CN115863574A - Negative electrode material, negative plate comprising negative electrode material and battery - Google Patents
Negative electrode material, negative plate comprising negative electrode material and battery Download PDFInfo
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Abstract
The invention provides a negative electrode material, a negative electrode plate comprising the negative electrode material and a battery. The cathode material has a core-shell structure, the core comprises a silicon-based material and a porous carbon material, the silicon-based material is distributed in pores of the porous carbon material, and the pores provide buffer space for the volume expansion of the silicon-based material; the shell layer comprises carbon nanofibers and titanium dioxide, the shell layer can effectively inhibit the volume expansion of Si and avoid the direct contact of the Si and electrolyte, and the structural stability of the cathode material is further improved. And outer layer of TiO 2 Can keep tiny volume change during the process of lithium ion de-intercalationThe amount of the compound is reduced (about 4%), which is beneficial to maintaining higher interface stability. The battery assembled by the negative electrode material has excellent cycling stability, higher cycling capacity retention rate and lower cycling volume expansion rate.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a negative electrode material, a negative plate comprising the negative electrode material and a battery.
Background
Lithium ion batteries are widely used in energy storage systems due to their advantages of high energy density, long cycle life, environmental friendliness, and the like. The development level of the cathode material as an important component of the lithium ion battery restricts the development of the lithium ion battery. Graphite is widely used as a negative electrode material for lithium ion batteries because of its advantages of reversible lithium intercalation/deintercalation capacity, high cycling stability, low and stable discharge platform, abundant resources and the like. But the low theoretical capacity of graphite (372 mA h g) -1 ) The pursuit of the modern society for the high-capacity lithium ion battery cannot be met. Therefore, the development of new high capacity anode materials is one of the major efforts in the field of current anode materials.
Silicon (Si) up to 4200mA h g -1 The capacity of the lithium ion battery is expected to become a next-generation commercialized high-performance negative electrode material for the lithium ion battery. However, the large volume expansion of Si materials during cycling can lead to pulverization of the materials, collapse of the electrode structure, and repeated formation of SEI films, ultimately resulting in low coulombic efficiency and rapid decay of capacity. These problems severely restrict the practical application of Si materials as anode materials.
In order to solve the problems, the industry prepares a silicon-carbon composite negative electrode material with high energy density and high cycle stability by compounding nano silicon, graphite and pyrolytic carbon. Although graphite and pyrolytic carbon relieve the volume expansion of silicon to a great extent, the conventional pyrolytic carbon coating can deform in volume along with the expansion of silicon, pores or cracks are easy to generate, a new SEI film is generated by contact with an electrolyte, and the pyrolytic carbon coating can continuously crack to expose new sites along with the continuous progress of the charging and discharging process, so that the repeated formation of the SEI film is caused, and finally, the low coulombic efficiency and the rapid capacity attenuation are caused.
Disclosure of Invention
The invention provides a negative electrode material, a negative electrode plate comprising the negative electrode material and a battery, aiming at the problem of capacity attenuation caused by volume expansion of the existing silicon-carbon composite material in the circulating process. The cathode material has a core-shell structure and comprises a shell layer and a core, wherein the core comprises a silicon-based material and a porous carbon material, the silicon-based material is distributed in pores of the porous carbon material, and the pores provide buffer space for the volume expansion of the silicon-based material; the shell layer comprises carbon nanofibers and titanium dioxide, can effectively buffer the volume expansion of the silicon-based material, avoids the direct contact of the silicon-based material and electrolyte, and can improve the structural stability of the cathode material; and the titanium dioxide can keep small volume change (about 4%) in the process of lithium ion de-intercalation, which is beneficial to maintaining higher interface stability, and the battery assembled by the cathode material has excellent cycle stability and lower expansion rate.
The purpose of the invention is realized by the following technical scheme:
an anode material, wherein the anode material comprises a shell layer and a core, and the shell layer comprises carbon nanofibers and titanium dioxide; the core comprises a silicon-based material and a porous carbon material.
According to the embodiment of the invention, the shell layer is coated on the surface of the core to form a core-shell structure; illustratively, the shell layer partially coats the core surface, or the shell layer completely coats the core surface.
According to an embodiment of the present invention, the porous carbon material has a specific surface area BET of 200m 2 /g～3000m 2 A ratio of/g, e.g. 200m 2 /g、400m 2 /g、600m 2 /g、800m 2 /g、1000m 2 /g、1200m 2 /g、1400m 2 /g、1600m 2 /g、1800m 2 /g、2000m 2 /g、2200m 2 /g、2400m 2 /g、2600m 2 /g、2800m 2 /g、3000m 2 (iv)/g or any point in the range consisting of any two of the endpoints. The porous carbon material has a too low specific surface area (e.g., less than 200 m) 2 In/g), the content of the deposited silicon-based material is also reduced, and the specific capacity of the obtained anode material is also low; the porous carbon material has too high a specific surface area (e.g. more than 3000 m) 2 In/g), the deposited silicon-based material cannot fill all pores, resulting in a large specific surface area of the negative electrode material, which in turn leads to low first efficiency.
According to an embodiment of the present invention, the porous carbon material has a pore size of 0.5nm to 2 μm, for example, 0.5nm, 1nm, 10nm, 20nm, 40nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1 μm, 2 μm or any point in the range of the above endpoints. The aperture of the porous carbon material is too small, the deposition difficulty of the silicon-based material is increased, and the low silicon content is easily caused, so that the specific capacity of the negative electrode material is influenced; the porous carbon material has an excessively large pore diameter, and the pores cannot be filled, resulting in a large specific surface area, resulting in a low first effect.
According to an embodiment of the present invention, the degree of graphitization of the porous carbon material is 30% to 100%, for example 30%, 50%, 60%, 70%, 80%, 90%, 100% or any point in the range of the above two endpoints. When the degree of graphitization of the porous carbon material is less than 30%, the compacted density and conductivity thereof are low, thereby affecting the volumetric energy density and rate performance of the battery.
According to an embodiment of the present invention, the median particle diameter Dv50 of the porous carbon material is 5 μm to 10 μm. For example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any point in the range between the two endpoints. The median diameter Dv50 of the porous carbon material is too low (for example, less than 5 μm), the specific surface area of the porous carbon material is large, and the side reactions in the battery are more, which affects the battery performance. If the median diameter Dv50 of the porous carbon material is too large (e.g., greater than 10 μm), the gaps between the particles are large when the porous carbon material is stacked on the electrode sheet, which may cause a decrease in the volumetric energy density of the battery.
According to an embodiment of the invention, the silicon-based material has a median particle diameter Dv50 of between 0.5nm and 10 μm. For example, 0.5nm, 1nm, 3nm, 5nm, 20nm, 40nm, 60nm, 80nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any of the ranges defined by the above two endpoints. The median diameter Dv50 of the silicon-based material is too large (for example, larger than 10 μm), and the outer coating is not enough to buffer the large volume expansion of silicon, so that the volume expansion is more serious, and the stability of the structure of the cathode material is not facilitated. The silicon-based material has a median particle size Dv50 that is too small (e.g., less than 5 nm) to be deposited into the pores of the porous carbon material.
According to an embodiment of the present invention, the silicon-based material includes at least one of silicon-containing materials such as silicon oxide materials (SiOx, 0<x <2), silicon carbon materials, silicon materials, and the like.
According to an embodiment of the present invention, the silicon-based material comprises a pyrolysis product of one or more of monosilane, disilane, chlorosilane, and chloromethylsilane. Wherein the pyrolysis temperature is 600-900 ℃, the pyrolysis time is 6-10 h, and the pyrolysis is carried out in inert atmosphere, such as at least one selected from high-purity argon and high-purity nitrogen.
According to an embodiment of the present invention, the core material comprises a silicon-based material and a porous carbon material, and the silicon-based material is distributed within pores of the porous carbon material.
According to an embodiment of the present invention, the shell layer includes carbon nanofibers and titanium dioxide, and the titanium dioxide is distributed on gaps and surfaces of the carbon nanofibers.
According to an embodiment of the invention, the silicon-based material is distributed within the pores of the porous carbon material to form a core.
According to an embodiment of the invention, the shell has a different contrast to the core under observation by a Transmission Electron Microscope (TEM), and the shell has a thickness of 20nm to 40nm, for example 20nm, 25nm, 30nm, 35nm, 40nm or any point in the range of the two endpoints mentioned above. When the thickness of the shell layer is too thin (such as less than 20 nm), the volume expansion of the silicon-based material is not sufficiently relieved; when the thickness of the shell layer is too thick (such as more than 40 nm), the difficulty of lithium ion deintercalation on the surface of the material is increased, the deintercalation of lithium ions is influenced, and the capacity is reduced.
According to an embodiment of the present invention, the carbon nanofibers have a diameter of 10nm to 200nm. For example, 10nm, 40nm, 80nm, 120nm, 160nm, 200nm, or any point in the range between the two endpoints. When the diameter of the carbon nanofiber is too large (such as larger than 200 nm), the distance of the lithium ion deintercalation process is increased, and the rapid charge and discharge are not facilitated.
According to an embodiment of the present invention, the carbon nanofibers have a length of 100nm to 2 μm. For example, 100nm, 400nm, 600nm, 800nm, 900nm, 1 μm, 2 μm, or any point in the range between the two endpoints. The carbon nanofibers are too short (e.g., less than 100 nm) to form a complete conductive network structure; if the length of the carbon nanofiber is too long (e.g., greater than 2 μm), the carbon nanofiber may be densely wound on the surface of the core, which may affect the transmission of electrons and lithium ions.
According to an embodiment of the present invention, the carbon nanofibers coated on the surface of the core are not densely packed but have more pores, and when the titanium dioxide is coated, it is distributed on the gaps and the surface of the carbon nanofibers to form a mixed coating layer including the carbon nanofibers and the titanium dioxide. That is, the titanium dioxide is distributed on the gaps and surfaces of the carbon nanofibers to form a mixed coating layer including the carbon nanofibers and the titanium dioxide.
According to an embodiment of the invention, the mass of the core is 40% to 65% of the total mass of the anode material, such as 40%, 45%, 50%, 55%, 60% or 65%.
According to an embodiment of the present invention, the mass of the shell layer accounts for 35% to 60% of the total mass of the anode material, for example, 35%, 40%, 45%, 50%, 55%, or 60%.
According to the embodiment of the invention, the mass percent content a of the silicon-based material in the negative electrode material is more than or equal to 20% and less than or equal to 40%, such as 20%, 25%, 30%, 35% or 40%.
According to the embodiment of the invention, the mass percentage content b of the carbon nano fibers in the negative electrode material is more than or equal to 30% and less than or equal to 50%, such as 30%, 35%, 40%, 45% or 50%.
According to the embodiment of the invention, the mass percent content c of the titanium dioxide in the negative electrode material is more than or equal to 5% and less than or equal to 30%, such as 5%, 10%, 15%, 20%, 25% or 30%.
According to the embodiment of the invention, the mass percentage content d of the porous carbon material in the anode material is 20% to 40%, such as 20%, 25%, 30%, 35% or 40%.
According to an embodiment of the present invention, the negative electrode material has a diffraction peak 1 in an X-ray powder diffraction (XRD) test in a range of 2 θ =26.4 ° ± 0.5 °, indicating that a graphitized carbon material is included in the negative electrode material; the presence of diffraction peak 2 in the range of 2 θ =28.4 ° ± 0.5 °, indicating that the anode material comprises a silicon-based material; the presence of diffraction peak 3 in the range of 2 θ =25.28 ° ± 0.5 ° indicates that the anode material includes titanium dioxide.
According to the embodiment of the invention, the anode material has a Raman shift of 1335-1345 cm in a Raman spectroscopy (Raman) test -1 (e.g., 1340 cm) -1 ) Has a characteristic Raman peak of 1, 1575-1585 cm -1 (e.g., 1580cm -1 ) Characteristic raman peak 2, belonging to the characteristic raman peak of carbon; the ratio x1/x2 of the peak intensity x1 of the characteristic Raman peak 1 and the peak intensity x2 of the characteristic Raman peak 2 satisfies 0.5<x1/x2 ≦ 2.0, indicating that the material comprises an amorphous carbon material (specifically carbon nanofibers).
According to the embodiment of the invention, the anode material has Raman shift of 501-511 cm in a Raman spectroscopy (Raman) test -1 (e.g., 506 cm) -1 ) The presence of characteristic raman peak 3 indicates that the negative electrode material comprises a silicon-based material.
According to the embodiment of the invention, the anode material has Raman shift of 136-147 cm in a Raman spectroscopy (Raman) test -1 (e.g., 141 cm) -1 ) The presence of characteristic raman peak 4 indicates that the negative electrode material comprises titanium dioxide.
According to the embodiment of the invention, the titanium dioxide has a high lithium deintercalation potential, generally 1.7V, can participate in the formation of SEI film and stably exists under the working voltage of the negative electrode, so that the interface property of the negative electrode is continuously and effectively improved. However, the lithium-releasing potential of other inorganic oxides (such as alumina) is relatively low, usually at-0.4V, and lithium is released and released along with the charging and discharging processes of the negative electrode, so that the formed product lithium-aluminum alloy can generate side reaction with the electrolyte and is easy to pulverize, and the effect of improving the surface property of the negative electrode is limited.
The invention also provides a preparation method of the anode material, which comprises the following steps:
1) Placing the porous carbon material in a vapor deposition furnace, then introducing silane gas and carrier gas, heating to crack silane, and preparing a silicon-carbon composite material with silicon-based materials distributed in pores of the porous carbon material;
2) Mixing the silicon-carbon composite material obtained in the step 1) with a metal catalyst;
3) Placing the silicon-carbon composite material mixed with the metal catalyst in a vapor deposition furnace, and then introducing carbon source gas and carrier gas to carry out vapor chemical deposition to obtain the silicon-carbon composite material coated by the carbon nanofibers;
4) And coating titanium dioxide on the surface of the silicon-carbon composite material coated with the carbon nanofibers through sol-gel and heat treatment processes to prepare the negative electrode material.
In the step 1) of the method, the deposition of the silicon-based material can be realized in the process of silane cracking, and the silicon-based material can be deposited into the pores of the porous carbon material.
In step 1), the silane gas is selected from one or more of monosilane, disilane, chlorosilane and chloromethylsilane. The temperature of the silane cracking is 600-900 ℃, and the time of the silane cracking is 6-10 h. The carrier gas is at least one of high-purity argon and high-purity nitrogen.
In step 2) of the above method, the metal catalyst is a metal compound containing at least one of iron, cobalt and nickel, specifically, iron chloride, cobalt chloride, nickel nitrate, and the like.
In the step 2) of the method, the mass ratio of the silicon-carbon composite material to the metal catalyst is 5 to 10.
In the above method step 3), the carbon source gas is at least one selected from methane, ethane, propane, ethylene, propylene, and acetylene. The temperature of the vapor phase chemical deposition is 600-1200 ℃, and the time of the vapor phase chemical deposition is 1-3 hours. The carrier gas is at least one selected from hydrogen, high-purity argon and high-purity nitrogen.
In the above method step 3), the carbon nanofibers generated during the cvd process are not densely packed but have many pores, and thus the coated titanium dioxide is distributed in the gaps and surfaces of the carbon nanofibers to form a mixed coating layer of the two.
In step 4), the sol-gel conditions are as follows: and (3) taking butyl titanate as a titanium source, adding ammonia water to prepare an alkaline environment (pH value: 11-13), wherein the mass ratio of the titanium source to the carbon nanofiber-coated silicon-carbon composite material prepared in the step 3) is 1 (0.2-1), and magnetically stirring for 15-24 hours at 35-50 ℃ in a water bath.
In step 4), the heat treatment process conditions are as follows: the temperature is 400-600 ℃, and the time is 2-5 h.
The invention also provides a negative plate which comprises the negative electrode material.
According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, and the negative electrode active material layer includes the above-described negative electrode material.
According to an embodiment of the present invention, the anode active material layer further includes hard carbon, soft carbon, or graphite such as artificial graphite and/or natural graphite.
According to an embodiment of the present invention, the anode active material layer further includes a conductive agent. In some embodiments, the conductive agent is selected from one or more of carbon black, acetylene black, ketjen black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes.
According to an embodiment of the present invention, the anode active material layer further includes a binder. In some embodiments, the binder is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, styrene butadiene rubber, and epoxy resin.
According to the embodiment of the invention, the negative electrode current collector is one or more selected from copper foil, carbon-coated copper foil and perforated copper foil.
According to the embodiment of the invention, the anode active material layer comprises the following components in percentage by mass:
0.5 to 99 weight percent of negative electrode material, 0 to 98.5 weight percent of graphite, 0.5 to 15 weight percent of conductive agent and 0.5 to 15 weight percent of binder.
Preferably, the negative electrode active material layer comprises the following components in percentage by mass:
48-95 wt% of graphite, 1-50 wt% of negative electrode material, 1-10 wt% of conductive agent and 1-10 wt% of binder.
According to an embodiment of the present invention, the negative electrode sheet may be specifically obtained by:
mixing the negative electrode material, optional graphite, a conductive agent and a binder in deionized water to obtain negative electrode slurry, coating the negative electrode slurry on a negative electrode current collector, drying at 80 ℃, slicing, transferring to a vacuum oven at 100 ℃ for drying for 12 hours, and finally rolling and slitting to obtain the negative electrode sheet.
The invention also provides a battery, which comprises the negative plate.
According to an embodiment of the invention, the battery is a lithium ion battery.
According to an embodiment of the invention, the battery further comprises a separator. In some embodiments, the separator is selected from one or more of polyethylene or polypropylene.
According to an embodiment of the invention, the battery further comprises an electrolyte. In some embodimentsThe electrolyte is a non-aqueous electrolyte, and the non-aqueous electrolyte comprises a carbonate solvent and a lithium salt. In some embodiments, the carbonate solvent is selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC). In some embodiments, the lithium salt is selected from LiPF 6 、LiBF 4 、LiSbF 6 、LiClO 4 、LiCF 3 SO 3 、LiAlO 4 、LiAlCl 4 、Li(CF 3 SO 2 ) 2 One or more of N, liBOB and LiDFOB.
The invention has the beneficial effects that:
the invention provides a negative electrode material, a negative electrode plate comprising the negative electrode material and a battery. The cathode material has a core-shell structure, the core comprises a silicon-based material and a porous carbon material, the silicon-based material is distributed in pores of the porous carbon material, and the pores provide buffer space for the volume expansion of the silicon-based material; the shell layer comprises carbon nanofibers and titanium dioxide, the shell layer can effectively inhibit the volume expansion of the silicon-based material and avoid the direct contact of the silicon-based material and electrolyte, and the structural stability of the cathode material is further improved. And TiO of the outer layer 2 The micro volume change (about 4 percent) can be kept in the process of lithium ion de-intercalation, and higher interface stability is favorably maintained. The battery assembled by the negative electrode material has excellent cycle stability, higher cycle capacity retention rate and lower cycle volume expansion rate.
Drawings
Fig. 1 is an XRD pattern of the anode material of example 1.
Fig. 2 is an SEM image of the porous carbon material (a) and the carbon nanofiber-wrapped silicon carbon composite (b) of example 1.
Fig. 3 is a TEM image of the anode material of example 1.
Fig. 4 is a lithium insertion and lithium removal curve of the negative electrode material of example 1.
Detailed Description
The preparation process of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the present invention, a Scanning Electron Microscope (SEM) analysis method, for example, a scanning electron microscope of Quanta 250FEG manufactured by FEI Corporation in the united states, is used for characterization of the surface morphology, microstructure, and particle size of the negative electrode material.
In the invention, a Transmission Electron Microscope (TEM) analysis method is adopted for characterizing the shell layer thickness of the anode material, such as a Japanese electron JEM-F200 field emission transmission electron microscope.
In the present invention, the characterization of the analysis of the composition structure of the negative electrode material is carried out by X-ray diffraction (XRD) method and Raman spectroscopy (Raman), for example, by test analysis using a Japanese-Patch automatic X-ray diffractometer model D/MAX2550, using Cu target and Ka ray
Is a radiation source, the scanning range is 10-80 degrees, and the scanning speed is 5 degrees/min; a micro laser Raman spectrometer model LabRAM Hr800 from HORIBA Jobin Yvon France was used.
In the invention, a Thermogravimetric (TG) analysis method is adopted for representing the relative contents of the components of the anode material, for example, a synchronous thermal analyzer with the model of Netzsch STA449 German Nachi company is used, and the test process is to heat the anode material from room temperature to 1000 ℃ in the air, wherein the heating rate is 10 ℃/min.
In the present invention, the specific surface area of the anode material is characterized by a Brunauer-Emmett-Teller (BET) test method, for example, a direct-reading dynamic flow method specific surface area analyzer of type Monosorb is used.
Example 1
1. 30g of graphitized porous carbon (commercially available, BET specific surface area 1600 m) 2 /g, aperture 800 nm) is placed in a chemical vapor deposition furnace, mixed gas of high-purity argon and monosilane with the volume ratio of 6. Mixing 30g of silicon-carbon composite material with 2g of nickel nitrate, 200ml of methanol/deionized water (volume ratio is 1. And (3) placing the sample mixed with the nickel nitrate into a deposition furnace, and introducing a mixed gas of argon, hydrogen and propylene in a volume ratio of 2.
2. Adding 20g of the silicon-carbon composite material coated by the carbon nano fiber obtained in the step 1 into 300mL of absolute ethyl alcohol, simultaneously adding 2mL of concentrated ammonia water (28 wt%), stirring and mixing uniformly, heating to 50 ℃, then slowly dropwise adding 3mL of tetrabutyl titanate, stirring vigorously for 20h, washing with ethanol and distilled water for multiple times after the reaction is finished, centrifuging to collect a sample, and finally drying in an air-blast drying oven at 80 ℃ for 12h. And (3) placing the dried sample in a vacuum tube furnace, and carrying out heat treatment for 3h at 650 ℃ in an argon atmosphere to obtain the negative electrode material of the embodiment 1.
Example 2
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: selecting a BET specific surface area of 2200m 2 A graphitized porous carbon having a pore diameter of 1 μm/g.
Example 3
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: the nickel nitrate is changed into cobalt nitrate.
Practice of example 4
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: the silane cracking temperature was raised to 900 ℃.
Example 5
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: propylene was changed to ethylene.
Comparative example 1
30g of graphitized porous carbon (commercially available, BET specific surface area 1600 m) 2 /g, the aperture is 800 nm), placing the silicon-carbon composite material in a chemical vapor deposition furnace, introducing mixed gas of high-purity argon and monosilane in a volume ratio of 6. And (2) adding 20g of the obtained silicon-carbon composite material into 300mL of absolute ethyl alcohol, simultaneously adding 2mL of concentrated ammonia water (28 wt%), stirring and mixing uniformly, heating to 50 ℃, then slowly dropwise adding 3mL of tetrabutyl titanate, stirring vigorously for 20h, washing with ethanol and distilled water for multiple times after the reaction is finished, centrifuging to collect a sample, and finally drying in an air-blowing drying oven at 80 ℃ for 12h. And (3) placing the dried sample in a vacuum tube furnace, and carrying out heat treatment for 3h at 650 ℃ in an argon atmosphere to obtain the cathode material of the comparative example 1.
Comparative example 2
30g of graphitized porous carbon (commercially available, BET specific surface area 1600 m) 2 /g, the aperture is 800 nm) is placed in a chemical vapor deposition furnace, mixed gas of high-purity argon and silane with the volume ratio of 6. And (2) adding 20g of the silicon-carbon composite material into 300mL of absolute ethyl alcohol, adding 2mL of concentrated ammonia water (28 wt%), stirring and mixing uniformly, heating to 50 ℃, then slowly dropwise adding 3mL of tetrabutyl titanate, stirring vigorously for 20h, washing with ethanol and distilled water for multiple times after the reaction is finished, centrifuging to collect a sample, and finally drying in a forced air drying oven at 80 ℃ for 12h. And (3) placing the dried sample in a vacuum tube furnace, and carrying out heat treatment for 3h at 650 ℃ in an argon atmosphere to obtain the cathode material of the comparative example 2.
Comparative example 3
30g of graphitized porous carbon (commercially available, BET specific surface area 1600 m) 2 Per g, pore diameter 800 nm) was placed in a chemical vapor deposition furnace, and a height of 6And heating the mixed gas of pure argon and monosilane to 700 ℃, preserving heat and depositing for 8h to obtain the silicon-carbon composite material with nano-silicon uniformly dispersed on the surface and in the pore channels of the graphitized porous carbon. Mixing 30g of silicon-carbon composite material with 2g of nickel nitrate, 200ml of methanol/deionized water (volume ratio is 1. And (3) placing the sample mixed with the nickel nitrate into a deposition furnace, and introducing mixed gas of argon, hydrogen and propylene in a volume ratio of 2.
Example 6
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: in step 1, the deposition time of the carbon nanofibers was changed to 20min.
Example 7
The preparation method of the anode material provided by the present embodiment is different from that of embodiment 1 only in that: in step 2, the amount of tetrabutyl titanate was changed to 1ml.
As shown in fig. 1, the XRD pattern of the anode material prepared in example 1 is compared with the characteristic diffraction peak of graphitized porous carbon (the characteristic diffraction peak of the graphitized carbon material exists at the 2 θ =26.4 ° ± 0.5 °), and the prepared anode material has more characteristic diffraction peaks of silicon and titanium dioxide at the 2 θ =28.4 ° ± 0.5 ° and 2 θ =25.28 ° ± 0.5 °, which indicates successful deposition of silicon and successful coating of titanium dioxide.
The graphitized porous carbon as the raw material for preparing the negative electrode material of preparation example 1 was subjected to Raman spectroscopic analysis (Raman) test at a Raman shift of 1340cm -1 Has a characteristic Raman peak 1 and a Raman shift of 1580cm -1 A characteristic raman peak 2 is present, both peaks belonging to the characteristic raman peak of carbon; the ratio x1/x2=0.06 of the peak intensity x1 of the characteristic raman peak 1 and the peak intensity x2 of the characteristic raman peak 2, and satisfies 0<x1/x2 is less than or equal to 0.5, which indicates that the preparation raw material is a highly graphitized carbon material.
The anode material prepared in example 1 was subjected to Raman spectroscopy (Raman) at a Raman shift of 1340cm -1 Is characterized by the presence of a characteristic Raman peak 1 at RamanDisplacement is 1580cm -1 A characteristic raman peak 2 is present, both peaks belonging to the characteristic raman peak of carbon; the ratio x1/x2=1.75 of the peak intensity x1 of the characteristic raman peak 1 and the peak intensity x2 of the characteristic raman peak 2 satisfies 0.5<x1/x2 ≦ 2.0, which indicates that the anode material comprises amorphous carbon, and further combines SEM image (FIG. 2) and TEM image (FIG. 3), which indicates that the amorphous carbon is carbon nanofiber, i.e. indicates successful synthesis of carbon nanofiber.
The median diameter Dv50 of the silicon-based material and the diameter D of the carbon nanofiber in the prepared cathode material CNF The test results of the shell layer thickness h, the silicon content a, the carbon nanofiber content b, and the titanium dioxide content c are shown in table 1.
Table 1 results of performance test of anode materials of examples and comparative examples
| Dv50 | D CNF (nm) | a | b | c | h(nm) | |
| Example 1 | 750nm | <200 | 30％ | 30％ | 10％ | 35 |
| Example 2 | 810nm | <200 | 29％ | 32％ | 9％ | 37 |
| Example 3 | 789nm | <200 | 31％ | 30％ | 9％ | 34 |
| Example 4 | 801nm | <200 | 28％ | 32％ | 10％ | 38 |
| Example 5 | 795nm | <200 | 29％ | 31％ | 10％ | 36 |
| Comparative example 1 | 774nm | / | 60％ | / | 20％ | 15 |
| Comparative example 2 | 756nm | / | 50％ | / | 10％ | 12 |
| Comparative example 3 | 745nm | <200 | 40％ | 30％ | / | 18 |
| Example 6 | 700nm | <200 | 35％ | 15％ | 20％ | 17 |
| Example 7 | 721nm | <200 | 36％ | 32％ | 2％ | 16 |
As can be seen from table 1, the median particle diameter of the silicon-based material in the negative electrode materials prepared in examples 1 to 5 was within 10 μm, the diameter of the carbon nanofiber was within 200nm, and the shell thickness was within 20nm to 40nm as seen from the TEM images. Meanwhile, the content a of silicon, the content b of carbon nanofibers and the content c of titanium dioxide in the negative electrode materials prepared in the embodiments 1 to 5 respectively satisfy that a is more than or equal to 20% and less than or equal to 40%, b is more than or equal to 30% and less than or equal to 50%, and c is more than or equal to 5% and less than or equal to 30%, so that the negative electrode material is ensured to have lower impurity content. The content of the carbon nanofiber of the cathode material prepared in the embodiment 6 is not more than 30% and not more than 50% of b, and the thickness of a shell layer is not more than 20 nm-40 nm; the content of titanium dioxide in the negative electrode material prepared in the embodiment 7 is not more than 5% and not more than 30%, and the thickness of a shell layer is not more than 20nm and not more than 40nm.
The content of the carbon nanofibers in the negative electrode material prepared in the comparative example 1 is 0, the thickness of the shell layer is 15nm, and the thickness does not satisfy 20 nm-40 nm; the content of the carbon nanofibers in the negative electrode material prepared in the comparative example 2 is 0, the thickness of the shell layer is 12nm, and the thickness does not satisfy 20 nm-40 nm; the content of titanium dioxide in the negative electrode material prepared in the comparative example 3 is 0, and the shell layer thickness is 18nm, which does not satisfy 20 nm-40 nm.
The negative electrode materials of the above examples and comparative examples were assembled into button half cells for testing, and the specific manufacturing method was as follows:
(1) Mixing the prepared negative electrode material, artificial graphite, superP, sodium carboxymethylcellulose and styrene butadiene rubber according to a mass ratio of 46.5;
(2) Coating the negative electrode slurry obtained in the step (1) on copper foil, drying in an oven at 80 ℃, and then transferring to a vacuum oven at 100 ℃ for drying for 12 hours to obtain the copper foil with the surface density of about 7.4mg/cm 2 The negative electrode sheet of (1);
(3) Under a dry environment, the negative plate in the step (2) is arranged at a position of about 1.2g/cm 3 Compacting, rolling, and then preparing a negative electrode wafer with the diameter of 12mm by using a sheet punching machine;
(4) In a glove box, the negative electrode wafer in the step (3) is taken as a working electrode, a metal lithium sheet is taken as a counter electrode, a polyethylene diaphragm with the thickness of 20 mu m is taken as an isolating membrane, and electrolyte is added to assemble a button type half cell;
(5) The performance of the half-cell button was tested using a blue electricity (LAND) test system at a test temperature of 25 ℃, in particular: embedding lithium to 0.005V by using a current of 0.1mA, standing for 10min, embedding lithium to 0.005V by using a current of 0.05mA, standing for 10min, then removing lithium to 1.5V by using a current of 0.1mA to obtain a primary lithium embedding and removing capacity, dividing the primary lithium embedding and removing capacity by the mass of the negative electrode material in the negative electrode wafer to obtain the gram capacity of the negative electrode material, measuring the thickness of the pole piece after 200 cycles, and dividing the difference value of the thickness and the initial thickness by the initial thickness to obtain the expansion rate of the thickness of the pole piece, wherein the test results are shown in Table 2.
Table 2 results of performance tests of button half-cells of examples and comparative examples
As can be seen from Table 2, the gram capacities of the half-cells prepared in examples 1 to 5 were all 1120 to 1340mA hr g -1 In between, the capacity retention rate after 200 cycles is more than 90%, and the thickness expansion rate of the pole piece after 200 cycles is less than 10%. The gram capacity, capacity retention rate and electrode sheet thickness expansion rate of the half-cells prepared in comparative examples 1 to 3 and examples 6 to 7 are greatly different from each other.
The capacity retention rate of the half-cell of comparative example 1 and comparative example 2 after 200 cycles is greatly reduced, and the expansion rate of the pole piece is greatly increased, mainly because the negative electrode material of comparative example 1 has inner carbon coating and outer titanium dioxide coating, but the volume of the silicon-based material expands along with the progress of the charging and discharging process, the inner carbon coating is easy to generate pores and cracks, thereby indirectly causing the volume deformation of the titanium dioxide, while the titanium dioxide coating layer in the negative electrode material of comparative example 2 can generate the volume deformation along with the silicon expansion, the coating layers of both comparative examples are easy to generate pores or cracks, the repeated formation of an SEI film is easy to cause the capacity attenuation, and the expansion rate of the pole piece is increased. The half-cell prepared in comparative example 3 has low capacity retention rate and large expansion rate of the pole piece because the coating of the outer layer carbon nanofiber is not dense, a plurality of pores exist, electrolyte can enter through the pores to directly contact with silicon to form an SEI film, and the SEI film is repeatedly formed along with the charging and discharging, so that the capacity is attenuated, and the expansion rate of the pole piece is increased.
Compared with comparative examples 1 to 3, the half-cell prepared in example 6 has improved capacity retention rate and reduced expansion rate of the electrode plate, but compared with examples 1 to 5, the capacity retention rate and the expansion rate of the electrode plate are reduced, mainly because the content of the carbon fiber in the coating layer is too low, so that the thickness of the coating layer is too low, the coating layer with low thickness is not enough to inhibit the volume expansion of silicon, and cracks occur along with the continuous charging and discharging process, so that the capacity is reduced, and the expansion rate is increased; the half-cell prepared in example 7 has improved capacity retention rate and reduced pole piece expansion rate compared with those of comparative examples 1 to 3, but has reduced capacity retention rate and increased pole piece expansion rate compared with those of examples 1 to 5, mainly because the content of titanium dioxide is too low, the thickness of the outer coating layer is too low, and the volume expansion of silicon cannot be effectively inhibited, so that the capacity is continuously reduced along with the large volume expansion generated in the lithium deintercalation process.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The negative electrode material is characterized by comprising a shell layer and a core, wherein the shell layer comprises carbon nanofibers and titanium dioxide; the core comprises a silicon-based material and a porous carbon material.
2. The anode material according to claim 1, wherein the porous carbon material satisfies at least one of:
a) Specific table of the porous carbon materialArea BET of 200m 2 /g～3000m 2 /g；
B) The pore diameter of the porous carbon material is 0.5 nm-2 mu m;
c) The graphitization degree of the porous carbon material is 30-100%;
d) The median particle diameter Dv50 of the porous carbon material is 5 to 10 [ mu ] m.
3. The negative electrode material as claimed in claim 1, wherein the silicon-based material has a median particle diameter Dv50 of 0.5nm to 10 μm.
4. The anode material of claim 1, wherein the core material comprises a silicon-based material and a porous carbon material, and the silicon-based material is distributed in pores of the porous carbon material;
and/or; the shell layer comprises carbon nanofibers and titanium dioxide, and the titanium dioxide is distributed on gaps and surfaces of the carbon nanofibers.
5. The anode material according to claim 1, wherein the shell layer has a thickness of 20nm to 40nm.
6. The negative electrode material according to claim 1, wherein the carbon nanofibers have a diameter of 10nm to 200nm; and/or the length of the carbon nanofiber is 100 nm-2 mu m.
7. The negative electrode material as claimed in claim 1, wherein the mass of the core is 40-65% of the total mass of the negative electrode material; the mass of the shell layer accounts for 35-60% of the total mass of the negative electrode material.
Preferably, in the negative electrode material, the mass percent a of the silicon-based material is more than or equal to 20% and less than or equal to 40%; and/or in the negative electrode material, the mass percentage content b of the carbon nano fiber is more than or equal to 30% and less than or equal to 50%; and/or in the negative electrode material, the mass percent content c of titanium dioxide is more than or equal to 5% and less than or equal to 30%; and/or in the negative electrode material, the mass percentage content d of the porous carbon material is more than or equal to 20% and less than or equal to 40%.
8. The negative electrode material according to claim 1, wherein the negative electrode material has a diffraction peak 1 in an X-ray powder diffraction (XRD) test in a range of 2 θ =26.4 ° ± 0.5 °, a diffraction peak 2 in a range of 2 θ =28.4 ° ± 0.5 °, and a diffraction peak 3 in a range of 2 θ =25.28 ° ± 0.5 °.
Preferably, the anode material has a Raman shift of 1335-1345 cm in a Raman spectroscopy (Raman) test -1 Has a characteristic Raman peak of 1, 1575-1585 cm -1 A characteristic Raman peak 2 is present, and the ratio x1/x2 of the peak intensity x1 of the characteristic Raman peak 1 and the peak intensity x2 of the characteristic Raman peak 2 satisfies 0.5<x1/x2≤2.0；
And/or the anode material has Raman shift of 501-511 cm in Raman spectrum analysis (Raman) test -1 A characteristic raman peak 3 is present; and/or the anode material has Raman shift of 136-147 cm in Raman spectrum analysis (Raman) test -1 There is a characteristic raman peak 4.
9. A negative electrode sheet comprising the negative electrode material according to any one of claims 1 to 8.
Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode material according to any one of claims 1 to 8.
Preferably, the anode active material layer further includes graphite, hard carbon, or soft carbon, and the graphite includes artificial graphite and/or natural graphite.
10. A battery comprising the negative electrode sheet of claim 9.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116936811A (en) * | 2023-09-18 | 2023-10-24 | 赣州立探新能源科技有限公司 | Negative electrode material, preparation method and application thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116936811A (en) * | 2023-09-18 | 2023-10-24 | 赣州立探新能源科技有限公司 | Negative electrode material, preparation method and application thereof |
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