CN115939359B - Silicon-based negative electrode material, preparation method thereof and lithium ion secondary battery - Google Patents
Silicon-based negative electrode material, preparation method thereof and lithium ion secondary battery Download PDFInfo
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Abstract
The invention discloses a silicon-based negative electrode material, which comprises a carbon-coated pre-lithiated silicon-based material, wherein the surface of the carbon-coated pre-lithiated silicon-based material contains LiF and Li 3 PO 4 And LiPO 2 F 2 . The invention also discloses a preparation method of the silicon-based anode material and a lithium ion secondary battery. The silicon-based anode material can reduce high residual alkali on the surface of the pre-lithiated silicon-based material, inhibit gas production of a pole piece and improve the electrochemical performance of a lithium ion secondary battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material, a preparation method thereof and a lithium ion secondary battery.
Background
The lithium ion battery becomes an energy storage device with the most wide application due to the characteristics of high energy density, long cycle life and the like, not only controls the consumer market fields of mobile phones, notebook computers, digital cameras and the like, but also is favored by the large-scale energy storage fields of electric automobiles, energy storage power stations and the like. The rapid expansion of application fields has placed increasing demands on the energy density of lithium ion batteries. Graphite is still the main negative electrode material of the current commercial lithium ion battery, and the specific capacity (372 mAh/g) of the graphite can not meet the requirement of high energy density, so searching for the negative electrode material with high capacity is always a research hot spot in the field of lithium ion batteries.
Silicon oxide (SiO) x ) The gram capacity of the material is generally 3 to 6 times that of the graphite negative electrode material, so the silicon oxide negative electrode material is a novel negative electrode material capable of effectively replacing the graphite negative electrode and improving the energy density of the lithium ion battery. However, the silicon oxide-based negative electrode material is lithiated, wherein lithium is preferentially mixed with the active materialThe oxygen reaction generates lithium silicon oxide, which is mostly electrochemically inactive, resulting in a large amount of active lithium being consumed during the first charge, which makes it difficult to improve the first charge efficiency of the lithium battery.
In order to improve the first charging efficiency of the silicon oxide-based negative electrode material, active metals such as lithium doped and magnesium doped are often selected in the industry to consume oxygen in the material in advance. However, after doping lithium, unreacted lithium supplementing agent remains on the surface of the material, so that more LiOH and Li are formed on the surface of the material 2 CO 3 So that the material surface exhibits a high pH. The high pH is not only detrimental to the binder but also reacts with the silicon in the material to produce hydrogen under the action of water, which would be detrimental to the preparation of the pole pieces.
Disclosure of Invention
The invention aims to solve the technical problem of providing a silicon-based negative electrode material which can reduce high residual alkali on the surface of the pre-lithiated silicon-based material, inhibit the gas production of a pole piece and improve the electrochemical performance of a lithium ion secondary battery.
In order to solve the technical problems, the invention provides the following technical scheme:
the first aspect of the invention provides a silicon-based anode material, which comprises a carbon-coated pre-lithiated silicon-based material, wherein the surface of the carbon-coated pre-lithiated silicon-based material contains LiF and Li 3 PO 4 And LiPO 2 F 2 。
Further, the silicon-based material comprises silicon oxide.
Further, the silicon-based material also comprises one or more of silicate, silicon nano particles and amorphous silicon.
The second aspect of the present invention provides a method for preparing the silicon-based anode material, comprising the steps of:
s1, uniformly mixing a carbon-coated pre-lithiated silicon-based material, a fluoridation reagent and phosphorus pentoxide in a protective atmosphere;
s2, heating the mixture obtained in the step S1 under the condition of continuous stirring so as to react;
s3, dissolving the reaction product obtained in the step S2 in a solvent, and continuously heating under a protective atmosphere to react;
and S4, filtering, washing and drying the reaction product obtained in the step S3 to obtain the silicon-based anode material.
Further, in step S1, the fluorinating agent includes one or more of ammonium fluoride, hydrogen fluoride, ammonium bifluoride, fluoroboric acid, and trifluoromethanesulfonic acid.
Further, in the step S1, the mass of the fluorinating agent is 0.05-20% of that of the carbon-coated pre-lithiated silicon-based material, and the mass of the phosphorus pentoxide is 0.02-10% of that of the carbon-coated pre-lithiated silicon-based material.
Further, in step S2, the heating temperature is 60 to 300 ℃.
Further, in step S3, the solvent is water and/or ethanol.
Further, in step S3, the heating temperature is higher than 60 ℃ and lower than the boiling point temperature of the solvent.
The third aspect of the invention provides a lithium ion secondary battery, which comprises a positive plate, a negative plate, a diaphragm and an electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate, and the active material in the negative plate is the silicon-based negative electrode material.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the fluoride reagent and phosphorus pentoxide react with the pre-lithiated silicon-based material in situ to convert residual alkali on the surface of the pre-lithiated silicon-based material into lithium fluoride, so that the pH value of the surface of the material is reduced, the serious gas production phenomenon of the material in the pulping process is inhibited, and the processing performance of the pole piece is improved.
2. The silicon-based anode material provided by the invention generates LiF and Li on the surface 3 PO 4 And LiPO 2 F 2 Wherein Li is 3 PO 4 And LiF is one of solid electrolyte film (SEI) components commonly found on the surface of active particles in lithium batteries, so that the silicon oxide-based negative electrode material can be optimized in lithium ion batteriesSurface SEI structure and composition; at the same time LIPO 2 F 2 Is an effective electrolyte additive in the lithium ion battery, and is beneficial to improving the cycle performance of the lithium ion battery.
Drawings
FIG. 1 is an SEM image of a silicon-based anode material;
FIG. 2 is a Li sample of XPS test results of a silicon-based anode material 1s Is a fitting spectrogram of (1);
FIG. 3 is a F of XPS test results of a silicon-based anode material 1s Is a fitting spectrogram of (1);
fig. 4 is a cycle life curve of the batteries in examples 1-2 and comparative examples 1-3.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
As described in the background art, in the lithiation process of the silicon oxide-based negative electrode material, lithium preferentially reacts with oxygen in the active material to generate lithium silicon oxide, and most of the lithium silicon oxide is electrochemically inactive, so that a large amount of active lithium is consumed in the first charging process, and the first charging efficiency of the lithium battery is difficult to improve. In order to improve the first charging efficiency of the silicon oxide-based negative electrode material, active metals such as lithium doped and magnesium doped are often selected in the industry to consume oxygen in the material in advance. However, after doping lithium, unreacted lithium supplementing agent remains on the surface of the material, so that more LiOH and Li are formed on the surface of the material 2 CO 3 So that the material surface exhibits a high pH. The high pH is not only detrimental to the binder but also reacts with the silicon in the material to produce hydrogen under the action of water, which would be detrimental to the preparation of the pole pieces.
In order to solve the technical problem, the invention provides the silicon-based negative electrode material, and the carbon-coated pre-lithiated silicon-based material is treated by adopting the fluoridation reagent and phosphorus pentoxide, so that the residual base number of the surface of the carbon-coated pre-lithiated silicon-based material is reduced, an effective SEI film can be pre-formed on the surface of the material, and the cycle performance of a battery is further improved.
Specifically, the silicon-based anode material provided by the invention comprises a carbon-coated pre-lithiated silicon-based material, wherein the surface of the carbon-coated pre-lithiated silicon-based material contains LiF and Li 3 PO 4 And LiPO 2 F 2 。
The silicon-based anode material is prepared by the following method:
s1, uniformly mixing a carbon-coated pre-lithiated silicon-based material, a fluoridation reagent and phosphorus pentoxide in a protective atmosphere;
s2, heating the mixture obtained in the step S1 under the condition of continuous stirring so as to react;
s3, dissolving the reaction product obtained in the step S2 in a solvent, and continuously heating under a protective atmosphere to react;
and S4, filtering, washing and drying the reaction product obtained in the step S3 to obtain the silicon-based anode material.
In the step S1, the main body of the silicon-based material is preferably silicon oxide SiO x (0<x<2) In other embodiments, the silicon-based material may include one or more of silicate, silicon nanoparticles, amorphous silicon, and other types of silicon oxygen compounds in addition to silicon oxide. The silicon-based material is subjected to pre-lithiation treatment, so that oxygen in the anode active material is consumed, and consumption of lithium element during primary charging is avoided. However, after the pre-lithiation treatment, residual alkali, residual salt LiOH and Li remain on the surface of the material 2 CO 3 Their presence causes the material surface to have a high pH.
The surface of the pre-lithiated silicon-based material is coated with a carbon layer, and the carbon layer can be formed by mixing the silicon-based material with the carbon material to adhere the carbon material to the surface of the silicon-based material. The carbon material may include natural graphite, artificial graphite, etc., which may improve the conductivity of the silicon-based material.
In the present invention, the fluorinating agent includes, but is not limited to, one or more of ammonium fluoride, hydrogen fluoride, ammonium bifluoride, fluoroboric acid, trifluoromethanesulfonic acid, preferably ammonium fluoride. The amount of the fluorinating agent added is 0.05% -20% by mass of the carbon-coated pre-lithiated silicon-based material, and may be, for example, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value between these values.
In the invention, P 2 O 5 The amount of the additive is 0.05% -10% of the mass of the carbon-coated pre-lithiated silicon-based material, and may be, for example, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between these values.
In the step S2, the carbon-coated pre-lithiated silicon-based material, the fluorinating agent and P 2 O 5 Is heated with constant stirring. The heating temperature may be 60 to 300℃and may be 60℃70℃ 80℃ 90℃ 100℃120℃150℃160℃180℃ 200℃220℃240℃250℃260℃280℃300℃or any value between these values.
In this step, taking ammonium fluoride and phosphorus pentoxide as examples, the reaction takes place as follows:
NH 4 F+LiOH——LiF+H 2 O+NH 3 ↑
4LiF+P 2 O 5 ——2Li 2 PO 2 F 2 +Li 2 O
from the above reaction formula, it can be seen that ammonium fluoride can react with residual alkali LiOH on the surface of silicon-based material to convert it into lithium fluoride LiF, and LiF can further react with P 2 O 5 React to form Li 2 PO 2 F 2 . The reaction is solid phase reaction, the reaction products are distributed on the surface of the silicon-based material in a dot form, and the coating surface is not particularly uniform.
In the step S3, after the reaction is performed for a period of time, the mixture after the reaction is dispersed in the solvent, stirred to be uniformly dispersed, and then heated to continue the reaction. Wherein the solvent can be water, ethanol or a mixed solvent composed of the water and the ethanol; the temperature of the heating is preferably lower than the boiling point temperature of the solvent and higher than 60 ℃. When water is used as a solvent, the heating temperature may be 60℃65℃70℃75℃ 80℃ 85℃ 90℃ 95℃ 100℃or any value between these values. When ethanol is used as a solvent, the heating temperature may be 60℃at 65℃at 70℃at 75℃or any value between these values.
In this step, the reaction occurring is a liquid phase reaction, the equation of which is as follows:
P 2 O 5 +3H 2 O——2H 3 PO 4
H 3 PO 4 +3LiOH——Li 3 PO 4 +3H 2 O
2H 3 PO 4 +3Li 2 CO 3 ——2Li 3 PO 4 +3CO 2 ↑+3H 2 O
as can be seen from the above reaction formula, phosphoric acid, which is a water-soluble product of phosphorus pentoxide, can react with residual alkali LiOH on the surface of the silicon-based material to convert the residual alkali LiOH into Li 3 PO 4 The method comprises the steps of carrying out a first treatment on the surface of the In addition, phosphoric acid can also be mixed with residual salt Li 2 CO 3 React to convert it into Li 3 PO 4 . These generated reactants are distributed on the surface of the silicon-based anode material in the form of particles.
The above steps S1 to S3 are required to be performed under a protective atmosphere including one of a nitrogen atmosphere, an inert gas atmosphere (helium, argon, etc.).
In the step S4, the slurry obtained by the reaction is filtered, washed and dried to obtain the LiF and Li-containing material 3 PO 4 And LiPO 2 F 2 Silicon-based anode material of (2). Wherein the washed solvent can be water or ethanol; the drying is preferably carried out by vacuum drying, the drying temperature preferably being 50 to 80 ℃, for example 50 ℃, 60 ℃, 70 ℃,80 ℃, or any value between these values.
The inventionIn the method, the carbon-coated pre-lithiated silicon-based material is treated by adopting a fluoridation reagent and phosphorus pentoxide, so that residual alkali and residual salt on the surface of the silicon-based anode material are converted into LiF and Li 3 PO 4 And Li (lithium) 2 PO 2 F 2 The pH value of the surface of the material is reduced, the serious gas production phenomenon of the material in the pulping process is inhibited, and the processing performance of the pole piece is improved. And reaction product Li 3 PO 4 And LiF is one of solid electrolyte membrane (SEI) components common to the surfaces of active particles in lithium batteries, and a layer of Li can be prepared on the surfaces of the active particles in advance by the method 3 PO 4 And LiF substances, so that the structure and the composition of the surface SEI film of the silicon-based anode material in the lithium ion battery can be optimized. At the same time, the reaction product LiPO 2 F 2 Is an effective electrolyte additive in the lithium ion battery, and is beneficial to improving the cycle performance of the lithium ion battery.
The invention also provides a lithium ion secondary battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate.
In the lithium ion secondary battery, the negative electrode plate is prepared from the silicon-based negative electrode material. The preparation method is as follows: preparing the silicon-based negative electrode material, the binder and the conductive agent into electrode slurry according to a certain proportion, coating the electrode slurry on at least one surface of a negative electrode current collector, and drying and tabletting to obtain the lithium ion battery negative electrode plate.
In a preferred embodiment, the negative electrode active material is a composite negative electrode material formed by mixing the silicon-based negative electrode material described above with a carbon material, wherein the carbon material includes, but is not limited to, a graphite material, which may be artificial graphite and/or natural graphite. Preferably, the carbon material is artificial graphite. The ratio of the silicon-based anode material to the carbon material may be (1 to 9): (1-9), for example, may be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, etc.
The kind and content of the above-mentioned conductive agent are not particularly limited, and may be selected according to actual demands. In some embodiments, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, ketjen black, carbon nanofibers, and the like. It will be appreciated that other conductive agents capable of performing the functions of the present application may be selected as desired without limitation without departing from the spirit of the present application.
The kind and content of the binder are not particularly limited and may be selected according to actual requirements. In some embodiments, the binder includes at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene butadiene rubber, sodium alginate, chitosan, polyethylene glycol, guar gum, and the like.
The type of the negative electrode current collector is not particularly limited, and may be selected according to practical requirements, for example, the negative electrode current collector may be a copper foil, a carbon-coated copper foil or a polymer conductive film, and preferably the negative electrode current collector is a copper foil.
In the lithium ion secondary battery, the preparation method of the positive electrode plate is the same as that of the negative electrode plate, and the positive electrode plate is prepared by preparing an electrode slurry from a positive electrode active material, a binder and a conductive agent according to a certain proportion, then coating the electrode slurry on at least one surface of a positive electrode current collector, and drying and tabletting the electrode slurry.
The positive electrode active material may be selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel manganese oxide, lithium cobalt oxide, lithium manganate, and doped and/or coated modified compounds thereof, but the present invention is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may be used. These positive electrode active materials may be used alone or in combination of two or more.
The type of the positive electrode current collector is not particularly limited, and may be selected according to practical requirements, for example, the positive electrode current collector may be an aluminum foil, a nickel foil or a polymer conductive film, and preferably the positive electrode current collector is an aluminum foil.
The types of the conductive agent and the binder in the positive plate refer to the negative plate, and the invention is not repeated.
In the lithium ion secondary battery, the type of separator is not particularly limited, and any separator material used in conventional batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, nonwoven fabric, multilayer composite films thereof, and modified separators obtained by subjecting the separator to ceramic modification, PVDF modification, and the like, may be used, but are not limited thereto.
In the lithium ion secondary battery, the electrolyte may be one or more of an organic liquid electrolyte, an organic solid electrolyte, a solid ceramic electrolyte, and a gel electrolyte. Preferably, the electrolyte is an organic liquid electrolyte obtained by dissolving a lithium salt in a nonaqueous organic solvent; wherein the lithium salt comprises lithium difluorophosphate (LiPO) 2 F 2 ) Lithium hexafluorophosphate (LiPF) 6 ) Lithium difluorooxalate phosphate (LiDFOP), lithium difluorosulfonimide (LiLSI), lithium bistrifluoromethane sulfonimide (LiTFSi), lithium tetrafluoroborate (LiBF) 4 ) And one or more of lithium difluorooxalato borate (LiDFOB). The nonaqueous organic solvent may include one or more of cyclic carbonate, chain carbonate, and carboxylate. Wherein the cyclic carbonate can be selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene carbonate and gamma-butyrolactone; the chain carbonate may be selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl Propyl Carbonate (MPC), methyl Acetate (MA), ethyl Acetate (EA), and Ethyl Propionate (EP).
In some embodiments, a certain amount of additives may also be added to the organic liquid electrolyte. The additive may include one or more of Vinylene Carbonate (VC), vinyl carbonate (VEC), vinyl sulfate (DTD), ethylene Sulfite (ES), methylene Methane Disulfonate (MMDS), 1, 3-Propane Sultone (PS), propylene sultone (PES), propylene sulfate (TMS), trimethylsilyl phosphate (TMSP), trimethylsilyl borate (TMSB), fluoroethylene carbonate (FEC).
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents, etc. used, unless otherwise specified, are commercially available.
Example 1
The pre-lithiated carbon-coated silica material is mixed with 0.05wt% NH under dry inert atmosphere 4 F. 0.02wt% of P 2 O 5 Adding into a container, stirring thoroughly, and heating to 100deg.C under stirring. After a period of reaction, water was added to the vessel, stirring was continued, and the reaction was carried out by heating to 80 ℃. And after the reaction is finished, filtering and washing the obtained mixed slurry, and vacuum drying at 80 ℃ to obtain the silicon-based anode material.
XPS can measure the binding energy of electrons to identify the chemical nature and composition of a material surface. Through analysis of atoms to be detected in different chemical states, the electron binding energy of the inner shell layer of the atoms to be detected is different, so that the element contained in the sample, the oxidation number and the molecular structure of the element can be identified through XPS spectrogram (Xu Dongwei. Reaction and mechanism research of the cyclic sulfonate-based electrolyte additive in a lithium ion battery [ D ]. Guangdong: university of North China, 2020).
And (3) drying the silicon-based anode material prepared in the embodiment 1 for 6 hours at 105 ℃, then spreading the silicon-based anode material on 2-3 mg of double-sided carbon conductive adhesive, adhering the double-sided carbon conductive adhesive on a sample table, etching the surface of the silicon-based anode material to a depth of 3-10 nm by adopting Al Ka as an X-ray emission source, and carrying out XPS test.
Li of XPS test result 1s Fitting spectrogram is shown in figure 2, F 1s The fitted spectrum is shown in figure 3. As can be seen from FIGS. 2 to 3, li 1s The fitting spectrogram shows lithium phosphate Li 3 PO 4 (688.3 eV), lithium difluorophosphate LiPO 2 F 2 (686.8 eV) and lithium fluoride LiF (684.5 eV), and F 1s Fitting of the spectrogram to displayShown with carbon fluoride CF x (688.5 eV), lithium difluorophosphate LiPO 2 F 2 (686.8 eV) and lithium fluoride LiF (684.5 eV) are present.
From this, it is understood that LiF and Li are simultaneously generated on the surface of the silicon-based anode material prepared in example 1 3 PO 4 And LiPO 2 F 2 。
Example 2
Pre-lithiated carbon-coated silica material with 4wt% NH under dry inert atmosphere filling 4 F. 2wt% of P 2 O 5 Adding into a container, stirring thoroughly, and heating to 100deg.C under stirring. After a period of reaction, water was added to the vessel, stirring was continued, and the reaction was carried out by heating to 80 ℃. And after the reaction is finished, filtering and washing the obtained mixed slurry, and vacuum drying at 80 ℃ to obtain the silicon-based anode material.
Comparative example 1
Pre-lithiated carbon-coated silica material with 4wt% NH under dry inert atmosphere filling 4 F is added into a container, stirred and mixed thoroughly, and then heated to 100 ℃ while stirring. After a period of reaction, water was added to the vessel, stirring was continued, and the reaction was carried out by heating to 80 ℃. And after the reaction is finished, filtering and washing the obtained mixed slurry, and vacuum drying at 80 ℃ to obtain the silicon-based anode material.
Comparative example 2
Pre-lithiated silicon oxide-on-carbon material is mixed with 2wt% P under dry inert atmosphere 2 O 5 Adding into a container, stirring thoroughly, and heating to 100deg.C under stirring. After a period of reaction, water was added to the vessel, stirring was continued, and the reaction was carried out by heating to 80 ℃. And after the reaction is finished, filtering and washing the obtained mixed slurry, and vacuum drying at 80 ℃ to obtain the silicon-based anode material.
Comparative example 3
Untreated pre-lithiated carbon-coated silica materials.
Test case
1. Preparation of lithium ion secondary battery
The preparation method of the positive plate comprises the following steps: mixing an anode active material NCM811, conductive carbon Super-P and a binder polyvinylidene fluoride PVDF according to a mass ratio of 97:2:1, adding a solvent N-methyl pyrrolidone NMP, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on an aluminum foil, and drying to obtain the anode sheet.
The preparation method of the negative plate comprises the following steps: mixing a composite anode material, conductive carbon Super-P, conductive carbon nano tube CNT, a binder sodium carboxymethylcellulose CMC and a binder styrene butadiene rubber SBR according to a mass ratio of 95:1.5:1.4:0.1:2, adding deionized water, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on a copper foil, and drying to obtain the anode sheet. The composite anode material is prepared by mixing the silicon-based anode materials prepared in the above examples and comparative examples and artificial graphite according to a ratio of 1:9.
Electrolyte solution: 1M LiPF 6 And DMC, EMC and FEC are prepared according to the volume ratio of 2:6:2.
And assembling the positive electrode plate, the negative electrode plate and the isolating film to obtain a battery core, placing the battery core in a shell, drying, injecting the electrolyte, packaging, standing, forming, separating and the like to obtain the lithium ion secondary battery, wherein the capacity of the lithium ion secondary battery is designed to be 8Ah.
2. Performance testing
(1) PH test
5.00g of the prepared silicon-based anode material is weighed to be accurate to 0.01g, placed in a 100mL glass beaker, 45mL of freshly boiled and cooled distilled water is added, a small amount of distilled water is added first, the sample is fully wetted by stirring with a glass rod, and then the rest of water is added completely. Then, the glass beaker is placed in an ultrasonic cleaner for ultrasonic treatment for 5min, and is stirred by a glass rod while ultrasonic treatment is carried out, and the glass beaker is taken out and placed to obtain supernatant for clarification. The supernatant was tested using a pH meter to obtain pH.
(2) Gas production test
Vacuum packaging 200g of slurry before coating in an aluminum-plastic film bag with a volume of 500ml, and measuring the volume V of the aluminum-plastic film bag with the slurry by adopting a drainage volumetric method 1 Then put at a constant temperature of 60 DEG CTesting primary volume V in a warm oven for 48h 2 Calculating the gas production volume V within 48 hours x =V 2 -V 1 。
(3) Cycle life test
The obtained lithium ion secondary battery was charged at a rate of 1C and discharged at a rate of 1C at 25C, and a full charge discharge cycle test was performed until the capacity of the lithium ion secondary battery was reduced to 80% of the initial capacity, and the number of cycles was recorded.
The above test results are shown in fig. 4 and table 1.
TABLE 1
As can be seen from the results of fig. 4 and table 1: the lithium ion secondary battery prepared in the comparative example 3 has the advantages that the pre-lithiated carbon-coated silicon oxide material in the negative electrode material is untreated, the residual alkali amount on the surface is high, the gas yield is high, the pH reaches 11.8, the gas yield reaches 31.2, and the cycle number is only 649. In comparative example 1, 4% NH was used 4 F, the pre-lithiated carbon-coated silicon oxide material is treated, the residual alkali amount and the gas production amount on the surface of the material are reduced, the pH value is reduced to 11.2, the gas production amount is reduced to 24.6, and the cycle number is increased to 911 cycles. In comparative example 2, 2% P was used 2 O 5 The pre-lithiated carbon-coated silica material is treated, the residual alkali amount and the gas production amount on the surface of the material are further reduced, the pH is 10.4, the gas production amount is 12.3, and the cycle number is increased to 986.
In example 1, 0.05wt% NH was used 4 F and 0.02wt% P 2 O 5 The pre-lithiated carbon-coated silica material is treated, the residual alkali and gas yield on the surface of the material are obviously reduced, the pH is reduced to 10.2, the gas yield is reduced to 16.4, and the number of circulation circles is increased to 1105. In example 2, 4wt% NH was used 4 F and 2wt% of P 2 O 5 The pre-lithiated carbon-coated silicon oxide material is treated, the pH value of the surface of the material is reduced to 9.5, the gas yield is reduced to 10.2, and the number of circulation circles reaches 1105 circles.
In conclusion, the pre-lithiated silicon-based material is treated by adopting a certain amount of fluoridation reagent and phosphorus pentoxide, so that the residual alkali on the surface of the material is obviously reduced, the gas yield in the pole piece processing process is reduced, and the cycle performance of the lithium ion secondary battery is greatly improved.
The above-described embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.
Claims (9)
1. The preparation method of the silicon-based anode material is characterized by comprising the following steps of:
s1, uniformly mixing a carbon-coated pre-lithiated silicon-based material, a fluoridation reagent and phosphorus pentoxide in a protective atmosphere;
s2, heating the mixture obtained in the step S1 under the condition of continuous stirring so as to react;
s3, dissolving the reaction product obtained in the step S2 in a solvent, and continuously heating under a protective atmosphere to react; the solvent is water and/or ethanol;
and S4, filtering, washing and drying the reaction product obtained in the step S3 to obtain the silicon-based anode material.
2. The method for producing a silicon-based anode material according to claim 1, wherein in step S1, the fluorinating agent comprises one or more of ammonium fluoride, hydrogen fluoride, ammonium bifluoride, fluoroboric acid, and trifluoromethanesulfonic acid.
3. The method for preparing a silicon-based anode material according to claim 1, wherein in the step S1, the mass of the fluorinating agent is 0.05% -20% of the carbon-coated pre-lithiated silicon-based material, and the mass of the phosphorus pentoxide is 0.02% -10% of the carbon-coated pre-lithiated silicon-based material.
4. The method of producing a silicon-based anode material according to claim 1, wherein in step S2, the heating temperature is 60 to 300 ℃.
5. The method of producing a silicon-based anode material according to claim 1, wherein in step S3, the heating temperature is higher than 60 ℃ and lower than the boiling temperature of the solvent.
6. A silicon-based negative electrode material prepared by the method according to any one of claims 1 to 5, wherein the silicon-based negative electrode material comprises a carbon-coated pre-lithiated silicon-based material, the surface of the carbon-coated pre-lithiated silicon-based material contains LiF, li 3 PO 4 And LiPO 2 F 2 。
7. The silicon-based anode material according to claim 6, wherein the silicon-based material contains silicon oxide.
8. The silicon-based anode material according to claim 7, further comprising one or more of silicate, silicon nanoparticles, amorphous silicon.
9. A lithium ion secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the separator being arranged to isolate the positive electrode sheet from the negative electrode sheet, characterized in that the active material in the negative electrode sheet is the silicon-based negative electrode material of claim 6.
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