CN108306007B - Method for improving negative electrode surface loading capacity of nano silicon of lithium ion battery by adopting sulfur template and hydrogen peroxide activation - Google Patents
Method for improving negative electrode surface loading capacity of nano silicon of lithium ion battery by adopting sulfur template and hydrogen peroxide activation Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for improving the loading capacity of a nano silicon negative electrode surface of a lithium ion battery by adopting sulfur template and hydrogen peroxide activation, which comprises the following steps: adding a sulfur-containing substance and an acid into the graphene dispersion liquid, and fully stirring to obtain a mixed dispersion liquid; adding nano silicon particles into absolute ethyl alcohol, and performing ultrasonic treatment to obtain uniform nano silicon dispersion liquid; mixing the two dispersion solutions, performing ultrasonic treatment again, and adding the mixture and hydrogen peroxide into a hydrothermal reaction kettle for hydrothermal reaction to obtain hydrogel; fully soaking the hydrogel, removing impurities, and then removing water; and carrying out desulfurization treatment to obtain the three-dimensional porous graphene-silicon macroscopic body. The method introduces gaps between the sheets in the three-dimensional graphene network and etches pores on the sheets respectively. On one hand, the high density of the active material is kept while the electrode expansion is relieved, on the other hand, the smooth ion transmission of the active material is ensured under the condition that the active material is made into a thick and dense electrode, and finally the volume performance and the surface capacity of the silicon negative electrode are improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for improving the loading capacity of a nano silicon negative electrode surface of a lithium ion battery by adopting sulfur templates and hydrogen peroxide activation.
Background
Silicon is taken as the lithium ion battery cathode material which has the most potential to replace graphite at present, has abundant reserves and has the specific capacity which is ten times of that of the latter. The current research on the silicon negative electrode is about the specific mass capacity (>1000mAh g-1) And cycle performance (>500 circles) and the research aspect of multiplying power performance is obtainedThe progress has been long but unfortunately, the progress has been more at low electrode loading: (<1mg cm-2) Or thin electrodes (<10um) was obtained. Silicon does not gain a mass energy density advantage over graphite as the negative electrode under practical battery conditions, i.e. based on the weight of the entire device. What is worse, the silicon as the alloy type negative electrode material has the problem of volume expansion in the processes of lithium insertion and lithium removal, which not only limits the cycle output of the silicon negative electrode mass specific capacity, but also limits the application of the silicon negative electrode in the practical battery (the practical battery cell volume change generally requires<5% and maximally 30%) resulting in a much less advantageous volumetric energy density compared to graphite anodes than theoretical calculations.
Considering the practical application of the silicon negative electrode and improving the mass fraction and the volume fraction of the silicon active material in the whole electrode, the high-energy-density (mass and volume) lithium ion battery taking silicon as the negative electrode needs to be really realized under the conditions of high active material loading capacity, high electrode density and high electrode structure stability; however, in the process of increasing the thickness of the electrode, higher requirements are placed on the conductivity of the electrode, particularly on the ion transport. In the case of a silicon negative electrode in which a large volume change occurs during lithium intercalation and lithium deintercalation, it is more difficult to maintain a low expansion rate and structural stability of the electrode during charge and discharge as the thickness of the electrode increases. Therefore, in order to ensure that the electrochemical performance of the thick electrode is fully exerted, enough space is needed to relieve the volume expansion of silicon, and enough space is provided to ensure smooth ion transmission. Meanwhile, with the rapid development of portable devices, miniaturization becomes an important trend of the development of energy storage devices, namely, the volumetric capacity becomes an increasingly important performance index of batteries. If too many voids are introduced into the active material during the electrode thickening process, the active material loading is increased, i.e., the surface capacity is increased, but eventually too much space is occupied, resulting in a lower volumetric specific capacity. Therefore, the electrode needs to be dense in the process of making the electrode thick. However, the electrode thickening is generally accomplished by increasing the internal porosity of the electrode and decreasing the tortuosity of ion transport, while the electrode densification is a process of saving the internal space of the electrode, including the internal space of the active particles, and even compressing the internal space of the electrode, and the two are restricted with each other. Thus, further densification of the thick electrode means a reduction in the active material internal space and the electrode internal space, i.e., further increase in ion transport tortuosity, and reduction in the reserved voids that buffer the volume expansion of silicon, which places more stringent requirements on the electrode bulk ion transport, volume change of the electrode, and structural stability.
Nanotechnology has been well applied in silicon negative electrode research, but nanotechnology leads to lower tap density of materials and repeated growth of SEI films. Carbon materials are often used to coat the nano-silicon material to achieve buffering of the volume expansion of silicon and limitation of the growth of SEI films. The pomegranate-type structure design of the silicon-carbon composite material is proposed by the Cui group in 2014, and excellent cycle performance is realized under the condition of high load. However, the tap density of the material was still low (0.47g cm)-3). Graphene as a two-dimensional material with an ultra-large specific surface area, high conductivity and high flexibility has been widely applied in the field of energy storage; the three-dimensional assembly of the graphene has good electronic conductivity and ion conductivity, and is well applied to the field of lithium ion battery cathodes. The capillary evaporation technology of the invention can obtain the highly densified three-dimensional graphene hard rod which can greatly improve the volume performance of the super capacitor as an electrode material. However, when the "hard rod" is applied to a silicon negative electrode of a lithium ion battery, the transport of lithium ions is limited by the microporous structure of the "hard rod". Furthermore, the dense structure does not provide enough buffer space for the volume change of silicon, and ultimately limits it to the material for thick electrode fabrication.
In summary, in order to achieve a high active material utilization rate in the process of thickening and densifying the electrode, the invention provides a method for improving the volume performance of a lithium ion battery nano silicon cathode by adopting a sulfur template and hydrogen peroxide activation, wherein gaps are respectively introduced between sheet layers in a three-dimensional graphene network and are etched into pores on the sheet layers. On one hand, the high density of the active material is kept while the expansion of the electrode is relieved, on the other hand, the smooth ion transmission of the active material is ensured under the condition that the active material is made into a thick and dense electrode, and finally the improvement of the volume performance of the silicon cathode is realized.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the method for improving the loading capacity of the nano silicon cathode surface of the lithium ion battery by adopting the sulfur template and hydrogen peroxide activation is provided, and gaps are respectively introduced between the sheet layers in the three-dimensional graphene network and are etched into pores on the sheet layers. On one hand, the high density of the active material is kept while the expansion of the electrode is relieved, on the other hand, the smooth ion transmission of the active material is ensured under the condition that the active material is made into a thick and dense electrode, and finally the improvement of the volume performance of the silicon cathode is realized.
In order to achieve the purpose, the invention adopts the following technical scheme:
the method for improving the negative electrode surface loading capacity of the lithium ion battery nano silicon by adopting the sulfur template and hydrogen peroxide activation at least comprises the following steps:
firstly, adding sulfur-containing substances and acid into graphene dispersion liquid to uniformly disperse the sulfur-containing substances, and fully stirring to obtain mixed dispersion liquid; the acid acts primarily to react with sulfur-containing species to form sulfur.
Secondly, adding nano silicon particles into absolute ethyl alcohol and/or water, and performing ultrasonic treatment to obtain a uniform nano silicon dispersion liquid;
thirdly, mixing the mixed dispersion liquid obtained in the first step and the nano-silicon dispersion liquid obtained in the second step, performing ultrasonic treatment again, and then adding the mixture and hydrogen peroxide into a hydrothermal reaction kettle for hydrothermal reaction to obtain graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, and then removing water to obtain a product to be treated;
and fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step to obtain the three-dimensional porous graphene-silicon macroscopic body.
According to the invention, a sulfur template method and a hydrogen peroxide activation method are adopted to respectively introduce gaps between sheets in the three-dimensional graphene network and etch pores on the sheets. Precisely introducing a reserved space in the capillary shrinkage process of the three-dimensional graphene hydrogel by controlling the usage amount of sulfur, so that the problem of volume expansion is solved at the level of active substance particles to relieve the expansion of the electrode under the condition of ensuring that the space requirement of silicon volume expansion is just met, and meanwhile, the high density of an active material is kept; in addition, in the process of continuously improving the loading capacity of the electrode active material, the thickness of the electrode is increased, the internal space of the electrode is reduced, namely the ion transmission tortuosity is further increased, so that the pores etched by the hydrogen peroxide in the sheet layer provide a shortcut for the ion penetration of the graphene sheet layer, the transmission path of lithium ions in the charging and discharging process is reduced, smooth ion transmission is ensured under the condition that the active material is made into a thick and dense electrode, and finally the volume performance and the surface capacity of the silicon cathode are improved.
As an improvement of the invention, in the first step, the mass ratio of the graphene dispersion liquid to the sulfur-containing substance to the acid is 1 (0.6-18) to (0.25-1.5), and the precursor proportion can accurately control the sulfur content within a certain range. The concentration of the graphene dispersion liquid is 2-6 mg/mL. Graphene oxide dispersions in this concentration range are most suitable for bridging to form a three-dimensional graphene-silicon-sulfur composite gel during hydrothermal processes.
As an improvement of the present invention, in the first step, the graphene dispersion liquid is at least one of a graphene oxide dispersion liquid, a nitrogen-doped modified graphene dispersion liquid and a porous graphene dispersion liquid, the sulfur-containing substance is at least one of a sublimed elemental sulfur, sodium thiosulfate and sodium sulfide, and the acid is at least one of hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, carbonic acid and acetic acid.
As an improvement of the invention, in the second step, the concentration of the nano-silicon dispersion liquid is 2-6 mg/mL.
In the third step, the volume ratio of the mixed dispersion liquid, the nano-silicon dispersion liquid and the hydrogen peroxide is 1 (0.5-1.5) to 0.001-0.003; the mass fraction of the hydrogen peroxide is 20-40%.
As an improvement of the invention, in the third step, the temperature of the hydrothermal reaction is 100-250 ℃, and the duration time of the hydrothermal reaction is 3-48 h.
As an improvement of the invention, in the fourth step, the moisture removal method is drying, the drying temperature is 60-90 ℃, and the drying duration is 6-72 h. The hydrothermal temperature is 100-250 ℃, the combination of sulfur and graphene oxide can be well driven, and meanwhile, in the hydrothermal process of 3-48 h, the graphene oxide lamella loaded with silicon and sulfur can be fully lapped to form the three-dimensional graphene-silicon-sulfur composite gel. In the drying process, the material is shrunk by capillary evaporation of water. Better shrinkage of the block can be realized at 60-90 ℃, and simultaneously block crushing caused by rapid shrinkage at higher temperature is avoided; the drying time of 6h-72h can realize full drying of the material.
As an improvement of the present invention, in the fifth step, the desulfurization treatment is heat treatment desulfurization, and the heat treatment desulfurization method comprises: heating to 300-500 ℃ at a heating rate of 3-20 ℃/min under the inert gas protection atmosphere, then keeping the temperature for 3-24 h, removing sulfur, and cooling to room temperature. The melting point and boiling point of the sulfur are low, and the heat treatment temperature of 300-500 ℃ can realize the complete removal of the sulfur.
As an improvement of the present invention, in the fifth step, the desulfurization treatment is solvent desulfurization: grinding the product to be treated, placing the product into carbon disulfide, and continuously stirring for 6-48 h to fully dissolve sulfur in the product to be treated into the carbon disulfide. The sulfur is easily dissolved in the carbon disulfide, and the sulfur can be thoroughly removed by the desulfurization of the carbon disulfide.
As an improvement of the invention, the three-dimensional porous graphene-silicon macroscopic body obtained in the fifth step has a rich pore structure, and the specific surface area is 200-800m2Per g, pore volume of 0.18-1.0cm3G, bulk density of 0.1-1.5g/cm3。
Compared with the prior art, the invention has at least the following advantages:
firstly, the method is mild in condition, simple to operate and green and pollution-free in preparation process, and the dense shrinkage of the three-dimensional graphene skeleton can be realized by utilizing the capillary evaporation effect of water, so that the high density of the active material is kept. And sulfur is used as a template, and a reserved space can be introduced to meet the volume expansion of silicon in the charging and discharging process after the sulfur is removed, so that pulverization and agglomeration of nano silicon are prevented, namely the problem of volume expansion is solved on the level of active substance particles to relieve the expansion of the electrode.
Secondly, hydrogen peroxide is in pores etched by the sheet layer, so that smooth ion transmission is ensured under the condition that the active material is made into a thick and dense electrode, and the volume performance of the nano silicon cathode is improved.
Thirdly, a proper space can be obtained by accurately controlling the content of sulfur in the three-dimensional porous graphene-silicon composite electrode material, and the transmission path of lithium ions in the charging and discharging process is reduced by introducing pores on a graphene sheet layer through hydrogen peroxide, so that high volume specific capacity is achieved under the condition of realizing high active substance loading capacity, and the obtained material has very important significance for improving the volume performance and surface capacity of the lithium ion battery.
Drawings
The invention and its advantageous effects are explained in detail below with reference to the accompanying drawings and the detailed description.
Fig. 1 is an SEM image of a three-dimensional porous graphene-silicon macroscopic material prepared in example 1 of the present invention.
Fig. 2 is a TEM image of a three-dimensional porous graphene-silicon macroscopic material prepared in example 1 of the present invention.
Fig. 3 is a nitrogen adsorption desorption isotherm (77K) of the three-dimensional porous graphene-silicon macroscopic material prepared in example 1 of the present invention.
Fig. 4 is a charge-discharge curve of a lithium ion battery made of the three-dimensional porous graphene-silicon macroscopic material according to example 1 of the present invention.
Detailed Description
The technical solutions of the present invention are described below with specific examples, but the scope of the present invention is not limited thereto.
Example 1
The embodiment provides a method for improving the negative electrode surface loading capacity of nano silicon of a lithium ion battery by adopting a sulfur template and hydrogen peroxide activation, which at least comprises the following steps:
firstly, taking 28.5mL of 4mg/mL graphene oxide dispersion liquid and placing the graphene oxide dispersion liquid into 100mL of baking ovenIn the cup, 3.41g of Na was added2S2O3·5H2O, then adding 28mL of 1M hydrochloric acid, and stirring for 30min to fully mix the mixture to obtain a mixed dispersion liquid;
secondly, taking 28.5mL of absolute ethyl alcohol, adding 57mg of nano silicon, and carrying out ultrasonic treatment for 20min to obtain a uniform dispersion liquid;
thirdly, mixing the dispersion liquid obtained in the first step and the dispersion liquid obtained in the second step, performing ultrasonic treatment for 20min, adding the mixture and 500 mu L of 30% hydrogen peroxide solution into a 100mL hydrothermal reaction kettle for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 180 ℃, and the duration of the hydrothermal reaction is 6h, so as to obtain the graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, fully drying the hydrogel at 70 ℃ for 48 hours, and removing water to obtain a product to be treated;
and fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step, specifically, under the protection of argon, heating to 400 ℃ at a heating rate of 10 ℃/min, then keeping the temperature for 6 hours, removing sulfur, and cooling to room temperature to obtain the three-dimensional porous graphene-silicon macroscopic body. The three-dimensional porous graphene-silicon macroscopic body has a rich pore structure and a specific surface area of 323m2Per g, pore volume of 0.47cm3(ii)/g, bulk Density of 0.89g/cm3。
The SEM image of the three-dimensional porous graphene-silicon macroscopic material prepared in example 1 is shown in fig. 1, and it can be seen from fig. 1 that: the three-dimensional porous graphene-silicon macroscopic body forms a reserved space between the sheet layers. A TEM image of the three-dimensional porous graphene-silicon macroscopic bulk material prepared in example 1 is shown in fig. 2, and there is significant etching on the surface of the sheet layer.
The nitrogen adsorption-desorption isotherm (77K) of the three-dimensional porous graphene-silicon macroscopic material prepared in example 1 is shown in fig. 3, and it can be seen from fig. 3 that: the pore structure of the three-dimensional porous graphene macroscopic body is mainly macroporous, and has mesopores and a small amount of micropores, so that a compact porous carbon skeleton structure is provided for the nano silicon active particles, the transmission of lithium ions and electrons is facilitated, and the volume expansion of the nano particles in the lithium embedding process can be buffered.
The charge-discharge curve of the lithium ion battery of the three-dimensional porous graphene-silicon macroscopic material prepared in example 1 is shown in fig. 4, and it can be seen from fig. 4 that: the three-dimensional graphene-silicon macroscopic body cathode material is used as a cathode material of a lithium ion battery and is 7mg cm-2The catalyst still has higher specific capacity and first-turn coulombic efficiency under the active material loading condition.
Example 2
The difference from example 1 is:
the dosage of the graphene oxide dispersion liquid is adjusted to 36mL and Na2S2O3·5H2The amount of O was adjusted to 1.63g, the amount of hydrochloric acid was adjusted to 13mL, the amount of anhydrous ethanol was adjusted to 36mL, and the amount of nanosilicon was adjusted to 72mg, which were the same as in example 1 and thus are not repeated herein.
The specific surface area of the three-dimensional porous graphene-silicon composite electrode material is 346m2Per g, pore volume of 0.41cm3G, bulk density of 0.93g/cm3。
Example 3
The difference from example 1 is:
the amount of the graphene oxide dispersion was adjusted to 39.3mL, Na2S2O3·5H2The amount of O was adjusted to 0.75g, the amount of hydrochloric acid was adjusted to 6.5mL, the amount of absolute ethanol was adjusted to 39.3mL, and the amount of nanosilicon was adjusted to 78.6mg, which were the same as in example 1 and thus are not repeated herein.
The specific surface area of the three-dimensional porous graphene-silicon composite electrode material is 384m2Per g, pore volume of 0.34cm3G, bulk density of 0.98g/cm3。
Example 4
The difference from example 1 is:
the amount of the graphene oxide dispersion was adjusted to 41.3mL, Na2S2O3·5H2The amount of O was adjusted to 0.31g, the amount of hydrochloric acid was adjusted to 2.5mL, the amount of absolute ethanol was adjusted to 41.3mL, and the amount of nanosilicon was adjusted to 82.6mg, which were the same as in example 1 and will not be repeated herein.
The specific surface area of the three-dimensional porous graphene-silicon composite electrode material is 402m2Per g, pore volume of 0.30cm3G, bulk density 1.02g/cm3。
Example 5
The difference from example 1 is:
the amount of the nano-silicon was adjusted to 85.5mg, and the rest was the same as in example 1, and the description thereof is omitted.
The specific surface area of the three-dimensional porous graphene-silicon composite electrode material is 302m2Per g, pore volume of 0.40cm3G, bulk density of 0.85g/cm3。
Example 6
The difference from example 2 is:
the amount of nano-silicon was adjusted to 108mg, and the rest was the same as example 2, and thus the description thereof is omitted.
The specific surface area of the three-dimensional porous graphene-silicon composite electrode material is 280m2Per g, pore volume of 0.35cm3(ii)/g, bulk Density of 0.81g/cm3。
Comparative example 1
In contrast to example 1, Na2S2O3·5H2The amount of O used was 0g, and the amount of hydrochloric acid used was 0mL, and the rest was the same as in example 1, and will not be described herein again.
In summary, as the desulfurization content increases, the more material headspace and, at the same time, the less density. The sulfur content is accurately regulated and controlled, a compact and porous three-dimensional graphene framework can be obtained, the volume expansion rate of silicon is 300 percent and is 7mg cm-2At a load of (2), still 1000mAh g is achieved-1Specific capacity of quality and 600mAh cm-3Volume to capacity of (a).
Example 7
The embodiment provides a method for improving the negative electrode surface loading capacity of nano silicon of a lithium ion battery by adopting a sulfur template and hydrogen peroxide activation, which at least comprises the following steps:
step one, putting 28.5mL of porous graphene dispersion liquid of 3mg/mL into a 100mL beaker, adding 0.5g of elemental sulfur, then adding 28mL of 1M nitric acid, and stirring for 30min to fully mix the elemental sulfur and the nitric acid to obtain mixed dispersion liquid;
secondly, taking 28.5mL of absolute ethyl alcohol, adding 65mg of nano silicon, and carrying out ultrasonic treatment for 30min to obtain a uniform dispersion liquid;
thirdly, mixing the dispersion liquid obtained in the first step and the dispersion liquid obtained in the second step, performing ultrasonic treatment for 30min, adding the mixture and 500 mu L of 35% hydrogen peroxide solution into a 100mL hydrothermal reaction kettle for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 200 ℃, and the duration of the hydrothermal reaction is 12h, so as to obtain the graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, fully drying the hydrogel at the temperature of 80 ℃ for 60 hours, and removing water to obtain a product to be treated;
and fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step, specifically, under the protection of argon, heating to 450 ℃ at a heating rate of 15 ℃/min, then keeping the temperature for 10 hours, removing sulfur, and cooling to room temperature to obtain the three-dimensional porous graphene-silicon macroscopic body. The three-dimensional porous graphene-silicon macroscopic body has a rich pore structure and a specific surface area of 332m2Per g, pore volume of 0.49cm3G, bulk density of 0.84g/cm3。
Example 8
The embodiment provides a method for improving the negative electrode surface loading capacity of nano silicon of a lithium ion battery by adopting a sulfur template and hydrogen peroxide activation, which at least comprises the following steps:
step one, putting 28.5mL of nitrogen-doped modified graphene dispersion liquid of 3mg/mL into a 100mL beaker, adding 0.9g of sodium sulfide, then adding 20mL of 1M sulfuric acid, and stirring for 30min to fully mix the mixture to obtain mixed dispersion liquid;
secondly, taking 28.5mL of absolute ethyl alcohol, adding 50mg of nano silicon, and carrying out ultrasonic treatment for 30min to obtain a uniform dispersion liquid;
thirdly, mixing the dispersion liquid obtained in the first step and the dispersion liquid obtained in the second step, performing ultrasonic treatment for 30min, adding the mixture and 500 mu L of 25% hydrogen peroxide solution into a 100mL hydrothermal reaction kettle for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 160 ℃, and the duration of the hydrothermal reaction is 24h, so as to obtain the graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, fully drying the hydrogel at 85 ℃ for 40 hours, and removing water to obtain a product to be treated;
and fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step, specifically, under the protection of argon, heating to 350 ℃ at a heating rate of 5 ℃/min, then keeping the temperature for 16 hours, removing sulfur, and cooling to room temperature to obtain the three-dimensional porous graphene-silicon macroscopic body. The three-dimensional porous graphene-silicon macroscopic body has a rich pore structure and a specific surface area of 356m2Per g, pore volume of 0.57cm3G, bulk density of 0.78g/cm3。
Example 9
The embodiment provides a method for improving the negative electrode surface loading capacity of nano silicon of a lithium ion battery by adopting a sulfur template and hydrogen peroxide activation, which at least comprises the following steps:
step one, putting 28.5mL of nitrogen-doped modified graphene dispersion liquid of 3mg/mL into a 100mL beaker, adding 0.6g of sodium sulfide, then adding 20mL of 1M sulfurous acid, and stirring for 30min to fully mix the mixture to obtain mixed dispersion liquid;
secondly, taking 28.5mL of absolute ethyl alcohol, adding 55mg of nano silicon, and carrying out ultrasonic treatment for 30min to obtain a uniform dispersion liquid;
thirdly, mixing the dispersion liquid obtained in the first step and the dispersion liquid obtained in the second step, performing ultrasonic treatment for 30min, adding the mixture and 500 mu L of 32% hydrogen peroxide solution into a 100mL hydrothermal reaction kettle for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 220 ℃, and the duration of the hydrothermal reaction is 16h, so as to obtain the graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, fully drying the hydrogel at the temperature of 75 ℃ for 45 hours, and removing water to obtain a product to be treated;
fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step, specifically, heating to 420 ℃ at a heating rate of 6 ℃/min under the protection of argon, then keeping the temperature for 8 hours, removing sulfur, and cooling to roomAnd (4) warming to obtain the three-dimensional porous graphene-silicon macroscopic body. The three-dimensional porous graphene-silicon macroscopic body has rich pore structures and a specific surface area of 383m2Per g, pore volume of 0.39cm3G, bulk density of 0.95g/cm3。
Example 10
The embodiment provides a method for improving the negative electrode surface loading capacity of nano silicon of a lithium ion battery by adopting a sulfur template and hydrogen peroxide activation, which at least comprises the following steps:
step one, putting 28.5mL of porous graphene dispersion liquid of 3mg/mL into a 100mL beaker, adding 0.3g of elemental sulfur, then adding 20mL of 1M acetic acid, and stirring for 30min to fully mix the elemental sulfur and the acetic acid to obtain mixed dispersion liquid;
secondly, taking 28.5mL of absolute ethyl alcohol, adding 51mg of nano silicon, and carrying out ultrasonic treatment for 30min to obtain a uniform dispersion liquid;
thirdly, mixing the dispersion liquid obtained in the first step and the dispersion liquid obtained in the second step, performing ultrasonic treatment for 30min, adding the mixture and 500 mu L of 22% hydrogen peroxide solution into a 100mL hydrothermal reaction kettle for hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 140 ℃, and the duration of the hydrothermal reaction is 42h, so as to obtain the graphene-silicon-sulfur composite hydrogel;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, fully drying the hydrogel at 65 ℃ for 70 hours, and removing water to obtain a product to be treated;
and fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step, specifically, grinding the product to be treated, placing the ground product into carbon disulfide, and continuously stirring for 20 hours to fully dissolve sulfur in the product to be treated into the carbon disulfide to obtain the three-dimensional porous graphene-silicon macroscopic body. The three-dimensional porous graphene-silicon macroscopic body has a rich pore structure and a specific surface area of 377m2Per g, pore volume of 0.58cm3G, bulk density of 0.99g/cm3。
Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (7)
1. A method for improving the volume performance of a lithium ion battery nano silicon cathode by adopting a sulfur template and hydrogen peroxide activation is characterized by at least comprising the following steps:
firstly, adding a sulfur-containing substance and acid into a graphene dispersion liquid, and fully stirring to obtain a mixed dispersion liquid;
secondly, adding nano silicon particles into absolute ethyl alcohol and/or water, and performing ultrasonic treatment to obtain a uniform nano silicon dispersion liquid;
thirdly, mixing the mixed dispersion liquid obtained in the first step and the nano-silicon dispersion liquid obtained in the second step, performing ultrasonic treatment again, and then adding the mixture and hydrogen peroxide into a hydrothermal reaction kettle for hydrothermal reaction to obtain graphene-silicon-sulfur composite hydrogel; the volume ratio of the mixed dispersion liquid, the nano-silicon dispersion liquid and the hydrogen peroxide is 1 (0.5-1.5) to 0.001-0.003; the mass fraction of the hydrogen peroxide is 20-40%; the temperature of the hydrothermal reaction is 100-250 ℃, and the duration time of the hydrothermal reaction is 3-48 h; pores are introduced into the graphene sheet layers through hydrogen peroxide, so that ion penetration shortcuts of the graphene sheet layers are provided, and a transmission path of lithium ions in the charging and discharging process is reduced;
step four, fully soaking the hydrogel obtained in the step three in deionized water to remove impurities, and then removing water to obtain a product to be treated;
fifthly, performing desulfurization treatment on the product to be treated obtained in the fourth step to obtain a three-dimensional porous graphene-silicon macroscopic body; the three-dimensional porous graphene-silicon macroscopic body has a rich pore structure and a specific surface area of 200-800m2Per g, pore volume of 0.18-1.0cm3G, bulk density of 0.1-1.5g/cm3。
2. The method of claim 1, wherein: in the first step, the mass ratio of the graphene dispersion liquid, the sulfur-containing substance and the acid is 1 (0.6-18) to (0.25-1.5), and the concentration of the graphene dispersion liquid is 2-6 mg/mL.
3. The method of claim 1, wherein: in the first step, the graphene dispersion liquid is at least one of graphene oxide dispersion liquid, nitrogen-doped modified graphene dispersion liquid and porous graphene dispersion liquid, the sulfur-containing substance is at least one of sublimed elemental sulfur, sodium thiosulfate and sodium sulfide, and the acid is at least one of hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, carbonic acid and acetic acid.
4. The method of claim 1, wherein: in the second step, the concentration of the nano-silicon dispersion liquid is 2-6 mg/mL.
5. The method of claim 1, wherein: in the fourth step, the moisture removal method is drying, the drying temperature is 60-90 ℃, and the drying duration is 6-72 h.
6. The method of claim 1, wherein: in the fifth step, the desulfurization treatment is heat treatment desulfurization, and the heat treatment desulfurization method comprises the following steps: heating to 300-500 ℃ at a heating rate of 3-20 ℃/min under the inert gas protection atmosphere, then keeping the temperature for 3-24 h, removing sulfur, and cooling to room temperature.
7. The method of claim 1, wherein: and in the fifth step, the desulfurization treatment is solvent desulfurization, the product to be treated is ground and then placed in carbon disulfide, and the mixture is continuously stirred for 6 to 48 hours, so that the sulfur in the product to be treated is fully dissolved in the carbon disulfide.
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