High-capacity low-expansion silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention relates to a preparation method of a high-capacity low-expansion silicon-carbon negative electrode material, which comprises the following steps: blending and grinding nano silicon powder, asphalt and sodium dodecyl benzene sulfonate, then uniformly stirring with natural graphite, defoaming, finally carrying out centrifugal spray drying at 270 DEG C, and carbonizing at 700 DEG C for 1 hour to obtain a base material; wherein the substance mass ratio of the natural graphite to the nanometer silicon powder to the asphalt to the sodium dodecyl benzene sulfonate is 100: 20: 10: 5. According to the silicon-carbon negative electrode material disclosed by the invention, the nano silicon powder, the asphalt and the sodium dodecyl benzene sulfonate are matched with the natural graphite to be improved and optimized to prepare a basic material; the low-expansion silicon-carbon negative electrode material integrating high conductivity, high cycle and high capacity is prepared through coordination and optimization of the raw materials.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of carbon negative electrode materials, in particular to a high-capacity low-expansion silicon-carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] As a core energy storage device in the field of new energy, the energy density and cycle stability of a lithium ion battery are key factors restricting the development of industries such as electric vehicles and energy storage power stations. As an important component of the lithium ion battery, the negative electrode material directly affects the comprehensive performance of the battery. The theoretical capacity of the currently commercialized graphite negative electrode material is only 372 mAh / g, which cannot meet the demand of high-energy-density batteries, and therefore the development of high-capacity negative electrode materials has become a research hotspot.

[0003] Silicon-based materials are considered as an ideal choice for the next generation of high-capacity negative electrode materials due to their extremely high theoretical specific capacity (4200 mAh / g), abundant reserves and environmental friendliness. However, the volume expansion of silicon is about 300% during the lithium ion insertion / extraction process, which leads to the collapse of the electrode structure, the shedding of active materials and the repeated rupture of the solid electrolyte interface (SEI) film, and seriously affects the cycle stability of the battery. This problem has become a core bottleneck restricting the practical application of silicon-based negative electrodes.

[0004] To solve the problem of volume expansion of silicon, researchers have proposed the design idea of silicon-carbon composite negative electrode materials. By combining silicon with carbon materials, the performance of silicon-based materials can be improved by utilizing the good electrical conductivity and certain volume buffering capacity of carbon materials. In the prior art, the preparation of silicon-carbon composite negative electrodes mainly adopts methods such as carbon coating, nano-silicon dispersion or mixing with graphite, but there are still the following shortcomings: Capacity and stability are difficult to balance: when the thickness of the pure carbon coating layer is insufficient, it cannot effectively inhibit the volume expansion of silicon; if the thickness is too high, the overall capacity of the material will be reduced, and the high capacity advantage of silicon will be sacrificed.

[0005] Poor compatibility of multiple interfaces: there are differences in interfacial energy between silicon, carbon and other inorganic additives (such as metal oxides and ceramic phases), which easily form interface defects, leading to stress concentration and structure collapse.

[0006] Insufficient dispersion uniformity: the surface energy of nano-silicon particles is high, and they are prone to agglomeration, leading to intensified local volume expansion; when the modifier or reinforcing phase is not uniformly dispersed in the matrix, it is difficult to form a continuous support network, and the anti-expansion effect is limited.

[0007] Poor stability of SEI film: the dramatic volume change of silicon will cause the repeated rupture and regeneration of the SEI film, consume the electrolyte and produce by-products, further exacerbating the "virtual increase" of the electrode volume and the capacity attenuation. SUMMARY

[0008] In view of the defects of the prior art, the purpose of the present application is to provide a preparation method of a silicon-carbon negative electrode material capable of achieving high capacity retention and low volume expansion in cooperation, which solves the problems in the above background art by constructing a high-capacity low-expansion silicon-carbon negative electrode material with a composite structure of "high-capacity active center-rigid support network-flexible buffer interface" and a preparation method thereof through multi-component cooperative design and interface optimization.

[0009] The technical problem solved by the present application adopts the following technical solutions: The present application provides a preparation method of a high-capacity low-expansion silicon-carbon negative electrode material, comprising the following steps: The nano-silicon powder, pitch and sodium dodecylbenzenesulfonate are blended and ground, then stirred uniformly with natural graphite, deaerated, and finally centrifugally spray dried at 270°C, carbonized at 700°C for 1h to obtain a base material; wherein the mass ratio of natural graphite, nano-silicon powder, pitch and sodium dodecylbenzenesulfonate is 100:20:10:5; The base material, modifier and ball milling liquid are blended and ball milled at a weight ratio of (11-15):(3-5):4 for 1h at a ball milling speed of 1000-1500r / min, then filtered, dried, and heat treated at 750-800°C for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the present application.

[0010] Preferably, the particle size of the pitch is 10-15µm, the coking value is 45-55%, the softening point is 150-200°C, the surface of the natural graphite is porous, the pore volume is 0.05-0.10cm / g, and the particle size is 10-20um.

[0011] Preferably, the preparation method of the modifier is: S01: The zinc oxide whisker is first stirred in a sufficient amount of a 5-8% mass fraction potassium permanganate solution, then washed with water, filtered, and dried to obtain dry zinc oxide whisker; S02: 2-3 parts of octadecyldimethylchlorosilane and 1-2 parts of nano-attapulgite are added to 5-8 parts of an ethanol aqueous solution and stirred uniformly to obtain an impregnating solution; The nano-titanium dioxide is immersed in an impregnating solution with a nano-titanium dioxide content of 3-5 times for ultrasonic immersion treatment, then filtered and dried to obtain modified nano-titanium dioxide agent; S03: 3-5 parts of modified nano-titanium dioxide agent, 1-3 parts of boron nitride and 1-2 parts of titanate coupling agent are added to 5-8 parts of lanthanum nitrate solution for blending and ball milling treatment, and then filtered and dried to obtain a complex solution; The dry zinc oxide whisker and the complex solution are stirred for sufficient treatment at a weight ratio of 7:11, then filtered and dried to obtain the modifier.

[0012] The modifier is prepared by improving and optimizing zinc oxide whiskers with potassium permanganate solution, and improving nano-titanium dioxide by immersing in a liquid, and then adding the improved nano-titanium dioxide, boron nitride and titanate coupling agent into lanthanum nitrate solution to blend and ball mill to obtain a complexing liquid; the dry zinc oxide whiskers are improved by the complexing liquid to prepare the modifier, which can enhance the high conductivity, high cycle and high capacity of the product in the system.

[0013] Preferably, the ultrasonic power of the ultrasonic immersion treatment is 350-400W, and the ultrasonic treatment is performed for 1h; the ball milling speed of the blending ball milling treatment is 1000-1500r / min, and the ball milling is performed for 2h.

[0014] Preferably, the mass fraction of the lanthanum nitrate solution is 4-7%.

[0015] Preferably, the preparation method of the ball milling liquid is as follows: S11: adding 2-3 parts of silane coupling agent and 2-3 parts of sodium silicate solution with a mass concentration of 5-8% into 8-12 parts of polyvinyl alcohol aqueous solution, and blending uniformly to obtain a base liquid; S12: blending and fully mixing nano-cellulose, sodium citrate solution and kaolin powder according to a weight ratio of (2-4):6:(3-5), and then washing with water, filtering, and drying to obtain an additive; stirring and treating the additive and the base liquid according to a weight ratio of 3:5, and then stopping ultrasonic treatment to obtain the ball milling liquid.

[0016] Preferably, the mass fraction of the polyvinyl alcohol aqueous solution is 5-8%, and the mass fraction of the sodium citrate solution is 8-12%.

[0017] The ball milling liquid is prepared by blending and optimizing nano-cellulose with sodium citrate solution and kaolin powder, and then blending and improving the base liquid prepared from polyvinyl alcohol aqueous solution and other raw materials, so that the ball milling liquid can enhance the coordination effect of the ball milling liquid and the modifier in the system, and the performance of the product is further improved.

[0018] Preferably, the silane coupling agent is silane coupling agent KH560.

[0019] Preferably, the stirring temperature of the stirring treatment is 50-55℃, the stirring speed is 750-850r / min, and the stirring is performed for 1h.

[0020] The application further provides a silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-expansion silicon-carbon negative electrode material.

[0021] Compared with the prior art, the application has the following beneficial effects: (1) The high-capacity low-expansion silicon-carbon negative electrode material of the present application, through "multi-component synergistic design + interface optimization + process adaptation", while retaining the high-capacity advantage of silicon-based materials, significantly inhibits volume expansion, solving the technical problem of "difficulty in balancing capacity and stability" in the prior art of silicon-carbon negative electrodes. Compared with existing silicon-carbon negative electrodes (usually capacity ≤ 1500 mAh / g), the reversible capacity of the negative electrode material of the present application can reach 2400-2500 mAh / g, and the capacity retention rate after 50 cycles is ≥95%, the volume expansion rate in 50 cycles is ≤15%, the electrode sheet has no obvious powdering or peeling, the coulombic efficiency after 50 cycles remains ≥98%, the capacity retention rate after 50 cycles is ≥98%); (2) By introducing nano-silicon powder, the surface energy of the nano-silicon powder is reduced through the dispersion effect of sodium dodecyl benzene sulfonate, agglomeration of the nano-silicon powder is avoided, the active sites of silicon are maximized to be exposed, and high-capacity contribution is ensured; natural graphite as the matrix provides a stable capacity base, the two form a "high capacity-high stability" complement, the amorphous carbon layer formed by the carbonization of pitch not only wraps the silicon particles and buffers their expansion, but also connects the graphite to build a continuous conductive network of "graphite-carbon layer-silicon", solving the problem of poor conductivity of silicon itself, and reducing the loss of capacity due to blocked electron conduction; (3) The inorganic phase of boron nitride, titanium dioxide, etc. in the modifier accounts for a low proportion, and is tightly combined with the matrix through a titanate coupling agent, avoiding dilution of the overall capacity due to "too many inert components", balancing the reinforcement effect and capacity retention, and the zinc oxide whisker forms a "steel skeleton" in the matrix, its high strength can resist the radial stress generated by the expansion of silicon, the layered structure of boron nitride buffers the shear stress through interlayer sliding, and the two cooperate to reduce macroscopic structural deformation, the zinc oxide whisker is pretreated with potassium permanganate to introduce hydroxyl groups, which react with the titanate coupling agent to strengthen the interface bonding with the carbon matrix and avoid "gap expansion" caused by interface separation; (4) The nano-cellulose in the ball milling liquid fills the gap between the particles, SiO2 formed by the conversion of sodium silicate forms an "inorganic-organic composite filler", compressing the available space for silicon expansion, sodium citrate inhibits the agglomeration of nano-silicon and the modifier through electrostatic repulsion, ensuring uniform distribution of conductive components (graphite, carbon layer), avoiding rate performance decline due to local insulation, the spherical structure formed by centrifugal spray drying improves the packing density, further reducing the expansion space, and the carbonization of polyvinyl alcohol forms a "flexible bonding network" with nano-cellulose, even if the silicon expands locally, this network can also disperse stress to the rigid skeleton (zinc oxide whisker) through deformation, avoiding overall electrode pulverization; (5) The "rigid reinforcing phase-flexible buffer phase-conductive carbon phase" three-dimensional network formed by the modifier and the ball milling liquid is not prone to fatigue fracture in repeated charge-discharge cycles (silicon expansion-contraction), ensuring long-term stability of the structure. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0023] The preparation method of the high-capacity low-expansion silicon-carbon negative electrode material in the embodiment comprises the following steps: The nano-silicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, and then stirred uniformly with the natural graphite, and then subjected to defoaming treatment, and finally subjected to centrifugal spray drying at 270°C, and then carbonized at 700°C for 1h to obtain a base material; wherein the mass ratio of the natural graphite, nano-silicon powder, pitch and sodium dodecyl benzene sulfonate is 100:20:10:5; The base material, modifier and ball milling liquid are blended and ball milled at a weight ratio of (11-15):(3-5):4 for 1h, the ball milling speed is 1000-1500r / min, after the ball milling is completed, the mixture is subjected to suction filtration and drying, and then subjected to heat treatment at 750-800°C for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the present application.

[0024] The particle size of the pitch in the embodiment is 10-15µm, the coking value is 45-55%, and the softening point is 150-200°C, the surface of the natural graphite is porous, the pore volume is 0.05-0.10cm / g, and the particle size is 10-20um.

[0025] The preparation method of the modifier in the embodiment is: S01: The zinc oxide whisker is first stirred sufficiently in a sufficient amount of mass fraction 5-8% potassium permanganate solution, and then subjected to water washing, suction filtration and drying to obtain dried zinc oxide whisker; S02: 2-3 parts of octadecyldimethylchlorosilane and 1-2 parts of nano-attapulgite are added to 5-8 parts of ethanol aqueous solution and stirred uniformly to obtain an impregnating liquid; The nano-titanium dioxide is ultrasonically impregnated in the impregnating liquid in an amount of 3-5 times the total amount of nano-titanium dioxide, after the impregnation is completed, the mixture is subjected to suction filtration and drying to obtain the modified nano-titanium dioxide agent; S03: 3-5 parts of the modified nano-titanium dioxide agent, 1-3 parts of boron nitride and 1-2 parts of titanate coupling agent are added to 5-8 parts of lanthanum nitrate solution and subjected to blending and ball milling treatment, after the ball milling is completed, a complexing liquid is obtained; The dried zinc oxide whisker and the complexing liquid are stirred sufficiently at a weight ratio of 7:11, after the stirring is completed, the mixture is subjected to suction filtration and drying to obtain the modifier.

[0026] The ultrasonic power of the ultrasonic immersion treatment of the embodiment is 350-400W, and the ultrasonic time is 1h; the ball milling speed of the blending ball milling treatment is 1000-1500r / min, and the ball milling time is 2h.

[0027] The mass fraction of the lanthanum nitrate solution of the embodiment is 4-7%.

[0028] The preparation method of the ball milling liquid of the embodiment is as follows: S11: 2-3 parts of a silane coupling agent and 2-3 parts of a sodium silicate solution with a mass concentration of 5-8% are added into 8-12 parts of a polyvinyl alcohol aqueous solution, and the mixture is uniformly blended to obtain a base liquid; S12: nanocellulose, a sodium citrate solution, and kaolin powder are uniformly blended according to a weight ratio of (2-4):6:(3-5), and then washed with water, filtered, and dried to obtain an additive; The additive and the base liquid are stirred according to a weight ratio of 3:5, and the stirring is stopped after ultrasonic treatment to obtain a ball milling liquid.

[0029] The mass fraction of the polyvinyl alcohol aqueous solution of the embodiment is 5-8%, and the mass fraction of the sodium citrate solution is 8-12%.

[0030] The silane coupling agent of the embodiment is silane coupling agent KH560.

[0031] The stirring temperature of the stirring treatment of the embodiment is 50-55°C, the stirring speed is 750-850r / min, and the stirring time is 1h.

[0032] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment.

[0033] Embodiment 1. The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment comprises the following steps: The nanosilicon powder, pitch, and sodium dodecyl benzene sulfonate are blended and ground, and then uniformly stirred with natural graphite, defoaming treatment, centrifugal spray drying at 270°C, and carbonization at 700°C for 1h to obtain a base material; the mass ratio of the natural graphite, nanosilicon powder, pitch, and sodium dodecyl benzene sulfonate is 100:20:10:5; The base material, modifier, and ball milling liquid are blended according to a weight ratio of 11:3:4, ball milling is performed at a speed of 1000r / min for 1h, and then the mixture is filtered, dried, and heat treated at 750°C for 1h to obtain the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment.

[0034] The particle size of the pitch of the embodiment is 10µm, the coking value is 45%, the softening point is 150°C, the surface of the natural graphite is porous, the pore volume is 0.05cm / g, and the particle size is 10um.

[0035] The preparation method of the modifier of the embodiment is as follows: S01: Stir the zinc oxide whisker in a sufficient amount of 5% mass fraction potassium permanganate solution, then wash with water, filter and dry to obtain dry zinc oxide whisker; S02: Add 2 parts of octadecyldimethylchlorosilane and 1 part of nano attapulgite into 5 parts of ethanol aqueous solution and stir to obtain an impregnating solution; Ultrasonic impregnation treatment is performed on the nano titanium dioxide in an impregnating solution with 3 times the total amount of nano titanium dioxide, and after the impregnation is completed, the mixture is filtered and dried to obtain the modified nano titanium dioxide agent; S03: 3 parts of the modified nano titanium dioxide agent, 1 part of boron nitride and 1 part of titanate coupling agent are added into 5 parts of lanthanum nitrate solution for blending and ball milling, and after the ball milling is completed, a complex solution is obtained; The dry zinc oxide whisker and the complex solution are stirred according to a weight ratio of 7:11, and after the stirring is completed, the mixture is filtered and dried to obtain the modifier.

[0036] The ultrasonic power of the ultrasonic impregnation treatment of the embodiment is 350 W, and the ultrasonic treatment is performed for 1 h; the ball milling speed of the blending and ball milling treatment is 1000 r / min, and the ball milling is performed for 2 h.

[0037] The mass fraction of the lanthanum nitrate solution of the embodiment is 4%.

[0038] The preparation method of the ball milling solution of the embodiment is as follows: S11: 2 parts of silane coupling agent and 2 parts of 5% mass concentration sodium silicate solution are added into 8 parts of polyvinyl alcohol aqueous solution, and the mixture is blended uniformly to obtain a base solution; S12: Nano cellulose, sodium citrate solution and kaolin powder are blended according to a weight ratio of 2:6:3, and then washed with water, filtered and dried to obtain an additive; The additive and the base solution are stirred according to a weight ratio of 3:5, and after the ultrasonic treatment is completed, a ball milling solution is obtained.

[0039] The mass fraction of the polyvinyl alcohol aqueous solution of the embodiment is 5%, and the mass fraction of the sodium citrate solution is 8%.

[0040] The silane coupling agent of the embodiment is silane coupling agent KH560.

[0041] The stirring temperature of the stirring treatment of the embodiment is 50℃, the stirring speed is 750 r / min, and the stirring is performed for 1 h.

[0042] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment.

[0043] Embodiment 2. The preparation method of the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment comprises the following steps: The nano-silicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, and then stirred uniformly with the natural graphite, and then defoaming treatment is performed, and finally centrifugal spray drying is performed at 270 DEG C, and then carbonization is performed at 700 DEG C for 1h to obtain a base material; wherein the mass ratio of the natural graphite, nano-silicon powder, pitch and sodium dodecyl benzene sulfonate is 100:20:10:5; The base material, modifier and ball milling liquid are blended and ball milled at a weight ratio of 15:5:4 for 1h, the ball milling speed is 1500r / min, after the ball milling is completed, suction filtration and drying are performed, and then heat treatment is performed at 800 DEG C for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment.

[0044] The particle size of the pitch of the embodiment is 15µm, the coking value is 55%, the softening point is 200 DEG C, the surface of the natural graphite is porous, the pore volume is 0.10cm / g, and the particle size is 20um.

[0045] The preparation method of the modifier of the embodiment is as follows: S01: The zinc oxide whisker is first stirred sufficiently in a sufficient amount of mass fraction 8% potassium permanganate solution, and then washed with water, suction filtered, and dried to obtain dry zinc oxide whisker; S02: 3 parts of octadecyl dimethyl chlorosilane and 2 parts of nano attapulgite are stirred uniformly in 8 parts of an ethanol aqueous solution to obtain an impregnating solution; The nano titanium dioxide is ultrasonically impregnated in the impregnating solution with a nano titanium dioxide amount of 5 times, after the impregnation is completed, suction filtration and drying are performed to obtain the modified nano titanium dioxide agent; S03: 5 parts of the modified nano titanium dioxide agent, 3 parts of boron nitride and 2 parts of titanate coupling agent are added to 8 parts of lanthanum nitrate solution for blending and ball milling treatment, after the ball milling is completed, a complex solution is obtained; The dry zinc oxide whisker and the complex solution are stirred sufficiently at a weight ratio of 7:11, after the stirring is completed, suction filtration and drying are performed to obtain the modifier.

[0046] The ultrasonic power of the ultrasonic impregnation treatment of the embodiment is 400W, and the ultrasonic treatment is performed for 1h; the ball milling speed of the blending and ball milling treatment is 1500r / min, and the ball milling treatment is performed for 2h.

[0047] The mass fraction of the lanthanum nitrate solution of the embodiment is 7%.

[0048] The preparation method of the ball milling liquid of the embodiment is as follows: S11: 3 parts of silane coupling agent and 3 parts of sodium silicate solution with a mass concentration of 8% are added to 12 parts of polyvinyl alcohol aqueous solution, and then blended uniformly to obtain a base liquid; S12: blend the nanocellulose, the sodium citrate solution and the kaolin powder according to a weight ratio of 4:6:5, and then perform water washing, suction filtration and drying to obtain an additive; S03: stir and treat the additive and the base liquid according to a weight ratio of 3:5, and then perform ultrasonic treatment to obtain a ball-milling liquid.

[0049] The mass fraction of the polyvinyl alcohol aqueous solution in this embodiment is 8%; and the mass fraction of the sodium citrate solution is 12%.

[0050] The silane coupling agent in this embodiment is silane coupling agent KH560.

[0051] The stirring temperature of the stirring treatment in this embodiment is 55°C, the stirring speed is 850 r / min, and the stirring time is 1 h.

[0052] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-swelling silicon-carbon negative electrode material in this embodiment.

[0053] Embodiment 3. The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material in this embodiment comprises the following steps: The nanosilicon powder, the pitch and the sodium dodecyl benzene sulfonate are blended and ground, and then are uniformly stirred with the natural graphite, and then are subjected to defoaming treatment, and finally are subjected to centrifugal spray drying at 270°C, and are carbonized at 700°C for 1 h to obtain a base material; wherein the mass ratio of the natural graphite, the nanosilicon powder, the pitch and the sodium dodecyl benzene sulfonate is 100:20:10:5. The base material, the modifier and the ball-milling liquid are blended according to a weight ratio of 13:4:4, and are ball-milled for 1 h at a ball-milling speed of 1250 r / min, and then are subjected to suction filtration and drying, and are subjected to heat treatment at 775°C for 1 h to obtain the high-capacity low-swelling silicon-carbon negative electrode material.

[0054] The particle size of the pitch in this embodiment is 12.5 µm, the coking value is 50%, the softening point is 175°C, the surface of the natural graphite is porous, the pore volume is 0.07 cm 3 / g, and the particle size is 15 µm.

[0055] The preparation method of the modifier in this embodiment is: S01: the zinc oxide whisker is first stirred in a sufficient amount of a potassium permanganate solution with a mass fraction of 6.5% until fully stirred, and then is subjected to water washing, suction filtration and drying to obtain dried zinc oxide whisker; S02: 2.5 parts of octadecyldimethylchlorosilane and 1.5 parts of nanometer attapulgite are uniformly stirred in 6.5 parts of an ethanol aqueous solution to obtain an impregnating solution; The nanometer titanium dioxide is ultrasonically impregnated in an impregnating solution with a total amount of 4 times that of the nanometer titanium dioxide, and then is subjected to suction filtration and drying after impregnation to obtain the modified nanometer titanium dioxide agent; S03: 4 parts of modified nano-titanium dioxide agent, 2 parts of boron nitride and 1.5 parts of titanate coupling agent are added into 6.5 parts of lanthanum nitrate solution for blending ball milling treatment; after the ball milling, a complexing liquid is obtained; The dry zinc oxide whisker and the complexing liquid are stirred and treated according to a weight ratio of 7:11; after the stirring, the mixture is extracted and dried to obtain the modifier.

[0056] The ultrasonic power of the ultrasonic immersion treatment in this embodiment is 375 W, and the ultrasonic treatment is performed for 1 h; the ball milling speed of the blending ball milling treatment is 1250 r / min, and the ball milling is performed for 2 h.

[0057] The mass fraction of the lanthanum nitrate solution in this embodiment is 5.5%.

[0058] The preparation method of the ball milling liquid in this embodiment is as follows: S11: 2.5 parts of silane coupling agent and 2.5 parts of sodium silicate solution with a mass concentration of 6.5% are added into 10 parts of polyvinyl alcohol aqueous solution, and the mixture is uniformly blended to obtain a base liquid; S12: nanocellulose, sodium citrate solution and kaolin powder are blended according to a weight ratio of 3:6:4, and then washed with water, extracted, and dried to obtain an additive; The additive and the base liquid are stirred according to a weight ratio of 3:5, and the ultrasonic treatment is performed to obtain a ball milling liquid.

[0059] The mass fraction of the polyvinyl alcohol aqueous solution in this embodiment is 6.5%, and the mass fraction of the sodium citrate solution is 10%.

[0060] The silane coupling agent in this embodiment is silane coupling agent KH560.

[0061] The stirring temperature of the stirring treatment in this embodiment is 52°C, the stirring speed is 800 r / min, and the stirring is performed for 1 h.

[0062] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-swelling silicon-carbon negative electrode material in this embodiment.

[0063] Embodiment 4. The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material in this embodiment comprises the following steps: The nanosilicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, and then uniformly stirred with natural graphite, defoaming treatment, centrifugal spray drying at 270°C, and carbonization at 700°C for 1 h to obtain a base material; wherein the mass ratio of natural graphite, nanosilicon powder, pitch and sodium dodecyl benzene sulfonate is 100:20:10:5; The base material, modifier and ball milling liquid are blended in a weight ratio of 12:3:4 for ball milling for 1h at a ball milling speed of 1100r / min, and after the ball milling is completed, the mixture is filtered and dried, and then heat treated at 760℃ for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the application.

[0064] The asphalt of this embodiment has a particle size of 12um, a coking value of 47%, a softening point of 170℃, and the surface of the natural graphite is porous with a pore volume of 0.06cm / g and a particle size of 12um.

[0065] The preparation method of the modifier of this embodiment is as follows: S01: The zinc oxide whisker is first stirred in a sufficient amount of a 6% mass fraction potassium permanganate solution, and then washed with water, filtered, and dried to obtain dry zinc oxide whisker; S02: 2 parts of octadecyl dimethyl chlorosilane and 1 part of nano attapulgite are uniformly stirred in 6 parts of an ethanol aqueous solution to obtain an impregnating solution; The nano titanium dioxide is ultrasonically impregnated in an impregnating solution with a nano titanium dioxide content of 4 times, and after the impregnation is completed, the mixture is filtered and dried to obtain the modified nano titanium dioxide agent; S03: 4 parts of the modified nano titanium dioxide agent, 2 parts of boron nitride and 1 part of a titanate coupling agent are added to 6 parts of a lanthanum nitrate solution for ball milling, and after the ball milling is completed, a complex solution is obtained; The dry zinc oxide whisker and the complex solution are uniformly stirred in a weight ratio of 7:11, and after the stirring is completed, the mixture is filtered and dried to obtain the modifier.

[0066] The ultrasonic power of the ultrasonic impregnation treatment of this embodiment is 360W, and the ultrasonic treatment is performed for 1h; the ball milling speed of the ball milling treatment is 1200r / min, and the ball milling treatment is performed for 2h.

[0067] The mass fraction of the lanthanum nitrate solution of this embodiment is 5%.

[0068] The preparation method of the ball milling liquid of this embodiment is as follows: S11: 2 parts of a silane coupling agent and 2 parts of a 6% mass concentration sodium silicate solution are added to 9 parts of a polyvinyl alcohol aqueous solution, and the mixture is uniformly blended to obtain a base liquid; S12: Nano cellulose, a sodium citrate solution and kaolin powder are blended in a weight ratio of 2:6:3, and then washed with water, filtered and dried to obtain an additive; The additive and the base liquid are stirred in a weight ratio of 3:5, and after the ultrasonic treatment is completed, a ball milling liquid is obtained.

[0069] The mass fraction of the polyvinyl alcohol aqueous solution of this embodiment is 5-8%, and the mass fraction of the sodium citrate solution is 8-12%.

[0070] The silane coupling agent of the present embodiment is silane coupling agent KH560.

[0071] The stirring temperature of the stirring treatment of the present embodiment is 52℃, the stirring speed is 770r / min, and the stirring time is 1h.

[0072] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-expansion silicon-carbon negative electrode material of the present embodiment.

[0073] Comparative Example 1. Different from Example 3 is that no modifier is added.

[0074] Comparative Example 2. Different from Example 3 is that no dry zinc oxide whisker is added in the modifier.

[0075] Comparative Example 3. Different from Example 3 is that no complexing liquid is added in the modifier.

[0076] Comparative Example 4. Different from Example 3 is that no modified nano-titanium dioxide agent is added in the complexing liquid.

[0077] Comparative Example 5. Different from Example 3 is that the modified nano-titanium dioxide agent is replaced by nano-titanium dioxide.

[0078] Comparative Example 6. Different from Example 3 is that no ball milling liquid is added.

[0079] Comparative Example 7. Different from Example 3 is that no nano-cellulose and kaolin powder is added in the ball milling liquid.

[0080] Comparative Example 8. Different from Example 3 is that the mass ratio of natural graphite, nano-silicon powder, pitch and sodium dodecyl benzene sulfonate is 80:40:10:5.

[0081] Comparative Example 9. Different from Example 3 is that the mass ratio of natural graphite, nano-silicon powder, pitch and sodium dodecyl benzene sulfonate is 110:10:10:5.

[0082] Comparative Example 10. Different from Example 3 is that the base material, modifier and ball milling liquid are in a weight ratio of 16:4:4. Comparative Example 11. Different from Example 3 is that the base material, modifier and ball milling liquid are in a weight ratio of 10:4:4. The conventional performance test of Examples 1-4 and Comparative Examples 1-11, the test of conductivity, cycle and capacity performance, the test method is as follows: First reversible capacity test The prepared silicon-carbon negative electrode material was mixed with a binder PVDF and a conductive agent Super P at a mass ratio of 8:1:1, N-methyl pyrrolidone was added to make a slurry, which was coated on a copper foil (thickness 80-100 μm), and then vacuum dried (120°C, 12 h) and punched into a circular sheet with a diameter of 12 mm as a working electrode; a metal lithium sheet was used as a counter electrode, Celgard 2400 was used as a separator, 1 mol / L LiPF6 (solvent: EC:DMC:EMC=1:1:1, volume ratio) was used as an electrolyte, and a CR2032 type button half battery was assembled in an argon glove box (water and oxygen content <0.1 ppm).

[0083] Charging and discharging tests were carried out at 0.1C rate (1C=4200 mA / g, based on the theoretical capacity of silicon) in the voltage range of 0.01-1.5 V (vs. Li + / Li) using a battery test system LAND CT2001A, and the first discharge capacity was the reversible capacity (taking the average value of 3 parallel experiments).

[0084] 50 cycle capacity retention rate test: The half battery was assembled as above, and a cycle test was carried out at 0.5C rate (the charging and discharging cut-off voltage was as above), the discharge capacities at the 1st and 50th times were recorded, and the capacity retention rate=(50th discharge capacity / 1st discharge capacity)×100%.

[0085] Method for testing volume expansion rate: An in-situ battery test platform with an optical microscope was used to monitor the thickness change of the electrode sheet in real time during the charging and discharging cycles, and the volume expansion rate at 50 cycles (volume expansion rate=(thickness after cycling-initial thickness) / initial thickness×100%) was calculated.

[0086] Method for testing coulombic efficiency: The half battery test was carried out as above, the charge and discharge capacities were recorded, the coulombic efficiency=(discharge capacity / charge capacity)×100%, and the coulombic efficiency at the 50th cycle was taken as the evaluation index.

[0087] The test results are as follows:

[0088] It can be seen from Examples 1-4 and Comparative Examples 1-11 that the product of the application can realize coordinated improvement of high conductivity, high cycle and high capacity performance; Without adding a modifier or a ball milling liquid in the product, the performance of the product is significantly poor, and the performance of the product is most significant when the two are used in combination and together. The dry zinc oxide whisker is not added in the modifier, the complex liquid is not added in the modifier, the modified nano titanium dioxide agent is not added in the complex liquid, the modified nano titanium dioxide agent is prepared by using nano titanium dioxide instead, the ball milling liquid is not added, the nano cellulose and kaolin powder are not added in the ball milling liquid, and the performance of the product has a poor trend, and only the product raw material obtained by the method has the most significant performance effect.

[0089] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0090] Furthermore, it should be understood that although the description is made according to the embodiments, not every embodiment contains only one independent technical solution, and the description is made in this way only for the sake of clarity, and those skilled in the art should consider the description as a whole, and the technical solutions in each embodiment can also be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing a high-capacity, low-expansion silicon-carbon anode material, characterized in that, Includes the following steps: Nano-silicon powder, asphalt, and sodium dodecylbenzenesulfonate are blended and ground together, then mixed evenly with natural graphite, degassed, and finally centrifuged and spray-dried at 270°C, and then carbonized at 700°C for 1 hour to obtain the base material; wherein the mass ratio of natural graphite, nano-silicon powder, asphalt, and sodium dodecylbenzenesulfonate is 100:20:10:

5. The base material, modifier and ball milling fluid are mixed and ball milled at a weight ratio of (11-15):(3-5):4 for 1 hour at a ball milling speed of 1000-1500 r / min. After ball milling, the mixture is filtered, dried and then heat-treated at 750-800℃ for 1 hour to obtain the high-capacity, low-expansion silicon-carbon anode material of the present invention.

2. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 1, characterized in that, The asphalt has a particle size of 10-15µm, a coking value of 45-55%, a softening point of 150-200℃, and the surface of the natural graphite is porous with a pore volume of 0.05-0.10cm³. / g, with a particle size of 10-20um.

3. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 1, characterized in that, The method for preparing the modifier is as follows: S01: First, stir the zinc oxide whiskers in a sufficient amount of potassium permanganate solution with a mass fraction of 5-8%, then wash with water, filter and dry to obtain dried zinc oxide whiskers; S02: Add 2-3 parts of octadecyl dimethyl chlorosilane and 1-2 parts of nano-attapulgite to 5-8 parts of an aqueous ethanol solution and stir evenly to obtain an impregnation solution; Nano-titanium dioxide is impregnated in an impregnation solution with a total amount of 3-5 times that of nano-titanium dioxide and subjected to ultrasonic impregnation. After impregnation, the solution is filtered and dried to obtain modified nano-titanium dioxide agent. SO3: 3-5 parts of modified nano titanium dioxide, 1-3 parts of boron nitride and 1-2 parts of titanate coupling agent are added to 5-8 parts of lanthanum nitrate solution and ball-milled. After ball milling, the compound solution is obtained. Dry zinc oxide whiskers and the compounding solution were stirred thoroughly at a weight ratio of 7:

11. After stirring, the mixture was filtered and dried to obtain the modifier.

4. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 3, characterized in that, The ultrasonic impregnation treatment uses an ultrasonic power of 350-400W and is performed for 1 hour; the ball milling treatment uses a ball milling speed of 1000-1500 r / min and is performed for 2 hours.

5. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 3, characterized in that, The lanthanum nitrate solution has a mass fraction of 4-7%.

6. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 1, characterized in that, The method for preparing the ball milling fluid is as follows: S11: Add 2-3 parts of silane coupling agent and 2-3 parts of sodium silicate solution with a mass concentration of 5-8% to 8-12 parts of polyvinyl alcohol aqueous solution, mix evenly to obtain matrix liquid; S12: Nanocellulose, sodium citrate solution and kaolin powder are mixed thoroughly in a weight ratio of (2-4):6:(3-5), then washed with water, filtered and dried to obtain the additive; The additives and matrix liquid were stirred at a weight ratio of 3:5, and after ultrasonic treatment, the ball milling slurry was obtained.

7. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 6, characterized in that, The polyvinyl alcohol aqueous solution has a mass fraction of 5-8%; the sodium citrate solution has a mass fraction of 8-12%.

8. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 6, characterized in that, The silane coupling agent is silane coupling agent KH560.

9. The method for preparing a high-capacity, low-expansion silicon-carbon anode material according to claim 6, characterized in that, The stirring temperature for the stirring process is 50-55℃, the stirring speed is 750-850 r / min, and the stirring time is 1 hour.

10. The silicon-carbon anode material prepared by the method for preparing a high-capacity, low-expansion silicon-carbon anode material as described in any one of claims 1-9.

Images