CN112599732B - Silicon negative electrode material for lithium ion battery and preparation method thereof - Google Patents

Silicon negative electrode material for lithium ion battery and preparation method thereof Download PDF

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CN112599732B
CN112599732B CN202011402836.6A CN202011402836A CN112599732B CN 112599732 B CN112599732 B CN 112599732B CN 202011402836 A CN202011402836 A CN 202011402836A CN 112599732 B CN112599732 B CN 112599732B
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陈超
陈宇
谢解解
李海东
秦益民
李沛
陈洪旭
朱红华
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Shanghai Aurora Technology Co ltd
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Abstract

The invention relates to a silicon negative electrode material for a lithium ion battery and a preparation method thereof, the method comprises the steps of firstly placing silicon nanoparticles in a bPEI solution for reaction to obtain aminated modified silicon nanoparticles, then adding the aminated modified silicon nanoparticles and an initiator into an ANI solution for reaction, and drying to obtain the silicon negative electrode material; the prepared silicon negative electrode material comprises a PANI network structure with nano pores and amination modified silicon nano particles at network nodes; the aminated modified silicon nanoparticles are connected with PANI covalent bonds through amino groups on bPEI on the surface of the aminated modified silicon nanoparticles; the amination modified silicon nanoparticles comprise silicon nanoparticles and bPEI (boron polyetherimide) with hydrogen bonds on the surfaces of the silicon nanoparticles, and the mass ratio of PANI to amination modified silicon nanoparticles is 3-5: 10; the weight average molecular weight of the bPEI is 45000-75000 g/mol; after the silicon negative electrode material is assembled into the button battery, the button battery has good charge-discharge cycle stability and double charge performance.

Description

Silicon negative electrode material for lithium ion battery and preparation method thereof
Technical Field
The invention belongs to the technical field of automobile engines, and relates to a silicon negative electrode material for a lithium ion battery and a preparation method thereof.
Background
In recent years, lithium ion batteries have been regarded by academia and industry as an ideal choice for battery systems for electric vehicles and large energy storage devices. As an important component of the battery, the current commercialized lithium ion battery mainly uses graphite carbon-based negative electrode materials, but the theoretical specific capacity value of the lithium ion battery is only 372mAhg-1And the requirement of the electric automobile on the high-specific-capacity battery can not be met far away. Among the numerous non-carbon based anode candidates, silicon has its highest theoretical specific capacity value (4200 mAhg)-1) Has received great attention from the academia. Although the theoretical lithium storage capacity of silicon is 11 times that of graphite, in the actual charging and discharging process, on average, each silicon atom is combined with 4.4 lithium atoms, so that the volume change of the silicon negative electrode reaches more than 300%, and the mechanical force generated by the severe volume shrinkage and expansion can cause the active material silicon to fall off from a current collector to lose electric contact, and cause the mechanical pulverization of the silicon, and finally cause the rapid reduction of the specific capacity value. In addition, the low conductivity of silicon as a semiconductor material also makes the charging performance of silicon cathode poor.
From the perspective of structural design, a three-dimensional network structure is constructed by crosslinking, in-situ polymerization, compounding and the like of an inactive material, such as a binder, in the negative electrode, and the active material silicon nanoparticles are limited in the grid, so that the movement of the silicon nanoparticles can be limited to a certain extent, the silicon nanoparticles are prevented from falling off from a current collector, and the cycle stability and the double charging performance of the silicon negative electrode are improved.
(1) In the existing negative electrode with a three-dimensional network structure, silicon nanoparticles are embedded in the pores of a binder grid, and the three-dimensional network structure is used for limiting the movement of the silicon nanoparticles through the grid structure and buffering the volume expansion of silicon through the space provided by the grid pores. However, in the actual lithium intercalation/deintercalation process, if the pore space of the grid cannot meet the severe volume expansion of silicon, the silicon nanoparticles still have a high possibility of being separated from the three-dimensional grid, so that the negative electrode fails.
(2) In the continuous charge-discharge cycle process, after the volume change of the silicon is repeatedly buffered, a three-dimensional network structure directly constructed in a covalent bond crosslinking mode or an in-situ polymerization mode can generate network structure damage, and the cycle performance is greatly reduced in the later period because the covalent bond has no reversibility and cannot be crosslinked again to form a new network structure.
(3) In addition, the binder constituting the three-dimensional network structure often does not have ionic and electronic conductivity, and thus the double charge performance of the silicon negative electrode cannot be effectively improved.
Therefore, there is a need for a more efficient three-dimensional network structure in order to improve both the cycle stability and the charging performance of a silicon anode.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a silicon negative electrode material for a lithium ion battery and a preparation method thereof, and particularly relates to an aminated modified silicon nanoparticle (Si @ bPEI) with a large amount of amino groups on the surface is prepared by forming strong hydrogen bonds between a large amount of amino groups on a branched chain of hyperbranched polyethyleneimine (bPEI) and the surface of a silicon nanoparticle (Si). And adding an aniline monomer (ANI) on the basis, and utilizing the higher surface activity of the Si @ bPEI nano particles and the abundant amino graft polymerization PANI on the surface to connect the Si @ bPEI together, thereby finally forming the novel conductive three-dimensional network structure silicon negative electrode material taking (Si @ bPEI) as a network node and conductive polymer PANI as a network framework.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a silicon negative electrode material for a lithium ion battery comprises a PANI network structure with nano pores and aminated modified silicon nanoparticles at network nodes; the aminated modified silicon nanoparticles are connected with PANI covalent bonds through amino groups on bPEI on the surface of the aminated modified silicon nanoparticles; the amination modified silicon nano-particles comprise silicon nano-particles and bPEI connected with the surface hydrogen bonds of the silicon nano-particles;
the mass ratio of the PANI to the aminated modified silicon nanoparticles is 3-5: 10; when the proportion of the silicon nanoparticles is too high, the conductivity of the whole network is reduced to a certain degree due to the non-conductivity of the silicon nanoparticles, so that the double charge performance of the cathode is weakened, and PANI cannot be effectively crosslinked into a three-dimensional network, so that the effects of buffering volume expansion and stress dispersion cannot be achieved, and the cycle life of the cathode is influenced; the proportion of active material silicon nano particles in the silicon cathode is too low, the proportion of inert material PANI is too high, so that the practical application value of the silicon cathode is limited, and the proportion of PANI is too high, so that PANI is directly polymerized to form a film and cannot form a three-dimensional network structure taking the silicon nano particles as cross-linking nodes; therefore, the proper proportion of the silicon nanoparticles is selected, so that the conductivity of the whole three-dimensional network can be improved, the effects of volume buffering and stress dispersion are improved, and the charge and discharge performance of the three-dimensional network is improved.
The weight average molecular weight of the bPEI is 45000-75000 g/mol. When the bPEI with the excessively small molecular weight is used, the bPEI grafted on the surface of the silicon nanoparticle has shorter and less branches extending outwards, so that enough PANI grafting sites cannot be generated to form a fully connected three-dimensional network, and the silicon nanoparticle can be separated from the three-dimensional network structure at the initial stage of circulation to fail; on the contrary, when the bPEI with the excessively large molecular weight is used, the bPEI with the excessively large molecular weight can spontaneously aggregate, the bPEI cannot be uniformly coated on the surface of the silicon nano-particle due to steric hindrance and other reasons, so that the amino groups on the surface of the silicon nano-particle are not increased, the amino groups on the surface of the silicon nano-particle are less due to less coating amount of the bPEI, a sufficient PANI grafting site cannot be generated to form a fully connected three-dimensional network, and the silicon nano-particle can be separated from the three-dimensional network structure at the initial stage of circulation to fail. Therefore, the bPEI with the proper molecular weight is selected, so that the surface of the silicon nanoparticle is uniformly coated with the bPEI, and enough PANI grafting sites are generated, thereby playing a key role in whether a three-dimensional network can be formed.
The preferable technical scheme is as follows:
the silicon negative electrode material for the lithium ion battery has the advantages that the average diameter of the silicon nanoparticles is 50-160 nm.
According to the silicon negative electrode material for the lithium ion battery, the amino content of the surface of the aminated modified silicon nanoparticle is 4-8 wt%.
After the silicon negative electrode material is assembled into the button battery, the voltage range is 0.03-3V and is 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is more than or equal to 80 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1When the specific capacity value of the negative electrode is not less than 250mAg of current density-1The specific capacity value is 70%.
The invention also provides a method for preparing the silicon negative electrode material for the lithium ion battery, which is characterized by comprising the following steps: firstly, placing the silicon nanoparticles in a bPEI solution for reaction I to obtain aminated modified silicon nanoparticles, then adding the aminated modified silicon nanoparticles and an initiator into an ANI solution for reaction II, and drying to obtain the silicon cathode material.
As a preferred technical scheme:
according to the silicon anode material for the lithium ion battery, the silicon nanoparticles are subjected to surface hydroxyl activation treatment before the reaction I. The silicon nanoparticles without surface hydroxyl activation treatment can also be directly subjected to reaction I to prepare the silicon cathode material, but the effect after the hydroxyl activation treatment is better.
According to the preparation method of the silicon anode material for the lithium ion battery, the solvent of the bPEI solution is water or ethanol, and the concentration is 5-20 wt%; the time of the reaction I is 1-12, and the temperature of the reaction I is 25-50 ℃. The bPEI solution has better dispersibility when the solvent is ethanol.
According to the preparation method of the silicon negative electrode material for the lithium ion battery, the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10: 3-5, the initiator is ammonium persulfate, and the addition amount of the initiator is 5-10 wt% of the mass of the ANI monomer.
According to the preparation method of the silicon anode material for the lithium ion battery, the solvent of the ANI solution is water or ethanol, and the concentration is 10-30 wt%; the reaction time of II is 0.5-2 h, and the temperature of II is 25-50 ℃.
The invention adopts the following principle:
the method adopts bPEI (a known hyperbranched oligomer binder, a branched chain contains a large amount of amino and has a hyperbranched structure) to carry out surface modification on silicon nanoparticles to obtain modified silicon nanoparticles with a large amount of free amino on the surface, and the structure is formed because the hyperbranched structure of bPEI and the amino on the branched chain and the silicon nanoparticles form a large amount of hydrogen bonds, so that the bPEI can be stably adsorbed on the surface of the silicon nanoparticles, and a large amount of free amino extending outwards is provided for the silicon nanoparticles to be used for graft polymerization of PANI;
the silicon nano material has high surface energy as a nano material, so that the silicon nano material is more active in an ANI solution, the contact probability of the silicon nano material and an ANI monomer is greatly increased, the contact probability of free amino on the surface of the modified silicon nano particle and the ANI monomer is improved, the efficiency of graft polymerization PANI with the amino on the surface of the silicon nano particle as a site is finally improved, and finally the silicon nano particles are mutually connected through continuous polymerization of the PANI to form a three-dimensional network structure with the silicon nano particle as a node and PNAI as a framework. Compared with the traditional silicon nano particles embedded in a three-dimensional network grid, in the structure, when the silicon nano particles generate volume expansion, a plurality of pores around the nodes can be fully utilized, and more space can be obtained to buffer the violent volume expansion of silicon; and the stress generated by the volume change of the silicon nanoparticles can be uniformly dispersed to the whole network framework through network nodes. Finally, the novel three-dimensional network structure effectively ensures the integrity of a space structure, electron transmission and an ion transport network of the silicon cathode in the continuous charge-discharge cycle process, thereby improving the cycle stability;
on the other hand, a large number of reversible hydrogen bonds formed in the surface modification process enable the bPEI and the silicon nanoparticles to have stronger interface reversibility, once the bPEI coated on the surface of the silicon particles serving as a cross-linking node and the hydrogen bonds between the bPEI and the silicon nanoparticles are broken, the hydrogen bonds can be formed again, the silicon nanoparticles are prevented from falling off from the three-dimensional network, the three-dimensional network is repaired to a certain extent, and the circulation stability is further improved. In the prior art, the three-dimensional network structure is often constructed by covalent bonds directly, so that the three-dimensional network structure is not reversible, and once the three-dimensional network structure is damaged, the three-dimensional network structure cannot be repaired spontaneously, so that the cycle stability is poor.
According to the cathode material with the PANI three-dimensional network framework and the amination modified silicon nanoparticles as the framework cross nodes, the nano-pore structure of the three-dimensional network framework enables lithium ions to be rapidly diffused to the surfaces of the silicon nanoparticles at the nodes, and the bPEI also has lithium ion transmission performance and is beneficial to the migration of the lithium ions to the surfaces of the silicon nanoparticles, so that the double-charging performance of the silicon cathode is improved. The PANI serving as a framework in the three-dimensional network structure has good electronic conductivity, electrons can be directly transmitted to the silicon nanoparticles serving as cross-linking nodes along the framework PANI, and the improvement of the double charge performance of the silicon cathode material is facilitated. However, the double charging performance has application value only based on a stable three-dimensional network structure, the stable three-dimensional network structure is established at first, and the double charging performance is improved based on high cycle stability.
Has the advantages that:
(1) the silicon cathode material for the lithium ion battery can effectively improve the cycling stability and the double charging performance of the silicon cathode; for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is more than or equal to 80 percent of the initial specific capacity value; the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when in useThe current density reaches 2000mAg-1When the specific capacity value of the negative electrode is not less than 250mAg of current density-170% of the specific capacity value;
(2) according to the preparation method of the silicon cathode material for the lithium ion battery, the silicon nanoparticles with the modified surfaces are used as the graft polymerization sites, so that a more effective three-dimensional network cathode structure is provided;
(3) the preparation method of the silicon cathode material for the lithium ion battery is simple and easy to implement, does not need to use toxic and harmful organic solvents, and avoids the use of a complex synthesis method for preparing the functional binder material.
Drawings
FIG. 1 is a scanning electron microscope topography of silicon negative electrode materials in examples 1 to 2 and comparative examples 1 to 4 of the present invention;
FIG. 2 is a graph showing the charge-discharge cycle performance of the silicon negative electrodes in examples 1 to 2 and comparative examples 1 to 4 of the present invention;
FIG. 3 is a graph showing the charge doubling performance of silicon cathodes in examples 1 to 2 and comparative examples 1 to 4 of the present invention.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing activated silicon nanoparticles with the average diameter of 120nm into a bPEI aqueous solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI connected with the surface hydrogen bonds of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 6.1 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI aqueous solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material ((Si @ bPEI)10/PANI 3); wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:3, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 3:10, and the scanning electron microscope image of the silicon cathode material is shown in figure 1;
after the prepared silicon cathode material is assembled into a button battery, the voltage range is 0.03-3V (the value is a range value in actual test), and the value is 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charge and discharge, the specific capacity value of the negative electrode was 92% of the initial specific capacity value (as shown in fig. 2);
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The value of specific capacity at that time is 76% (as shown in fig. 3).
Comparative example 1
A preparation method of a silicon negative electrode material comprises the following steps:
directly soaking 0.1g of silicon nano-particles in 20ml of water solution containing 0.05ANI of a monomer, adding an initiator APS, uniformly stirring, coating on a copper foil, and finally drying to obtain the silicon negative electrode material Si/PANI.
As shown in fig. 1, SEM tests show that the surface of the silicon negative electrode does not form a three-dimensional network structure morphology and forms a film directly; this is because the Si nanoparticles that were not soaked in bPEI solution were directly composited with PANI, and ANI was directly self-polymerized into PANI membrane because the surface of the silicon nanoparticles could not provide sites for PANI graft polymerization.
And pre-charging and discharging for 10 times at a current density of 250mAg-1 to activate the silicon cathode, and after 9 times of charging and discharging, the specific capacity is reduced to 47.6mAhg-1Failure; the current densities were set to 250mAg, respectively-1、500mAg-1、1000mAg-1And 2000mAg-1The double charge test was performed at an initial current density of 250mAg-1Then, after 5 times of charging and discharging, the specific capacity was reduced to 36.6mAhg-1And (4) failing. The rapid specific capacity decline is caused by the fact that PANI does not form a three-dimensional network structure, the volume expansion of silicon nanoparticles cannot be limited, and the silicon nanoparticles are directly separated from the PANI film, so that the silicon nanoparticles are separated from a silicon negative electrode current collector.
Comparative example 2
A method for preparing a silicon anode material for a lithium ion battery, which comprises the steps substantially the same as those of example 1, except that in the step (3), the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:1, and then PANI and the aminated modified silicon nanoparticles are linked by covalent bonds in the mass ratio of 1:10 in the prepared silicon anode material ((Si @ bPEI)10/PANI 1);
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 3.6 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current is denseThe degree reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value was 0.23%.
Comparative example 3
A method for preparing a silicon anode material for a lithium ion battery, which comprises the steps substantially the same as those of example 1, except that in the step (3), the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:7, and then PANI and the aminated modified silicon nanoparticles are linked by covalent bonds in the mass ratio of 7:10 in the prepared silicon anode material ((Si @ bPEI)10/PANI 7);
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 69 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-146% of the specific capacity value.
Comparative example 4
A method for preparing a silicon anode material for a lithium ion battery, which comprises the steps substantially the same as those of example 1, except that in the step (3), the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:9, and then PANI and the aminated modified silicon nanoparticles are linked by covalent bonds in the mass ratio of 9:10 in the prepared silicon anode material ((Si @ bPEI)10/PANI 9);
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1Carry out charging and dischargingAnd (3) testing the electrical cycle stability: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 32% of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 12%.
As can be seen by comparing comparative examples 2-4 with example 1, as shown in FIGS. 1-3, when the ratio of PANI to silicon nanoparticles is too low (i.e., comparative example 2), (Si @ bPEI)10/PANI1 cannot completely form a three-dimensional network structure; and the specific capacity value declines rapidly because the ANI content is too low, resulting in insufficient PANI polymerization and failure to connect silicon nanoparticles together to form a three-dimensional network. Because the three-dimensional network structure cannot be effectively formed to buffer the volume expansion of the silicon nanoparticles and inhibit the movement of the Si nanoparticles, the silicon nanoparticles cannot be effectively adhered to the current collector under the action of the binder; the main reason why the double charge performance is rapidly reduced is that an effective three-dimensional network cannot be formed, the silicon cathode fails after charging and discharging for only a plurality of times, and the test is terminated:
when the PANI ratio is too high (i.e., comparative examples 3 and 4), because PANI is agglomerated due to excessive PANI, a three-dimensional network structure cannot be formed, and sufficient pores are not provided for a buffer space for the silicon nanoparticles to undergo volume expansion, the main reason for the rapid decrease of the charging performance is that the pore structure of the three-dimensional network is destroyed, so that lithium ions cannot rapidly diffuse to the surface of the silicon nanoparticles;
in example 1, for the silicon nanoparticles modified by the bPEI solution, a layer of bPEI is adsorbed on the surface of the silicon nanoparticles due to the hydrogen bonds formed between the surface oxide layer of the silicon nanoparticles and a large number of amino groups on the branched chain of the bPEI, and a large number of sites are provided for the PANI graft polymerization by the amino groups on the surface of the bPEI, so that the silicon nanoparticles can be used as cross-linked nodes to form a three-dimensional network.
Comparative example 5
A method for preparing a silicon negative electrode material for a lithium ion battery, which comprises the substantially same steps as example 1, except that in the step (2), bPEI is replaced with pei having a weight average molecular weight of 100000g/mol, so that the amino group content on the surface of the prepared aminated modified silicon nanoparticle is 3.4 wt%; further, preparing a silicon negative electrode material by using the aminated modified silicon nano-particles;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 64 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value was 53%.
Comparative example 6
A preparation method of a silicon negative electrode material for a lithium ion battery, which comprises the steps substantially the same as those in example 1, except that in the step (2), bPEI is replaced by bPEI with the weight-average molecular weight of 10000g/mol, and the amino content of the surface of the prepared aminated modified silicon nano-particles is 2.6 wt%; further, preparing a silicon negative electrode material by using the aminated modified silicon nano-particles;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 36 percent of the initial specific capacity value;
for the button cell with activated silicon cathode, the current density is respectively250mAg-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 24%.
Comparing comparative examples 5 to 6 with example 1, it can be seen that:
the charge-discharge cycle stability and the double charge performance of the silicon cathode material in the comparative example 5 are worse, although the bPEI with larger molecular weight can be used to coat more bPEI on the surface of the nano-particles, after the bPEI molecules reach a certain degree, spontaneous agglomeration can occur, steric hindrance and other reasons can cause that a large amount of bPEI can not be coated on the surface of the silicon nano-particles, so that the amino on the surface of the silicon nano-particles is not increased, and less bPEI can cause that the amino on the surface of the silicon nano-particles is less, so that enough PANI grafting sites can not be generated to form a fully connected three-dimensional network, and the silicon nano-particles can be separated from the three-dimensional network structure at the initial stage of circulation to fail.
The charge-discharge cycle stability and the double charge performance of the silicon negative electrode material in comparative example 6 were worse because when bPEI with too small molecular weight was used, bPEI grafted on the surface of the silicon nanoparticles had shorter and less branches extending outward, and thus sufficient PANI grafting sites could not be generated to form a fully connected three-dimensional network, which resulted in failure of the silicon nanoparticles to leave the three-dimensional network structure at the early stage of the cycle.
Example 2
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing activated silicon nanoparticles with the average diameter of 120nm into a bPEI aqueous solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI connected with the surface hydrogen bonds of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 6 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI aqueous solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material ((Si @ bPEI)10/PANI 5); wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:5, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nanoparticles is 5:10, and the PANI and the aminated modified silicon nanoparticles are connected through covalent bonds; the shape of the silicon cathode material is shown in figure 1 by a scanning electron microscope;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 86% of the initial specific capacity value (as shown in fig. 2);
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The value of the specific capacity at time 74% (as shown in fig. 3).
Example 3
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing activated silicon nanoparticles with the average diameter of 120nm into a bPEI aqueous solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI connected with the surface hydrogen bonds of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 5.9 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI aqueous solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:4, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 4:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 89% of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 75%.
Example 4
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing the activated silicon nanoparticles with the average diameter of 50nm into a bPEI aqueous solution with the concentration of 20wt% (wherein the weight-average molecular weight of the bPEI is 45000g/mol), and reacting for 1h at the temperature of 25 ℃ to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI with hydrogen bonds on the surfaces of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 4.2 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI aqueous solution with the concentration of 10wt%, reacting for 0.5h at the temperature of 25 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:3, and the addition amount of ammonium persulfate is 5 wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 3:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 89% of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 78%.
Example 5
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing the activated silicon nanoparticles with the average diameter of 160nm into a bPEI aqueous solution with the concentration of 5 wt% (wherein the weight-average molecular weight of the bPEI is 75000g/mol), and reacting at the temperature of 50 ℃ for 12h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI with hydrogen bonds on the surfaces of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 7.7 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI aqueous solution with the concentration of 30wt%, reacting for 2h at the temperature of 50 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:3, and the addition amount of ammonium persulfate is 10wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 3:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 83 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 72%.
Example 6
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing the activated silicon nanoparticles with the average diameter of 120nm into a bPEI ethanol solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI with hydrogen bonds on the surface of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 6.7 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI ethanol solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:3, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 3:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 91% of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value at that time was 76%.
Example 7
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing the activated silicon nanoparticles with the average diameter of 120nm into a bPEI ethanol solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI with hydrogen bonds on the surface of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 6.5 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI ethanol solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:5, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 3:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 85% of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 70%.
Example 8
A preparation method of a silicon negative electrode material for a lithium ion battery comprises the following steps:
(1) activating hydroxyl on the surface of the silicon nano-particle: weighing 0.1g of silicon nanoparticles, adding the silicon nanoparticles into 50mL of 1mol/L HCl solution, carrying out ultrasonic treatment for 1h, and then washing the silicon nanoparticles with deionized water and ethanol respectively to obtain activated silicon nanoparticles;
(2) placing the activated silicon nanoparticles with the average diameter of 120nm into a bPEI ethanol solution with the concentration of 15 wt% (wherein the weight average molecular weight of bPEI is 60000g/mol), and reacting at the temperature of 35 ℃ for 6h to obtain aminated modified silicon nanoparticles consisting of the activated silicon nanoparticles and bPEI with hydrogen bonds on the surface of the activated silicon nanoparticles;
the amino group content of the surface of the aminated modified silicon nanoparticle is 6.6 wt%;
(3) adding the aminated modified silicon nano-particles and ammonium persulfate into an ANI ethanol solution with the concentration of 20wt%, reacting for 1h at the temperature of 35 ℃, and drying to obtain a silicon negative electrode material; wherein the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10:4, and the addition amount of ammonium persulfate is 8wt% of the mass of the ANI monomer;
the prepared silicon negative electrode material comprises a PANI three-dimensional network framework and amination modified silicon nano-particles at the crossed nodes of the framework; the mass ratio of the PANI to the aminated modified silicon nano-particles is 4:10, and the PANI and the aminated modified silicon nano-particles are connected through covalent bonds;
after the prepared silicon negative electrode material is assembled into a button battery, the voltage range is 0.03-3V and 250mAg-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is 88 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out a double charge performance test: when the current density reaches 2000mAg-1Then, the negative electrodeThe specific capacity value of (A) is that the current density is 250mAg-1The specific capacity value is 73%.

Claims (8)

1. A silicon negative electrode material for a lithium ion battery is characterized in that: the nano-silicon nanoparticle comprises a network structure which takes PANI as a network framework and has nano pores, and aminated modified silicon nanoparticles at network nodes; the aminated modified silicon nano-particles are connected with PANI covalent bonds through amino groups on hyperbranched polyethyleneimine on the surfaces of the aminated modified silicon nano-particles; the aminated modified silicon nanoparticles comprise silicon nanoparticles and hyperbranched polyethyleneimine of which the surfaces are in hydrogen bond connection;
the mass ratio of the PANI to the aminated modified silicon nanoparticles is 3-5: 10;
the weight average molecular weight of the hyperbranched polyethyleneimine is 45000-75000 g/mol;
the amino content of the surface of the aminated modified silicon nanoparticle is 4-8 wt%.
2. The silicon negative electrode material for the lithium ion battery as claimed in claim 1, wherein the average particle diameter of the silicon nanoparticles is 50 to 160 nm.
3. The silicon negative electrode material for the lithium ion battery as claimed in claim 2, wherein the voltage range of the silicon negative electrode material is 0.03-3V and is 250mAg after the silicon negative electrode material is assembled into a button battery-1The current density of the voltage source is pre-charged and discharged for 10 times to activate the silicon cathode;
for the button cell with activated silicon cathode, the current density is 500mAg-1And (3) carrying out a charge-discharge cycle stability test: after 100 times of charging and discharging, the specific capacity value of the negative electrode is more than or equal to 80 percent of the initial specific capacity value;
the current density of the button cell for activating the silicon cathode is 250mAg respectively-1、500mAg-1、1000mAg-1And 2000mAg-1And (3) carrying out rate performance test: when the current density reaches 2000mAg-1When the specific capacity value of the negative electrode is not less than 250mAg of current density-1The specific capacity value is 70%.
4. The method for preparing the silicon negative electrode material for the lithium ion battery according to any one of claims 1 to 3, wherein the method comprises the following steps: firstly, placing silicon nanoparticles in a hyperbranched polyethyleneimine solution to perform reaction I to obtain aminated modified silicon nanoparticles, then adding the aminated modified silicon nanoparticles and an initiator into an ANI solution to perform reaction II, and drying to obtain the silicon negative electrode material.
5. The preparation method of the silicon anode material for the lithium ion battery as claimed in claim 4, wherein the silicon nanoparticles are further subjected to surface hydroxyl activation treatment before the reaction I.
6. The preparation method of the silicon negative electrode material for the lithium ion battery according to claim 4, wherein the solvent of the hyperbranched polyethyleneimine solution is water or ethanol, and the concentration of the solvent is 5-20 wt%; the reaction I is carried out for 1-12 hours at 25-50 ℃.
7. The preparation method of the silicon negative electrode material for the lithium ion battery, according to claim 5, is characterized in that the mass ratio of the aminated modified silicon nanoparticles to the ANI monomer is 10: 3-5, the initiator is ammonium persulfate, and the addition amount of the initiator is 5-10 wt% of the mass of the ANI monomer.
8. The preparation method of the silicon anode material for the lithium ion battery according to claim 6, wherein the solvent of the ANI solution is water or ethanol, and the concentration of the solvent is 10-30 wt%; the reaction II is carried out for 0.5-2 hours at 25-50 ℃.
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