A high-capacity low-expansion silicon-carbon negative electrode material and a preparation method thereof

Abstract

The application discloses a preparation method of a high-capacity low-expansion silicon-carbon negative electrode material, which comprises the following steps: blending, grinding and stirring nano silicon powder, pitch and sodium dodecyl benzene sulfonate, uniformly mixing the mixture with natural graphite, performing defoaming treatment, and finally performing centrifugal spray drying at 270 DEG C and carbonization at 700 DEG C for 1 h to obtain a base material; wherein the mass ratio of the natural graphite, the nano silicon powder, the pitch and the sodium dodecyl benzene sulfonate is 100:20:10:5. The silicon-carbon negative electrode material is prepared by using the nano silicon powder, the pitch, the sodium dodecyl benzene sulfonate and the natural graphite, and then by using a modifier and a ball mill liquid to improve the base material, so that the silicon-carbon negative electrode material is prepared by optimizing the coordination between raw materials and has the advantages of high conductivity, high cycle and high capacity, and is a low-expansion silicon-carbon negative electrode material.

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:

[0005] 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, sacrificing the high capacity advantage of silicon.

[0006] Poor compatibility of multi-phase interface: there is an interface energy difference between silicon, carbon and other inorganic additives (such as metal oxides and ceramic phases), which easily forms interface defects, leading to stress concentration and structure collapse.

[0007] Insufficient dispersion uniformity: the surface energy of nano-silicon particles is high, which easily leads to agglomeration, resulting in 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.

[0008] 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 capacity attenuation. SUMMARY

[0009] In view of the defects of the prior art, the purpose of the present application is to provide a silicon-carbon negative electrode material preparation method capable of synergistically realizing high capacity retention and low volume expansion, which solves the problems raised 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" through multi-component synergistic design and interface optimization and a preparation method thereof.

[0010] The technical problem solved by the present application adopts the following technical solutions:

[0011] The present application provides a preparation method of a high-capacity low-expansion silicon-carbon negative electrode material, comprising the following steps:

[0012] 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, and 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;

[0013] 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.

[0014] Preferably, the particle size of the pitch 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.

[0015] Preferably, the preparation method of the modifier is:

[0016] 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;

[0017] 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;

[0018] The nano-titanium dioxide is ultrasonically impregnated in an impregnating solution with a nano-titanium dioxide content of 3-5 times, then filtered and dried to obtain the modified nano-titanium dioxide agent;

[0019] 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 into 5-8 parts of lanthanum nitrate solution for blending ball milling treatment, and after the ball milling is completed, a complexing liquid is obtained;

[0020] The dry zinc oxide whisker and the complexing liquid are fully stirred according to a weight ratio of 7:11, and after the stirring is completed, the mixture is extracted and dried to obtain the modifier.

[0021] The modifier is improved and optimized by using zinc oxide whisker and potassium permanganate solution, and the nano-titanium dioxide is improved by immersion in the immersion liquid. The improved nano-titanium dioxide is added into the lanthanum nitrate solution for blending ball milling treatment to obtain the complexing liquid. The dry zinc oxide whisker is further improved by the complexing liquid, and the prepared modifier enhances the high conductivity, high cycle and high capacity of the product in the system.

[0022] Preferably, the ultrasonic power of the ultrasonic immersion treatment is 350-400 W, and the ultrasonic treatment is performed for 1 h. The ball milling speed of the blending ball milling treatment is 1000-1500 r / min, and the ball milling is performed for 2 h.

[0023] Preferably, the mass fraction of the lanthanum nitrate solution is 4-7%.

[0024] Preferably, the preparation method of the ball milling liquid is as follows:

[0025] S11: 2-3 parts of silane coupling agent and 2-3 parts of 5-8% mass concentration sodium silicate solution are added into 8-12 parts of polyvinyl alcohol aqueous solution, and the mixture is uniformly blended to obtain a base liquid;

[0026] S12: Nano-cellulose, sodium citrate solution and kaolin powder are blended according to a weight ratio of (2-4):6:(3-5), and then washed with water, extracted, and dried to obtain an additive.

[0027] The additive and the base liquid are stirred according to a weight ratio of 3:5, and the ultrasonic treatment is completed to obtain a ball milling liquid.

[0028] 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%.

[0029] The ball milling liquid is improved by using nano-cellulose, sodium citrate solution and kaolin powder, and then by using the base liquid prepared from polyvinyl alcohol aqueous solution and other raw materials, so that the ball milling liquid enhances the coordination effect of the ball milling liquid and the modifier in the system, and the performance of the product is further improved.

[0030] Preferably, the silane coupling agent is silane coupling agent KH560.

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

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

[0033] Compared with the prior art, the application has the following beneficial effects:

[0034] (1) The high-capacity low-swelling silicon-carbon negative electrode material of the application is prepared by "multi-component synergistic design + interface optimization + process adaptation", which retains the high-capacity advantage of silicon-based materials while significantly inhibiting volume expansion, solves the technical problem that the capacity and stability of the silicon-carbon negative electrode are difficult to balance in the prior art, and compared with the existing silicon-carbon negative electrode (usually capacity ≤ 1500 mAh / g), the reversible capacity of the negative electrode material of the application can reach 2400-2500 mAh / g, the capacity retention rate is ≥ 95% after 50 cycles, the volume expansion rate is ≤ 15% in 50 cycles, the electrode sheet is not obviously powdered or peeled off, the coulombic efficiency is still maintained ≥ 98% after 50 cycles, and the capacity retention rate is ≥ 98% after 50 cycles;

[0035] (2) The application introduces nano silicon powder, reduces the surface energy of the nano silicon powder through the dispersion effect of sodium dodecyl benzene sulfonate, avoids the agglomeration of the nano silicon powder, maximizes the exposure of the active sites of silicon, and ensures high-capacity contribution; the natural graphite serves as a matrix to provide a stable capacity base, and 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 the expansion of the silicon particles, but also connects the graphite to construct a continuous conductive network of "graphite-carbon layer-silicon", solves the problem of poor conductivity of silicon itself, and reduces the loss of capacity due to the obstruction of electron conduction;

[0036] (3) The inorganic phase of boron nitride and titanium dioxide in the modifier accounts for a low proportion, and is tightly combined with the matrix through the titanate coupling agent, so that the overall capacity is not diluted due to "too many inert components", the reinforcing effect and capacity retention are balanced, the zinc oxide whisker forms a "steel skeleton" in the matrix, the high strength of the zinc oxide whisker 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 zinc oxide whisker is pretreated with potassium permanganate to introduce hydroxyl groups, which are reacted with the titanate coupling agent to strengthen the interface bonding with the carbon matrix and avoid "gap expansion" caused by interface separation;

[0037] (4) Nanocellulose in the ball-milling liquid fills the gap between kaolin powder particles, SiO2 converted from sodium silicate forms an "inorganic-organic composite filler", the available space of compressed silicon expansion is formed, sodium citrate inhibits the agglomeration of nanosilicon and modifiers through electrostatic repulsion, ensures the uniform distribution of conductive components (graphite, carbon layer), avoids the decrease of rate performance caused by local insulation, the spherical structure formed by centrifugal spray drying improves the packing density, further reduces the expansion space, and the carbonized polyvinyl alcohol forms a "flexible bonding network" with nanocellulose, which can disperse stress to the rigid skeleton (zinc oxide whisker) through deformation even if silicon expands locally, avoiding the overall pulverization of the electrode;

[0038] (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 (expansion-shrinkage of silicon), which ensures the long-term stability of the structure. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with specific embodiments. Obviously, the described embodiments are only part 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 labor fall within the scope of protection of the present application.

[0040] The preparation method of the high-capacity low-expansion silicon-carbon negative electrode material in the embodiment comprises the following steps:

[0041] The nanosilicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, then stirred uniformly with natural graphite, deaerated, and finally centrifugal spray dried at 270°C, and carbonized at 700°C for 1h to obtain the base material; wherein the mass ratio of natural graphite, nanosilicon powder, pitch and sodium dodecyl benzene sulfonate is 100:20:10:5;

[0042] 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 ball-milling, the mixture is filtered and dried, and then heat treated at 750-800°C for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the present application.

[0043] The particle size of the pitch in the embodiment 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.

[0044] The preparation method of the modifier in the embodiment is:

[0045] S01:stirring the zinc oxide whisker in a sufficient amount of 5-8% mass fraction potassium permanganate solution, then washing with water, suction filtration, and drying to obtain dry zinc oxide whisker;

[0046] S02:adding 2-3 parts of octadecyldimethylchlorosilane and 1-2 parts of nano attapulgite to 5-8 parts of ethanol aqueous solution to obtain an impregnating solution;

[0047] Nano titanium dioxide is immersed in an impregnating solution with a nano titanium dioxide content of 3-5 times, and ultrasonic immersion treatment is performed, then suction filtration and drying are performed after the immersion is completed to obtain modified nano titanium dioxide agent;

[0048] S03:adding 3-5 parts of modified nano titanium dioxide agent, 1-3 parts of boron nitride, and 1-2 parts of titanate coupling agent to 5-8 parts of lanthanum nitrate solution for ball milling treatment, and obtaining a complex solution after ball milling;

[0049] The dry zinc oxide whisker and the complex solution are stirred at a weight ratio of 7:11, suction filtration and drying are performed after the stirring is completed, and a modifier is obtained.

[0050] The ultrasonic power of the ultrasonic immersion treatment in this embodiment is 350-400 W, and the ultrasonic treatment is performed for 1 h; the ball milling speed of the ball milling treatment is 1000-1500 r / min, and the ball milling is performed for 2 h.

[0051] The mass fraction of the lanthanum nitrate solution in this embodiment is 4-7%.

[0052] The preparation method of the ball milling solution in this embodiment is as follows:

[0053] S11:adding 2-3 parts of silane coupling agent and 2-3 parts of 5-8% mass concentration sodium silicate solution to 8-12 parts of polyvinyl alcohol aqueous solution to obtain a base solution;

[0054] S12:adding nano cellulose, sodium citrate solution, and kaolin powder at a weight ratio of (2-4):6:(3-5), then washing with water, suction filtration, and drying to obtain an additive;

[0055] The additive and the base solution are stirred at a weight ratio of 3:5, and a ball milling solution is obtained after ultrasonic treatment.

[0056] The mass fraction of the polyvinyl alcohol aqueous solution in this embodiment is 5-8%, and the mass fraction of the sodium citrate solution is 8-12%.

[0057] The silane coupling agent in this embodiment is silane coupling agent KH560.

[0058] The stirring temperature of the stirring treatment in this embodiment is 50-55°C, the stirring speed is 750-850 r / min, and the stirring is performed for 1 h.

[0059] The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment.

[0060] Embodiment 1.

[0061] The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment comprises the following steps:

[0062] The nano-silicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, and then uniformly stirred with 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 1 h 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;

[0063] The base material, modifier and ball milling liquid are blended and ball milled at a weight ratio of 11:3:4 for 1 h, the ball milling speed is 1000 r / min, after the ball milling is completed, suction filtration and drying are performed, and then heat treatment is performed at 750 DEG C for 1 h to obtain the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment.

[0064] The particle size of the pitch of the embodiment is 10 µm, the coking value is 45%, the softening point is 150 DEG C, the surface of the natural graphite is porous, the pore volume is 0.05 cm / g, and the particle size is 10 um.

[0065] The preparation method of the modifier of the embodiment is:

[0066] S01: The zinc oxide whisker is first stirred in a sufficient amount of a 5% mass fraction potassium permanganate solution, and then washed with water, suction filtered and dried to obtain dried zinc oxide whisker;

[0067] S02: 2 parts of octadecyl dimethyl chlorosilane and 1 part of nano-attapulgite are uniformly stirred in 5 parts of an ethanol aqueous solution to obtain an impregnating solution;

[0068] The nano-titanium dioxide is ultrasonically impregnated in an impregnating solution with a nano-titanium dioxide content of 3 times, after the impregnation is completed, suction filtration and drying are performed to obtain the modified nano-titanium dioxide agent;

[0069] S03: 3 parts of the modified nano-titanium dioxide agent, 1 part of boron nitride and 1 part of a titanate coupling agent are added to 5 parts of a lanthanum nitrate solution for blending and ball milling treatment, after the ball milling is completed, a complex solution is obtained;

[0070] The dried zinc oxide whisker and the complex solution are uniformly stirred at a weight ratio of 7:11, after the stirring is completed, suction filtration and drying are performed to obtain the modifier.

[0071] The ultrasonic power of the ultrasonic immersion treatment of the embodiment is 350W, and the ultrasonic time is 1h; the ball milling speed of the blending ball milling treatment is 1000r / min, and the ball milling time is 2h.

[0072] The mass fraction of the lanthanum nitrate solution of the embodiment is 4%.

[0073] The preparation method of the ball milling liquid of the embodiment is as follows:

[0074] 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 are uniformly blended to obtain a base liquid;

[0075] S12: nanocellulose, sodium citrate solution and kaolin powder are uniformly blended according to a weight ratio of 2:6:3, and then are washed with water, filtered, and dried to obtain an additive;

[0076] The additive and the base liquid are stirred according to a weight ratio of 3:5, and then ultrasonic treatment is performed to obtain a ball milling liquid.

[0077] 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%.

[0078] The silane coupling agent of the embodiment is silane coupling agent KH560.

[0079] The stirring temperature of the stirring treatment of the embodiment is 50℃, the stirring speed is 750r / min, and the stirring time is 1h.

[0080] 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.

[0081] Embodiment 2.

[0082] The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment comprises the following steps:

[0083] The nanosilicon powder, pitch and sodium dodecyl benzene sulfonate are blended and ground, and then are uniformly stirred with natural graphite, and then are subjected to defoaming treatment, and finally are subjected to centrifugal spray drying at 270℃, and are carbonized at 700℃ for 1h to obtain a base material; wherein the mass ratio of the natural graphite, nanosilicon powder, pitch and sodium dodecyl benzene sulfonate is 100:20:10:5.

[0084] The base material, modifier and ball milling liquid are blended according to a weight ratio of 15:5:4, and are ball milled for 1h at a ball milling speed of 1500r / min, and then are filtered, dried, and subjected to heat treatment at 800℃ for 1h to obtain the high-capacity low-swelling silicon-carbon negative electrode material of the embodiment.

[0085] The asphalt of the embodiment has a particle size of 15 pm, a coking value of 55%, a softening point of 200°C, and the surface of the natural graphite is porous with a pore volume of 0.10 cm / g, and a particle size of 20 um.

[0086] The preparation method of the modifier of the embodiment is as follows:

[0087] S01: The zinc oxide whisker is first stirred in a sufficient amount of 8% mass fraction potassium permanganate solution, then washed with water, filtered, and dried to obtain dry zinc oxide whisker;

[0088] S02: 3 parts of octadecyldimethylchlorosilane and 2 parts of nano-attapulgite are uniformly stirred in 8 parts of an ethanol aqueous solution to obtain an impregnating solution;

[0089] The nano-titanium dioxide is ultrasonically impregnated in an impregnating solution with a nano-titanium dioxide content of 5 times, and after the impregnation is completed, the mixture is filtered and dried to obtain a modified nano-titanium dioxide agent;

[0090] S03: 5 parts of the modified nano-titanium dioxide agent, 3 parts of boron nitride, and 2 parts of a titanate coupling agent are added to 8 parts of a lanthanum nitrate solution for blending and ball milling, and after the ball milling is completed, a complex solution is obtained;

[0091] The dry zinc oxide whisker and the complex solution are uniformly stirred at a weight ratio of 7:11, and after the stirring is completed, the mixture is filtered and dried to obtain the modifier.

[0092] The ultrasonic impregnation treatment in the embodiment is performed at an ultrasonic power of 400 W for 1 h, and the blending and ball milling treatment is performed at a ball milling speed of 1500 r / min for 2 h.

[0093] The lanthanum nitrate solution in the embodiment has a mass fraction of 7%.

[0094] The preparation method of the ball milling solution in the embodiment is as follows:

[0095] S11: 3 parts of a silane coupling agent and 3 parts of a sodium silicate solution with a mass concentration of 8% are added to 12 parts of a polyvinyl alcohol aqueous solution for blending and uniformity, and a base solution is obtained;

[0096] S12: Nano-cellulose, a sodium citrate solution, and kaolin powder are blended at a weight ratio of 4:6:5, and after washing with water, filtering, and drying, an additive is obtained;

[0097] The additive and the base solution are stirred at a weight ratio of 3:5, and after the ultrasonic treatment is completed, a ball milling solution is obtained.

[0098] The polyvinyl alcohol aqueous solution in the embodiment has a mass fraction of 8%, and the sodium citrate solution has a mass fraction of 12%.

[0099] The silane coupling agent of the embodiment is silane coupling agent KH560.

[0100] The stirring temperature of the stirring treatment of the embodiment is 55°C, the stirring speed is 850r / min, and the stirring time is 1h.

[0101] 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.

[0102] Embodiment 3.

[0103] The preparation method of the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment comprises the following steps:

[0104] The nano-silicon powder, pitch, and sodium dodecyl benzene sulfonate are blended and ground, and then are uniformly stirred with natural graphite, and then are subjected to defoaming treatment, and finally are subjected to centrifugal spray drying at 270°C, and then are 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;

[0105] The base material, modifier, and ball milling liquid are blended at a weight ratio of 13:4:4, and are subjected to ball milling at a ball milling speed of 1250r / min for 1h, and after the ball milling is completed, are subjected to suction filtration and drying, and then are subjected to heat treatment at 775°C for 1h to obtain the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment.

[0106] The particle size of the pitch of the embodiment is 12.5µm, the coking value is 50%, the softening point is 175°C, the surface of the natural graphite is porous, the pore volume is 0.07cm 3 / g, and the particle size is 15um.

[0107] The preparation method of the modifier of the embodiment is:

[0108] S01: The zinc oxide whisker is first stirred in a sufficient amount of mass fraction 6.5% potassium permanganate solution, and then is subjected to water washing, suction filtration, and drying to obtain dried zinc oxide whisker;

[0109] S02: 2.5 parts of octadecyldimethylchlorosilane and 1.5 parts of nano-attapulgite are uniformly stirred in 6.5 parts of an ethanol aqueous solution to obtain an impregnating liquid;

[0110] The nano-titanium dioxide is ultrasonically impregnated in an impregnating liquid that is 4 times the total amount of the nano-titanium dioxide, and after the impregnation is completed, is subjected to suction filtration and drying to obtain the modified nano-titanium dioxide agent;

[0111] S03: 4 parts of the modified nano-titanium dioxide agent, 2 parts of boron nitride, and 1.5 parts of a titanate coupling agent are added to 6.5 parts of a lanthanum nitrate solution for blending and ball milling treatment, and after the ball milling is completed, a complex liquid is obtained;

[0112] The dry zinc oxide whisker and the complexing liquid are stirred and treated fully according to a weight ratio of 7:11, and after the stirring is completed, the mixture is extracted and dried to obtain the modifier.

[0113] The ultrasonic power of the ultrasonic immersion treatment of this embodiment is 375W, and the ultrasonic treatment lasts for 1h; the rotation speed of the ball milling of the blending ball milling treatment is 1250r / min, and the ball milling lasts for 2h.

[0114] The mass fraction of the lanthanum nitrate solution of this embodiment is 5.5%.

[0115] The preparation method of the ball milling liquid of this embodiment is as follows:

[0116] S11: 2.5 parts of a silane coupling agent and 2.5 parts of a sodium silicate solution with a mass concentration of 6.5% are added into 10 parts of a polyvinyl alcohol aqueous solution, and the mixture is blended uniformly to obtain a base liquid;

[0117] S12: The nanocellulose, the sodium citrate solution and the kaolin powder are blended fully according to a weight ratio of 3:6:4, and then the mixture is washed with water, extracted and dried to obtain an additive;

[0118] The additive and the base liquid are stirred and treated according to a weight ratio of 3:5, and after the ultrasonic treatment is completed, a ball milling liquid is obtained.

[0119] The mass fraction of the polyvinyl alcohol aqueous solution of this embodiment is 6.5%, and the mass fraction of the sodium citrate solution is 10%.

[0120] The silane coupling agent of this embodiment is silane coupling agent KH560.

[0121] The stirring temperature of the stirring treatment of this embodiment is 52℃, the stirring rotation speed is 800r / min, and the stirring lasts for 1h.

[0122] The silicon-carbon negative electrode material prepared by the preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of this embodiment.

[0123] Embodiment 4.

[0124] The preparation method of the high-capacity low-swelling silicon-carbon negative electrode material of this embodiment comprises the following steps:

[0125] The nanosilicon powder, the pitch and the sodium dodecyl benzene sulfonate are blended and ground, and then the mixture is stirred uniformly with the natural graphite, and then the mixture is subjected to defoaming treatment, and finally the mixture is subjected to centrifugal spray drying at 270℃ and carbonization at 700℃ for 1h 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.

[0126] 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. 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.

[0127] The asphalt of the 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.

[0128] The preparation method of the modifier of the embodiment is as follows:

[0129] 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;

[0130] 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 liquid;

[0131] The nano-titanium dioxide is ultrasonically impregnated in an impregnating liquid with a nano-titanium dioxide content of 4 times, and then filtered and dried to obtain the modified nano-titanium dioxide agent;

[0132] 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 then the ball milling is completed to obtain a complexing liquid;

[0133] The dry zinc oxide whisker and the complexing liquid are uniformly stirred in a weight ratio of 7:11, and then filtered and dried to obtain the modifier.

[0134] The ultrasonic power of the ultrasonic impregnation treatment of the 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 is performed for 2h.

[0135] The mass fraction of the lanthanum nitrate solution of the embodiment is 5%.

[0136] The preparation method of the ball milling liquid of the embodiment is as follows:

[0137] 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 then uniformly blended to obtain a base liquid;

[0138] 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;

[0139] The additive and the base liquid are stirred and treated in a weight ratio of 3:5, and the ultrasonic treatment is ended to obtain the ball-milling liquid.

[0140] 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%.

[0141] The silane coupling agent of the embodiment is silane coupling agent KH560.

[0142] The stirring temperature of the stirring treatment of the embodiment is 52°C, the stirring speed is 770 r / min, and the stirring time is 1 h.

[0143] The silicon-carbon negative electrode material is prepared by the preparation method of the high-capacity low-expansion silicon-carbon negative electrode material of the embodiment.

[0144] Comparative Example 1.

[0145] Different from Example 3 is that no modifier is added.

[0146] Comparative Example 2.

[0147] Different from Example 3 is that no dry zinc oxide whisker is added to the modifier.

[0148] Comparative Example 3.

[0149] Different from Example 3 is that no complex liquid is added to the modifier.

[0150] Comparative Example 4.

[0151] Different from Example 3 is that no modified nano-titanium dioxide agent is added to the complex liquid.

[0152] Comparative Example 5.

[0153] Different from Example 3 is that the modified nano-titanium dioxide agent is replaced by nano-titanium dioxide.

[0154] Comparative Example 6.

[0155] Different from Example 3 is that no ball-milling liquid is added.

[0156] Comparative Example 7.

[0157] Different from Example 3 is that no nano-cellulose and kaolin powder are added to the ball-milling liquid.

[0158] Comparative Example 8.

[0159] Different from Example 3 is that the mass ratio of the natural graphite, nano-silicon powder, pitch and sodium dodecylbenzenesulfonate is 80:40:10:5.

[0160] Comparative Example 9.

[0161] The difference between Example 3 is that the mass ratio of natural graphite, nano-silicon powder, pitch and sodium dodecyl benzene sulfonate is 110:10:10:5.

[0162] Comparative Example 10.

[0163] The difference between Example 3 is that the base material, modifier and ball milling liquid are in a weight ratio of 16:4:4;

[0164] Comparative Example 11.

[0165] The difference between Example 3 is that the base material, modifier and ball milling liquid are in a weight ratio of 10:4:4;

[0166] The conventional performance test of Examples 1-4 and Comparative Examples 1-11, the test of conductive, cycle and capacity performance, the test method is as follows:

[0167] First reversible capacity test

[0168] The half-cell is assembled and charged and discharged test: the prepared silicon-carbon negative electrode material is mixed with the binder PVDF, the conductive agent SuperP in a mass ratio of 8:1:1, N-methyl pyrrolidone is added to make a slurry, which is coated on a copper foil (thickness 80-100 μm), vacuum dried (120°C, 12h) and then punched into a circular sheet with a diameter of 12mm as a working electrode; the metal lithium sheet is used as the counter electrode, Celgard2400 is used as the separator, 1mol / L LiPF6 (solvent: EC:DMC:EMC=1:1:1, volume ratio) is used as the electrolyte, and the CR2032 type button half-cell is assembled in an argon glove box (water and oxygen content <0.1ppm).

[0169] The battery test system LAND CT2001A is used to perform charge and discharge test at 0.1C rate (1C=4200mA / g, based on the theoretical capacity of silicon) in the voltage range of 0.01-1.5V (vs.Li + / Li), and the first discharge capacity is the reversible capacity (taking the average value of 3 parallel experiments).

[0170] 50 cycle capacity retention rate test:

[0171] The half-cell is assembled as above, and the cycle test is performed at 0.5C rate (the charge and discharge cut-off voltage is the same as above), the discharge capacity of the 1st and the 50th is recorded, and the capacity retention rate=(the 50th discharge capacity / the 1st discharge capacity)×100%.

[0172] The test method of volume expansion rate:

[0173] The thickness change of the electrode sheet during the charge-discharge cycle was monitored in real time by using an in-situ battery test platform with an optical microscope, and the volume expansion rate at 50 cycles was calculated (volume expansion rate = (thickness after cycle - initial thickness) / initial thickness * 100%).

[0174] Coulomb efficiency test method:

[0175] As in the above half-cell test, the charge and discharge capacity of each cycle was recorded, and the coulomb efficiency = (discharge capacity / charge capacity) * 100%, and the coulomb efficiency of the 50th cycle was taken as the evaluation index.

[0176] The test results are as follows:

[0177]

[0178] From examples 1-4 and comparative examples 1-11, it can be seen that the product of the application can realize the coordinated improvement of high conductivity, high cycle and high capacity performance;

[0179] Without adding the modifier, without adding one of the ball milling liquid, the performance of the product is significantly deteriorated, and the performance effect of the product is most significant when the two are used together.

[0180] Without adding dry zinc oxide whiskers in the modifier, without adding the complex liquid in the modifier, without adding the modified nano titanium dioxide agent in the complex liquid, the modified nano titanium dioxide agent is replaced by nano titanium dioxide, without adding the ball milling liquid, without adding nano cellulose and kaolin powder in the ball milling liquid, the performance of the product has a deteriorating trend, and the performance effect of the product is most significant only when the product raw material obtained by the method of the application is used.

[0181] It is apparent to those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and that the application can be implemented in other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the application should be defined by the appended claims rather than by the foregoing description, and it is intended to encompass all changes falling within the meaning and range of equivalents of the claims.

[0182] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can 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-swelling silicon-carbon anode material, characterized in that, The method comprises the following steps: The nanometer silicon powder, asphalt and sodium dodecyl benzene sulfonate are blended and ground, then stirred with natural graphite, defoaming treatment, centrifugal spray drying at 270℃, carbonization at 700℃ for 1h, to obtain the base material; wherein the mass ratio of natural graphite, nanometer silicon powder, asphalt 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 ball milling, the mixture is filtered, dried, and then heat treated at 750-800℃ for 1h, to obtain the high-capacity low-expansion silicon-carbon negative electrode material; The preparation method of the modifier is: S01: The zinc oxide whisker is first stirred in a sufficient amount of 5-8% potassium permanganate solution, then washed with water, filtered, and dried to obtain dry zinc oxide whisker; S02: 2-3 parts of octadecyl dimethyl chlorosilane and 1-2 parts of nanometer attapulgite are stirred in 5-8 parts of ethanol water solution to obtain an impregnating solution; The nanometer titanium dioxide is ultrasonic impregnated in 3-5 times of the total amount of nanometer titanium dioxide impregnating solution, after impregnation, the mixture is filtered and dried to obtain the modified nanometer titanium dioxide agent; S03: 3-5 parts of the modified nanometer 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, to obtain a complex solution; The dry zinc oxide whisker and the complex solution are stirred at a weight ratio of 7:11, then filtered and dried to obtain the modifier; The preparation method of the ball milling liquid is: S11: 2-3 parts of silane coupling agent and 2-3 parts of 5-8% sodium silicate solution are added to 8-12 parts of polyvinyl alcohol aqueous solution, and then blended to obtain a base solution; S12: Nanocellulose, sodium citrate solution and kaolin powder are blended at a weight ratio of (2-4):6:(3-5), then washed with water, filtered and dried to obtain an additive; The additive and the base solution are stirred at a weight ratio of 3:5 to obtain the ball milling liquid.

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%, and a softening point of 150-200℃; the surface of the natural graphite is porous, with a pore volume of 0.05-0.10cm / g and a particle size of 10-20um.

3. The method of claim 1, wherein the high-capacity low-swelling silicon-carbon anode material is prepared by the steps of: preparing a mixture of a carbon source and a silicon source; and sintering the mixture to form the high-capacity low-swelling silicon-carbon anode material. The ultrasonic power for the ultrasonic impregnation treatment is 350-400W, and the ultrasonic treatment time is 1h; the ball milling speed for the blending and ball milling treatment is 1000-1500r / min, and the ball milling time is 2h.

4. The method of claim 1, wherein the high-capacity low-swelling silicon-carbon anode material is prepared by the steps of: preparing a mixture of a carbon source and a silicon source; mixing the mixture with a solvent; and drying the mixture to obtain the high-capacity low-swelling silicon-carbon anode material. The mass fraction of the lanthanum nitrate solution is 4-7%.

5. The method of claim 1, wherein the high-capacity low-swelling silicon-carbon anode material is prepared by the steps of: preparing a mixture of a carbon precursor and a silicon precursor; and sintering the mixture to form the high-capacity low-swelling silicon-carbon anode material. The mass fraction of the polyvinyl alcohol aqueous solution is 5-8%; the mass fraction of the sodium citrate solution is 8-12%.

6. The method of claim 1, wherein the high-capacity low-swelling silicon-carbon anode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the high-capacity low-swelling silicon-carbon anode material. The silane coupling agent is silane coupling agent KH560.

7. The method of claim 1, wherein the high-capacity low-swelling silicon-carbon anode material is prepared by the steps of: preparing a mixture of a silicon source, a carbon source, and a solvent; and heating the mixture to form the high-capacity low-swelling silicon-carbon anode material. The stirring temperature is 50-55℃, the stirring speed is 750-850r / min, and the stirring time is 1h.

8. The silicon-carbon negative electrode material prepared by the method of any one of claims 1-7.

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