Negative electrode lithium supplement agent, negative electrode pole piece and secondary battery

Abstract

The invention discloses a negative electrode lithium supplement agent, a negative electrode pole piece and a secondary battery, and belongs to the technical field of batteries. According to the negative electrode lithium supplement agent, the outer surface of the porous carbon core is coated with the metal lithium layer, meanwhile, the metal lithium layer adopts the specific compound to form the passivation layer, and the negative electrode lithium supplement agent meets the conditions that Sh1 / M is larger than or equal to 60 and smaller than or equal to 2000, and h2 / h1 is larger than or equal to 0.2 and smaller than or equal to 2. A new lithium removal mechanism can also be realized, and the phenomena of dead lithium and battery expansion generated in the circulation process are reduced; meanwhile, lithium ions can be supplemented in circulation, and irreversible lithium consumption is reduced; besides, the introduction of the passivation layer can also play a role of an artificial SEI film, weakens a desolvation energy barrier, and reduces brittleness and instability caused by consumption of the SEI film naturally synthesized on the surface of the lithium metal; therefore, the cycle performance and the safety performance of the secondary battery are effectively improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode lithium supplement, a negative electrode plate and a secondary battery. Background Art

[0002] At present, silicon is the negative electrode material with the highest known specific capacity, reaching 4200mAh / g. Compared with graphite negative electrode materials, silicon also has a higher lithium deintercalation potential, which can effectively avoid the precipitation of lithium during high-rate charge and discharge, and can improve the safety performance of the battery. However, silicon will produce a large volume effect during the charge and discharge process, leading to the collapse of the electrode structure and the peeling of the active material, causing the capacity to decay rapidly. In addition, the poor conductivity of silicon seriously affects the cycle life of lithium batteries. The compaction density of silicon-carbon negative electrode materials currently produced is generally low, and the improvement of energy density is not ideal. Metallic lithium is the most attractive negative electrode material in high-energy density batteries due to its high specific capacity (3860mAh / g) and extremely low electrode potential (-3.04V vs. standard hydrogen electrode potential). When the current negative electrode lithium supplement is added to the preparation of secondary batteries, internal temperature unevenness will occur during the cycle, resulting in local lithium precipitation of the pole piece, reduced cycle performance, and also reduced safety performance. Summary of the invention

[0003] The purpose of the present application is to solve the technical problem in the prior art that adding a lithium supplement to a negative electrode plate results in a decrease in the cycle performance and safety performance of a secondary battery, and to propose a negative electrode lithium supplement, a negative electrode plate and a secondary battery.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, a negative electrode lithium supplement is provided, wherein the negative electrode lithium supplement 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 includes a non-lithium compound and a lithium-containing compound, and the non-lithium compound includes at least one of 16,17-dihydroxyanthraquinone violet and guar gum;

[0006] The negative electrode lithium supplement agent satisfies 60≤A≤2000, 0.2≤B≤2;

[0007] Where A=Sh 1 / M,B=h 2 / h 1 ;

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

[0009] h 1 is the thickness of the metallic lithium layer;

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

[0011] h 2 is the thickness of the passivation layer.

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

[0013] As an embodiment of the present application, the h 1 0.1-1μm.

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

[0015] As an embodiment of the present application, the h 2 0.1-0.3μm.

[0016] As an embodiment of the present application, the negative electrode lithium supplement has a Dv50 particle size of 1-10 μm, 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 difluorobis(oxalate)phosphate.

[0019] In a second aspect of the present application, the present application provides a method for preparing a negative electrode lithium supplement, the preparation method comprising the following steps:

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

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

[0022] (3) In an inert gas environment, the composite is placed in a passivation layer premix solution, and then spray-dried to obtain a negative electrode lithium supplement agent.

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

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

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

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

[0027] Compared with the prior art, the beneficial effects of this application are:

[0028] The negative electrode lithium supplement provided in the present application is a lithium metal supplement which is formed by coating a metal lithium layer on the outer surface of a porous carbon core, and using a specific compound to form a passivation layer on the metal lithium layer, and the negative electrode lithium supplement meets 60≤Sh 1 / M≤2000 and 0.2≤h 2 / h 1 ≤2, when it is used for the negative electrode plate and then for the preparation of secondary batteries, it can not only store lithium in the cycle process, but also realize a new lithium removal mechanism, thereby reducing the dead lithium and battery expansion generated in the cycle process; at the same time, lithium ions can be replenished in the cycle to 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 SEI film naturally laminated on the surface of lithium metal; thereby effectively improving the cycle performance and safety performance of the secondary battery. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

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

[0031] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0032] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] In one embodiment of the present application, the present application provides a negative electrode lithium supplement, wherein the negative electrode lithium supplement 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;

[0034] The passivation layer comprises a non-lithium compound and a lithium-containing compound, wherein the non-lithium compound comprises at least one of 16,17-dihydroxyanthraquinone violet and guar gum;

[0035] The negative electrode lithium supplement agent satisfies 60≤A≤2000, 0.2≤B≤2;

[0036] Where A=Sh 1 / M,B=h 2 / h 1 ;

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

[0038] h 1 is the thickness of the metallic lithium layer;

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

[0040] h 2 is the thickness of the passivation layer.

[0041] The present invention has found that a negative electrode lithium supplement provided by the present invention is a lithium metal layer coated on the outer surface of the porous carbon core, and a specific compound is used to form a passivation layer on the lithium metal layer, and the negative electrode lithium supplement meets 60≤Sh 1 / M≤2000 and 0.2≤h 2 / h 1 ≤2, the negative electrode lithium replenisher satisfies the above relationship to ensure that the specific surface area of ​​the lithium metal will not exceed the specific surface area of ​​the porous carbon material on the basis of attaching as much lithium metal as possible on the surface of the porous carbon material. Therefore, when it is used for the negative electrode plate and then for the preparation of the secondary battery, it can not only store lithium during the cycle, but also realize a new lithium removal mechanism, thereby reducing the dead lithium and battery expansion generated during the cycle; at the same time, lithium ions can be replenished during the cycle to 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 SEI film naturally laminated on the surface of the lithium metal; thereby effectively improving the cycle performance and safety performance of the secondary battery.

[0042] Exemplarily, A may be any point value or any two point range value between 60-2000, for example, 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 one embodiment, A is 150-600. For example, it 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] Exemplarily, B may be any point value or any range of two points 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 one embodiment, B is 0.3-0.7, for example, 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 one embodiment, the S is 500-2000 m 2 / g.

[0047] It should be noted that the specific surface area S of the porous carbon is 77K, N 2 Adsorption test was performed.

[0048] For example, the S may be 500-2000 m 2 Any point value or any range value between two points, for example, 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 one embodiment, the S is 1000-1500 m 2 / g.

[0050] The present application found that the specific surface area of ​​porous carbon affects the deposition of metallic lithium on its surface, and also affects the subsequent storage of lithium and reduces the expansion of the battery. When S is further selected to be 500-2000m 2 / g, especially 1000-1500m 2 / g, the subsequent prepared secondary battery has better cycle performance and safety performance.

[0051] In one embodiment, the h 1 0.1-1μm.

[0052] It should be noted that the thickness of the metal lithium layer h 1 μm is obtained by combining focused ion beam (FIB) technology with scanning electron microscopy (SEM) or transmission electron microscopy (TEM) testing.

[0053] Exemplarily, the h 1 It can be any point value or any two point range value between 0.1-1μm, for example, it can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, etc.

[0054] In one embodiment, the h 1 0.3-0.6μm.

[0055] The research of this application found that the thickness of the metal lithium layer not only affects the storage effect of the negative electrode lithium supplement agent on lithium ions, but also affects the replenishment effect of lithium ions in the subsequent cycle process; when further selecting h 1 When the particle size is 0.1-1 μm, especially 0.3-0.6 μm, the cycle performance of the obtained secondary battery is better.

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

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

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

[0060] The research in this application found that the mass of lithium metal attached to the surface of 1g of porous carbon will not only affect the energy density of the secondary battery prepared subsequently, but also affect the replenishment of lithium ions consumed during the cycle by the negative electrode lithium replenisher. When M is further selected to be 0.3-8g, especially 1-4g, it can better reduce the irreversible lithium consumption and reduce the battery expansion during the cycle, thereby effectively improving the cycle performance and safety performance of the secondary battery.

[0061] In one embodiment, the h 2 0.1-0.3μm.

[0062] It should be noted that the thickness of the passivation layer h 2 It is obtained by focusing ion beam (FIB) technology combined with scanning electron microscopy (SEM) or transmission electron microscopy (TEM) testing.

[0063] For example, the thickness of the passivation layer h 2 It can be any point value or any two point range value between 0.1-0.3μm, for example, it can be 0.1μm, 0.12μm, 0.14μm, 0.16μm, 0.18μm, 0.2μm, 0.22μm, 0.24μm, 0.26μm, 0.28μm, 0.3μm, etc.

[0064] In one embodiment, the h 2 0.15-0.22μm.

[0065] The present application study found that a passivation layer within 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 one embodiment, the negative electrode lithium supplement has a Dv50 particle size of 1-10 μm, a porosity P of 30-60%, and a pore size r of 50-200 nm.

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

[0068] Exemplarily, the Dv50 particle size of the negative electrode lithium supplement may 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 may 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 may 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 research of the present application found that the Dv50 particle size, porosity and pore size of the negative electrode lithium supplement provided by the present application can better realize the transportation and storage of lithium ions within the above-mentioned range, and can also effectively improve the stability of the SEI film and facilitate the subsequent processing to form the negative electrode active material layer, thereby improving the cycle performance and safety performance of the secondary battery prepared subsequently.

[0070] In one 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, and carbon fibers.

[0071] In one embodiment, the lithium-containing compound includes at least one of lithium chloride, lithium acetate, lithium fluoride, and lithium difluorobis(oxalate)phosphate.

[0072] The present application has found that when the above-mentioned types of substances are selected, the comprehensive performance of the secondary battery obtained is better.

[0073] In one embodiment of the present application, the present application provides a method for preparing the negative electrode lithium supplement, the preparation method comprising the following steps:

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

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

[0076] (3) In an inert gas environment, the composite is placed in a passivation layer premix solution, and then spray-dried to obtain a negative electrode lithium supplement agent.

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

[0078] The present application study found that the mass of the non-lithium compounds and lithium-containing compounds in the passivation layer will affect the mechanical strength, toughness and stability of the artificial SEI film formed, and will also affect the transmission of lithium ions. When the mass of the non-lithium compounds and lithium-containing compounds are further selected to be within the above-mentioned ranges, the resulting secondary battery has better cycle performance and smaller volume expansion during the cycle, that is, higher safety.

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

[0080] In one embodiment, the solution of the non-lithium compound and the lithium-containing compound further comprises a binder. Exemplarily, the binder comprises polyvinylidene fluoride.

[0081] In one embodiment of the present application, the present application provides a negative electrode plate, which includes a negative electrode collector and a negative electrode active material layer arranged on at least one surface of the negative electrode collector, and the negative electrode active material layer includes a negative electrode active material, the negative electrode lithium supplement described in the present application, a binder and a thickener.

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

[0083] Illustratively, based on the total mass of the negative electrode active material layer, the mass percentage of the negative electrode lithium supplement may be any point value or any two point range values ​​between 0.1-0.8%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0084] The present application study found that the addition of a negative electrode lithium supplement in an appropriate mass percentage range can effectively reduce the dead lithium generated during the cycle, improve the cycle stability of the secondary battery, and at the same time avoid the occurrence of lithium plating, thereby improving the safety performance of the secondary battery.

[0085] In one embodiment, the negative electrode active material includes 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 includes at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polypropylene, and styrene-butadiene rubber.

[0087] In one embodiment, the thickener includes 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, and the secondary battery includes the negative electrode plate, the positive electrode plate, the electrolyte and the separator described in the present application.

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

[0090] The present application has no restrictions on the selection of positive electrode active materials, and conventional positive electrode active materials in the art can be used. For example, the positive electrode active material can be at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0091] The present application has no restrictions on the selection of the positive electrode conductive agent, and conventional positive electrode conductive agents in the art can be used. For example, the positive electrode conductive agent can be at least one of conductive carbon black, carbon nanotubes, and graphene.

[0092] The present application has no restrictions on the selection of the positive electrode binder, and conventional positive electrode binders in the art can be used. For example, the positive electrode binder can be at least one of polyvinylidene fluoride, lithium polyacrylate, polyvinyl acid, and styrene-butadiene rubber.

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

[0094] The present application has no restrictions on the selection of organic solvents, and conventional organic solvents in the art can be used. For example, the organic solvent can be at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0095] The present application has no restrictions on the selection of lithium salts, and conventional lithium salts in the art can be used. For example, the lithium salt can be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0096] The present application has no restrictions on the selection of additives, and conventional additives in the art can be used. For example, 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 embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery comprises the following steps:

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

[0100] S1. Add a non-lithium compound (16,17-dihydroxyanthraquinone violet, DHV), a lithium-containing compound (lithium chloride) and a binder (polytetrafluoroethylene, PVDF) into N-methylpyrrolidone and mix them evenly to obtain a passivation layer premix solution;

[0101] S2. coating metallic lithium on the outer surface of the porous carbon material (carbon nanotube) by a vapor phase chemical deposition method to obtain a composite;

[0102] S3. In a nitrogen gas environment, placing the composite in a passivation layer premixed solution, and then spray drying to obtain a negative electrode lithium supplement;

[0103] (2) Preparation of negative electrode sheet

[0104] The negative electrode material (graphite), negative electrode lithium supplement, conductive agent (conductive carbon black SP), binder (styrene-butadiene rubber), and thickener (sodium carboxymethyl cellulose) are fully mixed in a mass ratio of 97.7:0.4:0.5:0.7:0.7, coated on Cu foil at 105°C in vacuum, and rolled and slit to obtain a negative electrode sheet;

[0105] (3) Preparation of positive electrode sheet

[0106] The positive electrode material (lithium cobalt oxide), the conductive agent acetylene black (SP), and the binder (polyvinylidene fluoride) are fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 98:1.2:0.8, and then coated on an Al foil, and then dried, rolled, and slit to obtain a positive electrode sheet;

[0107] (4) Preparation of electrolyte

[0108] Lithium salt LiPF 6 A solution prepared with a non-aqueous organic solvent (ethylene carbonate: diethyl carbonate: propylene carbonate: propyl propionate: vinylene carbonate) = 25:25:15:31:4, mass ratio) at a mass ratio of 8:92 is used as an electrolyte for a lithium battery;

[0109] (5) Preparation of diaphragm

[0110] Alumina ceramic polyethylene (PE) porous polymer film is used as the isolation membrane;

[0111] (6) Preparation of secondary batteries

[0112] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of safety isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in a packaging shell, the electrolyte is injected and packaged to obtain a secondary battery.

[0113] Embodiment 2-5

[0114] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the porous carbon is adjusted to achieve the change in the specific surface area of ​​the porous carbon in Table 1-2.

[0115] Embodiment 6-9

[0116] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the amount of metallic lithium added is adjusted to achieve a change in the thickness of the metallic lithium layer.

[0117] Examples 10-13

[0118] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the metallic lithium is adjusted to achieve a change in the mass of lithium metal attached to 1g of the porous carbon surface.

[0119] Examples 14-17

[0120] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the amount of the passivation layer premix is ​​adjusted to achieve a change in the thickness of the passivation layer.

[0121] Examples 18-19

[0122] The embodiment of the present application provides a negative electrode lithium replenisher, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium replenisher, the negative electrode plate and the secondary battery and that of Example 1 is that the preparation parameters are adjusted to achieve the change of Dv50, P and r of the negative electrode lithium replenisher.

[0123] Embodiment 20

[0124] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation methods of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and the embodiment 1 is that the type of porous carbon is adjusted.

[0125] Embodiment 21

[0126] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation methods of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and the embodiment 1 is that the type of lithium-containing compound is adjusted.

[0127] Embodiment 22

[0128] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation methods of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and the embodiment 1 is that the type of non-lithium compound is adjusted.

[0129] Embodiment 23-24

[0130] The embodiment of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the addition amount of the lithium-containing compound and the non-lithium compound is adjusted to achieve a change in the mass ratio of the two.

[0131] Examples 25-26

[0132] The embodiment of the present application provides a negative electrode lithium replenisher, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium replenisher, the negative electrode plate and the secondary battery and that of Example 1 is that the addition amount of the negative electrode lithium replenisher is adjusted to achieve the change of its mass percentage in the negative electrode plate.

[0133] Comparative Example 1-2

[0134] The comparative example of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and that of Example 1 is that the porous carbon and its addition amount, and the addition amount of metallic lithium are adjusted to achieve the parameters in Table 1-2.

[0135] Comparative Examples 3-4

[0136] The comparative example of the present application provides a negative electrode lithium supplement, a negative electrode plate and a secondary battery. The difference between the preparation method of the negative electrode lithium supplement, the negative electrode plate and the secondary battery and Example 1 is that the thickness of the metal lithium layer and the passivation layer is adjusted to achieve the parameters in Table 1-2.

[0137] Comparative Example 5

[0138] The comparative example of the present application provides a negative electrode lithium replenisher, a negative electrode plate and a secondary battery. The preparation method of the negative electrode lithium replenisher, the negative electrode plate and the secondary battery is different from that of Example 1 in that a passivation layer is not introduced.

[0139] Comparative Example 6

[0140] The comparative example of the present application provides a negative electrode lithium replenisher, a negative electrode plate and a secondary battery. The difference between the preparation methods of the negative electrode lithium replenisher, the negative electrode plate and the secondary battery and Example 1 is that the passivation layer does not contain a lithium-containing compound.

[0141] Comparative Example 7

[0142] The comparative example of the present application provides a negative electrode lithium replenisher, a negative electrode plate and a secondary battery. The preparation method of the negative electrode lithium replenisher, the negative electrode plate and the secondary battery is different from that of Example 1 in that a metal lithium layer is not introduced.

[0143] Specific surface area S m of porous carbon materials of Examples and Comparative Examples 2 / g, thickness of the metal lithium layer h 1 μm, the mass of lithium metal attached to 1g of porous carbon surface, M g, and the thickness of the passivation layer, h 2 μm, A, B, Dv50 particle size of the negative electrode lithium supplement agent, porosity P, pore size r, type of porous carbon, type of lithium-containing compound, type of non-lithium compound, mass ratio m of lithium-containing compound and non-lithium compound, and amount n of the negative electrode lithium supplement agent added in the negative electrode active material layer are shown in Table 1-2;

[0144] Table 1

[0145]

[0146]

[0147] Table 2

[0148]

[0149]

[0150] The cycle performance test of the secondary battery prepared in the embodiment and the comparative example is specifically as follows: the ambient temperature is 25°C, and the cycle test is carried out on the Xinwei test cabinet, which is published as follows: 1) standby: 5min; 2) charge to 4.53V at 0.5C constant current and constant voltage, and the cut-off current is 0.02C; 3) standby: 5min; 4) discharge at 0.5C constant current, and the cut-off voltage is 3.0V; 5) cycle from step 1 to step 4 until the cycle capacity retention rate is 80% and the expansion rate of the battery is read;

[0151] The number of cycles when the cycle capacity retention rate is 80% and the corresponding battery expansion rate are recorded; the results are shown in Table 3;

[0152] Table 3

[0153]

[0154]

[0155] It can be seen from Table 3 that when the technical solution provided by the present application is adopted, the obtained product has excellent cycle performance and safety performance. When the cycle capacity retention rate is 80%, the number of cycles is more than 998, and the expansion rate is less than 14.5%;

[0156] It can be seen from Examples 1-26 and Comparative Examples 1-4 that when the negative electrode lithium supplement does not satisfy 60≤Sh 1 / M≤2000 or does not meet 0.2≤h 2 / h 1 ≤2, specifically, when the above relationship is not satisfied, several situations may occur. The first is that the lithium metal cannot completely wrap the porous carbon, and part of the lithium ions in the obtained secondary battery will be deposited on the porous carbon material during the cycle, resulting in dead lithium, which reduces the cycle performance of the secondary battery; the second is that when the lithium metal layer is too thick, there is more lithium metal in the outer layer of the porous carbon material, the conductive pore size is reduced, which affects the transmission of lithium ions and also significantly reduces the cycle performance of the obtained secondary battery; it can be seen from Examples 1-26 and Comparative Example 5 that when the passivation layer is not introduced into the negative electrode lithium supplement, the cycle performance of the obtained secondary battery is significantly reduced, and the expansion rate after the cycle also shows a certain increasing trend, that is, the safety is reduced; it can be seen from Examples 1-26 and Comparative Example 6 that 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 is also reduced to a certain extent; it can be seen from Examples 1-26 and Comparative Example 7 that when the metal lithium layer is not introduced, the cycle performance of the obtained secondary battery is significantly reduced, and the expansion rate after the cycle is also significantly increased, that is, the safety is significantly reduced.

[0157] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A negative electrode lithium supplement, characterized in that: The negative electrode lithium supplement 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 includes a non-lithium compound and a lithium-containing compound, and the non-lithium compound includes at least one of 16,17-dihydroxyanthraquinone violet and guar gum; The negative electrode lithium supplement agent satisfies 60≤A≤2000, 0.2≤B≤2; Where A = Sh1 / M, B = h2 / h1; S is the specific surface area of ​​the porous carbon material; h1 is the thickness of the metal lithium layer; M is the mass of lithium metal attached to 1 g of porous carbon surface; h2 is the thickness of the passivation layer.

2. The negative electrode lithium supplement according to claim 1, characterized in that: At least one of the following is met: 1) The S is 500-2000m 2 / g; 2) h1 is 0.1-1 μm; 3) the M is 0.3-8g; 4) The h2 is 0.1-0.3 μm.

3. The negative electrode lithium supplement according to claim 1, characterized in that: The negative electrode lithium supplement has a Dv50 particle size of 1-10 μm, a porosity P of 30-60%, and a pore size r of 50-200 nm.

4. The negative electrode lithium supplement according to claim 1, characterized in that: 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.

5. The negative electrode lithium supplement according to claim 1, characterized in that: The lithium-containing compound includes at least one of lithium chloride, lithium acetate, lithium fluoride, and lithium difluorobis(oxalate)phosphate.

6. The method for preparing the negative electrode lithium supplement agent according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) adding a non-lithium compound, a lithium-containing compound and a binder into N-methylpyrrolidone and mixing them evenly to obtain a passivation layer premix solution; (2) coating metallic lithium on the outer surface of the porous carbon material by a vapor phase chemical deposition method or a melting method to obtain a composite; (3) In an inert gas environment, the composite is placed in a passivation layer premix solution, and then spray-dried to obtain a negative electrode lithium supplement agent.

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

8. A negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, the negative electrode lithium supplement according to any one of claims 1 to 5, a binder and a thickener.

9. The negative electrode sheet according to claim 6, characterized in that: Based on the total mass of the negative electrode active material layer, the mass percentage of the negative electrode lithium supplement is 0.1-0.8%.

10. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet, the positive electrode sheet, the electrolyte and the separator as claimed in claim 8 or 9.

Images