A negative lithium supplementing agent, a negative electrode sheet, and a secondary battery

Abstract

The application discloses a negative electrode lithium supplementing agent, a negative electrode pole piece and a secondary battery, and belongs to the technical field of batteries. The negative electrode lithium supplementing agent provided by the application is coated with a metal lithium layer on the outer surface of a porous carbon inner core, a passivation layer is formed by using a specific compound on the metal lithium layer, and the negative electrode lithium supplementing agent satisfies 60<=Sh1 / M<=2000 and 0.2<=h2 / h1<=2. When the negative electrode lithium supplementing agent is used in the preparation of a negative electrode pole piece and then used in a secondary battery, lithium can be stored in the cycle process, a new delithiation mechanism can be realized, dead lithium and battery expansion phenomena generated in the cycle process can be reduced, lithium ions can be supplemented in the cycle, irreversible lithium consumption can be reduced, in addition, the introduction of the passivation layer can also play the role of an artificial SEI film, the desolvation energy barrier can be weakened, the brittleness and instability caused by the consumption of the SEI film naturally synthesized on the surface of lithium metal can be reduced, and thus the cycle performance and safety performance of the secondary battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and in particular to a negative electrode lithium supplementing agent, a negative electrode tab and a secondary battery. BACKGROUND

[0002] At present, silicon is the highest specific capacity negative electrode material known, reaching 4200 mAh / g. Compared with graphite negative electrode materials, silicon also has a higher lithium extraction potential, which can effectively avoid the precipitation of lithium during high-rate charging and discharging, and can improve the safety performance of the battery. However, silicon will produce a large volume effect during charging and discharging, which will cause the collapse of the electrode structure and the peeling of the active material, resulting in rapid capacity decay. In addition, the poor conductivity of silicon seriously affects the cycle life of lithium batteries. The silicon-carbon negative electrode material produced at the present stage has a generally low compaction density, which is not ideal for improving the energy density. Metal lithium is the most attractive negative electrode material in high-energy-density batteries due to its high specific capacity (3860 mAh / g) and extremely low electrode potential (-3.04 V vs. standard hydrogen electrode potential). The current negative electrode lithium supplementing agent added to the preparation of the secondary battery will cause local lithium precipitation in the electrode tab during the cycle process due to uneven internal temperature, resulting in a decrease in cycle performance and a decrease in safety performance. SUMMARY

[0003] The present application aims to solve the technical problem of the decrease in cycle performance and safety performance of the secondary battery caused by the addition of the lithium supplementing agent in the negative electrode tab in the prior art, and proposes a negative electrode lithium supplementing agent, a negative electrode tab and a secondary battery.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode lithium supplementing agent, which comprises a porous carbon core and a metal lithium layer attached to the surface of the porous carbon, and a passivation layer coated on the surface of the metal lithium layer.

[0005] The passivation layer comprises a non-lithium compound and a lithium-containing compound, and the non-lithium compound comprises at least one of 16,17-dihydroxyanthraquinone violet and guar gum.

[0006] The negative electrode lithium supplementing agent satisfies 60≤A≤2000 and 0.2≤B≤2.

[0007] Wherein A=Sh1 / M and B=h2 / h1.

[0008] S is the specific surface area of the porous carbon material.

[0009] h1 is the thickness of the metal lithium layer.

[0010] M is the mass of lithium metal attached to the surface of 1 g of porous carbon.

[0011] h2 is the thickness of the passivation layer.

[0012] As an embodiment of the present application, the S is 500-2000 m 2 / g.

[0013] As an embodiment of the present application, the h1 is 0.1-1 m.

[0014] As an embodiment of the present application, the M is 0.3-10 g.

[0015] As an embodiment of the present application, the h2 is 0.1-0.3 m.

[0016] As an embodiment of the present application, the negative lithium supplement agent has a Dv50 particle size of 1-10 m, a porosity P of 30-60%, and a pore size r of 50-200 nm.

[0017] As an embodiment of the present application, the porous carbon includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanotubes, conductive carbon black, reduced graphene oxide, graphene oxide, and carbon fibers.

[0018] As an embodiment of the present application, the lithium-containing compound includes at least one of lithium chloride, lithium acetate, lithium fluoride, and lithium difluorodioxalate phosphate.

[0019] In a second aspect of the present application, a preparation method of a negative lithium supplement agent is provided, which includes the following steps:

[0020] (1) adding a non-lithium compound, a lithium-containing compound, and a binder into N-methylpyrrolidone to mix uniformly to obtain a passivation layer premix;

[0021] (2) coating metallic lithium on the outer surface of the porous carbon material by a gas-phase chemical deposition method or a melting method to obtain a composite;

[0022] (3) placing the composite in the passivation layer premix under an inert gas environment, and then spray drying to obtain the negative lithium supplement agent.

[0023] As an embodiment of the present application, the mass ratio of the lithium-containing compound and the non-lithium compound is 1:(1-3).

[0024] In a third aspect of the present application, a negative electrode tab is provided, which includes a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, the negative active material layer including a negative active material, the negative lithium supplement agent of the present application, a binder, and a thickening agent.

[0025] As an embodiment of the present application, the mass percentage of the negative lithium supplement agent in the total mass of the negative active material layer is 0.1-0.8%.

[0026] In a fourth aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet, the positive electrode sheet, the electrolyte and the separator as described in the present application.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] The negative lithium supplementing agent provided by the present application coats a metal lithium layer on the outer surface of the porous carbon core, and a passivation layer is formed on the metal lithium layer by using a specific compound. When the negative lithium supplementing agent is used in the negative electrode sheet and then used in the preparation of a secondary battery, it can not only store lithium during the cycle process, but also realize a new delithiation mechanism, reduce the dead lithium and battery swelling phenomenon generated during the cycle process, supplement lithium ions during the cycle, reduce irreversible lithium consumption, and the introduction of the passivation layer can also play the role of an artificial SEI film, weaken the desolvation energy barrier, and reduce the brittleness and instability caused by the consumption of the natural SEI film on the surface of the lithium metal; thereby effectively improving the cycle performance and safety performance of the secondary battery. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0030] In the present application, the technical features described in an open manner include a closed technical solution composed of listed features, and also include an open technical solution containing listed features.

[0031] In the present application, if no special description is given, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when a range is referred to as an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0032] The reagents or instruments used in the present application are not marked with the manufacturer, and are all conventional products that can be obtained through market purchase.

[0033] In one embodiment of the present application, the present application provides a negative electrode lithium supplementing agent, the negative electrode lithium supplementing agent comprising a porous carbon core, a metal lithium layer attached to the surface of the porous carbon, and a passivation layer coated on the surface of the metal lithium layer;

[0034] The passivation layer comprises at least one of 16.17-dihydroxyanthraquinone violet and guar gum.

[0035] The negative electrode lithium supplementing agent satisfies 60≤A≤2000 and 0.2≤B≤2.

[0036] Wherein A=Sh1 / M and B=h2 / h1.

[0037] S is the specific surface area of the porous carbon material.

[0038] h1 is the thickness of the metal lithium layer.

[0039] M is the mass of lithium metal attached to the surface of 1 g of the porous carbon.

[0040] h2 is the thickness of the passivation layer.

[0041] The present application researches and finds that the negative electrode lithium supplementing agent provided by the present application coats a metal lithium layer on the outer surface of a porous carbon core, simultaneously forms a passivation layer on the metal lithium layer by using a specific compound, and satisfies 60≤Sh1 / M≤2000 and 0.2≤h2 / h1≤2. The negative electrode lithium supplementing agent satisfying the above relationship can ensure that, on the basis of as much lithium metal as possible being attached to the surface of the porous carbon material, the specific surface area of the lithium metal does not exceed the specific surface area of the porous carbon material, so that when the negative electrode lithium supplementing agent is used in a negative electrode sheet and then used in the preparation of a secondary battery, it can not only store lithium in the cycle process, but also realize a new delithiation mechanism, reduce the dead lithium and battery swelling phenomenon generated in the cycle process; at the same time, it can also supplement lithium ions in the cycle, reduce irreversible lithium consumption; in addition, the introduction of the passivation layer can also play the role of an artificial SEI film, weaken the desolvation energy barrier, and reduce the brittleness and instability caused by the consumption of the natural SEI film on the surface of the lithium metal; thereby effectively improving the cycle performance and safety performance of the secondary battery.

[0042] Exemplarily, the A can be any point value or any two-point range value between 60 and 2000, such as 60, 80, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, etc.

[0043] In an embodiment, A is 150-600. For example, A can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, etc. When A is further selected to be 150-600, the comprehensive performance of the secondary battery obtained is better.

[0044] Illustratively, B can be any point value or any two-point range value between 0.2-2, such as 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, etc.

[0045] In an embodiment, B is 0.3-0.7. For example, B can be 0.3, 0.4, 0.5, 0.6, 0.7, etc. When B is further selected to be 150-600, the comprehensive performance of the secondary battery obtained is better.

[0046] In an embodiment, S is 500-2000m 2 / g.

[0047] It should be noted that the specific surface area S of the porous carbon is obtained by 77K, N2 adsorption method.

[0048] Illustratively, S can be any point value or any two-point range value between 500-2000m 2 / g, such as 500m 2 / g, 600m 2 / g, 700m 2 / g, 800m 2 / g, 900m 2 / g, 1000m 2 / g, 1100m 2 / g, 1200m 2 / g, 1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g, 1700m 2 / g, 1800m 2 / g, 1900m 2 / g, 2000m 2 / g, etc.

[0049] In an embodiment, S is 1000-1500m 2 / g.

[0050] The present application finds that the specific surface area of the porous carbon will affect the deposition of metal lithium on its surface, and will also affect the subsequent storage of lithium and reduce the amplitude of battery expansion; when S is further selected to be 500-2000m 2 / g, especially 1000-1500 m 2 / g, the cycle performance and safety performance of the secondary battery prepared subsequently are more optimal.

[0051] In an embodiment, the h1 is 0.1-1 μm.

[0052] It should be noted that the thickness h1 of the metal lithium layer is obtained by using a focused ion beam (FIB) technology and a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0053] Illustratively, the h1 can be any point value or any two-point range value between 0.1-1 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc.

[0054] In an embodiment, the h1 is 0.3-0.6 μm.

[0055] The present application research finds that the thickness of the metal lithium layer not only affects the storage effect of lithium ions of the negative electrode lithium supplement agent, but also affects the supplement effect of lithium ions in the subsequent cycle process; when the h1 is further selected to be 0.1-1 μm, especially 0.3-0.6 μm, the cycle performance of the secondary battery obtained is more optimal.

[0056] In an embodiment, the M is 0.3-8 g.

[0057] It should be noted that the mass of the lithium metal attached to the surface of 1 g of porous carbon is obtained by electrochemical method, infrared or ultraviolet spectroscopy.

[0058] Illustratively, the mass M of the lithium metal attached to the surface of 1 g of porous carbon can be any point value or any two-point range value between 0.3-8 g, such as 0.3 g, 0.5 g, 0.8 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g, 8 g, etc.

[0059] In an embodiment, the M is 1-4 g.

[0060] The present application research finds that the mass of the lithium metal attached to the surface of 1 g of porous carbon not only affects the energy density of the secondary battery prepared subsequently, but also affects the supplement of consumed lithium ions in the cycle process of the negative electrode lithium supplement agent; when the M is further selected to be 0.3-8 g, especially 1-4 g, the irreversible lithium consumption can be better reduced, and the battery swelling in the cycle process can be reduced, thereby effectively improving the cycle performance and safety performance of the secondary battery.

[0061] In an embodiment, the h2 is 0.1-0.3 μm.

[0062] It should be noted that the thickness h2 of the passivation layer is obtained by a combination of focused ion beam (FIB) technology and scanning electron microscopy (SEM) or transmission electron microscopy (TEM) testing.

[0063] Exemplarily, the thickness h2 of the passivation layer can be any point value or any two-point range value between 0.1-0.3 μm, such as 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.2 μm, 0.22 μm, 0.24 μm, 0.26 μm, 0.28 μm, 0.3 μm, etc.

[0064] In an embodiment, the h2 is 0.15-0.22 μm.

[0065] The present application researches and finds that the passivation layer with a suitable thickness range can effectively form an artificial SEI film without affecting the transport of lithium ions, thereby effectively improving the cycle performance and safety performance of the secondary battery prepared subsequently.

[0066] In an embodiment, the Dv50 particle size of the negative electrode lithium supplementing agent is 1-10 μm, the porosity P is 30-60%, and the pore size r is 50-200 nm.

[0067] It should be noted that the Dv50 particle size of the negative electrode lithium supplementing agent is obtained by laser particle size instrument testing, the porosity P is obtained by nitrogen or argon gas adsorption method testing, and the pore size r is obtained by nitrogen or argon gas adsorption method testing.

[0068] Exemplarily, the Dv50 particle size of the negative electrode lithium supplementing agent can be any point value or any two-point range value between 1-10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The porosity P can be any point value or any two-point range value between 30-60%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc. The pore size r can be any point value or any two-point range value between 50-200 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, etc.

[0069] The application research finds that the Dv50 particle size, porosity and pore size of the negative electrode lithium supplementing agent provided by the application in the above range can better realize the transport and storage of lithium ions, and can also effectively improve the stability of the SEI film and facilitate the subsequent processing to form a negative electrode active material layer, thereby improving the cycle performance and safety performance of the secondary battery prepared subsequently.

[0070] In an embodiment, the porous carbon includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanotubes, conductive carbon black, reduced graphene oxide, graphene oxide, carbon fibers.

[0071] In an embodiment, the lithium-containing compound includes at least one of lithium chloride, lithium acetate, lithium fluoride, lithium difluorophosphate.

[0072] The application research finds that when the above type of substance is selected, the comprehensive performance of the secondary battery obtained is more optimal.

[0073] In an embodiment of the application, the application provides a preparation method of the negative electrode lithium supplementing agent, which includes the following steps:

[0074] (1) adding a non-lithium compound, a lithium-containing compound and a binder into N-methylpyrrolidone to mix uniformly to obtain a passivation layer premix solution;

[0075] (2) coating metal lithium on the outer surface of the porous carbon material by a gas phase chemical deposition method or a melting method to obtain a composite;

[0076] (3) placing the composite in the passivation layer premix solution under an inert gas environment, and then spray drying to obtain the negative electrode lithium supplementing agent.

[0077] In an embodiment, the mass ratio of the lithium-containing compound and the non-lithium compound is 1:(1-3).

[0078] The application research finds that the mass of the non-lithium compound and the lithium-containing compound in the passivation layer will affect the mechanical strength, toughness and stability of the artificial SEI film formed, and will also affect the transport of lithium ions. When the mass of the non-lithium compound and the lithium-containing compound is further selected to be within the above range, the cycle performance of the secondary battery obtained is more optimal, and the volume expansion during the cycle process is smaller, i.e., the safety is higher.

[0079] In an embodiment, the solvent in the solution of the non-lithium compound and the lithium-containing compound is N-methylpyrrolidone.

[0080] In an embodiment, the solution of the non-lithium compound and the lithium-containing compound further includes a binder. Illustratively, the binder includes polyvinylidene fluoride.

[0081] In one embodiment of the present application, the present application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a negative electrode lithium supplementing agent, a binder and a thickening agent.

[0082] In one embodiment, the mass percentage of the negative electrode lithium supplementing agent is 0.1-0.8% based on the total mass of the negative electrode active material layer.

[0083] Exemplarily, the mass percentage of the negative electrode lithium supplementing agent can be any point value or any range value between 0.1-0.8% based on the total mass of the negative electrode active material layer, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% and the like.

[0084] The present application researches find that the addition of the negative electrode lithium supplementing agent with a suitable mass percentage range can effectively reduce the dead lithium generated during the cycle process, improve the cycle stability of the secondary battery, and also avoid the occurrence of lithium precipitation phenomenon, thereby improving the safety performance of the secondary battery.

[0085] In one embodiment, the negative electrode active material comprises at least one of artificial graphite, natural graphite, hard carbon, silicon-containing graphite, silicon oxide-containing graphite, silicon and silicon oxide.

[0086] In one embodiment, the binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polypropylene and styrene butadiene rubber.

[0087] In one embodiment, the thickening agent comprises at least one of methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, sodium polyacrylate and sodium carboxymethyl cellulose.

[0088] In one embodiment of the present application, the present application provides a secondary battery, the secondary battery comprising the negative electrode sheet of the present application, a positive electrode sheet, an electrolyte and a separator.

[0089] In one embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

[0090] The present application does not have any limitation on the selection of the positive electrode active material, and a conventional positive electrode active material in the art can be used. Exemplarily, the positive electrode active material can be at least one of lithium cobaltate, lithium manganate, lithium nickel cobalt manganate and lithium nickel cobalt aluminate.

[0091] The selection of the positive electrode conductive agent is not limited in the present application, and a conventional positive electrode conductive agent in the art can be used. Illustratively, the positive electrode conductive agent can be at least one of conductive carbon black, carbon nanotube, and graphene.

[0092] The selection of the positive electrode binder is not limited in the present application, and a conventional positive electrode binder in the art can be used. Illustratively, the positive electrode binder can be at least one of polyvinylidene fluoride, lithium polyacrylate, polyvinyl acetate, and styrene butadiene rubber.

[0093] In an embodiment, the electrolyte comprises an organic solvent, a lithium salt, and an additive.

[0094] The selection of the organic solvent is not limited in the present application, and a conventional organic solvent in the art can be used. Illustratively, the organic solvent can be at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate.

[0095] The selection of the lithium salt is not limited in the present application, and a conventional lithium salt in the art can be used. Illustratively, the lithium salt can be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0096] The selection of the additive is not limited in the present application, and a conventional additive in the art can be used. Illustratively, the additive can be at least one of a film-forming additive, a conductive additive, and a flame-retardant additive.

[0097] Example 1

[0098] The embodiments of the present application provide a negative electrode lithium supplement agent, a negative electrode tab, and a secondary battery, and a preparation method thereof, which comprises the following steps:

[0099] (1) Preparation of the negative electrode lithium supplement agent

[0100] S1, a non-lithium compound (16, 17-dihydroxyanthraquinone violet, DHV), a lithium-containing compound (lithium chloride), and a binder (polytetrafluoroethylene, PVDF) are added into N-methylpyrrolidone and uniformly mixed to obtain a passivation layer premix solution;

[0101] S2, metal lithium is coated on the outer surface of the porous carbon material (carbon nanotube) by a gas phase chemical deposition method to obtain a composite;

[0102] S3, the composite is placed in the passivation layer premix solution under a nitrogen gas environment, and then spray dried to obtain the negative electrode lithium supplement agent;

[0103] (2) Preparation of the negative electrode tab

[0104] The negative electrode material (graphite), the negative electrode lithium supplement, the conductive agent (conductive carbon black SP), the binder (butyl rubber), and the thickening agent (sodium carboxymethyl cellulose) are mixed in a mass ratio of 97.7:0.4:0.5:0.7:0.7, and then coated on a Cu foil at 105 DEG C in a vacuum. After rolling and slitting, a negative electrode sheet is obtained.

[0105] (3) Preparation of the positive electrode sheet

[0106] The positive electrode material (lithium cobaltate), the conductive agent (acetylene black SP), and the binder (polyvinylidene fluoride) are mixed in a mass ratio of 98:1.2:0.8 in an N-methylpyrrolidone solvent system, and then coated on an Al foil. After drying, rolling, and slitting, a positive electrode sheet is obtained.

[0107] (4) Preparation of the electrolyte

[0108] A solution of lithium salt LiPF6 and non-aqueous organic solvent (vinyl carbonate: diethyl carbonate: propylene carbonate: propyl propionate: vinylene carbonate) = 25:25:15:31:4, mass ratio) is prepared in a mass ratio of 8:92, and used as the electrolyte of the lithium battery.

[0109] (5) Preparation of the separator

[0110] An alumina ceramic polyethylene (PE) porous polymer film is used as the separator.

[0111] (6) Preparation of the secondary battery

[0112] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a safe isolation role. An electrode assembly is obtained by winding. The electrode assembly is placed in a packaging shell, electrolyte is injected, and the secondary battery is obtained.

[0113] Examples 2-5

[0114] The examples of the application provide a negative electrode lithium supplement, a negative electrode sheet, and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode sheet, and the secondary battery and that of Example 1 is that the addition amount of metal lithium is adjusted to change the thickness of the metal lithium layer.

[0115] Examples 6-9

[0116] The examples of the application provide a negative electrode lithium supplement, a negative electrode sheet, and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode sheet, and the secondary battery and that of Example 1 is that the addition amount of metal lithium is adjusted to change the thickness of the metal lithium layer.

[0117] Examples 10-13

[0118] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the mass of the lithium metal attached to the surface of the 1g porous carbon is changed by adjusting the metal lithium.

[0119] Embodiments 14-17

[0120] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the thickness of the passivation layer is changed by adjusting the amount of the passivation layer premix.

[0121] Embodiments 18-19

[0122] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the Dv50, P and r of the negative lithium supplement agent are changed by adjusting the preparation parameters.

[0123] Embodiment 20

[0124] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the type of the porous carbon is adjusted.

[0125] Embodiment 21

[0126] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the type of the lithium-containing compound is adjusted.

[0127] Embodiment 22

[0128] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the type of the non-lithium compound is adjusted.

[0129] Embodiments 23-24

[0130] The embodiment of the present application provides a negative lithium supplement agent, a negative electrode sheet and a secondary battery, and the preparation method of the negative lithium supplement agent, the negative electrode sheet and the secondary battery is different from that of the embodiment 1, wherein the mass ratio of the lithium-containing compound and the non-lithium compound is changed by adjusting the addition amount of the lithium-containing compound and the non-lithium compound.

[0131] Embodiments 25-26

[0132] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the embodiment of the present application differ from those of example 1 in that the mass percentage in the negative electrode sheet is changed by adjusting the addition amount of the negative lithium supplement agent.

[0133] Comparative example 1-2

[0134] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the comparative example of the present application differ from those of example 1 in that the parameters in table 1-2 are achieved by adjusting the porous carbon and its addition amount, the addition amount of lithium metal.

[0135] Comparative example 3-4

[0136] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the comparative example of the present application differ from those of example 1 in that the parameters in table 1-2 are achieved by adjusting the thickness of the lithium metal layer and the passivation layer.

[0137] Comparative example 5

[0138] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the comparative example of the present application differ from those of example 1 in that the passivation layer is not introduced.

[0139] Comparative example 6

[0140] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the comparative example of the present application differ from those of example 1 in that the passivation layer does not contain a lithium-containing compound.

[0141] Comparative example 7

[0142] The negative lithium supplement agent, the negative electrode sheet and the secondary battery of the comparative example of the present application differ from those of example 1 in that the lithium metal layer is not introduced.

[0143] Specific surface area S m of the porous carbon material of the examples and comparative examples 2 / g, the thickness h1 of the lithium metal layer μm, the mass M of the lithium metal attached to 1 g of the porous carbon g, the thickness h2 of the passivation layer μm, A, B, the Dv50 particle size of the negative lithium supplement agent, the porosity P, the pore size r, the type of the porous carbon, the type of the lithium-containing compound, the type of the non-lithium compound, the mass ratio m of the lithium-containing compound and the non-lithium compound, the addition amount n of the negative lithium supplement agent in the negative active material layer as shown in table 1-2;

[0144] Table 1

[0145]

[0146]

[0147] Table 2

[0148]

[0149]

[0150] The secondary batteries prepared in the examples and comparative examples were tested for cycle performance, specifically, the cycle test was carried out at an ambient temperature of 25°C in a Neware test cabinet, and the results are as follows: 1) rest: 5 min; 2) constant current and constant voltage charging at 0.5 C to 4.53 V, with a cutoff current of 0.02 C; 3) rest: 5 min; 4) constant current discharging at 0.5 C, with a cutoff voltage of 3.0 V; 5) cycle from step 1 to step 4 until the cycle number at which the cycle capacity retention rate is 80% and the expansion rate of the battery at that cycle number;

[0151] The cycle number at which the cycle capacity retention rate is 80% and the corresponding expansion rate of the battery were recorded, and the results are shown in Table 3.

[0152] Table 3

[0153]

[0154]

[0155] As can be seen from Table 3, when the technical solutions provided in the present application are used, the products obtained have excellent cycle performance and safety performance, and when cycled to a cycle capacity retention rate of 80%, the cycle number is more than 998 cycles, and the expansion rate is less than 14.5%;

[0156] As can be seen from Examples 1-26 and Comparative Examples 1-4, when the negative lithium supplement agent does not satisfy 60≤Sh1 / M≤2000 or does not satisfy 0.2≤h2 / h1≤2, specifically, when the above relationship is not satisfied, several cases will occur, the first of which is that the lithium metal cannot completely wrap the porous carbon, and part of the lithium ions will be deposited on the porous carbon material during the cycle of the obtained secondary battery, resulting in a dead lithium phenomenon and reducing the cycle performance of the secondary battery; the second is that when the lithium metal layer is too thick, the outer layer of the porous carbon material has too much lithium metal, the transmission pore diameter is reduced, affecting the transmission of lithium ions, which will also significantly reduce the cycle performance of the obtained secondary battery; as can be seen from Examples 1-26 and Comparative Example 5, when no passivation layer is introduced into the negative lithium supplement agent, the cycle performance of the obtained secondary battery is significantly reduced, and the swelling rate after cycling also shows a certain increasing trend, i.e., the safety is reduced; as can be seen from Examples 1-26 and Comparative Example 6, when the passivation layer does not contain a lithium-containing compound, the cycle performance of the obtained secondary battery is significantly reduced, and the safety performance also has a certain degree of decline; as can be seen from Examples 1-26 and Comparative Example 7, when no metal lithium layer is introduced, the cycle performance of the obtained secondary battery is significantly reduced, and the swelling rate after cycling is also significantly increased, i.e., the safety is significantly reduced.

[0157] Finally, it should be noted that the above examples are used to illustrate the technical solutions of the present application and are not a limitation on the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A negative lithium supplementing agent, characterized by, The negative lithium supplement agent comprises a porous carbon core, a metal lithium layer attached to the surface of the porous carbon, and a passivation layer coated on the surface of the metal lithium layer. The passivation layer comprises a non-lithium compound and a lithium-containing compound, and the non-lithium compound comprises at least one of 16,17-dihydroxyanthraquinone violet and guar gum. The negative lithium supplement agent satisfies 60≤A≤2000 and 0.2≤B≤2. Wherein A=Sh1 / M and B=h2 / h1. S is the specific surface area of the porous carbon material; said S is 500-2000 m 2 / g; h1 is the thickness of the metal lithium layer, and the h1 is 0.1-1 μm. M is the mass of lithium metal attached to the surface of 1 g of the porous carbon, and the M is 0.3-8 g. h2 is the thickness of the passivation layer, and the h2 is 0.1-0.3 μm.

2. The negative lithium supplement agent according to claim 1, characterized in that, The Dv50 particle size of the negative lithium supplement agent is 1-10 μm, the porosity P is 30-60%, and the pore size r is 50-200 nm.

3. The negative lithium supplement agent according to claim 1, characterized in that, The porous carbon comprises at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, reduced graphene oxide, graphene oxide, and carbon fibers.

4. The negative lithium supplement agent according to claim 1, characterized in that, The lithium-containing compound comprises at least one of lithium chloride, lithium acetate, lithium fluoride, and lithium difluorodioxalate phosphate.

5. The method of producing a negative-electrode lithium supplementing agent according to any one of claims 1 to 4, wherein The preparation method comprises the following steps: (1) adding a non-lithium compound, a lithium-containing compound, and a binder into N-methylpyrrolidone to mix uniformly to obtain a passivation layer premix; (2) coating metal lithium on the outer surface of the porous carbon material by a gas phase chemical deposition method or a melting method to obtain a composite; (3) placing the composite in the passivation layer premix under an inert gas environment, and then spray drying to obtain a negative lithium supplement agent.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the lithium-containing compound to the non-lithium compound is 1:(1-3).

7. A negative electrode sheet characterized by comprising: The negative electrode tab comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, and the negative active material layer comprises a negative active material, a negative lithium supplement agent as claimed in any one of claims 1-4, a binder, and a thickening agent.

8. The negative electrode sheet according to claim 7, characterized by The mass percentage of the negative lithium supplement agent in the total mass of the negative active material layer is 0.1-0.8%.

9. A secondary battery characterized by comprising: The secondary battery comprises a negative electrode tab as claimed in claim 7 or 8, a positive electrode tab, an electrolyte, and a separator.

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