CN115642234A - Silicon-carbon negative electrode material with pore gradient structure, preparation method thereof and lithium ion battery - Google Patents
Silicon-carbon negative electrode material with pore gradient structure, preparation method thereof and lithium ion battery Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention relates to the technical field of lithium ion battery cathode materials, and discloses a silicon-carbon cathode material with a pore gradient structure, a preparation method of the silicon-carbon cathode material and a lithium ion battery. Silicon carbon negative pole material includes the kernel and the cladding is in the carbon coating of the surface of kernel, wherein, the kernel includes inlayer and superficial layer from inside to outside in proper order, and silicon carbon negative pole material's inside has gradient distribution's hole, and along the inlayer superficial layer and carbon coating, the porosity is the gradient from inside to outside and descends. The silicon-carbon cathode material with the pore gradient structure has the advantages that the internal pores are sequentially reduced from inside to outside to form a stable inner layer and a shallow surface layer, and meanwhile, the compact carbon coating layer is combined, so that the occurrence of side reactions and the outward expansion of silicon can be inhibited.
Description
Technical Field
The invention relates to the technical field of lithium ion battery cathode materials, in particular to a silicon-carbon cathode material with a pore gradient structure, a preparation method of the silicon-carbon cathode material and a lithium ion battery.
Background
The lithium ion battery which is commercially used at present mainly adopts pure graphite or a graphite/silicon-carbon mixture doped with a small amount of silicon as a negative electrode material, but because the theoretical specific capacity of the graphite is only 372mAh/g, and the specific capacity of the graphite/silicon-carbon mixture is generally below 500mAh/g, the further improvement of the specific energy of the lithium ion battery is limited, and the requirements of the development of new energy industries such as electric automobiles and the like at present cannot be met. The silicon cathode based on alloying reaction has the theoretical lithium storage capacity as high as 4200mAh/g, and is an ideal choice for the cathode material of the next generation lithium ion battery. However, the huge volume expansion (> 300%) of silicon during the alloying reaction with lithium leads to particle pulverization and deactivation, so that the cycling stability of silicon is poor, especially for a silicon-carbon negative electrode with high specific capacity.
CN109638229A discloses a silicon-carbon composite negative electrode material, a preparation method thereof, and a lithium ion battery, where the silicon-carbon composite negative electrode material is a core-shell structure material, where the core part includes nano-silicon, amorphous carbon, graphene, and carbon nanotubes, the surface of the nano-silicon is coated with the amorphous carbon, the nano-silicon coated with the amorphous carbon is distributed on the surfaces of the graphene and the carbon nanotubes, the carbon nanotubes form a three-dimensional cross-linked network, the graphene is uniformly distributed in the three-dimensional cross-linked network, and the shell part is a carbon layer. However, the pitch of CN109638229A is simply a double structure in which the pitch is sprayed on the surface of the core to form a structure having uniform voids inside and a carbon coating layer outside.
Therefore, the research and development of the porous silicon-carbon negative electrode material have important significance for solving the problem of the cycling stability of the silicon-based negative electrode.
Disclosure of Invention
The invention aims to overcome the defect of poor cycle stability of a silicon-based cathode in the prior art, and provides a silicon-carbon cathode material with a pore gradient structure, a preparation method thereof and a lithium ion battery.
In order to achieve the above object, a first aspect of the present invention provides a silicon-carbon negative electrode material with a pore gradient structure, where the silicon-carbon negative electrode material includes an inner core and a carbon coating layer coated on an outer surface of the inner core, where the inner core includes an inner layer and a shallow surface layer in sequence from inside to outside, and the silicon-carbon negative electrode material has pores distributed in a gradient manner inside, and the porosity decreases in a gradient manner from inside to outside along the inner layer, the shallow surface layer, and the carbon coating layer.
In a second aspect, the present invention provides a method for preparing the aforementioned silicon-carbon anode material with a pore gradient structure, wherein the method includes:
(1) Contacting nano silicon particles, a carbon source, a dispersing agent, a conductive agent and water to prepare slurry; carrying out spray granulation on the slurry, and then carrying out first calcination treatment to obtain a silicon-carbon composite inner core 1;
(2) Heating the mixture containing the silicon-carbon composite kernel 1, the solvent and the high-temperature asphalt 1, and performing second calcination treatment on the obtained silicon-carbon composite containing asphalt on the superficial layer to obtain a silicon-carbon composite kernel 2 with high porosity of the inner layer and low porosity of the superficial layer;
(3) And carrying out mechanical fusion or CVD (chemical vapor deposition) coating on the silicon-carbon composite core 2 and the high-temperature asphalt 2, and carrying out high-temperature carbonization treatment to obtain the silicon-carbon negative electrode material with a compact carbon coating layer on the outer part, high inner-layer porosity and low superficial-layer porosity.
The invention provides a lithium ion battery, wherein the lithium ion battery comprises the silicon-carbon negative electrode material with the pore gradient structure.
Through the technical scheme, the invention has the following beneficial effects:
(1) Through gradient pore design, a stable inner layer and a shallow surface layer are formed, and a compact carbon coating layer is combined, so that the problem of silicon-carbon cathode expansion is solved;
(2) The problem that the silicon cathode is insufficient in conductivity and the like is solved by adding the one-dimensional carbon material into the inner core, and meanwhile, the one-dimensional carbon material can play a role in winding and stabilizing the structure;
(3) The gradient porosity is gradually reduced to form a stable inner layer and a shallow surface layer, so that the generation of side reaction and outward expansion of silicon are inhibited;
(4) The outermost layer of the silicon-carbon negative electrode material is densely coated with carbon, so that the specific surface area is reduced, the tap density is increased, the direct contact between electrolyte and silicon is isolated, a good SEI (solid electrolyte interface) film is constructed, the first effect (first coulombic efficiency) of the material is improved, the capacity retention rate is improved, the tap density of the material is improved, and the material coating is facilitated;
(5) The preparation process is simple and easy to industrialize.
Drawings
FIG. 1 is a schematic structural diagram of a silicon carbon anode material with a pore gradient structure according to the present invention;
fig. 2 is an SEM electron micrograph of the silicon carbon negative electrode material having the pore gradient structure prepared in example 1 of the present invention.
Description of the reference numerals
1-an inner layer; 2-superficial layer; 3-a carbon coating layer;
4-one-dimensional carbon material; 5-nano silicon particles; 6-irregular internal porosity.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.
As mentioned above, in a first aspect of the present invention, there is provided a silicon-carbon negative electrode material with a pore gradient structure, as shown in fig. 1, the silicon-carbon negative electrode material includes an inner core and a carbon coating layer 3 coated on an outer surface of the inner core, where the inner core includes an inner layer 1 and a shallow surface layer 2 in sequence from inside to outside, and the silicon-carbon negative electrode material has pores distributed in a gradient manner inside, and the porosity decreases in a gradient manner from inside to outside along the inner layer, the shallow surface layer and the carbon coating layer.
The inventors of the present invention found that: the porosity of the porous silicon carbon negative electrode material in the prior art is not reasonably controlled, and the volume expansion cannot be well controlled. The silicon-carbon cathode material has the advantages that the internal pore structure is different from that of the prior art, the porosity is reduced from inside to outside in sequence, a stable inner layer and a shallow surface layer can be formed, and the silicon expansion tends to expand inwards by combining a compact carbon coating layer, so that a good expansion limiting effect is achieved.
Further, the conductive layer in the prior art does not have a good conductive function between the core and the outermost layer. The conductive agent is dispersed in the whole particle, can play a better conductive role, and makes up for the defect of the conductivity of the semiconductor silicon.
Furthermore, in the whole process of the prior art, sintering and crushing are carried out after direct ball milling, so that the structure of the material is not ordered and different in size, and the particles are not smooth enough, and some silicon powder can be exposed outside directly after crushing, which is not beneficial to subsequent coating; the invention carries out granulation treatment on the slurry, thereby overcoming the defect problems in the prior art.
Furthermore, the inventor of the present invention found that the pitch of CN109638229A in the prior art is uniformly distributed in the particles by spraying, and forms a structure with uniform voids inside and a carbon coating outside, which is only a simple dual structure. The asphalt is distributed on the shallow surface layer of the core under a special process, and after carbonization, a structure with high porosity of the core and low porosity of the shallow surface layer is formed. Meanwhile, the outermost part of the invention is also provided with a more compact carbon coating layer 3 with extremely low porosity, so the invention has a triple structure, which is sequentially as follows: an inner layer 1 with high porosity, a shallow surface layer 2 with low porosity and a carbon coating layer 3 with very low porosity. Based on the above, the expansion of silicon can be more effectively limited just by the structure with gradually reduced porosity from inside to outside, so that the cycle performance is optimized.
According to the present invention, as shown in fig. 1, the porosity of the inner layer 1 is 30 to 60%, the porosity of the shallow surface layer 2 is 10 to 30%, the porosity of the carbon coating layer (the porosity of the carbon coating layer 3 is <20%, preferably 1 to 10%; preferably, the porosity of the inner layer 1 is 40 to 50%, the porosity of the shallow surface layer 2 is 10 to 15%, the porosity of the carbon coating layer (the carbon coating layer 3) is 1 to 5%, more preferably, the porosity of the inner layer 1 is 40.6 to 47.5%, the porosity of the shallow surface layer 2 is 11.5 to 14.9%, and the porosity of the carbon coating layer (the carbon coating layer 3) is 1.2 to 4.8%.
According to the invention, the pore size distribution of the internal pores of the inner layer 1 is 10-1000nm, the pore size distribution of the internal pores of the shallow surface layer 2 is 5-20nm, and the pore size distribution of the internal pores of the carbon coating layer (carbon coating layer 3) is more than 0 and less than or equal to 10nm, preferably 0.01-10nm, and more preferably 1-10nm; more preferably, the pore size distribution of the internal pores of the inner layer 1 is 30 to 60nm, the pore size distribution of the internal pores of the superficial layer 2 is 5 to 10nm, and the pore size distribution of the internal pores of the carbon coating layer (carbon coating layer 3) is 1 to 5nm. In the invention, the inner layer 1 and the shallow surface layer 2 are stably formed through gradient pore design, and the problem of silicon-carbon cathode expansion can be solved by combining the compact carbon coating layer 3.
According to the invention, the average pressure which can be borne by the porous silicon-carbon negative electrode material is 400-1400MPa, preferably 500-1000MPa, and more preferably 674-899MPa.
According to the invention, D of the silicon-carbon anode material 50 5-30 μm; the tap density is 0.5-1.2g/cm 3 (ii) a The specific surface area is 0.5-40m 2 (ii)/g; preferably, D of the silicon-carbon negative electrode material 50 5-15 μm; the tap density is 0.8-1.1g/cm 3 (ii) a The specific surface area is 0.5-10m 2 (ii)/g; more preferably, D of the silicon-carbon anode material 50 5-8.8 μm; the tap density is 0.8-1g/cm 3 (ii) a The specific surface area is 0.5-7m 2 (ii)/g; more preferably, D of the silicon-carbon negative electrode material 50 8.2-8.8 μm; the tap density is 0.82-1g/cm 3 (ii) a The specific surface area is 0.5-6.3m 2 /g。
According to the invention, D is taken as the silicon-carbon anode material 50 The particle size of the inner layer 1 is 20-90%, preferably 20-50%; that is, in the present invention, D of the silicon-carbon anode material 50 Is 5-30 μm, and correspondingly, the particle size of the inner layer 1 is 1-27 μm, preferably 1-15 μm, and more preferably 2.1-5.2 μm.
According to the invention, the superficial layer 2 has a thickness of 0.25 to 12 μm; preferably, the thickness of the superficial layer 2 is 2-10 μm; more preferably, the superficial layer 2 has a thickness of 3 to 5.8 μm.
According to the invention, the thickness of the carbon coating layer (carbon coating layer 3) is 10nm to 1 μm; preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 10nm to 700nm; more preferably, the thickness of the carbon coating layer (carbon coating layer 3) is 10nm to 600nm.
According to the present invention, the coating amount of the carbon coating layer (carbon coating layer 3) is 1 to 20 wt%, preferably 10 to 20 wt% of the silicon-carbon negative electrode material.
According to the invention, the inner core comprises a silicon carbon composite and/or an amorphous carbon material; preferably, the silicon carbon composite includes nano silicon particles 5 and a conductive agent.
According to the invention, D of said nano-silicon particles 50 Is 30-500nm, preferably 30-100nm; in the invention, the nano silicon particles are silicon powder.
According to the present invention, the conductive agent includes a metallic material and/or a non-metallic material; preferably, the conductive agent includes a one-dimensional carbon material 4; more preferably, the one-dimensional carbon material 4 is a conductive carbon material; still further preferably, the conductive carbon material comprises one or more of single-walled CNTs (single-walled carbon nanotubes), multi-walled CNTs (multi-walled carbon nanotubes), and carbon fibers; wherein the carbon fiber comprises VGCF (vapor grown carbon fiber).
According to the present invention, the aspect ratio of the one-dimensional carbon material 4 is (20 to 20000): 1, preferably (100-300): 1.
the conductive agent is dispersed in the whole particle, and can play a better conductive role.
According to the invention, the silicon-carbon negative electrode material comprises silicon, a one-dimensional carbon material and amorphous carbon, and the weight ratio of the content of the silicon to the total content of the one-dimensional carbon material and the amorphous carbon is (40-80): (20-60) based on the total weight of the silicon-carbon negative electrode material.
In a second aspect, the present invention provides a method for preparing the aforementioned silicon-carbon anode material with a pore gradient structure, wherein the method includes:
(1) Contacting nano silicon particles, a carbon source, a dispersing agent, a conductive agent and water to prepare slurry; carrying out spray granulation on the slurry, and then carrying out first calcination treatment to obtain a silicon-carbon composite inner core 1;
(2) Heating the mixture containing the silicon-carbon composite kernel 1, the solvent and the high-temperature asphalt 1, and performing second calcination treatment on the obtained silicon-carbon composite containing asphalt on the shallow surface layer to obtain a silicon-carbon composite kernel 2 with high porosity of the inner layer 1 and low porosity of the shallow surface layer 2;
(3) And carrying out mechanical fusion or CVD (chemical vapor deposition) coating on the silicon-carbon composite core 2 and the high-temperature asphalt 2, and carrying out high-temperature carbonization treatment to obtain the silicon-carbon negative electrode material which is provided with a compact carbon coating layer 3 on the outer part, and has high porosity of the inner layer 1 and low porosity of the superficial layer 2.
According to the present invention, the conditions of the first calcination treatment, the second calcination treatment, and the high-temperature carbonization treatment are the same or different, and the respective sintering procedures include: the heating rate is 1-5 ℃/min, the final heating temperature is 600-1200 ℃, and the heat preservation time is 1-6 hours; preferably, the heating rate is 1-5 ℃/min, the final heating temperature is 900-1100 ℃, and the heat preservation time is 3-5 hours.
According to the invention, the sintering is carried out under an inert atmosphere; preferably, the inert atmosphere comprises nitrogen or argon.
According to the invention, the carbon source is selected from one or more of low-temperature asphalt, medium-temperature asphalt, high-temperature asphalt, water-soluble asphalt, phenolic resin, CMC, glucose and sucrose.
According to the invention, the dispersant comprises one or more of PVP (polyvinylpyrrolidone), CTAB (cetyltrimethylammonium bromide), polyethylene glycol and SDS (sodium dodecyl sulphate).
According to the invention, the nano silicon particles, the carbon source, the conductive agent and the dispersing agent are used in a weight ratio of (40-85): (5-50): (5-40): (5-20); preferably (60-80): (10-30): (20-40): (5-10).
According to the invention, in step (1), the solids content of the slurry is from 1 to 40% by weight, preferably from 20 to 30% by weight.
According to the present invention, in the step (2), the conditions of the heat treatment include: the temperature is 600-1200 ℃, and the preferable temperature is 900-1100 ℃; in the invention, under the heating condition, the high-temperature asphalt is completely dissolved, the solvent is slowly evaporated, the dissolved high-temperature asphalt is infiltrated into the pores of the silicon-carbon composite core 1 under the channel established by the solvent, and the infiltration amount of the asphalt is 5-30 wt%.
According to the present invention, in step (2), the solvent comprises one or more of tetrahydrofuran, NMP, toluene and xylene, preferably tetrahydrofuran.
According to the present invention, in the step (3), the coating is performed using at least one of a particle fusion machine, a VCJ machine, and CVD.
According to the present invention, the high temperature asphalt 1 is used in an amount of 5 to 30 wt%, preferably 20 to 30 wt%, based on the total weight of the silicon-carbon composite core 1.
According to the present invention, in step (3), the high temperature pitch 2 is used in an amount of 1 to 20 wt%, preferably 10 to 20 wt%, based on the total weight of the silicon carbon composite core 2.
According to the invention, the high-temperature asphalt 1 and the high-temperature asphalt 2 are the same or different and are respectively selected from one or more high-temperature asphalt with the softening point of 200 ℃, 250 ℃, 280 ℃ and 300 ℃.
The invention provides a lithium ion battery, wherein the lithium ion battery comprises the silicon-carbon negative electrode material with the pore gradient structure.
In the invention, a silicon-carbon negative electrode material with a pore gradient structure, a conductive agent, a binder and deionized water are mixed into slurry to be coated, dried and cut to obtain a pole piece; assembling a lithium sheet and a conventional electrolyte into a button half cell; wherein the silicon-carbon anode material with the pore gradient structure, the conductive agent and the binder are used in a weight ratio of (70-95): (0.1-10): (2-25).
The present invention will be described in detail below by way of examples.
In the following examples and comparative examples:
the hardness parameters are tested by a micro compression tester to obtain the parameters.
The porosity is statistically calculated by tomography (CT) and algorithms.
The tap density, the specific surface area and the particle size are measured by a tap density meter, a specific surface area analyzer and a laser particle analyzer to obtain data.
The thicknesses of the inner layer, the shallow surface layer and the carbon coating layer were measured by CP + SEM (ion cutting + scanning electron microscope) and counted to obtain data.
Example 1
This example illustrates a silicon carbon anode material with a pore gradient structure prepared according to the present invention.
(1) Get D 50 120g of 100nm silicon powder, 40g of carbon source high-temperature asphalt, 40g of CNTs (the length-diameter ratio of the CNTs is 200; carrying out spray granulation on the dispersed slurry to obtain a spray-granulated core; sintering the spray granulated core in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 350 ℃ at a heating rate of 5 ℃/min for 2 hours, heating from 350 ℃ to 900 ℃ at a heating rate of 2 ℃/min for 3 hours, and finally cooling to room temperature to obtain a sintered silicon-carbon composite kernel 1;
(2) Then, dispersing the silicon-carbon composite kernel 1 in tetrahydrofuran serving as a solvent, continuously adding 10% of high-temperature asphalt (the softening point is 250 ℃), and heating the mixture at 70 ℃ after the high-temperature asphalt is completely dissolved to slowly evaporate the tetrahydrofuran; infiltrating the dissolved asphalt into pores of the silicon-carbon composite material under a channel established by tetrahydrofuran, obtaining a silicon-carbon composite with asphalt on the shallow surface after the tetrahydrofuran is completely evaporated, and sintering the silicon-carbon composite in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, and finally cooling to room temperature to obtain a silicon-carbon composite inner core 2 with high porosity of an inner layer and low porosity of a superficial layer;
(3) Mechanically fusing a silicon-carbon composite core 2 and 10% high-temperature asphalt (the softening point is 280 ℃) by using a particle fusion machine, and performing high-temperature carbonization treatment, wherein the sintering procedure is as follows in an inert atmosphere: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, cooling to room temperature, and sieving with a 400-mesh sieve to obtain the silicon-carbon negative electrode material which is provided with a compact carbon coating layer on the outer part, has high inner layer porosity and low superficial layer porosity and has a pore gradient structure; the results are shown in Table 1.
Coating a film on the finished silicon-carbon negative electrode material with a pore gradient structure and assembling the finished silicon-carbon negative electrode material with the pore gradient structure with a CR 2032-button cell, wherein the silicon-carbon negative electrode material with the pore gradient structure, a conductive agent, a binder and deionized water are mixed according to the weight ratio of 90:3:7:200, mixing into slurry, coating, drying and cutting to obtain a pole piece; and assembling the lithium sheet and the conventional electrolyte into a button half cell, and carrying out charge and discharge tests. Charge and discharge cycles were performed at a rate of 1C. The battery charge-discharge test is carried out in a multi-channel tester, and the test voltage range of the silicon-carbon cathode material is 0.005V-0.8V; the results are shown in Table 2.
In addition, fig. 1 is a schematic structural diagram of a silicon carbon anode material having a pore gradient structure according to the present invention; as can be seen from fig. 1: the silicon-carbon negative electrode material comprises: an inner layer 1, a shallow surface layer 2 and a carbon coating layer 3; and, the inside has irregular internal pores 6, the porosity is decreased from inside to outside; the inner core further comprises a one-dimensional carbon material 4 and nano silicon particles 5, wherein the one-dimensional carbon material 4 can play a role in winding and stabilizing the structure.
FIG. 2 is an SEM electron micrograph of a silicon carbon anode material with a pore gradient structure prepared in example 1 of the invention; as can be seen from fig. 2: the silicon-carbon negative electrode material is internally provided with irregular internal pores 6, and the porosity is reduced from inside to outside; moreover, the outermost layer of the silicon-carbon negative electrode material is densely coated with carbon. In addition, in fig. 2 provided in the present invention, it should be noted that "Regulus" means "test under normal conditions".
Example 2
(1) Get D 50 160g of 50nm silicon powder, 20g of high-temperature asphalt, 20g of CNTs (the length-diameter ratio of the CNTs is 500; performing spray granulation on the dispersed slurry to obtain a spray-granulated core; sintering the spray granulated core in an inert atmosphere, wherein the sintering procedure is as follows: heating the silicon-carbon composite core to 300 ℃ at a heating rate of 5 ℃/min for 2 hours, heating the silicon-carbon composite core to 800 ℃ at a heating rate of 2 ℃/min from 300 ℃ for 3 hours, and finally cooling the silicon-carbon composite core to room temperature to obtain a sintered silicon-carbon composite core 1;
(2) Then, dispersing the silicon-carbon composite kernel 1 in tetrahydrofuran, continuously adding 30% of high-temperature asphalt (the softening point is 280 ℃), and after the high-temperature asphalt is completely dissolved, heating the mixture at 70 ℃ to slowly evaporate the tetrahydrofuran; the dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material under a channel established by tetrahydrofuran, after the tetrahydrofuran is completely evaporated, a silicon-carbon composite with asphalt on the shallow surface layer is obtained, and the silicon-carbon composite is sintered in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, and finally cooling to room temperature to obtain a silicon-carbon composite inner core 2 with high porosity of an inner layer and low porosity of a superficial layer;
(3) Mechanically fusing a silicon-carbon composite core 2 and 10% high-temperature asphalt (the softening point is 300 ℃) by using a particle fusion machine, and performing high-temperature carbonization treatment, wherein the sintering procedure is as follows in an inert atmosphere: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1100 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, cooling to room temperature, and sieving with a 400-mesh sieve to obtain the silicon-carbon negative electrode material which is provided with a compact carbon coating layer on the outer part, has high inner layer porosity and low superficial layer porosity and has a pore gradient structure; the results are shown in Table 1.
Coating a finished silicon-carbon negative electrode material with a pore gradient structure and assembling a CR 2032-button cell, wherein the silicon-carbon negative electrode material with the pore gradient structure, a conductive agent, a binder and deionized water are mixed according to a weight ratio of 90:3:7:200, mixing into slurry, coating, drying and cutting to obtain a pole piece; and assembling the lithium sheet and the conventional electrolyte into a button half cell, and carrying out charge and discharge tests. Charge and discharge cycles were performed at a rate of 1C. The battery charge and discharge test is carried out in a multi-channel tester, and the test voltage range of the silicon-carbon cathode material is 0.005V-0.8V; the results are shown in Table 2.
Example 3
(1) Get D 50 150g,25g of high-temperature asphalt, 25g of CNTs (the length-diameter ratio of the CNTs is 300; carrying out spray granulation on the dispersed slurry to obtain a spray-granulated core; sintering the spray granulated core in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 350 ℃ at a heating rate of 5 ℃/min for 2 hours, heating from 350 ℃ to 900 ℃ at a heating rate of 2 ℃/min for 3 hours, and finally cooling to room temperature to obtain a sintered silicon-carbon composite kernel 1;
(2) Then, dispersing the silicon-carbon composite kernel 1 in toluene, continuously adding 20% of high-temperature asphalt (the softening point is 250 ℃), and after the high-temperature asphalt is completely dissolved, heating the mixture at 100 ℃ to slowly evaporate the toluene; the dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material under a channel established by toluene, after the toluene is completely evaporated, the silicon-carbon composite material with asphalt on the shallow surface is obtained, and the sintering treatment is carried out on the silicon-carbon composite material in the inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, and finally cooling to room temperature to obtain a silicon-carbon composite inner core 2 with high porosity of an inner layer and low porosity of a superficial layer;
(3) Mechanically fusing a silicon-carbon composite core 2 and 10% high-temperature asphalt (the softening point is 280 ℃) by using a particle fusion machine, and performing high-temperature carbonization treatment, wherein the sintering procedure is as follows in an inert atmosphere: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, cooling to room temperature, and sieving with a 400-mesh sieve to obtain the silicon-carbon negative electrode material which is provided with a compact carbon coating layer on the outer part, has high inner layer porosity and low superficial layer porosity and has a pore gradient structure; the results are shown in Table 1.
Coating a film on the finished silicon-carbon negative electrode material with a pore gradient structure and assembling the finished silicon-carbon negative electrode material with the pore gradient structure with a CR 2032-button cell, wherein the silicon-carbon negative electrode material with the pore gradient structure, a conductive agent, a binder and deionized water are mixed according to the weight ratio of 90:3:7:200, mixing into slurry, coating, drying and cutting to obtain a pole piece; and assembling the lithium sheet and the conventional electrolyte into a button half cell, and carrying out charge and discharge tests. Charge and discharge cycles were performed at a rate of 1C. The battery charge-discharge test is carried out in a multi-channel tester, and the test voltage range of the silicon-carbon cathode material is 0.005V-0.8V; the results are shown in Table 2.
Example 4
(1) Get D 50 140g of 80nm silicon powder, 30g of high-temperature asphalt, 30g of VGCF (the length-diameter ratio of the VGCF is 100: 1), and 20g of SDS are sequentially dispersed in deionized water to prepare slurry, and the solid content of the slurry is adjusted to be 30 wt%; performing spray granulation on the dispersed slurry to obtain a spray-granulated core; sintering the spray granulated core in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 350 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 2 hours, heating from 350 ℃ to 900 ℃ at a heating rate of 2 ℃/min, keeping the temperature for 3 hours, and finally cooling to room temperature to obtain a sintered silicon-carbon composite kernel 1;
(2) Then, dispersing the silicon-carbon composite kernel 1 in toluene, continuously adding 15% of high-temperature asphalt (the softening point is 280 ℃), and after the high-temperature asphalt is completely dissolved, heating the mixture at 100 ℃ to slowly evaporate the toluene; the dissolved asphalt is infiltrated into the pores of the silicon-carbon composite material under a channel established by toluene, after the toluene is completely evaporated, a silicon-carbon composite with asphalt on the shallow surface layer is obtained, and the silicon-carbon composite is sintered in an inert atmosphere, wherein the sintering procedure is as follows: heating from room temperature to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating from 500 ℃ to 1000 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 3 hours, and finally cooling to room temperature to obtain a silicon-carbon composite inner core 2 with high porosity of an inner layer and low porosity of a superficial layer;
(3) Mechanically fusing 2% of silicon-carbon composite core and 5% of high-temperature asphalt (the softening point is 300 ℃) by using a particle fusion machine, and performing high-temperature carbonization treatment, wherein the sintering procedure is as follows in an inert atmosphere: heating to 500 ℃ from room temperature at a heating rate of 2 ℃/min, keeping the temperature for 1 hour, heating to 1200 ℃ from 500 ℃ at a heating rate of 1 ℃/min, keeping the temperature for 3 hours, cooling to room temperature, and sieving with a 400-mesh sieve to obtain a silicon-carbon negative electrode material which is provided with a compact carbon coating layer on the outer part, has a high porosity on the inner layer and a low porosity on the superficial layer and has a pore gradient structure; the results are shown in Table 1.
Coating a film on the finished silicon-carbon negative electrode material with a pore gradient structure and assembling the finished silicon-carbon negative electrode material with the pore gradient structure with a CR 2032-button cell, wherein the silicon-carbon negative electrode material with the pore gradient structure, a conductive agent, a binder and deionized water are mixed according to the weight ratio of 90:3:7:200, mixing into slurry, coating, drying and cutting to obtain a pole piece; and assembling the lithium sheet and the conventional electrolyte into a button half cell, and carrying out charge and discharge tests. Charge and discharge cycles were performed at a rate of 1C. The battery charge and discharge test is carried out in a multi-channel tester, and the test voltage range of the silicon-carbon cathode material is 0.005V-0.8V; the results are shown in Table 2.
Example 5
This example illustrates a silicon carbon anode material with a pore gradient structure prepared according to the present invention.
A silicon carbon anode material having a pore gradient structure was prepared in the same manner as in example 1, except that: the outermost layer was coated by CVD at 700 deg.C for 1 hr with acetylene gas at a flow rate of 1L/min.
The silicon-carbon negative electrode material with the compact carbon coating layer on the outer part, high porosity of the inner layer and low porosity of the superficial layer and a pore gradient structure is prepared; the results are shown in Table 1.
Assembling a button type half cell according to the same method as the embodiment 1, and carrying out charge and discharge tests; the results are shown in Table 2.
Comparative example 1
Spray granulation was performed as in example 1, except that the asphalt infiltration experiment was not performed, and the fusion coating of the granules was performed.
The performance parameters of the silicon-carbon anode material prepared by the method are shown in table 1.
The properties of the prepared lithium ion battery are shown in table 2.
Comparative example 2
A silicon carbon negative electrode material was prepared in the same manner as in example 1, except that: the "CNTs" is replaced by "SP", wherein SP is carbon black.
The performance parameters of the silicon-carbon anode material prepared by the method are shown in the table 1.
The properties of the prepared lithium ion battery are shown in table 2.
Comparative example 3
A silicon carbon negative electrode material was prepared in the same manner as in example 1, except that: in step (1), the slurry is not subjected to spray granulation, but a mixed evaporation method is adopted, specifically: the mixed slurry is stirred and evaporated to dryness at 90 ℃. Then sintering, and then carrying out asphalt infiltration and mechanical fusion coating. The performance parameters of the silicon-carbon anode material prepared by the method are shown in table 1.
The properties of the prepared lithium ion battery are shown in table 2.
TABLE 1
Remarking: in table 1, "carbon content (%)" refers to the percentage of the total content of the one-dimensional carbon material and the amorphous carbon, based on the total weight of the silicon-carbon negative electrode material, in which the prepared silicon-carbon negative electrode material includes silicon, the one-dimensional carbon material and the amorphous carbon.
It can be seen from the results in table 1 that the silicon-carbon negative electrode materials prepared in examples 1 to 5 of the present invention form a stable inner layer and a shallow surface layer, and can reduce the specific surface area and increase the tap density in combination with a compact carbon coating layer; in addition, the porosity is gradually decreased from the inside to the outside.
TABLE 2
As can be seen from the results in table 2, the silicon-carbon negative electrode materials prepared in examples 1 to 5 of the present invention can improve the first coulombic efficiency of the lithium ion battery, and can improve the capacity retention rate after 100 weeks.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (11)
1. The utility model provides a silicon carbon negative electrode material with pore gradient structure, silicon carbon negative electrode material includes the kernel and the cladding is in the carbon coating of the surface of kernel, its characterized in that, the kernel includes inlayer and superficial layer from inside to outside in proper order, and silicon carbon negative electrode material's inside has gradient distribution's hole, and along the inlayer superficial layer and carbon coating, the porosity is the gradient from inside to outside and steadilys decrease.
2. The silicon-carbon anode material as claimed in claim 1, wherein the porosity of the inner layer is 30-60%, the porosity of the superficial layer is 10-30%, and the porosity of the carbon coating layer is <20%, preferably 1-10%;
and/or the pore size distribution of the internal pores of the inner layer is 10-1000nm, the pore size distribution of the internal pores of the superficial layer is 5-20nm, and the pore size distribution of the internal pores of the carbon coating layer is greater than 0 and less than or equal to 10nm, preferably 0.01-10nm, and more preferably 1-10nm;
the average pressure born by the porous silicon-carbon negative electrode material is 400-1400MPa.
3. The silicon-carbon anode material of claim 1, wherein the inner core comprises a silicon-carbon composite and/or an amorphous carbon material;
preferably, the silicon-carbon composite includes nano-silicon particles and a conductive agent;
and/or, the conductive agent comprises a metallic material and/or a non-metallic material;
preferably, the conductive agent is a one-dimensional carbon material;
more preferably, the one-dimensional carbon material is a conductive carbon material;
still further preferably, the conductive carbon material comprises at least one of single-walled CNTs, multi-walled CNTs, and carbon fibers;
preferably, the aspect ratio of the one-dimensional carbon material is (20 to 20000): 1.
4. the silicon-carbon anode material of claim 3, wherein D of the nano-silicon particles 50 Is 30-500nm;
and/or the silicon-carbon negative electrode material comprises silicon, a one-dimensional carbon material and amorphous carbon, and the weight ratio of the content of the silicon to the total content of the one-dimensional carbon material and the amorphous carbon is (40-80): (20-60).
5. The silicon-carbon anode material of claim 1, wherein D of the silicon-carbon anode material 50 5-30 μm; the tap density is 0.5-1.2g/cm 3 (ii) a The specific surface area is 0.5-40m 2 /g；
And/or D of the silicon-carbon anode material 50 The grain size of the inner layer is 20-90% by taking the inner layer as a reference;
and/or the thickness of the shallow surface layer is 0.25-12 μm; the thickness of the carbon coating layer is 10nm-1 mu m;
and/or the coating amount of the carbon coating layer is 1-20 wt% of the silicon-carbon negative electrode material.
6. A method for preparing the silicon-carbon anode material with the pore gradient structure as described in any one of claims 1 to 5, wherein the method comprises the following steps:
(1) Contacting nano silicon particles, a carbon source, a dispersing agent, a conductive agent and water to prepare slurry; carrying out spray granulation on the slurry, and then carrying out first calcination treatment to obtain a silicon-carbon composite inner core 1;
(2) Heating the mixture containing the silicon-carbon composite kernel 1, the solvent and the high-temperature asphalt 1, and performing second calcination treatment on the obtained silicon-carbon composite containing asphalt on the superficial layer to obtain a silicon-carbon composite kernel 2 with high porosity of the inner layer and low porosity of the superficial layer;
(3) And carrying out mechanical fusion or CVD (chemical vapor deposition) coating on the silicon-carbon composite core 2 and the high-temperature asphalt 2, and carrying out high-temperature carbonization treatment to obtain the silicon-carbon negative electrode material with a compact carbon coating layer on the outer part, high inner-layer porosity and low superficial-layer porosity.
7. The method according to claim 6, wherein the conditions of the first calcination treatment, the second calcination treatment and the high-temperature carbonization treatment are the same or different, and the respective sintering procedures include:
the heating rate is 1-5 ℃/min, the final heating temperature is 600-1200 ℃, and the heat preservation time is 1-6 hours;
preferably, the sintering is carried out under an inert atmosphere;
preferably, the inert atmosphere comprises nitrogen or argon.
8. The method as claimed in claim 6, wherein, in the step (1), the nano silicon particles, the carbon source, the conductive agent and the dispersing agent are used in a weight ratio of (40-85): (5-50): (5-40) and (5-20);
and/or the carbon source is selected from one or more of low-temperature asphalt, medium-temperature asphalt, high-temperature asphalt, water-soluble asphalt, phenolic resin, CMC, glucose and sucrose;
and/or the dispersant comprises one or more of PVP, CTAB, polyethylene glycol and SDS.
9. The process of claim 6, wherein in step (2), the slurry has a solids content of 1-40 wt%;
and/or, in the step (2), the conditions of the heat treatment include: the temperature is 600-1200 ℃;
and/or, in step (3), the coating is performed using at least one of a particle fusion machine, a VCJ machine, and CVD.
10. The method of claim 6, wherein the solvent comprises one or more of tetrahydrofuran, NMP, toluene, and xylene;
and/or, in the step (2), the use amount of the high-temperature asphalt 1 is 5-30 wt% based on the total weight of the silicon-carbon composite core 1;
and/or, in the step (3), the high-temperature asphalt 2 is used in an amount of 1-20 wt% based on the total weight of the silicon-carbon composite core 2.
11. A lithium ion battery, characterized in that the lithium ion battery comprises the silicon carbon negative electrode material with a pore gradient structure as claimed in any one of claims 1 to 5.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115911341A (en) * | 2023-02-06 | 2023-04-04 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon negative electrode material, preparation method and application |
| CN116014141A (en) * | 2023-02-10 | 2023-04-25 | 江苏正力新能电池技术有限公司 | Porous silicon negative electrode material, silicon negative electrode sheet and lithium ion battery |
| CN117038941A (en) * | 2023-10-09 | 2023-11-10 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon anode material and preparation method and application thereof |
| EP4345942A1 (en) * | 2022-09-30 | 2024-04-03 | Beijing WeLion New Energy Technology Co., Ltd | Graphitized porous silicon-carbon anode material, preparation method thereof and lithium ion battery |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| EP4345942A1 (en) * | 2022-09-30 | 2024-04-03 | Beijing WeLion New Energy Technology Co., Ltd | Graphitized porous silicon-carbon anode material, preparation method thereof and lithium ion battery |
| CN115911341A (en) * | 2023-02-06 | 2023-04-04 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon negative electrode material, preparation method and application |
| CN115911341B (en) * | 2023-02-06 | 2024-05-28 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon anode material, preparation method and application |
| CN116014141A (en) * | 2023-02-10 | 2023-04-25 | 江苏正力新能电池技术有限公司 | Porous silicon negative electrode material, silicon negative electrode sheet and lithium ion battery |
| CN116014141B (en) * | 2023-02-10 | 2024-06-21 | 江苏正力新能电池技术有限公司 | Porous silicon negative electrode material, silicon negative electrode sheet and lithium ion battery |
| CN117038941A (en) * | 2023-10-09 | 2023-11-10 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon anode material and preparation method and application thereof |
| CN117038941B (en) * | 2023-10-09 | 2023-12-29 | 江苏正力新能电池技术有限公司 | Porous silicon-carbon anode material and preparation method and application thereof |
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