Composite graphite material, preparation method of composite graphite material, lithium ion battery and electronic device

Abstract

The invention discloses a composite graphite material, a preparation method of the composite graphite material, a lithium ion battery and an electronic device, the composite graphite material comprises carbon dots, the surfaces of the carbon dots have three forms of nitrogen, the three forms of nitrogen are pyridine nitrogen, pyrrole nitrogen and graphite nitrogen, and based on the total mass of the three forms of nitrogen, the mass ratio of the pyridine nitrogen is 60%-80%. The composite graphite material comprises pyridine nitrogen with a high mass ratio, lone pair electrons, not participating in a conjugated system, in pyridine nitrogen can form more active sites by introducing local electron defects, lithium ion adsorption is enhanced, and the gram volume of the composite graphite material is increased; a high-activity area formed by pyridine nitrogen is beneficial to promoting adsorption or desorption of lithium ions, and reaction activation energy and interface impedance are reduced, so that the charge-discharge capacity and the dynamic performance (charge-discharge rate) of the lithium ion battery are improved.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and in particular to a composite graphite material, a method for preparing the composite graphite material, a lithium-ion battery, and an electronic device. Background Art

[0002] Currently, lithium-ion batteries typically use graphite as the negative electrode, but the theoretical gram capacity of graphite is only 372mAh / g, which is far from meeting the needs of high-energy lithium-ion batteries. In addition, although the unique layered structure of graphite can achieve the embedding of lithium ions, the small interlayer spacing of graphite causes the diffusion resistance of lithium ions to be relatively large, and the solvent molecules accompanying the embedding process of lithium ions can cause the peeling and shedding of graphite sheets, thereby failing to achieve ideal kinetic performance (charge and discharge rate). Therefore, how to improve the charge and discharge capacity and kinetic performance (charge and discharge rate) of lithium-ion batteries while increasing the theoretical gram capacity of graphite has become a problem that needs to be solved urgently. Summary of the Invention

[0003] In view of this, the present application provides a composite graphite material, a method for preparing the composite graphite material, a lithium-ion battery, and an electronic device to solve the above technical problems.

[0004] The first aspect of the present application provides a composite graphite material including carbon dots, the surface of the carbon dots having three forms of nitrogen, namely pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen, and the mass proportion of pyridinic nitrogen based on the total mass of the three forms of nitrogen is 60% to 80%. The present application dopes the composite graphite material with a high mass proportion (60% to 80%) of pyridinic nitrogen, wherein the lone pair electrons in the pyridinic nitrogen that do not participate in the conjugated system can form more active sites by introducing local electronic defects, thereby enhancing the adsorption of lithium ions and improving the specific capacity of the composite graphite material. In addition, the high active area formed by the pyridinic nitrogen is conducive to promoting the adsorption or desorption of lithium ions, reducing the reaction activation energy and interfacial impedance, thereby improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0005] Based on the first aspect, in some possible embodiments, the carbon dots are spherical particles with a diameter ranging from 2 nm to 50 nm. The diameter of a spherical particle in this application refers to the diameter of the sphere (the shape of the carbon dots), i.e., twice the distance from the center of the sphere to any point on the surface. By controlling the diameter of the carbon dots to meet the above range, the present application further improves the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0006] Based on the first aspect, in some possible embodiments, based on the total mass of the three forms of nitrogen, the mass proportion of pyrrolic nitrogen is 11% to 23%, and the mass proportion of graphitic nitrogen is 6% to 21%. By controlling the mass proportions of pyrrolic nitrogen and graphitic nitrogen to meet the above ranges, the pyrrolic nitrogen and graphitic nitrogen exert a synergistic lithium storage mechanism, which can further ensure that the composite graphite material has a high gram capacity and further improve the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0007] Based on the first aspect, in some possible embodiments, the composite graphite material has a porous structure, wherein the pore diameter measured by nitrogen adsorption-desorption testing is less than or equal to 0.7 nm; based on the total number of pores in the composite graphite material, the number of pores with a pore diameter of 0.4 nm to 0.7 nm accounts for 60% to 80%. When the number of pores with a pore diameter of 0.4 nm to 0.7 nm in the composite graphite material of the present application meets the above range, it is beneficial to enhance desolvation and rapidly screen lithium ions, further improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0008] Based on the first aspect, in some possible embodiments, the Raman spectral characteristics of the composite graphite material satisfy the following: 1.2≤σ≤2, where σ is the Raman value of the composite graphite material. The researchers of this application have found that when the Raman value of the composite graphite material satisfies the above range, it is beneficial to enhance desolvation and rapidly screen lithium ions, further improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0009] Based on the first aspect, in some possible embodiments, the composite graphite material includes nitrogen, and the weight percentage of nitrogen is 0.05% to 0.5% based on the total weight of the composite graphite material. By regulating the weight percentage of nitrogen in the composite graphite material to meet the above range, the present application can further improve the gram capacity of the composite graphite material, as well as the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0010] Based on the first aspect, in some possible embodiments, the specific surface area BET of the composite graphite material is 1.4 m 2 / g to 5m 2 The present invention further improves the gram capacity of the composite graphite material, as well as the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery by controlling the specific surface area of ​​the composite graphite material to meet the above range.

[0011] The second aspect of the present application provides a method for preparing a composite graphite material, comprising: subjecting a pyridine monomer containing an amino group and an organic solvent to a solvothermal reaction to obtain a mixed liquid; stirring and dissolving the mixed liquid, a graphite material and an organic solvent, and then drying the mixture to obtain a composite graphite material.

[0012] In the above preparation method, a pyridine monomer containing an amino group and an organic solvent are subjected to a solvent thermal reaction to obtain a mixed solution, the mixed solution including a carbon point material, the carbon point material having three forms of nitrogen, wherein the three forms of nitrogen are pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen. Further, after the mixed solution, the graphite material and the organic solvent are stirred and dissolved and then dried, the organic solvent evaporates, and the carbon point material in the mixed solution is adsorbed on the surface of the graphite material under the action of van der Waals force and electrostatic force, thereby preparing the composite graphite material of the present application. The composite graphite material contains a high-quality proportion (60% to 80%) of pyridinic nitrogen, wherein the lone pair electrons in the pyridinic nitrogen that do not participate in the conjugated system can form more active sites by introducing local electronic defects, thereby enhancing the adsorption of lithium ions and improving the gram capacity of the composite graphite material. In addition, the high active area formed by pyridinic nitrogen is conducive to promoting the adsorption or desorption of lithium ions, reducing the reaction activation energy and interfacial impedance, thereby improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery.

[0013] Based on the second aspect, in some possible embodiments, the temperature of the solvothermal reaction is 150° C. to 210° C., and the time of the solvothermal reaction is 16 h to 30 h.

[0014] During the above preparation process, when the temperature and time of the solvent thermal reaction meet the above ranges, the agglomeration problem of the synthesized carbon dots can be alleviated and the stability of the carbon dots can be improved, further improving the gram capacity of the composite graphite material and the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0015] Based on the second aspect, in some possible embodiments, the pyridine monomer containing an amino group is at least one of 2,3-diaminopyridine, 2,4-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine, or 3,5-diaminopyridine. The pyridine monomer containing an amino group provides three forms of nitrogen (pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen) in the composite graphite material, resulting in a higher gram capacity of the composite graphite material and a high charge and discharge capacity and good kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0016] Based on the second aspect, in some possible embodiments, the organic solvent is ethanol and / or N,N-dimethylformamide.

[0017] The third aspect of the present application provides a lithium-ion battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising the composite graphite material provided in the first aspect of the present application, and based on the total mass of the negative electrode active material, the mass proportion of the composite graphite material is 0.5% to 100%.

[0018] When the composite graphite material accounts for 0.5% to 100% of the total mass of the negative electrode active material, the composite graphite material has a higher gram capacity, and the lithium ion battery has a high charge and discharge capacity and good kinetic performance (charge and discharge rate).

[0019] The fourth aspect of the present application provides an electronic device, comprising the lithium-ion battery provided in the third aspect of the present application. The lithium-ion battery has high charge and discharge capacity and good dynamic performance (charge and discharge rate), which is beneficial to improving the service life of the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a volume distribution diagram of carbon dot particles in the composite graphite material in Example 7 of the present application.

[0021] Figure 2 This is a scanned image of the nitrogen element in the composite graphite material in Example 7 of the present application.

[0022] Figure 3 This is a diagram showing the mass ratios of the three forms of nitrogen in the composite graphite material in Example 7 of the present application.

[0023] Figure 4 This is the pore size differential curve of the composite graphite material in Example 7 of the present application.

[0024] Figure 5 This is the Raman spectrum test result of the composite graphite material in Example 7 of the present application.

[0025] Figure 6A This is an optical image of the negative electrode plate in Example 7 of the present application under normal light.

[0026] Figure 6B This is an optical image of the negative electrode plate under ultraviolet light in Example 7 of the present application.

[0027] Figure 7 This is the first cycle charge-discharge curve of the composite graphite material in Comparative Example 1 and Example 7 of the present application.

[0028] Figure 8 This is the third cycle charge-discharge curve of the composite graphite material in Comparative Example 1 and Example 7 of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0030] Composite graphite materials

[0031] In one embodiment of the present application, a graphite material is provided including carbon dots, the surface of which has three forms of nitrogen, namely pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen. Based on the total mass of the three forms of nitrogen, the mass proportion of pyridinic nitrogen is 60% to 80%. For example, the mass proportion of pyridinic nitrogen is 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or a range consisting of any two of these values. When the mass proportion of pyridinic nitrogen is too low, for example, below the lower limit of the present application, it is not conducive to improving the capacity of the graphite material. Without being limited to any theory, the inventors of the present application have found that when the mass proportion of pyridinic nitrogen is within the above range, the lone pairs of electrons in the pyridinic nitrogen that are not involved in the conjugated system can form more active sites by introducing local electronic defects, thereby enhancing the adsorption of lithium ions and helping to increase the specific capacity of the composite graphite material. In addition, the highly active areas formed by pyridinic nitrogen are conducive to promoting the adsorption or desorption of lithium ions, reducing the reaction activation energy and interfacial impedance, thereby improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0032] In one embodiment of the present application, the carbon dots are spherical particles, and the diameter of the spherical particles is 2nm to 50nm. For example, the diameter of the spherical particles is 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 15nm, 17nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, or a range consisting of any two of these values. When the diameter of the spherical particles is too large, for example, greater than the upper limit of the present application, the particle stability is poor and it is easy to settle; when the diameter of the spherical particles is too small, for example, less than the lower limit of the present application, the particles are easy to agglomerate. Without being limited to any theory, the inventors of the present application have found that when the diameter of the spherical particles is within the above range, the particles can be uniformly dispersed and stably present in the solvent, which is beneficial to further improve the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery.

[0033] In one embodiment of the present application, based on the total mass of the three forms of nitrogen, the mass proportion of pyrrolic nitrogen is 11% to 23%, and the mass proportion of graphitic nitrogen is 6% to 21%. For example, the mass proportion of pyrrolic nitrogen is 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23% or a range consisting of any two of these values. When the mass proportion of pyrrolic nitrogen is too high, for example, higher than the upper limit of the present application, it is not conducive to improving the capacity of the composite graphite material. Without being limited to any theory, the inventors of the present application have found that when the mass proportion of pyrrolic nitrogen is within the above range, the high proportion of pyridinic nitrogen can store higher lithium ions, further improving the gram capacity of the composite graphite material, as well as the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery. For example, the mass proportion of graphitic nitrogen is 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21% or a range consisting of any two of these values. When the mass proportion of graphitic nitrogen is too high, for example, higher than the upper limit value of this application, it is not conducive to improving capacity. Without being limited to any theory, the inventors of this application have found that when the mass proportion of graphitic nitrogen is within the above range, the high proportion of pyridinic nitrogen can store more lithium ions, further improving the gram capacity of the composite graphite material, as well as the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery.

[0034] In one embodiment of the present application, the composite graphite material has a porous structure, and the pore size measured by the nitrogen adsorption-desorption test is less than or equal to 0.7nm; based on the total number of pores in the composite graphite material, the number of pores with a pore size of 0.4nm to 0.7nm accounts for 60% to 80%. For example, the number of pores with a pore size of 0.4nm to 0.7nm accounts for 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or a range consisting of any two of the values. When the number of pores with a pore size of 0.4nm to 0.7nm meets the above range, the present application is conducive to enhancing the desolvation effect, quickly screening lithium ions, and further improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery.

[0035] In one embodiment of the present application, the Raman spectral characteristics of the composite graphite material satisfy the following: 1.2≤σ≤2, where σ is the Raman value of the composite graphite material. For example, σ is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range consisting of any two of these values. The researchers of the present application found that when the Raman value of the composite graphite material satisfies the above range, it is beneficial to enhance the desolvation effect, rapidly screen lithium ions, and further improve the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0036] In one embodiment of the present application, the composite graphite material includes nitrogen, and the mass proportion of the nitrogen element is 0.05% to 0.5% based on the total mass of the composite graphite material. For example, the mass proportion of the nitrogen element is 0.05%, 0.07%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, 0.42%, 0.44%, 0.46%, 0.48%, 0.5%, or a range consisting of any two of these values. When the mass proportion of the nitrogen element is too high, for example, higher than the upper limit of this application, the compaction density of the material will be affected; when the mass proportion of the nitrogen element is too low, for example, lower than the lower limit of this application, the capacity of the composite graphite material will be affected. Without being limited to any theory, the inventors of the present application have found that when the mass proportion of nitrogen element is within the above range, the storage of lithium ions can be increased and the composite graphite material can have a suitable compaction density, thereby improving the transmission efficiency of lithium ions, further improving the gram capacity of the composite graphite material and the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0037] In one embodiment of the present application, the specific surface area BET of the composite graphite material is 1.4 m 2 / g to 5m 2 / g. For example, BET is 1.4m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 1.9m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.5m 2 / g、3m 2 / g, 3.2m 2 / g, 3.4m 2 / g, 3.5m 2 / g, 3.6m 2 / g, 3.8m 2 / g、4m2 / g, 4.2m 2 / g, 4.4m 2 / g, 4.6m 2 / g, 4.8m 2 / g、5m 2 / g or a range consisting of any two of these values. Without being limited to any theory, the inventors of the present application have discovered that when the BET specific surface area of ​​the composite graphite material is within the above range, the gram capacity of the composite graphite material, as well as the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery are further improved.

[0038] The present application also provides a preparation method, which comprises: uniformly dispersing a pyridine monomer containing an amino group and an organic solvent by ultrasonic dispersion, and then transferring the mixture to the lining of a reactor for solvent thermal reaction to obtain a mixed liquid; stirring and dissolving the mixed liquid, graphite material and organic solvent, and then transferring the mixture to an oil bath at 180°C to dry the organic solvent to obtain a powdered composite graphite material; then transferring the powdered composite graphite material to a blast drying oven for drying treatment at a temperature of 100°C and a drying time of 48 hours; and finally filtering through a 500-mesh sieve to prepare the composite graphite material of the present application.

[0039] In the above preparation method, a pyridine monomer containing an amino group and an organic solvent are subjected to a solvent thermal reaction to obtain a mixed solution, the mixed solution including a carbon point material, the carbon point material having three forms of nitrogen, wherein the three forms of nitrogen are pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen. Further, after the mixed solution, the graphite material and the organic solvent are stirred and dissolved and then dried, the organic solvent evaporates, and the carbon point material in the mixed solution is adsorbed on the surface of the graphite material under the action of van der Waals force and electrostatic force, thereby preparing the composite graphite material of the present application. The composite graphite material contains a high-quality proportion (60% to 80%) of pyridinic nitrogen, wherein the lone pair electrons in the pyridinic nitrogen that do not participate in the conjugated system can form more active sites by introducing local electronic defects, thereby enhancing the adsorption of lithium ions and improving the gram capacity of the composite graphite material. In addition, the high active area formed by pyridinic nitrogen is conducive to promoting the adsorption or desorption of lithium ions, reducing the reaction activation energy and interfacial impedance, thereby improving the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion battery.

[0040] The solvothermal reaction described in this application is developed on the basis of the hydrothermal method, which refers to a synthetic method in which the original mixture reacts in a closed system such as an autoclave, using organic matter or non-aqueous solvent as solvent, at a certain temperature and autogenous pressure of the solution.

[0041] In one embodiment of the present application, the graphite material includes at least one of artificial graphite and natural graphite.

[0042] In one embodiment of the present application, the temperature of the solvothermal reaction is 150° C. to 210° C., and the time of the solvothermal reaction is 16 h to 30 h.

[0043] During the above preparation process, when the temperature and time of the solvent thermal reaction meet the above ranges, the performance of the synthesized carbon dots is optimal, further improving the gram capacity of the composite graphite material and the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0044] In one embodiment of the present application, the pyridine monomer containing an amino group is at least one of 2,3-diaminopyridine, 2,4-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine, or 3,5-diaminopyridine. The pyridine monomer containing an amino group provides three forms of nitrogen (pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen) in the composite graphite material, resulting in a higher gram capacity of the composite graphite material and a high charge and discharge capacity and good kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0045] In one embodiment of the present application, the organic solvent is ethanol and / or N,N-dimethylformamide. The organic solvent in the above preparation process serves as a reaction medium.

[0046] Negative electrode

[0047] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode active material and, optionally, a conductive agent, a binder, and a thickener. The negative electrode active material includes the composite graphite material of the present application.

[0048] In one embodiment of the present application, the mass proportion of the composite graphite material is 0.5% to 100% based on the total mass of the negative electrode active material. For example, the mass proportion of the composite graphite material is 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 47.5%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 88.5%, 90%, 95%, 100%, or a range consisting of any two of these values. When the composite graphite material accounts for 0.5% to 100% of the total mass of the negative electrode active material, the composite graphite material has a higher gram capacity, and the lithium ion battery has a high charge and discharge capacity and good kinetic performance (charge and discharge rate).

[0049] The negative electrode active materials in the present application may also include but are not limited to natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloy, Sn, Sn-O, SnO2, spinel structured Li4Ti5O 12 , Li-Al alloy.

[0050] The specific type of conductive agent is not particularly limited and can be selected according to needs. For example, the conductive agent includes, but is not limited to, conductive graphite, superconducting carbon, at least one of acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0051] The specific type of binder is not particularly limited and can be selected according to needs. For example, the binder includes but is not limited to at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose.

[0052] The specific type of thickener is not subject to specific limitation and can be selected according to needs. As an example, the thickener includes but is not limited to sodium carboxymethyl cellulose (CMC).

[0053] Isolation film

[0054] The material and shape of the separator used in the lithium-ion battery of the present application are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic material formed of a material that is stable to the electrolyte of the present application.

[0055] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film may be used.

[0056] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0057] electrolyte

[0058] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt and an optional additive. The organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no restriction on the electrolyte used in the electrolyte according to the present application, and it may be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In one embodiment of the present application, the additive includes at least one of fluoroethylene carbonate and 1,3-propane sultone.

[0059] Positive electrode

[0060] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active material layer contains a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0061] The positive electrode active material layer also includes a binder to bond the positive electrode material particles to facilitate film formation and improve the bonding strength between the positive electrode active material layer and the positive electrode current collector. In some embodiments, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0062] The positive electrode active material layer may further comprise a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0063] lithium-ion batteries

[0064] The lithium-ion battery of the present application also includes a shell (such as a packaging bag) for accommodating the above-mentioned positive electrode sheet, separator, negative electrode sheet and electrolyte, as well as other components known in the field of electrochemistry. The present application does not limit the above-mentioned other components. The present application has no special restrictions on the shell, which can be a shell known in the art, as long as the purpose of the present application can be achieved. For example, an aluminum-plastic film packaging bag can be used. The present application has no special restrictions on the type of lithium-ion battery, which can include any device for generating electrochemical reactions. The lithium-ion battery containing the above-mentioned composite graphite material has a high charge and discharge capacity and good kinetic performance (charge and discharge rate).

[0065] electronic devices

[0066] The lithium-ion battery is applied to an electronic device to power a load in the electronic device. Furthermore, the lithium-ion battery has a high charge and discharge capacity and good kinetic performance (charge and discharge rate), which helps to increase the service life of the electronic device. The electronic device may include, but is not limited to, a notebook computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0067] Example 1

[0068] <Preparation of composite graphite material>

[0069] 50 g of 2,3-diaminopyridine and 400 g of ethanol were ultrasonically dispersed in a 1000 mL single-necked flask, and then transferred to the lining of the reactor for a solvent thermal reaction (the temperature of the solvent thermal reaction was 180 ° C, and the solvent thermal reaction time was 24 h) to obtain a mixed solution; 200 g of artificial graphite, 50 g of the mixed solution, and 300 g of N, N-dimethylformamide were placed in a 2000 mL three-necked flask and transferred to an oil bath at 180 ° C to dry the organic solvent to obtain a powdered composite graphite material, and the powdered composite graphite material was transferred to a blast drying oven for drying treatment. The drying treatment temperature was 100 ° C and the drying treatment time was 48 h. Finally, it was filtered through a 500 mesh sieve to prepare the composite graphite material of the present application.

[0070] <Preparation of negative electrode sheet>

[0071] The composite graphite material, used as the negative electrode active material, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were uniformly dispersed in an appropriate amount of deionized water at a mass ratio of 97:1.2:1.8 to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was evenly coated on one surface of a 10 μm thick current collector copper foil and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode active material layer and a coating thickness of 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was dried under vacuum at 120°C for 1 hour, and then cold pressed, cut, and slit to obtain the negative electrode sheet ready for use.

[0072] <Preparation of positive electrode sheet>

[0073] The positive electrode active material, lithium cobalt oxide (LiCoO2), the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), were thoroughly stirred in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a mass ratio of 96.3:2.2:1.5 to form a uniform positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was evenly coated on one surface of a 10 μm thick positive electrode current collector aluminum foil and dried at 120°C for 1 hour to obtain a positive electrode sheet coated on one side with a 60 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. The sheet was dried under vacuum at 120°C for 1 hour, and then cold pressed, cut, and slit to obtain the positive electrode sheet ready for use.

[0074] <Preparation of Electrolyte>

[0075] In an argon atmosphere glove box with a water content of less than 10ppm, the non-aqueous organic solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. Then, fluoroethylene carbonate and 1,3-propane sultone were added, dissolved and stirred thoroughly, and then lithium salt LiPF6 was added and mixed evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass proportion of LiPF6 is 12.5%, the mass proportion of fluoroethylene carbonate is 2%, the mass proportion of 1,3-propane sultone is 2%, and the balance is the non-aqueous organic solvent.

[0076] <Preparation of Separator>

[0077] A polyethylene porous polymer film with a thickness of 7 μm was used as the separator.

[0078] <Preparation of button-type lithium-ion batteries>

[0079] The negative electrode was cut into a Φ (diameter) = 14 mm disc as the working electrode, and a Φ (diameter) = 18 mm metal lithium sheet was used as the reference electrode. The two were separated by a Φ (diameter) = 20 mm isolation membrane. An appropriate amount of electrolyte was added to assemble a CR2430 button lithium-ion battery.

[0080] Example 2 to Example 26

[0081] Except for adjusting the relevant preparation parameters according to Table 1 in <Preparation of Composite Graphite Material>, the other conditions / preparation methods are the same as those in Example 1, wherein, in Examples 17 to 21 and 26, the negative electrode active material comprises a composite graphite material and an artificial graphite material, wherein the mass proportion of the composite graphite material in the negative electrode active material is listed in Table 1.

[0082] Comparative Example 1

[0083] Except in the preparation of the negative electrode sheet, where the composite graphite material was replaced with artificial graphite material, the other conditions / preparation methods were the same as those in Example 1.

[0084] Comparative Example 2

[0085] Except in the preparation of the composite graphite material, where the temperature of the solvothermal reaction was 250 °C and the time of the solvothermal reaction was 16 h, the other conditions / preparation methods were the same as those in Example 1.

[0086] Comparative Example 3

[0087] Except in the preparation of the composite graphite material, where the reaction kettle was a magnetic coupling high-temperature and high-pressure reaction kettle, the other conditions / preparation methods were the same as those in Example 1.

[0088] Testing Method

[0089] (1) Element Content Testing

[0090] The content of nitrogen element in the composite graphite material was quantitatively tested using a Shimadzu / Kratos X-ray photoelectron spectrometer AXIS SUPRA+.

[0091] (2) Pore Structure Testing

[0092] The pore size structure of the composite graphite material was characterized using a Micromeritics ASAP 2460 physical adsorption analyzer produced by the United States. The composite graphite material sample needed to be vacuum-activated at 200 - 250 °C for at least 6 h before testing to remove the adsorbed water vapor and impurities in the pores. The activated sample was tested in a liquid nitrogen environment at -196 °C to obtain the N2 adsorption-desorption isotherm. Using the Brunauer-Emmett-Teller (BET) method, the specific surface area (SBET) of the sample was calculated by selecting the test points within the relative pressure range of 0.05 < P / P0 < 0.30, and the total pore volume of the sample was calculated by taking the single-point adsorption volume at P / P0 = 0.95. When the pore size of the material was smaller than the N2 molecular size, CO2 could be selected as the probe molecule for pore structure characterization at 0 °C, and the DFT method was used to calculate the pore size distribution of the sample.

[0093] (3) Raman Spectroscopy Testing

[0094] The Raman test was carried out on a DXR laser micro-Raman spectrometer in the United States with a laser wavelength of 532 nm. A square area with a side length of 100 microns was selected on the composite graphite material sample, and 100 points were scanned within this area. The Id / Ig of these 100 points was calculated, and the average value was calculated by statistically analyzing these 100 Id / Ig values.

[0095] (4) Coin-Type Lithium-Ion Battery Testing

[0096] The test involves placing the button cell on a blue battery tester for testing. The test process is as follows: first, discharge at 0.05C to 0V, second, let it rest for 5 minutes, third, discharge at 50μA to 0V, fourth, let it rest for 5 minutes, fifth, discharge at 20μA to 0V, sixth, let it rest for 5 minutes, seventh, charge at 0.1C to 2V, eighth, let it rest for 5 minutes, and repeat steps 1 to 8 twice. Then, discharge at 1C to 0V, let it rest for 5 minutes, and charge at 0.1C to 2V, concluding the test. The cumulative capacity of the first, third, and fifth discharge processes in each cycle is the discharge capacity. Charging at 0.1C to 2.0V is the charge capacity. The charge capacity is divided by the weight of the composite graphite material to obtain the gram capacity of the composite graphite material. The charge capacity is divided by the discharge capacity to obtain the initial coulombic efficiency.

[0097] (5) EDS energy dispersive X-ray spectroscopy elemental analysis test

[0098] Based on the characteristic X-rays produced by the interaction between electrons and matter, when a high-energy electron beam strikes the sample surface, the atoms in the sample are excited and emit characteristic X-rays. The energy of these X-rays is directly related to the atomic number of the element, and each element has its own unique characteristic X-ray energy. The EDS detector determines the types of elements present in the composite graphite material sample and their relative content by measuring the energy and intensity of these X-rays.

[0099] (6) Nanoparticle size potential analyzer particle size test

[0100] The size and particle size distribution of the carbon dots were measured using a nanoparticle size potential analyzer to understand the overall structure of the prepared carbon dots.

[0101] (7) X-ray photoelectron spectroscopy (XPS)

[0102] XPS is an advanced surface analysis technology. Its working principle is to use X-rays to irradiate the sample to be tested. The inner electrons of the sample will escape after being excited, and then their number and kinetic energy will be measured, and finally the electron energy spectrum will be obtained. XPS characterization can not only perform qualitative and quantitative analysis on the elemental composition of the sample, but also accurately characterize the chemical state information of a single element. In the field of carbon dot research, XPS characterization is an important means to obtain electron energy information and quantitatively analyze the elemental composition and chemical bond composition of the sample. It is usually combined with EDS energy spectrum to analyze the chemical element composition of carbon dots and the type and content of organic groups on the surface of carbon dots. The experimental steps of this article are as follows: smear the carbon dot powder on a glass slide, perform full scan and narrow scan tests with an X-ray photoelectron spectrometer, and then use XPS PAK41 software to process the data, separate the peaks, and integrate to obtain the proportion of the three forms of nitrogen content.

[0103] (8) Raman spectroscopy

[0104] A Renishaw Raman spectrometer from the UK, using a helium-neon laser source with a wavelength of 633nm, was used. No sample pretreatment was required before measurement. The spectra scattered from the catalyst surface were collected to analyze the structure and properties of the composite graphite material samples.

[0105] (9) Optical image

[0106] Use a digital camera to take optical images of the laminated battery electrodes under natural light and ultraviolet light (wavelength of 365nm).

[0107] (10) Diameter test of spherical particles

[0108] The diameter of spherical particles is analyzed using dynamic light scattering. The principle is that when laser irradiates the suspension, the Brownian motion of the tiny particles causes the scattered light intensity to fluctuate over time, and the fluctuation speed is inversely proportional to the particle size.

[0109] Figure 1 The volume distribution diagram of carbon dot particles of the composite graphite material in Example 7 is shown in FIG. Figure 1 It can be seen that the diameter of carbon dot particles is mainly distributed in the range of 2nm to 50nm.

[0110] Figure 2 This is a surface scan of the nitrogen element of the composite graphite material in Example 7, from Figure 2 It can be seen that nitrogen is mainly distributed on the surface of graphite composite materials.

[0111] Figure 3 The mass ratio of the three forms of nitrogen in the composite graphite material in Example 7 is shown in FIG. Figure 3 It can be seen that among the three forms of nitrogen (pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen), the mass proportion of pyridinic nitrogen is significantly higher than the mass proportion of pyrrolic nitrogen and the mass proportion of graphitic nitrogen.

[0112] Figure 4 is the pore size differential curve of the composite graphite material in Example 7, Figure 4 It can be seen that the composite graphite material of the present application has pores of different pore sizes, wherein the pore diameters are all less than or equal to 0.7 nm.

[0113] Figure 5 The Raman spectrum test results of the composite graphite material in Example 7 are as follows: Figure 5 It can be seen that the composite graphite material of the present application has a larger Raman value.

[0114] Figure 6A is an optical image of the negative electrode sheet in Example 7 under normal light, Figure 6BThis is the optical image of the negative electrode in Example 7 under ultraviolet light. Figure 6A and Figure 6B It can be seen that the electrode prepared using the composite graphite material doped with pyridine nitrogen and carbon dots of the present application exhibits dazzling fluorescence under ultraviolet light.

[0115] Figure 7 The first cycle charge-discharge curve of the composite graphite material in Comparative Example 1 and Example 7 is shown in FIG. Figure 7 It can be seen that after the composite graphite material of the present application is added to the button-type lithium-ion battery in Example 7, the charge and discharge capacity and dynamic performance (charge and discharge rate) of the button-type lithium-ion battery are improved.

[0116] Figure 8 The third cycle charge-discharge curve of the composite graphite material in Comparative Example 1 and Example 7 of this application is shown in FIG. Figure 8 It can be seen that after the composite graphite material of the present application is added to the button-type lithium-ion battery in Example 7, the charge and discharge capacity and dynamic performance (charge and discharge rate) of the button-type lithium-ion battery are improved.

[0117] The preparation conditions of Examples 1 to 26 are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] The relevant characteristics and performance parameters of Examples 1 to 26 and Comparative Examples 1 to 3 are recorded in Tables 2 and 3.

[0122] Table 2

[0123]

[0124]

[0125] Note: “ / ” in Table 2 indicates that there is no corresponding substance or parameter.

[0126] Table 3

[0127]

[0128]

[0129] It can be seen from Tables 1 to 3 that, compared with Comparative Examples 1 to 3, Examples 1 to 26 add the composite graphite material of the present application, and the composite graphite material is doped with a high mass proportion (60% to 80%) of pyridinic nitrogen, and the lithium-ion battery has a high charge and discharge capacity while also having good kinetics (charge and discharge rate).

[0130] In Examples 1 to 12, different types of pyridine monomers containing amino groups and organic solvents are used as reactants to prepare the composite graphite material of the present application. Since the pyridine monomer containing amino groups provides three forms of nitrogen (pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen) in the composite graphite material, the composite graphite material has a higher gram capacity, and the lithium-ion battery has a high charge and discharge capacity and good kinetic performance (charge and discharge rate).

[0131] In Examples 13 to 16, changing the temperature and time of the solvothermal reaction during the preparation process will affect the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery.

[0132] Compared with Example 1, Examples 17 to 21 affect the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium-ion battery by changing the mass proportion of the composite graphite material of the present application in the negative electrode active material.

[0133] Compared with Example 1, Examples 22 to 26 are prepared by changing the temperature of the solvent thermal reaction during the preparation process. The time of the solvent thermal reaction and the mass proportion of the composite graphite material in the negative electrode active material, compared with Example 1, the charge and discharge capacity and kinetic performance (charge and discharge rate) of the lithium ion batteries of Examples 22 to 26 are slightly reduced; however, compared with Comparative Examples 1 to 3, the lithium ion batteries have high charge and discharge capacity and good kinetic performance (charge and discharge rate). It can be seen that when preparing the composite graphite material of the present application, the following conditions are met: the temperature of the solvent thermal reaction is 150°C to 210°C, the time of the solvent thermal reaction is 16h to 30h, and the mass proportion of the composite graphite material in the negative electrode active material is 0.5% to 100%, the prepared lithium ion battery has a high charge and discharge capacity and good kinetic performance (charge and discharge rate).

[0134] The above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solution of the present application may be modified or replaced with equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A composite graphite material, characterized in that: The composite graphite material includes carbon dots, and the surface of the carbon dots has three forms of nitrogen, namely pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen. Based on the total mass of the three forms of nitrogen, the mass of the pyridinic nitrogen accounts for 60% to 80%.

2. The composite graphite material according to claim 1, characterized in that The carbon dots are spherical particles, and the diameter of the spherical particles is 2 nm to 50 nm.

3. The composite graphite material according to claim 1, characterized in that Based on the total mass of the three forms of nitrogen, the mass proportion of the pyrrolic nitrogen is 11% to 23%, and the mass proportion of the graphitic nitrogen is 6% to 21%.

4. The composite graphite material according to claim 1, characterized in that The composite graphite material has a porous structure, and the pore size measured by nitrogen adsorption-desorption test is less than or equal to 0.7 nm; Based on the total number of pores in the composite graphite material, the number of pores with a pore diameter of 0.4 nm to 0.7 nm accounts for 60% to 80%.

5. The composite graphite material according to claim 1, characterized in that The Raman spectrum characteristics of the composite graphite material satisfy: 1.2≤σ≤2, σ is the Raman value of the composite graphite material; and / or the specific surface area of ​​the composite graphite material is 1.4m 2 / g to 5m 2 / g.

6. The composite graphite material according to claim 1, characterized in that The composite graphite material includes nitrogen, and based on the total mass of the composite graphite material, the mass proportion of the nitrogen is 0.05% to 0.5%.

7. A method for preparing a composite graphite material according to any one of claims 1 to 6, characterized in that: include: A pyridine monomer containing an amino group and an organic solvent are subjected to a solvothermal reaction to obtain a mixed solution; The mixed liquid, the graphite material and the organic solvent are stirred and dissolved, and then dried to obtain the composite graphite material; The temperature of the solvent thermal reaction is 150° C. to 210° C., and the time of the solvent thermal reaction is 16 h to 30 h.

8. The method for preparing a composite graphite material according to claim 7, wherein: The preparation method further satisfies at least one of the following conditions: (1) The pyridine monomer containing an amino group is at least one of 2,3-diaminopyridine, 2,4-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine or 3,5-diaminopyridine; (2) The organic solvent is ethanol and / or N,N-dimethylformamide.

9. A lithium-ion battery comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material layer, characterized in that: The negative electrode active material layer includes a negative electrode active material, wherein the negative electrode active material includes the composite graphite material according to any one of claims 1 to 6, and based on the total mass of the negative electrode active material, the mass proportion of the composite graphite material is 0.5% to 100%.

10. An electronic device, characterized in that: Comprising the lithium-ion battery as claimed in claim 9.

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