CN115377393A - Negative electrode material, preparation method thereof and lithium ion battery - Google Patents

Abstract

The present application provides a negative electrode material, a preparation method thereof, and a lithium-ion battery, wherein the negative electrode material includes a graphite flake core and amorphous carbon, and the graphite flake core includes multi-layer graphite flakes that are interlaced and curled, and at least part of the graphite flakes pass through Mortise and tenon structure connection; at least part of the amorphous carbon is located on the surface of the graphite flake core to form a carbon coating, and at least part of the amorphous carbon is embedded in the graphite flake core. The negative electrode material and the preparation method thereof of the present application can reduce the volume expansion of the negative electrode material and improve the rate performance and cycle stability of the negative electrode material.

Description

Negative electrode material and preparation method thereof, lithium ion battery

technical field

The present application relates to the technical field of negative electrode materials, in particular, to a negative electrode material, a preparation method thereof, and a lithium ion battery.

Background technique

Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution.

At present, graphite negative electrodes have been recognized as ideal negative electrodes for lithium-ion batteries. Graphite negative electrodes are mainly divided into artificial graphite and natural graphite. The main advantages of artificial graphite are good cycle performance, good compatibility with electrolyte, and relatively balanced indicators in all aspects. Its main disadvantages are relatively low capacity and high cost. The main advantages of natural graphite are high capacity, high compaction density and low price, but its disadvantages are also significant, such as uneven particle size, more surface defects, poor compatibility with electrolyte, and more side reactions. . In order to solve some problems existing in natural graphite anode, the key to improving its performance is to modify natural graphite. The current modification treatment methods are difficult to prepare graphite anode materials with excellent properties such as high first efficiency, high capacity, high compaction density, and high energy density.

Based on this, there is an urgent need to develop a negative electrode material that can reduce the cyclic expansion rate of the material while simultaneously having high first efficiency, high capacity, and high compaction density.

Contents of the invention

In view of this, the present application proposes a negative electrode material, a preparation method thereof, and a lithium ion battery, which can reduce the volume expansion of the negative electrode material and improve the rate performance and cycle stability of the negative electrode material.

In the first aspect, the present application provides a negative electrode material, the negative electrode material includes a graphite flake core and amorphous carbon, the graphite flake core includes multi-layer graphite flakes that are interlaced and curled, and at least part of the graphite flakes are formed by mortise and tenon joints. structural connection;

At least part of the amorphous carbon is located on the surface of the graphite flake core to form a carbon coating, and at least part of the amorphous carbon is embedded in the graphite flake core.

In some embodiments, the carbon coating layer has a thickness of 10 nm to 120 nm.

In some embodiments, the negative electrode material has pores.

In some embodiments, the cross section porosity of the negative electrode material is 0.5%-8.5%.

In some embodiments, the negative electrode material has pores, and the average pore diameter of the pores is 0.1 nm˜10 nm.

In some embodiments, the amorphous carbon comprises resinous carbon.

In some embodiments, the median particle size of the negative electrode material is A μm, 10≤A≤25.

In some embodiments, the degree of graphitization of the negative electrode material is B%, and 90≤B≤96.

In some embodiments, the median particle size of the negative electrode material is A μm, the degree of graphitization of the negative electrode material is B%, and 0.5≤A*(1-B)≤2.5;

In some embodiments, the OI value of the negative electrode material is C, 0.5≤C≤5.0;

In some embodiments, the mass content D% of amorphous carbon in the negative electrode material, 0≤D≤1;

In some embodiments, the OI value of the negative electrode material is C, the mass content of amorphous carbon in the negative electrode material is D%, and 1≤[(C-0.5)/2]*D ^-1/2 ≤ 2.

In some embodiments, the powder compacted density of the negative electrode material is 1.75g/cm ³ to 1.90g/cm ³ ;

In some embodiments, the powder tap density of the negative electrode material is 1.3g/cm ³ to 1.5g/cm ³ ;

In some embodiments, the specific surface area of the negative electrode material is 0.3m ² /g˜1.2m ² /g;

In some embodiments, the sphericity of the negative electrode material is 0.7-1.0;

In some embodiments, in the Raman spectrum, the negative electrode material has a carbon characteristic peak D and a carbon characteristic peak G, the peak intensity ID of the carbon characteristic peak D _and the peak intensity I G of the carbon characteristic peak _G The ratio I _D /I _G , 1.5≤I _D /I _G ≤4.5.

In a second aspect, the present application provides a method for preparing an anode material, comprising the following steps:

When the natural flake graphite is spheroidized, the coating slurry containing the water-soluble resin is sprayed onto the surface of the spheroidized graphite for coating to obtain a spheroidized composite;

The spheroidized composite is subjected to carbonization treatment to obtain the negative electrode material.

In some embodiments, the coating slurry further includes water, and the mass ratio of the water-soluble resin to the water is 1:(10-35).

In some embodiments, the water-soluble resin includes at least one of phenolic resin, urea-formaldehyde resin, epoxy resin, polyurethane resin, polyester resin and polyacrylic resin.

In some embodiments, the coating slurry has a viscosity of 50 cp-100 cp.

In some embodiments, the stirring speed of the coating slurry is 500r/min˜1000r/min.

In some embodiments, the stirring time of the coating slurry is 0.5h-2h.

In some embodiments, the mass ratio of the natural flake graphite to the water-soluble resin is (10-30):1.

In some embodiments, when the natural flake graphite is subjected to spheroidization treatment, the step of spraying the coating slurry containing water-soluble resin onto the surface of the spheroidized graphite for coating is carried out in a spherical graphite with a spraying device. in chemical equipment.

In some embodiments, the power of the main engine of the spheroidization equipment is 25kW-45kW.

In some embodiments, the rotating speed of the spheroidizing equipment is 200r/min-500r/min.

In some embodiments, the spray flow rate of the coating slurry is 5 mL/min-30 mL/min.

In some embodiments, the spheroidization treatment time is 2h-10h.

In some embodiments, before carbonizing the spheroidized composite, the method further includes: drying the spheroidized composite.

In some embodiments, before carbonizing the spheroidized composite, the method further includes: drying the spheroidized composite, and the temperature of the drying treatment is 60° C. to 120° C.

In some embodiments, before carbonizing the spheroidized composite, the method further includes: drying the spheroidized composite for 12 hours to 24 hours.

In some embodiments, the temperature of the carbonization treatment is 700°C to 1250°C.

In some embodiments, the time of the carbonization treatment is 4h-8h.

In some embodiments, the method comprises the steps of:

When the spheroidization equipment with a spray device is used to spheroidize the natural flake graphite for 4h to 8h, the coating slurry containing water-soluble resin and water is sprayed onto the surface of the spheroidized graphite for coating to obtain Spheroidized compound; wherein, the mass ratio of the water-soluble resin to the water is 1: (15-25), the viscosity of the coating slurry is 60cp-80cp, the natural flake graphite and the water-soluble The mass ratio of the resin is (15-20):1, the power of the host of the spheroidizing equipment is 30kW-40kW, and the spray flow rate of the coating slurry is 10mL/min-20mL/min;

Put the spherical compound at 80℃～100℃ for drying treatment for 16h～20h;

The dried spheroidized compound is placed at 800° C. to 1000° C. for carbonization treatment for 4 hours to 6 hours to obtain the negative electrode material.

In a third aspect, the present application provides a lithium ion battery, comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method for preparing the negative electrode material described in the second aspect.

The technical solution of the present application has at least the following beneficial effects:

First, the negative electrode material provided by the present application includes a graphite flake inner core and amorphous carbon, and the graphite flake inner core includes multi-layer graphite flakes that are staggered and curled; the graphite flakes in the graphite flake inner core are connected by a mortise and tenon structure, which This structure has strong structural stability and mechanical strength, which can inhibit and buffer the expansion of graphite during cycling, increase the transmission path of lithium ions inside graphite, and improve the transmission rate of lithium ions and electrons. The mass transfer rate inside the material can be well matched with the charge transfer rate during discharge, which effectively reduces the polarization problem of the material during high rate charge and discharge, reduces the impedance of the material, and makes graphite Lithium precipitation does not occur; it can also allow the electrolyte to enter the interior of the graphite core, which increases the compatibility and wettability of the flake graphite and the electrolyte, and improves the gram capacity and energy density of the material; the amorphous carbon embedded in the flake graphite core , the pores and defects inside the flake graphite are significantly reduced, which increases the density of the internal structure of the material and the structural strength of the material, which is conducive to improving the compaction density and energy density of the material, and is also conducive to improving the processing performance of the material; in addition , the amorphous carbon embedded in the flake graphite core makes the particle interior of the material also isotropic, which can improve the rate performance of the material.

The carbon coating coated on the outside of the flake graphite core works together with the self-mosaic structure of the flake graphite core to further inhibit the expansion of graphite during the cycle, which is conducive to improving the compatibility between the material and the electrolyte, and contributing to the solid-state electrolyte. The formation of the film reduces the side reaction between the electrolyte and the surface of the material; when performing high-current charge and discharge, the carbon coating layer coated on the surface can play a role of protection and buffer, reducing the material's in the process of high-current charge-discharge and long cycle. The expansion and peeling problems that occur can improve the rate performance and cycle stability of the material.

Secondly, in the preparation method of the negative electrode material provided by the present application, coating and spheroidization are carried out simultaneously. Flake graphite is curled under the centrifugal force generated by the spheroidization treatment, and the layers are tightly wrapped to form spherical graphite, which increases the isotropy of graphite; the graphite is coated with a coating slurry containing water-soluble resin, and the spherical graphite During the treatment, the resin is coated on the surface of the spheroidized graphite particles, and at least part of the resin enters the interior of the spheroidized graphite particles, so that the transmission paths and channels of lithium ions are wrapped between the curly flake graphite layers and in the interlayer gap. Resin, the resin is carbonized to form amorphous carbon, so that the defects and gaps between the flake graphite sheets and the sheets are effectively filled, which increases the density of the spherical graphite structure, reduces the defects of graphite, and increases the spherical graphite. Effective electrochemical reaction active sites on the surface and inside; it is beneficial to improve the compaction density and energy density of the material, and it is also beneficial to improve the processing performance of the material; and the overall process is simple, which effectively reduces the production cost.

Description of drawings

Fig. 1 is the structural representation of the graphite inner core of the negative electrode material that the present embodiment provides;

Fig. 2 is the schematic flow chart of the preparation method of the negative electrode material that this embodiment provides;

Fig. 3 is the SEM picture of the negative electrode material that embodiment 1 makes;

Fig. 4 is the SEM enlarged view of the negative electrode material that embodiment 1 makes;

Fig. 5 is the SEM sectional view of the negative electrode material that embodiment 1 makes;

Fig. 6 is the SEM sectional view of the negative electrode material that embodiment 17 makes;

Fig. 7 is the SEM sectional view of the negative electrode material that embodiment 18 makes;

Fig. 8 is the comparison diagram of the powder conductivity curves of negative electrode materials prepared in Example 1, Example 17 and 18;

FIG. 9 is a comparison chart of impedance performance of button batteries made of negative electrode materials prepared in Example 1, Example 17 and Example 18. FIG.

Detailed ways

The following descriptions are preferred implementations of the embodiments of the present invention. It should be pointed out that those skilled in the art can make some improvements and modifications without departing from the principles of the embodiments of the present invention. These improvements And retouching are also regarded as the scope of protection of the embodiments of the present invention.

Specifically, the present application provides a negative electrode material. As shown in FIG. 1, the negative electrode material includes a graphite flake core and amorphous carbon. Graphite is connected by mortise and tenon structure;

At least part of the amorphous carbon is located on the surface of the graphite flake core to form a carbon coating, and at least part of the amorphous carbon is embedded in the graphite flake core.

The negative electrode material provided by the present application includes a graphite flake core and amorphous carbon, and the graphite flake core includes multilayer graphite flakes that are interlaced and curled; the graphite flakes in the graphite flake core are connected by a mortise and tenon structure. It has strong structural stability and mechanical strength, can inhibit and buffer the expansion of graphite during cycling, increases the transmission path of lithium ions inside graphite, and improves the transmission rate of lithium ions and electrons. When charging and discharging at a high rate The mass transfer rate inside the material can be well matched with the charge transfer rate, which effectively reduces the polarization problem of the material when charging and discharging at a high rate, reduces the impedance of the material, and prevents graphite from occurring during the rate charge and discharge process. Lithium analysis; it can also allow the electrolyte to enter the interior of the graphite core, which increases the compatibility and wettability of the flake graphite and the electrolyte, and improves the gram capacity and energy density of the material; the amorphous carbon embedded in the flake graphite core, the scale The pores and defects inside the graphite are significantly reduced, which increases the density of the internal structure of the material and the structural strength of the material, which is conducive to improving the compaction density and energy density of the material, and is also conducive to improving the processing performance of the material; in addition, the mosaic The amorphous carbon in the flake graphite core makes the particle interior of the material also isotropic, which can improve the rate performance of the material.

The carbon coating coated on the outside of the flake graphite core works together with the self-mosaic structure of the flake graphite core to further inhibit the expansion of graphite during the cycle, which is conducive to improving the compatibility between the material and the electrolyte, and contributing to the solid-state electrolyte. The formation of the film reduces the side reaction between the electrolyte and the surface of the material; when performing high-current charge and discharge, the carbon coating layer coated on the surface can play a role of protection and buffer, reducing the material's in the process of high-current charge-discharge and long cycle. The expansion and peeling problems that occur can improve the rate performance and cycle stability of the material.

In some embodiments, at least part of the graphite flakes are connected by a mortise and tenon structure. The mortise and tenon structure means that the graphite flakes are inlaid with each other (intricately intertwined), and each layer is interlaced and closely connected. It can also be understood that at least part of the graphite flakes are embedded in the adjacent graphite flakes. , There is also a small amount of amorphous carbon as a support between the sheets, which increases the structural strength of this spherical graphite. This structure has good structural stability and mechanical strength, which is conducive to evenly dispersing the stress in different directions on the flake graphite core, which can reduce the expansion rate of the material during the cycle, and has a good buffering effect. When the flake graphite core is subjected to external force and/or internal stress of the structure, the mortise and tenon structure is not easy to be damaged but will make the core more compact, maintaining the consistency and stability of the overall structure, during the charging and discharging process and the battery cycle process It is not easy to lose powder and fall off in the middle.

In some embodiments, the negative electrode material has pores. The existence of pores provides a good transmission channel for the diffusion of lithium ions and the infiltration of electrolyte, increases the transmission rate of ions and electrons, and can also store a certain amount of lithium ions, which is conducive to improving the capacity of negative electrode materials.

In some embodiments, the average pore diameter of the pores is 0.1nm to 10nm, specifically 0.1nm, 0.5nm, 0.8nm, 1.0nm, 1.5nm, 2.5nm, 3.5nm, 5nm, 6.5nm, 7nm, 8nm , 9nm or 10nm, etc., are not limited here. It can be understood that the pores are mainly the pores between the sheets formed by the staggered lamination of graphite flakes, or the pores formed by the curling of graphite flakes. Preferably, the average pore size of the pores is 1.25nm-2.65nm, and the pore size distribution of the pores is narrow, which can increase the compacted density of the material, and can also improve the rate performance and capacity of the material.

In some embodiments, at least a portion of the amorphous carbon fills the aforementioned pores.

In some embodiments, the aforementioned amorphous carbon includes resinous carbon, ie, amorphous hard carbon. The particles of the negative electrode material are evenly inlaid with amorphous hard carbon materials from the inside to the outside. The existence of hard carbon provides more channels for the transmission of lithium ions and electrons, which greatly increases the rate performance of the material. At the same time, the hard carbon The presence of the material reduces the expansion rate of the material during the charge and discharge process, so that the material has a certain buffer during the cycle.

In some embodiments, the sectional porosity of the negative electrode material is 0.5% to 8.5%, specifically 0.5%, 0.7%, 0.9%, 1.5%, 2.0%, 3.5%, 5.0%, 6.5%, 7.5%. , 8.0% or 8.5%, etc., are not limited here. If the cut surface porosity is too high, the isotropy of the negative electrode material is poor, which affects the first effect and cycle stability of the negative electrode material, and affects the rate performance of the material. Preferably, the cross section porosity of the negative electrode material is 2.5%-5.5%.

In some embodiments, the median particle size of the negative electrode material is A μm, 10≤A≤25; optionally, the median particle size of the negative electrode material can specifically be 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 17 μm, 18 μm , 19 μm, 20 μm, 22 μm or 25 μm, etc., are not limited here. The median particle size of the negative electrode material is preferably 15 μm to 17 μm. Within this particle size range, the uniformity of the surface coating of the negative electrode material can be improved, and the interior of the material is denser, which is conducive to obtaining products with small specific surface area and high tap density. , can reduce the loss of lithium ions, reduce the irreversible capacity loss in the charge and discharge process, and improve the electrochemical performance of the negative electrode material.

In some embodiments, the degree of graphitization of the negative electrode material is B%, 90≤B≤96; optionally, the degree of graphitization of the negative electrode material can be specifically 90%, 91%, 92%, 93%, 94% %, 95% or 96%, etc., are not limited here.

In some embodiments, the median diameter of the negative electrode material is A μm, the degree of graphitization of the negative electrode material is B%, and 0.5≤A*(1-B)≤2.5; A*(1-B ) can specifically be 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.3 or 2.5, etc., which are not limited here. It is understandable that after the flake graphite is coated, the degree of graphitization of the negative electrode material will be significantly reduced due to the introduction of amorphous carbon. In this application, by controlling the amount of the coating layer formed by amorphous carbon, that is, by controlling the relationship between the median particle size and the degree of graphitization of the material, the material can maintain a corresponding particle size and degree of graphitization, and avoid excessively thick carbon The particle size caused by the cladding layer is too large, which causes the degree of graphitization of the material to decrease, thereby improving the rate performance and energy density of the material.

In some embodiments, the OI value of the negative electrode material is C, 0.5≤C≤5.0; optionally, the OI value of the negative electrode material can be 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5 or 5.0, etc., are not limited here. In this application, the OI value of the negative electrode material is the ratio of the peak area C004 of the (004) plane to the peak area C110 of the (110) plane of the negative electrode material particles measured by X-ray diffraction. When the OI value is within the above range, the crystal orientation of the negative electrode material particles is better, which is conducive to the deintercalation of lithium ions and the improvement of the kinetic properties of the material.

In some embodiments, the mass content of amorphous carbon in the negative electrode material D%, 0≤D≤1; the mass content of amorphous carbon can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5% , 0.6%, 0.7%, 0.8%, 0.9% or 1.0%, etc., are not limited here.

In some embodiments, the OI value of the negative electrode material is C, the mass content of amorphous carbon in the negative electrode material is D%, and 1≤[(C-0.5)/2]*D ^-1/2 ≤ 2. The value of [(C-0.5)/2]*D ^-1/2 may be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8 or 2, etc., which is not limited here. It can be understood that the amorphous carbon embedded or filled in the graphite flake core and the carbon coating coated on the outside of the graphite flake core make the inside and outside of the particle of the material isotropic, which is conducive to the deintercalation of lithium ions , which can improve the rate performance of the material. That is, by controlling the relationship between the OI value of the material and the mass content C of amorphous carbon, the rate performance and high capacity of the material can be improved.

In some embodiments, the thickness of the carbon coating layer is 10nm to 120nm, specifically 10nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 60nm, 80nm, 90nm, 100nm, 110nm or 120nm, etc. , is not limited here. Preferably, a carbon coating with a suitable thickness can suppress the expansion rate of the negative electrode material, improve the defects on the surface of the flake graphite core, and will not bring new defects, reduce the polarization reaction on the surface of the negative electrode material, and help improve the negative electrode material. The compatibility with the electrolyte increases the charge-discharge performance and cycle stability of the negative electrode material. When charging and discharging with a large current, the carbon coating on the surface can play a certain role in protection and buffering, reducing the negative electrode material in large The problem of swelling and peeling off during current charge and discharge and long cycle can still maintain high specific capacity under high current discharge, and the capacity retention rate after 2000 cycles at 3C rate is 91%, showing excellent rate performance and cycle stability. Preferably, the thickness of the carbon coating layer is 20nm-60nm.

In some embodiments, the negative electrode material particles are spherical or spherical. The spherical particle shape makes the negative electrode material have better tap density, high isotropy, low specific surface area, and low surface defects, which makes the negative electrode material have higher compaction density and better charge and discharge performance. The reversible capacity and first efficiency of negative electrode materials are higher.

In some embodiments, the sphericity of the negative electrode material is 0.7 to 1.0, specifically 0.7, 0.8, 0.85, 0.89, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 1.0, etc. limited. In this application, sphericity refers to the ratio of the shortest diameter to the longest diameter of a particle.

It can be understood that the higher the sphericity, the better the isotropy of the negative electrode material, and the higher the bulk density of the particles, which makes the internal structure of the material denser, the porosity is relatively lower, and the structural strength is better.

In some embodiments, the powder compacted density of the negative electrode material is 1.75g/cm ³ -1.90g/cm ³ , specifically 1.75g/cm ³ , 1.76g/cm ³ , 1.78g/cm ³ , 1.79g /cm ³ , 1.80g/cm ³ , 1.82g/cm ³ , 1.85g/cm ³ , 1.87g/cm ³ or 1.90g/cm ³ etc. The compaction density of the negative electrode material is positively correlated with the compaction density of the negative electrode sheet, which is conducive to improving the energy density of the battery.

In some embodiments, the powder tap density of the negative electrode material is 1.3g/cm ³ -1.5g/cm ³ , specifically 1.3g/cm ³ , 1.32g/cm ³ , 1.35g/cm ³ , 1.36g /cm ³ , 1.38g/cm ³ , 1.42g/cm ³ , 1.45g/cm ³ , 1.47g/cm ³ or 1.50g/cm ³ etc. Controlling the tap density within the above range is beneficial to improve the processability of the material and improve the energy density of the battery.

In some embodiments, the specific surface area ratio of the negative electrode material is 0.3m ² /g˜1.2m ² /g. Specifically, it can be 0.3m ² /g, 0.5m ² /g, 0.6m ² /g, 0.7m ² /g, 0.8m 2 /g, ^{0.9m 2} /g, 1.0m ² /g or 1.2m ² /g etc., without limitation here; it is understandable that an excessively large specific surface area will easily lead to the formation of an SEI film, consume too much irreversible lithium salt, and reduce the initial efficiency of the battery. Considering the cost of the preparation process, the specific surface area will be controlled at 0.3 m ² /g～1.2m ² /g.

In some embodiments, in the Raman spectrum, the negative electrode material has a carbon characteristic peak D and a carbon characteristic peak G, the peak intensity ID of the carbon characteristic peak D _and the peak intensity I G of the carbon characteristic peak _G The ratio is I _D /I _G , 1.5≤I _D /I _G ≤4.5, and I _D /I _G can be 1.5, 1.7, 1.8, 1.9, 2.0, 2.3, 2.5, 2.8, 3.0, 3.5, 3.8, 4.0 , 4.2 or 4.5, etc.

In the Raman spectrum of the negative electrode material, if I _D / I _G is within the above range, it can ensure that there are fewer defects on the negative electrode material, and the material has a high degree of graphitization, which can improve its own strength and conductivity, and charge and discharge the negative electrode material During the process, there will be no phenomenon of falling powder and shedding.

The present application also provides a method for preparing an anode material, as shown in FIG. 2 , the method includes the following steps S100-S200:

S100, when the natural flake graphite is subjected to spheroidization treatment, the coating slurry containing water-soluble resin is sprayed onto the surface of the spheroidized graphite for coating to obtain a spheroidized composite;

S200, performing carbonization treatment on the spheroidized composite to obtain a negative electrode material.

In the preparation method of the negative electrode material provided by the present application, coating and spheroidization are carried out simultaneously. The flake graphite curls under the centrifugal force generated by the spheroidization treatment, and the layers are tightly wrapped to form spherical graphite, which increases the isotropy of the graphite; the graphite is coated with a coating slurry containing a water-soluble resin, and the coating effect more uniform. During the spheroidization process, the resin is coated on the surface of the spheroidized graphite particles, and at least part of the resin enters the interior of the spheroidized graphite particles, so that the transmission path and channel of lithium ions are between the curled flake graphite layers and the interlayer gap. The resin is wrapped inside, and the resin is carbonized to form amorphous carbon, so that the defects and gaps between the flake graphite sheets and the sheets are effectively filled, which increases the density of the spherical graphite structure, reduces graphite defects, and increases The effective electrochemical reaction active sites on the surface and inside of spherical graphite; it is conducive to improving the compaction density and energy density of the material, and is also conducive to improving the processing performance of the material.

This method has the advantages of simple process, simple equipment, easy regulation, and low production energy consumption. It effectively combines the two processes of coating and spheroidization, so that the coating effect and spheroidization effect have been greatly improved. , the prepared resin carbon-coated graphite material has the characteristics of high vibration, high compaction, high first effect and low specific surface area. At the same time, the sphericity and surface coating uniformity of the obtained negative electrode material are very excellent, which effectively reduces the production cost. .

The following describes the program in detail:

Before step S100, the method also includes:

A coating slurry is prepared comprising a water soluble resin and water.

It can be understood that the use of water as a solvent and the water-soluble resin as a coating agent reduces the production cost on the one hand, and on the other hand increases the convenience and safety of actual production by using water as a solvent.

In some embodiments, the water-soluble resin includes at least one of phenolic resin, urea-formaldehyde resin, epoxy resin, polyurethane resin, polyester resin and polyacrylic resin.

In some embodiments, the coating slurry has a viscosity of 50cp to 100cp, specifically 50cp, 55cp, 60cp, 65cp, 70cp, 75cp, 80cp, 85cp, 90cp, 95cp or 100cp, etc., which is not limited here . Preferably, the coating slurry has a viscosity of 60cp-80cp.

In some embodiments, the mass ratio of the water-soluble resin to the water is 1:(10-35); specifically, it can be 1:10, 1:12, 1:15, 1:18, 1:20, 1:25, 1:28, 1:30, 1:32 or 1:35, etc., are not limited here. When the water-soluble resin is added in a large amount, the viscosity of the coating slurry is too high, and agglomeration and agglomeration between the coating slurry are prone to occur during the process of coating and spheroidization, and there will be more large particles in the negative electrode material. Particles will affect the yield of sieving during sieving, and will also affect the morphology of the final negative electrode material, so that the thicker the carbon coating layer coated on the surface of the flake graphite core, the higher the disorder of the material surface, The specific surface area increases and the tap density decreases. When the amount of water-soluble resin added is less, the content of amorphous carbon inside and on the surface of the flake graphite core decreases, and the surface of the flake graphite core has more defects, and the porosity of the negative electrode material will also increase, resulting in the loss of the final negative electrode material. The specific surface area increases and the tap density decreases. Preferably, the mass ratio of the water-soluble resin to the water is 1:(15-25).

In some embodiments, the prepared coating slurry is pre-loaded into the spray device of the spheroidization equipment, and the stirring function is turned on to prevent the coating slurry from settling.

In some embodiments, the stirring speed of the coating slurry is 500r/min～1000r/min; specifically, it can be 500r/min, 550r/min, 600r/min, 650r/min, 700r/min, 750r/min , 800r/min, 900r/min or 1000r/min etc. are not limited here.

In some embodiments, the stirring time of the coating slurry is 0.5h to 2h, specifically 0.5h, 1h, 1.2h, 1.4h, 1.5h, 1.8h or 2h, etc., but not limited to the above-mentioned .

S100, when the natural flake graphite is subjected to spheroidization treatment, spray coating slurry containing a water-soluble resin onto the surface of the spheroidized graphite for coating to obtain a spheroidized composite.

In some embodiments, the mass ratio of natural flake graphite to water-soluble resin is (10-30):1, specifically 10:1, 15:1, 18:1, 20:1, 22:1, 25:1 1, 28:1 or 30:1, etc., but not limited to the above list. Preferably, the mass ratio of natural flake graphite to water-soluble resin is (15-20):1.

Understandably, by controlling the concentration of the water-soluble resin in the coating slurry and the mass ratio of the water-soluble resin to the flake graphite, the morphology, specific surface area and tap density of the coated negative electrode material can be adjusted.

In some embodiments, step S100 is performed in a spheroidizing device equipped with a shower device.

In this application, the working principle of the spheroidizing equipment is mainly that the graphite flakes are curled by themselves under the action of centrifugal force under the action of high-speed stirring, and the viscosity of the coating slurry is added, and they are interleaved and connected together. The spheroidization equipment in this application is quite different from the traditional spheroidization equipment. The traditional spheroidization equipment mainly grinds some edges and corners of the material through mechanical action, which will reduce the yield of the material during the grinding process. The yield of the spheroidizing equipment adopted in this application can be close to 100%, which can effectively improve the yield of the product.

In some embodiments, the main power of the spheroidizing equipment is 25kW-45kW; specifically, it can be 25kW, 28kW, 30kW, 32kW, 35kW, 38kW, 40kW or 45kW, etc., which is not limited here. If the power of the main engine is too high, the spheroidized graphite flakes will be broken up; if the power of the main engine is too small, the phenomenon of agglomeration and wall sticking of the coating slurry and graphite flakes will occur. Preferably, the main engine power of the spheroidizing equipment is 30kW-40kW.

In some embodiments, the rotational speed of the spheroidizing equipment is 200r/min-500r/min; specifically, it can be 200r/min, 250r/min, 300r/min, 350r/min, 400r/min or 500r/min, etc. , is not limited here.

In some embodiments, the spray flow rate of the coating slurry is 5mL/min-30mL/min; specifically, it can be 5mL/min, 10mL/min, 15mL/min, 20mL/min, 25mL/min or 30mL/min min, etc., are not limited here. Preferably, the spray flow rate of the coating slurry is 10mL/min-20mL/min;

In some embodiments, the spheroidization treatment time is 2h to 10h, specifically 2h, 3h, 4h, 5h, 6h, 7h, 8h or 10h, etc., but is not limited to the above list. Preferably, the spheroidization treatment time is 4h-8h.

Before step S200, the method further includes: drying the spheroidized composite.

In some embodiments, the temperature of the drying treatment is 60°C to 120°C; specifically, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 100°C, 110°C or 120°C etc., but not limited to the above enumeration. Preferably, the temperature of the drying treatment is 80°C to 100°C.

In some embodiments, the drying time is 12h to 24h, specifically 12h, 14h, 15h, 16h, 17h, 18h, 19h, 20h or 24h, etc., but is not limited to the above list. Preferably, the drying time is 16h-20h.

S200, performing carbonization treatment on the spheroidized composite to obtain a negative electrode material.

In some embodiments, the temperature of the carbonization treatment is 700°C to 1250°C; specifically, it can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1200°C °C or 1250 °C, etc., but not limited to the above list. Preferably, the temperature of the drying treatment is 800°C to 1000°C.

In some embodiments, the time for the carbonization treatment is 4h-8h, specifically 4h, 5h, 6h, 7h or 8h, etc., but not limited to the above list. Preferably, the drying time is 4h-6h.

The method also includes: sieving and demagnetizing the carbonized material to obtain the negative electrode material.

In some embodiments, the screening method is any one of fixed screen, drum screen, resonance screen, roller screen, vibrating screen and chain screen, and the mesh number of screening is 100-500 mesh. The mesh size can be 100 mesh, 200 mesh, 250 mesh, 325 mesh, 400 mesh, 500 mesh, etc. Preferably, the mesh size of the sieve is 250 mesh, and the particle size of the negative electrode material is controlled within the above range, which is beneficial to the negative electrode Improvement of material processing performance.

In some embodiments, the demagnetization equipment is any one of permanent magnet drum magnetic separator, electromagnetic iron remover and pulsating high-gradient magnetic separator. The discharge effect of substances on lithium-ion batteries and the safety of batteries during use.

The embodiment of the present invention also provides a lithium ion battery, using the negative electrode material provided in the above embodiments of the present invention or the negative electrode material prepared by using the preparation method of the negative electrode material provided in the above embodiments of the present invention. The lithium ion battery provided by the embodiment of the present invention has the advantages of high capacity, high first effect, long cycle life, excellent rate performance and low expansion.

testing method:

1) Particle size of negative electrode material:

The particle size test method refers to GB/T 19077-2016. It can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Co., Ltd., UK.

2) The test method for the specific surface area of the negative electrode material:

At constant temperature and low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, the adsorption amount of the monomolecular layer of the sample is obtained based on the Brownauer-Etter-Taylor adsorption theory and its formula (BET formula), so as to calculate The specific surface area of the material.

3) Test method of compaction density:

The pressure method is to apply a certain pressure to the powder and keep the pressure for a period of time, then test the thickness L of the powder, and test the compaction density.

4) Test method of tap density:

Use Baxter to vibrate, weigh a certain amount of sample, and test the tap density at 300times/min and vibrate 3000 times.

5) SEM test:

SEM characterization was carried out on a transmission electron microscope with an operating voltage of 200kV to observe the structure of the negative electrode material.

6) Test method for carbon coating thickness:

The material is processed by FIB-SEM equipment, and the average thickness of the carbon coating is measured in SEM.

7) Morphological test method of material particles:

The morphology of the material particles was measured by scanning electron microscopy.

8) Test methods for cross-section porosity and average pore diameter of negative electrode material particles:

A three-electrode ion gun is used to generate plasma by applying a discharge voltage of 0-4KV, and at the same time apply an acceleration voltage of 0-6KV to accelerate the plasma, and then form a plasma beam with certain energy and direction. In the ion milling method, the sample is bombarded with a plasma beam, and the surface atoms are sputtered away from the sample surface, thereby achieving the purpose of grinding (also called stress-free thinning). The E3500 uses argon as the plasma source. The energy of the argon ion beam is low, it will not be transmitted to the inside of the sample, and there is almost no damage to the sample. After the cutting is completed, the specific surface area of the powder sample is tested by the gas adsorption method at a low temperature controlled by liquid nitrogen cooling.

The average pore diameter and sectional porosity calculated from the BJH adsorption cumulative total pore volume and the BJH adsorption cumulative total pore internal surface area.

9) Test method for graphitization degree of negative electrode material:

When X-rays are projected into the crystal, they are scattered by the atoms and electrons in the crystal. Due to the periodic arrangement of atoms in the crystal, there is a fixed phase difference between these scattered waves, which interfere in space, causing the scattered waves to strengthen each other in some scattering directions and cancel each other in some directions, so that diffraction occurs. . The diffractometer automatically records the diffraction pattern of the sample, and analyzes the diffraction pattern to obtain the sample information; use silicon as the internal standard, add it to graphite and mix it to test XRD, calculate d002, graphitization degree = 100*(3.44-d002 )/(3.44-3.354) (unit: %)

10) Test method of OI value of negative electrode material:

The ratio of the peak area C004 of the (004) plane to the peak area C110 of the (110) plane of the obtained negative electrode material particles was measured by X-ray diffraction spectrum.

11) Test method for the mass content of amorphous carbon in the negative electrode material:

The mass content of amorphous carbon was tested by thermogravimetric analysis.

12) Test method for sphericity of negative electrode material:

The sample is tested by means of projection photography, and the equivalent value of sphericity is obtained by calculating the projected figure, sphericity = equivalent circumference of projected figure/circumference of projected figure.

13) Electrochemical performance test method

The negative electrode material (the negative electrode material in this embodiment) and the conductive agent (carbon black SP), styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are configured according to the ratio of 95:2:1.5:1.5 Slurry, Evenly coated and dried on copper foil to make negative pole pieces, assembled into a button battery in an argon atmosphere glove box, the separator used is a polypropylene microporous membrane, and the electrolyte used is 1.0mol/L lithium hexafluorophosphate (solvent is The mixed solution of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate), and the counter electrode used is metal lithium sheet.

The first discharge capacity/first discharge efficiency test is carried out on the LAND battery tester. The charging and discharging conditions are as follows: standing for 2h; discharging: 0.1C to 0.005V, 0.09C, 0.08C...0.02C to 0.001V; standing for 15min; : 0.1C to 1.5V; stand for 15min.

The rate performance test of the coin half-cell was carried out at 25±2°C, and the charge-discharge specific capacity and Coulombic efficiency of 0.2C, 1C and 2C were obtained. Charge-discharge conditions for charge rate test: ① put 0.1C to 0.01V, constant voltage for 5 hours, charge 0.1C to 1.5V; ② put 0.2C to 0.01V, constant voltage to 0.01C, charge 0.2C to 1.5V; ③ 0. Put 2C to 0.01V, constant voltage to 0.01C, 2C to 1.5V; ④ 0.2C to 0.01V, constant voltage to 0.01C, 0.2C to 1.5V; ⑤ 1C to 0.01V, constant voltage to 0.01C ; Charge 0.2C to 1.5V; ⑥ Put 2C to 0.01V.

Full battery test: the negative electrode material prepared in each embodiment is used as the negative electrode active material, according to the mass percentage of the negative electrode active material, conductive agent, binder, and dispersant is 95.2:1.5:2:1.3, dissolved in the solvent and mixed, Control the solid content to 50wt%, coat it on an 8 μm thick copper foil current collector, and dry it in vacuum to obtain a negative electrode sheet; lithium iron phosphate, polyvinylidene fluoride, and conductive agent carbon black are used in a mass ratio of 95:2 : 3 mixed with solvent NMP (N-methylpyrrolidone), coated on a 16 μm thick aluminum foil, and vacuum-dried to obtain a positive electrode sheet; , drying, liquid injection, sealing, formation, and volume separation to make 554065 soft-pack lithium-ion batteries.

The obtained pouch battery was charged and discharged on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd., under normal temperature conditions, 1C/1C current charge and discharge, the charge and discharge voltage was limited to 3.0-4.35V, and the first effect and 500 cycles were performed. Capacity retention test.

The embodiments of the present invention will be further described below in several embodiments. Wherein, the embodiments of the present invention are not limited to the following specific embodiments. Within the scope of unchanging master rights, changes can be implemented as appropriate.

Example 1

A preparation method of negative electrode material, comprising the following steps:

(1) Add 30g of phenolic resin to 400mL of water and stir and mix evenly to obtain a resin slurry. The mass ratio of phenolic resin to water in the resin slurry is 1:20, that is, the amount of phenolic resin added is 5%; the obtained resin slurry The viscosity is 80cp;

(2) Slowly add the resin slurry into the spray tank of the spheroidization equipment, turn on the stirring function in the spray tank, the rotation speed is 200rpm, and the stirring time is 1h; add 300g of natural flake graphite and natural flake graphite to the spherical equipment The mass ratio of the amount of graphite added to the phenolic resin is 15:1, the host power of the equipment is 45kW, the rotation speed is 300rpm, the time of spheroidization is 6h, and the flow rate of resin slurry spraying is 25mL/ min; to obtain a spheroidized composite, the spheroidized composite includes a graphite core and a resin coating layer on the surface of the graphite core.

(3) Dry the spheroidized compound at 100°C for 24 hours to remove the moisture contained in the compound;

(4) After drying, the spheroidized composite is subjected to high-temperature carbonization treatment at 1050° C., and the high-temperature carbonization time is 6 hours;

(5) The spheroidized compound after the carbonization treatment is sieved under a 250 mesh sieve, and then classified and demagnetized to obtain the negative electrode material. Fig. 3 is the SEM of the negative electrode material obtained in this embodiment 1 4 is an enlarged SEM image of the negative electrode material prepared in Example 1.

As shown in Figure 4, the negative electrode material prepared in this embodiment includes a graphite flake core and amorphous carbon. The graphite flake core includes multilayer graphite flakes that are staggered and curled. Part of the graphite flakes are connected by a mortise and tenon structure; The amorphous carbon is located on the surface of the flake graphite core to form a carbon coating, and part of the amorphous carbon is embedded in the interior of the flake graphite core.

Example 2

The difference from Example 1 is that in step (1), 10 g of phenolic resin was added into 400 mL of water, stirred and mixed evenly to obtain resin slurry.

Example 3

The difference from Example 1 is that in step (1), 20 g of phenolic resin was added to 400 mL of water, stirred and mixed evenly to obtain resin slurry.

Example 4

The difference from Example 1 is that in step (1), 40 g of phenolic resin was added to 400 mL of water, stirred and mixed uniformly to obtain a resin slurry, that is, the amount of phenolic resin added was 10%.

Example 5

The difference from Example 1 is that in step (1), 50 g of phenolic resin was added into 400 mL of water, stirred and mixed evenly to obtain resin slurry.

Example 6

The difference from Example 1 is that in step (1), 60 g of phenolic resin was added into 400 mL of water, stirred and mixed evenly to obtain a resin slurry.

Example 7

The difference from Example 1 is that in step (1), 80 g of phenolic resin was added into 400 mL of water, stirred and mixed evenly to obtain a resin slurry.

Example 8

The difference from Example 1 is that in step (1), 100 g of phenolic resin was added to 400 mL of water, stirred and mixed evenly to obtain resin slurry.

The negative electrode materials prepared in Examples 1-8 were tested, and the test results are shown in Table 1 below;

Table 1 The effect of resin addition on the particle morphology of negative electrode materials

From the test data of Examples 1 to 5 in Table 1, it can be seen that the specific surface area of the negative electrode material decreases first and then increases with the increase of the amount of resin added, and the specific capacity of the negative electrode material used for the button battery also increases first and then decreases. Small. This is because as the amount of resin coating increases, some pores and defects on the surface and inside of the flake graphite core particles will be covered and filled by amorphous carbon, and the specific surface area of the prepared negative electrode material will decrease. will increase, and as the thickness of the carbon coating layer increases, the sphericity of the morphology of the prepared negative electrode material is also higher.

When the amount of resin (water-soluble resin) added reaches 30g, the specific surface area of the prepared negative electrode material is the smallest, the specific capacitance is the largest, and the first effect is also the highest. When the amount of resin added exceeds 30g, as the amount of resin added increases, the thickness of the carbon coating layer on the surface of the flake graphite core particle increases, and after the gaps and defects on the surface are completely filled with carbon, the excess carbon will be in Its surface further produces a new coating layer, and the new coating layer is amorphous carbon. Therefore, with the increase of amorphous carbon, the pores on the surface of amorphous carbon increase, which instead leads to an increase in the ratio of the negative electrode material and surface defects. It will also increase, which will increase the irreversible capacity of the material to a large extent, so that the specific capacity of the prepared negative electrode material will be reduced, and the first effect will also be reduced. directly affect the electrochemical performance.

Therefore, adding an appropriate amount of resin can reduce the specific surface of the negative electrode material through coating and carbonization, improve the first effect of the negative electrode material, reduce the expansion during charge and discharge, and effectively improve the stability and cycle performance of the material; finally, the negative electrode material is obtained After the battery is made, it can have better compatibility with propylene carbonate (PC)-based electrolyte, which greatly improves the reversible capacity and rate performance of the battery.

From the test data of Examples 1, 4, 6 to 8 in Table 1, it can be seen that with the increase of the amount of resin added, the mass content of amorphous carbon in the negative electrode material also increases, and the median particle size (D50) of the negative electrode material It also increases; with the increase of the median particle size (D50), the graphitization degree of the material also gradually decreases, and it is negatively correlated with the median particle size (D50). After spheroidization and coating, the negative electrode particles The larger is, the more mass content of amorphous carbon will be, which will further affect the degree of graphitization of the material.

As the coating amount increases, the specific capacity and first effect loss of the negative electrode material are relatively small, the compaction density also increases with the increase of the median particle size, and the rate performance (charging at room temperature 6C) increases with the increase of the amorphous carbon content. The increase also increases gradually. When the mass content of amorphous carbon in the negative electrode material reaches 4.5%, the increase rate performance of the negative electrode material decreases with the increase of the amount of resin added, because with the increase of the mass content of amorphous carbon, too thick carbon package Covering, the increase of pores on the surface of amorphous carbon will lead to an increase in the specific surface of the negative electrode material, and the increase in surface defects will increase the irreversible capacity of the material to a large extent, making the specific capacity of the negative electrode material As it decreases, the first effect also decreases.

Example 9

The difference from Example 1 is that in step (4), the dried spheroidized composite is subjected to high-temperature carbonization treatment at 750° C., and the high-temperature carbonization time is 6 hours.

Example 10

The difference from Example 1 is that in step (4), the dried spheroidized composite is subjected to high-temperature carbonization treatment at 850° C., and the high-temperature carbonization time is 6 hours.

Example 11

The difference from Example 1 is that in step (4), the dried spheroidized composite is subjected to high-temperature carbonization treatment at 950° C., and the high-temperature carbonization time is 6 hours.

Example 12

The difference from Example 1 is that in step (4), the dried spheroidized composite is subjected to high-temperature carbonization treatment at 1150° C., and the high-temperature carbonization time is 6 hours.

Example 13

The difference from Example 1 is that in step (4), the dried spheroidized composite is subjected to high-temperature carbonization treatment at 1250° C., and the high-temperature carbonization time is 6 hours.

The negative electrode materials prepared in Examples 1, 9-13 were tested, and the test results are shown in Table 2 below;

Table 2 Effect of carbonization temperature on the electrochemical performance of negative electrode materials

According to the data in Table 2, when the amount of resin added is constant, as the carbonization temperature increases, the thickness of the carbon coating layer on the surface of the flake graphite core particle becomes smaller, and the specific surface area of the negative electrode material first decreases and then increases . When the carbonization temperature is 1050°C, the specific surface area of the negative electrode material is the smallest. When the carbonization temperature exceeds 1050°C, the specific surface area of the prepared negative electrode material increases with the increase of the carbonization temperature.

During the high-temperature carbonization process, the specific surface area of the prepared negative electrode material decreases with the increase of the carbonization temperature within 750 ° C to 1050 ° C; The reduction of the shaped carbon leads to the thinning of the carbon coating on the surface of the flake graphite core particles, and the part with more defects on the surface of the flake graphite core particles may not be completely covered by carbon, so that the specific surface area of the negative electrode material increases accordingly; when carbonization When the temperature is too low, the carbonization of the spheroidized compound is not complete, so that the carbon coating layer is too thick after carbonization, resulting in the increase of surface defects, which in turn affects the electrochemical performance of the negative electrode material, and the specific capacitance is correspondingly reduced. reduce.

Example 14

The difference from Example 1 is that the added water-soluble resin is urea-formaldehyde resin.

Example 15

The difference from Example 1 is that the added water-soluble resin is epoxy resin.

Example 16

The difference from Example 1 is that the added water-soluble resin is polyacrylic acid resin.

The negative electrode materials prepared in Examples 1, 14-16 were tested, and the test results are shown in Table 3 below;

Table 3 The influence of different resins on the electrochemical performance of negative electrode materials

Different types of water-soluble resins can achieve better sphericity for the prepared negative electrode materials, and can also have high specific capacity and high first effect. Forming a carbon coating on the surface of the inner core can inhibit the occurrence of side reactions and improve Electrochemical properties of negative electrode materials.

Embodiment 17 (individual spheroidization)

(1) Add 300g of natural flake graphite to the spherical equipment, add 400mL of water to the spray tank of the spheroidizing equipment, and when spheroidizing, the main engine power of the equipment is 45kW, the speed is 300rpm, and the time for spheroidizing For 6h, the flow rate of the spray of water is 25mL/min, obtains the graphite after spheroidizing;

(2) Dry the spheroidized compound at 100°C for 24 hours to remove the moisture contained in the compound;

(3) After drying, the spheroidized composite is subjected to high-temperature carbonization treatment at 1050° C., and the high-temperature carbonization time is 6 hours;

(4) The spheroidized compound after the carbonization treatment is sieved under a 250-mesh sieve, and then classified and demagnetized to obtain the negative electrode material.

Embodiment 18 (coated separately)

(1) 20g of water-soluble phenolic resin and 300g of natural graphite flakes are added to the VC mixing equipment together, and after mixing for 40min, the mixture is obtained;

(2) The mixture is subjected to high-temperature carbonization at 1050° C., and the high-temperature carbonization time is 6 hours;

(3) The material after the carbonization treatment is sieved under a 250-mesh sieve, and then classified and demagnetized to obtain the negative electrode material.

Example 19

(1) 20g of water-soluble phenolic resin and 300g of natural graphite flakes are added to the VC mixing equipment together, and after mixing for 40min, the mixture is obtained;

(2) Add the mixture into a container, add 400mL of deionized water, and stir for 1 hour under the action of a strong stirrer at a speed of 200r/min to obtain a compound;

(3) The composite is dried at 100°C for 24 hours to remove the moisture contained in the composite;

(4) The dried composite is subjected to high-temperature carbonization treatment at 1050° C., and the high-temperature carbonization time is 6 hours;

(5) The compound after the carbonization treatment is sieved under a 250-mesh sieve, and then classified and demagnetized to obtain the negative electrode material.

Example 20

(1) 20g of water-soluble phenolic resin and 300g of natural graphite flakes are added to the VC mixing equipment together, and after mixing for 40min, the mixture is obtained;

(2) The mixture is subjected to high-temperature carbonization treatment at 1050° C., and the high-temperature carbonization time is 6 hours;

(3) Add 300g of carbonized material into the spherical equipment, and add 400mL of water into the spray tank of the spherical equipment. When performing spherical equipment, the power of the host machine is 45kW, the speed is 300rpm, and the time for spherical equipment is 6h, the flow rate of the spray of water is 25mL/min, obtains the graphite after spheroidizing;

(4) Dry the spheroidized compound at 100°C for 24 hours to remove the moisture contained in the compound;

(5) The dried spheroidized compound is sieved under a 250-mesh sieve, and then classified and demagnetized to obtain the negative electrode material.

The negative electrode materials prepared in Examples 1, 17-20 were tested, and the test results are shown in Table 4 below;

Table 4 The influence of different preparation processes on the electrochemical performance of negative electrode materials

According to the test data in Table 4, it can be seen that in Example 1, the spheroidization treatment is performed while the liquid phase is coated, and the flake graphite is curled under the centrifugal force generated by the spheroidization treatment, and the layers are tightly wrapped to form spherical graphite. The isotropy of the graphite is increased, and the graphite is coated with the coating slurry containing the water-soluble resin, so that the prepared negative electrode material has a more regular spherical shape. Since the coating process is carried out simultaneously, the pores generated by the flake graphite curl will be filled by the resin, making the carbon coating layer inside and on the surface of the carbonized negative electrode material denser, and the negative electrode material has a higher tap density, low Specific surface area, high compaction density, fewer surface defects, higher first effect of the material, less damage to the irreversible capacity, and the material can exhibit a higher specific capacity.

Compared with the single spheroidization process of Example 17 or the single solid phase coating process of Example 18, and the single liquid phase coating process of Example 19, the obtained negative electrode material has a higher sphericity and a lower tap density. Higher, better capacity, first effect, compaction and cycle performance, achieving the effect of 1+1>2.

The two processes of spheroidization + coating are carried out simultaneously. Compared with separate liquid phase coating, separate spheroidization, coating after spheroidization, and spheroidization after coating, the surface of the prepared negative electrode material The coating is more uniform, the carbon coating layer on the surface is denser, the pores on the surface of the negative electrode material are less, and the defects are relatively less, and the side reactions that occur when in contact with the electrolyte are relatively less, and the internal structure of the negative electrode material is more compact. The compact strength is better, the overall uniformity is better, and the negative electrode material can show more excellent electrochemical performance.

Figure 8 is a comparison of the powder conductivity curves of negative electrode materials obtained in Example 1, Example 17, and 18. As shown in Figure 8, the graphite negative electrode material obtained when the two processes of spheroidization + coating are carried out simultaneously The electrical conductivity is significantly better than that of the graphite anode material obtained by a separate spheroidization and a separate coating process; the shape of the material after spheroidization is more uniform, the difference between particles is smaller, and the edges, corners and defects on the surface of the material It will be significantly reduced, which is very helpful to increase the conductivity of the material. At the same time, the coating increases the isotropy of the material. A layer of amorphous carbon is coated on the graphite surface, and the amorphous carbon will be connected to the pores on the graphite surface. Filling increases the compactness of the graphite material and increases the density of the graphite material, thereby further improving the conductivity of the material.

Fig. 9 is a comparison chart of impedance performance of button batteries made of negative electrode materials in Examples 1, 17 and 18, as shown in Fig. The impedance of the anode material produced by the two processes synchronously is the smallest, and the impedance spectrum of the anode material obtained by the separate spheroidization and single coating process is obviously increased. After separate spheroidization, the surface of the material particles will be more rounded, the edges and corners and defects will be reduced, and the negative electrode material will become more regular, but the interior of the negative electrode material is relatively loose and the problem of surface pores is difficult to solve, so the separate spheroidization process can be obtained The material impedance is larger. Similarly, it is difficult to control the uniformity of the particle morphology by a single coating process, and due to the large particle difference, it is difficult to control the coating uniformity and the thickness of the coating layer, so the impedance of the negative electrode material obtained Also relatively large. Therefore, the spheroidization + coating process is carried out simultaneously, which can improve the sphericity and uniformity of the particles of the negative electrode material, and improve the uniformity and density of the carbon coating layer, so that the impedance of the negative electrode material is relatively higher than that of a single-process spherical Melting and encapsulation are significantly reduced.

Table 5 Comparison of lithium ion diffusion coefficients of negative electrode materials by different preparation processes

According to the test data in Table 5, it can be seen that the negative electrode materials prepared in Examples 1, 17, and 18 were further assembled into full batteries, and the rate performance, charge and discharge DCR, normal temperature EIS, low temperature EIS, and activation energy of the assembled full batteries were tested and compared. From the data in the table, it can be seen that the charge and discharge rate performance of the material is the best when the two processes of spheroidization and coating are carried out simultaneously. The rate retention rate is as high as 84.7% when charging at 3C, and the discharge rate performance is also the same when discharging at 3C. In addition, comparing the impedance of the three materials at room temperature (25°C), the impedance of the anode material produced by the two processes of spheroidization + coating simultaneously is smaller than that of the single spheroidization process and the single coating process. Moreover, the solid-phase diffusion coefficient of Li+ is significantly higher than that of the single spheroidization process and the single coating process, which is consistent with the test results of the rate performance of the negative electrode material, and further proves that the spheroidization + coating process is carried out simultaneously. The interface film resistance Rf, the charge transfer resistance Rct and the diffusion resistance of the negative electrode material are reduced (the lithium ion diffusion coefficient DLi+ is small). Even at a lower temperature (0°C), it exhibits good low-temperature performance. Although the impedance of the material obtained by the three processes is significantly higher than that at room temperature, the negative electrode obtained when the two processes of spheroidization and coating are carried out simultaneously The material still exhibits the lowest impedance, and the reaction activation energy of the negative electrode material prepared when the two processes of spheroidization + coating are carried out simultaneously is lower, and the kinetic performance of the negative electrode material is better, which is mainly due to the fact that the spheroidization + coating When the two coating processes are carried out simultaneously, the isotropy of the negative electrode material is better, which shortens the path of lithium ion transmission and improves the rate performance of the negative electrode material.

Comparative example 1

The difference from Example 1 is that the resin slurry prepared in step (1) is directly added to the spheroidizing equipment, instead of spraying the resin slurry in the spheroidizing process through the spray tank in step (2) material.

The negative electrode material that this comparative example makes comprises flake graphite inner core and amorphous carbon, and flake graphite inner core comprises the multi-layer flake graphite that wraps layer by layer, and the amorphous carbon of part is positioned at the surface of flake graphite inner core to form carbon coating layer, and part Amorphous carbon is embedded inside the flake graphite core.

The negative electrode materials prepared in Comparative Example 1 and Example 1 were compared and tested, and the test comparison results are shown in Table 6 below;

Table 6 Effects of Different Preparation Processes on the Performance of Anode Materials

It can be seen from Table 6 that during the preparation process, the way of adding the resin slurry has a great influence on the various indicators and properties of spherical graphite. When the resin slurry is directly added to the spheroidizing equipment, compared with Example 1 (added by spraying equipment), the median particle size of the spherical graphite obtained is significantly larger, the sphericity of the particles is obviously decreased, and the thickness of the carbon coating is also larger. As the amplitude increases, the average pore diameter of the pores also increases significantly, and the specific surface area also increases accordingly, and the capacity and first effect decrease significantly. This is mainly because the resin slurry is directly added to the spheroidizing equipment, which makes flake graphite easy to agglomerate and agglomerate. , so that the particle size becomes larger. In addition, adding all the resin slurry directly will make the internal phase of the spherical graphite particles uneven, and will also lead to poor coating compactness. At the same time, adding too much slurry at one time will make the coating thickness also decrease. The large number of pores in the flake graphite core cannot be fully filled, the average pore diameter of the material increases, and the specific surface area is also larger. The increased specific surface area also indicates that there are more surface defects in the negative electrode material, which further leads to the material The capacity and first effect are reduced.

Therefore, the negative electrode material prepared by the ordinary spheroidization process only makes the flake graphite sheets wrap layer by layer to form a spherical flake graphite core, which is difficult to form a mortise and tenon structure. Firstly, the inner density of the flake graphite core is poor. There are many defects and pores; secondly, the structural strength of the entire spherical graphite is very poor, and the entire sphere is prone to dissociation; finally, the spherical graphite formed by ordinary spheroidization is not as high as the present invention, and the surface edges and corners and defects are more.

In the negative electrode material provided by this application, part of the flake graphite is connected by a mortise and tenon structure, which can improve the structural stability and mechanical strength of the material, and can inhibit and buffer the expansion of graphite during the cycle; the amorphous carbon embedded in the flake graphite core , the pores and defects inside the graphite flakes are significantly reduced, which increases the density of the internal structure of the material and increases the structural strength of the material; the carbon coating layer outside the graphite flake core interacts with the self-mosaic structure of the graphite flake core , to further inhibit the expansion of graphite during cycling. The synergistic effect of flake graphite, inlaid amorphous carbon and carbon coating can significantly enhance the structural strength of the material, inhibit volume expansion, and increase the compaction density and capacity density of the material.

Although the present application is disclosed as above with preferred embodiments, it is not used to limit the claims. Any person skilled in the art can make some possible changes and modifications without departing from the concept of the present application. Therefore, the present application The scope of protection shall be based on the scope defined by the claims of the present application.

Claims (10)

1. The negative electrode material is characterized by comprising a scale graphite core and amorphous carbon, wherein the scale graphite core comprises a plurality of layers of scale graphite which are staggered, stacked and curled, and at least part of the scale graphite is connected through a mortise and tenon joint structure;

at least part of the amorphous carbon is positioned on the surface of the scale graphite core to form a carbon coating layer, and at least part of the amorphous carbon is embedded in the scale graphite core.

2. The anode material according to claim 1, characterized by comprising at least one of the following features (1) to (6):

(1) The thickness of the carbon coating layer is 10 nm-120 nm;

(2) The anode material has pores;

(3) The porosity of the section of the negative electrode material is 0.5-8.5%;

(4) The negative electrode material is provided with pores, and the average pore diameter of the pores is 0.1-10 nm;

(5) The negative electrode material is provided with a pore space, and at least part of the amorphous carbon is filled in the pore space;

(6) The amorphous carbon includes resin carbon.

3. The anode material according to claim 1, characterized by comprising at least one of the following features (1) to (6):

(1) The median particle size of the negative electrode material is A mu m, and A is more than or equal to 10 and less than or equal to 25;

(2) The graphitization degree of the negative electrode material is B%, and B is more than or equal to 90 and less than or equal to 96;

(3) The median particle size of the negative electrode material is A mu m, the graphitization degree of the negative electrode material is B%, and A (1-B) is more than or equal to 0.5 and less than or equal to 2.5;

(4) The OI value of the negative electrode material is C, and C is more than or equal to 0.5 and less than or equal to 5.0;

(5) The mass content D% of the amorphous carbon in the negative electrode material is more than 0 and less than or equal to 1;

(6) The OI value of the negative electrode material is C, the mass content D% of the amorphous carbon in the negative electrode material is more than or equal to 1 [ (C-0.5)/2 ]]*D ^-1/2 ≤2。

4. The negative electrode material according to any one of claims 1 to 3, characterized by comprising at least one of the following features (1) to (5):

(1) The powder compaction density of the negative electrode material is 1.75g/cm ³ ～1.90g/cm ³ ；

(1) The powder tap density of the cathode material is 1.3g/cm ³ ～1.5g/cm ³ ；

(3) The specific surface area of the negative electrode material is 0.3m ² /g～1.2m ² /g；

(4) The sphericity of the negative electrode material is 0.7-1.0;

(5) In a Raman spectrum, the cathode material has a carbon characteristic peak D and a carbon characteristic peak G, and the peak intensity I of the carbon characteristic peak D _D Peak intensity I with said carbon characteristic peak G _G Ratio of (1) _D /I _G ，1.5≤I _D /I _G ≤4.5。

5. The preparation method of the anode material is characterized by comprising the following steps of:

when the natural crystalline flake graphite is subjected to spheroidization, coating slurry containing water-soluble resin is sprayed to the surface of the spheroidized graphite for coating, so that a spheroidized compound is obtained;

and carbonizing the spherical compound to obtain the cathode material.

6. The method for producing the anode material according to claim 5, characterized by comprising at least one of the following features (1) to (6):

(1) The coating slurry also comprises water, and the mass ratio of the water-soluble resin to the water is 1: (10-35);

(2) The water-soluble resin comprises at least one of phenolic resin, urea resin, epoxy resin, polyurethane resin, polyester resin and polyacrylic resin;

(3) The viscosity of the coating slurry is 50-100 cp;

(4) The stirring speed of the coating slurry is 500 r/min-1000 r/min;

(5) The stirring time of the coating slurry is 0.5-2 h;

(6) The mass ratio of the natural crystalline flake graphite to the water-soluble resin is (10-30): 1.

7. the method for preparing the negative electrode material according to claim 5, wherein the step of spraying a coating slurry containing a water-soluble resin onto the surface of the spheroidized graphite to coat the surface of the spheroidized graphite is performed in a spheroidizing device with a spraying device when the natural crystalline flake graphite is spheroidized; the production method includes at least one of the following features (1) to (4):

(1) The host power of the spherical equipment is 25 kW-45 kW;

(2) The rotating speed of the spheroidizing equipment is 200 r/min-500 r/min;

(3) The spraying flow rate of the coating slurry is 5 mL/min-30 mL/min;

(4) The spheroidization time is 2-10 h.

8. The method for producing the anode material according to any one of claims 5 to 7, characterized by comprising at least one of the following features (1) to (5):

(1) Before the spheroidal composite is subjected to carbonization treatment, the method further comprises: drying the spherical compound;

(2) Before the spheroidal composite is subjected to carbonization treatment, the method further comprises: drying the spherical compound at 60-120 deg.c;

(3) Before the spheroidal composite is subjected to carbonization treatment, the method further comprises: drying the spherical compound for 12-24 h;

(4) The temperature of the carbonization treatment is 700-1250 ℃;

(5) The carbonization time is 4-8 h.

9. The method for preparing the anode material according to claim 5, comprising the steps of:

when the natural crystalline flake graphite is subjected to spheroidization treatment for 4 to 8 hours by utilizing spheroidization equipment with a spraying device, spraying coating slurry containing water-soluble resin and water onto the surface of the spheroidized graphite for coating to obtain a spheroidized compound; wherein the mass ratio of the water-soluble resin to the water is 1: (15-25), the viscosity of the coating slurry is 60-80 cp, and the mass ratio of the natural crystalline flake graphite to the water-soluble resin is (15-20): 1, the power of a host machine of the spherical equipment is 30 kW-40 kW, and the spraying flow of the coating slurry is 10 mL/min-20 mL/min;

drying the spherical compound at 80-100 ℃ for 16-20 h;

and (3) putting the dried spherical compound at 800-1000 ℃ for carbonization for 4-6 h to obtain the cathode material.

10. A lithium ion battery comprising the negative electrode material according to any one of claims 1 to 4 or the negative electrode material produced by the method for producing the negative electrode material according to any one of claims 5 to 9.

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