Negative electrode active material, and preparation method therefor and use thereof

Abstract

A negative electrode active material, and a preparation method therefor and a use thereof. The negative electrode active material comprises a graphite material, and the graphite material comprises first graphite and second graphite. Two types of graphite having a certain pressure-relief rebound rate are selected, and are combined with a Dn10 range controlled and a distribution width limited. A negative electrode sheet can have high particle packing density and compaction level, so that good electrical contact between negative electrode active materials and sufficient infiltration of an electrolyte can both be ensured, thereby prolonging high-temperature cycle life while considering charging capability and energy density.

Description

A negative electrode active material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a negative electrode active material and a preparation method and application thereof. Background Art

[0002] Lithium batteries are important rechargeable batteries widely used in mobile electronic devices, electric vehicles, and other fields. In lithium batteries, the anode material plays a key role in storing and releasing lithium ions. Active materials that can be used as anode materials for lithium batteries include silicon-based materials, metal oxides, and graphite.

[0003] Silicon is a high-capacity negative electrode material. Compared to graphite, the theoretical specific capacity of silicon is as high as 4200mAh / g, which is about 10 times that of graphite. Silicon-based negative electrode materials can significantly improve the energy density of lithium batteries. However, the volume expansion of silicon materials can cause serious structural damage during the charge and discharge process, resulting in a sharp decrease in cycle life. Metal oxides (such as tin compounds, lithium titanate, etc.) have also been widely studied as negative electrode materials for lithium batteries. These materials have higher theoretical specific capacity and more electron transfer reaction sites, and therefore can provide more lithium ion storage capacity. However, these materials have problems with capacity fading and safety. Graphite is one of the most common negative electrode materials for lithium batteries. It has high electrical conductivity, stable potential and good cycle life. Graphite negative electrode materials are widely used in commercial lithium-ion batteries, but their capacity is relatively close to the limit and cannot meet the growing demand.

[0004] Lithium-ion batteries (LIBs) are widely used in portable electronic devices due to their lightweight, low cost, and long cycle life. However, with the continuous upgrading of electronic digital products, the demand for LIB energy density and fast charging capabilities is increasing. To meet these demands, the development of new anode active materials is still needed.

[0005] Summary of the Invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems in the prior art. To this end, the present invention provides a negative electrode active material.

[0007] The present invention also provides a negative electrode plate.

[0008] The present invention also provides a method for preparing a negative electrode plate.

[0009] The present invention also provides the use of the negative electrode active material or the negative electrode plate in a secondary battery, a battery module, a battery pack or an electrical device.

[0010] The first aspect of the present invention provides a negative electrode active material, including a graphite material, wherein the graphite material includes graphite 1 and graphite 2, the powder compaction pressure relief rebound rate v of graphite 1 and graphite 2 is 5% to 12%, the ratio c of the number distribution particle size Dn10 of graphite 1 and graphite 2 is 1.2 to 3.5, the particle size distribution width of graphite 1 and graphite 2 satisfies 0.5 to 2.0, the Dv50 particle size d1 of graphite 1 is 10 μm to 15 μm, and the Dv50 particle size d2 of graphite 2 is 5 μm to 10 μm.

[0011] One of the technical solutions of the present invention regarding the negative electrode active material has at least the following beneficial effects:

[0012] The present invention selects two types of graphite with certain pressure relief rebound rates, controls the Dn10 range, and limits the distribution width, thereby achieving a high particle packing density and compaction level for the negative electrode plate. This ensures good electrical contact between the negative electrode active materials and sufficient electrolyte infiltration, thereby improving high-temperature cycle life while balancing charging capacity and energy density. Specifically:

[0013] First, powder compaction pressure relief rebound is positively correlated with electrode roll rebound; a lower pressure relief rebound rate indicates lower electrode roll rebound. However, the pressure relief rebound cannot be too small. Limiting the pressure relief rebound range can alleviate the effect of core tension on electrolyte extrusion at corners, effectively improving the electrolyte's ability to penetrate perpendicular to the electrode at the corner arc. Limiting the range and designing according to the formula relationship between specific surface area and particle size can effectively improve the problem of lithium deposition at corners. The three factors work together to satisfy the above relationship and solve the problem of lithium deposition at corners.

[0014] Secondly, Dn10 can more accurately reflect the content of fine particles in the powder particles. Controlling the Dn10 ratio of the two graphites can control the filling rate of the gaps between the graphite particles and increase the packing density.

[0015] Thirdly, controlling the width of the particle size distribution can control the fine powder content. If it is too narrow, there will be fewer fine particles, which is not conducive to small particles filling the pores; if it is too large, there will be more fine particles, which will consume more electrolyte, cause more side reactions, and worsen the high-temperature cycle.

[0016] Fourthly, particle size (Dv50) is strongly correlated with the lithium-ion transport pathway; smaller particles facilitate lithium insertion. It is also related to the specific capacity of graphite. Controlling the Dv50 of graphite 1 and 2 can control the negative electrode's charge capacity. Larger particle sizes increase specific capacity and, consequently, energy density.

[0017] The present invention selects two types of graphite with certain pressure relief rebound rates, controls the Dn10 range, and limits the distribution width to achieve a high particle packing density and high compaction level for the negative electrode plate, ensuring good electrical contact between the negative electrode active materials.

[0018] In addition, the pressure relief rebound range is limited, and the effect of the buffer core tension on the electrolyte extrusion at the corner is buffered, effectively improving the electrolyte's penetration ability perpendicular to the electrode at the corner arc.

[0019] The specific surface area range is limited so that the electrolyte has sufficient infiltration area to improve the electrolyte penetration effect and weaken the side reaction problems caused by too large a specific surface area, while taking into account high temperature stability and initial effect.

[0020] Limiting the particle size range of active materials further ensures the ion diffusion dynamics at the corners, reduces concentration polarization and electrochemical polarization, effectively reduces the risk of lithium plating at the corners, and takes into account the charging capacity and energy density levels while ensuring high-temperature cycle life.

[0021] According to some embodiments of the present invention, the graphite material includes at least one of artificial graphite and natural graphite.

[0022] According to some embodiments of the present invention, the specific surface area s of the negative electrode active material is 1.0 m 2 / g~2.0m 2 / g.

[0023] According to some embodiments of the present invention, the compression-release rebound rate of the powders of graphite 1 and graphite 2 is 5% to 8%.

[0024] According to some embodiments of the present invention, the particle size distribution width of the graphite 1 and the graphite 2 satisfies 0.5 to 1.5.

[0025] According to some embodiments of the present invention, the mass ratio of the graphite 2 in the negative electrode active material is 5% to 40%.

[0026] According to some embodiments of the present invention, the mass ratio of the graphite 1 to the graphite 2 is 1 to 5:1.

[0027] According to some embodiments of the present invention, the specific surface area s of the negative electrode active material, the powder compaction pressure release rebound rate v and the Dv50 particle size d1 of graphite 1 satisfy the relationship: s-0.02×d1≤30v.

[0028] According to some embodiments of the present invention, the method for preparing the graphite material comprises the following steps:

[0029] (1) mixing a graphite precursor and asphalt, heating and keeping the mixture warm to obtain a granulated semi-finished product;

[0030] (2) Graphitizing the product of step (1) to obtain the graphite material.

[0031] According to some embodiments of the present invention, the mass ratio of the graphite precursor to the pitch is 7-9:1-2.

[0032] According to some embodiments of the present invention, the heating and heat preservation temperature is 250°C to 550°C.

[0033] According to some embodiments of the present invention, the heating and heat preservation time is 5 hours to 48 hours.

[0034] According to some embodiments of the present invention, the temperature of the graphitization treatment is 2800°C to 3500°C.

[0035] According to some embodiments of the present invention, the graphitization treatment time is 10 hours to 200 hours.

[0036] According to some embodiments of the present invention, the graphite precursor includes petroleum coke or needle coke.

[0037] By selecting asphalt as the coating agent, the residual carbon content of the coating layer after coating carbonization can be controlled to be 5% to 15%.

[0038] A second aspect of the present invention provides a negative electrode plate, the raw materials for preparing the negative electrode plate include the negative electrode active material of the present invention.

[0039] One of the technical solutions for the negative electrode sheet of the present invention has at least the following beneficial effects:

[0040] The negative electrode plate of the present invention, due to the use of the negative electrode active material of the present invention, possesses all the beneficial effects of the negative electrode active material. It can have a high particle packing density and plate compaction level, which can not only ensure good electrical contact between the negative electrode active materials, but also ensure sufficient electrolyte infiltration, solve the problem of lithium deposition in corners, and improve high-temperature cycle life while balancing charging capacity and energy density.

[0041] According to some embodiments of the present invention, the raw materials for preparing the negative electrode sheet further include a binder and a dispersant.

[0042] According to some embodiments of the present invention, the binder comprises styrene-butadiene rubber.

[0043] According to some embodiments of the invention, the dispersant comprises sodium carboxymethylcellulose.

[0044] The third aspect of the present invention provides a method for preparing the negative electrode plate of the present invention, comprising the following steps: mixing the negative electrode active material of the present invention with a binder and a dispersant to form a negative electrode slurry, coating the slurry on a negative electrode collector, and drying the slurry to obtain the negative electrode plate.

[0045] A technical solution of the present invention in a method for preparing a negative electrode sheet has at least the following beneficial effects:

[0046] The preparation method of the present invention does not require expensive equipment and complicated process control, has undemanding reaction conditions, has readily available raw materials, has low production costs, and is easy to industrialize.

[0047] A fourth aspect of the present invention provides use of the negative electrode active material or negative electrode plate of the present invention in a secondary battery, a battery module, a battery pack or an electrical device.

[0048] The present invention relates to a technical solution for the application of negative electrode active materials or negative electrode sheets in secondary batteries, battery modules, battery packs, or electrical devices, which has at least the following beneficial effects:

[0049] The negative electrode active material or negative electrode plate of the present invention, due to the use of the negative electrode active material of the present invention, has all the beneficial effects of the negative electrode active material. The negative electrode plate can have a high particle packing density and plate compaction level, which can not only ensure good electrical contact between the negative electrode active materials, but also ensure sufficient electrolyte infiltration, solve the problem of lithium deposition in corners, and improve high-temperature cycle life while taking into account the charging capacity and energy density level. Specifically:

[0050] For secondary batteries, higher particle packing density and electrode compaction levels can increase the loading of negative electrode active materials, improve the battery's energy density, and thus extend battery life. Good electrical contact can enhance electronic conductivity, reduce resistance loss, and increase battery charging speed and efficiency. A higher electrode compaction level can enhance the contact between the negative electrode active material and the electrolyte, allowing the electrolyte to more fully penetrate the negative electrode active material, reducing the interfacial impedance between the electrolyte and the negative electrode active material, and improving the battery's high-temperature cycle life.

[0051] For battery modules, higher particle packing density and electrode compaction levels can increase the loading capacity of negative electrode active materials, thereby improving the module's energy density, allowing the module to accommodate more charge and store more energy within a limited space. Good electrical contact can reduce internal resistance and improve current transmission capacity, allowing the battery module to output high power more quickly.

[0052] For battery packs, it can enhance battery pack safety. Higher particle packing density and electrode compaction levels can reduce voids within the battery, limiting the formation of lithium dendrites, thereby reducing the risk of internal short circuits and improving battery pack safety. Higher electrode compaction levels can also reduce the interfacial impedance between the negative electrode active material and the electrolyte, improving the battery pack's charge transfer efficiency and extending the battery's cycle life.

[0053] For electrical devices, this can increase their endurance. Higher energy density can provide larger batteries, extending their battery life and meeting the needs of long-term use. It can also improve the performance and stability of electrical devices. Good electrical contact and fully infiltrated electrolytes can enhance battery efficiency, reduce energy loss, and enhance the overall performance and stability of electrical devices.

[0054] Therefore, the secondary battery, battery module, battery pack or electrical device using the negative electrode active material or negative electrode sheet of the present invention can have better performance in terms of energy density, charging capacity, high temperature cycle life, power output, safety and cycle life. DETAILED DESCRIPTION

[0055] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0056] In some embodiments of the present invention, a negative electrode active material is provided, including a graphite material, the graphite material including graphite 1 and graphite 2, the powder compaction pressure relief rebound rate of graphite 1 and graphite 2 is 5% to 12%, the ratio c of the number distribution particle size Dn10 of graphite 1 and graphite 2 is 1.2 to 3.5, the particle size distribution width of graphite 1 and graphite 2 satisfies 0.5 to 2.0, the particle size Dv50 of graphite 1 is 10 μm to 15 μm, and the particle size Dv50 of graphite 2 is 5 μm to 10 μm.

[0057] It should be noted that Dn10 represents the particle size corresponding to when the cumulative percentage reaches 10%, that is, the number of particles with a particle size smaller than the particle size corresponding to Dn10 accounts for 10% of the total number of all particles, which can more accurately and intuitively reflect the content of fine particles.

[0058] Dv50 refers to the particle size corresponding to when the cumulative volume percentage of the negative electrode active material reaches 50%, that is, the median particle size of the volume distribution.

[0059] Particle size distribution width: expressed as (Dn90-Dn10) / Dn50.

[0060] It can be understood that the present invention selects two types of graphite with certain pressure relief rebound rates, controls the Dn10 range, and limits the distribution width to achieve a combination. This allows the negative electrode plate to have a high particle packing density and plate compaction level, ensuring both good electrical contact between the negative electrode active materials and sufficient electrolyte infiltration, thereby improving high-temperature cycle life while balancing charging capacity and energy density.

[0061] First, powder compaction pressure rebound is positively correlated with electrode roll rebound; a lower pressure rebound rate indicates lower electrode roll rebound. However, the pressure rebound cannot be too small. Limiting the pressure rebound range can alleviate the effect of core tension on electrolyte extrusion at corners, effectively improving electrolyte penetration perpendicular to the electrode at the corner arc. Limiting the range and designing according to the formula relationship between specific surface area and particle size can effectively improve the problem of lithium deposition at corners. The three factors work together to meet the above relationship to solve the problem of lithium deposition at corners.

[0062] Secondly, Dn10 can more accurately reflect the content of fine particles in the powder particles. Controlling the Dn10 ratio of the two graphites can control the filling rate of the gaps between the graphite particles and increase the packing density.

[0063] Thirdly, controlling the width of the particle size distribution can control the fine powder content. If it is too narrow, there will be fewer fine particles, which is not conducive to small particles filling the pores; if it is too large, there will be more fine particles, which will consume more electrolyte, cause more side reactions, and worsen the high-temperature cycle.

[0064] Fourthly, particle size (Dv50) is strongly correlated with the lithium-ion transport pathway; smaller particles facilitate lithium insertion. It is also related to the specific capacity of graphite. Controlling the Dv50 of graphite 1 and 2 can control the negative electrode's charge capacity. Larger particle sizes increase specific capacity and, consequently, energy density.

[0065] It should be noted that the present invention selects two types of graphite with certain pressure relief rebound rates, controls the Dn10 range, and limits the distribution width to achieve a high particle packing density and high compaction level for the negative electrode plate, ensuring good electrical contact between the negative electrode active materials.

[0066] In addition, the pressure relief rebound range is limited, and the effect of the buffer core tension on the electrolyte extrusion at the corner is buffered, effectively improving the electrolyte's penetration ability perpendicular to the electrode at the corner arc.

[0067] The specific surface area range is limited so that the electrolyte has sufficient infiltration area to improve the electrolyte penetration effect and weaken the side reaction problems caused by too large a specific surface area, while taking into account high temperature stability and initial effect.

[0068] Limiting the particle size range of active materials further ensures the ion diffusion dynamics at the corners, reduces concentration polarization and electrochemical polarization, effectively reduces the risk of lithium plating at the corners, and takes into account the charging capacity and energy density levels while ensuring high-temperature cycle life.

[0069] The specific surface area s of the active material, the powder compaction pressure relief rebound rate v and the Dv50 particle size d1 of graphite 1 satisfy the relationship: s-0.02×d1≤30v. The three work together to solve the problem of lithium deposition in corners.

[0070] In some embodiments of the present invention, the graphite material includes at least one of artificial graphite and natural graphite.

[0071] In some embodiments of the present invention, the specific surface area s of the negative electrode active material is 1.0 m 2 / g~2.0m 2 / g.

[0072] In some embodiments of the present invention, the compression-release rebound rate of the powders of Graphite 1 and Graphite 2 is 5% to 8%.

[0073] In some embodiments of the present invention, the particle size distribution width of the first graphite and the second graphite satisfies 0.5 to 1.5.

[0074] In some embodiments of the present invention, the mass ratio of graphite II in the negative electrode active material is 5% to 40%.

[0075] In some embodiments of the present invention, the mass ratio of graphite 1 to graphite 2 is 1 to 5:1.

[0076] In some embodiments of the present invention, the specific surface area s of the negative electrode active material, the powder compaction pressure release rebound rate v, and the Dv50 particle size d1 of graphite 1 satisfy the following relationship: s-0.02×d1≤30v.

[0077] In some embodiments of the present invention, the method for preparing the graphite material comprises the following steps:

[0078] (1) mixing a graphite precursor and asphalt, heating and keeping the mixture warm to obtain a granulated semi-finished product;

[0079] (2) Graphitizing the product of step (1) to obtain the graphite material.

[0080] In some embodiments of the present invention, the mass ratio of the graphite precursor to the pitch is 7-9:1-2.

[0081] In some embodiments of the present invention, the heating and insulation temperature is 250°C to 550°C.

[0082] In some embodiments of the present invention, the heating and heat preservation time is 5 hours to 48 hours.

[0083] In some embodiments of the present invention, the temperature of the graphitization treatment is 2800°C to 3500°C.

[0084] In some embodiments of the present invention, the graphitization treatment time is 10 hours to 200 hours.

[0085] In some embodiments of the present invention, the graphite precursor includes petroleum coke or needle coke.

[0086] It should be noted that, by selecting asphalt as the coating agent, the residual carbon content of the coating layer after coating and carbonization can be controlled to be 5% to 15%.

[0087] In some other embodiments of the present invention, a negative electrode plate is provided, and the raw materials for preparing the negative electrode plate include the negative electrode active material of the present invention.

[0088] It can be understood that the negative electrode plate of the present invention, due to the use of the negative electrode active material of the present invention, possesses all the beneficial effects of the negative electrode active material. The negative electrode plate can have a high particle packing density and plate compaction level, which can not only ensure good electrical contact between the negative electrode active materials, but also ensure sufficient electrolyte infiltration, solve the problem of lithium deposition in corners, and improve high-temperature cycle life while taking into account the charging capacity and energy density levels.

[0089] In some embodiments of the present invention, the raw materials for preparing the negative electrode sheet further include a binder and a dispersant.

[0090] In some embodiments of the present invention, the binder comprises styrene-butadiene rubber.

[0091] In some embodiments of the present invention, the dispersant comprises sodium carboxymethylcellulose.

[0092] In some other embodiments of the present invention, a method for preparing the negative electrode sheet of the present invention is provided, comprising the following steps: mixing the negative electrode active material of the present invention with a binder and a dispersant to form a negative electrode slurry, coating the slurry on a negative electrode current collector, and drying the slurry to obtain a negative electrode sheet.

[0093] It can be understood that the preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are easily available, the production cost is low, and it is easy to industrialize.

[0094] In some other embodiments of the present invention, there is provided use of the negative electrode active material or negative electrode plate of the present invention in a secondary battery, a battery module, a battery pack or an electrical device.

[0095] It can be understood that the negative electrode active material or negative electrode plate of the present invention, due to the use of the negative electrode active material of the present invention, has all the beneficial effects of the negative electrode active material. The negative electrode plate can have a high particle packing density and plate compaction level, which can not only ensure good electrical contact between the negative electrode active materials, but also ensure sufficient infiltration of the electrolyte, solve the problem of lithium deposition in corners, and improve the high-temperature cycle life while taking into account the charging capacity and energy density level. Specifically:

[0096] For secondary batteries, higher particle packing density and electrode compaction levels can increase the loading of negative electrode active materials, improve the battery's energy density, and thus extend battery life. Good electrical contact can enhance electronic conductivity, reduce resistance loss, and increase battery charging speed and efficiency. A higher electrode compaction level can enhance the contact between the negative electrode active material and the electrolyte, allowing the electrolyte to more fully penetrate the negative electrode active material, reducing the interfacial impedance between the electrolyte and the negative electrode active material, and improving the battery's high-temperature cycle life.

[0097] For battery modules, higher particle packing density and electrode compaction levels can increase the loading capacity of negative electrode active materials, thereby improving the module's energy density, allowing the module to accommodate more charge and store more energy within a limited space. Good electrical contact can reduce internal resistance and improve current transmission capacity, allowing the battery module to output high power more quickly.

[0098] For battery packs, it can enhance battery pack safety. Higher particle packing density and electrode compaction levels can reduce voids within the battery, limiting the formation of lithium dendrites, thereby reducing the risk of internal short circuits and improving battery pack safety. Higher electrode compaction levels can also reduce the interfacial impedance between the negative electrode active material and the electrolyte, improving the battery pack's charge transfer efficiency and extending the battery's cycle life.

[0099] For electrical devices, this can increase their endurance. Higher energy density can provide larger batteries, extending their battery life and meeting the needs of long-term use. It can also improve the performance and stability of electrical devices. Good electrical contact and fully infiltrated electrolytes can enhance battery efficiency, reduce energy loss, and enhance the overall performance and stability of electrical devices.

[0100] Therefore, the secondary battery, battery module, battery pack or electrical device using the negative electrode active material or negative electrode sheet of the present invention can have better performance in terms of energy density, charging capacity, high temperature cycle life, power output, safety and cycle life.

[0101] The technical solutions of the present invention will be better understood with reference to the specific embodiments and comparative examples below.

[0102] In the examples and comparative examples, graphite was prepared by ourselves. Through the following preparation method, the pressure relief rebound rate can be regulated by controlling the graphitization temperature.

[0103] It should be noted that when the graphitization temperature is high, the graphite growth is complete, the crystallinity is high, the active material is relatively soft, and the pressure relief rebound rate is low. It should also be noted that the residual carbon content corresponds to the coating amount on the surface of the graphite material. The higher the residual carbon content, the larger the coating area and the lower the specific surface area.

[0104] The preparation method of graphite comprises the following steps:

[0105] Use petroleum coke or needle coke as raw material (i.e. graphite precursor);

[0106] The precursor and the binder high-temperature asphalt are mixed uniformly in a certain mass ratio of 7-9:1-2 (the condition in the embodiment is 8:2), and then put into a horizontal kettle together, heated between 250°C and 550°C (the condition in the embodiment is 300°C) and kept warm for 5h to 48h (the condition in the embodiment is 24h) to obtain a granulated semi-finished product;

[0107] After high-temperature graphitization treatment, the graphitization temperature is 2800° C. to 3500° C. (see Table 1 for specific conditions) and the graphitization time is 10 hr to 200 hr (90 hr in the embodiment) to obtain a graphite negative electrode active material.

[0108] Asphalt is selected as the coating agent, and the residual carbon content of the coating layer after coating and carbonization is controlled to be 5% to 15% (see Table 1 for the specific residual carbon content).

[0109] Example 1

[0110] A negative electrode active material contains a graphite material, wherein the graphite material includes graphite 1 and graphite 2.

[0111] The powder compaction pressure relief rebound rate v of Graphite 1 and Graphite 2 is 5%.

[0112] The ratio c of the number distribution particle sizes Dn10 of graphite 1 and graphite 2 is 1.2.

[0113] The particle size distribution width of graphite 1 and graphite 2 is 0.7.

[0114] The Dv50 particle size d1 of the graphite 1 is 10 μm, and the Dv50 particle size d2 of the graphite 2 is 5 μm.

[0115] The specific surface area of ​​the negative electrode active material is 1.2 m 2 / g.

[0116] The specific surface area s of the negative electrode active material, the powder compaction pressure release rebound rate v and the Dv50 particle size d1 of graphite 1 satisfy the relationship: s-0.02×d1≤30v.

[0117] Graphite 1 and graphite 2 are mixed evenly to obtain a negative electrode active material.

[0118] The negative electrode active material, binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose were dissolved in deionized water at a weight ratio of 98:1:1. The mixture was thoroughly stirred and mixed to obtain different negative electrode slurries. After drying, the slurries were cold pressed, trimmed, cut, and slit to produce negative electrode sheets for lithium-ion batteries.

[0119] Preparation of positive electrode sheet:

[0120] The positive electrode active material NCM523, the conductive agent acetylene black, and the binder PVDF were mixed in a mass ratio of 97:2:1, and the solvent NMP was added. The mixture was stirred under a vacuum stirrer until the system became uniform to obtain a positive electrode slurry.

[0121] The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. The positive electrode sheets are then obtained by cold pressing and cutting.

[0122] Preparation of electrolyte:

[0123] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0124] Preparation of isolation membrane:

[0125] A polyethylene film is selected as the separator.

[0126] Preparation of lithium-ion batteries:

[0127] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation layer, and then wound to obtain a bare cell;

[0128] The bare battery cell is placed in an outer packaging shell, dried and injected with electrolyte, and then goes through vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.

[0129] Based on Example 1, Examples 2-19 and Comparative Examples 1-9 were designed, as shown in Tables 1-2.

[0130] Table 1

[0131] Table 2

[0132] In Table 1 and Table 2, Dn10 and Dv50 of the negative electrode active materials were measured using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) according to the particle size distribution laser diffraction method GB / T 19077-2016 to obtain Dn10 and Dv50.

[0133] Powder compaction density measurement: A compaction density meter (CARVER, USA) was used according to GB / T 24533-2019, a test method for the compaction of graphite anode materials. The 5T compaction density value PD1 was recorded. After standing for 30 minutes, the powder pressing height was measured again and the compaction density PD2 was calculated. The pressure relief rebound rate v = (PD1-PD2) / PD1.

[0134] The compaction density PD of the coating on the negative electrode sheet: First measure the coating surface density of the negative electrode sheet, then measure the thickness of the negative electrode film with a micrometer (measure at least 10 places and take the average value), according to the compaction density of the coating = the coating surface density of the negative electrode sheet (mg / cm 2 ) / thickness of negative electrode film (cm), and calculate the negative electrode film compaction density PD (unit: mg / cm 3 ), and then convert to g / cm 3 .

[0135] Performance Testing

[0136] Dynamic performance test:

[0137] At 25°C, the lithium-ion batteries prepared in the Examples and Comparative Examples were fully charged at 5C and fully discharged at 1C 50 times, then fully charged at 5C. The negative electrode sheets were then disassembled and the lithium deposition on the negative electrode sheet surfaces was observed. A lithium deposition area of ​​less than 5% on the negative electrode surface was considered mild, a lithium deposition area of ​​5% to 40% on the negative electrode surface was considered moderate, and a lithium deposition area of ​​more than 40% on the negative electrode surface was considered severe.

[0138] High temperature cycle performance test:

[0139] At 45° C., the lithium-ion batteries prepared in the examples and comparative examples were charged at a 4.5C rate and discharged at a 1C rate for full charge and discharge cycle testing until the capacity of the lithium-ion battery was less than 80% of the initial capacity, and the number of cycles was recorded.

[0140] Volume energy density (Wh / L) = battery capacity (mAh) × 3.6 (V) / (thickness (cm) × width (cm) × length (cm)).

[0141] The results are shown in Table 3.

[0142] Table 3

[0143] The negative electrode active material or negative electrode plate of the present invention, due to the use of the negative electrode active material of the present invention, has all the beneficial effects of the negative electrode active material. The negative electrode plate can have a high particle packing density and plate compaction level, which can not only ensure good electrical contact between the negative electrode active materials, but also ensure sufficient infiltration of the electrolyte, thereby improving the high-temperature cycle life while taking into account the charging capacity and energy density level, and also having excellent kinetic performance, solving the problem of lithium deposition in corners. Specifically:

[0144] For secondary batteries, higher particle packing density and electrode compaction levels can increase the loading of negative electrode active materials, improve the battery's energy density, and thus extend battery life. Good electrical contact can enhance electronic conductivity, reduce resistance loss, and increase battery charging speed and efficiency. A higher electrode compaction level can enhance the contact between the negative electrode active material and the electrolyte, allowing the electrolyte to more fully penetrate the negative electrode active material, reducing the interfacial impedance between the electrolyte and the negative electrode active material, and improving the battery's high-temperature cycle life.

[0145] For battery modules, higher particle packing density and electrode compaction levels can increase the loading capacity of negative electrode active materials, thereby improving the module's energy density, allowing the module to accommodate more charge and store more energy within a limited space. Good electrical contact can reduce internal resistance and improve current transmission capacity, allowing the battery module to output high power more quickly.

[0146] For battery packs, it can enhance battery pack safety. Higher particle packing density and electrode compaction levels can reduce voids within the battery, limiting the formation of lithium dendrites, thereby reducing the risk of internal short circuits and improving battery pack safety. Higher electrode compaction levels can also reduce the interfacial impedance between the negative electrode active material and the electrolyte, improving the battery pack's charge transfer efficiency and extending the battery's cycle life.

[0147] For electrical devices, this can increase their endurance. Higher energy density can provide larger batteries, extending their battery life and meeting the needs of long-term use. It can also improve the performance and stability of electrical devices. Good electrical contact and fully infiltrated electrolytes can enhance battery efficiency, reduce energy loss, and enhance the overall performance and stability of electrical devices.

[0148] Therefore, the secondary battery, battery module, battery pack or electrical device using the negative electrode active material or negative electrode sheet of the present invention can have better performance in terms of energy density, charging capacity, high temperature cycle life, power output, safety and cycle life.

[0149] It can be seen from Examples 6 to 9, 13 to 15 and Comparative Examples 1 / 3 that by controlling the two graphites having a pressure relief rebound rate v of 5% to 12%, and matching the Dn10 ratio of the two graphites to meet the range of 1.2 to 3.5 and the particle size distribution width of graphite 1 to meet the range of 0.5 to 2.0, the filling rate of the gaps between the graphite particles can be controlled and the bulk density can be increased. When the range is exceeded, the bulk density is poor and the energy density is low.

[0150] From Examples 1 to 19 and Comparative Examples 2 / 3, it can be seen that when the powder pressure relief rebound rate v is too high, the compaction density is significantly reduced and the energy density is low. When the graphite particle size distribution width is too wide, the fine powder has a significantly poor performance in high temperature cycling and thickness expansion.

[0151] It can be seen from Examples 1 to 19 and Comparative Examples 4 / 7 / 9 that among the specific surface area, pressure relief rebound rate, and graphite particle size, if the particle size is too large or the specific surface area is too small, serious lithium deposition at the corners will occur. It can be seen from Examples 1 and 12 and Comparative Example 9 that increased pressure relief rebound can alleviate lithium deposition at the corners, improve high-temperature cycle performance and inhibit cycle expansion, but solving the problem of lithium deposition at the corners requires the cooperation of specific surface area, pressure relief rebound rate, and graphite particle size. A single factor cannot solve the problem of lithium deposition at the corners. For example, in Comparative Example 9, the pressure relief rebound is very high, which is beneficial to improving the permeability of the electrolyte perpendicular to the electrode at the corner arc. However, the particle size is too large, the lithium ion transmission path is increased, and it still leads to lithium deposition at the corners. In addition, the particle size is too large, the high-temperature cycle performance is significantly reduced, and the thickness expansion is increased.

[0152] It can be seen from Examples 1 to 19 and Comparative Example 8 that even if the specific surface area, pressure relief rebound rate, and graphite Dv50 particle size are within the scope of this application, but do not satisfy the relationship s-0.02×d1≤30v, moderate lithium deposition will still occur in the corner area.

[0153] As can be seen from Examples 1 to 19 and Comparative Examples 1 to 9, the present application selects two types of graphite with a certain pressure relief rebound rate, controls the Dn10 range, and limits the distribution width and particle size to match them. This allows the negative electrode to have a higher particle packing density and a higher level of compaction. Furthermore, by limiting the specific surface area and particle size range, and working in synergy with the pressure relief rebound rate, Dn10, and particle size distribution, good electrical contact between the negative electrode active materials is ensured, thereby taking into account both energy density and high-temperature cycle performance. In addition, by regulating the specific surface area, pressure relief rebound rate, and graphite-Dv50 particle size to satisfy the relationship s-0.02×d1≤30v, the problem of lithium deposition in corners is solved while taking into account charging capacity, energy density, and high-temperature cycle performance.

[0154] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the relevant technical field without departing from the spirit of the present invention.

Claims

1. A negative electrode active material, characterized in that, It includes a graphite material, the graphite material includes Graphite One and Graphite Two, the powder compaction pressure relief rebound rate v of Graphite One and Graphite Two is 5% - 12%, the ratio c of the number distribution particle size Dn10 of Graphite One and Graphite Two is 1.2 - 3.5, the particle size distribution width of Graphite One and Graphite Two satisfies 0.5 - 2.0, the Dv50 particle size d1 of Graphite One is 10μm - 15μm, and the Dv50 particle size d2 of Graphite Two is 5μm - 10μm.

2. The negative electrode active material according to claim 1, characterized in that, The specific surface area s of the negative electrode active material is 1.0 m 2 / g to 2 m 2 / g.

3. The negative electrode active material according to claim 1, characterized in that, The powder compaction pressure relief rebound rate v of Graphite One and Graphite Two is 5% - 8%.

4. The negative electrode active material according to claim 1, characterized in that, The particle size distribution width of Graphite One and Graphite Two satisfies 0.5 - 1.

5.

5. The negative electrode active material according to claim 1, characterized in that, The mass ratio of Graphite Two in the negative electrode active material is 5% - 40%.

6. The negative electrode active material according to claim 1, wherein The mass ratio of Graphite One and Graphite Two is 1 - 5:

1.

7. The negative electrode active material according to any one of claims 1 to 6, characterized in that, There is a relationship between the specific surface area s, the powder compaction pressure relief rebound rate v of the negative electrode active material and the Dv50 particle size d1 of Graphite One: s - 0.02×d1 ≤ 30v.

8. The negative electrode active material according to any one of claims 1 to 6, characterized in that, The preparation method of the graphite material includes the following steps: (1) Mix a graphite precursor and pitch and heat for heat preservation to obtain a granulation semi-finished product; (2) Graphitize the product of step (1) to obtain the graphite material.

9. The negative electrode active material according to claim 8, characterized in that, The temperature of the graphitization treatment is 2800°C - 3500°C; and / or, the time of the graphitization treatment is 10h - 200h.

10. A negative electrode plate, characterized in that, The preparation raw materials include the negative electrode active material according to any one of claims 1 to 9.

11. A method for preparing the negative electrode sheet as described in claim 10, characterized in that, It includes the following steps: After mixing the negative electrode active material according to any one of claims 1 to 7 with a binder and a dispersant to make a negative electrode slurry, coat it on a negative electrode current collector, and dry to obtain the negative electrode plate.

12. Application of a negative electrode active material according to any one of claims 1 to 9 or a negative electrode plate according to claim 10 in a secondary battery, a battery module, a battery pack or an electrical device.

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