Graphite composite material, preparation method thereof, negative electrode and battery

Abstract

The invention relates to a graphite composite material, a preparation method thereof, a negative electrode and a battery, the graphite composite material comprises a graphite inner core and a coating layer coating the graphite inner core, and the coating layer comprises porous carbon coating the graphite inner core and elemental phosphorus deposited in and on the surface of the porous carbon. The performance of a conventional graphite negative electrode is reduced during high-rate charging and discharging, and the compatibility with an electrolyte is limited; according to the invention, the surface of the graphite core is firstly coated with the porous carbon, and then the phosphorus is deposited on the surface and in the pores of the porous carbon coating layer, so that the defects in the prior art are overcome, and the cycling stability and rate capability of the graphite negative electrode are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to an electrode material, in particular to a graphite composite material, a preparation method thereof, a negative electrode and a battery. Background Art

[0002] To meet the growing demand for portable electronic products and electric vehicles, it is urgent to improve the fast charging capability of lithium-ion batteries. The graphite anode is widely considered to be one of the components that limits the fast charging capability of lithium-ion batteries. Because the graphite surface has slow electrochemical reaction kinetics, mainly including Li + Desolventization of solid electrolyte interface membrane (SEI) and transport within SEI.

[0003] The method of adding film-forming additives to the electrolyte can improve the film-forming quality of SEI, but this method has the following limitations: the film-forming additives only work when they diffuse on the electrode surface, but due to the low driving force and slow diffusion rate, an uneven and discontinuous SEI film is formed; the film-forming additives remain in the electrolyte, resulting in continuous growth of the SEI film side and a continuous increase in internal resistance; the SEI film is mainly composed of inorganic components such as Li2CO3, LiF and Li2O, and is easily damaged as the volume of graphite particles changes.

[0004] In this regard, how to effectively reduce the side reactions between the electrolyte and graphite and improve the fast charging performance and cycle stability of graphite negative electrode materials is an urgent problem to be solved in this field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a graphite composite material, a preparation method thereof, a negative electrode and a battery. The graphite composite material can overcome the defects of conventional graphite negative electrodes such as decreased performance during high-rate charge and discharge and limited compatibility with electrolytes, and has good electrochemical properties.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a graphite composite material, the graphite composite material comprising:

[0008] Graphite core;

[0009] The coating layer includes porous carbon coating the graphite core and phosphorus element deposited in the pores and on the surface of the porous carbon.

[0010] The graphite composite material provided by the present invention comprises a porous carbon coating the graphite core and a phosphorus element deposited in the pores and on the surface of the porous carbon. The phosphorus element is uniformly loaded on the porous carbon layer, and during the cycle, it can induce the composition change of the SEI layer on the graphite surface to form Li3P with higher ionic conductivity, which can enhance the Li + The graphite composite material provided by the present invention can improve the cycle stability and rate performance without affecting the specific capacity, thereby improving the conductivity and ion diffusion performance, being suitable for rapid ion insertion and extraction, and improving the rate performance of the material. On the other hand, it can play a certain isolation role, thereby reducing the side reaction between the graphite core and the electrolyte and improving the cycle stability. Therefore, the graphite composite material provided by the present invention can improve the cycle stability and rate performance without affecting the specific capacity.

[0011] Preferably, in the graphite composite material, the phosphorus content is 0.1wt%-1wt%;

[0012] Preferably, the specific surface area of the graphite composite material is 0.3 m 2 / g-2m 2 / g.

[0013] In a second aspect, the present invention provides a method for preparing a graphite composite material, the preparation method comprising the following steps:

[0014] S1, mixing graphite and a coating agent, and carbonizing them to obtain porous carbon-coated graphite;

[0015] S2. Performing phosphorus deposition treatment on the porous carbon-coated graphite to obtain a graphite composite material.

[0016] The surface of graphite is relatively smooth, which is not conducive to the deposition and coating of phosphorus. The present invention first mixes graphite with a coating agent, and obtains porous carbon-coated graphite through carbonization treatment, so as to form some holes on the graphite surface, thereby facilitating the deposition and coating of phosphorus. The deposition and coating of phosphorus can induce the formation of a stable SEI layer during the cycle process, and phosphorus is deposited on the surface and in the pores of the porous carbon-coated graphite, which can reduce the increase in specific surface area caused by the provision of a porous carbon coating layer, reduce the contact between the graphite composite material and the electrolyte, and improve the cycle stability and rate performance; the preparation method provided by the present invention is simple and easy to implement, and is suitable for the industrial production of graphite composite materials.

[0017] Preferably, the specific surface area of the graphite composite material is smaller than the specific surface area of the porous carbon-coated graphite.

[0018] Preferably, the specific surface area of the porous carbon-coated graphite is 2 m 2 / g-13m 2 / g;

[0019] Preferably, the specific surface area of the graphite composite material is 0.3 m2 / g - 2m 2 / g.

[0020] Preferably, in the step S1, the mass of the coating agent is 5%-15% of the total mass of the graphite and the coating agent.

[0021] Preferably, the coating agent includes any one or a combination of at least two of zinc gluconate, zinc oxalate, zinc citrate, zinc lactate, or zinc glycyrrhizinate.

[0022] Preferably, the carbonization treatment includes a first sintering, a second sintering, a third sintering, and a fourth sintering sequentially carried out in a protective atmosphere.

[0023] Preferably, the temperature of the first sintering is 110°C - 130°C; the temperature of the second sintering is 280°C - 320°C; the temperature of the third sintering is 580°C - 620°C; the temperature of the fourth sintering is 1100°C - 1200°C.

[0024] Preferably, in the step S2, the phosphorus deposition treatment includes: mixing a phosphorus source with the porous carbon-coated graphite, and performing a heat treatment to deposit phosphorus in the pores and on the surface of the porous carbon coating layer.

[0025] Preferably, the mass of the phosphorus source is 1%-5% of the total mass of the porous carbon-coated graphite and the phosphorus source.

[0026] Preferably, the heat treatment includes a first heat treatment and a second heat treatment carried out sequentially.

[0027] Preferably, the temperature of the first heat treatment is 460°C - 500°C.

[0028] Preferably, the temperature of the second heat treatment is 280°C - 350°C.

[0029] Preferably, after the heat treatment, it further includes a step of introducing an oxygen-containing gas to remove white phosphorus.

[0030] In a third aspect, the present invention provides a negative electrode, and the negative electrode includes a negative electrode active material; the negative electrode active material includes the graphite composite material described in the first aspect, or includes the graphite composite material prepared by the preparation method described in the second aspect.

[0031] In a fourth aspect, the present invention provides a battery, and the battery includes the negative electrode described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The graphite composite material provided by the present invention comprises a porous carbon coating the graphite core and a phosphorus element deposited in the pores and on the surface of the porous carbon. The phosphorus element is uniformly loaded on the porous carbon layer, and during the cycle, it can induce the composition change of the SEI layer on the graphite surface to form Li3P with higher ionic conductivity, which can enhance the Li + The graphite composite material provided by the present invention can improve the cycle stability and rate performance without affecting the specific capacity, thereby improving the conductivity and ion diffusion performance, being suitable for rapid ion insertion and extraction, and improving the rate performance of the material. On the other hand, it can play a certain isolation role, thereby reducing the side reaction between the graphite core and the electrolyte and improving the cycle stability. Therefore, the graphite composite material provided by the present invention can improve the cycle stability and rate performance without affecting the specific capacity.

[0034] (2) The surface of graphite is relatively smooth, which is not conducive to the deposition and coating of phosphorus. The present invention first mixes graphite with a coating agent, and then obtains porous carbon-coated graphite through carbonization treatment, so as to form some holes on the graphite surface, which is conducive to the deposition and coating of phosphorus. The deposition and coating of phosphorus can induce the formation of a stable SEI layer during the cycle process. Moreover, phosphorus is deposited on the surface and in the pores of the porous carbon-coated graphite, which can reduce the increase in specific surface area caused by the provision of a porous carbon coating layer, reduce the contact between the graphite composite material and the electrolyte, and improve the cycle stability and rate performance. The preparation method provided by the present invention is simple and easy to implement, and is suitable for the industrial production of graphite composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 : is a SEM picture of graphite used in a specific embodiment of the present invention.

[0036] Figure 2 This is a SEM image of the porous carbon-coated graphite in Example 1 of the present invention.

[0037] Figure 3 This is a SEM image of the graphite composite material in Example 1 of the present invention.

[0038] Figure 4 This is the EDS image of the graphite composite material in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] A certain embodiment of the present invention provides a graphite composite material, the graphite composite material comprising:

[0041] Graphite core.

[0042] A coating layer, the coating layer includes porous carbon coating the graphite core and elemental phosphorus deposited in the pores and on the surface of the porous carbon.

[0043] For the graphite composite material provided by the present invention, the coating layer includes porous carbon coating the graphite core and elemental phosphorus deposited in the pores and on the surface of the porous carbon. The elemental phosphorus is uniformly loaded on the porous carbon layer. During the cycling process, it can induce changes in the composition of the SEI layer on the graphite surface to form Li3P with higher ionic conductivity. On the one hand, it can enhance the transport of Li + , improve the electrical conductivity and ionic diffusion performance, be suitable for rapid ion insertion and extraction, improve the rate performance of the material. On the other hand, it can play a certain isolation role, thereby reducing the side reaction between the graphite core and the electrolyte and improving the cycle stability. Therefore, the graphite composite material provided by the present invention can improve the cycle stability and rate performance without affecting the specific capacity.

[0044] In some embodiments, in the graphite composite material, the content of the elemental phosphorus is 0.1 wt% - 1 wt%, for example, it can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable. Preferably, the content of the elemental phosphorus is 0.1 wt% - 0.7 wt%.

[0045] In some embodiments, the specific surface area of the graphite composite material is 0.3 m 2 / g - 2 m 2 / g, for example, it can be 0.3 m 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 1 m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g or 2 m 2 / g, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0046] An embodiment of the present invention provides a preparation method of a graphite composite material. The preparation method includes the following steps:

[0047] S1. Mix graphite and a coating agent, and perform carbonization treatment to obtain porous carbon-coated graphite;

[0048] S2. Perform phosphorus deposition treatment on the porous carbon-coated graphite to obtain the graphite composite material.

[0049] The graphite in the present invention includes artificial graphite and / or natural graphite. The surface of the graphite is relatively smooth, which is not conducive to the deposition and coating of phosphorus. First, the graphite is mixed with a coating agent, and then carbonized to obtain porous carbon-coated graphite, forming some pores on the surface of the graphite, which is conducive to the deposition and coating of phosphorus. The deposition and coating of phosphorus can induce the formation of a stable SEI layer during the cycle. Moreover, phosphorus is deposited on the surface and in the pores of the porous carbon-coated graphite, which can reduce the increase in specific surface area caused by the setting of the porous carbon coating layer, reduce the contact between the graphite composite material and the electrolyte, and improve the cycle stability and rate performance. The preparation method provided by the present invention is simple and feasible, and is suitable for the industrial production of graphite composite materials.

[0050] In some embodiments, the method of mixing graphite and the coating agent includes kneading.

[0051] Optionally, the coating agent includes a solid coating agent and / or a coating agent solution.

[0052] In some embodiments, the solvent in the coating agent solution includes water or absolute ethanol.

[0053] When mixing the graphite and the coating agent solution in the present invention, the mixing temperature is appropriately increased to completely evaporate the solvent. Optionally, the mixing temperature is 80 °C, 81 °C, 82 °C, 83 °C, 84 °C or 85 °C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0054] In some embodiments, the specific surface area of the graphite composite material is smaller than that of the porous carbon-coated graphite.

[0055] In some embodiments, the specific surface area of the graphite composite material is smaller than that of the graphite.

[0056] In some embodiments, the specific surface area of the porous carbon-coated graphite is 2 m 2 / g - 13 m 2 / g, for example, it can be 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 8 m 2 / g, 10 m 2 / g or 13 m 2 / g, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0057] In some embodiments, the specific surface area of the graphite composite material is 0.3 m 2 / g - 2 m 2 / g, for example, it can be 0.3 m 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 1 m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g or 2 m 2 / g, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0058] The amount of the coating agent affects the thickness of the porous carbon coating layer. If the amount of the coating agent is too small, the thickness of the porous carbon coating layer is too thin, which affects the deposition and coating of phosphorus. If the amount of the coating agent is too large, the capacity of the graphite composite material will be reduced. Therefore, it is necessary to control the relative amount of the coating agent and graphite.

[0059] In some embodiments, in the step S1, the mass of the coating agent is 5%-15% of the total mass of the graphite and the coating agent. For example, it can be 5%, 6%, 8%, 10%, 12% or 15%, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0060] In some embodiments, the coating agent includes any one or a combination of at least two of zinc gluconate, zinc oxalate, zinc citrate, zinc lactate or zinc glycyrrhizinate. Typical but non-limiting combinations include the combination of zinc gluconate and zinc oxalate, the combination of zinc oxalate and zinc citrate, the combination of zinc citrate and zinc lactate, the combination of zinc lactate and zinc glycyrrhizinate, the combination of zinc gluconate, zinc oxalate and zinc citrate, the combination of zinc citrate, zinc lactate and zinc glycyrrhizinate, or the combination of zinc gluconate, zinc oxalate, zinc citrate, zinc lactate and zinc glycyrrhizinate.

[0061] In some embodiments, the carbonization treatment includes a first sintering, a second sintering, a third sintering and a fourth sintering sequentially carried out in a protective atmosphere; the first sintering is used to remove the crystal water on the surface of the material; the second sintering is used to decompose the coating agent into oxides and water; the third sintering is used to remove the water generated by the second sintering; the fourth sintering is used to sublime the oxides generated by the second sintering.

[0062] Optionally, the gas used for the protective atmosphere includes nitrogen and / or inert gas; the inert gas includes any one or a combination of at least two of helium, neon or argon. Typical but non-limiting combinations include the combination of helium and neon, the combination of neon and argon, the combination of helium and argon, or the combination of helium, neon and argon.

[0063] Taking zinc gluconate as an example of the coating agent, zinc gluconate begins to decompose into zinc oxide and water during the second sintering, then the water generated by the second sintering is removed during the third sintering, and finally the zinc oxide is sublimated during the fourth sintering.

[0064] In some embodiments, the temperature of the first sintering is 110°C - 130°C. For example, it can be 110°C, 115°C, 120°C, 125°C, or 130°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0065] Optionally, in order to fully remove the crystal water on the material surface, the time of the first sintering is more than 2h. For example, it can be 2h, 2.2h, 2.5h, 2.8h, or 3h, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0066] In some embodiments, the temperature of the second sintering is 280°C - 320°C. For example, it can be 280°C, 290°C, 300°C, 310°C, or 320°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0067] In some embodiments, the temperature of the third sintering is 580°C - 620°C. For example, it can be 580°C, 590°C, 600°C, 610°C, or 620°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0068] In order to fully decompose the coating agent, optionally, the temperature of the second sintering is more than 3h. For example, it can be 3h, 3.2h, 3.5h, 3.6h, or 4h, etc.; the temperature of the third sintering is more than 1.5h. For example, it can be 1.5h, 1.6h, 1.8h, 1.9h, or 2h, etc.

[0069] In some embodiments, the temperature of the fourth sintering is 1100°C - 1200°C. For example, it can be 1100°C, 1130°C, 1150°C, 1180°C, or 1200°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0070] In order to fully sublimate the oxides generated by the second sintering, optionally, the time of the fourth sintering is more than 16h. For example, it can be 16h, 17h, 18h, 19h, or 20h, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0071] In some embodiments, in the step S2, the phosphorus deposition treatment includes: mixing a phosphorus source with the porous carbon-coated graphite, and performing heat treatment to deposit phosphorus in the pores and on the surface of the porous carbon coating layer.

[0072] The amount of the phosphorus source affects the electrochemical performance of the obtained graphite composite material. If the amount of the phosphorus source is too much, the capacity and rate performance of the graphite composite material will be reduced; if the amount of the phosphorus source is too little, the deposition and coating effect of the phosphorus source will be reduced. Therefore, it is necessary to control the appropriate amount of the phosphorus source.

[0073] In some embodiments, the mass of the phosphorus source is 1%-5% of the total mass of the porous carbon-coated graphite and the phosphorus source. For example, it can be 1%, 2%, 3%, 4%, or 5%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0074] In some embodiments, the phosphorus source is red phosphorus.

[0075] In some embodiments, the heat treatment includes a first heat treatment and a second heat treatment performed in sequence; the first heat treatment sublimes the phosphorus source; the second heat treatment deposits the sublimated phosphorus source in and on the pores of the porous carbon-coated graphite.

[0076] In some embodiments, the heat treatment is carried out under vacuum conditions; optionally, the absolute vacuum degree of the vacuum conditions is below 50 Pa. For example, it can be 10 Pa, 20 Pa, 30 Pa, 40 Pa, or 50 Pa, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0077] In some embodiments, the temperature of the first heat treatment is 460°C - 500°C. For example, it can be 460°C, 470°C, 480°C, 490°C, or 500°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0078] In the present invention, the time of the first heat treatment needs to ensure the full sublimation of the phosphorus source. Optionally, the time of the first heat treatment is 4 h or more. For example, it can be 4 h, 4.2 h, 4.5 h, 4.8 h, or 5 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0079] In some embodiments, the temperature of the second heat treatment is 280°C - 350°C. For example, it can be 280°C, 290°C, 300°C, 305°C, 310°C, 315°C, 320°C, 330°C, 340°C, or 350°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0080] In the present invention, the time of the second heat treatment needs to ensure the full coating of the recrystallized phosphorus source. Optionally, the time of the second heat treatment is 24 h or more. For example, it can be 24 h, 25 h, 26 h, 27 h, or 28 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0081] In some embodiments, after the heat treatment, it further includes a step of introducing an oxygen-containing gas to remove white phosphorus.

[0082] In the present invention, in order to achieve the purpose of removing white phosphorus by introducing an oxygen-containing gas, the temperature of the introduced oxygen-containing gas is room temperature (15°C - 30°C), and the time is more than 6 hours. For example, it can be 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but it is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0083] In some embodiments, the oxygen-containing gas is compressed air.

[0084] An embodiment of the present invention provides a negative electrode, which includes a negative electrode current collector and a negative electrode active material disposed on at least one side of the negative electrode current collector.

[0085] The negative electrode active material includes the graphite composite material of any embodiment.

[0086] In some embodiments, the negative electrode active material optionally includes a negative electrode conductive agent. The present invention has no particular limitation on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode active material optionally includes a negative electrode binder. The present invention has no particular limitation on the type of the negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0088] In some embodiments, the negative electrode active material optionally includes other additives. As an example, the other additives include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0089] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0090] The negative electrode active material is usually formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing a graphite composite material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0091] In some embodiments, the negative electrode does not exclude other additional functional layers in addition to the negative electrode active material. For example, in some embodiments, the negative electrode further includes a conductive bottom layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode active material. In some embodiments, the negative electrode sheet of the present invention further includes a protective layer covering the surface of the negative electrode active material.

[0092] A certain embodiment of the present invention also provides a battery.

[0093] In some embodiments, the battery includes a lithium-ion battery.

[0094] Generally, a lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charge and discharge process of the lithium-ion battery, lithium ions are embedded and extracted back and forth between the positive electrode and the negative electrode. The separator is disposed between the positive electrode and the negative electrode, which can prevent the short circuit between the positive and negative electrodes and at the same time allow active ions to pass through. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0095] In some embodiments, the positive electrode of the lithium-ion battery includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material. The positive electrode active material may include a lithium sheet or a lithium-containing transition metal oxide.

[0096] Optionally, the lithium-containing transition metal oxide includes lithium iron phosphate or nickel cobalt manganese ternary material, and the nickel cobalt manganese ternary material may include one or more of lithium nickel cobalt manganese oxide and its modified compounds. The modified compounds of lithium nickel cobalt manganese oxide may include materials well known in the art, for example, may include doped-modified or surface-modified lithium nickel cobalt manganese oxide.

[0097] In some embodiments, the tap density of the positive electrode film layer can be 3.0 g / cm 3 to 3.8 g / cm 3 and can be optionally 2.9 g / cm 3 to 3.6 g / cm 3 .

[0098] The tap density of the positive electrode film layer has the meaning well-known in the art and can be tested by the equipment and methods known in the art. The tap density of the positive electrode film layer = the areal density of the positive electrode film layer / the thickness of the single-sided positive electrode film layer. The areal density of the positive electrode film layer has the meaning well-known in the art and can be tested by the equipment and methods known in the art. For example, take a positive electrode sheet after single-sided coating and cold pressing (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), punch it into small round pieces, and weigh them; then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode sheet and weigh the weight of the current collector. The areal density of the positive electrode film layer = (the weight of the small round piece - the weight of the current collector) / the area of the small round piece.

[0099] In some embodiments, the positive electrode film layer may optionally further include a positive electrode conductive agent. The present invention does not particularly limit the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the positive electrode film layer may optionally further include a positive electrode binder. The present invention does not particularly limit the type of the positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0101] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0102] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0103] In some embodiments, lithium metal can be used to replace the positive electrode of the lithium-ion battery.

[0104] In some embodiments, the material of the separator includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0105] In a lithium-ion battery, the main functions of the electrolyte include providing a transmission medium for ions, including additives, solvents, and metal salts.

[0106] In some embodiments, the additives in the electrolyte include any one or at least two combinations of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinylene carbonate (VC), ethylene vinylene carbonate (VEC), or lithium bis(oxalato)borate (LiBOB). Typical but non-limiting combinations include the combination of FEC and PS, the combination of PS and VC, the combination of VC and VEC, the combination of FEC, PS, and VC, the combination of VC, VEC, and LiBOB, or the combination of FEC, PS, VC, VEC, and LiBOB.

[0107] In some embodiments, the solvents in the electrolyte include ethyl methyl carbonate (EMC) and / or ethylene carbonate (EC).

[0108] In some embodiments, the metal salt in the electrolyte is a lithium salt.

[0109] In some embodiments, the lithium salt includes any one or at least two combinations of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), or lithium hexafluoroarsenate (LiAsF6). Typical but non-limiting combinations include the combination of LiPF6 and LiBF4, the combination of LiBF4 and LiClO4, the combination of LiClO4 and LiAsF6, the combination of LiPF6, LiBF4, and LiClO4, or the combination of LiPF6, LiBF4, LiClO4, and LiAsF6.

[0110] To clearly illustrate the technical solution of the present invention, the particle size D10 of the graphite (see the SEM diagram in the following Examples, Comparative Examples, and Control Example 1) Figure 1 ) is 10.26 μm, the particle size D50 is 17.18 μm, the particle size D90 is 28.06 μm, the specific surface area is 1.18 m 2 / g, and the tapped density is 0.93 g / cm 3 .

[0111] Example 1

[0112] This embodiment provides a graphite composite material, which includes a graphite core and a coating layer covering the graphite core, wherein the coating layer includes porous carbon covering the graphite core and phosphorus element deposited in the pores and on the surface of the porous carbon.

[0113] The preparation method of the graphite composite material in this embodiment comprises the following steps:

[0114] (1) 1.8 kg of graphite and an anhydrous ethanol solution of zinc gluconate were kneaded at 80°C until the anhydrous ethanol was completely evaporated to obtain a kneaded mixture. The mass of the zinc gluconate was 10% of the total mass of the graphite and the zinc gluconate.

[0115] The anhydrous ethanol solution of zinc gluconate is prepared according to the ratio of 20g zinc gluconate dissolved in 2kg anhydrous ethanol.

[0116] (2) In a nitrogen atmosphere, the kneaded mixture was sintered at 120°C for 2 h to expel the crystal water on the surface of the material; then, it was sintered at 300°C for 3 h, and the zinc gluconate began to decompose into zinc oxide and water. It was further sintered at 600°C for 1.5 h; and finally, it was sintered at 1150°C for 16 h to completely decompose the zinc oxide to obtain porous carbon-coated graphite (see SEM image). Figure 2 ).

[0117] The specific surface area of porous carbon-coated graphite is 4.45 m 2 / g 3 .

[0118] (3) The uniformly mixed red phosphorus and porous carbon-coated graphite are placed in a rotary kiln, with the red phosphorus accounting for 3% of the total mass of the porous carbon-coated graphite and the red phosphorus. The rotary kiln is then replaced with nitrogen twice and evacuated to 50 Pa. The kiln is heat treated at 480° C. for 4 h to sublime the red phosphorus. The temperature is lowered to 320° C. and kept at this temperature for 24 h to allow the red phosphorus to recrystallize and coat the surface of the porous carbon-coated graphite. The temperature is naturally lowered to room temperature (25° C.), and compressed air is passed through for 6 h to allow the residual white phosphorus to be discharged in the form of P2O5, thereby obtaining a graphite composite material (see SEM image). Figure 3 ).

[0119] The specific surface area and phosphorus content of the graphite composite material obtained in this example are shown in Table 1.

[0120] Depend on Figure 1 and Figure 2 It can be seen that the morphology of the material does not change significantly before and after porous carbon coating; Figure 3 The graphite composites in the graphite matrix can clearly observe the surface particles; Figure 4 This is the EDS element distribution diagram of the graphite composite material, and it can be observed that phosphorus is uniformly loaded on the porous carbon-coated graphite.

[0121] Example 2

[0122] This embodiment provides a graphite composite material, which includes a graphite core and a coating layer covering the graphite core, wherein the coating layer includes porous carbon covering the graphite core and phosphorus element deposited in the pores and on the surface of the porous carbon.

[0123] The preparation method of the graphite composite material in this embodiment comprises the following steps:

[0124] (1) Graphite and an anhydrous ethanol solution of zinc gluconate are kneaded at 80° C. until the anhydrous ethanol is completely evaporated to obtain a kneaded mixture. The mass of the zinc gluconate is 15% of the total mass of the graphite and the zinc gluconate.

[0125] The anhydrous ethanol solution of zinc gluconate is prepared according to the ratio of 20g zinc gluconate dissolved in 2kg anhydrous ethanol.

[0126] (2) In a nitrogen atmosphere, the kneaded mixture was sintered at 110°C for 2 h to expel the crystal water on the surface of the material; then, it was sintered at 280°C for 3 h, and the zinc gluconate began to decompose into zinc oxide and water. The mixture was then sintered at 580°C for 1.5 h. Finally, it was sintered at 1100°C for 16 h to completely decompose the zinc oxide to obtain porous carbon-coated graphite.

[0127] The specific surface area of porous carbon-coated graphite is 10.48 m 2 / g.

[0128] (3) The uniformly mixed red phosphorus and porous carbon-coated graphite are placed in a rotary kiln, with the red phosphorus accounting for 5% of the total mass of the porous carbon-coated graphite and the red phosphorus. The rotary kiln is then replaced with nitrogen twice and evacuated to 50 Pa. The red phosphorus is heat treated at 460° C. for 4 h to sublime. The temperature is lowered to 280° C. and kept at this temperature for 24 h to allow the red phosphorus to recrystallize and coat the surface of the porous carbon-coated graphite. The temperature is naturally lowered to room temperature (25° C.), and compressed air is passed through for 6 h to allow the residual white phosphorus to be discharged in the form of P2O5, thereby obtaining a graphite composite material.

[0129] The specific surface area and phosphorus content of the graphite composite material obtained in this example are shown in Table 1.

[0130] Example 3

[0131] This embodiment provides a graphite composite material, which includes a graphite core, a porous carbon coating layer covering the graphite core, and a phosphorus coating layer covering the surface of the porous carbon coating layer.

[0132] The preparation method of the graphite composite material in this embodiment comprises the following steps:

[0133] (1) Under the temperature condition of 80 °C, knead and mix graphite with an absolute ethanol solution of zinc gluconate until the absolute ethanol completely evaporates to obtain a kneaded mixture. The mass of zinc gluconate is 5% of the total mass of graphite and zinc gluconate.

[0134] The absolute ethanol solution of zinc gluconate is prepared according to the ratio of 20 g of zinc gluconate dissolved in 2 kg of absolute ethanol.

[0135] (2) In a nitrogen atmosphere, the kneaded mixture is sintered at 130 °C for 2 h to remove the crystal water on the material surface; then sintered at 320 °C for 3 h, during which zinc gluconate begins to decompose into zinc oxide and water, and continue to sinter at 620 °C for 1.5 h; finally sintered at 1200 °C for 16 h to completely decompose zinc oxide, obtaining porous carbon-coated graphite.

[0136] The specific surface area of the porous carbon-coated graphite is 12.57 m 2 / g

[0137] (3) Place the uniformly mixed red phosphorus and porous carbon-coated graphite in a rotary furnace. Red phosphorus accounts for 1% of the total mass of porous carbon-coated graphite and red phosphorus. Then replace nitrogen twice in the rotary furnace and evacuate to 50 Pa; heat-treat at 500 °C for 4 h to sublimate red phosphorus; cool down to 350 °C and keep warm for 24 h to recrystallize red phosphorus on the surface of the porous carbon-coated graphite; naturally cool down to room temperature (25 °C) and pass compressed air for 6 h to discharge the remaining white phosphorus in the form of P2O5, obtaining a graphite composite material.

[0138] The specific surface area and phosphorus content of the graphite composite material obtained in this example are shown in Table 1.

[0139] Example 4

[0140] This example provides a graphite composite material, which is the same as Example 1 except that red phosphorus accounts for 7% of the total mass of porous carbon-coated graphite and red phosphorus.

[0141] The specific surface area and phosphorus content of the graphite composite material obtained in this example are shown in Table 1.

[0142] Example 5

[0143] This example provides a graphite composite material, which is the same as Example 1 except that red phosphorus accounts for 0.5% of the total mass of porous carbon-coated graphite and red phosphorus.

[0144] The specific surface area and phosphorus content of the graphite composite material obtained in this example are shown in Table 1.

[0145] Example 6

[0146] This embodiment provides a graphite composite material, which is the same as that of Embodiment 1 in all respects except that the mass of zinc gluconate is 20% of the total mass of graphite and zinc gluconate.

[0147] The specific surface area and phosphorus content of the graphite composite material obtained in this embodiment are shown in Table 1.

[0148] Embodiment 7

[0149] This embodiment provides a graphite composite material, which is the same as that of Embodiment 1 in all respects except that the mass of zinc gluconate is 2% of the total mass of graphite and zinc gluconate.

[0150] The specific surface area and phosphorus content of the graphite composite material obtained in this embodiment are shown in Table 1.

[0151] Comparative Example 1

[0152] This comparative example provides a graphite composite material, which includes a graphite core and a phosphorus coating layer covering the graphite core.

[0153] The preparation method of the graphite composite material in this comparative example includes the following steps:

[0154] Replace nitrogen twice in a rotary kiln and evacuate to 50 Pa, then place the uniformly mixed red phosphorus and the graphite in Embodiment 1 in the rotary kiln; heat-treat at 480 °C for 4 h to sublime the red phosphorus; cool down to 320 °C and keep warm for 24 h to recrystallize the red phosphorus on the surface of the graphite; naturally cool down to room temperature (25 °C), and pass compressed air for 6 h to discharge the remaining white phosphorus in the form of P2O5 to obtain the graphite composite material.

[0155] The ratio of red phosphorus to graphite is the same as that in Embodiment 1.

[0156] In this comparative example, since there is no porous carbon coating layer, it is difficult for the phosphorus coating layer to coat the graphite core.

[0157] Performance Characterization

[0158] Use a laser particle size analyzer to test the specific surface area of the graphite composite material obtained in the above embodiments and the content of elemental phosphorus in the graphite composite material. The obtained results are shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162] The graphite in Example 1 was used as Control Example 1, and the porous carbon-coated graphite in Example 1 was used as Control Example 2. The graphite composite materials obtained in the above examples and comparative examples were used to assemble a coin cell. The cycle performance and rate performance were then tested using a blue power test system. The results are shown in Table 1:

[0163] (I) Using a negative electrode material that has been sieved through a 300-mesh screen, the negative electrode material, SBR, CMC, and SP are uniformly mixed in deionized water at a mass ratio of 94.5:2.5:1.5:1.5; a uniform slurry with a solid content of 45% is prepared; after coating on a current collector copper foil, the slurry is dried and rolled to obtain a surface density of 9.6±1 mg / cm 2 ; Then cut into circular pole pieces with a diameter of 14 mm, vacuum dry at a temperature of 80°C for 6 hours to prepare the negative pole piece.

[0164] (II) Diethyl carbonate (DEC) and ethylene carbonate (EC) are uniformly mixed in a volume ratio of 1:1, and then solid lithium hexafluorophosphate (LiPF6) as a lithium salt is added thereto for dissolution. At this time, the content of lithium hexafluorophosphate is 0.8 mol / L.

[0165] (III) A lithium sheet with a thickness of 1 mm and a diameter of 10 mm is used as the counter electrode of the half-cell to provide a lithium source, and then the negative electrode sheet is placed opposite to the lithium sheet via a separator (polyethylene film), and after injecting the electrolyte, a 2430 button cell is prepared.

[0166] The cycle performance test conditions are as follows: 200 charge and discharge cycles are performed at a constant current of 1C in the voltage range of 0.01V-2.5V, and the retention rate of 200 cycles is obtained by dividing the 200th charge capacity by the 1st charge capacity (first capacity).

[0167] The rate performance test conditions are as follows: within the voltage range of 5mV to 2V, the obtained button cell is subjected to constant current charge and discharge test, the current density is 0.1C (1C=4.8mA), and the capacity retention rate obtained by dividing the charge capacity at 1.2C by the charge capacity at 0.05C is the rate performance.

[0168] Table 2

[0169] Initial capacity (mAh / g) Cyclic capacity retention rate (%) Rate performance Example 1 356.5 0.962 0.484 Example 2 352.8 0.958 0.453 Example 3 355.5 0.956 0.449 Example 4 355.9 0.901 0.320 Example 5 357.0 0.946 0.409 Example 6 350.9 0.960 0.403 Example 7 356.9 0.949 0.400 Control Example 1 358.4 0.930 0.350 Control Example 2 357.4 0.940 0.390 Comparative Example 1 357.9 0.926 0.370

[0170] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A graphite composite material, characterized in that, The graphite composite material includes: A graphite core; A coating layer, which includes porous carbon coating the graphite core and elemental phosphorus deposited in and on the pores of the porous carbon.

2. The graphite composite material according to claim 1, characterized in that, The content of elemental phosphorus in the graphite composite material is 0.1 wt% - 1 wt%; the specific surface area of the graphite composite material is 0.3 m 2 / g - 2 m 2 / g.

3. A preparation method of a graphite composite material, characterized in that, The preparation method includes the following steps: S1. Mix graphite and a coating agent, and perform carbonization treatment to obtain porous carbon-coated graphite; S2. Perform phosphorus deposition treatment on the porous carbon-coated graphite to obtain the graphite composite material.

4. The preparation method according to claim 3, characterized in that, The specific surface area of the graphite composite material is smaller than that of the porous carbon-coated graphite; and / or, the specific surface area of the porous carbon-coated graphite is 2 m 2 / g - 13 m 2 / g; and / or, the specific surface area of the graphite composite material is 0.3 m 2 / g - 2 m 2 / g.

5. The preparation method according to claim 3 or 4, characterized in that, In the step S1, the mass of the coating agent is 5%-15% of the total mass of the graphite and the coating agent; And / or, the coating agent includes any one or a combination of at least two of zinc gluconate, zinc oxalate, zinc citrate, zinc lactate, or zinc glycyrrhizinate.

6. The preparation method according to claim 5, characterized in that, The carbonization treatment includes a first sintering, a second sintering, a third sintering, and a fourth sintering sequentially carried out in a protective atmosphere; the temperature of the first sintering is 110°C - 130°C; the temperature of the second sintering is 280°C - 320°C; the temperature of the third sintering is 580°C - 620°C; the temperature of the fourth sintering is 1100°C - 1200°C.

7. The preparation method according to claim 3 or 4, characterized in that, In the step S2, the phosphorus deposition treatment includes: mixing a phosphorus source and the porous carbon-coated graphite, and performing heat treatment to deposit phosphorus in and on the pores of the porous carbon coating layer; And / or, the mass of the phosphorus source is 1%-5% of the total mass of the porous carbon-coated graphite and the phosphorus source.

8. The preparation method according to claim 7, wherein The heat treatment includes a first heat treatment and a second heat treatment carried out sequentially; the temperature of the first heat treatment is 460°C - 500°C; the temperature of the second heat treatment is 280°C - 350°C. And / or, after the heat treatment, it further includes a step of introducing an oxygen-containing gas to remove white phosphorus.

9. A negative electrode, characterized in that, The negative electrode includes a negative electrode active material; the negative electrode active material includes the graphite composite material described in claim 1, or includes the graphite composite material prepared by the preparation method described in any one of claims 2-8.

10. A battery, characterized in that, The battery includes the negative electrode described in claim 9.

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