Anode material and method for preparing the same, and lithium-ion battery

Abstract

The negative electrode material of the present invention has a relatively high Young's modulus, which allows it to maintain its microscopic crystalline structure better during lithium ion insertion and removal, resulting in smaller irreversible deformation and better cycle performance. [Solution] The present invention provides a negative electrode material and a method for preparing the same, as well as a lithium-ion battery, and more specifically relates to the field of lithium-ion batteries. The Young's modulus E of the negative electrode material is in the range of 8 GPa ≤ E ≤ 17 GPa, and the negative electrode material includes natural graphite and a coating layer applied to the surface of the natural graphite.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and specifically to a negative electrode material, a method for preparing the same, and a lithium-ion battery.

Background Art

[0002] With the development of lithium-ion batteries, high-capacity batteries have become a current research hotspot. Natural graphite has the advantages of high capacity and large tap density, and since its graphitization is not required, energy consumption and carbon dioxide emissions can be extremely significantly reduced, making it very suitable for use as a negative electrode of a lithium-ion battery under the background of carbon neutrality. However, due to the relatively soft material of natural graphite itself, relatively large volume deformation occurs during the insertion and extraction process of lithium ions and cannot be recovered, that is, irreversible deformation occurs, and this characteristic poses a relatively large problem for the cycle performance of lithium-ion batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of the problems existing in the above prior art, the present invention provides a negative electrode material, a method for preparing the same, and a lithium-ion battery in order to improve the expansion problem of natural graphite.

Means for Solving the Problems

[0004] In order to achieve the above object and other related objects, a first aspect of the present invention provides a negative electrode material, wherein the range of the Young's modulus E of the negative electrode material is 8 GPa ≤ E ≤ 17 GPa, and the negative electrode material includes natural graphite and a coating layer coated on the surface of the natural graphite.

[0005] In one embodiment of the present invention, the range of the powder tap density P of the negative electrode material under 80 MPa is 1.66 ≤ P ≤ 1.74 g / cm 3 is.

[0006] In one embodiment of the present invention, after the negative electrode material is cold-compressed at 160 MPa for 10 seconds, the micropore volume V with a pore diameter of 0.2 to 2 nm 0.2-2 is such that 14 ≤ V 0.2-2 ≤ 20 cm 3 / Kg.

[0007] In one embodiment of the present invention, the coating layer contains amorphous carbon, and the mass of the amorphous carbon accounts for 2.5% to 6% of the mass of the natural graphite.

[0008] In one embodiment of the present invention, the particle size Dv50 of the negative electrode material is 5 μm to 20 μm.

[0009] Another aspect of the present invention provides a method for preparing a negative electrode material, and the preparation method includes performing a pulverization and shaping treatment on a natural flaky graphite raw material to obtain a graphite precursor; performing a thermal shaping treatment on the graphite precursor, and then adopting a stepwise temperature reduction method to perform a cooling and quenching treatment on the graphite precursor to obtain a spheroidization precursor; vacuum baking the spheroidization precursor, and then forming a coating layer on the surface of the spheroidization precursor to obtain a negative electrode material. and includes.

[0010] In one embodiment of the present invention, the step of performing a thermal shaping treatment on the graphite precursor, and then adopting a stepwise temperature reduction method to perform a cooling and quenching treatment on the graphite precursor to obtain the spheroidization precursor includes transferring the graphite precursor into a jet mill and heating it to a first temperature, and performing an ultra-high frequency thermal shaping at 100 Hz to 140 Hz for 0.5 h to 2 h; then introducing a first inert gas into the jet mill to reduce the temperature to a second temperature, and maintaining ventilation for 1 h to 3 h at the second temperature while performing shaping; further introducing a second inert gas into the jet mill to reduce the temperature to a third temperature, maintaining ventilation for 1 h to 3 h while performing shaping to obtain the spheroidization precursor. Here, the first temperature is between 600°C and 800°C. The temperature difference between the first temperature and the second temperature is between 100°C and 400°C. The temperature difference between the second temperature and the third temperature is between 100°C and 400°C. The flow rate L1 of the first inert gas is 5 L / min to 10 L / min. The flow rate L2 of the second inert gas is between 30 L / min and 60 L / min.

[0011] In one embodiment of the present invention, the vacuum roasting temperature is 450°C to 550°C. The step of forming the coating layer on the surface of the spheroidized precursor is, The steps include transferring the precursor after vacuum roasting into a solution containing a dissolved carbon-containing precursor, stirring, filtering and drying, and recovering the powder, The process then includes the step of firing the powder in an inert gas atmosphere at 750°C to 1100°C for 4 to 8 hours to produce the negative electrode material, And / or, the particle size Dv50 of the graphite precursor is between 30 μm and 50 μm, and the particle size distribution width (Dv90-Dv10) / Dv50 < 1.1.

[0012] In one embodiment of the present invention, the carbon-containing precursor comprises one or more of the following: C9 petroleum resin, phenolic resin, and pitch.

[0013] The present invention further provides a lithium-ion battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises any of the above-described negative electrode materials or a negative electrode material prepared by any of the above-described preparation methods. [Effects of the Invention]

[0014] The anode material of the present invention has a relatively high Young's modulus, which allows the anode material particles to have relatively high mechanical strength, better maintains the microscopic crystalline structure during lithium ion insertion and deinsertion, and exhibits relatively small irreversible deformation, resulting in better cycle performance. Furthermore, the anode material's relatively high Young's modulus keeps the material's powder pressure density within an appropriate range, while simultaneously ensuring a relatively high porosity at the electrode sheet level, resulting in excellent rapid charging performance. Moreover, the anode material can maintain a larger micropore volume under high pressure, enabling it to have more high-speed lithium insertion channels, thus ensuring that the material exhibits better rapid charging performance under relatively high energy density conditions.

[0015] This invention utilizes natural flake graphite as a raw material when preparing anode materials. By adjusting the heat treatment process, a stepwise cooling method is used to rapidly cool the precursor, allowing the material to retain the superior kinetic performance of natural graphite while simultaneously achieving a relatively high Young's modulus, thereby realizing the characteristics of low expansion and long cycles. The preparation method of this invention can effectively improve the expansion performance of natural graphite, is simple and easy to operate, and significantly reduces anode costs and energy consumption. [Brief explanation of the drawing]

[0016] To more clearly illustrate embodiments of the present invention or technical solutions in the prior art, the accompanying drawings that may be used in the description of embodiments or the prior art are briefly introduced below. Clearly, the accompanying drawings in the following description represent only some embodiments of the present invention, and those skilled in the art can obtain other embodiments based on these accompanying drawings without requiring any creative work.

[0017] [Figure 1] This is a flowchart of one embodiment of the method for preparing the negative electrode material of the present invention. [Modes for carrying out the invention]

[0018] The following describes embodiments of the present invention through specific examples, and those skilled in the art will readily understand other advantages and effects of the present invention from what is disclosed herein. The present invention can also be implemented or applied in yet another different specific embodiment, and the details of each item herein can be modified or changed in various ways based on different perspectives and applications without departing from the spirit of the invention. It should be noted that, where not inconsistent, the following embodiments and features can be combined with each other. Test methods in the following embodiments that do not specify concrete conditions are usually carried out according to standard conditions or according to conditions recommended by each manufacturer.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those ordinarily understood by those skilled in the art. Terms used in this specification are solely for the purpose of describing specific embodiments and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more related enumerations.

[0020] In this text, unless otherwise specified, a numerical range is considered continuous in its distribution of selectable numbers, and includes both numerical endpoints of that range (i.e., the minimum and maximum values), as well as each number between these two endpoints. When multiple numerical ranges are provided to describe a feature or characteristic, these ranges may be merged.

[0021] In this text, the measurement of Young's modulus is based on GB / T 34186-2017, the measurement of powder pressure density is based on GB / T 24533-2009, and the measurement of micropore volume is based on GB / T 19587-2017.

[0022] While natural graphite has advantages such as high capacity and high compressive density, its material is relatively soft, and relatively large volume deformation (irreversible deformation that does not return to its original state after expansion) occurs during the lithium ion insertion and deinsertion process, posing a major challenge to the cycle performance of lithium-ion batteries. Among existing technologies, there is a method to improve the expansion performance of natural graphite by graphitizing it, but although this method can improve the expansion performance of natural graphite, it drastically increases costs and energy consumption, and worsens the low-temperature performance of natural graphite.

[0023] Based on this, the present invention provides a negative electrode material, a method for preparing the negative electrode material, and a lithium-ion battery containing the negative electrode material. By controlling the Young's modulus of the negative electrode material, the particles are given a certain hardness, which allows for better maintenance of the microscopic crystalline structure during lithium ion insertion and removal, resulting in smaller irreversible deformation and thus better cycle performance.

[0024] A first aspect of the present invention provides a negative electrode material comprising natural graphite and a coating layer applied to the surface of the natural graphite, wherein the Young's modulus E of the negative electrode material is in the range of 8 GPa ≤ E ≤ 17 GPa. Young's modulus represents the degree of initial length change within a unit cross-section after a powder is subjected to a constant tensile stress, and it reflects the deformation state of the material under stress. The formula for calculating Young's modulus is E = σ / ε, where σ represents the stress within a unit area of ​​the material and ε represents the strain within a unit length. As can be seen from the formula for calculating Young's modulus, when the stress σ within a unit area of ​​the material is kept constant, a larger Young's modulus E explains that the larger the strain ε within a unit length, the smaller the material is, and the less deformable it is, i.e., the harder it is. Conversely, a smaller Young's modulus E explains that the larger the strain ε within a unit length, the more deformable the material is, i.e., the less hard it is. During the charging and discharging process of a lithium-ion battery, lithium ions are inserted into and removed from the negative electrode material. If the negative electrode material has low hardness (is soft), relatively large volume deformation occurs during the lithium ion insertion and removal process, and this deformation is irreversible, which is detrimental to the lithium-ion battery's cycle performance. On the other hand, if the negative electrode material has high hardness, it maintains its microscopic crystalline structure better during the lithium ion insertion and removal process, resulting in smaller irreversible deformation and better cycle performance for the lithium-ion battery. However, if the negative electrode material is excessively hard, it is difficult to compress, resulting in an excessively low compressive density of the negative electrode, which affects the battery's energy density. Therefore, having the Young's modulus of the negative electrode material within an appropriate range maintains good mechanical strength, does not affect the compressive density of the negative electrode, and thus provides better cycle performance. The Young's modulus E of conventional natural graphite is 5 GPa or less, resulting in a soft texture and poor cycle performance. The Young's modulus E of the anode material of the present invention is within the range of 8 GPa ≤ E ≤ 17 GPa, and while retaining the dynamics of natural graphite, it can also have the characteristics of a low expansion long cycle. In some embodiments, the Young's modulus E of the anode material can be 8 GPa, 10 GPa, 13 GPa, or 17 GPa, etc.

[0025] In one example, the range of the powder pressure density P of the negative electrode material under 80 MPa is 1.66 ≤ P ≤ 1.74 g / cm³.3 It is as follows. The bulk density of powder represents the total mass of the powder sample under a unit volume, and it refers to the process in which the powder material, under the action of an external pressure, the particles are rearranged, the voids are reduced, and thereby its density is increased. Therefore, under different external pressures, the anode material exhibits different bulk density values. The bulk density of the anode material of the present invention selects 80 MPa as the measurement pressure, corresponding to the preparation conditions of the battery anode. The bulk density of powder is closely related to the tap density of the anode sheet. The greater the bulk density of powder, the greater the tap density of the anode sheet. On the other hand, the tap density of the sheet affects the performance of the battery. When the bulk density of the anode material is too high, the tap density of the sheet becomes too high, the gap between particles becomes small, the infiltration performance of the sheet deteriorates further, and moreover, the insertion / desorption behavior of lithium ions therein becomes difficult, increasing the polarization of the battery. When the bulk density of powder is too low, the tap density of the sheet becomes too low, and although the infiltration performance of the sheet can be improved to a certain extent, the contact performance between anode particles and between anode particles and the current collector deteriorates, further leading to a decrease in the electron conductivity performance of the anode. Therefore, the anode material having an appropriate bulk density of powder means that the anode sheet has an appropriate tap density.

[0026] Furthermore, the bulk density of the anode material is related to the mechanical strength of the powder itself. The greater the mechanical strength, the higher the hardness of the powder particles and the more difficult it is to be compacted. Therefore, the bulk density P of the anode material and the Young's modulus E of the material show a negative correlation, that is, the greater the Young's modulus E, the smaller the bulk density P, and the smaller the Young's modulus E, the greater the bulk density P. Affected by the Young's modulus E, the bulk density P of the anode material of the present invention under 80 MPa is 1.66 ≦ P ≦ 1.74 g / cm 3 It can maintain a relatively high energy density of natural graphite and at the same time guarantee a relatively high porosity between the layers of the electrode sheet, thereby having excellent rapid charging performance. In some embodiments, the bulk density P of the anode material under 80 MPa is 1.66 g / cm 3 , 1.70 g / cm 3 or 1.74 g / cm 3 etc. can be the case.

[0027] In one example, the negative electrode material was cold-compressed at 160 MPa for 10 seconds, and then the pore size was reduced to a fine pore volume V of 0.2 to 2 nm. 0.2-2 is 14≦V 0.2-2 ≤20cm 3 This is / kg. In other words, the total volume of micropores with a pore size of 0.2~2 nm is 14-20 cm³. 3 It is / kg. Specifically, 14cm 3 / kg, 16cm 3 / kg, 18cm 3 / kg or 20cm 3 The volume can be as follows: / kg, etc. The micropore volume has a significant effect on the electrochemical performance of the anode material. Micropores can provide more active sites, increasing the specific surface area of ​​the material, thereby improving the kinetics of the electrochemical reaction. Furthermore, the presence of micropores is advantageous for electrolyte infiltration and ion diffusion, which is extremely important for the rapid charging performance and cycle stability of the battery. However, if the micropore volume is too large, it leads to an increase in side reactions, and if the micropore volume is too small, the kinetic performance of the electrochemical reaction of the anode material is poor. When the anode material of the present invention is cold-compressed for 10s under 160MPa, the micropore volume becomes 14-20cm³. 3 Reaching a weight of / kg means that the negative electrode material has abundant voids, can provide a relatively large number of high-speed lithium insertion channels, and guarantees a relatively high energy density while also having relatively good fast-charging performance.

[0028] Furthermore, the fact that the anode material maintains a good void structure even under high pressure of 160 MPa is due to an improvement in the mechanical performance of the anode material itself. The Young's modulus of the anode material in this application is significantly improved compared to existing natural graphite, which means that the particle hardness of the anode material has clearly improved. This improvement in particle hardness makes the material less susceptible to compressive deformation and even crushing under external forces, thereby enabling the anode material to maintain an abundant void structure even under high pressure.

[0029] In one embodiment, the coating layer is amorphous carbon. The surface of natural graphite has abundant functional groups, and by coating the natural graphite surface with amorphous carbon, direct contact between the natural graphite and the electrolyte can be avoided, thereby reducing side reactions. Furthermore, the amorphous carbon coating can also restrict the expansion of natural graphite, further improving its expansion problem. The amorphous carbon can be, for example, hard carbon or soft carbon. In addition, the mass of amorphous carbon accounts for 2.5% to 6% of the mass of natural graphite, specifically 2.5%, 4%, or 6%.

[0030] In one embodiment, the particle size Dv50 of the negative electrode material is 5 μm to 20 μm. Dv50 represents the particle size corresponding to the point where the cumulative volume distribution reaches 50% in the particle size distribution. Specific examples of negative electrode material particle sizes Dv50 include 5 μm, 10 μm, 15 μm, or 20 μm.

[0031] A second aspect of the present invention provides a method for preparing an anode material, the anode material produced by employing this preparation method having a relatively high Young's modulus, thereby allowing the anode material to retain the dynamics of natural graphite while also possessing low expansion and long cycle characteristics.

[0032] Referring to Figure 1, the above-mentioned method for preparing the negative electrode material is: S1, a step of crushing and shaping natural flake graphite raw material to obtain a graphite precursor, S2, the graphite precursor is subjected to a thermal shaping treatment, and then the graphite precursor is subjected to a rapid cooling treatment using a stepwise cooling method to obtain a spheroidized precursor. S3, the step of vacuum roasting the spheroidizing precursor, then forming a coating layer on the surface of the spheroidizing precursor to obtain a negative electrode material, It includes at least [this].

[0033] Specifically, step S1 uses natural flake graphite as the raw material, and it is necessary to pre-treat it before crushing and shaping to remove impurity minerals from the raw material. The pre-treatment includes washing and flotation. First, the natural flake graphite is washed with water to remove mud, dust, and other impurities from the graphite surface, preparing it for the subsequent flotation process. Flotation involves adding flotation agents to differentiate the selective adhesion of graphite particles and other impurity minerals on the water surface, thereby separating graphite from other minerals and improving the purity of the natural flake graphite.

[0034] Since natural flake graphite has relatively large particle sizes, reaching micrometers and even millimeters, it is necessary to crush and shape the natural flake graphite after pretreatment to obtain a graphite precursor with an appropriate particle size distribution. Specifically, this involves high-frequency shaping of natural flake graphite that has undergone water washing and flotation to reduce the size Dv50 of millimeter-sized natural flake graphite to 30-50 μm, and removing relatively large and relatively small sizes by classification, so that the particle size distribution width is (Dv90-Dv10) / Dv50 < 1.1. The above-mentioned high-frequency shaping can employ a shaping method that is common in this art. For example, a honeycomb mill can be used to shape natural flake graphite under a high frequency of 90 Hz for 6 hours. The honeycomb mill can effectively disperse and de-aggregate aggregated graphite flakes, reduce the breakdown into large flake graphite, and improve the quality of the graphite product. It needs to be explained that Dv90 represents the particle size corresponding to the point where the cumulative volume distribution reaches 90% in the particle size distribution, and Dv10 represents the particle size corresponding to the point where the cumulative volume distribution reaches 10% in the particle size distribution. The particle size distribution width (Dv90-Dv10) / Dv50 is an index for measuring particle size uniformity; a larger particle size distribution width indicates a wider particle size distribution, i.e., a greater difference between large and small particles. The closer the particle size distribution width is to 0, the more uniform the particle size is and the higher the size consistency. Step S1 reduces the particle size Dv50 of the natural flake graphite to 30-50 μm, and by setting the particle size distribution width (Dv90-Dv10) / Dv50 < 1.1, the negative electrode material that is finally manufactured can meet the required particle size. For example, the Dv50 of the graphite precursor can be 30 μm, 40 μm, or 50 μm, and the particle size distribution width (Dv90-Dv10) / Dv50 can be 1, 0.5, or 0.

[0035] Step S2 first involves performing a thermal shaping treatment on the graphite precursor obtained in Step S1. Specifically, this includes collecting the graphite precursor obtained in Step S1, transferring it to a jet mill, raising the temperature to a first temperature, and performing ultra-high frequency thermal shaping to improve its sphericity and compensate for the powder pressure density of the material. Here, the first temperature for thermal shaping is 600°C to 800°C, for example, 600°C, 700°C, or 800°C. If the thermal shaping temperature is excessively high, the degree of graphitization increases, destroying the original properties of natural graphite. On the other hand, if the thermal shaping temperature is excessively low, it leads to insufficient heat, and the target mechanical performance cannot be achieved in the subsequent cooling and rapid quenching process. Exemplaryly, the thermal shaping frequency is 100Hz to 140Hz, for example, 100Hz, 120Hz, or 140Hz, and the thermal shaping time is 0.5h to 2h, for example, 0.5h, 1h, 1.5h, or 2h.

[0036] After thermal shaping is complete, the graphite precursor is subjected to a rapid cooling treatment to obtain higher mechanical performance. Rapid cooling treatment involves stepwise temperature reduction of the thermally shaped precursor using an inert gas, which can be nitrogen gas, helium gas, argon gas, etc. Stepwise temperature reduction involves lowering the temperature to a certain level, holding it for a certain period of time, then lowering it to another level of temperature, holding it for a certain period of time, and repeating this process until the set temperature is reached. The temperature difference between each rapid cooling treatment should not be excessively large, as excessively large temperature differences can easily cause microcracks to form inside the graphite. In this invention, the temperature difference between rapid cooling treatments is 100 to 400°C, specifically 100°C, 200°C, 300°C, or 400°C. The number of rapid cooling treatments is at least one, preferably two, as too many treatments will not significantly improve performance and will instead lead to increased energy consumption.

[0037] In one embodiment, the cooling and rapid cooling process is specifically After ultra-high frequency thermal shaping is complete, a first inert gas is introduced into the jet mill to cool it down to a second temperature, and the shaping is performed while maintaining ventilation at the second temperature for 1 to 3 hours. The second inert gas is again introduced into the jet mill to lower the temperature to the third temperature, and the material is shaped while maintaining aeration for 1 to 3 hours to obtain a spheroidized precursor. Includes.

[0038] Here, the temperature difference between the second temperature and the thermoforming temperature (first temperature) is 100°C to 400°C, and the temperature difference between the second temperature and the third temperature is also 100°C to 400°C. For example, the first temperature could be 800°C, the second 400°C, and the third 200°C, or again, for example, the first 600°C, the second 400°C, and the third 200°C. After each cooling and rapid cooling process is complete, the crystal structure can be stabilized and the fixed microscopic structure can be maintained by holding the material in heat for 1 to 3 hours. The holding time can be 1 hour, 2 hours, or 3 hours, and can be specifically selected according to the actual production requirements.

[0039] Since the flow rate of the inert gas affects the cooling rate, it is necessary to set the flow rate of the inert gas within an appropriate range. Because the initial temperature during the first cooling is high, the cooling rate should not be excessive, and therefore, the flow rate of the first inert gas should be relatively low. On the other hand, the second cooling is a repeat cooling on the basis of the first cooling, and its initial temperature is relatively lower, so the flow rate of the inert gas can be appropriately increased during the second cooling. In some embodiments, the flow rate L1 of the first inert gas is 5 L / min to 10 L / min, and exemplary, the flow rate L1 of the first inert gas can be 5 L / min, 8 L / min, or 10 L / min, etc. The flow rate L2 of the second inert gas is 30 L / min to 60 L / min, and exemplary, the flow rate L2 of the second inert gas can be 30 L / min, 40 L / min, 50 L / min, or 60 L / min, etc. The first and second inert gases are each independently selected from nitrogen gas, argon gas, or helium gas. That is, the first and second inert gases may be the same or different, but it is preferable that the first and second inert gases are the same, as this reduces production operations and simplifies the operating process.

[0040] Step S3 involves roasting the spheroidized precursor obtained in Step S2 under vacuum to remove crystalline water and organic groups from the material. The vacuum roasting temperature is 450°C to 550°C, and can be exemplified as 450°C, 500°C, or 550°C. The roasting time can be selected according to the actual production conditions, for example, 1 to 3 hours. After roasting is complete, the material is cooled to room temperature, and then a coating layer is formed on the roasted precursor to obtain the anode material. The anode material contains natural graphite and a coating layer, and the anode material produced by the above preparation method has a relatively high Young's modulus, appropriate powder pressure density and micropore volume, retains the dynamics of natural graphite, and combines the characteristics of low expansion and long cycle, improving the expansion problem when using natural graphite as an anode.

[0041] In one embodiment, the coating layer formed on the precursor is amorphous carbon, and the amorphous carbon coating process is as follows: The material after vacuum roasting is transferred to a solution containing a dissolved carbon-containing precursor, stirred, filtered and dried, and the powder is recovered. Next, the powder is calcined at 750°C to 1100°C for 4 to 8 hours under an inert gas atmosphere to produce the anode material. This anode material is a natural graphite surface coated with an amorphous carbon layer. The amorphous carbon coating avoids direct contact between the natural graphite and the electrolyte, reducing side reactions. Furthermore, the amorphous carbon can also restrict the expansion of the natural graphite, further improving the problem of natural graphite expansion.

[0042] The carbon-containing precursor in this step is a carbon source for amorphous carbon and includes, but is not limited to, one or more types of C9 (9 carbon atoms in the main chain) petroleum resin, phenolic resin, and pitch. Furthermore, the carbon-containing precursor is C9 petroleum resin, which has a small molecular weight and can make the amorphous carbon coating more uniform. The specific steps are as follows: After roasting, the product powder is transferred through piping into a toluene solution in which C9 petroleum resin is dissolved. The mass fraction of C9 petroleum resin in the toluene solution is not limited and can be set according to the amount of coating. After stirring for a certain period of time, the powder is recovered by filtration and drying. The stirring and drying method is not limited and any method that can disperse and mix the materials in this field and drying method can be adopted, for example, magnetic stirring, vacuum drying box drying, etc. The recovered powder is then calcined and carbonized under an inert gas atmosphere to obtain amorphous carbon-coated natural graphite. The firing temperature is 750°C to 1100°C, for example, 750°C, 900°C, 1000°C, or 1100°C, and the firing time is 4 to 8 hours, for example, 4 hours, 6 hours, or 8 hours.

[0043] The particle size Dv50 of the negative electrode material manufactured after the above steps is 5 μm to 20 μm.

[0044] A third aspect of the present invention provides a lithium-ion battery, the lithium-ion battery including a non-aqueous electrolyte lithium battery, a solid lithium battery, and the like. Taking a non-aqueous electrolyte lithium battery as an example, the lithium-ion battery includes a negative electrode sheet, a positive electrode sheet, and a separator placed between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet includes the negative electrode material described above or a negative electrode material prepared by the preparation method described above.

[0045] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer installed on at least one surface of the negative electrode current collector. The negative electrode current collector can be made of materials conventional in the art, such as copper foil or carbon-coated copper foil, and the negative electrode active material layer can be installed on one surface of the negative electrode current collector or on both surfaces. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, wherein the negative electrode active material is selected from materials capable of lithium ion insertion and removal, and in this invention, the negative electrode active material is the negative electrode material described above. In other embodiments, the negative electrode material may be a combination of the negative electrode material described above and other materials, such as a silicon-based negative electrode material, where the silicon-based negative electrode material is silicon oxide SiO x(0 < x < 2), including silicon-carbon materials, silicon monocrystal, etc. However, this application is not limited to these materials listed above, and other conventional materials that can be used as the negative electrode active material can also be used. These negative electrode active materials can be used alone or in combination of two or more. The negative electrode conductive agent can improve the electron conductivity, collect minute currents between the negative electrode active materials and between the negative electrode active material and the negative electrode current collector, reduce the contact resistance of the battery, and accelerate the electron movement speed. In some embodiments, the negative electrode conductive agent includes at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotube, graphene. Optionally, the negative electrode conductive agent is conductive carbon black, or a combination of carbon fiber and conductive carbon black, or a combination of carbon nanotube and graphene, etc. The binder is used to adhere the negative electrode active material and the negative electrode conductive agent, provide a certain adhesive force to the negative electrode active material layer, and adhere it to the negative electrode current collector. As an example, the negative electrode binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), styrene-acrylic ester, acrylic acid-based multi-component copolymer. For example, the negative electrode binder is polyvinylidene fluoride, or a combination of styrene-butadiene rubber and carboxymethyl cellulose, etc. The ratios of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder can refer to the conventional settings in this field.

[0046] An example of the preparation process of the negative electrode sheet is as follows. First, the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder are mixed and stirred in a solvent such as deionized water at a certain mixing ratio to make it uniform to form a negative electrode slurry. Further, the negative electrode slurry is applied to the negative electrode current collector, and through processes such as drying, roll rolling, and cutting, a negative electrode sheet is obtained.

[0047] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer installed on at least one surface of the positive electrode current collector. The positive electrode current collector can be made of conventional materials in this field, such as aluminum foil or carbon-coated aluminum foil, and the positive electrode active material layer can be installed on one surface of the positive electrode current collector or on both surfaces. The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, where the positive electrode active material can be any positive electrode material applicable to lithium-ion batteries, i.e., any compound that reversibly intercalates and deintercalates lithium ions can be used. For example, the positive electrode active material can be a ternary material, such as nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), iron-lithium positive electrode materials such as lithium iron phosphate (LFP), manganese-iron-lithium phosphate (LMFP), and also conventional materials such as lithium cobalt oxide and lithium manganese oxide. These materials can be used individually or in combination. The positive electrode binder is any one or more of the following: polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylic acid ester, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, or styrene-butadiene rubber (SBR). The positive electrode conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotubes, or graphene. Selectively, the conductive agent may be conductive carbon black, a composition of carbon fiber and conductive carbon black, or a composition of carbon nanotubes and graphene, etc. The ratios of the positive electrode active material, positive electrode conductive agent, and positive electrode binder can refer to conventional settings in this art.

[0048] An example of the preparation process for a positive electrode sheet is as follows: First, the positive electrode active material, positive electrode conductive agent, and positive electrode binder are mixed and stirred in a solvent such as N-methylpyrrolidone (NMP) in a fixed ratio to form a homogeneous positive electrode slurry. Next, the positive electrode slurry is applied onto a positive electrode current collector, and after processes such as drying, roll rolling, and cutting, a positive electrode sheet is obtained.

[0049] A separator is placed between the positive and negative electrode sheets to isolate them, preventing short circuits within the battery while simultaneously allowing lithium ions to move between the positive and negative electrodes, thus enabling the battery's charging and discharging process. The separator can be made from porous materials such as polyethylene (PE), polypropylene (PP), glass fiber, or composite membranes. The separator thickness is 9-18 μm, the air permeability is 180 s / 100 mL-380 s / 100 mL, and the porosity is 30-50%.

[0050] Lithium-ion batteries also contain an electrolyte, which plays a role in conducting lithium ions during the battery's charging and discharging process. The electrolyte contains an organic solvent and a lithium salt, which can be selected from one or more of the following: lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoride arsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Furthermore, the lithium salt is selected from lithium hexafluoride phosphate or a combination of lithium hexafluoride phosphate and other lithium salts, for example, a combination of lithium hexafluoride phosphate and lithium bisfluorosulfonylimide, which have good overall performance. The organic solvent can be selected from one or more of the following: ethylene fluorocarbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Functional additives may also be included in the electrolyte, such as ethylene fluorocarbonate (FEC), propenyl-1,3-sultone (PST), tetravinylsilane (TVSI), vinylene carbonate (VC), ethylene sulfate (DTD), etc., and can be added according to the demands of actual production.

[0051] Battery assembly: The prepared positive electrode sheet, separator, and negative electrode sheet are arranged in sequence, with the separator positioned between the positive and negative electrode sheets to act as an separator, and a bare cell is obtained by winding or lamination. The bare cell is loaded into a battery case, and a lithium-ion battery is obtained through processes such as assembly, liquid injection, chemical conversion, and volume division.

[0052] In other embodiments, the lithium-ion battery may be a solid-state lithium-ion battery, and the electrolyte of the solid-state lithium-ion battery is solid. Common solid electrolytes include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc., which will not be described in detail here, but those skilled in the art can select them according to their actual production needs.

[0053] It is necessary to explain that the structures of the lithium-ion batteries mentioned above, which are not described in detail, can all be implemented by referring to existing technologies and are therefore not described in detail here.

[0054] The lithium-ion battery of the present invention can be used in electronic devices in the form of a single battery, battery module, or battery pack, and provides power to them. Electronic devices include, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric vehicles, new energy vehicles, ships, and spacecraft. Among these, electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft. New energy vehicles may be pure electric vehicles, hybrid vehicles, or augmented-cycle vehicles.

[0055] The technical plan of the present invention will be described in detail below with reference to several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the equipment used in the examples is commercially available.

[0056] Example 1 This embodiment provides a negative electrode material comprising natural graphite and amorphous carbon, wherein the amorphous carbon uniformly coats the surface of the natural graphite, and the amount of amorphous carbon accounts for 4% of the mass of natural graphite. The Young's modulus E of the negative electrode material is 13 GPa, and the powder pressure density P is 1.7 g / cm³. 3 Therefore, the micropore volume V 0.2-2 16.7cm 3The value is / kg, and the particle size Dv50 of the negative electrode material is 12.1 μm.

[0057] This embodiment also provides a method for preparing the negative electrode material described above, and includes the following steps. Step 1: Natural flake graphite that has undergone water washing and flotation is subjected to high-frequency shaping at 90 Hz in a honeycomb mill for 6 hours, reducing the millimeter-sized natural flake graphite size Dv50 to 30-50 μm, and removing relatively large and relatively small sizes through classification, so that the particle size distribution width (Dv90-Dv10) / Dv50 is less than 1.1. Step 2: The powder described above is collected and transferred to a jet mill. The temperature is raised to T1: 600°C, and ultra-high frequency shaping is performed at 120 Hz for 1 hour. Then, inert gas is introduced from the top of the jet mill to cool down to T2: 400°C, the inert gas flow rate is set to L1: 10 L / min, and shaping is performed while maintaining aeration for 2 hours. After that, inert gas is introduced again from the top of the jet mill to cool down to T3: 200°C, the inert gas flow rate L2 is set to 30 L / min, and shaping is performed while maintaining aeration for 2 hours. Then heating is stopped to obtain a spheroidized precursor. Step 3: The spheroidizing precursor described above is vacuum roasted at 500°C for 1 hour, then cooled to room temperature, and transferred through piping into a toluene solution containing dissolved C9 petroleum resin (C9 petroleum resin mass fraction: 20%), stirred for 5 hours, and then filtered and dried to collect the powder. Step 4: The powder described above is calcined at 900°C in an inert gas atmosphere for 6 hours, and then cooled to room temperature to obtain amorphous carbon-coated spheroidized natural graphite with a particle size of 12.1 μm.

[0058] Referring to Table 1, the present invention also provides Examples 2 to 8 and Comparative Examples 1 to 7.

[0059] The difference between Example 2 and Example 1 is that the Young's modulus E of the negative electrode material is 17 GPa, and the powder pressure density P is 1.66 g / cm³. 3 , micropore volume V 0.2-2 19.2cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 11.5μm. Change the thermoforming temperature T1 in the preparation method to 800°C.

[0060] The difference between Example 3 and Example 1 is that the Young's modulus E of the negative electrode material is 8 GPa, and the powder pressure density P is 1.74 g / cm³. 3 , micropore volume V 0.2-2 14.5cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 13.2μm. The first cooling quenching temperature T2 in the preparation method is changed to 500°C.

[0061] The difference between Example 4 and Example 1 is that the Young's modulus E of the negative electrode material is 11 GPa, and the powder pressure density P is 1.72 g / cm³. 3 , micropore volume V 0.2-2 15.6cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 12.7μm. Change the inert gas flow rate L1 in the preparation method to 5 L / min.

[0062] The difference between Example 5 and Example 1 is that the Young's modulus E of the negative electrode material is 16 GPa, and the powder pressure density P is 1.68 g / cm³. 3 , micropore volume V 0.2-2 17.8cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 11.6 μm. Change the inert gas flow rate L2 in the preparation method to 60 L / min.

[0063] The difference between Example 6 and Example 1 is that the Young's modulus E of the negative electrode material is 16 GPa, and the powder pressure density P is 1.67 g / cm³. 3 , micropore volume V 0.2-2 11.4cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 11.4μm. In the preparation method, change the heat shaping temperature T1 to 700°C, the inert gas flow rate L1 to 8 L / min, and L2 to 40 L / min.

[0064] The difference between Example 7 and Example 1 is that the Young's modulus E of the negative electrode material is 8 GPa, and the powder pressure density P is 1.77 g / cm³. 3 , micropore volume V 0.2-2 14cm 3The material is / kg, with a particle size Dv50 of the negative electrode material being 8.9μm, and amorphous carbon coating accounting for 2.5% of the natural graphite mass. The mass fraction of C9 petroleum resin in the toluene solution obtained by dissolving C9 petroleum resin in step 3 of the preparation method is 12.5%.

[0065] The difference between Example 8 and Example 1 is that the Young's modulus E of the negative electrode material is 17 GPa, and the powder pressure density P is 1.67 g / cm³. 3 , micropore volume V 0.2-2 20cm 3 The material is / kg, with a negative electrode material particle size Dv50 of 12.8μm, and amorphous carbon coating accounts for 6% of the natural graphite mass. In step 3 of the preparation method, the mass fraction of C9 petroleum resin in the toluene solution in which C9 petroleum resin is dissolved is 30%.

[0066] The difference between Comparative Example 1 and Example 1 is that the Young's modulus E of the negative electrode material is 6 GPa, and the powder pressure density P is 1.82 g / cm³. 3 , micropore volume V 0.2-2 15.6cm 3 The value is / kg, and the Dv50 is 14.3μm. The preparation method does not include a heat forming step.

[0067] The difference between Comparative Example 2 and Example 1 is that the Young's modulus E of the negative electrode material is 5 GPa, and the powder pressure density P is 1.85 g / cm³. 3 , micropore volume V 0.2-2 12.3cm 3 The value is / kg, and Dv50 is 15.2μm. The preparation method does not involve heat shaping or a T2 heating step; instead, it is rapidly cooled directly at the T3 temperature.

[0068] The difference between Comparative Example 3 and Example 1 is that the Young's modulus E of the negative electrode material is 20 GPa, and the powder pressure density P is 1.60 g / cm³. 3 , micropore volume V 0.2-2 21.3cm 3 The value is / kg, and Dv50 is 10.9μm. The incubation step is omitted after rapid cooling at T2 temperature during the preparation method.

[0069] Comparative Example 4 used commercially available natural graphite. The differences from Example 1 were that the Young's modulus E of the negative electrode material was 2 GPa, and the powder pressure density P was 1.79 g / cm³. 3 , micropore volume V 0.2-2 10.1cm 3 The value is / kg, and Dv50 is 11.2μm.

[0070] The difference between Comparative Example 5 and Example 1 is that the Young's modulus E of the negative electrode material is 22 GPa, and the powder pressure density P is 1.63 g / cm³. 3 , micropore volume V 0.2-2 22.4cm 3 The value is / kg, and Dv50 is 11.7μm. In the preparation method, a primary quenching treatment is employed, meaning T2 is set to 200°C, and the T3 quenching process is omitted.

[0071] The difference between Comparative Example 6 and Example 1 is that the Young's modulus E of the negative electrode material is 27 GPa, and the powder pressure density P is 1.54 g / cm³. 3 , micropore volume V 0.2-2 32.7cm 3 The value is / kg, and Dv50 is 10.6μm. In the preparation method, the heat shaping temperature T1 is 1000°C, and the rapid cooling treatment temperature T2 is 400°C.

[0072] The difference between Comparative Example 7 and Example 1 is that amorphous carbon is not coated. The Young's modulus E of the negative electrode material is 6 GPa, and the powder pressure density P is 1.82 g / cm³. 3 , micropore volume V 0.2-2 14cm 3 The value is / kg, and the particle size Dv50 of the negative electrode material is 10.6μm. In the preparation method, after the roasting in step S3 is completed, the preparation is finished by cooling to room temperature, and mixing with the toluene solution containing dissolved C9 petroleum resin and the calcination in step S4 are not performed.

[0073] Table 1 shows the parameter characteristics and preparation method parameters of the negative electrode materials for Examples 1-8 and Comparative Examples 1-7.

[0074] [Table 1] JPEG2026116193000003.jpg79160

[0075] To verify the performance of the negative electrode material of the present invention, the inventors applied the negative electrode materials of Examples 1 to 8 and Comparative Examples 1 to 7 to lithium-ion batteries and performed performance measurements on each lithium-ion battery. The configuration of the lithium-ion batteries and the measurement method are as follows, and the measurement results can be found in Table 2.

[0076] A lithium-ion battery contains a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet, separator, and negative electrode sheet are wound together to form an electrocore, which is then packaged in a packaging shell and injected with the electrolyte to manufacture a soft pack battery.

[0077] In this process, the negative electrode sheet is prepared by mixing the negative electrode material obtained in the example or comparative example, a conductive agent (SP), a binder (PAA and SBR, with a mass ratio of 1.3:0.5), and a thickening agent carboxymethylcellulose (CMC) in a mass ratio of 97.2:0.5:1.8:0.5 (total 100 parts by mass). Then, 82 parts by mass of deionized water is added and mixed uniformly to obtain a negative electrode slurry. Next, the negative electrode slurry is uniformly applied onto a copper foil. Further processes such as drying, roll rolling, and cutting are followed to prepare and obtain a negative electrode sheet.

[0078] Preparation of positive electrode sheet: Positive electrode active material NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), PVDF, and SP are mixed in a mass ratio of 97:1.8:1.2 (total 100 parts by mass), and then 82 parts by mass of NMP are added to obtain a positive electrode slurry. The obtained positive electrode slurry is applied to at least one surface of an aluminum foil, dried, roll-rolled, and compressed to obtain the final product.

[0079] Separator: A polyethylene thin film with a thickness of 11 μm, an air permeability of 230 s / 100 mL, and a porosity of 40%.

[0080] The electrolyte used is a commercially available electrolyte (manufacturer: Xinya Shanshan New Materials Technology (Quzhou) Co., Ltd., model number: E3).

[0081] Battery performance measurement method (1) Full cell initial efficiency Full cell charging capacity: A lithium-ion battery is charged to 4.35V with a 1C current, and the charging capacity at this stage is recorded as c1. Then, constant voltage charging is performed down to a cutoff current of 0.05C, and the charging capacity at this stage is recorded as c2. The full cell charging capacity is the sum of c1 and c2. Full cell discharge capacity: After letting a fully charged cell rest for 30 minutes, discharge it to 2.8V with a 1C current and record the discharge capacity c3 at this stage, which is the full cell discharge capacity. Initial efficiency = Full cell discharge capacity c3 / Full cell charge capacity (c1 + c2) × 100%.

[0082] (2) Quick charging time The battery is directly charged with a 0.33C current to an 8% SOC state, and then the charging windows at 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% are defined as c1, c2, c3, c4, c5, c6, c7, and c8 respectively by measuring the three electrode windows. The battery is then charged up to 80% using step charge charging, specifically using c1 for 8%-10%, c2 for 10%-20%, and so on. The charging time from 8% to 80% SOC is recorded and used as the evaluation criterion for rapid charging capability. The calculation formula is as follows. T(8%-80%)=(0.02 / c1+0.1 / c2+0.1 / c3+0.1 / c4+0.1 / c5+0.1 / c6+0.1 / c7+0.1 / c8)*60.

[0083] (3) Number of cycles at room temperature Under 25°C conditions, the system was cycled using a charge-discharge format of 0.21 A / g (calculated using the positive electrode active material mass) and 2.8-4.25 V. The number of cycles at 80% initial capacity was recorded to determine the material's cycle performance effect.

[0084] (4) Number of storage days At 25°C, the constant volume is recorded as C0 with a current of 0.33C. The core is then stored under high-temperature conditions of 60°C. After that, the core is removed at 7-day intervals, and its capacity is measured at room temperature and recorded as C1, C2, ..., Cn. The number of days until Cn first falls below 80% of C0 is used as the evaluation criterion for storage capacity and is recorded as the number of storage days.

[0085] Table 2 shows the performance of the assembled batteries in Examples 1-8 and Comparative Examples 1-7.

[0086] [Table 2]

[0087] As can be seen from Tables 1 and 2, the Young's modulus, powder compaction, and micropore volume of the anode material can be adjusted by controlling the heat treatment parameters during the preparation process. The Young's modulus of the anode materials produced in Examples 1 to 8 was clearly improved compared to commercially available natural graphite (Comparative Example 4), and the cycle performance, rapid charging performance, and storage performance of the assembled battery at room temperature were clearly improved compared to Comparative Example 4. This explains that by appropriately improving the Young's modulus of the anode material, the microscopic crystalline structure is maintained during lithium ion insertion and removal, irreversible deformation is reduced, and thereby the cycle performance is improved. At the same time, the improvement in the Young's modulus of the anode material also changes the powder compaction and micropore volume accordingly, resulting in good porosity and good electrolyte permeability, thereby providing good rapid charging performance.

[0088] In Example 7, the amount of amorphous carbon coating on the negative electrode material is less compared to the other examples, resulting in relatively large volume expansion of the negative electrode material and inferior stability, thus resulting in a smaller number of cycles compared to the other examples. In Example 8, the amount of amorphous carbon coating on the negative electrode material is more compared to the other examples, resulting in inferior powder compaction of the negative electrode material, lower porosity (compared to the other examples) and inferior electrolyte permeability at the same actual pressure density of the electrode sheet, thus resulting in a smaller number of cycles.

[0089] The Young's modulus, powder compaction, or micropore volume of the negative electrode materials in Comparative Examples 1-3 and 5-6 exceed the limits set forth in this application, and the cycle performance, rapid charging performance, and storage performance of the assembled batteries are all inferior to those of Examples 1-8. The negative electrode material of Comparative Example 7 contains only natural graphite, and the surface of the natural graphite is not coated with amorphous carbon. Since the surface activity of amorphous carbon is better than that of natural graphite, when the surface of the natural graphite is not coated with amorphous carbon, side reactions are reduced and high-temperature storage performance is relatively better compared to when amorphous carbon is coated, but rapid charging performance and cycle performance are worse.

[0090] The negative electrode material provided in this invention has a relatively high Young's modulus, and the negative electrode material particles have relatively high mechanical strength, which allows for better maintenance of the microscopic crystalline structure during lithium ion insertion and removal, resulting in relatively small irreversible deformation and thus better cycle performance. Furthermore, the relatively high Young's modulus of the negative electrode material maintains the powder compaction of the material within an appropriate range, possessing high energy density while simultaneously ensuring relatively high porosity at the electrode sheet level, resulting in excellent rapid charging performance. Moreover, the negative electrode material retains a relatively large volume of micropores under high pressure and has a relatively large number of rapid lithium insertion channels, ensuring that the material has relatively good rapid charging performance under conditions of relatively high energy density. Therefore, this invention has very high utility and significance by effectively overcoming some of the practical problems in existing technologies.

[0091] The above-described embodiments are illustrative in illustrating the principles and effects of the present invention and do not limit the invention. Those skilled in the art can modify or alter the above-described embodiments without violating the spirit and scope of the invention. Therefore, any equivalent modifications or alterations completed by those skilled in the art without departing from the spirit and technical concept disclosed herein should still be incorporated into the claims of the present invention. [Industrial applicability]

[0092] This invention relates to the field of lithium-ion batteries, and more specifically to negative electrode materials, methods for preparing the same, and lithium-ion batteries. [Explanation of Symbols]

[0093] S1, S2, S3, S4 Step

Claims

1. The range of Young's modulus E for the negative electrode material is 8 GPa ≤ E ≤ 17 GPa. The negative electrode material is characterized by comprising natural graphite and a coating layer applied to the surface of the natural graphite.

2. The range of the powder pressure density P of the aforementioned negative electrode material at 80 MPa is 1.66 ≤ P ≤ 1.74 g / cm³. ３ The negative electrode material according to claim 1, characterized in that it is the same as the one described in claim 1.

3. The anode material is cold-compressed at 160 MPa for 10 s, and then the pore size is reduced to a fine pore volume V of 0.2 to 2 nm. ０．２－２ 14 ≤ V ０．２－２ ≤20cm ３ The negative electrode material according to claim 1, characterized in that it is / kg.

4. The coating layer contains amorphous carbon, The negative electrode material according to claim 1, characterized in that the mass of the amorphous carbon accounts for 2.5% to 6% of the mass of the natural graphite.

5. The negative electrode material according to claim 1, characterized in that the particle size Dv50 of the negative electrode material is 5 μm to 20 μm.

6. A method for preparing a negative electrode material according to claim 1, The steps include: crushing and shaping a natural flake-like graphite raw material to obtain a graphite precursor; The graphite precursor is subjected to a heat shaping treatment, and then the graphite precursor is subjected to a rapid cooling treatment using a stepwise cooling method to obtain a spheroidized precursor. The steps include: vacuum roasting the spheroidizing precursor, then forming a coating layer on the surface of the spheroidizing precursor to obtain a negative electrode material; A method for preparing a negative electrode material, characterized by including the following:

7. The step of performing the thermal shaping treatment on the graphite precursor, and then performing the rapid cooling treatment on the graphite precursor using a stepwise cooling method to obtain the spheroidized precursor is as follows: The graphite precursor is transferred to a jet mill and heated to a first temperature, and ultra-high frequency thermoshaping is performed at 100 Hz to 140 Hz for 0.5 to 2 hours. Subsequently, the first inert gas is introduced into the jet mill to lower the temperature to a second temperature, and the shaping process is performed while maintaining ventilation at the second temperature for 1 to 3 hours. Furthermore, the step of introducing a second inert gas into the jet mill to lower the temperature to a third temperature, maintaining aeration for 1 to 3 hours while simultaneously performing shaping to obtain the spheroidized precursor is included. Here, the first temperature is between 600°C and 800°C. The temperature difference between the first temperature and the second temperature is between 100°C and 400°C. The temperature difference between the second temperature and the third temperature is 100°C to 400°C. Flow rate L of the first inert gas １ The flow rate is between 5 L / min and 10 L / min. Flow rate L of the second inert gas ２ The method for preparing a negative electrode material according to claim 6, characterized in that the flow rate is 30 L / min to 60 L / min.

8. The temperature for the vacuum roasting is between 450°C and 550°C. The step of forming the coating layer on the surface of the spheroidized precursor is, The steps include transferring the precursor after vacuum roasting into a solution containing a dissolved carbon-containing precursor, stirring, filtering and drying, and recovering the powder, The process then includes the step of firing the powder in an inert gas atmosphere at 750°C to 1100°C for 4 to 8 hours to produce the negative electrode material, The method for preparing a negative electrode material according to claim 6, characterized in that the particle size Dv50 of the graphite precursor is 30 μm to 50 μm and the particle size distribution width (Dv90 - Dv10) / Dv50 < 1.

1.

9. The method for preparing a negative electrode material according to claim 8, characterized in that the carbon-containing precursor includes one or more types of C9 petroleum resin, phenolic resin, and pitch.

10. Includes a negative electrode sheet, A lithium-ion battery characterized in that the negative electrode sheet includes the negative electrode material described in any one of claims 1 to 5 or the negative electrode material prepared by the preparation method described in any one of claims 6 to 9.

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