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CN118431422A - Composite negative electrode material and preparation method thereof, negative electrode sheet and battery - Google Patents

Composite negative electrode material and preparation method thereof, negative electrode sheet and battery Download PDF

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Publication number
CN118431422A
CN118431422A CN202310116394.6A CN202310116394A CN118431422A CN 118431422 A CN118431422 A CN 118431422A CN 202310116394 A CN202310116394 A CN 202310116394A CN 118431422 A CN118431422 A CN 118431422A
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silicon
composite anode
anode material
carbon
carbon material
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Inventor
徐少洪
钱华玉
闫远滔
张宁月
程振柯
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BYD Co Ltd
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BYD Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention relates to the technical field of negative electrode materials, and discloses a composite negative electrode material, a preparation method thereof, a negative electrode plate and a battery. The composite anode material comprises a silicon-carbon material and an interface modifier, wherein the silicon-carbon material also contains oxygen, and the content of the oxygen is 0.1-5wt% based on the total mass of the silicon-carbon material; the chemical composition of the interface modifier is A aBbHcOd, and the element A is one or more of Mg, al and Ca; b element is selected from one or more of S, P, C, H is hydrogen element, O is oxygen element; at least part of oxygen in the silicon carbon material forms a chemical bond with the A element in the interface modifier. The composite anode material can tightly connect the silicon-carbon material and the conductive agent together by utilizing chemical bonds, thereby reducing the loss of electrical contact in the circulation process and obviously improving the circulation capacity retention rate of the lithium ion battery.

Description

Composite negative electrode material, preparation method thereof, negative electrode plate and battery
Technical Field
The invention relates to a negative electrode material, in particular to a composite negative electrode material, a preparation method thereof, a negative electrode plate and a battery.
Background
It is known that silicon anode materials have a problem of great volume expansion during charge and discharge. This large volumetric expansion of the silicon material can cause cracking of the silicon material, leading to continuous consumption of electrolyte, and can greatly accelerate mechanical cracking of the electrode, leading to loss of electrical contact between the silicon material and the conductive agent. Wherein the loss of capacity due to the lack of electrical contact occupies a substantial portion of the cyclic capacity loss of the silicon material. In order to improve the capacity loss caused by the lack of electrical contact, an organic coating modified silicon material may be used. Although the organic matters can be well adhered to the surface of the silicon material, along with the progress of charge-discharge cycle, the huge volume change of the silicon anode material in the charge-discharge process still causes the organic matters to separate from the surface of the silicon material and form a physical gap, thereby damaging the conductive network and finally causing capacity loss.
Accordingly, it is desirable to provide a silicon anode material that can enhance the bonding strength with a conductive agent.
Disclosure of Invention
The invention aims to solve the problem of poor adhesion between a conductive agent and a silicon material in the prior art, and provides a composite anode material, a preparation method thereof, an anode electrode and a battery.
In order to achieve the above object, a first aspect of the present invention provides a composite anode material, wherein the anode material comprises a silicon carbon material and an interface modifier; wherein the silicon-carbon material also contains oxygen, and the content of the oxygen is 0.1-5wt% based on the total mass of the silicon-carbon material; the chemical composition of the interface modifier is A aBbHcOd, and the element A is one or more of Mg, al and Ca; b element is selected from one or more of S, P, C, H is hydrogen element, O is oxygen element, a is 1-3, B is 1-3, c is 0-6, d is 4-12; at least part of oxygen in the silicon carbon material forms a chemical bond with the A element in the interface modifier.
The second aspect of the invention provides a preparation method of a composite anode material, wherein the method comprises the following steps: and mixing the silicon-carbon material, the interface modifier and the optional modification accelerator to obtain the composite anode material.
A third aspect of the present invention provides a negative electrode tab comprising a current collector and a dressing layer coated on the current collector, the dressing layer comprising a composite negative electrode material, optionally graphite, a conductive agent, a binder; the composite anode material is the composite anode material of the first aspect of the invention or the composite anode material prepared by the preparation method of the second aspect of the invention.
A fourth aspect of the invention provides a battery comprising the negative electrode tab of the third aspect of the invention.
Through the technical scheme, the beneficial technical effects obtained by the invention are as follows:
1) In the composite anode material provided by the invention, the element A in the interface modifier can form a chemical bond with oxygen in the silicon-carbon material, and the element B can form a chemical bond with hydroxyl in the conductive agent added during preparation of the electrode plate. When the composite negative electrode material is used for preparing the negative electrode plate, the composite negative electrode material can form better bonding strength with the conductive agent, and the negative electrode plate can avoid or reduce the falling of the conductive agent on the surface of the silicon material in the charging and discharging process, and can prevent the loss of electrical contact caused by the damage of a conductive network due to the physical gap formed by the falling of the conductive agent, thereby improving the cycle capacity retention rate of the lithium ion battery;
2) The preparation method of the composite anode material provided by the invention is simple to operate, the adopted interface modifier is a general chemical reagent, the price is low, the production cost is low, the negative effect on electrochemical reaction is avoided, and the preparation method is suitable for industrial popularization.
Drawings
FIG. 1 is an XPS-Mg pattern of the composite anode material prepared in example 1;
FIG. 2 is an XPS-S spectrum of an electrode prepared from the composite anode material of example 1;
Fig. 3 is a normal temperature cycle graph of lithium ion batteries prepared using example 1 and comparative example 1.
Detailed Description
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The first aspect of the invention provides a composite anode material, which comprises a silicon-carbon material and an interface modifier; wherein the silicon-carbon material also contains oxygen, and the content of the oxygen is 0.1-5wt% based on the total mass of the silicon-carbon material; the chemical composition of the interface modifier is A aBbHcOd, and the element A is one or more of Mg, al and Ca; b element is selected from one or more of S, P, C, H is hydrogen element, O is oxygen element, a is 1-3, B is 1-3, c is 0-6, d is 4-12; at least part of oxygen in the silicon carbon material forms a chemical bond with the A element in the interface modifier.
In a preferred embodiment, the silicon-carbon material has a silicon element content of 30 to 60wt% based on the total mass of the silicon-carbon material; the content of carbon element is 35-69.9wt%.
In the present invention, the silicon carbon material is a composite material of silicon and carbon containing a small amount of oxygen. Wherein, the lithium reaction is carried out between silicon and lithium ion to provide high specific capacity; the carbon material has high conductivity, and can improve the ion transfer rate of the surface of the electrode material, thereby improving the rate capability of the lithium ion battery; meanwhile, the carbon substrate can also buffer the swelling and pulverization phenomena of silicon particles, so that the cycle life of the battery can be effectively prolonged. So that the proper silicon and carbon content helps to improve the specific capacity and the cycle stability of the silicon-carbon material.
In a preferred embodiment, the content of oxygen element is 0.5 to 3wt% and the content of silicon element is 44 to 55wt% based on the total mass of the silicon carbon material; the content of carbon element is 42-55.5wt%. At this time, the mass percentages of silicon and carbon are equivalent, so that the specific capacity and the cycle life of the composite anode material can be effectively balanced, and silicon particles can be uniformly dispersed in a carbon skeleton (when the mass of silicon and carbon is equivalent because the density of silicon is greater than that of carbon, the volume of carbon is greater than that of silicon). From the integral structure of the material, when the uniformly dispersed silicon particles undergo lithiation reaction, the expansion force born by the material as a whole is relatively dispersed, so that the pulverization phenomenon caused by the concentrated expansion of the silicon particles can be reduced or relieved, and the circulation stability of the material is further improved.
In the invention, when the content of oxygen element is more than 5wt%, the surface impedance of the composite anode material is overlarge, and the cycle performance of the lithium ion battery is affected; when the oxygen content is less than 0.1wt%, the silicon carbon material has too few active sites to bond with the interface modifier, and the bonding strength is reduced. When the oxygen content is 0.5-3wt%, the composite anode material has the best cycle performance and lower surface impedance.
In a preferred embodiment, the silicon in the silicon-carbon material comprises amorphous silicon having an average particle size of 0.5-15nm, preferably 0.8-2nm.
In a preferred embodiment, the silicon in the silicon-carbon material further comprises silicon grains.
In the invention, the average grain diameter of silicon is small, the specific surface area is large, the contact activity with lithium self-reaction is more, meanwhile, the smaller the grain volume expansion rate is smaller, the grain diameter of uniformly dispersed silicon grains is smaller from the aspect of the integral structure of the material, the smaller the expansion force born by the integral material is relatively smaller, thus the pulverization caused by the concentrated expansion of the silicon grains can be reduced or relieved, and the circulation stability of the material is further improved.
In a preferred embodiment, the a element is selected from Mg and/or Al, preferably Mg; the B element is selected from S and/or P, preferably S.
In a preferred embodiment, the interface modifier is selected from one or more of MgSO4、AlPO4、CaSO4、Mg(HSO4)2、Mg(H2PO4)2、MgHPO4、Al(HSO4)3、Al(H2PO4)3、Al2(HPO4)3、Al3(SO4)2、Mg3(PO4)2, preferably MgSO 4 and/or Mg 3(PO4)2.
In a preferred embodiment, the silicon carbon material is contained in an amount of 97.5 to 99.9wt% and the interface modifier is contained in an amount of 0.1 to 2.5wt% based on the total mass of the composite anode material.
In a preferred embodiment, the negative electrode material further comprises a modification accelerator, wherein the modification accelerator is selected from one or more of ammonium chloride, sodium carbonate, sodium bicarbonate, sodium acetate, preferably sodium carbonate and/or sodium acetate.
In the invention, a small amount of the modification accelerator can enable the interface modifier to be bonded with the silicon carbon material and the conductive agent more easily, so that the impedance performance of the composite anode material is further improved.
In a preferred embodiment, the silicon-carbon material is contained in an amount of 91 to 99.85wt%, preferably 96.62 to 99.38wt%, based on the total mass of the composite anode material; the interfacial modifier is present in an amount of 0.05 to 6.5wt%, preferably 0.12 to 2.9wt%; the content of the modifying accelerator is 0.1 to 2.5wt%, preferably 0.48 to 1.95wt%.
In the invention, the content of each component in the composite anode material is calculated according to the feeding amount. When the content of the silicon-carbon material is 96.62-99.38wt%, the content of the interface modifier is 0.12-2.9wt%, and the content of the modification accelerator is 0.48-1.95wt%, the composite anode material has the highest specific capacity and the best structural stability, so that higher energy density and longer cycle life are provided for the battery.
In a preferred embodiment, the average particle size of silicon in the composite anode material is 0.5 to 15nm, preferably 0.8 to 2nm. The silicon within the particle size range can relieve the lithiation scale effect of silicon, further relieve lithiation expansion and prolong the cycle life of the composite anode material.
In the invention, the average grain size of silicon in the composite anode material is basically the same as that of silicon of the silicon-carbon raw material used for preparing the composite anode material.
The second aspect of the invention provides a preparation method of a composite anode material, wherein the method comprises the following steps: and mixing the silicon-carbon material, the interface modifier and the optional modification accelerator to obtain the composite anode material.
In the present invention, the preparation method of the composite anode material may be that the silicon-carbon material and the interface modifier according to the first aspect of the present invention are mixed to react to obtain the composite anode material, or that the silicon-carbon material, the interface modifier and the modification accelerator according to the first aspect of the present invention are mixed to react to obtain the composite anode material.
In a preferred embodiment, the mixing reaction comprises a wet mixing reaction and/or a dry ball milling reaction; wherein the wet mixing reaction comprises: adding a silicon-carbon material, an interface modifier and an optional modification accelerator into an alcohol solution, stirring for 12-48h at 40-60 ℃, and then filtering and crushing to obtain a composite anode material; the dry ball milling reaction comprises the following steps: mixing the silicon-carbon material, the interface modifier and the optional modification accelerator with grinding balls, and ball milling for 1-10h at a rotating speed of 1000-3000r/min to obtain the composite anode material. Wherein, the ball milling process can generate heat, which is beneficial to the reaction among the silicon-carbon material, the interface modifier and the optional modification accelerator.
A third aspect of the present invention provides a negative electrode tab comprising a current collector and a dressing layer coated on the current collector, the dressing layer comprising a composite negative electrode material, optionally graphite, a conductive agent, a binder; the composite anode material is the composite anode material of the first aspect of the invention or the composite anode material prepared by the preparation method of the second aspect of the invention.
In the invention, the element A in the interface modifier has positive charges, and can form covalent bonds with oxygen atoms in the silicon-carbon material to enhance the connection between the silicon-carbon material and the interface modifier. The outermost layer of the B element atoms has unpaired lone pair electrons, has low electronegativity, is easy to give electrons, and can form hydrogen bonds with hydroxyl groups on the conductive agent. Therefore, the interface modifier plays a bridging role in the invention, can directly connect the conductive agent with the silicon carbon material through chemical bonds, can enhance the connection strength between the conductive agent and the silicon carbon material, and reduces the loss of electrical contact in the circulation process. In addition, the interface modifier selected in the invention does not react with other substances in the battery, and the service performance of the battery is not affected.
In a preferred embodiment, the element B in the composite anode material is bonded to the hydroxyl group in the conductive agent.
In a preferred embodiment, the dressing layer includes 1 part by weight of the composite anode material, 0 to 100 parts by weight of graphite, 0.1 to 1 part by weight of the conductive agent, and 0.5 to 1.5 parts by weight of the binder.
In a preferred embodiment, the dressing layer includes 1 part by weight of the composite anode material, 8 to 30 parts by weight of graphite, 0.4 to 0.6 part by weight of the conductive agent, and 0.8 to 1.2 parts by weight of the binder.
In a preferred embodiment, the conductive agent comprises conductive carbon black and carbon nanotubes; further preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:0.05-0.25. The binder includes, but is not limited to, polyacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate and modified products thereof, and mixed binders composed of the foregoing kinds of binders mixed in various different proportions.
The present invention will be described in detail by examples.
The silicon carbon materials in the examples and comparative examples were purchased from Group 14technologies, inc. Wherein the oxygen content in the silicon-carbon material 1 is 2.6wt%, the silicon content is 49.4wt%, the carbon content is 48wt%, the silicon in the silicon-carbon material comprises intangible silicon, and the average grain diameter of the silicon is 1.0nm.
The silicon-carbon material 2 has an oxygen content of 0.5wt%, a silicon content of 49wt% and a carbon content of 55.5wt%, and the silicon comprises amorphous silicon having an average particle diameter of 1.0nm.
The silicon-carbon material 3 has an oxygen content of 5wt%, a silicon content of 48wt%, and a carbon content of 47wt%, and the silicon in the silicon-carbon material includes shaped silicon having an average particle diameter of 2.0nm.
The silicon-carbon material 4 has an oxygen content of 0.15wt%, a silicon content of 50wt% and a carbon content of 49.85wt%, and the silicon comprises amorphous silicon having an average particle diameter of 15nm.
The silicon-carbon material 5 has an oxygen content of 8wt%, a silicon content of 50wt%, and a carbon content of 42wt%, and the silicon includes amorphous silicon having an average particle diameter of 18nm.
Example 1
2Kg of a silicon carbon material 1, 10g of an interface modifier magnesium sulfate and 10g of a modification accelerator sodium carbonate are added into 10L of absolute ethyl alcohol, stirred for 4 hours at 55 ℃ at a rotating speed of 400r/min, and then filtered and dried to obtain a composite anode material.
Example 2
The same as in example 1, except that 2.5g of interface modifier magnesium sulfate and 10g of modification accelerator sodium carbonate were added.
Example 3
The same as in example 1, except that 60g of interface modifier magnesium sulfate and 10g of modification accelerator sodium carbonate were added.
Example 4
The same as in example 1, except that 1g of interface modifier magnesium sulfate and 10g of modification accelerator sodium carbonate were added.
Example 5
The same as in example 1, except that 90g of interface modifier magnesium sulfate and 10g of modification accelerator sodium carbonate were added.
Example 6
2Kg of a silicon carbon material 1, 5g of an interface modifier magnesium phosphate and 25g of a modification accelerator sodium acetate are added into 10L of absolute ethyl alcohol, stirred for 4 hours at 55 ℃ at a rotating speed of 400r/min, and then filtered and dried to obtain a composite anode material.
Example 7
The procedure is as in example 6, except that no modification accelerator is added.
Example 8
The same as in example 6, except that the silicon carbon material 1 was replaced with an equal mass of the silicon carbon material 2.
Example 9
The same as in example 6, except that the silicon carbon material 1 was replaced with an equal mass of the silicon carbon material 3.
Example 10
The same as in example 6, except that the silicon carbon material 1 was replaced with an equal mass of the silicon carbon material 4.
Example 11
Mixing 2kg of silicon carbon material 1, 10g of interface modifier magnesium sulfate and 40g of modification accelerator sodium carbonate, loading into a high-energy ball milling tank, adding 200g of zirconia grinding balls with diameters of 0.2mm, 0.5mm and 1mm (the mass ratio of the zirconia grinding balls of 0.2mm, 0.5mm and 1mm is 1:3:5) into the ball milling tank, sealing, ball milling for 5 hours at a rotational speed of 2000r/min, wherein the ball milling temperature is 50 ℃, and separating the zirconia grinding balls to obtain the composite anode material.
Comparative example 1
The same as in example 7, except that: no interface modifier was added.
Comparative example 2
The same as in example 7, except that: the silicon carbon material 1 is replaced with an equal mass of silicon carbon material 5.
Comparative example 3
The same as in example 7, except that: the interface modifier is potassium sulfate with equal mass.
Comparative example 4
The same as in example 7, except that: the interface modifier is magnesium nitrate with equal mass.
Wherein, the compositions of the composite anode materials prepared in examples 1-11 and comparative examples 1-4 are shown in Table 1 according to the calculation of the charge:
TABLE 1
Test example 1
XPS-Mg characterization is carried out on the composite anode material prepared in the example 1, and the result is shown in figure 1.
As is clear from fig. 1, a side peak appears on the main peak side of Mg element, and the formation of this peak indicates that the electron cloud density of a part of atoms in Mg atoms is changed. This is due to the fact that Mg atoms form at least partially chemical bonds with oxygen atoms of the silicon carbon material. The electronegativity of the Mg atoms is different from that of the oxygen atoms, electrons flow between the atoms, and the electron cloud density of the Mg atoms is indirectly changed.
XPS-Mg characterization is carried out on the composite anode materials prepared in the examples 2-11, and the characterization result is basically the same as that of the example 1.
Test example 2
The composite anode material prepared in the example 1, graphite, a conductive agent (the mass ratio of conductive carbon black to carbon nano tube is 1:0.1) and polyacrylic acid are mixed according to the mass ratio of 1:9:0.5:1, adding a proper amount of water, kneading for 1h at a solid content of about 60%, adding water to adjust the viscosity of the slurry to 5000 Pa.s, preparing the negative electrode slurry, coating the prepared negative electrode slurry on a copper foil current collector, drying, and cold pressing to obtain the negative electrode plate. XPS-S characterization is carried out on the obtained negative electrode plate, and the result is shown in figure 2.
As can be seen from fig. 2, the XPS spectrum peak of the S element is branched, and this is due to chemical reaction between at least part of the S atoms in the modifier and the hydroxyl groups in the conductive agent, so as to form chemical bonds. And because of the difference of electronegativity of the two, electron withdrawing capability is different, thus the bond causes electrons to flow between two different atoms, and electron cloud density is changed to form double peaks.
According to the combination of XPS-Mg characterization and XPS-S characterization results, the Mg element and the S element in the interface modifier can tightly connect the silicon carbon material and the conductive agent together through chemical bonds, so that the bonding strength between the silicon carbon material and the conductive agent can be improved, the capacitance loss caused by electric contact loss in the cycling process of the lithium ion battery is reduced, and the cycling capacity retention rate of the lithium ion battery is remarkably improved. In addition, the chemical bond connection mode between the silicon carbon material and the conductive agent is also beneficial to conducting electrons between the silicon carbon material and the conductive agent, can reduce resistance, is beneficial to reducing polarization and heating of the battery in the charge and discharge process, and further improves the battery performance.
XPS-S characterization was performed on the composite anode materials prepared in examples 2-11, and the characterization results were substantially the same as example 1.
Test example 3
The composite anode materials of examples 1 to 11 and comparative examples 1 to 4 were prepared into lithium ion batteries, and then the impedance of the lithium ion batteries was tested and subjected to a normal temperature cycle test. The impedance after 1000 cycles and the capacity retention after 1000 cycles are shown in table 2.
The lithium ion battery is assembled according to the following method:
The composite anode materials in examples 1-11 and comparative examples 1-4 were respectively mixed with graphite, a conductive agent (the mass ratio of conductive carbon black to carbon nanotubes is 1:0.1), and polyacrylic acid according to a mass ratio of 1:9:0.5:1, adding a proper amount of water, kneading for 1h at a solid content of about 60%, and adding water to adjust the viscosity of the slurry to 5000 Pa.s, thereby preparing the cathode slurry. And coating the prepared negative electrode slurry on a copper foil current collector, drying, and cold pressing to obtain a negative electrode plate.
Lithium cobaltate was mixed with a conductive agent (SP) and PVDF according to 100: mixing in a ratio of 1:1, adding NMP (N-methyl pyrrolidone), stirring for 1h to obtain positive electrode slurry with solid content of about 80%, coating the prepared positive electrode slurry on an aluminum foil current collector, drying and cold pressing to obtain the positive electrode plate. After cutting the positive and negative plates into plates with 50 mm, taking a polyethylene porous membrane with the surface coated with an alumina ceramic layer and the thickness of 25 mu m as a diaphragm, taking an equal mass mixed solution of ethylene carbonate and dimethyl carbonate containing 1mol/L lithium hexafluorophosphate as an electrolyte, and assembling the positive plate, the diaphragm, the negative plate and the electrolyte into the 3Ah soft package laminated battery in an Ar gas glove box with the water content and the oxygen content of less than 5 ppm.
The normal temperature cycle test method comprises the following steps: after the capacity division of the batteries prepared in the examples and comparative examples was completed, the batteries were placed in an incubator at 25.+ -. 2 ℃ and charged and discharged at a voltage range of 2.8-4.25V at a current of 1C, and the cycle was continued for 1000 times. The capacity retention (%) is a percentage obtained by dividing the discharge capacity after 1000 cycles by the first discharge capacity.
The testing method of the battery impedance comprises the following steps: the impedance test was performed on the cells after 1000 cycles at room temperature using HIOKI BT3562A battery hitestea apparatus.
TABLE 2
Among them, 1000 test results of example 1 and comparative example 1 were plotted as a normal temperature cycle curve, as shown in fig. 3. As can be seen from fig. 3, the composite anode material provided by the invention uses chemical bonds to tightly connect the silicon-carbon material and the conductive agent together, so that the damage of the conductive network caused by the separation of the adhesive and the silicon anode material in the cycle process of the lithium ion battery can be effectively avoided, and the cycle performance of the lithium ion battery can be remarkably improved.
Test example 4
Referring to test example 3, the composite anode material prepared in example 1 and the composite anode material (i.e., silicon carbon material 1) in comparative example 1 were prepared into lithium ion batteries, differing from each other in that the mass ratio of the composite anode material to graphite was changed, and the capacity retention rate of the lithium ion batteries after 1000 cycles and the impedance test results after 1000 cycles were tested are shown in table 3.
Test example 5
The composite anode materials prepared in example 1 and comparative example 1 were prepared into 2025 type coin cells, and then the anode specific capacity of 2025 type coin cells was tested (note: this anode specific capacity can be understood as the specific capacity of the active material in 2025 type coin cells, that is, the specific capacity of the active material composed of the silicon-carbon anode material and optional graphite; here, the anode does not represent the actual anode in 2025 type coin cells, only for uniformity of name in the pouch cell). The 2025 button cell preparation method and the negative electrode specific capacity test method are as follows:
The silicon-carbon negative electrode material prepared in example 1 was mixed with graphite, a conductive agent (the mass ratio of conductive carbon black to carbon nanotubes is 1:0.1) and polyacrylic acid according to a mass ratio of 1:9:0.5:1, adding a proper amount of water, kneading for 1h at a solid content of about 60%, and adding water to adjust the viscosity of the slurry to 5000 Pa.s, thereby preparing the cathode slurry. And coating the prepared negative electrode slurry on a copper foil current collector, drying, and cold pressing to obtain a negative electrode plate.
The method comprises the steps of taking a metal lithium sheet with the diameter of 17mm and the thickness of 1mm as a negative electrode, taking a polyethylene porous membrane with the surface coated with an alumina ceramic layer and the thickness of 25 mu m as a diaphragm, taking an equal mass mixed solution of ethylene carbonate and dimethyl carbonate containing 1mol/L lithium hexafluorophosphate as an electrolyte, and assembling the prepared negative electrode sheet, diaphragm, metal lithium sheet and electrolyte into a 2025 button cell in an Ar gas glove box with the water content and the oxygen content of less than 5 ppm. And on a Xinwei electrochemical test cabinet, discharging to 5mV at a rate of 0.05C, then charging to 1.5V at a rate of 0.05C, and calculating the specific capacity of the negative electrode according to the charging capacity at the moment.
Referring to test example 4, a series of 2025 type button cells were prepared using the silicon-carbon anode material prepared in example 1, with the mass ratio of the composite anode material to graphite changed, and the test results of the anode specific capacity are shown in table 3.
TABLE 3 Table 3
As is clear from the data in table 3, the specific capacity decreased, the impedance decreased, and the 1000-turn capacity retention increased as the graphite amount increased. When the mass ratio of the composite anode material to the graphite is 1: and when the specific capacity is between 8 and 30, the battery with relatively large specific capacity, low impedance and good cycle performance can be obtained.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims (12)

1. A composite anode material, characterized in that the anode material comprises a silicon-carbon material and an interface modifier; wherein the silicon-carbon material also contains oxygen, and the content of the oxygen is 0.1-5wt% based on the total mass of the silicon-carbon material; the chemical composition of the interface modifier is A aBbHcOd, and the element A is one or more of Mg, al and Ca; b element is selected from one or more of S, P, C, H is hydrogen element, O is oxygen element, a is 1-3, B is 1-3, c is 0-6, d is 4-12; at least part of oxygen in the silicon carbon material forms a chemical bond with the A element in the interface modifier.
2. The composite anode material according to claim 1, wherein the silicon element content in the silicon carbon material is 30 to 60wt% based on the total mass of the silicon carbon material; the content of the carbon element is 35 to 69.9 weight percent;
Preferably, the silicon-carbon material contains 0.5-3wt% of oxygen element and 44-55wt% of silicon element based on the total mass of the silicon-carbon material; the content of the carbon element is 42-55.5wt%;
Preferably, the average particle size of silicon in the silicon-carbon material is 0.5-15nm, preferably 0.8-2nm.
3. The composite anode material according to claim 1 or 2, wherein the interface modifier is selected from one or more of MgSO4、AlPO4、CaSO4、Mg(HSO4)2、Mg(H2PO4)2、MgHPO4、Al(HSO4)3、Al(H2PO4)3、Al2(HPO4)3、Al3(SO4)2、Mg3(PO4)2, preferably MgSO 4 and/or Mg 3(PO4)2.
4. A composite anode material according to any one of claims 1 to 3, wherein the silicon carbon material is contained in an amount of 97.5 to 99.9wt% and the interface modifier is contained in an amount of 0.1 to 2.5wt%, based on the total mass of the composite anode material.
5. The composite anode material of any one of claims 1-4, wherein the composite anode material further comprises a modification promoter; wherein the modifying accelerator is one or more selected from ammonium chloride, sodium carbonate, sodium bicarbonate and sodium acetate; preferably sodium carbonate and/or sodium acetate.
6. The composite anode material according to claim 5, wherein the silicon carbon material is present in an amount of 91-99.85wt%, preferably 96.62-99.38wt%, based on the total mass of the composite anode material; the interfacial modifier is present in an amount of 0.05 to 6.5wt%, preferably 0.12 to 2.9wt%; the content of the modifying accelerator is 0.1 to 2.5wt%, preferably 0.48 to 1.95wt%.
7. The composite anode material according to any one of claims 1-6, wherein the average particle size of silicon in the composite anode material is 0.5-15nm, preferably 0.8-2nm.
8. A method for preparing a composite anode material, the method comprising: mixing the silicon-carbon material, the interface modifier and the optional modification accelerator according to any one of claims 1-7 to obtain the composite anode material.
9. The method for preparing a composite anode material according to claim 8, wherein the mixing reaction comprises a wet mixing reaction and/or a dry ball milling reaction;
Preferably, the wet mixing comprises: adding the silicon-carbon material, the interface modifier and the optional modification accelerator into an alcohol solution, stirring for 12-48h at 40-60 ℃, and then filtering and crushing to obtain the composite anode material;
Preferably, the dry ball milling comprises: mixing the silicon carbon material, the interface modifier and the optional modification accelerator with grinding balls, and ball milling for 1-10h at a rotating speed of 1000-3000r/min to obtain the composite anode material.
10. The negative electrode plate is characterized by comprising a current collector and a dressing layer coated on the current collector, wherein the dressing layer comprises a composite negative electrode material, optional graphite, a conductive agent and a binder; wherein the composite anode material is the composite anode material according to any one of claims 1 to 7 or the composite anode material prepared by the preparation method according to claim 8 or 9;
Preferably, the conductive agent contains hydroxyl groups, and the element B in the composite anode material is bonded with the hydroxyl groups in the conductive agent;
Preferably, the conductive agent includes conductive carbon black and carbon nanotubes; further preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:0.05-0.25.
11. The negative electrode tab of claim 10 wherein the dressing layer comprises 1 part by weight of the composite negative electrode material, 0-100 parts by weight of graphite, 0.1-1 parts by weight of the conductive agent, and 0.5-1.5 parts by weight of the binder;
Preferably, the dressing layer comprises 1 part by weight of the composite anode material, 8-30 parts by weight of graphite, 0.4-0.6 part by weight of the conductive agent and 0.8-1.2 parts by weight of the binder.
12. A battery comprising the negative electrode tab of claim 10 or 11.
CN202310116394.6A 2023-01-31 2023-01-31 Composite negative electrode material and preparation method thereof, negative electrode sheet and battery Pending CN118431422A (en)

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