A negative electrode material, a preparation method thereof, a negative electrode sheet, and a lithium ion battery

Abstract

The application provides a negative electrode material and a preparation method thereof, a negative electrode sheet and a lithium ion battery, and particularly relates to the technical field of lithium ion batteries. The negative electrode material comprises nano metal particles and conductive gel, the nano metal particles comprise nano tin particles and / or nano germanium particles; the conductive gel is coated on the surface of the nano metal particles, and the conductive gel has a three-dimensional porous structure; wherein the mass content of the conductive gel in the negative electrode material is 29% to 58%, and the mass content of the nano metal particles is 42% to 71%. The conductive gel with a three-dimensional porous structure can effectively inhibit the volume expansion of the nano metal material and stabilize the electrode structure, so that the charge and discharge dynamics performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high working voltage, large energy density, low cost, no memory, good safety, etc., and are widely used in digital products such as mobile phones, notebook computers, cameras, new energy vehicles, energy storage, etc. At present, the mainstream negative electrode material of commercialized lithium ion batteries is graphite, but the theoretical specific capacity of graphite is limited, which cannot meet the development needs of high power, miniaturization and high capacity of lithium ion batteries. Therefore, developing negative electrode materials with higher energy density is crucial for the development of high-capacity batteries.

[0003] Nanometer metal materials, such as tin-based materials and germanium-based materials, have the advantages of high specific capacity, moderate lithium extraction voltage, abundant natural reserves, low price, high safety and environmental protection, etc., and have attracted the attention of researchers, and are considered as one of the next generation of lithium ion battery negative electrode materials. However, nanometer metal particles will expand by more than 300% during the lithium extraction process. The material deformation caused by this volume expansion will cause a large impedance in the battery, and the material will powder and fall off in the battery, resulting in poor cycle performance and rapid capacity decay of the battery, which seriously affects the use experience of the battery. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium ion battery to improve the volume expansion problem of nanometer metal materials as negative electrodes during the cycle process.

[0005] To achieve the above-mentioned objects and other related objects, the first aspect of the present application provides a negative electrode material, which comprises nanometer metal particles and conductive gel, the nanometer metal particles comprise nanometer tin particles and / or nanometer germanium particles, the conductive gel is coated on the surface of the nanometer metal particles, and the conductive gel has a three-dimensional porous structure; wherein the mass content of the conductive gel in the negative electrode material is 29% to 58%, and the mass content of the nanometer metal particles is 42% to 71%.

[0006] In an embodiment of the present application, the mass content of the conductive gel in the negative electrode material is 34% to 50%, and the mass content of the nanometer metal particles is 50% to 66%.

[0007] In an embodiment of the present application, the conductive gel is formed by polymerization and cross-linking reaction of a conductive monomer and an organic acid, wherein the conductive monomer comprises at least one of aniline, aniline derivative, thiophene, thiophene derivative, pyrrole, and pyrrole derivative; and the organic acid comprises at least one of phytic acid, citric acid, succinic acid, and tartaric acid.

[0008] In an embodiment of the present application, the C element spectrum of the negative electrode material in XPS test corresponds to C=O bond at 284.9 eV and O-C=O bond at 286.7 eV.

[0009] In an embodiment of the present application, the peak intensity ratio of the C=O bond to the O-C=O bond is (3.2-3.8):1.

[0010] In an embodiment of the present application, the nano metal particles comprise primary particles and / or secondary particles formed by agglomeration of the primary particles, wherein the particle size of the primary particles is 50-100 nm, and the particle size of the secondary particles is 200-400 nm.

[0011] The second aspect of the present application provides a preparation method of a negative electrode material, comprising the following steps:

[0012] dispersing nano metal particles into a solvent to obtain a first dispersion liquid;

[0013] dispersing an oxidizing agent into a solvent to obtain a second dispersion liquid;

[0014] adding an organic acid and a conductive monomer into the first dispersion liquid, and then adding the second dispersion liquid after uniform dispersion, to obtain a nano metal particle negative electrode material coated with conductive gel.

[0015] In an embodiment of the present application, the addition amount of the organic acid accounts for 6-60% of the mass of the nano metal particles.

[0016] In an embodiment of the present application, the addition amount of the conductive monomer accounts for 10-50% of the mass of the nano metal particles.

[0017] In an embodiment of the present application, the addition amount of the oxidizing agent accounts for 0.15-10% of the mass of the nano metal particles.

[0018] In an embodiment of the present application, the conductive monomer comprises at least one of aniline, aniline derivative, thiophene, thiophene derivative, pyrrole, and pyrrole derivative.

[0019] In an embodiment of the present application, the organic acid comprises at least one of phytic acid, citric acid, succinic acid, and tartaric acid.

[0020] In an embodiment of the present application, the oxidizing agent comprises at least one of ammonium persulfate, hydrogen peroxide, ferric chloride, benzoyl peroxide, cerium ammonium sulfate, sodium persulfate, and cerium sulfate.

[0021] In an embodiment of the present application, the solvent comprises at least one of deionized water, methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, acetone, dimethylformamide, dimethyl sulfoxide, and ethyl acetate.

[0022] A third aspect of the present application provides a negative electrode tab, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer is composed of the negative electrode material.

[0023] A fourth aspect of the present application provides a lithium ion battery, comprising the negative electrode tab described above.

[0024] The negative electrode material of the present application comprises nano metal particles and conductive gel, the conductive gel is coated on the surface of the nano metal particles, and the conductive gel has a three-dimensional porous structure. The negative electrode material uses the three-dimensional porous structure of the conductive gel to inhibit the volume expansion problem of the nano metal particles, and stabilizes the electrode structure; at the same time, the three-dimensional porous structure and the nano structure can promote the transmission of electrons and ions, thereby improving the stability and electrochemical performance of the metal nano material negative electrode.

[0025] The present application uses the polymerization cross-linking reaction of the conductive monomer and the organic acid to perform in-situ coating of the conductive gel on the surface of the nano metal particles, so as to form the negative electrode material of the in-situ composite of the conductive gel-nano metal material. The preparation method is simple, high in preparation efficiency, and strong in scalability. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0027] Figure 1 The scanning electron microscope (SEM) picture of the negative electrode material of the present application;

[0028] Figure 2 The spectrum of the C element in the X-ray photoelectron spectroscopy (XPS) test of the negative electrode material in an embodiment of the present application;

[0029] Figure 3 The flowchart in an embodiment of the preparation method of the negative electrode material of the present application. DETAILED DESCRIPTION

[0030] Following specific examples illustrate embodiments of the present application, and other advantages and benefits of the present application will be readily understood by those skilled in the art upon consideration of the disclosure. The present application can be embodied in other different specific embodiments or applications, and the various details of the disclosure can be modified in light of different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict, if necessary.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0032] Unless otherwise defined, or if used in any contradictory manner, the terms or phrases used herein have the following meanings:

[0033] As used herein, "a", "an", and "the" mean one or more, unless otherwise specified or made clear from the context.

[0034] As used herein, "preferably", "more preferably", "even more preferably" and the like are used to describe embodiments or examples of the application that are particularly advantageous. It is understood that these terms are not used to limit the scope of the application. If a statement is made that a particular embodiment or example is "preferable", "more preferable", "even more preferable", etc., it is understood that this statement does not limit the scope of the application to only that embodiment or example, unless otherwise specified or made clear from the context.

[0035] As used herein, "further", "furthermore", "in addition" and the like are used to describe additional features or embodiments that are advantageous. It is understood that these terms are not used to limit the scope of the application to only those embodiments or features that are described.

[0036] As used herein, ranges of values are intended to include the values within the range, unless otherwise specified or made clear from the context. When multiple ranges of values are provided to describe a feature or characteristic, the ranges of values can be combined.

[0037] The present application provides a negative electrode material and a preparation method thereof, a negative electrode sheet and a lithium ion battery. By coating a conductive gel on the surface of a nano metal particle, the three-dimensional porous structure of the conductive gel is used to inhibit the volume expansion of the nano metal particle, while promoting the transmission of electrons and ions, thereby improving the stability and electrochemical performance of the nano metal material structure.

[0038] Please refer toFigure 1 The first aspect of the present application provides a negative electrode material, which comprises nano-metal particles and conductive gel, the conductive gel is coated on the surface of the nano-metal particles, and the conductive gel has a three-dimensional porous structure, and the nano-metal particles are distributed inside the pores of the conductive gel. The nano-metal particles can be any metal or alloy material that can be used as a negative electrode active material. For example, the nano-metal particles comprise nano-tin particles and / or nano-germanium particles. That is, the nano-metal particles can only contain one of the above-mentioned materials, such as nano-tin particles or nano-germanium particles. Alternatively, the nano-metal particles can contain two of the above-mentioned materials, such as a combination of nano-tin particles and nano-germanium particles, and the ratio of nano-tin particles to nano-germanium particles in the combination is not limited and can be mixed in any ratio. Those skilled in the art can select according to actual needs. The nano-metal particles have the advantages of high specific capacity, moderate lithium intercalation and deintercalation voltage, high safety, environmental protection, etc. However, there is a serious volume expansion during the deintercalation of lithium. The surface of the nano-metal particles is coated with conductive gel, and the three-dimensional porous structure of the conductive gel can inhibit the volume expansion of the nano-metal particles during the cycle process and promote the transmission of electrons and ions, thereby improving the electrochemical performance of the negative electrode. In addition, the conductive gel is a polymer material that simultaneously has the excellent performance of gel and organic conductor. It has a high specific surface area and a three-dimensional continuous conductive network. The conductive gel can replace the binder and conductive agent in the electrode. At the same time, the three-dimensional porous structure of the conductive gel effectively enhances the electrical contact between the metal particles and shortens the charge transmission path, thereby improving the transmission efficiency of electrons and ions and enhancing the stability and electrochemical performance of the nano-metal material negative electrode. Figure 1 The SEM picture of the nano-tin particles coated with conductive gel (device model: TESCAN MIRA3 LMH) shows that the composite material coated with conductive gel forms a three-dimensional porous microstructure and nanostructure inside. This structure provides additional buffer space for the volume expansion of tin particles, significantly improving the structural stability of the tin negative electrode.

[0039] In order to meet the use requirements of the negative electrode material, the mass content of the conductive gel in the negative electrode material is 29% to 58%, and the mass content of the nano-metal particles is 42% to 71%. Further, the mass content of the conductive gel in the negative electrode material is 34% to 50%, and the mass content of the nano-metal particles is 50% to 66%. For example, the mass content of the conductive gel in the negative electrode material is 34%, and the mass content of the nano-metal particles is 66%. Alternatively, the mass content of the conductive gel in the negative electrode material is 45%, and the mass content of the nano-metal particles is 55%. Alternatively, the mass content of the conductive gel is 50%, and the mass content of the nano-metal particles is 50%.

[0040] In an embodiment, the conductive gel is formed by cross-linking polymerization of a conductive monomer (organic molecule) and an organic acid. The conductive monomer includes at least one of aniline, aniline derivative, thiophene, thiophene derivative, pyrrole, and pyrrole derivative. The conductive monomer can be used alone or in combination. For example, the conductive monomer can be aniline, thiophene, or a combination of thiophene and pyrrole. Preferably, the conductive monomer is aniline and / or aniline derivative. Aniline itself has good conductivity, and thus, there is no need to add additional conductive material. The organic acid includes at least one of phytic acid, citric acid, succinic acid, and tartaric acid. For example, the organic acid can be phytic acid, citric acid, or a combination of succinic acid and tartaric acid. To form a conductive gel with uniform coating and good quality, the mass ratio of the conductive monomer to the organic acid is 1:(0.8-3.2). For example, the mass ratio can be 1:0.8, 1:1.5, 1:2.0, 1:2.5, or 1:3.2.

[0041] The conductive gel is formed by cross-linking polymerization of organic molecules. The conductive gel contains covalent bonds C=O and O-C=O, which are formed during the cross-linking polymerization reaction. The covalent bonds C=O and O-C=O can make the conductive gel more cohesive and stable. In addition, the covalent bonds can make the conductive gel more tightly and uniformly coated on the surface of the nano-metal particles, thereby effectively inhibiting the volume expansion of the nano-metal particles, improving the structural stability of the composite material, and improving the electrochemical performance. The covalent bonds can be measured by X-ray photoelectron spectroscopy (XPS) (XPS equipment model: Thermo Scientific, Escalab 250Xi) for the negative electrode material. Figure 2 The XPS spectrum of the negative electrode material of Example 3 is shown. As can be seen from the XPS spectrum, Figure 2 The C=O bond corresponds to a position around 284.9 eV, and the O-C=O bond corresponds to a position around 286.7 eV. The formation of the conductive gel can be confirmed by XPS testing. In addition, the inventors have found that when the peak intensity ratio of the C=O bond to the O-C=O bond in the conductive gel is (3.2-3.8):1, the conductive gel can exhibit excellent performance. For example, the peak intensity ratio of the C=O bond to the O-C=O bond in the conductive gel can be 3.2:1, 3.5:1, or 3.8:1. The peak intensity ratio can be adjusted by adjusting the ratio of the conductive monomer to the organic acid in the conductive gel.

[0042] In an embodiment, the nano-metallic particles include primary particles and / or secondary particles formed by agglomeration of the primary particles, wherein the primary particles have a particle size of 50 nm to 100 nm, for example, 50 nm, 80 nm or 100 nm, and the secondary particles have a particle size of 200 nm to 400 nm, for example, 200 nm, 300 nm or 400 nm. The small size of the active material can effectively shorten the diffusion distance of lithium ions, and therefore the nano-metallic particles are beneficial to a large rate of charge and discharge of the electrode material to a certain extent. However, the nano particles are prone to agglomeration, and therefore the nano-metallic particles can contain both primary particles and secondary particles, or even all secondary particles. Agglomeration of the nano particles can lose the nano particle characteristics, thereby affecting the cycle performance. The coating of the conductive gel can make the nano-metallic particles uniformly dispersed in the three-dimensional network of the conductive gel, so as to alleviate the agglomeration and volume expansion of the nano particles during the charging and discharging process.

[0043] Referring to Figure 3 The second aspect of the present application provides a preparation method of the above negative electrode material, which includes the following steps:

[0044] S1, dispersing the nano-metallic particles into a solvent to obtain a first dispersion liquid;

[0045] S2, dispersing an oxidizing agent into a solvent to obtain a second dispersion liquid;

[0046] S3, adding an organic acid and a conductive monomer into the first dispersion liquid, and then adding the second dispersion liquid after uniform dispersion, to obtain the nano-metallic particle negative electrode material coated with the conductive gel.

[0047] Specifically, the nanometallic particles in step S1 can be any metal material that can be used as negative active material, as an example, the nanometallic particles include nanotin particles and / or nanogermanium particles, for example, the nanometallic particles are nanotin particles, or nanogermanium particles; or a combination of nanotin particles and nanogermanium particles. The solvent is used to disperse the nanometallic particles, the solvent is selected from at least one of deionized water, methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, acetone, dimethylformamide, dimethyl sulfoxide, ethyl acetate; further, the solvent is selected from at least one of deionized water, ethanol, isopropanol, ethyl acetate, and further, the solvent is deionized water and / or ethanol. The dispersion treatment can select any technical means that can uniformly disperse solid particles in the art, such as ultrasonic treatment or high-speed stirring, etc. The amount of solvent added in this step is adaptively increased with the increase of the mass of nanometallic particles, as long as the nanometallic particles can be uniformly dispersed. As an example, 0.2g-5g of nanometallic particles can be added with 1-50ml of solvent, for example, 0.2g of nanometallic particles can be added with 1ml of solvent, or 2g of nanometallic particles can be added with 10ml of solvent; or 5g of nanometallic particles can be added with 50ml of solvent, etc.

[0048] Step S2 is to uniformly disperse the oxidizing agent in the solvent to obtain an oxidizing agent dispersion (second dispersion). The oxidizing agent mainly plays a catalytic role in the polymerization process of the conductive gel, therefore, the amount of the oxidizing agent in this step is related to the amount of the subsequent conductive monomer and organic acid. The solvent in this step is used to disperse the oxidizing agent, and the amount of the solvent added is as long as the oxidizing agent can be uniformly dispersed. As an example, the mass of the oxidizing agent in the second dispersion is 0.15-10% of the mass of the nanometallic particles, for example, it can be 0.15%, 5%, 8% or 10%, etc.; and the amount of the solvent added is 2-20ml, for example, it can be 2ml, 10ml, 15ml or 20ml, etc.

[0049] In some embodiments, the oxidizing agent includes at least one of ammonium persulfate, hydrogen peroxide, ferric trichloride, benzoyl peroxide, ammonium ceric sulfate, sodium persulfate, and ceric sulfate. The oxidizing agent can be selected from any one of the listed materials, for example, ammonium persulfate, or hydrogen peroxide, or ammonium ceric sulfate, etc. The oxidizing agent can also be selected from a combination of any two or more of the above-listed materials, for example, a combination of ammonium persulfate and hydrogen peroxide, or a combination of benzoyl peroxide, ammonium ceric sulfate and sodium persulfate, etc. It is to be understood that when the oxidizing agent is selected as a combination of two or more, the ratio between the components in the combination is not limited, and they can be mixed in any ratio.

[0050] The solvent in step S2 includes at least one of deionized water, methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, acetone, dimethylformamide, dimethyl sulfoxide, and ethyl acetate; further, the solvent is at least one of deionized water, ethanol, isopropanol, and ethyl acetate, and more further, the solvent is deionized water and / or ethanol. The solvent in this step can be the same as or different from the solvent in step S1, and is preferably the same. The dispersion treatment in this step includes, but is not limited to, ultrasonic, high-speed stirring.

[0051] It should be noted that steps S1 and S2 have no sequence, and step S1 can be performed first, and then step S2, or step S2 can be performed first, and then step S1; or steps S1 and S2 can be performed simultaneously.

[0052] In step S3, the organic acid, the conductive monomer, and the second dispersion liquid configured in step S2 are added to the first dispersion liquid configured in step S1, and the conductive monomer is allowed to undergo a polymerization cross-linking reaction at room temperature to form a layer of conductive gel on the surface of the nano-metallic particle; then the solvent is removed, and finally the nano-metallic negative electrode material coated with the conductive gel is obtained.

[0053] In step S3, the organic acid, the conductive monomer, and the second dispersion liquid configured in step S2 are added to the first dispersion liquid configured in step S1, and the conductive monomer is allowed to undergo a polymerization cross-linking reaction at room temperature to form a layer of conductive gel on the surface of the nano-metallic particle; then the solvent is removed, and finally the nano-metallic negative electrode material coated with the conductive gel is obtained.

[0054] In step S3, the amount of the organic acid added is 6% to 60% of the mass of the nano-metallic particle; further, the amount of the organic acid added is 10% to 50% of the mass of the nano-metallic particle, for example, 20%, 30%, or 40%, etc. The added mass of the conductive monomer is 10% to 50% of the mass of the nano-metallic particle; further, the added mass of the conductive monomer is 10% to 40% of the mass of the nano-metallic particle, for example, 10%, 20%, 30%, or 40%, etc.

[0055] Preferably, when the organic acid, the conductive monomer, and the second dispersion liquid containing the oxidizing agent are added to the first dispersion liquid, the organic acid and the conductive monomer are added first, and then the second dispersion liquid is added after being uniformly dispersed by ultrasonic, because the conductive monomer will rapidly undergo polymerization cross-linking after meeting the oxidizing agent, and the conductive gel formed is more uniform after the organic acid and the conductive monomer are uniformly dispersed and then the oxidizing agent is added.

[0056] In step S3, the method for removing the solvent is one or a combination of several methods of vacuum drying, spray drying, freeze drying, and filter drying, and the combination of filter drying and vacuum drying is preferred.

[0057] After the step S3, the negative electrode material coated with the conductive gel and the nano metal particles is obtained, the conductive gel has excellent performances of both gel and organic conductor, and no additional conductive agent and binder needs to be added in the preparation of the negative electrode, the volume expansion of the nano metal is effectively inhibited, the electrode structure is stabilized, the charge conduction efficiency is improved, the reversible capacity is higher, and the charge and discharge dynamics performance is excellent.

[0058] The third aspect of the present application provides a negative electrode tab, which comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer is composed of the negative electrode material described above.

[0059] Specifically, the negative electrode current collector can be selected from metal foils, such as copper foils or carbon-coated copper foils, etc. The negative electrode current collector has a first surface and a second surface arranged oppositely along the thickness direction thereof, and the negative electrode active material layer can be arranged on one of the first surface and the second surface, or arranged on both surfaces. The negative electrode active material layer is formed by directly coating the negative electrode material described above on the negative electrode current collector and drying. In some embodiments, the single-sided thickness of the negative electrode active material layer is 7-9 μm, such as 7 μm, 8 μm or 9 μm, etc.

[0060] The fourth aspect of the present application provides a lithium ion battery, which comprises the negative electrode tab or the negative electrode material described above. The lithium ion battery can be a liquid lithium ion battery (non-aqueous electrolyte) or a solid-state lithium ion battery (solid-state electrolyte), which is not limited herein.

[0061] Hereinafter, the structure of the liquid lithium ion battery is described in detail: the lithium ion battery comprises a positive electrode tab, a negative electrode tab, a non-aqueous electrolyte and a separator, wherein the negative electrode tab is the negative electrode tab described above, which is formed by directly coating the negative electrode material on the negative electrode current collector and drying.

[0062] The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector. The positive electrode current collector is, for example, an aluminum foil or a carbon-coated aluminum foil. The positive electrode active material layer can be disposed on one side surface of the positive electrode current collector or on both side surfaces. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material can be any positive electrode material suitable for a lithium ion battery, i.e., a compound that reversibly intercalates and deintercalates lithium ions. As an example, the positive electrode active material can be a ternary material, such as a nickel-cobalt-manganese ternary material (NCM), a nickel-cobalt-aluminum ternary material (NCA), etc., an iron lithium positive electrode material, such as lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), etc., or a traditional material, such as lithium cobaltate, lithium manganate, etc. These materials can be used alone or in combination. The binder is, for example, any one or more of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, etc. The conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotube, graphene, etc. Optionally, the conductive agent is conductive carbon black, or a combination of carbon fiber and conductive carbon black, or a combination of carbon nanotube and graphene, etc. The proportions of the positive electrode active material, the conductive agent, and the binder can be set according to conventional settings in the art.

[0063] The positive electrode tab can be prepared as follows. The positive electrode active material, the conductive agent, and the binder are mixed in a solvent, such as N-methyl pyrrolidone (NMP), in a certain ratio to form a positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. After drying, rolling, and tab cutting, etc., the positive electrode tab is obtained.

[0064] The separator is disposed between the positive electrode tab and the negative electrode tab to separate the positive electrode tab and the negative electrode tab, prevent internal short circuit of the battery, and allow lithium ions to move between the positive electrode and the negative electrode to achieve the charging and discharging process of the battery. The separator can be a porous material, such as a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, or a composite film. The thickness of the separator is 9 to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL, and the porosity is 30% to 50%.

[0065] The non-aqueous electrolyte plays a role of conducting lithium ions in the charging and discharging process of the battery. The non-aqueous electrolyte includes an organic solvent and a lithium salt, and the lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Further, the lithium salt is selected from lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts, such as a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, which have better comprehensive performance. The organic solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0066] The non-aqueous electrolyte can also include functional additives, such as fluoroethylene carbonate (FEC), propylene-1,3-sulfonic acid lactone (PST), tetraethenylsilane (TVSI), vinylene carbonate (VC), and vinyl sulfate (DTD), which can be added according to actual production needs.

[0067] Battery assembly: The prepared positive electrode sheet, separator, and negative electrode sheet are placed in sequence, with the separator between the positive and negative electrode sheets to play a role of isolation, and a bare cell is obtained by winding or stacking. The bare cell is loaded into a battery shell, and after processes such as assembly, liquid injection, formation, and capacity distribution, a lithium ion battery is obtained.

[0068] In other embodiments, the lithium ion battery is a solid-state lithium ion battery, and the electrolyte of the solid-state lithium ion battery is solid. Common solid-state electrolytes include oxide solid-state electrolytes, halide solid-state electrolytes, and sulfide solid-state electrolytes, which will not be described here, and can be selected by a person skilled in the art according to actual production needs.

[0069] It should be noted that the structures not described in detail in the above lithium ion battery can be set according to the prior art, and will not be described here.

[0070] The lithium ion battery of the present application can be used in the form of a single battery, a battery module or a battery pack for electronic devices to provide power for them. The electronic devices include, but are not limited to, mobile phones, tablets, notebook computers, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric plane toys, etc., and the spacecraft can include airplanes, rockets, space shuttles and spacecraft, etc. The new energy vehicles can be pure electric vehicles, hybrid electric vehicles or extended range vehicles, etc.

[0071] The technical solutions of the present application are described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are commercially available.

[0072] Example 1

[0073] This example provides a negative electrode material, which comprises nano-tin particles and a conductive gel coated on the surface of the nano-tin particles, wherein the mass content of the conductive gel in the negative electrode material is 29.58%, and the mass content of the nano-tin is the balance (70.42%).

[0074] The preparation process of the negative electrode material of this example is as follows:

[0075] 1) Take 0.5g of nano-tin particles into a sample bottle, add 10mL of deionized water, and perform ultrasonic treatment to obtain a first dispersion liquid;

[0076] 2) Add 0.05g of ammonium persulfate to 10mL of deionized water and uniformly disperse to obtain a second dispersion liquid;

[0077] 3) Add 0.16g of phytic acid and 0.05g of aniline to the first dispersion liquid, perform ultrasonic treatment, then add the second dispersion liquid, and the aniline is rapidly polymerized and crosslinked after being added to the second dispersion liquid containing the oxidant, and then the solvent is removed to prepare a nano-tin composite material coated with a conductive gel.

[0078] Example 2

[0079] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 34.21%.

[0080] In the preparation method, 0.1g of aniline is added in step 3).

[0081] Example 3

[0082] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 41.86%.

[0083] 0.2 g of aniline was added in step 3) of the preparation method.

[0084] Example 4

[0085] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 45.05%.

[0086] 0.25 g of aniline was added in step 3) of the preparation method.

[0087] Example 5

[0088] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 31.51%.

[0089] 0.03 g of phytic acid was added in step 3) of the preparation method.

[0090] Example 6

[0091] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 33.33%.

[0092] 0.05 g of phytic acid was added in step 3) of the preparation method.

[0093] Example 7

[0094] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 47.37%.

[0095] 0.25 g of phytic acid was added in step 3) of the preparation method.

[0096] Example 8

[0097] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 50%.

[0098] 0.3 g of phytic acid was added in step 3) of the preparation method.

[0099] Example 9

[0100] The difference between this example and Example 1 is that the mass content of the conductive gel in the negative electrode material is 58%.

[0101] 0.3 g of phytic acid and 0.25 g of aniline were added in step 3) of the preparation method.

[0102] Example 10

[0103] The difference between this example and example 3 is that 0.16 g of phytic acid is added in step 3) of the preparation method, and 0.2 g of thiophene is added.

[0104] Example 11

[0105] The difference between this example and example 3 is that 0.16 g of phytic acid is added in step 3) of the preparation method, and 0.2 g of thiophene is added.

[0106] Example 12

[0107] The difference between this example and example 3 is that 0.16 g of phytic acid is added in step 3) of the preparation method, and 0.2 g of thiophene is added.

[0108] Example 13

[0109] The difference between this example and example 3 is that 0.16 g of phytic acid is added in step 3) of the preparation method, and 0.2 g of thiophene is added.

[0110] Example 14

[0111] The difference between this example and example 3 is that the nano-tin particles in step 1) of the preparation method are replaced by nano-germanium particles.

[0112] Comparative Example 1

[0113] The difference between this example and example 3 is that no oxidant ammonium persulfate is added in the preparation method, i.e. there is no step 2.

[0114] Comparative Example 2

[0115] The difference between this example and example 3 is that no organic acid (phytic acid) is added in step 3) of the preparation method.

[0116] Comparative Example 3

[0117] The difference between this example and example 3 is that no conductive monomer (aniline) is added in step 3) of the preparation method.

[0118] To verify the performance of the negative electrode material of the application, the negative electrode materials formed by the negative electrode materials of examples 1-14 and comparative examples 1-3 are subjected to resistivity tests, and are used in batteries to test the battery performance, and the test results are shown in table 1, and the test method is as follows:

[0119] Battery assembly:

[0120] Electrode fabrication: The negative electrode materials of each embodiment and comparative example are uniformly coated on copper foil, dried in a vacuum drying oven at 110°C for 12 hours, and then cut into appropriate sizes to serve as battery negative electrode sheets; the single-sided coating thickness of the negative electrode material makes the thickness of the negative electrode active material layer formed after drying 8μm.

[0121] Separator: Celgard 2400 polypropylene membrane is selected as the separator.

[0122] Electrolyte: Ethyl carbonate and diethyl carbonate in a volume ratio of 1:1 are used as solvents, and LiPF6 is used as lithium salt. The concentration of LiPF6 in the electrolyte is 1.0 mol / L.

[0123] A coin cell (CR 2025 type) assembled with a lithium metal sheet as the counter electrode and the aforementioned negative electrode sheet as the negative electrode.

[0124] (1) Conductive gel content test: Weigh a portion of the negative electrode material and record the weight as M0. Place it in a thermogravimetric analyzer (NETZSCH STA449F3). In an oxygen atmosphere, heat the temperature from 25℃ to 1000℃ at a heating rate of 10℃ / min. After reaching 1000℃, keep it at that temperature for 30 minutes to end the test. After it cools down, take it out and weigh it to get M1. The conductive gel content W = (M0-M1) / M0.

[0125] (2) Resistivity test: The resistivity of the negative electrode sheets made of each negative electrode material was tested using a four-probe resistivity tester.

[0126] (3) Electrochemical testing equipment: NEWARE CT-4008T, with a test voltage range of 0.01–1.5 V. At 0.1 Ag... -1 At the given current density, the ratio of the first discharge specific capacity to the first charge specific capacity is used as the material's first charge-discharge efficiency (first coulombic efficiency). Using 0.5 Ag... -1 The current is used to perform charge-discharge cycle tests, and the discharge capacity in each cycle is recorded.

[0127] Capacity retention after 100 cycles = discharge capacity after 100 cycles / discharge capacity in the first cycle × 100%.

[0128] Table 1: Preparation parameters and performance of negative electrode materials in Examples 1-14 and Comparative Examples 1-3

[0129]

[0130]

[0131] As can be seen from Table 1, the negative electrode materials of Examples 1 to 14 all form three-dimensional conductive gel networks, and the resistivity of the negative electrode sheet formed by the negative electrode material is obviously reduced compared with that of Comparative Examples 1-3, indicating that the formation of the conductive gel improves the conductivity of the electrode; the first coulombic efficiency and cycle capacity retention of the battery using the negative electrode material of Examples 1 to 14 are improved compared with those of Comparative Examples 1-3, indicating that the formation of the conductive gel can inhibit the volume expansion of the nano-metal particles and improve the stability of the electrode. The test results of Comparative Examples 1-14 show that when the content of the conductive gel in the negative electrode material is 34% to 50%, the performance of the negative electrode material is better.

[0132] As can be seen from Comparative Examples 1-4, under the premise of keeping other conditions unchanged, appropriately increasing the addition amount of the conductive monomer increases the content of the conductive gel in the negative electrode material. The performance of the negative electrode material first improves and then decreases with the increase of the content of the conductive gel, because the content of the nano-metal particles decreases as the content of the conductive gel in the negative electrode material increases, and the performance of the negative electrode material is best when the ratio of the conductive gel to the nano-metal particles is moderate.

[0133] As can be seen from Comparative Examples 5-8, under the premise of keeping other conditions unchanged, appropriately increasing the addition amount of phytic acid increases the content of the conductive gel in the negative electrode material. When the addition amount of the organic acid accounts for 32% of the mass of the nano-metal particles and the addition amount of the conductive monomer accounts for 40% of the mass of the nano-metal particles, the performance of the negative electrode material is best.

[0134] As can be seen from Comparative Example 3 and Examples 10-14, different types of organic acids and different types of conductive monomers can all form three-dimensional conductive gels on the surface of the nano-metal particles, thereby improving the stability and electrochemical performance of the nano-metal material. Among them, the negative electrode material formed by using aniline as the conductive monomer and phytic acid as the organic acid has the best performance.

[0135] As can be seen from Comparative Example 3 and Comparative Examples 1-3, when no oxidizing agent is added, the organic acid and the conductive monomer cannot undergo cross-linking reaction, so that a three-dimensional conductive gel network cannot be formed on the surface of the nano-tin particles, resulting in reduced performance. In the absence of either the organic acid or the conductive monomer, the oxidizing agent cannot play its due catalytic role, and the conductive gel can only be formed by catalysis of the oxidizing agent when both the organic acid and the conductive monomer are present.

[0136] The negative electrode material of the present application is coated with conductive gel on the surface of nano metal particles, and the three-dimensional porous structure of the conductive gel can inhibit the volume expansion of the nano metal particles and stabilize the electrode structure. At the same time, the three-dimensional porous structure and nano structure can promote the transmission of electrons and ions, thereby improving the stability and electrochemical performance of the metal nano material negative electrode. In addition, the in-situ coating of the conductive gel on the surface of the nano metal particles is carried out by the polymerization and cross-linking reaction of the conductive monomer and the organic acid, which is simple and easy to operate, and the negative electrode material has good conductivity, and no additional conductive agent is needed when preparing the electrode. Therefore, the present application effectively overcomes some practical problems in the prior art, and has high utilization value and use significance.

[0137] The above examples only illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea disclosed by the present application should be covered by the claims of the present application.

Claims

1. A negative electrode material, characterized by, Comprise: Nano metal particles, the nano metal particles comprising nano tin particles and / or nano germanium particles; Conductive gel, coated on the surface of the nano metal particles, and the conductive gel has a three-dimensional porous structure; Wherein, the conductive gel is formed by polymerization and cross-linking of a conductive monomer and an organic acid, the conductive monomer comprising at least one of aniline, aniline derivative, thiophene, thiophene derivative, pyrrole, pyrrole derivative; the organic acid comprising at least one of phytic acid, citric acid, succinic acid, tartaric acid; The mass content of the conductive gel in the negative electrode material is 29% to 58%, and the mass content of the nano metal particles is 42% to 71%; The C element spectrum of the XPS test of the negative electrode material has a C=O bond corresponding to the position of 284.9eV and an O-C=O bond corresponding to the position of 286.7eV, and the peak intensity ratio of the C=O bond to the O-C=O bond is (3.2~3.8):

1.

2. The negative electrode material according to claim 1, characterized in that, The mass content of the conductive gel in the negative electrode material is 34% to 50%, and the mass content of the nano metal particles is 50% to 66%.

3. The negative electrode material of claim 1, wherein, The nano metal particles comprise primary particles and / or secondary particles formed by agglomeration of the primary particles, the particle size of the primary particles is 50nm to 100nm, and the particle size of the secondary particles is 200nm to 400nm.

4. A method of producing the negative electrode material according to any one of claims 1 to 3, characterized by, Comprise the following steps: Disperse the nano metal particles into a solvent to obtain a first dispersion liquid; Disperse the oxidizing agent into a solvent to obtain a second dispersion liquid; Add an organic acid and a conductive monomer to the first dispersion liquid, disperse uniformly, and then add the second dispersion liquid to prepare a nano metal particle negative electrode material coated with a conductive gel.

5. The preparation method according to claim 4, characterized in that, Comprise one or more of the following: The added amount of the organic acid accounts for 6% to 60% of the mass of the nano metal particles; The added amount of the conductive monomer accounts for 10% to 50% of the mass of the nano metal particles; The added amount of the oxidizing agent accounts for 0.15% to 10% of the mass of the nano metal particles.

6. The preparation method according to claim 4, characterized in that, Comprise one or more of the following: The conductive monomer comprises at least one of aniline, aniline derivative, thiophene, thiophene derivative, pyrrole, pyrrole derivative; The organic acid comprises at least one of phytic acid, citric acid, succinic acid, tartaric acid; The oxidizing agent comprises at least one of ammonium persulfate, hydrogen peroxide, ferric trichloride, benzoyl peroxide, cerium ammonium sulfate, sodium persulfate, and cerium sulfate; The solvent comprises at least one of deionized water, methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, acetone, dimethylformamide, dimethyl sulfoxide, and ethyl acetate.

7. A negative electrode sheet characterized by comprising: Comprise a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, the negative electrode active material layer being composed of the negative electrode material of any one of claims 1-3.

8. A lithium-ion battery, characterized by, Comprise the negative electrode sheet of claim 7.

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