Negative electrode material, negative electrode plate and battery

Abstract

The invention provides a negative electrode material, a negative plate and a battery, the negative electrode material comprises a carbon matrix and an active substance, the carbon matrix has holes, the active substance is at least partially distributed in the holes, the area proportion alpha of the holes with the aperture greater than 50nm in any cross section of the negative electrode material is less than or equal to 10%; wherein alpha is obtained by the following test method: the sum of the cross-sectional areas of pores with the pore diameter of more than 50nm in the region of the cross section of the single negative electrode material particle is recorded as S0, and the cross-sectional area of the single negative electrode material particle in the region is recorded as S, the area ratio of pores with the pore diameter larger than 50 nm in the cross section of a single negative electrode material particle is defined as alpha ', alpha' = S0 / S, alpha is the arithmetic average of alpha 'values of at least 10 negative electrode material particles, and the problems that in the prior art, the first efficiency is low, the volume expansion rate is large, and the cycle performance and the processing performance are poor are solved.

Description

[0001] This application claims the priority of Chinese patent application No. 202410020730.1, filed on February 6, 2024. This application cites the entire text of the above Chinese patent application. Technical Field

[0002] The present invention relates to the technical field of new energy materials, and in particular to a negative electrode material, a negative electrode sheet and a battery. Background Art

[0003] Lithium-ion batteries have the advantages of high energy density, long service life and no environmental pollution, and have been widely used in the 3C field. With the development of the market, lithium-ion batteries are not only widely used in mobile devices such as smart phones and portable computers, but also in large equipment such as electric vehicles and power tools. In order to improve the energy density of batteries, silicon-based negative electrode materials have the advantages of low voltage platform, environmental friendliness and abundant resources, and are one of the most promising materials for realizing high-capacity lithium-ion batteries. However, the existing ordinary silicon-based materials have large volume expansion during charging and discharging, which easily leads to particle pulverization and then falls off the current collector. In addition, the repeated changes in the volume of silicon-based active materials during the electrochemical cycle also lead to the continuous destruction and regeneration of the SEI film formed on the surface of the silicon-based active material, resulting in continuous consumption of lithium ions, affecting its stability, and the battery capacity will drop rapidly during the long cycle. Therefore, in order to improve the user experience and improve the stability of silicon-based lithium-ion batteries, it is necessary to provide a low-expansion, high-capacity silicon-based negative electrode material.

[0004] In the prior art, by compounding metals, oxides, organic polymers, carbon and other materials with silicon, its volume change is alleviated and the electrochemical stability is improved. Among them, carbon materials have excellent electrical conductivity and mechanical properties. Compounding with silicon can not only effectively alleviate volume expansion, but also improve electrode conductivity and obtain a stable SEI film. Silicon-carbon composite materials are the first silicon-based negative electrode materials to enter commercialization. At present, the preparation of silicon-carbon composite negative electrode materials mainly includes two technical routes. One is to grind silicon powder to nanoscale (about 80-100nm), then compound with carbon source precursor, and further coat to form silicon-carbon negative electrode materials. Since the size of nano-silicon used in this method is still relatively large, it is difficult to effectively solve the huge volume expansion problem during the lithium extraction process of silicon. The second is to first prepare a porous carbon material skeleton, and then deposit nano-silicon (<10nm) by silane deposition. The silicon-carbon composite material prepared in this way can effectively alleviate the volume expansion problem during the lithium extraction process due to the small size of nano-silicon, which is a hot research method at present. At present, the preparation of porous carbon by biomass method is an important direction, but the porous carbon prepared from biomass usually has macropores with relatively large diameters. The large number of macropores affects the compaction performance of the porous carbon, making the prepared negative electrode material unable to meet the demand of high compaction. Moreover, the macropores in the porous carbon are generated during the natural growth process and are difficult to completely remove, resulting in low initial efficiency of the negative electrode material, large volume expansion rate, and poor cycle performance and processing performance. Summary of the invention

[0005] The main purpose of the present invention is to provide a negative electrode material, a negative electrode sheet and a battery to solve the problems of low initial efficiency, large volume expansion rate, poor cycle performance and processing performance of negative electrode materials in the prior art.

[0006] In order to achieve the above object, according to one aspect of the present invention, there is provided a negative electrode material, comprising a carbon matrix and an active substance, wherein the carbon matrix has pores, the active substance is at least partially distributed in the pores, and the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material is α, satisfying: α≤10%;

[0007] Wherein, α is obtained by the following test method: in the figure shown by SEM section processing of a single negative electrode material particle, select any A×B area, wherein A=1μm~10μm, B=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic average of the α' values ​​of at least 10 negative electrode material particles.

[0008] Furthermore, the oil absorption value dbq2 of the carbon matrix satisfies: 120ml / 100g≤dbq2≤200ml / 100g; the oil absorption value dpq1 of the negative electrode material satisfies: 30ml / 100g≤dpq1≤80ml / 100g, and (dbq2-dbq1) / dbq1>0.5.

[0009] Furthermore, the specific surface area of ​​the carbon matrix is ​​S1 m 2 / g, the pore volume of the carbon matrix is ​​P1 cm 3 / g, the specific surface area of ​​the negative electrode material is S2 m 2 / g, the pore volume of the negative electrode material is P2 cm 3 / g; S1, P1, S2, P2 satisfy the following relationship:

[0010] C1 = S1 / (P1*100);

[0011] 10≤C1≤25;

[0012] C2 = S2 / (P2*100);

[0013] 1≤C2≤50.

[0014] Furthermore, the specific surface area of ​​the carbon matrix is ​​500 m 2 / g to 2500m 2 / g.

[0015] Furthermore, the pore volume of the carbon matrix is ​​0.3 cm 3 / g to 2cm 3 / g.

[0016] Furthermore, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g to 10m 2 / g.

[0017] Furthermore, the pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1cm 3 / g.

[0018] Furthermore, the pore volume of the negative electrode material is smaller than that of the carbon matrix.

[0019] Furthermore, the ratio of the volume of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is A; the ratio of the volume of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is B; wherein, 1≤A≤1.9, 1.3≤B≤2.5, and B / A≥1.

[0020] Furthermore, the pores in the carbon matrix include micropores, the volume proportion of the micropores in the total pore volume is greater than or equal to 70%, and the pore diameter of the micropores is less than or equal to 2 nm.

[0021] Furthermore, the average particle size of the active material is 0.1 nm to 50 nm.

[0022] Furthermore, the average pore size of the negative electrode material is 0.45 nm to 50 nm.

[0023] Furthermore, the pores of the negative electrode material include micropores, the volume proportion of the micropores in the pores is less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm.

[0024] Furthermore, the pores of the negative electrode material include mesopores, the volume proportion of the mesopores in the pores is greater than or equal to 80%, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm.

[0025] Furthermore, the pores of the negative electrode material include macropores, the volume proportion of the macropores in the pores is less than or equal to 20%, and the pore diameter of the macropores is greater than 50 nm.

[0026] Furthermore, the particle size D50 of the negative electrode material is 5 μm to 20 μm.

[0027] Furthermore, the particle size distribution of the negative electrode material is (D90-D10) / D50 is 0.9 to 5.

[0028] Furthermore, the compaction density of the negative electrode material at 1T pressure is 0.8g / cm 3 Up to 1.3g / cm 3 .

[0029] Furthermore, the tap density of the negative electrode material after 3000 vibrations is 0.5 g / cm 3 Up to 1.5g / cm 3 .

[0030] Furthermore, the active material includes a single substance and / or a compound of at least one element selected from Si, Sn, Ge, Pb, Ag, Mg, Zn, Ga, In, Sb, and Bi.

[0031] Further, the carbon matrix includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers and graphene.

[0032] Furthermore, the negative electrode material also includes a coating layer, which is disposed on at least a portion of the surface of the carbon matrix, and the coating layer includes a carbon material, and the carbon material includes at least one of graphene, soft carbon and hard carbon.

[0033] Further, the active material includes a silicon-based material, and the silicon-based material includes at least one of amorphous silicon, crystalline silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, and silicon alloy.

[0034] Furthermore, the powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm.

[0035] Furthermore, the average gas production of the negative electrode material at 25° C. over 7 days is less than or equal to 1 mL / g.

[0036] Furthermore, the mass proportion of carbon element in the negative electrode material is 40% to 60%.

[0037] Furthermore, the mass proportion of silicon in the negative electrode material is 37% to 55%.

[0038] According to another aspect of the present invention, a negative electrode sheet is provided, and the negative electrode sheet comprises the negative electrode material as above.

[0039] According to another aspect of the present invention, a battery is provided, comprising a negative electrode, wherein the electrode sheet used for the negative electrode is the negative electrode sheet as described above.

[0040] Applying the technical solution of the present invention, the negative electrode material includes a carbon matrix and an active substance distributed in the pores of the carbon matrix. The carbon matrix has pores, which is conducive to providing more active substance deposition sites, so that the active substance can be deposited at least in the pores of the carbon matrix. At the same time, the porous skeleton of the carbon matrix can form a conductive network, which is conducive to the electron transmission during the charging and discharging process, thereby reducing the polarization of the battery material and improving the conductivity and cycle stability. In addition, the proportion of macropores in the negative electrode material is relatively small. When used as a negative electrode material, the occurrence of side reactions between the negative electrode material and the electrolyte can be reduced during the first charging and discharging process, reducing gas production, and improving the first efficiency, expansion performance and cycle performance of the negative electrode material. Finally, the small proportion of macropores in the negative electrode material can improve the tap density and compaction density of the negative electrode material, reduce the problems of breakage and cracking of the negative electrode material during the roller pressing process when the negative electrode material is made into a pole piece, and improve the processing performance of the negative electrode material. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0042] As described in the background technology, the prior art has problems such as low initial efficiency, large volume expansion rate, poor cycle performance and processing performance. In order to solve the above problems, the present invention provides a negative electrode material, including a carbon matrix and an active substance, the carbon matrix has pores, and the active substance is at least partially distributed in the pores. The area of ​​pores with a pore diameter greater than 50 nm in any cross-section of the negative electrode material accounts for α, satisfying: α≤10%.

[0043] Among them, α is obtained by the following test method: in the figure shown by SEM section processing of a single negative electrode material particle, select any A×B area, where A=1μm~10μm, B=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic mean of the α' values ​​of at least 10 negative electrode material particles.

[0044] The negative electrode material provided by the present invention includes a carbon matrix and an active substance distributed in the pores of the carbon matrix. The carbon matrix has pores, which is conducive to providing more active substance deposition sites, so that the active substance can be deposited at least in the pores of the carbon matrix. At the same time, the porous skeleton of the carbon matrix can form a conductive network, which is conducive to the electron transmission during the charging and discharging process, thereby reducing the polarization of the battery material and improving the conductivity and cycle stability. In addition, the proportion of macropores in the negative electrode material is relatively small. When used as a negative electrode material, the occurrence of side reactions between the negative electrode material and the electrolyte can be reduced during the first charging and discharging process, reducing gas production, and improving the first efficiency, expansion performance and cycle performance of the negative electrode material. Finally, the small proportion of macropores in the negative electrode material can improve the tap density and compaction density of the negative electrode material, reduce the problems of breakage and cracking of the negative electrode material during the roller pressing process, and improve the processing performance of the negative electrode material.

[0045] In some embodiments, the oil absorption value dbq2 of the carbon matrix satisfies: 120ml / 100g≤dbq2≤200ml / 100g; the oil absorption value dpq1 of the negative electrode material satisfies: 30ml / 100g≤dpq1≤80ml / 100g, and (dbq2-dbq1) / dbq1>0.5. The negative electrode material having the above-mentioned specific carbon matrix oil absorption value, negative electrode material oil absorption value, oil absorption value difference and small macropore area ratio, its active material mainly enters the carbon matrix and is mainly deposited in the pores. On the one hand, more active substances enter the pores of the carbon matrix, so that the material has a higher energy density and can also reduce the direct contact between the active substances and the electrolyte, reduce the occurrence of adverse side reactions, and improve the cycle performance of the negative electrode material; on the other hand, the active substances are deposited in the carbon matrix, so that the active substances are not easy to agglomerate, which can reduce the volume expansion of the negative electrode material, and the negative electrode material after the active substances are deposited still has a rich pore structure to accommodate oil absorption, which can further reduce the volume expansion of the negative electrode material.

[0046] For negative electrode materials, pore volume and specific surface area affect their conductivity and the occurrence of side reactions. The larger the pore volume of the negative electrode material and the more pores in the material, the worse the conductivity of the material. The larger the specific surface area, the greater the surface energy of the material, and the more side reactions it will have. In some embodiments, the specific surface area of ​​the carbon matrix is ​​S1 m 2 / g, the pore volume of the carbon matrix is ​​P1cm 3 / g, the specific surface area of ​​the negative electrode material is S2 m 2 / g, the pore volume of the negative electrode material is P2cm 3 / g; S1, P1, S2, P2 satisfy the following relationship: C1 = S1 / (P1*100); 10≤C1≤25; C2 = S2 / (P2*100); 1≤C2≤50. In order to allow the negative electrode material to have sufficient buffer space to alleviate the volume expansion during charging and discharging, and to reduce the occurrence of side reactions between the negative electrode material and the electrolyte during charging and discharging, the specific surface area and pore volume of the negative electrode material are limited as above, and the specific surface area and pore volume of the carbon matrix are limited to obtain a carbon matrix skeleton with both high pore volume and high structural strength, so as to facilitate the subsequent deposition of active materials and ensure that the final negative electrode material has sufficient buffer space.

[0047] In some embodiments, the specific surface area of ​​the carbon matrix is ​​500 m 2 / g to 2500m 2 / g, specifically 500m 2 / g、700m 2 / g、900m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g, 2000m 2 / g, 2200m 2 / g, 2500m 2 / g or any value within the range formed by any two of the above values, which is not limited here. The matrix with a specific surface area within the above range has a higher site for accommodating active substances for subsequent deposition of active substances.

[0048] In some embodiments, the pore volume of the carbon matrix is ​​0.3 cm 3 / g to 2cm 3 / g, the specific pore volume can be 0.3cm 3 / g, 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 2cm 3 / g or any value within the range formed by any two of the above values. The carbon matrix with a pore volume within the above range has abundant pores, which can accommodate the active material and reserve space for the volume expansion of the active material.

[0049] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g to 10m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g or any value within the range formed by any two of the above values. When the specific surface area of ​​the negative electrode material is large, the SEI film will consume excessive lithium salts, and the volume effect will easily cause electrical separation between particles, resulting in reduced reversible capacity and coulombic efficiency of the battery. In this embodiment, under the limited specific surface area range, the capacity of the first discharge ratio and the first coulombic efficiency of the battery can be more effectively improved.

[0050] In some embodiments, the pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1cm 3 / g. For example, the pore volume of the negative electrode material can be 0.001cm 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.03cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g or any value within the range formed by any two of the above values. After the active material is filled in the pores of the carbon matrix, the remaining pores in the carbon matrix can reserve space for the volume expansion of the active material, alleviate the expansion effect of the negative electrode material, and improve the cycle stability of the negative electrode material. The remaining pores in the carbon matrix can also adsorb or accommodate a small amount of gas produced by the reaction of part of the active material with the electrolyte or pulping, thereby improving the gas production of the negative electrode material. Under the pore volume defined in this embodiment, the cycle stability of the negative electrode material can be better improved and the gas production of the negative electrode material can be improved.

[0051] In some embodiments, the pore volume of the negative electrode material is smaller than the pore volume of the carbon matrix. The total pore volume of the negative electrode material is significantly lower than the total pore volume of the carbon matrix, and the active material can be relatively evenly filled in the pores inside the porous skeleton of the carbon matrix, so that most of the pores of the carbon matrix are reduced in pore volume after being filled with the active material, so that the pores of the carbon matrix are effectively and relatively evenly filled with the active material, thereby improving the specific capacity of the negative electrode material.

[0052] In some embodiments, the ratio of the volume of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is A; the ratio of the volume of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is B; wherein, 1≤A≤1.9, 1.3≤B≤2.5, and B / A≥1, the carbon matrix with A value within the above range and the negative electrode material with B value within the above range, the carbon matrix has a higher micropore ratio to facilitate the deposition of active substances, and the negative electrode material after the deposition of active substances has a smaller micropore ratio in order to obtain a negative electrode material with a higher specific capacity.

[0053] In some embodiments, the pores in the carbon matrix include micropores, the volume proportion of the micropores in the total pore volume is greater than or equal to 70%, and the pore size of the micropores is less than or equal to 2nm. For example, the volume proportion of the micropores can be 70%, 75%, 80%, 85%, 90%, 95%, 99% or any value within the range formed by any two of the above values.

[0054] In some specific embodiments, the carbon matrix obtained after etching the negative electrode material (after etching away the silicon material in the negative electrode material) is tested to obtain the volume ratio of the micropores of the carbon matrix in the total pore volume. The micropore ratio of the negative electrode material after etching is controlled within the above range, which can reduce the aggregation of the active material on the surface of the carbon matrix during the deposition process, increase the content of the active material in the carbon matrix and the uniformity of the distribution of the active material, and thus improve the specific capacity and mechanical properties of the negative electrode material. The specific method for etching the negative electrode material can be: adding a 1M nitric acid solution to the negative electrode material and soaking it for 4 hours, and then dripping a 20% mass fraction HF acid solution into the negative electrode material drop by drop, which will produce yellow smoke, and repeatedly dripping until no yellow smoke is produced in the solution; finally, using a 1M nitric acid solution to digest the residue, and then washing and drying, to obtain the negative electrode material after removing the silicon particles, that is, the carbon matrix.

[0055] In some specific embodiments, the pore volume of the carbon matrix obtained after etching the negative electrode material (i.e., after etching away the silicon material in the negative electrode material) is 0.3 cm 3 / g to 2cm 3 / g. For example, the pore volume of the carbon matrix obtained after etching the negative electrode material can be 0.3cm 3 / g, 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 2cm 3 / g or any value within the range formed by any two of the above values. When the negative electrode material is etched (ie, the carbon matrix), it has abundant pores, which can accommodate the active material and reserve space for the volume expansion of the active material.

[0056] In some specific embodiments, the pore volume of the carbon matrix obtained after etching the negative electrode material is 0.5 cm 3 / g to 1.4cm 3 / g. For example, the pore volume can be 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g or any value within the range formed by any two of the above values.

[0057] In some embodiments, the average particle size of the active material (such as silicon particles) is 0.1nm to 50nm. For example, the average particle size of the active material can be 0.1nm, 0.5nm, 1nm, 3nm, 5nm, 8nm, 10nm, 20nm, 30nm, 40nm, 50nm or any value within the range composed of any two of the above values. By setting the average particle size of the active material, the mechanical stress when the volume expansion of the active material occurs can be reduced, so that the secondary battery maintains a good battery capacity, and reduces the irreversible capacity loss, and can also shorten the electron and ion transmission path. At the same time, the size of the active material is reduced, and the gap between adjacent active materials is increased, which can reserve space for the volume expansion of the active material. Under the average particle size range of the active material defined in this embodiment, a higher battery capacity can be obtained and the volume expansion of the negative electrode material can be alleviated.

[0058] In some embodiments, the average particle size of the active material is further preferably 0.1 nm to 5 nm. For example, the average particle size of the active material can be 0.1 nm, 0.3 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any value within the range formed by any two of the above values.

[0059] In some embodiments, the average pore size of the negative electrode material is 0.45nm to 50nm. For example, the average pore size of the negative electrode material can be 0.45nm, 0.65nm, 0.85nm, 1nm, 3nm, 5nm, 8nm, 10nm, 20nm, 30nm, 40nm, 50nm or any value within the range formed by any two of the above values. The distribution of the active material in the pores of the carbon matrix will affect the pore volume and average pore size of the negative electrode material. For example, under the same conditions, the more active material adheres to the surface of the carbon matrix, the larger the pore volume of the negative electrode material will be, and the average pore size will be slightly reduced. Under the average pore size range of the negative electrode material defined in this embodiment, the active material can be more distributed in the pores of the carbon matrix to obtain a higher negative electrode material cycle performance and capacity retention rate.

[0060] In some embodiments, the pores of the negative electrode material include micropores, the volume proportion of the micropores in the pores is less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm. For example, the volume proportion of the micropores of the negative electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value within the range formed by any two of the above values.

[0061] In some embodiments, the pores of the negative electrode material include mesopores, the volume proportion of the mesopores in the pores is greater than or equal to 80%, and the pore size of the mesopores is greater than 2 nm and less than or equal to 50 nm. For example, the volume proportion of the mesopores in the negative electrode material can be 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or any value within the range formed by any two of the above values.

[0062] In some embodiments, the pores of the negative electrode material include macropores, the volume proportion of the macropores in the pores is less than or equal to 20%, and the pore size of the macropores is greater than 50 nm. For example, the volume proportion of the macropores of the negative electrode material can be 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, or any value within the range formed by any two of the above values.

[0063] Since the molecular size generated by the electrolyte is generally less than or equal to the pore size of the micropores, under the strong capillary adsorption capacity of the micropores, the adsorption capacity of the negative electrode material is in direct proportion to the pore volume of the micropores to a large extent. For example, as the volume of the micropores increases, the adsorption capacity of the negative electrode material increases, thereby increasing the side reactions between the negative electrode material and the electrolyte. Therefore, controlling the pore volume ratio of the micropores of the negative electrode material can reduce the reaction sites where the negative electrode material and the electrolyte undergo side reactions, thereby reducing the thickening of the solid electrolyte membrane (SEI membrane) caused by the continuous intrusion of the electrolyte, which is beneficial to improving the cycle performance of the negative electrode material. In addition, the distribution of pores is also closely related to the deposition of active substances. For example, the deposition of active substances in the pores of the carbon matrix results in a small proportion of micropores in the material, while if the active substances are deposited on the surface of the carbon matrix, a good sealing effect (especially micropores) cannot be achieved, which will increase the volume ratio of micropores in the material. Mesopores with increased volume percentage can reserve sufficient buffer space for the volume expansion of active materials, effectively alleviate the volume expansion of active materials, and reduce the risk of excessive local expansion stress and pulverization of negative electrode materials due to uneven volume changes of active materials during the cycle, which is beneficial to improving the particle structure stability and cycle stability of negative electrode materials. Controlling the volume percentage of micropores, mesopores, and macropores in negative electrode materials within the above range is more conducive to improving the uniformity of the distribution of active materials inside negative electrode materials.

[0064] In some embodiments, the particle size D50 of the negative electrode material is 5 μm to 20 μm. For example, the particle size D50 of the negative electrode material can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, or any value within the range formed by any two of the above values. The D50 of the negative electrode material is within the above range, which is conducive to improving the cycle performance of the negative electrode material.

[0065] In some embodiments, the particle size distribution (D90-D10) / D50 of the negative electrode material of the present application is 0.9 to 5. For example, the particle size distribution (D90-D10) / D50 of the negative electrode material can be 0.9, 1, 1.2, 1.5, 2, 2.6, 3, 3.5, 4, 4.3, 4.6, 4.8, 5 or any value within the range formed by any two of the above values. When the particle size distribution of the negative electrode material is within the above range, the large particles with larger particle sizes and the small particles with smaller particle sizes of the negative electrode material can cooperate with each other, and the small particles fill the pores between the large particles, which can improve the tap density of the negative electrode material. Among them, the measured volume-based cumulative particle size distribution D10 represents the particle size corresponding to the cumulative particle size distribution percentage of the powder reaching 10%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, and D90 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 90%.

[0066] In some embodiments, the compaction density of the negative electrode material at a pressure of 1 T is 0.8 g / cm 3 Up to 1.3g / cm 3 For example, the compaction density of the negative electrode material of the present application under a pressure of 1T can be 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 Or any value within the range formed by any two of the above values. Controlling the compaction density within the above range helps to reduce the diffusion path in the negative electrode material, thereby improving the rate performance of the battery.

[0067] In some embodiments, the tap density of the negative electrode material after 3000 vibrations is 0.5 g / cm 3 Up to 1.5g / cm 3 For example, the tap density can be 0.5 g / cm 3 , 0.7g / cm 3 , 0.9g / cm 3 , 1.1g / cm 3 , 1.3g / cm 3 , 1.5g / cm 3 Or any value within the range formed by any two of the above values. Controlling the tap density within the above range is conducive to forming a suitable compactness of the internal structure of the negative electrode material, thereby improving the transmission and conduction of electrons, increasing the battery energy density, extending the cycle life and improving safety performance.

[0068] In some embodiments, the active material includes a single substance and / or a compound of at least one element selected from Si, Sn, Ge, Pb, Ag, Mg, Zn, Ga, In, Sb, and Bi.

[0069] In some embodiments, the active material includes at least one of a silicon-based material, a tin-based material, a germanium-based material, and a lead-based material. For example, a silicon-based material is used as a component of the negative electrode active material to increase the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery.

[0070] In some embodiments, the active material includes a silicon-based material, and the silicon-based material includes at least one of amorphous silicon, crystalline silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, and silicon alloy. For example, amorphous silicon expands isotropically during lithium insertion, which can reduce pore collapse, inhibit the rapid attenuation of the specific capacity of the negative electrode material, and is more conducive to improving the lithium insertion cycle performance of the negative electrode material. Among them, the silicon-oxygen material includes silicon oxide SiO x , wherein 0<x≤2, silicon oxide is a silicon-oxygen composite, comprising oxygen atoms and silicon atoms, the molar ratio of oxygen atoms to silicon atoms is 0 to 2 and does not include 0, which can be Si, SiO 0.2 、SiO 0.5 、SiO 0.8 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 or SiO2, etc., or a compound with the chemical formula SiOx, and of course other values ​​within the above range, which are not limited in this application. The silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, etc. Of course, it should be noted that in some cases, the silicon alloy includes single silicon particles and alloys.

[0071] In some embodiments, the morphology of the active material includes at least one of a dot shape, a sphere shape, an ellipsoid shape, and a flake shape.

[0072] In some embodiments, the purity of the active material is greater than 99%. Taking silicon-based materials as active materials as an example, high-purity silicon-based materials are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of the battery.

[0073] In some embodiments, the carbon matrix includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers and graphene. The carbon matrix is ​​selected from the above materials, which can provide pore distribution sites for the active material and form a conductive network.

[0074] In some embodiments, the negative electrode material further includes a coating layer, which is disposed on at least part of the surface of the carbon matrix, and the coating layer includes a carbon material, and the carbon material includes at least one of graphene, soft carbon and hard carbon. The coating layer located on the outer layer of the negative electrode material has good electrical conductivity on the one hand, which can improve the electrical conductivity of the negative electrode material, and on the other hand, it can coat the active material exposed on the surface of the carbon matrix, reduce the continuous oxidation of the exposed active material during the placement process, and reduce the reduction in the specific capacity and the first coulomb efficiency (ICE) of the negative electrode material; the coating layer can also reduce the direct contact between the active material and the electrolyte, improve the stability of the SEI film, and thus improve the first coulomb efficiency of the negative electrode material.

[0075] In some embodiments, the coating layer may be a single-layer coating layer formed of the above-mentioned single material, or a coating layer formed by a combination of the above-mentioned multiple materials, or a multi-layer coating layer formed of a single material, or a multi-layer coating layer formed of multiple materials, etc. The layer structure of the coating layer can be selected according to actual needs. It can be understood that when the coating layer is a multi-layer coating structure, the density is higher.

[0076] In some embodiments, the thickness of the coating layer is 1nm to 300nm. For example, the thickness of the coating layer can be 1nm, 30nm, 50nm, 150nm, 200nm, 250nm, 300nm or any value within the range composed of any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the gas production of the dissolved active material reacting with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial to the stability of the particle structure of the negative electrode material during the cycle, and can reduce the exposed active material on the surface of the negative electrode material, reduce the exposed active material to cause a large amount of SEI to be generated during the charge and discharge process, and improve the specific capacity and electrochemical performance of the negative electrode material. In some embodiments, the thickness of the coating layer is preferably 1nm to 50nm, and more preferably the thickness of the coating layer is 1nm to 30nm. Thereby facilitating rapid reversible deintercalation.

[0077] In some embodiments, the mass proportion of the coating layer in the negative electrode material is less than or equal to 10%. For example, the mass proportion of the coating layer in the negative electrode material can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or any value within the range formed by any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas produced by the reaction of the dissolved active substance with the electrolyte. The mass proportion of the coating layer in the negative electrode material is within the above range, which can ensure the amount of lithium that can be inserted into the negative electrode material, thereby ensuring the charge and discharge capacity of the battery prepared with the negative electrode material.

[0078] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm. For example, the powder conductivity of the negative electrode material can be 0.5 S / cm, 0.7 S / cm, 0.9 S / cm, 1.1 S / cm, 1.3 S / cm, 1.5 S / cm, 1.7 S / cm, 1.9 S / cm, 2.0 S / cm, or any value within the range formed by any two of the above values.

[0079] In some embodiments, the average gas production of the negative electrode material at a temperature of 25°C over 7 days is less than or equal to 1 mL / g. For example, the average gas production of the negative electrode material at a temperature of 25°C over 7 days can be 0.1 mL / g, 0.3 mL / g, 0.5 mL / g, 0.7 mL / g, 0.9 mL / g, 1.0 mL / g, or any value within the range formed by any two of the above values. The gas production value of the negative electrode material is controlled within the above range, indicating that most of the active substances can be relatively evenly distributed in the pores of the carbon matrix, and the direct contact between the active substances and the electrolyte is reduced, thereby reducing the side reactions of the dissolved active substances with the electrolyte or pulping (such as silicon hydrolysis into silicate and hydrogen), effectively reducing the gas production value of the negative electrode material.

[0080] In some embodiments, the mass proportion of carbon in the negative electrode material is 40% to 60%. The carbon element includes a carbon matrix and a carbon coating layer. When the mass proportion of carbon is within this range, a sufficient carbon-based substrate can be established to provide sufficient distribution sites for the active material, which is conducive to forming an effective conductive network and improving conductivity and cycle stability.

[0081] In some embodiments, the mass percentage of silicon in the negative electrode material is 37% to 55%. When the mass percentage of silicon is within this range, the secondary battery can store a higher amount of electricity, that is, the first discharge specific capacity is higher.

[0082] According to another aspect of the present invention, there is also provided a method for preparing a negative electrode material, comprising the following steps:

[0083] Step S1, calcining the metal organic framework at 750° C. to 850° C. in an inert gas atmosphere to obtain a porous carbon material; wherein the metal organic framework is obtained by a coordination reaction between an organic ligand and a zinc ion, and the molar ratio of the organic ligand to the zinc ion is 3 to 5:1;

[0084] Step S2, mixing the porous carbon material with an alkali in a solid phase, and then heating the mixture to 700°C to 900°C at a heating rate of 1°C / min to 5°C / min for activation for 1 hour to 3 hours, washing the mixture after activation to remove residual alkali, and drying the mixture to obtain a carbon matrix;

[0085] Step S3, using an active material precursor to perform vapor deposition on a carbon matrix to obtain a negative electrode material;

[0086] The present invention provides a method for preparing anode materials. First, a metal organic framework containing elements such as C, N, O and Zn is calcined and pyrolyzed to carbonize the carbon element to obtain a carbon framework. At the same time, Zn is volatilized in the form of steam at high temperature to form micropores. H2, CO, CO2 and NO generated during the high temperature pyrolysis process are x Gases such as argon and argon can also play a pore-forming role, and finally form a porous carbon material with a microporous structure, and the Zn site retained in the porous carbon material is conducive to the subsequent catalytic growth of Si at the site, thereby improving the efficiency and uniformity of the deposition of active substances in the pores; the porous carbon material is then mixed with an alkali and activated to obtain a carbon matrix with micropores as the main pore structure, so as to be used for subsequent vapor deposition; when the active substance is deposited, the active substance enters the pores of the carbon matrix, and the micropores are almost completely effectively filled, with mainly unfilled mesopores and a small amount of macropore structures remaining.

[0087] In some embodiments, in order to obtain a porous carbon material with a more ordered porous structure, the organic ligand is selected from at least one of 2-methylimidazole, benzimidazole, terephthalic acid, and 2,5-dihydroxyterephthalic acid. The above organic ligand can form a stable metal-organic skeleton structure with zinc ion metal, so that the finally prepared carbon matrix has a special ordered porous structure with a higher specific surface area and mass transfer rate.

[0088] In some embodiments, the zinc ions are provided by a soluble salt of zinc, and the soluble salt of zinc is selected from at least one of nitrates, chlorides, and acetates; preferably, the preparation steps of the metal organic framework are as follows: dissolving the soluble salt of zinc in a first solvent to obtain a metal salt solution, and dissolving the organic ligand in a second solvent to obtain an organic ligand solution; under stirring conditions, adding the organic ligand solution to the metal salt solution, and the organic ligand and zinc ion coordinate to form a metal organic framework; more preferably, after the organic ligand solution is added, stirring is performed for 10 to 30 minutes, and then standing for 12 to 48 hours to precipitate a solid product, and the solid product is washed and vacuum dried to obtain a metal organic framework; more preferably, the first solvent and the second solvent are independently selected from at least one of methanol, ethanol, water, capronitrile, acetone, and N,N-dimethylformamide.

[0089] In some embodiments, in order to obtain a microporous structure with uniform pore size and abundant pores, the heating rate in step S1 is 5°C / min to 15°C / min. For example, the specific heating rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, or any value within the range formed by any two of the above values.

[0090] In some embodiments, the calcination time is 1 h to 3 h, and the specific heating rate can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any value within the range formed by any two of the above values.

[0091] In some embodiments, in step S1 , the inert gas includes at least one of nitrogen or argon.

[0092] In some embodiments, in order to remove impurities in the micropores, step S1 also includes: after the calcination is completed, washing the calcined product with an acid solution; the acid solution is selected from at least one of a hydrofluoric acid aqueous solution, a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, a nitric acid aqueous solution, and a phosphoric acid aqueous solution; preferably, the concentration of the acidic substance in the acid solution is 0.5 mol / L to 5 mol / L.

[0093] In some embodiments, in order to obtain a richer pore structure, in step S2, the mass ratio of carbon material to alkali is 3 to 5:1, specifically 3:1, 3.2:1, 3.5:1, 3.4:1, 4:1, 4.2:1, 4.5:1, 5:1. Of course, it can also be other values ​​within the above mass ratio range, which is not limited here.

[0094] In some embodiments, in order to remove residual alkaline impurities in the pores, in step S2, washing includes pickling and washing with hot water to neutrality after pickling; preferably, in step S2, the acid solution used in pickling is a hydrochloric acid aqueous solution with a mass fraction of 2% to 8%.

[0095] In some embodiments, the active material precursor includes a silicon source, and a silicon source and a diluent gas are introduced into a carbon matrix to perform a vapor deposition reaction to form silicon particles in the pores of the carbon matrix to obtain a negative electrode material.

[0096] In some embodiments, the silicon source includes at least one of monosilane, disilane, trisilane, and tetrasilane.

[0097] In some embodiments, the temperature of the vapor deposition reaction is 400°C to 600°C. The temperature of the vapor deposition reaction can specifically be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C or any value within the range formed by any two of the above values.

[0098] In some embodiments, the time of the vapor deposition reaction is 1 h to 20 h. The time of the vapor deposition reaction can specifically be 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h or any value within the range formed by any two of the above values; preferably 2 h to 10 h.

[0099] In some embodiments, the volume of the silicon source introduced is 1% to 80%, based on the sum of the volumes of the silicon source and the dilution gas introduced as 100%; preferably, the silicon source includes at least one of monosilane, disilane, monochlorosilane (monochlorosilane), dichlorosilane (dichlorosilane), trichlorosilane (trichlorosilane), and tetrachlorosilane (tetrachlorosilane); preferably, the dilution gas is selected from one of an inert gas and hydrogen.

[0100] In some embodiments, after vapor deposition of a carbon matrix using a vapor-phase active material precursor, the method further includes: mixing the vapor-deposited material with a carbon source and performing a heating treatment to obtain a coating layer.

[0101] In some embodiments, the carbon source includes at least one of a gaseous carbon source and a solid carbon source.

[0102] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0103] In some embodiments, the flow rate of the gaseous carbon source is 0.1 L / min to 100 L / min, specifically 0.1 L / min, 1 L / min, 10 L / min, 30 L / min, 600 L / min, 100 L / min or any value within the range formed by any two of the above values.

[0104] In some embodiments, the solid carbon source includes at least one of sucrose, fructose, glucose, asphalt, phenolic resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0105] In some embodiments, the mass ratio of the solid carbon source to the material obtained by vapor deposition is (1-100):100, specifically 1:100, 10:100, 30:100, 50:100, 80:100 and 100:100 or any value within the range of any two of the above mass ratios.

[0106] In some embodiments, the temperature of the heating treatment is 600°C to 1100°C, and the temperature of the heating treatment can be 600°C, 650°C, 700°C, 800°C, 900°C, 1000°C and 1100°C or any value within the range formed by any two of the above values. If the temperature of the heating treatment is lower than 600°C, the carbonization of the coating material is incomplete, and a dense coating layer cannot be obtained; if the temperature of the heating treatment is higher than 1100°C, the active material (such as silicon-based active material) is crystallized, resulting in poor cycle performance and expansion performance of the negative electrode material.

[0107] In some embodiments, the holding time of the heating treatment is 2 hours to 10 hours. Specifically, the holding time of the heating treatment can be 2 hours, 5 hours, 7 hours, 8 hours and 10 hours or any value within the range formed by any two of the above values.

[0108] In some embodiments, after mixing the vapor-deposited material and the coating material and subjecting them to a heat treatment, the method further comprises the steps of screening and grading the obtained material.

[0109] According to another aspect of the present invention, a negative electrode sheet is provided, and the negative electrode sheet comprises the negative electrode material as above.

[0110] According to another aspect of the present invention, a secondary battery (such as a lithium ion battery, a sodium ion battery, etc.) is provided, comprising a housing, an electrode assembly and an electrolyte / electrolyte. The electrode assembly and the electrolyte / electrolyte are both located in the housing.

[0111] The outer shell can be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery can also be a steel shell battery, an aluminum shell battery, etc.

[0112] The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly may be a laminated structure, which is formed by alternately stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence. In other embodiments, the electrode assembly may also be a winding structure, which is formed by stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence and then winding them.

[0113] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector. The positive electrode current collector may be made of aluminum foil or nickel foil, or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly embed and de-embed metal ions. In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide, a sodium transition metal composite oxide, and the like. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0114] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or may be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0115] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0116] Example 1

[0117] Step 1, preparation of metal organic framework: 3 mol of Zn(NO3)2·6H2O is dissolved in 3 L of methanol to obtain a metal salt solution, 12 mol of 2-methylimidazole is dissolved in 3 L of methanol to obtain an organic ligand solution, the organic ligand solution is quickly added to the metal salt solution while stirring, after the addition is completed, the solution is stirred for 15 minutes, and then the obtained solution is allowed to stand for 24 hours to precipitate a solid product, and finally the obtained solid product is washed with methanol for multiple times, and vacuum dried at 80°C for 12 hours to obtain a metal organic framework.

[0118] Step 2: Place the metal organic framework in a tubular furnace, heat it to 800°C at a heating rate of 10°C / min in an argon environment and keep it at a constant temperature for 2 hours for calcination. After the calcination is completed, cool it naturally to room temperature, and then wash the calcined product with 2 mol / L HF aqueous solution and distilled water for multiple times to remove residual metal impurities. Finally, vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0119] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 800°C, the heating rate is 2°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0120] Step 4: Place the carbon substrate in a CVD device, then introduce monosilane and N2 into the CVD device in a volume ratio of 1:3, raise the temperature to 500°C for vapor deposition reaction, the reaction time is 5 hours, and the deposition pressure is set to 10 kPa to obtain the negative electrode material.

[0121] Example 2

[0122] Step 1, preparation of metal organic framework: 4 mol of ZnCl2·4H2O is dissolved in 4 L of methanol to obtain a metal salt solution, 12 mol of benzimidazole is dissolved in 4 L of methanol to obtain an organic ligand solution, the organic ligand solution is quickly added to the metal solution while stirring, and after the addition is completed, the solution is stirred for 15 minutes, and then the obtained solution is allowed to stand for 24 hours to precipitate a solid product, and finally the obtained solid product is washed with methanol for multiple times, and vacuum dried at 80°C for 12 hours to obtain a metal organic framework.

[0123] Step 2: Place the precursor in a tubular furnace, heat to 850°C at a heating rate of 5°C / min in an argon environment and keep the temperature constant for 1 hour for calcination. After the calcination is completed, cool it naturally to room temperature, wash the calcined product with 2 mol / L HF aqueous solution and distilled water for multiple times to remove residual metal impurities, and finally vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0124] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 700°C, the heating rate is 5°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0125] Step 4: Place the carbon substrate in a CVD device, then introduce disilane and H2 into the CVD device in a volume ratio of 1:6, raise the temperature to 580°C for vapor deposition reaction, the reaction time is 10 hours, and the deposition pressure is set to 5 kPa to obtain the negative electrode material.

[0126] Example 3

[0127] Step 1, preparation of metal organic framework: 2 mol of Zn(CH3COOH)2·2H2O is dissolved in 2 L of methanol to obtain a metal salt solution, 10 mol of terephthalic acid is dissolved in 2 L of methanol to obtain an organic ligand solution, the organic ligand solution is quickly added to the metal solution while stirring, and after the addition is completed, the solution is stirred for 15 minutes, and then the obtained solution is allowed to stand for 24 hours to precipitate a solid product. Finally, the obtained solid product is washed with methanol for multiple times, and vacuum dried at 80°C for 12 hours to obtain a metal organic framework.

[0128] Step 2: Place the precursor in a tubular furnace, heat to 750°C at a heating rate of 15°C / min in an argon environment and keep the temperature constant for 3 hours for calcination. After the calcination is completed, cool it naturally to room temperature, and then wash the calcined product with 2 mol / L HF aqueous solution and distilled water for multiple times to remove residual metal impurities. Finally, vacuum dry it at 80°C for 12 hours to obtain a porous carbon material.

[0129] Step 3. The mass ratio of the porous carbon material to KOH is 4:1, and the activation is carried out at 900°C, the heating rate is 1°C / min, and the activation time is 2h. The activated product is washed with a 5% hydrochloric acid aqueous solution and hot water to neutrality, and then dried to obtain a carbon matrix.

[0130] Step 4: Place the carbon substrate in a CVD device, then introduce trichlorosilane and H2 into the CVD device in a volume ratio of 3:2, raise the temperature to 600°C for vapor deposition reaction, the reaction time is 2h, and the deposition pressure is set to 1kPa to obtain the negative electrode material.

[0131] Example 4

[0132] The only difference from Example 1 is that step 4 further includes preparing a coating layer on the product obtained after the vapor deposition reaction is completed. The specific steps are as follows:

[0133] The product obtained after the vapor deposition reaction is completed is placed in a reaction furnace, and methane gas is introduced with a methane flow rate of 10L / min. Heat treatment is performed at 750°C and kept warm for 4 hours. The obtained material is screened and graded to obtain the negative electrode material.

[0134] Wherein, the thickness of the coating layer in the negative electrode material is 200nm.

[0135] Example 5

[0136] The same as Example 1, except that 2-methylimidazole is replaced by terephthalic acid.

[0137] Example 6

[0138] The same as Example 1, except that 2-methylimidazole is replaced by 2,5-dihydroxyterephthalic acid.

[0139] Example 7

[0140] The same as Example 1, the only difference is that the amount of 2-methylimidazole used in step 1 is 15 mol.

[0141] Example 8

[0142] The same as Example 1, the only difference is that the activation temperature in step 3 is 900°C.

[0143] Example 9

[0144] The only difference from Example 1 is that the heating rate in step three is 4° C. / min.

[0145] Comparative Example 1

[0146] The only difference between the above method and Example 1 is that the amount of 2-methylimidazole used in step 1 is 18 mol.

[0147] Comparative Example 2

[0148] The only difference between it and Example 1 is that the activation temperature in step 3 is 1000°C.

[0149] Comparative Example 3

[0150] The only difference between it and Example 1 is that the heating rate in step 3 is 8° C. / min.

[0151] Performance Testing:

[0152] (1) Alpha test of materials:

[0153] α is obtained by the following test method: in the figure shown by SEM section processing of a single negative electrode material particle, select any A×B area, where A=1μm~10μm, B=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, 10 negative electrode material particles are tested, α is the arithmetic mean of the α' values ​​of the 10 negative electrode material particles, and the α' and α test results of the negative electrode material are shown in Table 1.

[0154] (2) Pore size, pore size distribution (volume ratio of micropores, mesopores and macropores), pore volume and specific surface area test: The test was performed using a specific surface area and pore size analyzer (TriStar 3000, Micromeritics, USA).

[0155] Among them, HF was used to etch the silicon-based active material in the negative electrode material to obtain a carbon matrix, which was used as the object for testing to obtain the micropore ratio, specific surface area and pore volume of the carbon matrix. The test results of the micropore ratio are shown in Table 2, and the specific surface area S2 and pore volume P2 of the carbon matrix are shown in Table 3;

[0156] The pore size distribution and average pore size test results of the negative electrode material are shown in Table 2, and the specific surface area S1 and pore volume P1 of the negative electrode material are shown in Table 3.

[0157] (3) Particle size and particle size distribution test: The D10, D50, and D90 of the material were measured using a laser particle size analyzer. The particle size D50 and particle size distribution (D90-D10) / D50 of the negative electrode material are shown in Table 2.

[0158] (4) Test method for average particle size of silicon-based active material: The diameter of silicon-based active material in transmission electron microscope image is mathematically counted and the average value is calculated to obtain the average particle size of active material. The result is shown in 2.

[0159] (5) Carbon content test: The carbon content (mass percentage) of the material was tested using an infrared carbon-sulfur analyzer (CSI, Elter, Germany). The results are shown in Table 3.

[0160] (6) Silicon content test: The silicon content of the material was tested in accordance with GBT / 38823-2020. Test equipment: atmosphere furnace (Sigma SGM.VB11 / 17DF). Test parameters: calcination temperature was 1300°C. The results are shown in Table 3.

[0161] (7) Tap density test: The tap density of the material was tested using a tap density meter (Contacor, USA, DAT-6-220). The specific steps are as follows: the sample was placed in a measuring cylinder and vibrated 3000 times. The volume of the measuring cylinder after tapping was read and the tap density was calculated. The tap density test results of the negative electrode material are shown in Table 4.

[0162] (8) Compaction density test: The compaction density of the material was tested using a compaction density meter (McNor, CARVER 4350) in accordance with GB / T 24533-2019. The compaction density test results of the negative electrode material are shown in Table 4.

[0163] (9) Powder conductivity test: The powder resistance test system (Mitsubishi Chemical, Japan, MCP-PD51) was used to test the conductivity of the material under a pressure of 20 kN. The powder conductivity of the negative electrode material under 20 kN is shown in Table 4.

[0164] (10) Oil absorption value test: Using an oil absorption value tester (ASAHI SOUKEN, S-500, Japan), a powder sample was placed in a mixing chamber, and oil (DBP) was dripped into the sample at a constant rate, and the sample was stirred at a rotating wing speed of 630 r / min. The oil absorption value (mL / 100 g) of the sample was calculated by detecting the viscosity change of the torque. The oil absorption value data are shown in Table 4.

[0165] (11) Gas production test:

[0166] 1.1. Prepare various slurries in a certain proportion (add water to CMC to form glue after uniform dispersion, the mass percentage of CMC in the glue is 1.4%, take 10g of glue and mix with 10g of sample to make slurry).

[0167] 1.2. At room temperature (25°C), put the slurry into an aluminum-plastic film bag, record the mass of the slurry, and then seal it to form a sealed aluminum-plastic film bag.

[0168] 1.3. Measure the volume of generated gas: Fix the sealed aluminum-plastic film bag at the bottom of the container and immerse it completely in water. Record the initial volume of the aluminum-plastic film bag, and then record the volume of the aluminum-plastic film bag every 24 hours for 7 consecutive days.

[0169] 1.4. The 7-day average gas production of the negative electrode material was calculated based on the volume change of the aluminum-plastic film. The results are shown in Table 4.

[0170] (12) Battery performance test:

[0171] 1.1. First charge and discharge specific capacity and first coulombic efficiency test: The negative electrode slurry was prepared according to the mass ratio of negative electrode material, conductive carbon black and PPA of 70:15:15, coated on copper foil, and made into negative electrode sheet after drying. Metal lithium sheet was used as counter electrode, and button cells were assembled in a glove box filled with Ar gas. Then, the button cells were charged and discharged at a current density of 0.1C in the charge and discharge range of 0.01V to 1.5V. The first discharge specific capacity and first coulombic efficiency (ICE) of the button cells are shown in Table 5.

[0172] 1.2. Capacity retention rate and pole piece thickness expansion rate test: A negative electrode slurry was prepared according to a mass ratio of 92:2:2:2:2 of a mixture of negative electrode material and graphite, Super-P, KS-6, CMC, and SBR, and the mixture was coated on a copper foil and dried to form a negative electrode sheet, wherein the proportion of negative electrode material and graphite in the mixture of negative electrode material and graphite was determined by the initial lithium delithiation capacity of the manufactured lithium battery (in this test, the initial lithium delithiation capacity of the lithium battery was uniformly 480 mAh / g). A metal lithium sheet was used as a counter electrode and button cells were assembled in a glove box filled with Ar gas. Then, the button cells were charged and discharged 50 times at a current density of 1 C in the charge and discharge range of 0.01 V to 1.5 V to obtain the capacity retention rate of the battery after 50 cycles and the pole piece thickness expansion rate after 50 cycles, as shown in Table 5 for details.

[0173] Table 1

[0174]

[0175] Table 2

[0176]

[0177]

[0178] Table 3

[0179]

[0180]

[0181] Table 4

[0182]

[0183] Table 5

[0184]

[0185]

[0186] As shown in Tables 1 to 4, the negative electrode material prepared in the embodiment of the present invention has a smaller negative electrode material oil absorption value (dpq1 is 43ml / 100g to 68ml / 100g), a larger difference in oil absorption value before and after silicon deposition ((dpq2-dpq1) / dpq1 is 1.33 to 3.19), and a smaller macropore area ratio (the area ratio of pores with a pore diameter greater than 50nm is α≤10%). The above data show that more silicon in the negative electrode material enters the carbon matrix and is mainly deposited in the pores of the carbon matrix, and the negative electrode material after silicon deposition is mainly mesopores that are not completely filled with micropores. When the above negative electrode material is used as a negative electrode material, it can reduce The silicon particles are less in direct contact with the electrolyte, which reduces the occurrence of adverse side reactions between the negative electrode material and the electrolyte, improves the cycle performance of the material, and makes the negative electrode material have a higher capacity retention rate. As shown in Table 5, the battery capacity retention rate after 50 cycles is above 90%; in addition, the pores after silicon deposition still have a rich mesoporous structure, which can reduce the volume expansion of the negative electrode material. As shown in Table 5, the thickness expansion rate of the electrode sheet after 50 cycles is less than 40%, and the macropore volume and area of ​​the negative electrode material after silicon deposition account for a small proportion, which can improve the tap density of the negative electrode material (as shown in Table 4, the tap density of the negative electrode material prepared in the embodiment is 0.7 g / cm 3 As well as effectively reducing the specific surface area of ​​the composite material (as shown in Table 3, compared with the carbon matrix, the specific surface area and pore volume of the negative electrode material obtained after silicon deposition on the carbon matrix in the embodiment are significantly reduced), thereby reducing the occurrence of side reactions between the material and the electrolyte during the first charge and discharge process, and improving the first efficiency, expansion performance and cycle performance of the negative electrode material.

[0187] In Comparative Example 1, a relatively high amount of organic ligand was added to obtain a negative electrode material with a relatively high proportion of macropore area (19.9%). Compared with Example 1, the pore volume of the carbon matrix increased slightly and the pore volume of the negative electrode material remained basically unchanged, while the specific surface areas of the carbon matrix and the negative electrode material were greatly improved, and the proportion of macropores (23%) increased significantly, resulting in the deterioration of the first efficiency and expansion performance of the negative electrode material, especially the significant decrease in the first coulomb.

[0188] In Comparative Example 2, a higher activation temperature was used to obtain a negative electrode material with a higher macropore area and volume ratio. Compared with Example 1, the specific surface area of ​​the carbon matrix increased significantly while the pore volume of the carbon matrix remained unchanged, indicating that at a lower activation temperature, as the activation temperature increases, the specific surface area and pore volume of the porous carbon material increase, which is conducive to the formation of mesopores. If the temperature is too high, excessive vaporization may cause the collapse of the pores to form macropores that are interconnected, resulting in a significant increase in the specific surface area of ​​the carbon matrix. Under the same silicon deposition process as in Example 1, the macropore area ratio and volume ratio of the obtained negative electrode material increase, resulting in the deterioration of the initial efficiency and expansion performance of the negative electrode material, especially a significant decrease in the cycle performance.

[0189] In Comparative Example 3, a higher heating rate was used to obtain a negative electrode material with a higher macropore area and volume ratio. When the heating rate was low, the reaction between the activator KOH and the carbon material was relatively mild, and a large number of microporous structures were formed during the reaction. As the heating rate increased, the high-temperature activation process became more and more intense, and the corrosion effect of KOH became stronger, causing the pore walls of the activated carbon material to become thinner and thinner, causing the previously formed micropores to continue to expand and transform into mesopores and macropores. In Comparative Example 3, a negative electrode material with a higher macropore area and volume ratio was prepared at a higher heating rate (8°C / min), which reduced the initial efficiency, expansion performance and cycle performance of the negative electrode material.

[0190] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises a carbon matrix and an active material, wherein the carbon matrix has pores, the active material is at least partially distributed in the pores, and the area ratio of pores with a pore diameter greater than 50 nm in any cross section of the negative electrode material is α, satisfying: α≤10%; Wherein, the α is obtained by the following test method: in the figure shown by SEM section processing of a single negative electrode material particle, select any A×B area, wherein A=1μm~10μm, B=1μm~10μm, the sum of the cross-sectional areas of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle in the region is recorded as S0, the cross-sectional area of ​​a single negative electrode material particle in the region is recorded as S, and the area ratio of pores with a pore size greater than 50nm in the cross section of a single negative electrode material particle is defined as α', α'=S0 / S, and α is the arithmetic mean of the α' values ​​of at least 10 negative electrode material particles.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (2): (1) The oil absorption value dbq2 of the carbon matrix satisfies: 120 ml / 100 g ≤ dbq2 ≤ 200 ml / 100 g; the oil absorption value dpq1 of the negative electrode material satisfies: 30 ml / 100 g ≤ dpq1 ≤ 80 ml / 100 g, and (dbq2-dbq1) / dbq1>0.5; (2) The specific surface area of ​​the carbon matrix is ​​S1 m 2 / g, the pore volume of the carbon matrix is ​​P1 cm 3 / g, the specific surface area of ​​the negative electrode material is S2 m 2 / g, the pore volume of the negative electrode material is P2 cm 3 / g; S1, P1 cm 3 / g, the S2 m 2 / g, P2 cm 3 / g satisfies the following relationship: C1 = S1 / (P1*100); 10≤C1≤25； C2 = S2 / (P2*100); 1≤C2≤50。 3. The negative electrode material according to claim 1 or 2, characterized in that: The negative electrode material includes at least one of the following features (1) to (5): (1) The specific surface area of ​​the carbon matrix is ​​500 m 2 / g to 2500m 2 / g; (2) The pore volume of the carbon matrix is ​​0.3 cm 3 / g to 2cm 3 / g; (3) The specific surface area of ​​the negative electrode material is 0.5 m 2 / g to 10m 2 / g; (4) The pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1cm 3 / g; (5) The pore volume of the negative electrode material is smaller than the pore volume of the carbon matrix.

4. The negative electrode material according to claim 1 or 2, characterized in that: The ratio of the volume of nitrogen adsorbed by the carbon matrix at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is A; The ratio of the volume of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume of nitrogen adsorbed at 10% partial pressure is B; Among them, 1≤A≤1.9, 1.3≤B≤2.5, and B / A≥1.

5. The negative electrode material according to claim 1 or 2, characterized in that: The negative electrode material includes at least one of the following features (1) to (10): (1) The pores in the carbon matrix include micropores, the volume proportion of the micropores in the total pore volume is greater than or equal to 70%, and the pore diameter of the micropores is less than or equal to 2 nm; (2) The average particle size of the active substance is 0.1 nm to 50 nm; (3) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (4) The pores of the negative electrode material include micropores, the volume of the micropores in the pores accounts for less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm; (5) The pores of the negative electrode material include mesopores, the volume proportion of the mesopores in the pores is greater than or equal to 80%, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm; (6) The pores of the negative electrode material include macropores, the volume proportion of the macropores in the pores is less than or equal to 20%, and the pore diameter of the macropores is greater than 50 nm; (7) The particle size D50 of the negative electrode material is 5 μm to 20 μm; (8) The particle size distribution (D90-D10) / D50 of the negative electrode material is 0.9 to 5; (9) The compaction density of the negative electrode material under a pressure of 1T is 0.8 g / cm 3 Up to 1.3g / cm 3 ; (10) The tap density of the negative electrode material after 3000 vibrations is 0.5 g / cm 3 Up to 1.5g / cm 3 .

6. The negative electrode material according to claim 1 or 2, characterized in that: The negative electrode material includes at least one of the following features (1) to (3): (1) The active material comprises a single substance and / or a compound of at least one element selected from Si, Sn, Ge, Pb, Ag, Mg, Zn, Ga, In, Sb, and Bi; (2) The carbon matrix includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers and graphene; (3) The negative electrode material further includes a coating layer, which is disposed on at least a portion of the surface of the carbon substrate, and the coating layer includes a carbon material, and the carbon material includes at least one of graphene, soft carbon and hard carbon.

7. The negative electrode material according to claim 1, characterized in that The active material includes a silicon-based material, and the silicon-based material includes at least one of amorphous silicon, crystalline silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, and a silicon alloy.

8. The negative electrode material according to claim 7, characterized in that The negative electrode material includes at least one of the following features (1) to (4): (1) The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S / cm to 2 S / cm; (2) The average gas production of the negative electrode material at 25°C over 7 days is less than or equal to 1 mL / g; (3) The mass proportion of carbon element in the negative electrode material is 40% to 60%; (4) The mass percentage of silicon in the negative electrode material is 37% to 55%.

9. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 8.

10. A battery, characterized in that: It comprises a negative electrode, and the electrode sheet used for the negative electrode is the negative electrode sheet according to claim 9.

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