CN109841803B - Silicon-carbon composite material, preparation method thereof and secondary battery containing material - Google Patents
Silicon-carbon composite material, preparation method thereof and secondary battery containing material Download PDFInfo
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Abstract
The invention relates to the technical field of secondary batteries, in particular to a silicon-carbon composite material, a preparation method thereof and a secondary battery containing the material. The inner core of the silicon-carbon composite material is a porous silicon-containing substance, the porous silicon-containing substance contains metal elements, and the surface of the porous silicon-containing substance is provided with a carbon coating layer; the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.2-0.8. The silicon-carbon composite material provided by the invention is a porous silicon composite material with a self-supporting structure, and the material not only has excellent cycle performance of the traditional hollow/porous structure material, but also can resist the large pressure of a compaction process and keep the structure of the material not to be damaged, so that the aim of preparing a long-life high-energy-density battery is fulfilled.
Description
Technical Field
The invention relates to the field of secondary batteries, in particular to a silicon-carbon composite material, a preparation method thereof and a secondary battery containing the material.
Background
With the increasing popularization of various portable electronic devices and the accelerated development of electric vehicles and renewable energy storage systems, people have higher and higher requirements on the energy density, power density, cycle life, safety and other properties of lithium ion batteries. Lithium cobaltate (anode)/graphite (cathode) system lithium commonly used at presentThe energy density of the ion battery is close to the theoretical limit, and in order to further improve the energy density of the battery, novel anode and cathode materials are in urgent need of development. In the aspect of negative electrode materials, the actual specific capacity (up to 360mAh/g) of graphite is close to the theoretical specific capacity (372mAh/g), and silicon has a much higher theoretical specific capacity (3600 mAh/g) than graphite and a low discharge platform (0.2V vs. Li)+/Li) and abundant resources, etc. are receiving wide attention. However, the silicon negative electrode material has huge volume change in the lithium intercalation and deintercalation process, which causes the material to be easily pulverized and broken, peeled from a current collector and subjected to continuous interface side reaction, so that the specific capacity of the material is rapidly reduced in the circulation process, and the commercialization process of the silicon negative electrode material is severely limited.
In order to solve the above problems, the design of structures such as nano-scale, composite, hollow/porous silicon materials has become a research focus. However, the silicon-based composite material with the hollow/porous structure has the problem of no pressure resistance in practical battery application. In the actual electrode preparation process, the thickness of the electrode piece needs to be reduced through a compaction process so as to improve the energy density of the final battery, but the surface coating layer of the currently reported hollow/porous material is usually broken and crushed after being subjected to a large pressure action, the reserved expanded space in the material is extruded and released, the material and the battery still face large volume expansion in the charging and discharging process, the interface side reaction between the material and electrolyte is still continuously carried out, and the original advantages of the material are lost; however, if the electrode sheet is directly used without a compaction process, the electrode is easy to fall off in the subsequent process, and the energy density of the prepared battery is greatly reduced, so that the battery has no advantages compared with a battery taking graphite as a negative electrode material.
Disclosure of Invention
The primary object of the present invention is to provide a silicon carbon composite material.
The second purpose of the invention is to provide a preparation method of the silicon-carbon composite material.
The third purpose of the invention is to provide a battery containing the silicon-carbon composite material.
In order to achieve the purpose of the invention, the technical scheme is as follows:
the invention relates to a silicon-carbon composite material,
the inner core of the silicon-carbon composite material is a porous silicon-containing substance, the porous silicon-containing substance contains metal elements, and the surface of the porous silicon-containing substance is provided with a carbon coating layer;
the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.2-0.8; preferably, the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.25 to 0.40.
The technical scheme of the invention at least has the following beneficial effects:
the silicon-carbon composite material provided by the invention is a porous silicon composite material with a self-supporting structure, and the material not only has excellent cycle performance of the traditional hollow/porous structure material, but also can resist the large pressure of a compaction process in the battery preparation process and keep the self structure from being damaged, so that the purpose of preparing a long-life high-energy density lithium ion secondary battery is achieved.
Drawings
FIG. 1a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in example 1;
FIG. 1b is a SEM image of a silicon-carbon composite material prepared in example 1, which is scattered into a phase;
FIG. 2a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in comparative example 1;
FIG. 2b is a SEM image of the phase scattered of the silicon-carbon composite material prepared in comparative example 1;
FIG. 3a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in comparative example 2-2;
FIG. 3b is a SEM image of the phase of the silicon-carbon composite material prepared in comparative example 2-2;
FIG. 4a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in comparative example 4;
fig. 4b is a SEM image of the silicon carbon composite prepared in comparative example 4, which is scattered into a phase.
Detailed Description
The present invention relates in a first aspect to a silicon carbon composite material,
the inner core of the silicon-carbon composite material is a porous silicon-containing substance, the porous silicon-containing substance contains metal elements, and the surface of the porous silicon-containing substance is provided with a carbon coating layer;
the metal elements in the porous silicon-containing substance are beneficial to forming a porous structure in the material, and can play a role in improving the electronic conductivity in the material, so that enough support points can be arranged between the surface carbon layer and the porous silicon substance to resist the damage to the internal structure of the material caused by cold pressing of the pole piece, the compression resistance is improved, and the application of the material under high pressure density is facilitated; the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.2 to 0.8. The porous silicon composite material with the self-supporting structure not only has excellent cycle performance of the traditional hollow/porous structure material, but also can resist the large pressure of a compaction process and keep the self structure not to be damaged, so that the lithium ion secondary battery with long service life and high energy density can be prepared.
Further, the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.25 to 0.40.
The specific surface area ratio of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is obtained by respectively measuring the specific surface area of the prepared silicon-carbon composite material and the specific surface area of the porous silicon-containing substance, and the surface carbon layer is removed to obtain the porous silicon substance by calcining the silicon-carbon composite material in an air atmosphere at a certain temperature; and measuring the obtained porous silicon-containing substance to obtain the specific surface area of the porous silicon-containing substance. In the above test method, the calcination temperature and time are determined according to the kind of the porous siliceous material, and in general, the calcination temperature is controlled to 300-700 ℃ and the calcination time is controlled to 2-24 h. When the calcining temperature is too low or the calcining time is too short, the surface carbon layer is not easy to oxidize and remove; when the calcination temperature is too high or the calcination time is too long, the porous silicon-containing substance is easily oxidized.
The silicon-containing substance comprises silicon, silicon oxide, silicon composite and silicon-containing substanceExamples of the substance include at least one of the following: silicon, silicon oxide (SiO)x，0<x is less than or equal to 2), a silicon-iron compound and a silicon-nickel compound.
In the present invention, the value of the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is referred to as BET coefficient.
The ratio (BET coefficient) of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is controlled to be 0.2-0.8, so that the porous volume in the porous silicon-containing substance can be ensured to be enough to accommodate the volume of lithium intercalation expansion of the silicon-containing substance, and the inner core formed by the porous silicon-containing substance can be ensured to have enough supporting framework to maintain the integrity of the silicon-carbon composite material in the high-pressure cold pressing process. The silicon-carbon composite material provided by the invention has the advantage of good cycle stability while obtaining higher cell energy density under high pressure density. When the ratio (BET coefficient) of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is less than 0.2, pores in the porous silicon-containing substance are too large, and the occupation ratio of the inner core skeleton with a porous structure is too small, so that the specific capacity of the whole silicon-carbon composite material is reduced, and meanwhile, the silicon-carbon composite material is very easy to damage after cold pressing, and the advantages of the original porous structure are lost; when the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance (BET coefficient) is greater than 0.8, the pores inside the porous silicon-containing substance are too small to accommodate the volume expansion generated when the silicon-containing substance is fully intercalated with lithium, and finally the surface carbon layer is spread and broken, resulting in the reduction of the cycle performance of the silicon-carbon composite material.
As an improvement of the silicon-carbon composite material, the thickness of a coating layer of silicon-carbon composite material particles is 10-500 nm; the cladding layer preferably has a thickness of 50-100 nm.
If the coating carbon layer is too thin, the material is also easy to crack under pressure, and the coating layer is also easy to be uneven; on the other hand, if the coating carbon layer is too thick, the transport of lithium ions into the material is easily restricted, resulting in a low capacity of the material.
As an improvement of the silicon-carbon composite material, the ratio of the median particle diameter of the silicon-carbon composite material to the median particle diameter of the porous silicon-containing substance is 1.00-1.02.
In the present invention, the value of the ratio of the median particle diameter of the silicon-carbon composite particles to the median particle diameter of the porous silicon-containing substance is referred to as a particle diameter coefficient.
The ratio (particle size coefficient) of the median particle size of the silicon-carbon composite material to the median particle size of the porous silicon-containing substance is controlled to be 1.00-1.02, so that a coating layer on the surface of silicon-carbon composite material particles is in contact with a core with a porous structure, enough supporting points are arranged between the surface coating layer and the core to resist damage to the internal structure of the material when the pole piece is cold-pressed, the compression resistance is improved, the application of the material under high pressure density is facilitated, the improvement of the energy density of a battery core is facilitated, and good cycle performance is considered; the increase of the surface coating layer and the core supporting point with a porous structure is also beneficial to Li in the charge and discharge process+The diffusion of (2) is beneficial to the multiplying power performance of the battery cell. When the ratio of the median particle diameter of the silicon-carbon composite material to the median particle diameter of the porous silicon-containing substance is too large, the contact supporting points between the surface coating layer and the porous silicon-containing substance are fewer, and the material is extremely easy to collapse in structure after cold pressing and is not beneficial to the electrochemical performance of the material.
As an improvement of the silicon-carbon composite material of the present invention, the amount of the metal element contained in the silicon-carbon composite material is 0.1 wt.% to 5 wt.%; preferably, the content of metallic elements is 0.1 wt.% to 2.5 wt.%; preferably, the metal element is selected from one or more of titanium, iron, copper, nickel, cobalt, manganese, silver, gold and tin; preferably, the metal element is metal particles, and the particle size of the metal particles is 5nm-500 nm; more preferably, the metal particles have a particle size of 20nm to 100 nm.
In the invention, because the particle size of the metal particles can directly determine the pore size of the etched porous silicon-containing substance and the number of the supporting points of the porous silicon-containing substance and the surface carbon coating layer, the metal particles with the particle size of 20-100nm can ensure that the porous silicon-containing substance can keep higher strength and have a proper number of supporting points with the surface coated carbon layer.
As an improvement of the silicon-carbon composite material, the pore size of the porous structure of the porous silicon-containing substance in the silicon-carbon composite material is 5nm-500 nm; the preferred pore size is 20nm to 100 nm.
In the invention, when the pore diameter of the porous structure of the porous silicon-containing substance in the silicon-carbon composite material is too small, the whole pore volume in the material is also too small, the volume expansion of the material after lithium embedding is difficult to accommodate, and the surface carbon layer is still easy to crack; when the pore diameter is too large, the internal framework of the material is fragile, the material is easy to break under high pressure, and the material cannot be applied under the condition of high pressure density.
The second aspect of the present invention is a method for preparing the silicon-carbon composite material, which at least comprises the following steps:
1) distributing metal particles on the surface of the silicon-containing substance particles;
2) carrying out carbon coating treatment on the surfaces of the silicon-containing substance particles distributed with the metal particles;
3) putting the coated silicon-carbon composite material into acidic/alkaline etching liquid for etching treatment;
4) washing, filtering and drying the etched particles to obtain the silicon-carbon composite material;
in the preparation method, the step 2) is carried out before the step 3), namely, carbon coating is carried out firstly and then etching is carried out; if porous silicon is prepared firstly and then carbon coating is carried out, the carbon coating layer of the prepared material is attached to the surface of the porous silicon material, when the material is embedded with lithium to expand, the surface carbon layer of the material is often damaged firstly, so that the electronic conductivity of the material is reduced, and the electrochemical performance of the material is finally influenced. Meanwhile, a plurality of supporting points exist between the carbon coating layer and the porous core of the silicon-carbon composite material, so that the cold pressing process with higher compaction can be endured, a plurality of lithium ion transmission channels can be provided, and the material is ensured to have better rate performance.
As a modification of the preparation method of the present invention, the metal particles in step 1) are preferably metal particles, and the metal particles are selected from one or more of titanium, iron, copper, nickel, cobalt, manganese, silver, gold, and tin particles; and preferably silver, copper or tin particles; more preferably silver particles; the particles of the siliceous material in step 1) are preferably micron-sized particles.
In the production method of the present invention, the metal particles are preferably silver, copper or tin particles because these metal elements have higher catalytic etching activity, and silver particles are more preferably used.
As an improvement to the preparation method of the present invention, the particle diameter of the metal particles in step 1) is preferably 5nm to 500 nm; more preferably 20nm to 100 nm.
In step 1) of the present invention, the method for distributing the nano-metal particles on the surface of the particles of the silicon-containing substance includes a mechanical mixing method, a liquid phase reduction method, a gas phase reduction method, a magnetron sputtering method, and the like. The selection of the specific method varies depending on the kind of the metal particles used. Generally, the liquid phase reduction method is preferred because the method is simple and easy to industrialize, is compatible with various metal elements, and is convenient for regulating and controlling the size of the distributed metal particles.
In step 2) of the present invention, the method of coating carbon on the surface of the particles of the silicon-containing substance mainly includes a vapor deposition method (CVD), a liquid phase coating method, and a solid phase mixing method, and the present invention preferentially uses the CVD method because the carbon obtained by using the CVD method can coat the surface of the particles more uniformly.
As an improvement of the preparation method of the invention, the etching solution in the step 3) is selected from one or more of hydrofluoric acid, sulfuric acid, nitric acid, sodium hydroxide, calcium hydroxide, barium hydroxide and potassium hydroxide; preferably, the etching liquid is hydrofluoric acid; the etching efficiency of hydrofluoric acid on silicon is highest; preferably the concentration of hydrofluoric acid used for etching is 5-40 wt.%; more preferably, the concentration of hydrofluoric acid is from 10 wt.% to 20 wt.%. When the concentration of hydrofluoric acid is too high, the porous silicon is etched faster, so that the pores of the porous silicon are larger, and the structural strength of the material is reduced; when the concentration of hydrofluoric acid is too low, the particle etching efficiency is slow, and a long time is required to reach a preset target, which is not beneficial to production.
The third aspect of the invention relates to a battery, which further comprises a positive pole piece, a negative pole piece, a separation film and electrolyte, wherein the negative pole piece comprises a current collector and the silicon-carbon composite material coated on the current collector.
The present application is further illustrated with reference to specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
Example 1
1. Preparation of silicon-carbon composite material
SiO particles with the D50 particle size of 6.5 mu m are put into AgNO3Standing in HF solution for 5min, AgNO3Can be reduced by SiO, and a layer of Ag nano particles (with the particle diameter of about 50nm) can be uniformly coated on the surface of the SiO particles. With CH4As a carbon source, the SiO material coated by the Ag nano particles is subjected to CVD treatment for 2 hours at 700 ℃ so that the surface of the material is uniformly coated with a layer of carbon. Add post-CVD powder to 10 wt.% H of HF2O2And etching the solution for 2 hours, filtering the solution for multiple times, washing the solution by using deionized water, and finally drying the solution to obtain the silicon-carbon composite material in the embodiment 1. The prepared silicon-carbon composite material is used as a negative active material.
2. Preparation of negative pole piece
Mixing the prepared negative electrode active material, a conductive agent SP and a binder Li-PAA according to a mass ratio of 80: 10: 10, adding the negative active material and the conductive agent SP into the aqueous solution of Li-PAA, and continuously stirring to obtain negative active material slurry. Coating the negative active material slurry on the surface of the copper foil by using a scraper, and drying to obtain the negative pole piece. The negative pole piece is subjected to cold pressing treatment, so that the pole piece compaction reaches 1.7g/cm commonly used in commerce3Preparing a small disk with the diameter of 14mm by using a puncher after cold pressing of the negative pole piece, wherein the loading capacity of the negative active substance on the negative pole piece is 4mg/cm2。
3. Preparation of half-cells
And matching and assembling the negative pole piece and the lithium piece into a button type half battery, wherein the assembling process of the battery is carried out in a glove box filled with argon. Wherein Celgard2300 membrane is used as a separation membrane, and the electrolyte is LiPF with 1mol/L6Dissolved in a solution of EC: DMC: FEC (volume ratio 4.5:4.5: 1).
Example 2
Mixing D50 granulesSiO particles with the diameter of 6.5 mu m and nano Cu particles (100nm) are mixed and ball-milled for 30min at 400rpm, and the Cu nano particles can be uniformly coated on the surfaces of the SiO particles with the micron order. With CH4As a carbon source, the SiO material coated by the Cu nano-particles is subjected to CVD treatment for 2 hours at 700 ℃ so that the surface of the material is uniformly coated with a layer of carbon. Add post-CVD powder to 20 wt.% H of HF2O2And etching the solution for 2 hours, filtering, washing and finally drying the solution for multiple times to obtain the silicon-carbon composite material of the embodiment 2. The prepared silicon-carbon composite material is used as a negative active material.
The same procedure as in example 1 for preparing a negative electrode sheet and a button half cell was followed to obtain the silicon-carbon composite material of example 2, prepare the obtained silicon-carbon composite material as a negative electrode active material, and obtain the button half cell of example 2.
Example 3
SiO particles with the particle size of D50 being 6.5 mu m are added into SnCl2Adding dissolved NaBH into the solution while stirring4Solution, Sn nanoparticles (300nm) would be BH4Reduced out and deposited on the surface of the SiO-particles. With CH4As a carbon source, the SiO material coated by the Sn nano particles is subjected to CVD treatment for 2 hours at 700 ℃ so that the surface of the material is uniformly coated with a layer of carbon. Add post-CVD powder to 30 wt.% H of HF2O2The solution was etched for 2 hours, filtered, washed, and finally dried many times to obtain the negative active material of example 3.
The silicon carbon composite of example 3 was obtained as in the procedure for the preparation of negative electrode sheets and button half cells of example 1. The resulting silicon-carbon composite was prepared as a negative active material and the button half cell of example 3 was obtained.
Comparative example 1
SiO is used as silicon raw material, CH is used4And (3) directly coating a layer of carbon on the surface of the SiO by using a CVD (chemical vapor deposition) method as a carbon source to obtain the carbon-coated SiO silicon-carbon composite material without holes inside. The prepared silicon-carbon composite material is used as a negative active material.
The button half-cell of comparative example 1 was obtained in the same way as the procedure for the preparation of the negative electrode tab and of the button half-cell of example 1.
Comparative examples 2-1 and 2-2
Comparative example 2-1 was prepared identically to comparative example 2-2, and comparative example 2-1 and comparative example 2-2 were prepared following the procedure of example 1, except that: and removing the metal particles distributed on the surface, and directly carrying out CVD carbon coating and HF etching to obtain the self-supporting porous silicon-carbon composite material. The prepared silicon-carbon composite material is used as a negative active material.
Negative electrode pieces and button half cells were prepared according to the method of example 1 except that comparative examples 2-1 had a compacted density of 0.8g/cm3Comparative examples 2 to 2 had a compacted density of 1.7g/cm3. The button half-cells of comparative example 2-1 and comparative example 2-2 were obtained.
Comparative example 3
Comparative example 3 was prepared according to the procedure of example 1, except that: and placing the CVD carbon coating step after the HF etching step, namely etching and coating carbon to obtain the silicon-carbon composite material with the surface carbon layer tightly attached to the surface of the porous silicon core. The prepared silicon-carbon composite material is used as a negative active material.
The button half-cell of comparative example 3 was obtained as in the procedure for the preparation of the negative electrode tab and of the button half-cell of example 1.
Comparative example 4
Comparative example 4 was prepared according to the procedure of example 2, except that: and (3) replacing the Cu particles with the particle size of about 600nm with the Cu particles with the particle size of 100nm, and performing ball milling and mixing to obtain the silicon-carbon composite material of the comparative example 4. The prepared silicon-carbon composite material is used as a negative active material.
The button half-cell of comparative example 4 was obtained as in the procedure for the preparation of the negative electrode tab and of the button half-cell of example 1.
The silicon-carbon composite and the button half cell of each example and comparative example were tested according to the following test methods, criteria and results:
measuring the BET specific surface area of the silicon-carbon composite material by using a BET specific surface area analyzer; measuring the particle size distribution of the final silicon-carbon composite material by using a particle size distribution instrument, and calculating the particle size coefficient of the final silicon-carbon composite material by taking the particle size of D50 as the average particle size of the material; measuring the size of the metal particles by observing the surface of the metal-coated particles by SEM; the particles were cut by Ar ion polishing technique and observed for pore size and carbon layer thickness inside the material in combination with SEM. The metal particle size and the internal pore size were obtained by taking 10 particle samples for observation and averaging.
And step two, calcining each silicon-carbon composite material in the step one at 600 ℃ for 2h to obtain a corresponding silicon-containing substance core. Measuring the BET specific surface area of the inner core of the siliceous matter using a BET specific surface area analyzer; calculating according to the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the silicon-containing substance core to obtain a BET coefficient; measuring the particle size distribution of the silicon-containing substance core by using a particle size distribution instrument, and calculating the particle size coefficient of the silicon-containing substance core by taking the D50 particle size as the average particle size of the material; the particles were cut by Ar ion polishing technique and observed for pore size and carbon layer thickness inside the material in combination with SEM. The metal particle size and the internal pore size were obtained by taking 10 particle samples for observation and averaging.
The types and contents of the metal elements, the particle sizes of the metal particles, the thicknesses of the carbon layers, the particle size coefficients, and the BET coefficients of the silicon-carbon composites obtained in the examples and comparative examples are shown in table 1.
TABLE 1
The basic electrochemical performance test method of each example and comparative example is as follows, and the test results are shown in table 2.
(1) Retention rate of circulating capacity
And (3) carrying out constant current charging and discharging on the deduction electricity by using a battery charging and discharging instrument, wherein the cut-off voltage is set to be 0.01-1.5V, and the current density is set to be 100 mA/g.
The cycle capacity retention ratio of 100cls is 100 th turn charge capacity/first turn charge capacity × 100%
(2) Pole piece full-embedding rebound rate
Taking the cold-pressed negative pole pieces of the embodiments and the comparative examples, measuring the thickness of the pole pieces by using a micrometer, and averaging 8 groups of pole piece tests to obtain the initial pole piece thickness;
discharging the button cell of each embodiment and the comparative example to 0.01V, then detaching the button cell to obtain a fully embedded pole piece, measuring the thickness of the fully embedded pole piece by using a micrometer, and taking an average value of 8 groups of pole piece tests and recording the average value as the thickness of the fully embedded pole piece;
and finally, calculating to obtain the full embedding rebound rate of the pole piece, wherein the specific formula is as follows:
the full-embedded rebound rate of the pole piece is (full-embedded pole piece thickness-initial pole piece thickness)/initial pole piece thickness multiplied by 100%.
TABLE 2
As can be seen from table 2, the silicon-carbon composite material as the negative active material in each example having the self-supporting porous structure has less pole piece rebound and better cycle performance compared to the silicon-carbon composite material as the negative active material in each comparative example, which is directly related to that the porous structure can reduce the lithium intercalation expansion of the particles, and the self-supporting porous core can maintain the stability of the porous structure under high pressure density.
As can be seen from the data in tables 1 and 2, the silicon-carbon composite materials prepared in examples 1 and 2 have different process parameters such as the types of metal elements, the particle sizes, and the concentration of hydrofluoric acid, so that the silicon-carbon composite material prepared in example 2 has more pores, and the more pores affect the pressure resistance of the silicon-carbon composite material, the pole piece full-embedding rebound rate of the pole piece, and the retention rate of 100cls cycle capacity, compared with the silicon-carbon composite material prepared in example 1.
As can be seen from comparative example 1, if the material is a conventional carbon-coated porous silicon-containing material, the material as the negative active material does not contain metal particles, the full-embedding rebound rate of the electrode piece is as high as 70%, and the capacity retention rate of 100 cycles is only 32%; this is because the material as the anode active material in comparative example 1 does not have a self-supporting porous structure.
As can be seen from the comparative example 2-1, under the condition of no cold pressing, the internal hollow structure of the material of the comparative example 2-1 is complete, and the material can keep smaller full-insert rebound rate and better cycle performance.
From comparative examples 2-2, it can be seen that the same material as in comparative example 2-1 was subjected to cold pressing, the material was pressed, the inner hollow region was flattened, the surface carbon layer was damaged, the full-inlaid rebound rate of the material was significantly increased, and the cycle performance was also significantly reduced.
According to comparative example 3, the carbon is coated after etching, so that the BET coefficient of the material is too large, the full-embedding rebound rate of the material is low, the conductivity of the material is affected due to cracking and breaking of the surface carbon layer in the full-embedding process, and the 100-turn cycle capacity retention rate of the material is 85% and is lower than that of the materials in examples 1 to 3. According to comparative example 4, the larger particle size (600nm) and the smaller BET coefficient (0.18) of the metal particles lead to a material having a self-supporting porous structure, but the larger particle size of the metal particles leads to a fragile porous skeleton of the material, which is also difficult to withstand the pressure under high compaction, and finally leads to poor cycle performance of the material.
FIG. 1a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in example 1, and FIG. 1b is a SEM image of scattered phase formation of the silicon-carbon composite material prepared in example 1; fig. 2a is a secondary electron phase-forming SEM image of the silicon carbon composite material prepared in comparative example 1, and fig. 2b is a scattered phase-forming SEM image of the silicon carbon composite material prepared in comparative example 1.
As can be seen by comparing fig. 1a and fig. 2a, the surface morphology of the silicon carbon composite particle with a porous structure in fig. 1a is not significantly different from the surface morphology of the conventional dense particle in fig. 2a, but by detecting the scattering phase of the particle, as shown in fig. 1b and fig. 2b, fig. 1b presents a region with alternating light and dark due to the porous structure, which indicates that the particle in fig. 1b has a porous structure inside, and pores are uniformly distributed in the porous core skeleton, and at the same time, there are more support points between the core skeleton and the surface-coated carbon layer; and the outline of the whole particle is only shown in fig. 2b, and no light and dark regions exist, so that the particle has no porous structure inside, which is consistent with the preparation process of the material of the comparative example 1, and the material of the comparative example 1 is not etched in the preparation process, so that the porous structure does not exist inside the particle.
FIG. 3a is a SEM image of secondary electron phase formation of the silicon-carbon composite material prepared in comparative example 2-2, and FIG. 3b is a SEM image of scattering phase formation of the silicon-carbon composite material prepared in comparative example 2-2; fig. 4a is a secondary electron phase-forming SEM image of the silicon carbon composite material prepared in comparative example 4, and fig. 4b is a scattered phase-forming SEM image of the silicon carbon composite material prepared in comparative example 4.
As shown in fig. 3a and 4a, the combination of the internal skeleton and the surface-coated carbon layer of the prepared silicon-carbon composite material is fragile simply by etching with hydrofluoric acid or by using metal element particles with particle sizes outside the optional range of the invention; further detecting the scattered phase of the prepared silicon-carbon composite material, as can be seen from fig. 3b and 4b, the pores inside the material are mainly distributed between the core and the coated carbon layer, and only a few support points are arranged inside the core skeleton and the coated carbon layer; and as can be seen from table 2, the electrochemical properties of the particles prepared in comparative examples 2-2 and 4 deteriorate faster after being compressed, because the hollow structure of the particles is easily broken due to the fact that the particles prepared in comparative examples 2-2 and 4 have only a few supporting points inside, and thus the electrochemical properties of the material deteriorate faster after being compressed.
Through the performance comparison of the above examples and comparative examples, the self-supporting porous silicon carbon negative electrode material disclosed by the invention can bear the cold pressing of conventional high-pressure density to keep the structural integrity, so that the full-embedding rebound of a pole piece can be obviously reduced, and the cycle performance of the material is improved; also embodies the effectiveness of the preparation method designed by the invention.
Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.
Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.
Claims (15)
1. The silicon-carbon composite material is characterized in that an inner core of the silicon-carbon composite material is a porous silicon-containing substance, the porous silicon-containing substance contains a metal element, and the surface of the porous silicon-containing substance is provided with a carbon coating layer;
the metal element is metal particles;
the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.2-0.8.
2. The silicon-carbon composite material according to claim 1, wherein the ratio of the specific surface area of the silicon-carbon composite material to the specific surface area of the porous silicon-containing substance is 0.25 to 0.40.
3. The silicon-carbon composite material according to claim 1, wherein the cladding layer has a thickness of 10-500 nm.
4. The silicon-carbon composite material according to claim 3, wherein the cladding layer has a thickness of 50-100 nm.
5. The silicon-carbon composite of claim 1, wherein the ratio of the median particle size of the silicon-carbon composite to the median particle size of the porous silicon-containing substance is in the range of 1.00 to 1.02.
6. The silicon-carbon composite material according to claim 1, wherein the silicon-containing substance is selected from one or more of silicon, silicon oxide and a silicon composite.
7. The silicon-carbon composite according to claim 1, wherein the content of the metal element in the silicon-carbon composite is 0.1 wt.% to 5 wt.%.
8. The silicon-carbon composite according to claim 7, wherein the content of the metal element in the silicon-carbon composite is 0.1 wt.% to 2.5 wt.%.
9. The silicon-carbon composite material according to claim 1, wherein the metal element is selected from one or more of titanium, iron, copper, nickel, cobalt, manganese, silver, gold, and tin.
10. The silicon-carbon composite material according to claim 9, wherein the metal particles have a particle size of 5nm to 500 nm.
11. The silicon-carbon composite material according to claim 10, wherein the metal particles have a particle size of 20nm to 100 nm.
12. The silicon-carbon composite material according to claim 1, wherein the porous silicon-containing substance has a pore size of 5nm to 500 nm.
13. The silicon-carbon composite material according to claim 12, wherein the porous silicon-containing substance has a pore size of 20nm to 100 nm.
14. Method for the preparation of a silicon-carbon composite material according to any of claims 1 to 13, characterized in that it comprises at least the following steps:
1) distributing metal particles on the surface of the silicon-containing substance particles;
2) carrying out carbon coating treatment on the surfaces of the silicon-containing substance particles distributed with the metal particles;
3) putting the coated silicon-carbon composite material into acidic/alkaline etching liquid for etching treatment;
4) and washing, filtering and drying the etched particles to obtain the silicon-carbon composite material.
15. A battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises the silicon-carbon composite material according to any one of claims 1 to 13.
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| CN110265640A (en) * | 2019-06-11 | 2019-09-20 | 上海大学 | A method for preparing carbon-coated porous silicon materials for lithium battery electrodes |
| CN111244417B (en) * | 2020-01-17 | 2022-04-15 | 天津大学 | Preparation method of micron silicon-carbon composite negative electrode material with long cycle life |
| CN111525114A (en) * | 2020-05-09 | 2020-08-11 | 四川聚创石墨烯科技有限公司 | Method for continuously preparing current collector-free silicon-carbon negative electrode paper |
| JP7612543B2 (en) * | 2021-09-17 | 2025-01-14 | 株式会社豊田自動織機 | Method for producing negative electrode active material |
| CN114614000B (en) * | 2022-04-12 | 2023-08-18 | 浙江极氪智能科技有限公司 | A negative electrode active material, a negative electrode for a battery, and a battery |
| CN115621448A (en) * | 2022-10-31 | 2023-01-17 | 河南佰利新能源材料有限公司 | Silicon carbon composite material and its preparation method and application |
| CN118367133B (en) * | 2023-01-17 | 2026-01-16 | 宁德时代新能源科技股份有限公司 | Negative electrode material, negative electrode plate, electrode assembly, battery and electricity utilization device |
| CN119092700B (en) * | 2023-10-31 | 2025-10-17 | 贝特瑞新材料集团股份有限公司 | Negative electrode material, preparation method thereof, negative electrode plate and lithium ion battery |
| CN118888732B (en) * | 2024-08-09 | 2025-11-04 | 惠州亿纬锂能股份有限公司 | A silicon-carbon composite material, its preparation method and application |
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