or tungsten.

[0012] In some embodiments of the present application, the negative electrode modification layer further includes a binder. The binder can provide adhesion between the components in the modification layer and between the negative electrode modification layer and the current collector, improving the stability of the modification layer in the negative electrode sheet.

[0013] In some embodiments of the present application, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride - hexafluoropropylene, or tetrafluoroethylene - hexafluoroethylene copolymer. Thus, the structural stability of the negative electrode modification layer can be further improved.

[0014] In some embodiments of the present application, based on the total weight of lithium sulfide, the binder, the lithium - phobic metal, and the lithium - philic metal in the lithium alloy, the mass content of lithium sulfide is 1% - 16%, the total mass content of the lithium - phobic metal and the lithium - philic metal in the lithium alloy is 75% - 98%, and the mass content of the binder is 1% - 10%.

[0015] Optionally, based on the total weight of lithium sulfide, the binder, the lithium - phobic metal, and the lithium - philic metal in the lithium alloy, the mass content of lithium sulfide is 2% - 8%, the total mass content of the lithium - phobic metal and the lithium - philic metal in the lithium alloy is 85% - 95%, and the mass content of the binder is 3% - 7%. Among them, controlling lithium sulfide within this range can not only play a good role in guiding lithium and stabilizing the SEI film, but also further avoid excessive impedance on the negative electrode side and improve the rate performance of the battery.

[0016] In some embodiments of the present application, in each unit area of the negative electrode sheet, the total weight of lithium sulfide, the binder, the lithium - phobic metal, and the lithium - philic metal in the lithium alloy is 0.3mg / cm 2 ~1.0mg / cm 2 . Thus, while strongly inhibiting the growth of dendrites, the impact on the quality and volume energy density of the battery cell is reduced.

[0017] In some embodiments of the present application, the negative electrode sheet further includes a lithium metal negative electrode layer, and the lithium metal negative electrode layer is located on the side of the negative electrode modification layer away from the negative electrode current collector.

[0018] In some embodiments of the present application, the negative electrode current collector includes at least one of copper foil, titanium foil, or stainless steel.

[0019] In a second aspect, the present application provides a negative electrode composition, comprising lithium sulfide, a lithium - philic metal, and a lithium - phobic metal; wherein, the molar ratio of the lithium - philic metal to the lithium - phobic metal is (1 - 30)∶1.

[0020] During the first lithium deposition process of the negative electrode composition provided by this application, the lithiumophilic metal can form a lithium alloy with lithium. The lithium alloy has a high lithium conductivity, which is beneficial to the rapid lateral and longitudinal migration of lithium metal at a high current density. On the one hand, it promotes the uniform deposition of lithium, and on the other hand, it can reduce the polarization potential of the negative electrode; lithium sulfide has the ability to conduct lithium ions and stabilize the negative electrode interface. The lithium-phobic metal can exist stably and has high conductivity, which helps to uniform the electric field on the electrode surface and can avoid the side reaction of direct contact between lithium metal and the electrolyte to a certain extent. Thus, the negative electrode composition and the negative electrode modification layer formed after lithium deposition can effectively protect the negative electrode plate and improve the cycle performance, rate performance and safety performance of the battery.

[0021] In some embodiments of this application, the molar ratio of the lithiumophilic metal to the lithium-phobic metal is (2-10):1. Thereby, while enabling the battery to have high safety and cycle stability, the rate performance of the battery can be improved.

[0022] In some embodiments of this application, the ratio of the total mass of the lithiumophilic metal and the lithium-phobic metal to the mass of lithium sulfide is (4-60):1.

[0023] Optionally, the ratio of the total mass of the lithiumophilic metal and the lithium-phobic metal to the mass of lithium sulfide is (10-50):1.

[0024] In some embodiments of this application, the lithiumophilic metal includes at least one of zinc, indium, aluminum, magnesium, silver, tin, gallium, antimony, bismuth or germanium. Optionally, the lithiumophilic metal includes indium. Thereby, the lithium-indium alloy formed by indium and the subsequently deposited lithium has a higher affinity for lithium, improving the migration of ions.

[0025] In some embodiments of this application, the resistivity of the lithium-phobic metal at 20 °C is less than 15 μΩ·cm. Optionally, the lithium-phobic metal includes at least one of copper, iron, nickel, cobalt or tungsten.

[0026] In some embodiments of this application, the negative electrode composition further includes a binder.

[0027] In some embodiments of this application, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer. Thereby, it is beneficial to maintain the structural stability of the modification layer.

[0028] In some embodiments of this application, based on the total weight of the negative electrode composition, the mass content of lithium sulfide is 1%-16%, the total mass content of the lithium-phobic metal and the lithiumophilic metal is 75%-98%, and the mass content of the binder is 1%-10%.

[0029] Optionally, based on the total weight of the negative electrode composition, the mass content of lithium sulfide is 2% to 8%, the total mass content of lithium-phobic metal and lithium-philic metal is 85% to 95%, and the mass content of the binder is 3% to 7%. Among them, controlling lithium sulfide within this range can not only play a good role in guiding lithium and stabilizing the SEI film, but also further avoid excessive impedance on the negative electrode side and improve the rate performance of the battery.

[0030] In some embodiments of the present application, the median particle size Dv of the lithium-philic metal 50 is 20 nm to 500 nm, and the median particle size Dv of the lithium-phobic metal 50 is 50 nm to 200 nm. Thus, the lithium-philic metal and the lithium-phobic metal cooperate with each other, enabling the formed negative electrode modification layer to further homogenize the electric field and promote ion conduction.

[0031] In a third aspect, the present application provides a method for preparing a negative electrode sheet, including:

[0032] Preparing a composite layer:

[0033] Applying the negative electrode composition described in the second aspect of the present application onto a negative electrode current collector to form a composite layer;

[0034] Pre-depositing lithium metal:

[0035] Making the lithium-philic metal in the composite layer form a lithium alloy with the deposited lithium ions, thereby forming a negative electrode modification layer on the surface of the negative electrode current collector.

[0036] In the preparation method of the present application, the negative electrode composition and the deposited lithium ions can in-situ generate a negative electrode modification layer on the surface of the current collector, enabling the negative electrode sheet to have the properties of high conductivity / lithium conduction / lithium philicity, while forming a barrier protection for lithium metal, thereby improving the cycle performance, rate performance, and safety performance of the lithium-ion battery. In addition, the method of the present application can directly regulate the composition of the negative electrode composition, easily obtain a negative electrode modification layer with better performance, and improve the applicability of the negative electrode sheet.

[0037] In some embodiments of the present application, in each unit area of the negative electrode sheet, the weight of the negative electrode composition is 0.3 mg / cm 2 to 1.0 mg / cm 2 . Thus, while strongly inhibiting the growth of dendrites, the influence on the quality and volume energy density of the battery cell is reduced.

[0038] In some embodiments of the present application, the process of pre-depositing metallic lithium further includes: continuously forming a lithium metal negative electrode layer on the negative electrode modification layer by depositing lithium ions.

[0039] In some embodiments of the present application, the conditions for pre-depositing lithium metal include: the current density is 0.5 mA / cm2 ~2 mA / cm 2 Thus, while ensuring the preparation efficiency, the lithium alloying and the formation of the lithium metal negative electrode layer can be further promoted.

[0040] In some embodiments of the present application, the pre-deposition enables the pre-deposited capacity of lithium on the negative electrode sheet to be 1 mAh / cm 2 ~20 mAh / cm 2 Thus, while forming a lithium alloy of lithium and a lithiophilic metal, the thickness of the lithium metal layer can be further controlled, and the problems that the excessive lithium metal layer affects the cell volume and the mass energy density and that the too low lithium metal layer may cause premature drop of the battery capacity due to the rapid depletion of lithium can be avoided as much as possible. Thus, the comprehensive performance of the battery is improved.

[0041] Fourthly, the present application provides a battery, including the negative electrode sheet described in the first aspect of the present application or the negative electrode sheet prepared by the preparation method described in the third aspect of the present application.

[0042] Fifthly, the present application provides an electrical device, including the battery described in the fourth aspect of the present application.

[0043] The additional aspects and advantages of the present application will be partly given in the following description, partly become obvious from the following description, or be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. In the drawings:

[0045] Figure 1 is a schematic diagram of a negative electrode sheet according to an embodiment of the present application;

[0046] Figure 2 is an exploded view of a battery cell according to an embodiment of the present application;

[0047] Figure 3 is an exploded view of a battery cell according to an embodiment of the present application;

[0048] Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0049] Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0050] Figure 6 is Figure 5 the exploded view of the battery pack shown in a preferred embodiment of the present application;

[0051] Figure 7 It is a schematic diagram of an electrical device using the battery of an embodiment of the present application as a power source.

[0052] Explanation of reference numerals:

[0053] 1: Battery pack; 2: Upper box body; 3: Lower box body; 4: Battery module; 5: Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 6: Negative electrode tab; 61 Negative current collector; 62 Negative modification layer; 621 Lithium sulfide particles; 622 Lithium alloy particles; 623 Lithium-phobic metal particles. Specific embodiments

[0054] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0055] In the present application, the mention of "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments.

[0056] The "range" disclosed in the present application is defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit, and the selected lower limit and / or upper limit define the boundary of a specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range not explicitly recorded, and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single value itself can be used as a lower limit or an upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0057] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0058] If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0059] Unless otherwise specified, the terms "include", "comprise", "contain", "have" as mentioned in this application are open-ended and can also be closed-ended. For example, the terms "include", "comprise", "contain", "have" can mean that other components not listed can also be included or comprised, or it can only include or comprise the listed components. Additionally, in this application, the terms "a plurality of", "a variety of", "at least one" refer to more than two. "Above" and "below" include the number itself. For example, "more than two" includes two itself, such as two, three, four, or more.

[0060] Unless otherwise specified, in this application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, in this text, the character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0061] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "include" and "have" in the description and claims of this application, and any variations thereof, are intended to cover non-exclusive inclusion. Unless otherwise stated, the terms used in this application have the well-known meaning commonly understood by those skilled in the art. Unless otherwise stated, the values of the various parameters mentioned in this application can be measured using various common measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0062] Lithium-ion batteries with lithium metal as the anode have an ultra-high theoretical energy density and thus have received extensive research attention. However, compared with the graphite and other carbon material anodes with an insertion / extraction mechanism in commercial lithium-ion batteries, the lithium metal anode in lithium-ion batteries belongs to a metal deposition / stripping mechanism and has problems such as the growth of metal dendrites. Specifically, the inherent roughness, defects, and non-uniform composition of the lithium metal anode interface result in non-uniform properties of the anode interface, and "hot spot" regions with relatively high electric field / ion field intensity are extremely likely to form during cycling, which in turn causes non-uniform deposition and stripping of lithium metal, forming dendrites and dead lithium. On the one hand, this will cause a large amount of electrolyte to react with lithium to form a solid electrolyte interface (SEI film), consuming limited active lithium and electrolyte; on the other hand, the grown dendrites will pierce the separator, leading to short circuit between the positive and negative electrodes and posing a safety hazard.

[0063] To this end, a first aspect of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode modification layer located on the surface of the negative electrode current collector. The negative electrode modification layer contains lithium sulfide, a lithium alloy, and a lithium-phobic metal. Among them, the lithium alloy is formed by lithium and a lithium-philic metal, and the atomic molar ratio of the lithium-philic metal to the lithium-phobic metal in the lithium alloy is (1 to 30):1.

[0064] In the negative electrode plate of the present application, introducing the negative electrode modification layer on the surface of the current collector can endow the negative electrode with the properties of high conductivity / lithium conductivity / lithium philicity, and to a certain extent form a barrier protection for the lithium metal in the negative electrode plate, improving the cycle performance, rate performance, and safety performance of the battery. Specifically, lithium sulfide (Li2S) has the ability to conduct lithium ions and stabilize the negative electrode interface. The lithium alloy has a lithium-philic property, which can effectively reduce the initial nucleation overpotential of the negative electrode lithium metal, promote the uniform nucleation of subsequent lithium metal on the negative electrode surface, and inhibit dendrite growth. The lithium-phobic metal has high stability and conductivity, which helps to uniform the electric field on the electrode surface. By introducing this modification layer to create a dendrite-free growth behavior itself can also avoid the side reaction of direct contact between the lithium metal in the negative electrode and the electrolyte to a certain extent, improving the cycle life of the battery; controlling the relative content of the lithium-philic metal and the lithium-phobic metal can avoid too high resistance while inhibiting dendrite growth. In this way, while ensuring safety, the battery has high rate performance.

[0065] In the present application, a lithium-philic metal refers to a metal that can form a lithium alloy with lithium. The lithium-philic metal has high wettability to lithium, and the Gibbs free energy (ΔG) of these metals reacting with molten lithium is usually less than 0 in the temperature range of 180°C to 300°C. Specific examples of the lithium-philic metal include, but are not limited to, Mg, Ca, Sc, Al, Se, Sr, Sn, In, Ba, Ag, Zn, Sb, Rh, Ir, Pb, Au, Ge, Ga, etc. A lithium-phobic metal refers to a metal with poor wettability to lithium, and the Gibbs free energy (ΔG) of reacting with molten lithium is usually greater than 0. Specific examples of the lithium-phobic metal include, but are not limited to, Cu, Ti, V, Ni, Co, Mn, Fe, Cr, W, Re, Cs, etc.

[0066] In some embodiments, the lithium-philic metal includes at least one of zinc (Zn), indium (In), aluminum (Pb), magnesium (Mg), silver (Ag), tin (Sn), gallium (Ga), antimony (Sb), bismuth (Bi), or germanium (Ge). Optionally, the lithium-philic metal includes indium. Thus, the lithium-indium alloy formed by indium and lithium has a higher affinity for lithium, improving the migration of ions.

[0067] In some embodiments, the resistivity of the lithium-phobic metal at 20°C is lower than 15 μΩ·cm. From the perspective of cost reduction, optionally, the lithium-phobic metal includes at least one of copper, iron, nickel, cobalt, or tungsten.

[0068] According to the present application, in the negative electrode modification layer, the lithium alloy (lithium-lithiophilic metal) helps to inhibit dendrite formation. The lithium-phobic metal has a lithium-phobic property and has high electrical conductivity, and can stably exist in the electrolyte and the charge-discharge environment. For this reason, controlling the atomic molar ratio of the lithiophilic metal in the lithium alloy to the lithium-phobic metal to be (1 to 30):1 can enable the battery to have high comprehensive performance. As some examples, in the negative electrode modification layer, the atomic molar ratio of the lithiophilic metal to the lithium-phobic metal can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 15:1, 17:1, 20:1, 25:1, 30:1, etc.

[0069] Optionally, the atomic molar ratio of the lithiophilic metal in the lithium alloy to the lithium-phobic metal is (2 to 10):1. Thereby, while enabling the battery to have high safety and cycle stability, the rate performance of the battery can be improved.

[0070] In some embodiments, the ratio of the total mass of the lithiophilic metal and the lithium-phobic metal in the lithium alloy to the mass of lithium sulfide is (4 to 60):1, such as 4:1, 5:1, 8:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 18:1, 20:1, 25:1, 30:1, 40:1, 45:1, 47:1, 50:1, 60:1, etc.

[0071] Optionally, the ratio of the total mass of the lithiophilic metal and the lithium-phobic metal in the lithium alloy to the mass of lithium sulfide is (10 to 50):1.

[0072] In some embodiments, the negative electrode modification layer further includes a binder. The binder can provide adhesion between the components in the modification layer and between the negative electrode modification layer and the current collector, and improve the stability of the modification layer in the negative electrode plate. The binder can, for example, include an oil-soluble binder. In this way, it can be miscible with organic solvents during slurry preparation, and the organic solvents are more likely to volatilize when forming a coating, reducing the impact on the battery due to solvent residue.

[0073] Optionally, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, CAS No.: 9011-17-0), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Thereby, it is beneficial to maintain the structural stability of the modification layer.

[0074] In some embodiments, in the negative electrode modification layer, based on the total weight of lithium sulfide, the binder, the lithium-phobic metal, and the lithiophilic metal in the lithium alloy,

[0075] The mass content of lithium sulfide is 1% to 16%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 16%, etc.;

[0076] The total mass content of lithiumophilic metals in lithiumophobic metals and lithium alloys is 75% to 98%, such as 75%, 78%, 79%, 80%, 85%, 86%, 87%, 89%, 90%, 91%, 92%, 93%, 95%, 98%, etc.;

[0077] The mass content of the binder is 1% to 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0078] It can be understood that the mass of the lithiumophilic metal in the lithium alloy refers to the mass contributed by the lithiumophilic metal atoms. For example, if the lithiumophilic metal is indium, the mass of the lithiumophilic metal in the lithium alloy refers to the mass of indium atoms in the lithium-indium alloy.

[0079] Furthermore, in the negative electrode modification layer, based on the total weight of lithium sulfide, the binder, lithiumophobic metals, and lithiumophilic metals in the lithium alloy, the mass content of lithium sulfide is 2% to 8%, the total mass content of lithiumophobic metals and lithiumophilic metals in the lithium alloy is 85% to 95%, and the mass content of the binder is 3% to 7%. Thus, controlling lithium sulfide within this range can not only play a good role in lithium conduction and stabilizing the SEI film, but also further avoid excessive impedance on the negative electrode side and improve the rate performance of the battery.

[0080] In this application, for each unit area of the negative electrode sheet, the total weight of lithium sulfide, the binder, lithiumophobic metals, and lithiumophilic metals in the lithium alloy can be, for example, 0.1 mg / cm 2 ~2 mg / cm 2 . In some embodiments, for each unit area of the negative electrode sheet, the total weight of lithium sulfide, the binder, lithiumophobic metals, and lithiumophilic metals in the lithium alloy is 0.3 mg / cm 2 ~1.0 mg / cm 2 , such as 0.3 mg / cm 2 , 0.4 mg / cm 2 , 0.5 mg / cm 2 , 0.6 mg / cm 2 , 0.7 mg / cm 2 , 0.8 mg / cm 2 , 0.9 mg / cm 2 , 1.0 mg / cm 2etc. Thus, while strongly inhibiting the growth of dendrites, the influence on the quality and volumetric energy density of the battery cell is reduced. Optionally, in the negative electrode sheet per unit area, the total weight of lithium sulfide, binder, lithium-phobic metal and lithium-philic metal in the lithium alloy is 0.4 mg / cm 2 ~0.6 mg / cm 2 .

[0081] According to the present application, generally, the thickness of the negative electrode modification layer can be, for example, 2 μm to 8 μm, such as 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc.

[0082] In some embodiments, the negative electrode sheet further includes a lithium metal negative electrode layer, and the lithium metal negative electrode layer is located on a side of the negative electrode modification layer away from the negative electrode current collector.

[0083] In the present application, the negative electrode current collector can be, for example, a metal foil. In some embodiments, the negative electrode current collector includes at least one of copper foil, titanium foil or stainless steel.

[0084] In the present application, the thickness of the negative electrode current collector can be selected according to the specific application of the battery. Generally, the thickness of the negative electrode current collector can be 4 μm to 20 μm, such as 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc.

[0085] The second aspect of the present application provides a negative electrode composition, comprising lithium sulfide, a lithium-philic metal and a lithium-phobic metal, and the atomic molar ratio of the lithium-philic metal to the lithium-phobic metal is (1 to 30):1.

[0086] During the first lithium deposition process of the negative electrode composition provided by the present application, the lithium-philic metal can form a lithium alloy with lithium. On the one hand, it promotes the uniform deposition of lithium, and on the other hand, it can reduce the polarization potential of the negative electrode; lithium sulfide has the ability to conduct lithium ions and stabilize the negative electrode interface, and the lithium-phobic metal can stably exist and has high conductivity, which helps to uniform the electric field on the electrode surface and can avoid the side reaction of direct contact between lithium metal and the electrolyte to a certain extent. Thus, the negative electrode composition and the negative electrode modification layer formed after lithium deposition can effectively protect the negative electrode sheet and improve the cycle performance, rate performance and safety performance of the battery.

[0087] In some embodiments, the negative electrode composition further includes a binder.

[0088] Unless otherwise specified, the descriptions of the lithium-philic metal, the lithium-phobic metal and the binder are as described in the first aspect of the present application, and will not be repeated here.

[0089] As some examples, in the negative electrode composition, the lithiumophilic metal and the lithium-phobic metal can be in a ratio of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 15:1, 17:1, 20:1, 25:1, 30:1, etc.

[0090] Optionally, in the negative electrode composition, the molar ratio of the lithiumophilic metal to the lithium-phobic metal is (2-10):1. Thereby, while enabling the battery to have high safety and cycle stability, the rate performance of the battery can be improved.

[0091] In some embodiments, in the negative electrode composition, the ratio of the total mass of the lithiumophilic metal and the lithium-phobic metal to the mass of lithium sulfide is (4-60):1, such as 4:1, 5:1, 8:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 18:1, 20:1, 25:1, 30:1, 40:1, 45:1, 47:1, 50:1, 60:1, etc.

[0092] Optionally, in the negative electrode composition, the ratio of the total mass of the lithiumophilic metal and the lithium-phobic metal to the mass of lithium sulfide is (10-50):1.

[0093] In some embodiments, based on the total weight of the negative electrode composition,

[0094] the mass content of lithium sulfide is 1% - 16%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 16%, etc.;

[0095] the total mass content of the lithium-phobic metal and the lithiumophilic metal is 75% - 98%, such as 75%, 78%, 79%, 80%, 85%, 86%, 87%, 89%, 90%, 91%, 92%, 93%, 95%, 98%, etc.;

[0096] the mass content of the binder is 1% - 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0097] Optionally, based on the total weight of the negative electrode composition, the mass content of lithium sulfide is 2% - 8%, the total mass content of the lithium-phobic metal and the lithiumophilic metal is 85% - 95%, and the mass content of the binder is 3% - 7%. Thereby, controlling lithium sulfide within this range can not only play a good role in lithium conduction and stabilizing the SEI film, but also further avoid excessive impedance on the negative electrode side and improve the rate performance of the battery.

[0098] In some embodiments, the median particle size (D V50) ranges from 20 nm to 500 nm, and the median particle size (Dv 50 ) of the lithium-phobic metal ranges from 50 nm to 200 nm. Thus, the lithium-philic metal and the lithium-phobic metal cooperate with each other, enabling the formed negative electrode modification layer to further uniform the electric field and promote ion conduction. In this application, the median particle size Dv50 can be obtained by the particle size distribution - laser diffraction method with reference to the GB / T 19077-2016 standard.

[0099] As some examples, the Dv of the lithium-philic metal 50 is, for example, 20 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 300 nm, etc.

[0100] As some examples, the Dv of the lithium-phobic metal 50 is, for example, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, etc.

[0101] The third aspect of this application provides a method for preparing a negative electrode sheet, including:

[0102] Preparing a composite layer:

[0103] Applying the negative electrode composition described in the second aspect of this application on the negative electrode current collector to form a composite layer;

[0104] Pre-depositing lithium metal:

[0105] Making the lithium-philic metal in the composite layer form a lithium alloy with lithium ions, thereby forming a negative electrode modification layer on the surface of the negative electrode current collector.

[0106] In the preparation method of this application, the negative electrode composition cooperates with the deposited lithium ions to in-situ generate a negative electrode modification layer on the surface of the current collector, enabling the negative electrode sheet to have the properties of high conductivity / lithium conductivity / lithium philicity, while forming a barrier protection for lithium metal, thereby improving the cycle performance, rate performance, and safety performance of the lithium-ion battery.

[0107] In some embodiments, the negative electrode composition and a solvent (such as NMP) can be mixed to form a slurry, and the slurry is coated on the negative electrode current collector and dried to form the composite layer.

[0108] In some embodiments, in each unit area of the negative electrode sheet, the weight of the negative electrode composition is 0.3 mg / cm 2 ~1 mg / cm 2 , thus, while strongly inhibiting the growth of dendrites, the influence on the quality and volume energy density of the battery cell is reduced. Optionally, in each unit area of the negative electrode sheet, the weight of the negative electrode composition is 0.4 mg / cm 2 ~0.6 mg / cm 2 .

[0109] As some examples, the methods for forming the composite layer include:

[0110] Mixing and grinding a lithiophilic metal and a lithium-phobic metal uniformly to obtain a dry metal mixture;

[0111] Mixing and grinding the dry metal mixture, lithium sulfide, and a binder uniformly to obtain a negative electrode composition;

[0112] Stirring the negative electrode composition and a solvent uniformly to obtain a modified layer slurry;

[0113] Coating the modified layer slurry on the negative electrode current collector and drying it under vacuum to form the composite layer.

[0114] In some embodiments, the thickness of the composite layer formed on the current collector can be 0.5 μm to 2 μm, such as 0.5 μm, 1 μm, 1.2 μm, 1.5 μm, 2 μm, etc. Thus, the formed negative electrode modified layer can fully exert the effects of conducting electricity, conducting lithium, and being lithiophilic, has good interfacial stability, and at the same time enables the battery to have a high energy density.

[0115] In the present application, in the step of pre-depositing lithium metal, lithium can penetrate into the composite layer to form a lithium alloy with the lithiophilic metal, and the composite layer swells to form the negative electrode modified layer.

[0116] In some embodiments, the process of pre-depositing metallic lithium further includes: forming a lithium metal negative electrode layer on the negative electrode modified layer by depositing lithium ions continuously. In this case, the pre-depositing of metallic lithium can be divided into a first stage and a second stage that are carried out continuously. In the first stage, lithium ions penetrate into the composite layer to form a lithium alloy with the lithiophilic metal. In the second stage: lithium ions continue to deposit on the negative electrode modified layer to form a lithium metal negative electrode layer.

[0117] In some embodiments, the conditions for pre-depositing lithium metal include: a current density of 0.5 mA / cm 2 ~2 mA / cm 2 . Thus, while ensuring the preparation efficiency of the electrode sheet, the alloying of lithium and the formation of the lithium metal negative electrode layer can be further promoted.

[0118] In some embodiments, lithium metal pre-deposition can be carried out by assembling a half-cell.

[0119] As some examples, the methods for pre-depositing lithium metal include:

[0120] Using the negative electrode current collector formed with the composite layer as the working electrode, a lithium-copper composite tape as the counter electrode, 1 mol / L LiPF6 as the electrolyte (solvent: EC and EMC, volume ratio 3:7) as the electrolyte, and PE as the separator, at 1 mA / cm2 At a current density, the working electrode is discharged to 0 V. During this process, lithium forms an indium-lithium alloy with the lithiumophilic metal in the composite layer. During this process, the voltage continues to drop below 0 V, and lithium ions are deposited to form lithium metal until the lithium deposition capacity reaches a certain capacity, obtaining a negative electrode sheet. In this method, it can be detected by X-ray photoelectron spectroscopy (XPS) that indium elements basically exist in the form of lithium-indium alloy.

[0121] In some embodiments, the pre-deposition enables the pre-deposition capacity of lithium metal on the negative electrode sheet to be 1 mAh / cm 2 ~20 mAh / cm 2 , for example 1 mAh / cm 2 , 3 mAh / cm 2 , 5 mAh / cm 2 , 10 mAh / cm 2 , 15 mAh / cm 2 and so on.

[0122] As some examples, Figure 1 is a schematic diagram of a negative electrode sheet with a negative electrode modification layer formed thereon. Figure 1 In, the negative electrode sheet 6 includes a negative electrode current collector 61 and a negative electrode modification layer 62 on its surface. The negative electrode modification layer 62 contains lithium sulfide particles 621, lithium alloy particles 622 (formed by lithiumophilic metal and deposited Li + formed) and lithium-phobic metal particles 623.

[0123] The fourth aspect of the present application provides a battery, including the negative electrode sheet described in the first aspect of the present application or the negative electrode sheet prepared by the preparation method described in the third aspect of the present application.

[0124] In the present application, the battery can be a secondary battery. It can be understood that the secondary battery can be a lithium-ion battery. In some embodiments, the secondary battery further includes a positive electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, which can prevent short circuit between the positive and negative electrodes and at the same time allow ions to pass through.

[0125] [Positive electrode sheet]

[0126] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector.

[0127] In the present application, the positive current collector may be, for example, a metal foil or a composite current collector. The metal foil is, for example, an aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. Among them, the materials of the metal layer include, but are not limited to, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.; the polymer materials of the polymer base layer may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0128] In the present application, the positive electrode film layer may include a positive electrode active material. The positive electrode active material may be a type commonly used in lithium-ion batteries. In some embodiments, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, which can also be abbreviated as NCM333); LiNi 0.5 Co 0.2 Mn 0.3 O2, which can also be abbreviated as NCM523; LiNi 0.5 Co 0.25 Mn 0.25 O2, which can also be abbreviated as NCM211; LiNi 0.6 Co 0.2 Mn 0.2 O2, which can also be abbreviated as NCM622; LiNi 0.8 Co 0.1 Mn 0.1 O2, which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 015 Al 0.05 O2) and their modified compounds, etc. at least one. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4, which can also be abbreviated as LFP), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, composites of lithium manganese iron phosphate and carbon, etc. at least one.

[0129] In the present application, the positive electrode film layer may optionally include a conductive agent. However, the type of the conductive agent is not specifically limited and can be selected according to actual needs. As some examples, the conductive agent for the positive electrode material can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In the present application, the positive electrode film layer may also optionally include a binder. As some examples, the binder for the positive electrode material can be one or more of styrene-butadiene rubber (SBR), aqueous acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0131] The present application does not particularly limit the preparation method of the positive electrode sheet, and it can be prepared with reference to the existing methods. For example, the positive electrode slurry is coated on the positive electrode current collector and dried and cold-pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing components such as the positive electrode active material, optionally the conductive agent, and optionally the binder in a solvent (such as N-methylpyrrolidone) and stirring evenly.

[0132] As some examples, the ratio of the areal loading of the positive electrode active material in the positive electrode sheet to the areal loading of the negative electrode modification layer in the negative electrode sheet is 30 to 60:1, such as 50:1. Among them, the areal loading of the negative electrode modification layer is calculated based on the weight of the negative electrode composition. Optionally, the areal loading of the positive electrode active material in the positive electrode sheet is 20 mg / cm 2 ~40 mg / cm 2 .

[0133] In addition, the positive electrode sheet of the present application does not exclude other additional functional layers other than the positive electrode film layer. For example, the positive electrode sheet may further include a conductive bottom layer (such as composed of a conductive agent and a binder) disposed between the positive electrode current collector and the positive electrode film layer. For another example, the positive electrode sheet further includes a protective layer covering the surface of the positive electrode film layer.

[0134] [Electrolyte]

[0135] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0136] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0137] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0138] In some embodiments, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0139] In some embodiments, the electrolyte may further optionally include additives. The additives may include, for example, negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature or low-temperature performance, and the like.

[0140] [Separator membrane]

[0141] The separator membrane is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through. The present application does not particularly limit the type of the separator membrane, and various porous structure separator membranes well-known in the art can be selected.

[0142] In some embodiments, the material of the separator membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Additionally, the separator membrane can be a single-layer film or a multi-layer composite film. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0143] In some embodiments, a ceramic coating and / or a metal oxide coating are also provided on the separator membrane.

[0144] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0145] In some embodiments, the battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0146] In some embodiments, the outer package may include a housing and a cover plate. The housing may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover plate can be disposed on the opening to close the receiving cavity. The electrode assembly may be encapsulated in the receiving cavity.

[0147] In some embodiments, the outer package of the battery is a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0148] In other embodiments, the outer package of the battery is a soft package, such as a pouch soft package. The material of the soft package may be plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0149] The battery of the present application may include a battery cell form, a battery module form, and a battery pack form. The battery cell, battery module, and battery pack of the present application will be described below with reference to the accompanying drawings as appropriate.

[0150] The present application places no particular limitation on the shape of the battery, which may be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a battery cell 5 having a square structure as an example.

[0151] In some embodiments, referring to Figure 3 , the outer package may include a housing 51 and a top cover assembly 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be disposed on the opening to close the receiving cavity. The positive electrode plate, negative electrode plate, and separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell may be one or more, and those skilled in the art can select according to specific actual requirements.

[0152] In some embodiments, the battery can be assembled into a battery module. The number of batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] Figure 4 is a battery module 4 as an example. Referring to Figure 4 , in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other arbitrary manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0154] Optionally, the battery module 4 may further include a housing having an accommodation space, and a plurality of battery cells 5 are accommodated in the accommodation space.

[0155] In some embodiments, the above battery modules may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0156] Figure 5 and Figure 6 is a battery pack 1 as an example. Refer to Figure 5 and Figure 6 , in the battery pack 1, a battery box and a plurality of battery modules 4 disposed in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0157] The fifth aspect of the present application provides an electrical device, including the battery described in the fourth aspect of the present application.

[0158] The battery, battery module, and battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but are not limited thereto.

[0159] As the electrical device, the battery, battery module, or battery pack can be selected according to its usage requirements.

[0160] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the battery, a battery pack or a battery module can be used.

[0161] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and a battery can be used as the power source.

[0162] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For the reagents or instruments not specified with the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0163] Example 1

[0164] (1) Preparation of the modified layer slurry

[0165] Mix indium powder (Dv 50 = 50 nm) and copper powder (Dv 50 = 100 nm) in a molar ratio of 6:1 and grind evenly to obtain a metal mixed dry material;

[0166] Mix the metal mixed dry material, lithium sulfide, and PVDF-HFP in a mass ratio of 89:6:5 to obtain a negative electrode composition, and add NMP solvent, and stir evenly at 500 rpm to obtain the modified layer slurry.

[0167] (2) Preparation of the negative electrode sheet

[0168] Coat the modified layer slurry on one side of a copper foil (thickness 12 μm), and form a uniform composite layer on the copper foil surface through vacuum drying. The areal loading of the negative electrode composition is 0.5 mg / cm 2 . Cut the negative electrode sheet into a rectangle of 41 mm × 51 mm and weld the tab.

[0169] Pre-deposit lithium metal by assembling a half-cell: Use the copper foil with the formed composite layer as the working electrode, use a lithium-copper composite tape as the counter electrode (lithium-copper composite tape: laminate a 50-μm-thick lithium foil with a 12-μm-thick copper foil by rolling, and cut it into a rectangle of 41 mm × 51 mm and weld the tab), 1 mol / L LiPF6 as the electrolyte (solvent: EC and EMC, volume ratio 3:7) as the electrolyte, and PE as the separator. At a current density of 1 mA / cm 2 , discharge the working electrode to 0 V. During this process, lithium ions form an indium-lithium alloy with indium in the composite layer, continue to discharge the voltage below 0 V, and lithium ions deposit to form a lithium metal negative electrode layer until the lithium deposition capacity reaches 5 mAh·cm -2 to obtain the negative electrode sheet.

[0170] Examples 2 - 7

[0171] Prepare the negative electrode sheet according to the method of Example 1, except that when preparing the modified layer slurry, adjust the molar ratio of indium powder and copper powder.

[0172] Examples 8 - 12

[0173] Prepare the negative electrode sheet according to the method of Example 1, except that when preparing the modified layer slurry, adjust the mass of lithium sulfide, and correspondingly adjust the amount of the metal mixed dry material, so that the total amount of the two and the mass ratio of the binder remain at 95:5.

[0174] Example 13

[0175] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the slurry for the modified layer, indium powder and copper powder were mixed to form a metal mixed dry material at a molar ratio of 5:1, and the metal mixed dry material, lithium sulfide and PVDF-HFP were fed at a mass ratio of 86:7:7 to form a negative electrode composition.

[0176] Examples 14-15

[0177] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the slurry for the modified layer, indium powder was replaced with zinc powder (Dv 50 = 50 nm), silver powder (Dv 50 = 50 nm).

[0178] Comparative Example 1

[0179] The negative electrode sheet was prepared according to the method of Example 1, except that a copper foil without any modification (the same as in Example 1) was used as the negative electrode current collector:

[0180] Pre-deposition of lithium metal was carried out by assembling a half-cell: using the copper foil as the working electrode, a lithium-copper composite strip (the same as in Example 1) as the counter electrode, 1 mol / L LiPF6 as the electrolyte (solvent: EC and EMC, volume ratio 3:7) as the electrolyte, and PE as the separator. At a current density of 1 mA / cm 2 the working electrode was discharged to below 0 V, and lithium ions were deposited to form a lithium metal negative electrode layer until the lithium deposition capacity reached 5 mAh·cm -2 to obtain the negative electrode sheet.

[0181] Comparative Example 2

[0182] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the slurry for the modified layer, lithium sulfide and copper powder were not added, that is, only PVDF-HFP and indium powder were mixed and ground at a mass ratio of 5:95 to prepare the slurry.

[0183] Comparative Example 3

[0184] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the slurry for the modified layer, lithium sulfide and indium powder were not added, that is, only PVDF-HFP and copper powder were mixed and ground at a mass ratio of 5:95 to prepare the slurry.

[0185] Comparative Example 4

[0186] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the slurry for the modified layer, copper powder was not added, that is, only indium powder, lithium sulfide and PVDF-HFP were mixed and ground at a mass ratio of 89:6:5 to prepare the slurry.

[0187] Comparative Example 5

[0188] The negative electrode sheet was prepared according to the method of Example 1, except that when preparing the modified layer slurry, indium powder was not added, that is, only copper powder, lithium sulfide, and PVDF-HFP were mixed and ground in a mass ratio of 89:6:5 to prepare the slurry.

[0189] In the above examples and comparative examples, the specific amounts of the modified layer raw materials are shown in Table 1.

[0190] Table 1

[0191]

[0192] Note: "Pro / Li (n / n)" represents the molar ratio of the lithium-philic metal to the lithium-phobic metal; "areal loading" represents the weight of the negative electrode composition per unit area in the negative electrode sheet; "In / 50" represents indium powder with Dv 50 = 50 nm, "Cu / 100" represents copper powder with Dv 50 = 100 nm, "Zn / 50" represents zinc powder with Dv 50 = 50 nm, "Ag / 50" represents silver powder with Dv 50 = 50 nm.

[0193] Testing Part

[0194] 1. Preparation of the battery

[0195] [Positive electrode sheet]

[0196] The positive electrode active material lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), the conductive agent acetylene black, and the binder polytetrafluoroethylene (PVDF) were mixed in a mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) solvent was added and stirred until completely uniform to obtain the positive electrode slurry.

[0197] The positive electrode slurry was uniformly coated on both sides of the aluminum foil current collector, and the active material loading was 25 mg / cm 2 , and after drying and cold pressing steps, it was then slit into rectangles of 40 mm × 50 mm as the positive electrode sheet.

[0198] [Separator]

[0199] The polypropylene film was used as the separator

[0200] [Electrolyte]

[0201] LiPF6 with a concentration of 1 mol / L was used as the electrolyte, where the solvents were EC and EMC, and the volume ratio of the two was 3:7.

[0202] Stack a positive electrode plate and two negative electrode plates in sequence, and place a separator between the positive and negative electrodes to completely isolate the positive and negative electrodes and avoid short circuits. Subsequently, weld the tab to the positive electrode, place the bare battery cell in an aluminum-plastic film, inject the electrolyte, and vacuum heat-press and seal it. The sealed battery cell is left standing for 8 h, and then performance testing can be carried out. The laminated battery prepared by this method has a rated capacity of 140 mAh.

[0203] 2. Performance Testing

[0204] 2-1) First-week Capacity Testing

[0205] The testing process of the first-week capacity is as follows: At 25 °C, charge the battery prepared above at a constant current of 0.2C to 4.3V, and then charge it at a constant voltage until the current decays to 0.13C; during the discharging process, discharge it at a rate of 1C until the battery voltage drops to 2.8V, and then obtain the first-week discharging capacity.

[0206] 2-2) Cycle Performance Testing

[0207] The testing process of the cycle performance is as follows: At 25 °C, charge the battery at a constant current of 0.2C to 4.3V, and then charge it at a constant voltage until the current decays to 0.13C; during the discharging process, discharge it at a rate of 1C until the battery voltage drops to 2.8V, at this time, obtain the initial cycle capacity, repeat the above charge-discharge regime 150 times, record the discharging capacities at 50 cycles and 150 cycles, and divide the discharging capacity by the first-week discharging capacity to obtain the capacity retention rates at 50 cycles and 150 cycles.

[0208] The test results are shown in Table 2.

[0209] Table 2

[0210]

[0211]

[0212] Comparing Examples 1-15 with Comparative Examples 1-5 shows that introducing a modification layer formed by a negative electrode composition on the negative electrode plate in this application can inhibit the growth of metal dendrites and improve the rate performance, safety, and cycle stability of the battery.

[0213] Analysis of Examples 1-7 shows that controlling the molar ratio of the lithiumophilic metal to the lithium-phobic metal in the negative electrode composition to be (2-10):1 can further improve the comprehensive performance of the battery.

[0214] Comparing Example 1 with Examples 8-12 shows that controlling the lithium sulfide in the negative electrode composition to account for 2wt%-8wt% can further promote lithium conduction and stabilize the SEI film, and the impedance on the negative electrode side is also small.

[0215] It can be seen from the comparison between Example 1 and Examples 14-15 that when indium powder is used as the lithiumophilic metal, the formed lithium-indium alloy has a higher affinity for lithium and is beneficial to the migration of lithium ions.

[0216] By comparing and analyzing Example 1 with Comparative Examples 1-5, it can be seen that the negative electrode sheet prepared from the copper foil current collector without the modification layer does not have the ability of uniform lithium metal deposition / stripping, and cannot achieve the effects of inhibiting dendrites and realizing long cycle life. In addition, adding a single lithiumophilic metal or lithium-phobic metal cannot achieve the effects of both lithium conduction / lithium affinity and good electrical conductivity. The cycle stability of the battery is poor and the safety is not high.

[0217] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered by the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode plate, characterized in that, It includes a negative current collector and a negative electrode modification layer located on the surface of the negative current collector. Among them, the negative electrode modification layer contains lithium sulfide, a lithium alloy formed by lithium and a lithium-philic metal, and a lithium-phobic metal, and the atomic molar ratio of the lithium-philic metal to the lithium-phobic metal in the lithium alloy is (1 to 30):

1.

2. The negative electrode sheet according to claim 1, wherein, The atomic molar ratio of the lithium-philic metal to the lithium-phobic metal in the lithium alloy is (2 to 10):

1.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the total mass of the lithium-philic metal and the lithium-phobic metal in the lithium alloy to the mass of lithium sulfide is (4 to 60):1, and can be optionally (10 to 50):

1.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The lithium-philic metal includes at least one of zinc, indium, aluminum, magnesium, silver, tin, gallium, antimony, bismuth or germanium; Optionally, the lithium-philic metal includes indium.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The resistivity of the lithium-phobic metal at 20 °C is lower than 15 μΩ·cm; Optionally, the lithium-phobic metal includes at least one of copper, iron, nickel, cobalt or tungsten.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The negative electrode modification layer further includes a binder; Optionally, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer.

7. The negative electrode sheet according to claim 6, characterized in that, Based on the total weight of lithium sulfide, the binder, the lithium-phobic metal and the lithium-philic metal in the lithium alloy, the mass content of lithium sulfide is 1% to 16%, the total mass content of the lithium-phobic metal and the lithium-philic metal in the lithium alloy is 75% to 98%, and the mass content of the binder is 1% to 10%; Optionally, based on the total weight of lithium sulfide, the binder, the lithium-phobic metal and the lithium-philic metal in the lithium alloy, the mass content of lithium sulfide is 2% to 8%, the total mass content of the lithium-phobic metal and the lithium-philic metal in the lithium alloy is 85% to 95%, and the mass content of the binder is 3% to 7%.

8. The negative electrode sheet according to claim 6 or 7, characterized in that, In the negative electrode sheet per unit area, the total weight of lithium sulfide, binder, lithium-phobic metal and lithium-philic metal in the lithium alloy is 0.3 mg / cm 2 ~1.0 mg / cm 2 .

9. The negative electrode sheet according to any one of claims 1-8, characterized in that, The negative electrode sheet further includes a lithium metal negative electrode layer, and the lithium metal negative electrode layer is located on the side of the negative electrode modification layer away from the negative current collector.

10. The negative electrode sheet according to any one of claims 1-9, characterized in that, The negative current collector includes at least one of copper foil, titanium foil or stainless steel.

11. A negative electrode composition, characterized in that, It contains lithium sulfide, a lithium-philic metal and a lithium-phobic metal; among them, the molar ratio of the lithium-philic metal to the lithium-phobic metal is (1 to 30):

1.

12. The negative electrode composition according to claim 11, wherein The molar ratio of the lithium-philic metal to the lithium-phobic metal is (2 to 10):

1.

13. The negative electrode composition according to claim 11 or 12, characterized in that, The ratio of the total mass of the lithium-philic metal and the lithium-phobic metal to the mass of lithium sulfide is (4 to 60):1, and can be optionally (10 to 50):

1.

14. The negative electrode composition according to any one of claims 11-13, characterized in that, The lithium-philic metal includes at least one of zinc, indium, aluminum, magnesium, silver, tin, gallium, antimony, bismuth or germanium; Optionally, the lithium-philic metal includes indium.

15. The negative electrode composition according to any one of claims 11-14, characterized in that, The resistivity of the lithium-phobic metal at 20 °C is lower than 15 μΩ·cm; Optionally, the lithium-phobic metal includes at least one of copper, iron, nickel, cobalt or tungsten.

16. The negative electrode composition according to any one of claims 11-15, characterized in that, The negative electrode composition further includes a binder; Optionally, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer.

17. The negative electrode composition according to claim 16, characterized in that, Based on the total weight of the negative electrode composition, the mass content of lithium sulfide is 1% to 16%, the total mass content of the lithium-phobic metal and the lithium-philic metal is 75% to 98%, and the mass content of the binder is 1% to 10%; Optionally, based on the total weight of the negative electrode composition, the mass content of lithium sulfide is 2% to 8%, the total mass content of lithium-phobic metal and lithium-philic metal is 85% to 95%, and the mass content of the binder is 3% to 7%.

18. The negative electrode composition according to any one of claims 11-17, characterized in that, The median particle size Dv of the lithiumophilic metal 50 is 20 nm to 500 nm, and the median particle size Dv of the lithium-phobic metal 50 is 50 nm to 200 nm.

19. A method for preparing a negative electrode plate, characterized in that, Comprising: Preparing a composite layer: Applying the negative electrode composition according to any one of claims 11-18 on a negative electrode current collector to form a composite layer; Pre-depositing lithium metal: Making the lithium-philic metal in the composite layer form a lithium alloy with the deposited lithium ions to form a negative electrode modification layer on the surface of the negative electrode current collector.

20. The preparation method according to claim 19, characterized in that, In the negative electrode sheet per unit area, the weight of the negative electrode composition is 0.3 mg / cm 2 ~1.0 mg / cm 2 .

21. The preparation method according to claim 19 or 20, characterized in that, The process of pre-depositing metallic lithium further includes: continuously forming a lithium metal negative electrode layer on the negative electrode modification layer by depositing lithium ions.

22. The preparation method according to any one of claims 19-21, characterized in that, The conditions for pre-depositing lithium metal include: a current density of 0.5 mA / cm 2 ~2 mA / cm 2 ; Optionally, the pre-deposition results in a pre-deposited lithium capacity of 1 mAh / cm 2 ~20 mAh / cm 2 .

23. A battery, characterized in that, Comprising the negative electrode sheet according to any one of claims 1-10 or the negative electrode sheet prepared by the preparation method according to any one of claims 19-22.

24. An electrical device, characterized in that, Comprising the battery according to claim 23.

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