A loose porous carbon box conductive agent carbon material, a preparation method thereof and application thereof in lithium ion batteries

Abstract

The application discloses a kind of loose porous carbon box conductive agent carbon materials and preparation method and application thereof.The loose porous carbon box conductive agent carbon material is prepared by 1200-1500 DEG C high temperature graphitization of conductive agent carbon material precursor under protective atmosphere;The conductive agent carbon material precursor is obtained by washing and freeze-drying after high-temperature coating of solid powder by coating machine under protective atmosphere;Solid powder is prepared by ball milling of industrial powder salt and hot-melt polymer material;High-temperature coating is composed of hot-melt and coke discharge, and freeze-drying refers to that material is dispersed in water after washing, and after being made into suspension, it is frozen below freezing point, and water in material is directly sublimated into water vapor from solid ice by vacuum extraction.The loose porous carbon box conductive agent has porous structure, and larger reticular structure is beneficial to the adhesion of active substance, can form efficient conductive network, enhances the conduction capacity of electron, and improves the electrochemical performance of lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to carbon materials, in particular to a loose porous carbon box conductive agent carbon material and a preparation method and application thereof, the application being the application of the loose porous carbon box conductive agent carbon material as a negative electrode conductive agent of a lithium ion battery; and belongs to the technical field of negative electrode conductive agent materials of lithium ion batteries. BACKGROUND

[0002] With the increasing shortage of non-renewable energy sources such as oil, it is urgent to seek an environmentally friendly and sustainable green clean new energy source. As a new type of sustainable energy, lithium ion batteries are widely used in many portable electronic products, such as mobile phones, notebook computers, etc., and are also used in electric vehicles and energy storage systems. The structure of a lithium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator. During the charging process, Li + migrates from the positive electrode to the negative electrode through the electrolyte, and the discharging process is the reverse, Li + migrates from the negative electrode to the positive electrode through the electrolyte, and the lithium ion battery can be continuously charged and discharged, Li + shuttles between the positive and negative electrodes. Compared with other types of batteries, lithium ion batteries have higher energy density, longer cycle life and lower self-discharge rate. However, it also has some problems, such as capacity decay, safety and cost challenges.

[0003] In the normal charging and discharging process, the participation of lithium ions and electrons is required, which requires that the electrodes of the lithium ion battery must be mixed conductors of ions and electrons, and the electrode reaction can only occur at the junction of the electrolyte, the conductive agent and the active material. The positive electrode active material is mostly a transition metal oxide or a transition metal phosphate, which is a semiconductor or an insulator with poor conductivity; although the negative electrode graphite material has slightly better conductivity, but in multiple charging and discharging, the expansion and contraction of the graphite material reduces the contact between the graphite particles and increases the gap, and even some of them are separated from the current collector, becoming dead active material and no longer participating in the electrode reaction. In lithium ion batteries, the conductive agent is one of the important components of the battery and is an indispensable key material in the large current charging and discharging process of lithium ion batteries. It collects micro-currents between active component substances and between active substances and current collectors, helps charge transfer between the electrolyte and the electrode, and builds an efficient and robust conductive network, which can significantly improve the electron transfer rate, reduce the contact resistance, promote the penetration of the electrolyte to the electrode, thereby playing an important role in improving the conductivity, capacity, rate performance and cycle performance of the battery. In addition, the conductive agent can also improve the processability of the electrode sheet, promote the infiltration of the electrolyte to the electrode sheet, effectively improve the migration rate of lithium ions in the electrode material, reduce polarization, and thereby improve the charging and discharging efficiency and service life of the electrode. The conductive agent can fill the gaps between particles caused by the expansion and contraction of the electrode material, thereby maintaining the conductivity of the electrode and improving the cycle life and stability of the battery.

[0004] According to the market price range, the conductive agent can be divided into basic type conductive agent and high performance conductive agent, wherein the basic type conductive agent includes conductive carbon black, multi-arm carbon nanotube and the like. As a conductive additive, the structure of the conductive carbon black is generally spherical particle aggregate with a diameter less than 100 nm. Although the conductive carbon black is cheap, the relatively low electronic conductivity of the carbon black cannot form a good conductive network, has high resistance and is easy to be polarized, which affects the electrochemical reaction kinetics on the cathode side and significantly reduces the efficiency of the battery. Moreover, the carbon black is usually prepared by burning hydrocarbon compounds in industry, which has poor controllability, pollutes the environment and has poor regulation on the structure and performance of the product. Compared with the conductive carbon black, the multi-wall carbon nanotube has excellent conductivity, but has poor dispersibility and is easy to be aggregated, which affects the overall performance of the composite material; and the transition metal salt needs to be used as a catalyst in the preparation process, which may cause heavy metal pollution to the environment; because a large amount of organic matter and acid-base substances are contained in the wastewater, improper treatment will pollute the water quality. The high performance conductive agent is single-wall carbon nanotube, graphene and composite material thereof. The conductive agent has excellent conductivity and special physical and chemical properties, but the initial coulombic efficiency (ICE) of the conductive agent is very low, which reduces the initial coulombic efficiency of the battery after being added. The single-wall carbon nanotube is generally prepared by using laser evaporation method and chemical vapor deposition method, and the laser evaporation method has high equipment cost and high energy consumption, which leads to high production cost and low yield. The vapor deposition method has high equipment cost and produces toxic and corrosive by-products in the production process, which harms the environment and the operating personnel, thereby limiting the large-scale production. At present, the preparation methods of graphene include mechanical peeling method, chemical vapor deposition method and the like, which have low yield, complex technology and high cost, thereby limiting the large-scale commercial production.

[0005] Chinese invention patent application 201710792812.8 discloses a composite conductive agent, a lithium ion battery pole piece and a lithium ion battery. By introducing a new type of composite conductive agent, a pole piece with a developed effective conductive network on the surface can be prepared by adding a small amount of the conductive agent, so that the prepared lithium ion battery has excellent rate discharge, low temperature discharge, high temperature storage and cycle performance. The composite conductive agent in the present application includes single-wall or few-wall carbon nanotubes and graphene nanosheets; the specific surface area of the single-wall or few-wall carbon nanotubes is 200-1500 m 2 / g, the tube diameter is 1-10 nm, and the tube length is greater than 5 μm; the diameter of the graphene nanosheet is 0.2-2 μm, the specific surface area is less than 1800 m 2 / g, and the thickness is less than 2 nm. However, the use of single-wall carbon nanotubes and graphene nanosheets in the technology will greatly increase the cost of the battery, and the specific surface area of the composite conductive agent of the technology is too high, which will cause more side reactions during the charging and discharging process and affect the overall initial coulombic efficiency of the battery.

[0006] Based on the problems existing in the prior art, it is imperative to develop a conductive agent with low cost, environmental friendliness, scalable production, high conductivity and high initial coulomb efficiency, which is the key to improving the conductivity of lithium ion batteries, which is very beneficial to improve the service life of lithium ion batteries and promote the development of lithium ion batteries, and will promote the healthy development of new energy industry. SUMMARY

[0007] In order to overcome the problems of high price, complex preparation process and dispersion difficulty of the existing lithium ion battery conductive agent, the present application provides a loose porous carbon box conductive agent carbon material and its preparation method, which has the advantages of simple process, low cost, good safety, environmental friendliness, excellent conductivity and improved battery cycle life, and has the advantage of large-scale production.

[0008] Another object of the present application is to provide the application of the loose porous carbon box conductive agent carbon material in the lithium ion battery conductive agent, which can form an efficient conductive network in the lithium ion battery, provide a faster electron transmission channel and lower resistance, thereby improving the overall conductivity of the battery and improving the electrochemical performance of the battery.

[0009] The object of the present application is achieved by the following technical solutions:

[0010] A loose porous carbon box conductive agent carbon material is prepared by high-temperature graphitization of a conductive agent carbon material precursor under a protective atmosphere at 1200-1500 DEG C; the conductive agent carbon material precursor is obtained by high-temperature coating of a solid powder through a coating machine, followed by water washing and freeze-drying under a protective atmosphere; the solid powder is prepared by ball milling of industrial salt and hot-melt high molecular material, and the melting point of the industrial salt is higher than that of the selected hot-melt high molecular material; the high-temperature coating consists of hot melting and coke removal, the hot melting temperature is 150-220 DEG C, and the time is 1-3 h; the coke removal temperature is 600-700 DEG C, and the coke removal time is 2-4 h; the freeze-drying refers to dispersing the water-washed material in water, preparing a suspension, freezing below the freezing point, and directly sublimating the water in the material from solid ice to water vapor by vacuum pumping.

[0011] The preparation method of the loose porous carbon box conductive agent carbon material comprises the following steps:

[0012] 1) uniformly preparing a solid powder by ball milling of industrial salt and hot-melt high molecular material;

[0013] 2) under a protective atmosphere, the solid powder is coated by a coating machine at high temperature, then washed with water, and freeze-dried to obtain a conductive agent carbon material precursor; the high temperature coating consists of hot melting and coke discharging, the hot melting temperature is 150-220 DEG C, and the time is 1-3h; the coke discharging temperature is 600-700 DEG C, and the coke discharging time is 2-4h; the freeze-drying refers to that the material after washing with water is dispersed in water, a suspension is prepared, and then frozen below the freezing point, and the water in the material is directly sublimated from solid ice to water vapor by vacuumizing;

[0014] 3) under a protective atmosphere, the conductive agent carbon material precursor is prepared into a loose porous carbon box conductive agent carbon material by high temperature graphitization at 1200-1500 DEG C.

[0015] To further achieve the purpose of the application, preferably, the ball milling time is 2.5-4h, and the rotating speed is 25-45rpm.

[0016] Preferably, the industrial powder salt is one or more of sodium chloride, potassium chloride, sodium sulfate and potassium sulfate; and the hot melt polymer material is one or more of asphalt, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP).

[0017] Preferably, the mass ratio of the hot melt polymer material and the industrial powder salt is 0.05-0.1:1; and the ball for ball milling is a zirconium ball, and the mass ratio of the zirconium ball and the material to be ball milled is 0.21-0.22:1.

[0018] Preferably, the rotating speed of the coating machine is 30-45rpm, and the protective atmosphere flow rate of the coating machine is 40-50mL / min.

[0019] Preferably, the freeze-drying temperature is-60--40 DEG C, and the freeze-drying time is 8-12h.

[0020] Preferably, the washing with water refers to soaking the material with pure water and then filtering, and repeatedly washing until no industrial powder salt is left.

[0021] Preferably, the high temperature graphitization time is 3-4h, and the heating rate is 2-5 DEG C / min; in steps 2) and 3), the protective atmosphere is a nitrogen or argon atmosphere.

[0022] The application of the loose porous carbon box conductive agent carbon material in preparing a lithium ion battery negative electrode.

[0023] Preferably, the lithium ion negative electrode material, binder and loose porous carbon box conductive agent carbon material are mixed to prepare a lithium ion battery negative electrode slurry, which is uniformly coated on a copper foil, and the lithium ion battery negative electrode sheet is prepared after sheet pressing; the lithium ion negative electrode material is a silicon / carbon material (SBaS-420-L material from Guangdong Electric Co., Ltd. Xinneng New Energy Co., Ltd., which is a silicon / amorphous carbon / graphite composite material with a reversible capacity of about 420 mAh / g), the binder is TRD-104A (TRD binder special for lithium ion batteries) and CMC (sodium carboxymethyl cellulose), and the mass ratio of the negative electrode material, binder and loose porous carbon box conductive agent carbon material is (95-96) :(2-4) :(1-2).

[0024] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0025] 1) The existing preparation technology of lithium ion battery conductive agent includes combustion of hydrocarbon compounds and chemical vapor deposition method. The method of preparing conductive agent material by combustion of hydrocarbon compounds has poor controllability, pollutes the environment, and has poor regulation and control of the structure and performance of the product. The chemical vapor deposition method needs to consume a large amount of energy to maintain a high-temperature environment, which not only increases the preparation cost, but also causes a certain burden to the environment, and the yield is low and it is difficult to realize large-scale, continuous and stable production. In order to solve the problems in the use of conductive agent materials and further improve the performance of lithium ion batteries, the present application prepares a loose porous carbon box conductive agent carbon material by combining template method, high-temperature coating method and freeze-drying. The high-temperature coating process has the advantages of simple method, strong operability, low cost, and can quickly and large-scalely coat organic carbon source on the surface of the sacrificial agent.

[0026] 2) The present application uses industrial powder salt as a hard template because industrial powder salt has a higher melting point than the selected thermally fusible polymer, is easy to dissolve in water, and has a low cost. The carbon material after removing the template is in the form of a carbon box. The conductive agent designed in this way has a high specific surface area and a loose void structure on the surface, which can provide more reactive surfaces, fill the particle voids caused by the expansion and contraction of the electrode material, and thus maintain the conductivity of the electrode, improve the cycle life and stability of the battery. The large two-dimensional network structure is also beneficial to increasing the adsorption of substances and providing a conductive bridge between active substances, so that lithium ions can more easily enter and diffuse, thereby improving the overall electrical conductivity of the battery.

[0027] 3)The porous carbon box conductive agent carbon material prepared at high temperature has good high-temperature resistance, so that the lithium ion battery can be stably operated for a long time under high-temperature conditions; the porous carbon box conductive agent carbon material can form a continuous conductive network in the electrode, enhances the electron conduction capacity, and improves the performance of the lithium ion battery, especially the high-temperature performance of the lithium ion battery is obviously improved. Test results of the embodiment show that the porous carbon box conductive agent carbon material has a large surface area, can obviously reduce the internal resistance of the lithium ion battery, and greatly improves the cycle stability of the lithium ion battery.

[0028] 4)The porous carbon box conductive agent obtained by the method has a porous structure, and the large network structure is beneficial to the adhesion of active substances, can form an efficient conductive network, enhances the electron conduction capacity, provides a faster electron transmission channel and a lower resistance, improves the overall conductivity of the battery, and thus improves the electrochemical performance of the lithium ion battery.

[0029] 5)The porous carbon box conductive agent carbon material synthesized by the method can be used as a negative electrode conductive agent of a lithium ion battery. When the mass ratio of industrial salt and pitch is 40:3, the material as a conductive agent is subjected to electrochemical test on a silicon-carbon material, and the test results show that, compared with SP, the material has excellent performance: at 25 DEG C, under a current density of 0.1 C, the first coulombic efficiency is > 90%; after 800 cycles at a rate of 1 C, the capacity retention rate of the material is 90.46%; and after 1000 cycles at a rate of 0.75 C, the capacity retention rate of the material is 87.87%.

[0030] 6)The raw materials used in the method are widely available, and the preparation method is various, which provides a reference for people to prepare a lithium ion battery conductive agent material with excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The XRD patterns of the conductive agent carbon material precursor before graphitization and the porous carbon box conductive agent carbon material after graphitization prepared in Example 1.

[0032] Figure 2 The nitrogen adsorption-desorption curve of the carbon box conductive agent carbon material prepared in Example 1.

[0033] Figure 3 The pore size distribution graph of the carbon box conductive agent carbon material prepared in Example 1.

[0034] Figure 4 The SEM graph of the carbon box conductive agent carbon material prepared in Example 1.

[0035] Figure 5 The first three cycle charge-discharge curve graph of the lithium ion half battery prepared in Example 1 at 25 DEG C and a rate of 0.1 C.

[0036] Figure 6 The long cycle performance test results of the lithium ion half-batteries prepared for Example 1 and Comparative Example 1 at 1C rate are shown in the figure.

[0037] Figure 7 The long cycle performance of the lithium ion half-batteries prepared for Example 1 at 0.75C rate for 1000 cycles is shown in the figure.

[0038] Figure 8 The lithium ion diffusion rate comparison of the lithium ion half-batteries prepared for Example 1 and Comparative Example 1 during the charging process is shown in the figure.

[0039] Figure 9 The lithium ion diffusion rate comparison of the lithium ion half-batteries prepared for Example 1 and Comparative Example 1 during the discharging process is shown in the figure. Specific implementation method

[0040] The application will be further described below in conjunction with the examples, comparative examples and the accompanying drawings, but the embodiments of the application are not limited thereto. It should be noted that if the following processes are not specifically described in detail, they can be realized or understood by those skilled in the art according to the prior art. If the reagents or instruments used are not marked with the manufacturer, they are considered to be conventional products that can be purchased on the market.

[0041] The application is characterized in that the loose porous carbon box conductive agent carbon material is prepared by template method, high-temperature coating method and freeze-drying cooperation. The template method is to use industrial powder salt as a hard template, and to prepare a solid powder material by ball milling the industrial powder salt and a hot melt polymer material. The industrial powder salt has the characteristics of higher melting point than the selected hot melt polymer, easy solubility in water and low cost, and the carbon material after removing the template is in the form of a carbon box. The conductive agent designed in this way has a high specific surface area and a loose void structure on the surface, which can provide more reactive surfaces, fill the particle voids caused by the expansion and contraction of the electrode material, maintain the conductivity of the electrode, and improve the cycle life and stability of the battery. The large two-dimensional network structure is also beneficial to increasing the adsorption of substances and providing a conductive bridge between active substances, so that lithium ions can more easily enter and diffuse, thereby improving the overall conductivity of the battery.

[0042] The high-temperature coating is composed of hot melting and discharging, and is characterized by controlling the hot melting temperature to be 150-220 DEG C, the time to be 1-3h, the discharging temperature to be 600-700 DEG C, and the discharging time to be 2-4h; the solid powder material is coated by the coating machine under a protective atmosphere, and then is washed and freeze-dried to obtain the carbon material precursor of the conductive agent. The freeze-drying refers to that the material after washing is dispersed in water, and is prepared into a suspension which is then frozen below the freezing point, and the water in the material is directly sublimated from solid ice into water vapor through vacuumizing. The high-temperature coating process has the advantages of simple method, strong operability, low cost, and the organic carbon source can be quickly and massively coated on the surface of the sacrificial agent. The carbon material precursor of the conductive agent is graphitized at 1200-1500 DEG C under a protective atmosphere to obtain the loose porous carbon box conductive agent, which presents a two-dimensional self-assembled net-like carbon box structure, and a large number of pores are distributed in the carbon box; the conductive carbon material has macropores, micropores and / or mesopores, the size of the cubic pore hole of the self-assembled net-like carbon box is 4-15 microns, the size of the surface pore is 20-100nm, the specific surface area is 100-240m 2 / g, and the tap density of the loose carbon box conductive agent is 1.0-1.8g / cm 3 .

[0043] As known from the above, the loose porous carbon box conductive agent is prepared by graphitizing the carbon material precursor of the conductive agent at 1200-1500 DEG C under a protective atmosphere; the carbon material precursor of the conductive agent is obtained by coating the solid powder through a coating machine under a protective atmosphere, and then washing and freeze-drying; the solid powder is prepared by ball milling the industrial powder salt and the hot-melt high molecular material, and the melting point of the industrial powder salt is higher than that of the selected hot-melt high molecular material; the high-temperature coating is composed of hot melting and discharging, the hot melting temperature is 150-220 DEG C, the time is 1-3h, the discharging temperature is 600-700 DEG C, the discharging time is 2-4h, and the freeze-drying refers to that the material after washing is dispersed in water, prepared into a suspension which is then frozen below the freezing point, and the water in the material is directly sublimated from solid ice into water vapor through vacuumizing.

[0044] The preparation method of the loose porous carbon box conductive agent includes the following steps:

[0045] 1) preparing the uniform solid powder by ball milling the industrial powder salt and the hot-melt high molecular material;

[0046] 2) under the protection of atmosphere, the solid powder is coated by a coating machine at high temperature, then washed with water, and freeze-dried to obtain a conductive agent carbon material precursor; the high temperature coating consists of hot melting and coke discharging, the hot melting temperature is 150-220℃, and the time is 1-3h; the coke discharging temperature is 600-700℃, and the coke discharging time is 2-4h; the freeze-drying refers to that the material after washing with water is dispersed in water, a suspension is prepared, and then frozen below the freezing point, and the water in the material is directly sublimated from solid ice to water vapor through vacuumizing;

[0047] 3) under the protection of atmosphere, the conductive agent carbon material precursor is prepared into a loose porous carbon box conductive agent carbon material by high temperature graphitization at 1200-1500℃.

[0048] As for the ball milling process control involved in the above preparation method, the selection of industrial powder salt and hot-melt polymer material, the proportion range of the amount of hot-melt polymer material and industrial powder salt, the specific control process of the coating machine, the temperature and time control of freeze-drying, the specific method of water washing, and the time and temperature rising speed of high temperature graphitization, etc. can be obtained by optimization according to the requirements of the above template method, the requirements of high temperature coating and the purpose of the present application, combined with the common sense in the field.

[0049] The loose porous carbon box conductive agent carbon material obtained by the present application can be applied in the preparation of lithium ion battery negative electrode. Specifically, the lithium ion negative electrode material, the binder and the loose porous carbon box conductive agent carbon material are mixed to prepare a lithium ion battery negative electrode slurry, which is uniformly coated on a copper foil, and then pressed to obtain the lithium ion battery negative electrode sheet; the lithium ion negative electrode material is a silicon-carbon material, the binder is TRD-104A and CMC, and the mass ratio of the negative electrode material, the binder and the loose porous carbon box conductive agent carbon material is (95-96):(2-4):(1-2).

[0050] The feasibility of the above loose porous carbon box conductive agent carbon material and its preparation method is verified by specific examples and comparative examples, and the performance advantages of the above template method, high temperature coating method and freeze-drying in preparing the loose porous carbon box conductive agent carbon material compared with the same kind of material in the prior art in terms of cycle stability are proved by tests and comparative examples, especially through the three-step method of the examples, the process advantages of the present application in terms of low cost, safety and environmental friendliness are embodied.

[0051] Example 1

[0052] A preparation method of a loose porous carbon box conductive agent carbon material, comprising the following steps:

[0053] (1) Take 2 Kg of industrial NaCl powder, 150 g of pitch, 10 Kg of zirconia balls, and pour them into a ball mill tank. Use a high-energy ball mill at a speed of 30 rpm for 3 h. After ball milling, separate the zirconia balls using a vibrating sieve machine to obtain a uniform brown powder.

[0054] (2) The powder obtained in the previous step is coated at high temperature in a high-temperature coating machine at a speed of 40 rpm, with an inert gas (argon) flow rate of 40 mL / min, and a temperature program of: increasing the temperature to 200°C at a rate of 200°C / h, and maintaining the temperature for 1 h; then increasing the temperature to 600°C at a rate of 200°C / h, and maintaining the temperature for 2 h. After coating, a black powder and a small amount of solid block are obtained.

[0055] (3) The solid block in the coated material is removed by a vibrating sieve machine, and NaCl is removed by water washing and filtration. The washed material is then dispersed in 2 L of pure water, and freeze-dried in a freeze-drier at a temperature of -50°C for 9 h to obtain a fluffy conductive carbon material precursor. The obtained conductive carbon material precursor is graphitized in a tube furnace at a temperature of 5°C / min to 1300°C under an argon atmosphere, and maintained for 4 h to obtain the final fluffy porous carbon box conductive carbon material.

[0056] This example provides a lithium ion half-cell: take 1.425 g of silicon-carbon composite material (SBaS-420-L material purchased from Guangdong Electric Power Co., Ltd. Qianli New Energy Co., Ltd., which is a silicon / amorphous carbon / graphite composite material with a reversible capacity of about 420 mAh / g), 0.027 g of CMC (sodium carboxymethyl cellulose), 0.033 g of TRD (lithium ion battery special TRD binder), and 0.015 g of the prepared fluffy porous carbon box conductive carbon material, mix them in a mortar, and then move them to a finger bottle. Add 15 ml of distilled water, and magnetically stir for 12 h. Then, use a glass rod to coat the material on a flat copper foil. After the material is dried, press the sheet to make an electrode. Use a metal lithium sheet as a counter electrode, and assemble a CR2016 type button cell in a glove box.

[0057] Figure 1The XRD patterns of the conductive carbon material precursor before graphitization and the porous carbon box conductive carbon material after graphitization prepared in Example 1 are shown. It can be seen that the XRD spectrum has two diffraction peaks, respectively at about 25° and 43°, corresponding to the (002) and (100) two crystal faces. Generally speaking, the (002) crystal face of the material represents the longitudinal size of the graphite crystallite sheet layer, and the higher and narrower the characteristic diffraction peak shape is, the more regular the spatial arrangement of the crystallite sheet layer is, and the greater the mutual orientation degree is. Moreover, the position of the (002) diffraction peak is related to the interlayer spacing of the graphite crystallite, and the more right the peak position is, the smaller the interlayer spacing is, and the more compact the graphite crystallite arrangement is. The (100) crystal face represents the lateral size of the crystallite, and the higher and narrower the characteristic diffraction peak shape is, the greater the diameter of the graphite crystallite sheet layer is, and the higher the ring condensation degree is. It can be clearly seen that the (002) peak of the GHC is shifted to the right, and the peak shape is narrowed, compared with the sample before graphitization, which shows that the interlayer spacing of the conductive carbon box after the reaction is reduced, and the crystallinity is increased.

[0058] Figure 2 The nitrogen adsorption-desorption curve of the carbon box conductive carbon material prepared in Example 1 is shown. It can be seen from the figure that the specific surface area of the material is 238.09 m 2 g -1 A larger specific surface area can provide more active surface, thereby improving the catalytic effect and reaction rate of the battery, and also improving the carrying capacity of the electrode material, promoting electron transmission and ion diffusion, and reducing the electrochemical reaction resistance.

[0059] Figure 3 The pore size distribution graph of the carbon box conductive carbon material prepared in Example 1 is shown. The mesoporous and microporous structure on the surface of the material is beneficial to accelerating the penetration of the electrolyte and shortening the transmission path of lithium ions.

[0060] Figure 4 The SEM graph of the carbon box conductive carbon material prepared in Example 1 is shown. The carbon box conductive carbon material presents a two-dimensional self-assembled net-like carbon box structure, and a large number of loose small holes are distributed in the inside; the size of the cubic hole of the self-assembled net-like carbon box is 4-15 μm, and the size of the surface pore is 20-100 nm. The larger flaky structure shows that the contact between the conductive agent and the active material is point-surface contact rather than the conventional point-point contact form, which can maximize the role of the conductive agent and reduce the amount of the conductive agent. In the case of smaller amount, a conductive network can be better formed. In addition, the material has many small pore structures, which is beneficial to providing rich lithium ion diffusion migration paths and electron transmission paths, and accelerating the penetration process of the electrolyte.

[0061] Figure 5The first three cycles of charge-discharge curves of lithium ion half battery prepared for example 1 at 25℃, 0.1C rate. As can be seen from the figure, the first coulombic efficiency of the composite prepared with carbon box as conductive agent is about 91%, and the first three cycles of constant current charge-discharge curves are basically coincided, which shows that the material has good cycle stability.

[0062] Figure 6 The long cycle performance test results of lithium ion half battery prepared for example 1 and comparative example 1 at 1C rate. As can be seen from the figure, after 800 cycles, the capacity retention rate of the material is 90.46%, which shows that the material has excellent electrochemical stability.

[0063] Figure 7 The long cycle performance of lithium ion half battery prepared for example 1 at 0.75C rate for 1000 cycles. As can be seen from the figure, after 1000 cycles, the capacity retention rate of the material is 87.87%, which shows that the material has excellent electrochemical stability.

[0064] Figure 8 And Figure 9 The lithium ion diffusion rate comparison chart of lithium ion half battery prepared for example 1 and comparative example 1 in the process of charge and discharge, wherein Figure 8 represents the discharge process, Figure 9 represents the charging process. As can be seen from the figure, the average lithium ion diffusion rate of the lithium ion half battery in the process of charge and discharge is calculated as follows: 8.205*10 -10 cm 2 ·s -1 (discharge) and 8.459*10 -10 cm 2 ·s -1 (charge), compared with the average lithium ion diffusion rate of comparative example 1 (7.09*10 -10 cm 2 ·s -1 ) and comparative example 2 (7.15*10 -10 cm 2 ·s -1 ), the lithium ion transport capacity is improved.

[0065] Example 2

[0066] A preparation method of loose porous carbon box conductive carbon material, comprising the following steps:

[0067] (1) weigh 2Kg of industrial NaCl powder, 100g of pitch, 10Kg of zirconia ball into the ball mill tank, and ball mill with high energy ball mill at 25rpm for 4h. After ball milling, separate the zirconia ball with vibration sieve machine, and get uniform brown powder.

[0068] (2) The powder obtained above was coated at high temperature in a high-temperature coating agent, the coating machine rotated at 30 rpm, the inert gas (argon) flowed at 40 mL / min, and the temperature program was as follows: the temperature was raised to 150°C at a rate of 200°C / h, and held for 1.5 h; then the temperature was raised to 600°C at a rate of 200°C / h, and held for 4 h. After coating, black powder and a small amount of block solid were obtained.

[0069] (3) The block solid in the coated material was removed by a vibrating screen, and NaCl was removed by water washing and filtration. The washed material was then dispersed in 2 L of pure water, and freeze-drying was performed using a freeze-drier at a temperature of -40°C for 10 h. A fluffy conductive carbon material precursor was obtained by freeze-drying. Graphitization of the obtained conductive carbon material precursor was performed in a tube furnace at 3°C / min to 1200°C under an argon atmosphere, and held for 4 h. The final fluffy porous carbon box conductive carbon material was obtained.

[0070] This example provides a lithium ion half-cell: the process of CR2016 type button cell is the same as that of Example 1.

[0071] Example 3

[0072] A method for preparing a fluffy porous carbon box conductive carbon material, comprising the following steps:

[0073] (1) 2 Kg of industrial NaCl powder, 200 g of pitch, and 10 Kg of zirconia balls were weighed into a ball mill jar, and high-energy ball milling was performed at a speed of 40 rpm for 2.5 h. After ball milling, the zirconia balls were separated by a vibrating screen, and a uniform brown powder was obtained.

[0074] (2) The powder obtained above was coated at high temperature in a high-temperature coating agent, the coating machine rotated at 45 rpm, the inert gas (argon) flowed at 40 mL / min, and the temperature program was as follows: the temperature was raised to 250°C at a rate of 200°C / h, and held for 2 h; then the temperature was raised to 700°C at a rate of 200°C / h, and held for 3 h. After coating, black powder and a small amount of block solid were obtained.

[0075] (3) The block solid in the coated material was removed by a vibrating screen, and NaCl was removed by water washing and filtration. The washed material was then dispersed in 2 L of pure water, and freeze-drying was performed using a freeze-drier at a temperature of -30°C for 12 h. A fluffy conductive carbon material precursor was obtained by freeze-drying. Graphitization of the obtained conductive carbon material precursor was performed in a tube furnace at 2°C / min to 1500°C under an argon atmosphere, and held for 3 h. The final fluffy porous carbon box conductive carbon material was obtained.

[0076] This example provides a lithium ion half-cell: the process of CR2016 type button cell is the same as that of Example 1.

[0077] Example 4

[0078] A method for preparing a loose porous carbon box conductive agent carbon material, comprising the following steps:

[0079] (1) Take 2Kg industrial NaCl powder salt, 100g polyvinyl chloride, 10Kg zirconium oxide balls into the ball mill tank, and use a high-energy ball mill at a speed of 45rpm for 4h. After ball milling, separate the zirconium balls with a vibrating screen machine to obtain a uniform powder.

[0080] (2) The obtained powder is coated at high temperature in a high-temperature coating agent, the coating machine speed is 40rpm, the inert gas (argon) flow rate is 40mL / min, and the temperature rising program is: rising to 180℃ at a rate of 200℃ / h, and keeping for 2h; then rising to 700℃ at a rate of 200℃ / h, and keeping for 2h. After coating, black powder and a small amount of block solid are obtained.

[0081] (3) The block solid in the coated material is removed by a vibrating screen machine, and NaCl is removed by water washing and filtration. Then the washed material is dispersed in 2L pure water, and freeze-drying is carried out by using a freeze-drying machine: the freeze-drying temperature is -50℃, and the time is 8h. The loose conductive agent carbon material precursor is obtained by freeze-drying. The obtained conductive agent carbon material precursor is graphitized in a tube furnace: the temperature is raised to 1200℃ at a rate of 5℃ / min under argon atmosphere, and kept for 4h. The final loose porous carbon box conductive agent carbon material is obtained.

[0082] This example provides a lithium ion half-cell: the process of CR2016 type button cell is the same as that of example 1.

[0083] Example 5

[0084] A method for preparing a loose porous carbon box conductive agent carbon material, comprising the following steps:

[0085] (1) Take 2Kg industrial NaCl powder salt, 150g polyvinylidene fluoride, 10Kg zirconium oxide balls into the ball mill tank, and use a high-energy ball mill at a speed of 30rpm for 4h. After ball milling, separate the zirconium balls with a vibrating screen machine to obtain a uniform powder.

[0086] (2) The obtained powder is coated at high temperature in a high-temperature coating agent, the coating machine speed is 40rpm, the inert gas (argon) flow rate is 40mL / min, and the temperature rising program is: rising to 220℃ at a rate of 200℃ / h, and keeping for 3h; then rising to 600℃ at a rate of 200℃ / h, and keeping for 3h. After coating, black powder and a small amount of block solid are obtained.

[0087] (3) The block solid in the coated material is removed by a vibrating screen, and NaCl is removed by water washing and filtration. The washed material is dispersed in 2 L of pure water, and freeze-drying is performed: the freeze-drying temperature is -50°C, and the freeze-drying time is 10 h, and a fluffy conductive carbon material precursor is obtained by freeze-drying. Graphitization of the obtained conductive carbon material precursor is performed in a tube furnace: the temperature is increased to 1300°C at a rate of 5°C / min under an argon atmosphere, and the temperature is maintained for 3 h, and a final fluffy porous carbon box conductive carbon material is obtained.

[0088] A lithium ion half-cell: the process of a CR2016 type button cell is the same as that of Example 1.

[0089] Example 6

[0090] The present example provides a method for preparing a fluffy porous carbon box conductive carbon material, comprising the following steps:

[0091] (1) 2 Kg of industrial NaCl powder, 100 g of polyvinylpyrrolidone, and 10 Kg of zirconium oxide balls are weighed and poured into a ball mill jar, and a high-energy ball mill is used to mill at a speed of 40 rpm for 4 h. After ball milling, the zirconium balls are separated out by a vibrating screen, and a uniform powder is obtained.

[0092] (2) The obtained powder is coated in a high-temperature coating agent at a coating machine speed of 45 rpm and an inert gas (argon) flow rate of 40 mL / min, and the temperature is increased to 180°C at a rate of 200°C / h, and the temperature is maintained for 1 h; then the temperature is increased to 700°C at a rate of 200°C / h, and the temperature is maintained for 2 h. After coating, a black powder and a small amount of block solid are obtained.

[0093] (3) The block solid in the coated material is removed by a vibrating screen, and NaCl is removed by water washing and filtration. The washed material is dispersed in 2 L of pure water, and freeze-drying is performed: the freeze-drying temperature is -50°C, and the freeze-drying time is 9 h, and a fluffy conductive carbon material precursor is obtained by freeze-drying. Graphitization of the obtained conductive carbon material precursor is performed in a tube furnace: the temperature is increased to 1300°C at a rate of 5°C / min under an argon atmosphere, and the temperature is maintained for 4 h, and a final fluffy porous carbon box conductive carbon material is obtained.

[0094] The present example provides a lithium ion half-cell: the process of a CR2016 type button cell is the same as that of Example 1.

[0095] Comparative Example 1

[0096] A lithium ion half-cell: the process of a CR2016 type button cell is the same as that of Example 1, and only the conductive agent material is changed, and the conductive agent used is conductive carbon black SP.

[0097] Comparative Example 2

[0098] A lithium ion half battery: CR2016 type button cell process and embodiment 1 is the same, only change the conductive agent material, the conductive agent used is multi-walled carbon tube.

[0099] Performance test

[0100] The conductive agent materials prepared by the above examples and comparative examples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area test (BET) and four-probe resistance tester (Four-probe Tester), etc. The morphology, component content and chemical bond type of the material are analyzed.

[0101] The conductive agent materials prepared by the above examples and comparative examples are tested by constant current charge and discharge and long cycle test, etc. The long cycle stability, anti-large current interference ability and lithium storage performance of the material surface obtained by the examples and comparative examples are tested.

[0102] The present application mainly uses conductive carbon material with good conductivity, simple preparation process and environmental friendliness. The loose porous carbon box conductive agent carbon material is prepared by combining template method, high temperature coating method and freeze drying, and is used as negative electrode conductive agent for lithium ion battery. After the battery prepared by the above examples is stored for 24h, the battery tester (Shenzhen Xinwei) and BTS8.0.0 software are used to test the long cycle performance of the battery. The preparation characteristics and electrochemical performance of the samples of embodiments 1-6 are shown in Table 1, and the electrochemical performance of the lithium ion half battery prepared by comparative example 1 is shown in Table 2.

[0103] Table 1 Characteristics of conductive agent prepared in examples 1-6 and electrochemical test results of lithium ion half battery at 25℃

[0104]

[0105] Table 2 Characteristics of conductive agent prepared in comparative example 1 and electrochemical test results of lithium ion half battery at 25℃

[0106]

[0107] According to the test results in Table 1 and Table 2, it can be seen that the prepared conductive carbon box conductive agent has lower resistivity than the prior art conductive carbon black SP and multi-walled carbon tube, indicating better conductivity. The specific surface area is much higher than that of SP, which can provide more active surface, thereby improving the catalytic effect and reaction rate of the battery, and also improving the carrying capacity of the electrode material, promoting electron transmission and ion diffusion, and reducing the electrochemical reaction resistance. The electrochemical performance measured by using the material prepared by the application as the negative electrode conductive agent of the lithium ion battery is obviously better than that of the traditional conductive agent of the conductive carbon black and the multi-walled carbon tube.

[0108] As can be clearly seen from the test results in Table 1 and Table 2, the cycle performance of the lithium ion half-cell prepared by using the carbon box in the examples is obviously better than that of the comparative examples. This is because the prepared conductive carbon box has a two-dimensional and ultra-thin structure, and the reticular carbon box structure indicates that the conductive agent and the active material are in contact through "face-point" contact. Compared with the "point-line" contact between the carbon tube and the active material and the "point-point" contact between the carbon black and the active material, a good conductive network can be built by the lapping of the reticular conductive agent at a smaller amount, greatly improving the conductivity of the entire electrode. Thus, the conductive threshold of the entire electrode can be reached at a smaller amount, so that the active material exhibits better electrochemical performance and the energy density of the battery is improved. The conductive carbon box can form a conductive network better, so the conductive effect is much better than that of the conductive carbon black and the multi-walled carbon tube.

[0109] As can be seen from Comparative Examples 1 to 3, based on the same pitch carbon source, the mass ratio of the powder salt and the carbon source is 2Kg:150g, which shows more excellent cycle stability and conductivity. This is because a too thick carbon layer will hinder the diffusion of lithium ions and reduce the ionic conductivity of the electrode sheet, and a too thin carbon layer will make the conductive material easy to break.

[0110] As can be seen from Comparative Examples 1 to 6, when the carbon source is pitch and the mass ratio of the carbon source and the industrial powder salt is 3:40, the specific surface area of the conductive agent is 238.09m 2 ·g -1 The resistivity is 0.035Ω·cm. When the performance of the silicon-carbon material is tested by using the application as the conductive agent, the capacity retention rate of the material is as high as 90.46% after 800 cycles at a rate of 1C, and the capacity retention rates of other examples of the application are also at the same order of magnitude.

[0111] As can be seen from the above examples and comparative examples, the application has the following characteristics:

[0112] The present application uses high-temperature process as the main process for preparation, quickly and effectively coats the carbon source on the surface of industrial salt powder, and graphitizes at a subsequent high temperature. Meanwhile, the industrial salt powder is combined as a sacrificial agent and a pore-forming agent to participate in the synthesis of the precursor. Meanwhile, the raw materials required by the process are widely sourced and low in cost; the raw materials and chemical reagents involved in the process are common medicines, and have the characteristics of environmental friendliness and low cost; in summary, the present application has the potential for commercial large-scale production.

[0113] The loose porous carbon box conductive agent carbon material of the present application presents a two-dimensional self-assembled net-like carbon box structure, with a large number of loose pore structures distributed inside. This structure can form a continuous conductive network in the electrode active material, enhancing the electron conduction ability.

[0114] The loose porous carbon box conductive agent carbon material of the present application has excellent conductivity and great application potential in the field of lithium ion batteries.

[0115] The loose porous carbon box conductive agent carbon material of the present application can be used to make a pole piece with a developed effective conductive network on the surface when a small amount of the conductive agent is added, so that the lithium ion battery produced has excellent cycle performance. The present application not only has low cost and can be produced on a large scale, but also has a suitable specific surface area, solving the problems of high cost, non-scalability and excessive specific surface area affecting the initial coulomb efficiency of the conductive agent used in Chinese invention patent application 201710792812.8.

[0116] Overall, the present application mainly uses different hot-melt polymer materials to coat the surface of industrial salt powder under high temperature conditions, then removes the salt powder by washing after carbonization, freezes and dries, and finally obtains the loose porous carbon box conductive agent carbon material after high-temperature graphitization. The sheet structure of the conductive agent can better form a conductive network, improve the overall conductivity of the battery, and improve the cycle stability of the material. In addition, the material has many small pore structures, which is beneficial to provide rich lithium ion diffusion migration paths and electron transmission paths, and accelerate the penetration process of the electrolyte.

[0117] The above examples are part of the embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all shall be included in the protection scope of the present application.

Claims

1. A porous carbon conductive agent carbon material, characterized in that: It is prepared by graphitizing a conductive carbon material precursor at a high temperature of 1200-1500℃ under a protective atmosphere; the conductive carbon material precursor is obtained by coating a solid powder at high temperature using a coating machine under a protective atmosphere, followed by water washing and freeze-drying; the solid powder is obtained by ball milling industrial powdered salt and a hot-melt polymer material, wherein the melting point of the industrial powdered salt is higher than that of the selected hot-melt polymer material; the high-temperature coating consists of hot melting and coke removal, wherein the hot melting temperature is 150-220℃ and the time is 1-3 hours; the coke removal temperature is 600-700℃ and the coke removal time is 2-4 hours; the freeze-drying refers to dispersing the washed material in water to form a suspension, freezing it below the freezing point, and then sublimating the water in the material directly from solid ice to water vapor by vacuuming.

2. The method for preparing the porous carbon conductive material according to claim 1, characterized in that... Includes the following steps: 1) A uniform solid powder was prepared by ball milling industrial powdered salt and hot-melt polymer materials; 2) Under a protective atmosphere, the solid powder is coated at high temperature using a coating machine, then washed with water and freeze-dried to obtain a conductive carbon material precursor. The high-temperature coating consists of hot melting and coke removal. The hot melting temperature is 150–220°C and the time is 1–3 hours. The coke removal temperature is 600–700°C and the coke removal time is 2–4 hours. The freeze-drying refers to dispersing the washed material in water to form a suspension, freezing it below the freezing point, and then sublimating the water in the material directly from solid ice to water vapor by vacuuming. 3) Under a protective atmosphere, the conductive carbon material precursor is graphitized at a high temperature of 1200-1500℃ to obtain a loose and porous carbon box conductive carbon material.

3. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The ball milling time is 2.5 to 4 hours, and the rotation speed is 25 to 45 rpm.

4. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The industrial powdered salt is one or more of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate; the hot-melt polymer material is one or more of asphalt, polyvinyl chloride, polyvinylidene fluoride, and polyvinylpyrrolidone.

5. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The mass ratio of the hot-melt polymer material to the industrial powdered salt is 0.05 to 0.1:1; the balls used for ball milling are zirconium balls, and the mass ratio of the zirconium balls to the material being ball-milled is 0.21 to 0.22:

1.

6. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The coating machine operates at a speed of 30–45 rpm, and the protective atmosphere flow rate is 40–50 mL / min.

7. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The freeze-drying temperature is -60 to -40°C, and the freeze-drying time is 8 to 12 hours.

8. The method for preparing the porous carbon conductive agent carbon material according to claim 2, characterized in that, The water washing refers to soaking the material in pure water, filtering it, and rinsing it repeatedly until no industrial salt powder is present.

9. The method for preparing the porous carbon conductive material according to claim 2, characterized in that, The high-temperature graphitization time is 3-4 hours, and the heating rate is 2-5℃ / min; in steps 2) and 3), the protective atmosphere is nitrogen or argon.

10. The application of the porous carbon conductive carbon material according to claim 1 in the preparation of lithium-ion battery anodes.

11. The application of the porous carbon conductive carbon material according to claim 10 in the preparation of lithium-ion battery anodes, characterized in that, A lithium-ion battery negative electrode slurry is prepared by mixing lithium-ion negative electrode material, binder, and porous carbon conductive agent carbon material. The slurry is then uniformly coated on copper foil and pressed into a sheet to obtain the lithium-ion battery negative electrode sheet. The lithium-ion negative electrode material is silicon-carbon material, and the binder is TRD-104A and CMC. The mass ratio of the negative electrode material, binder, and porous carbon conductive agent carbon material is (95-96):(2-4):(1-2).

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