Negative electrode material and preparation method thereof, negative electrode plate and lithium ion battery
By loading metal compounds on the carbon substrate to form a flat strip fiber negative electrode material, the problems of low capacity and poor stability of the negative electrode material of lithium-ion battery are solved, and higher electrochemical performance and cycling stability are achieved.
Patent Information
- Application Number
- CN202510350169.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-24
- Publication Date
- 2025-07-08
AI Technical Summary
The theoretical specific capacity of the negative electrode materials of existing lithium-ion batteries is low, has poor conductivity, slow kinetic reactions, and large volume changes during charging and discharging, resulting in poor electrochemical performance and cycle stability.
Flat strip fiber anode material is used to load metal compounds on the carbon substrate to form a conductive network, alleviate volume expansion, improve interfacial electron transmission, and improve the electrochemical performance of the material.
It enhances the cycle stability and electrochemical performance of lithium-ion batteries, reduces polarization losses, and improves the electrochemical performance of materials.
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Figure CN120280469A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrochemical materials, and more particularly to a negative electrode material, a preparation method thereof, a negative electrode sheet, and a lithium ion battery. Background Art
[0002] As a secondary energy storage device, lithium ion batteries are widely used in small portable electronic products and electric vehicles, and have extremely high application prospects. A lithium ion battery is composed of four main raw materials: a positive electrode, a negative electrode, a separator, and an electrolyte. Among them, the negative electrode material is one of the key factors affecting the capacity, cycle performance, and rate performance of lithium ion batteries.
[0003] At present, the common negative electrode materials for lithium ion batteries are carbon-based negative electrode materials, including graphite and its derivatives. The theoretical specific capacity of such negative electrode materials is relatively low and cannot meet the requirements of social development. Transition metal compounds (metal oxides, phosphides, sulfides, and selenides) as new electrode materials have received extensive attention due to their high theoretical capacity and low reduction potential. However, these compounds have poor electrical conductivity, slow kinetic reactions, and large volume changes during charge and discharge, resulting in poor electrochemical performance and cycle stability of the materials. Summary of the Invention
[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a negative electrode material, a preparation method thereof, a negative electrode sheet, and a lithium ion battery.
[0005] In a first aspect of the present invention, a negative electrode material is provided. The negative electrode material is a flat strip-shaped fiber, and its components include: a carbon substrate and a metal compound, and the metal compound is loaded on the carbon substrate. Specifically, the form of the metal compound loaded on the carbon substrate includes that the metal compound is coated or encapsulated inside the carbon substrate, and / or the metal compound is exposed on the surface of the carbon substrate to provide active sites.
[0006] According to the negative electrode material of the embodiment of the present invention, it has at least the following beneficial effects: the negative electrode material is a flat strip-shaped fiber, and its components include a carbon substrate and a metal compound loaded on the carbon substrate. The negative electrode material can be used for the preparation of a negative electrode sheet. Among them, by loading the metal compound on the carbon substrate, a structural buffer can be provided for the volume change during the insertion and extraction of lithium ions by the metal compound, alleviating volume expansion, and improving the cycle stability of the material. The flat strip-shaped fiber morphology of the negative electrode material can increase the electrical contact between materials, improve interfacial electron transport, reduce the contact resistance, thereby reducing the polarization loss of the material at high discharge rates and large currents, and improving the electrochemical performance of the material.
[0007] Furthermore, the negative electrode material can generally be used to construct a negative electrode material layer on the surface of the negative electrode current collector of the negative electrode sheet. The negative electrode material with a flat strip-shaped fiber morphology can serve as a structural skeleton in the negative electrode material layer and form a conductive network, which can buffer the volume expansion during the process of lithium ion insertion and extraction, and enhance the interfacial electron transport as a conductive network.
[0008] The negative electrode material is a flat strip-shaped fiber, and its fiber flatness value F can be defined as: F = W / T - 1 > 0, where W represents the width of the fiber radial cross-section, and T represents the thickness of the fiber radial cross-section. The flatness value F of the conventional circular cross-section fiber is equal to 0, and the connection method between the conventional circular cross-section fibers is generally "point-to-point" connection, usually having a large contact resistance and poor interfacial electron transport. For the flat strip-shaped fiber negative electrode material, due to its certain flatness, the contact area between the fibers can be increased, forming a "face-to-face" contact, which can reduce the contact resistance and improve the interfacial electron transport.
[0009] In some embodiments of the present invention, the flatness value F of the flat strip-shaped fiber satisfies: 0 < F = W / T - 1 < 10, where W is the radial cross-sectional width of the flat strip-shaped fiber, 800 nm ≤ W ≤ 2000 nm; T is the radial cross-sectional thickness of the flat strip-shaped fiber, 100 nm ≤ T ≤ 800 nm. For the above flat strip-shaped fiber anode material, the contact area between the fibers is higher, which can further reduce the contact resistance and improve the interfacial electron transport. For example, the flatness value F of the flat strip-shaped fiber can be any value among 0.4, 0.5, 0.8, 1.0, 1.2, 1.5, 1.6, 1.8, 2.0, 2.3, 2.5, 2.7, 2.9, 3.0, 3.1, 3.3, 3.5, 3.6, 3.8, 4.0, 4.2, 4.5, 4.7, 5.2, 5.5, 5.8, 6.0, 6.2, 6.5, 7.0, 7.2, 7.6, 7.8, 8.0, 8.5, 8.8, 9.0, 9.5, 10.0 or the range value of any two of them; W can be any value among 800 nm, 850 nm, 900 nm, 920 nm, 950 nm, 1000 nm, 1100 nm, 1180 nm, 1200 nm, 1250 nm, 1300 nm, 1320 nm, 1350 nm, 1400 nm, 1450 nm, 1500 nm, 1560 nm, 1600 nm, 1650 nm, 1700 nm, 1800 nm, 1850 nm, 1900 nm, 1950 nm, 2000 nm or the range value of any two of them; T can be any value among 100 nm, 120 nm, 150 nm, 200 nm, 250 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 450 nm, 500 nm, 560 nm, 600 nm, 650 nm, 680 nm, 700 nm, 720 nm, 750 nm, 800 nm or the range value of any two of them.
[0010] In some embodiments of the present invention, the anode material is a flat strip-shaped fiber with a porous structure on the surface. Among them, the porous structure on the surface can improve the infiltration of the electrolyte and disperse stress, thereby enhancing the electrochemical performance of the material.
[0011] In some embodiments of the present invention, the metal element in the metal compound is selected from at least one of Mo, W, Cu, Zn, Fe, Co, Ni, Sn, Sb, and Bi.
[0012] In some embodiments of the present invention, the metal element in the metal compound may be selected from at least two of Mo, W, Cu, Zn, Fe, Co, Ni, Sn, Sb, and Bi. Specifically, two or more metal compounds may be added to make the system contain two or more metal elements. Further, the components can be adjusted according to needs. For example, based on the need for high energy density, alloying reaction-type metal elements such as Sn, Sb, and Bi that can participate in the lithium insertion reaction can be selected; for another example, based on the requirement of cycle stability, the proportion of non-lithium insertion active metal elements (such as Fe, Ni, Cu) can be increased. Through the cooperation of multiple metal elements, a multi-level and multi-stage structural buffer can be provided to disperse the stress generated by volume changes and improve the cycle stability of the material.
[0013] In some embodiments of the present invention, the metal compound is selected from a combination of metal phosphides and metal oxides or metal phosphides. Further, the chemical formula of the metal phosphide is MP x , and the chemical formula of the metal oxide is MO y , where 0 < x < 5, 0 ≤ y ≤ 3; M is at least one of Mo, W, Cu, Zn, Fe, Co, Ni, Sn, Sb, and Bi. Among them, the metal phosphide and the metal oxide have a relatively high theoretical capacity, and the metal phosphide can utilize the metal components in-situ generated by the conversion reaction to provide a local conductive network to improve the capacity output of the phosphorus component. However, if only the metal phosphide or a combination of the metal phosphide and the metal oxide is used, the volume effect during the ion insertion and extraction process will limit the performance. By dispersing it in the carbon substrate and coating it with the carbon substrate, the interfacial electron transfer and the cycle performance of the material can be improved. In addition, if the metal compound is a combination of a metal phosphide and a metal oxide, due to the different discharge potential platforms of the metal phosphide and the metal oxide, when the metal phosphide and the metal oxide are dispersed in the carbon substrate, a multi-level and multi-stage structural buffer can also be provided to disperse the stress generated by volume changes and improve the cycle stability of the material. Further, since the metal phosphide has a lower potential and a relatively higher capacity than the metal oxide, if the metal compound is a combination of a metal phosphide and a metal oxide, the content of the metal phosphide can be controlled to be greater than that of the metal oxide.
[0014] In some embodiments of the present invention, by mass percentage, the components of the negative electrode material include: 10% - 90% carbon substrate and 10% - 90% metal compound. For example, in the components of the negative electrode material, the mass percentage content of the carbon substrate can be any value among 10%, 12%, 15%, 18%, 20%, 23%, 25%, 26%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 46%, 48%, 50%, 55%, 60%, 68%, 70%, 75%, 80%, 90% or the range value formed by any two of them; the mass content of the metal compound can be any value among 10%, 20%, 25%, 30%, 42%, 40%, 55%, 52%, 54%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 74%, 75%, 77%, 80%, 82%, 85%, 88%, 90% or the range value formed by any two of them. In the whole system, the carbon substrate serves as a structural carrier and a conductive network, and the metal compound serves as the main active substance.
[0015] In some embodiments of the present invention, the particle size of the metal compound is 20 nm - 100 nm. For example, the particle size of the metal compound can be any value among 20 nm, 30 nm, 50 nm, 80 nm, 100 nm or the range value formed by any two of them.
[0016] In some embodiments of the present invention, the diameter of the carbon substrate is 800 nm - 2000 nm. For example, the diameter of the carbon substrate can be any value among 800 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm, 2000 nm or the range value formed by any two of them. Among them, the statement of the diameter of the carbon substrate refers to the square root of the cross-sectional area of the flat strip-shaped fiber negative electrode material by referring to the circular cross-section fiber.
[0017] Since if the particles of the metal compound are too large and the size of the carbon substrate is too small, the metal compound cannot be loaded on the carbon substrate, by controlling the particle size of the metal compound and the diameter of the carbon substrate within the above ranges, the effective loading of the metal compound on the carbon substrate can be effectively ensured.
[0018] In the second aspect of the present invention, a preparation method of the aforementioned negative electrode material is proposed, including the following steps:
[0019] S1. Mix raw materials including phosphorus-containing polyoxoacid, metal salt, phosphorus-supplementing material, conductive polymer monomer and polymer to prepare a spinning solution with a solvent;
[0020] S2. Perform electrospinning using the spinning solution to obtain spinning fibers;
[0021] S3. Subject the spun fibers to pre-oxidation treatment and sintering treatment in sequence to obtain the anode material.
[0022] In some embodiments of the present invention, in step S1, the phosphorus-containing heteropolyacid is selected from at least one of phosphotungstic heteropolyacid, phosphomolybdic heteropolyacid, and phosphotungstomolybdic heteropolyacid. The above phosphorus-containing heteropolyacids can be used as a phosphorus source, a molybdenum / tungsten source, an oxidant, and a catalyst to initiate the dispersion polymerization of conductive polymer monomers and serve as a dopant for conductive polymers.
[0023] In the above preparation method, the blending of the phosphorus-containing heteropolyacid and the conductive polymer monomer in the spinning solution serves as the basis for forming flat strip-shaped fibers. Moreover, in the case of blending the phosphorus-containing heteropolyacid and the conductive polymer monomer, when the content of the phosphorus-containing heteropolyacid is high, the charge repulsion inside the fiber is strong, and the flatness of the product material is low; while when the content of the phosphorus-containing heteropolyacid is low, the charge repulsion inside the fiber is weak, and the flatness of the product material is high.
[0024] In some embodiments of the present invention, the mass ratio of the phosphorus-containing heteropolyacid to the phosphorus supplement material is 1:3 to 1:8; and / or, the dosage of the metal salt accounts for 10% to 50% of the phosphorus supplement material. By adjusting the raw material composition ratio as above, the surface porous structure and surface morphology of the flat strip-shaped fiber anode material can be controlled, thereby controlling the specific surface area of the material and improving the electrolyte infiltration of the interface.
[0025] In some embodiments of the present invention, the metal salt is selected from at least one of metal chlorides and metal sulfates.
[0026] In some embodiments of the present invention, the conductive polymer monomer is selected from at least one of pyrrole, thiophene, and aniline.
[0027] In some embodiments of the present invention, the high molecular polymer is selected from at least one of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), and polymethyl methacrylate (PMMA).
[0028] In some embodiments of the present invention, the phosphorus supplement material is selected from at least one of phosphoric acid, phosphates, phytic acid, and phytates. In the process of preparing the spinning solution, the phosphorus supplement material can be first mixed with the solvent to obtain a mixed solution, then the phosphorus-containing heteropolyacid is dissolved in the mixed solution, and then the conductive polymer monomer, the high molecular polymer, and the metal salt are added in sequence as above to mix and prepare the spinning solution.
[0029] In some embodiments of the present invention, step S1 includes: dissolving the phosphorus-containing polyheteroacid and the phosphorus supplement material in a solvent; then adding the conductive polymer monomer and mixing evenly; then adding the high molecular polymer, heating and stirring to dissolve at 40 - 60 °C; then adding the metal salt at room temperature and magnetically stirring until dispersed to obtain the spinning solution.
[0030] In some embodiments of the present invention, in step S2, during the electrospinning process, the humidity is controlled to be 20% to 70%, for example, it can be any value among 20%, 25%, 30%, 35%, 40%, 50%, 55%, 60%, 70% or any range value formed by any two of them.
[0031] In some embodiments of the present invention, single-nozzle electrospinning is used for the electrospinning.
[0032] The electrospinning method is used to form polymer nanofibers through the generation and stretching process of charged jets. During the flight of the jets, they experience a series of bending, stretching and jittering processes due to the repulsive force between charges and are accompanied by the volatilization of the solvent and finally solidify to form fibers. By combining a phosphorus-containing heteropolyacid and a metal salt providing a metal element as an internal filling of the polymer fiber to regulate the internal charge distribution, flat strip-shaped fibers with a non-circular cross-section are obtained.
[0033] In step S3, the spun fibers are first pre-oxidized and then sintered at high temperature. Among them, through the pre-oxidation treatment, the polymer can form a non-plastic heat-resistant ladder structure, thereby inhibiting the formation of a large blocky morphology due to the excessive aggregation of the polymer during the high-temperature sintering process.
[0034] In some embodiments of the present invention, in step S3, the pre-oxidation treatment is heating and pre-oxidizing in an air atmosphere at 150 to 300 °C; the sintering treatment is carried out in an inert atmosphere at 500 °C to 1000 °C.
[0035] In some embodiments of the present invention, the time of the pre-oxidation treatment can be controlled within 1 h to 3 h; the time of the sintering treatment can be controlled within 1 h to 10 h.
[0036] In the third aspect of the present invention, a negative electrode sheet is proposed, which includes any one of the foregoing negative electrode materials; or a negative electrode material prepared by the preparation method of any one of the foregoing negative electrode materials.
[0037] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector; the material of the negative electrode material layer includes the negative electrode material.
[0038] In some embodiments of the present invention, the material of the negative electrode material layer further includes a conductive agent and a binder.
[0039] In the fourth aspect of the present invention, a lithium-ion battery is proposed, which includes a positive electrode sheet, a separator and any one of the foregoing negative electrode sheets; the separator is sandwiched between the positive electrode sheet and the negative electrode sheet. Description of the Drawings
[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, where:
[0041] Figure 1 SEM cross-sectional view of the flat strip-shaped fiber prepared in Example 2;
[0042] Figure 2 SEM image of the flat strip-shaped fiber prepared in Example 5;
[0043] Figure 3 SEM image of the conventional circular cross-section fiber in Comparative Example 1. Specific Embodiments
[0044] The concept of the present invention and the technical effects generated will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.
[0045] Example 1
[0046] This example presents a negative electrode material, which is a flat strip-shaped fiber. Its components include a carbon substrate and metal compounds dispersed in the carbon substrate. The metal compounds are tungsten phosphide, tin oxide, and antimony oxide.
[0047] The preparation method of this negative electrode material includes the following steps:
[0048] S1. Add 1 g of phosphotungstic acid (i.e., phosphotungstic heteropolyacid) and 3 g of phosphoric acid to 10 mL of dimethylformamide and stir to dissolve; then add 0.5 mL of thiophene and continue stirring, add 1.2 g of PVP, and heat and stir at 50 °C until completely dissolved; finally, add 0.5 g of stannous chloride and 0.5 g of antimony chloride at room temperature and continue magnetic stirring until completely dispersed to obtain a spinning solution.
[0049] S2. Transfer the prepared spinning solution to a 10 mL syringe, perform electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and receive the spun fibers.
[0050] S3. Heat-treat the spun fibers. Specifically, first pre-oxidize at 200 °C for 2 h in an air atmosphere; then sinter at 700 °C for 5 h in a nitrogen atmosphere to obtain the negative electrode material. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in this negative electrode material is approximately 21.6%, and the weight percentages of tungsten phosphide, tin oxide, and antimony oxide are 32.8%, 24.7%, and 20.9% respectively.
[0051] Example 2
[0052] This example presents a negative electrode material, which is a flat strip-shaped fiber. Its components include a carbon base material and metal compounds dispersed in the carbon base material. Among them, the metal compounds are tungsten phosphide, tin oxide, and antimony oxide.
[0053] The preparation method of this negative electrode material includes the following steps:
[0054] S1. Add 1 g of phosphotungstic acid and 4 g of phytic acid into 10 mL of dimethylformamide and stir to dissolve; then add 0.5 mL of pyrrole and continue stirring, add 1.2 g of PVP, heat and stir at 50 °C until completely dissolved; finally, add 0.4 g of stannous chloride and 0.6 g of antimony chloride at room temperature and continue magnetic stirring until completely dispersed to obtain a spinning solution.
[0055] S2. Transfer the prepared spinning solution into a 10 mL syringe, perform electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 12 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and receive the spun fibers.
[0056] S3. Perform heat treatment on the spun fibers. Specifically, pre-oxidize at 230 °C for 1 h in an air atmosphere first; then sinter at 700 °C for 5 h in a nitrogen atmosphere to obtain the negative electrode material, and its SEM image is shown in Figure 1. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in this negative electrode material is about 20.3%, and the weight percentages of tungsten phosphide, tin oxide, and antimony oxide are 34.2%, 21.2%, and 24.3% respectively.
[0057] Example 3
[0058] This example presents a negative electrode material, which is a flat strip-shaped fiber. Its components include a carbon base material and metal compounds dispersed in the carbon base material. Among them, the metal compounds are tungsten phosphide, nickel phosphide, and tin oxide.
[0059] The preparation method of this negative electrode material includes the following steps:
[0060] S1. Add 1 g of phosphotungstic acid and 8 g of phosphoric acid into 15 mL of dimethylformamide and stir to dissolve; then add 0.5 mL of aniline and continue stirring, add 1.2 g of PVP, heat and stir at 50 °C until completely dissolved; finally, add 0.4 g of stannous chloride and 0.6 g of nickel chloride at room temperature and continue magnetic stirring until completely dispersed to obtain a spinning solution.
[0061] S2. Transfer the prepared spinning solution into a 10 mL syringe, perform electrospinning using a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and collect the spun fibers.
[0062] S3. Heat-treat the spun fibers. Specifically, first pre-oxidize at 200 °C for 2 h in an air atmosphere; then sinter at 700 °C for 5 h in a nitrogen atmosphere to obtain the negative electrode material. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in this negative electrode material is approximately 19.1%, and the weight percentages of tungsten phosphide, nickel phosphide, and tin oxide are 27.6%, 30.2%, and 23.1% respectively.
[0063] Example 4
[0064] This example presents a negative electrode material, which is a flat strip-shaped fiber, and its components include a carbon substrate and metal compounds dispersed in the carbon substrate. Among them, the metal compounds are tungsten phosphide, tin oxide, and copper oxide.
[0065] The preparation method of this negative electrode material includes the following steps:
[0066] S1. Add 1 g of phosphotungstic acid and 4 g of phytic acid to 15 mL of dimethylformamide and stir to dissolve; then add 0.5 mL of aniline and continue stirring, add 1.2 g of PVP, heat and stir at 50 °C until completely dissolved; finally, add 0.25 g of stannous chloride and 0.3 g of copper chloride at room temperature and continue magnetic stirring until completely dispersed to obtain the spinning solution.
[0067] S2. Transfer the prepared spinning solution into a 10 mL syringe, perform electrospinning using a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and collect the spun fibers.
[0068] S3. Heat-treat the spun fibers. Specifically, first pre-oxidize at 200 °C for 2 h in an air atmosphere; then sinter at 800 °C for 3 h in a nitrogen atmosphere to obtain the negative electrode material. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in this negative electrode material is approximately 24.2%, and the weight percentages of tungsten phosphide, tin oxide, and copper oxide are 33.7%, 19.5%, and 22.6% respectively.
[0069] Example 5
[0070] This example presents a negative electrode material, which is a flat strip-shaped fiber, and its components include a carbon substrate and metal compounds dispersed in the carbon substrate. Among them, the metal compounds are tungsten phosphide, tin oxide, and antimony oxide.
[0071] The preparation method of the negative electrode material comprises the following steps:
[0072] S1. Add 1 g of phosphotungstic acid and 4 g of phytic acid into 15 mL of dimethylformamide, stir and dissolve them, then add 0.5 mL of aniline and continuously stir, add 1.2 g of PVP, heat and stir at 50 °C until completely dissolved; finally, add 0.33 g of stannous chloride and 0.33 g of antimony chloride at room temperature and continuously stir magnetically until completely dispersed to obtain a spinning solution.
[0073] S2. Transfer the prepared spinning solution into a 10 mL syringe, carry out electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and collect the electrospun fibers.
[0074] S3. Carry out heat treatment on the electrospun fibers, specifically, pre-oxidize at 200 °C for 2 h in an air atmosphere first; then sinter at 700 °C for 3 h in a nitrogen atmosphere to obtain the negative electrode material, and its SEM image is as Figure 2 shown. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in the negative electrode material is about 23.7%, and the weight percentages of tungsten phosphide, tin oxide, and antimony oxide are 31.9%, 20.1%, and 19.1% respectively.
[0075] Example 6
[0076] This example provides a negative electrode material, which is a flat strip-shaped fiber, and its components include a carbon substrate and metal compounds dispersed in the carbon substrate. Among them, the metal compounds are tungsten phosphide, tin oxide, and nickel oxide.
[0077] The preparation method of the negative electrode material comprises the following steps:
[0078] S1. Add 1 g of phosphotungstic acid and 4 g of phytic acid into 15 mL of dimethylformamide, stir and dissolve them; then add 0.5 mL of aniline and continuously stir, add 1.2 g of PVP, heat and stir at 50 °C until completely dissolved; finally, add 0.7 g of stannous chloride and 0.6 g of nickel chloride at room temperature and continuously stir magnetically until completely dispersed to obtain a spinning solution.
[0079] S2. Transfer the prepared spinning solution into a 10 mL syringe, carry out electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and collect the electrospun fibers.
[0080] S3. Heat-treat the spun fibers. Specifically, first pre-oxidize them at 200 °C for 2 h in an air atmosphere; then sinter them at 900 °C for 2 h in a nitrogen atmosphere to obtain the negative electrode material. Combining thermogravimetric analysis and ICP testing, the weight percentage of the carbon component in this negative electrode material is approximately 21.9%, and the weight percentages of tungsten phosphide, tin oxide, and nickel oxide are 25.2%, 27.0%, and 25.9% respectively.
[0081] Comparative Example 1
[0082] This comparative example presents a negative electrode material, which is a strip-shaped fiber with a circular cross-section. Its preparation method includes the following steps:
[0083] Add 0.5 g of phosphotungstic acid and 1 g of phosphoric acid to 9 mL of dimethylformamide and stir to dissolve; then add 1 g of PVP and heat and stir at 50 °C until completely dissolved; finally, add 0.5 g of stannous chloride at room temperature and continuously stir magnetically until completely dispersed to obtain the spinning solution.
[0084] Transfer the prepared spinning solution into a 10 mL syringe, perform electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and receive the spun fibers.
[0085] Heat-treat the spun fibers. Specifically, first pre-oxidize them at 250 °C for 2 h in an air atmosphere; then sinter them at 600 °C for 2 h in a nitrogen atmosphere to obtain the negative electrode material, and its SEM image is as Figure 3 shown.
[0086] Comparative Example 2
[0087] This comparative example presents a negative electrode material, which is a strip-shaped fiber with a circular cross-section. Its preparation method includes the following steps:
[0088] Add 1 g of PVP to 10 mL of dimethylformamide and heat and stir at 50 °C until completely dissolved to obtain the spinning solution.
[0089] Transfer the prepared spinning solution into a 10 mL syringe, perform electrospinning with a 20G nozzle, and set the electrospinning parameters as follows: negative high voltage -2 kV, positive high voltage 9 - 15 kV, injection speed 0.1 - 0.15 mm / min, receiving distance 10 - 15 cm, and receive the spun fibers.
[0090] Heat-treat the spun fibers. Specifically, first pre-oxidize them at 280 °C for 2 h in an air atmosphere; then sinter them at 600 °C for 2 h in a nitrogen atmosphere to obtain the negative electrode material.
[0091] Relevant tests for examples and comparative examples
[0092] The fiber cross-sectional dimensions and flatness of the negative electrode materials in Examples 1-6 and Comparative Examples 1-2 were tested respectively. The synthesized materials were used as active substances, and lithium sheets were used as counter electrodes for assembling half-cells. The electrolyte was 1M LiPF6 / EC:DEC (volume ratio 1:1), and the charge transfer impedance was tested by AC impedance. Then, at a charge-discharge cut-off voltage of 0.01-1.5V and a charge-discharge current density of 1mA / cm 2 , the cycle efficiency was tested 200 times at 0.5C, and the capacity retention rate of the battery was tested. The results are shown in Table 1.
[0093] Table 1
[0094]
[0095]
[0096] According to Table 1, by comparing Examples 1-3, it can be seen that by adjusting the mass ratio of the phosphorus-containing heteropolyacid (phosphotungstic acid) and the phosphorus-supplementing material (phosphoric acid / phytic acid), the fiber flatness of the negative electrode material can be controlled. The more the amount of the phosphorus-supplementing material, the weaker the charge repulsion inside the fiber, and the higher the fiber flatness; the lower the amount of the phosphorus-supplementing material, the stronger the charge repulsion inside the fiber, and the lower the fiber flatness.
[0097] By comparing Examples 4-6, it can be seen that by maintaining a certain mass ratio of the phosphorus-containing heteropolyacid and the phosphorus-supplementing material and increasing the amount of the metal salt, the fiber flatness of the negative electrode material remains basically unchanged, but the stability of the system can be enhanced, the conductivity can be improved, the cycle capacity retention rate can be increased, and active particles can be exposed on the fiber surface.
[0098] By comparing Examples 1-6 and Comparative Examples 1 and 2, it can be seen that the battery constructed with the flat strip-shaped fibrous negative electrode material including the carbon substrate and the metal compound loaded on the carbon substrate in Examples 1-6 has a lower charge transfer impedance and a higher capacity retention rate.
[0099] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.
Claims
1. A negative electrode material, characterized in that, The negative electrode material is flat strip-shaped fibers, and its components include: a carbon substrate and a metal compound, and the metal compound is loaded on the carbon substrate.
2. The negative electrode material according to claim 1, wherein The metal element in the metal compound is selected from at least one of Mo, W, Cu, Zn, Fe, Co, Ni, Sn, Sb, and Bi; And / or, the metal compound is selected from a combination of a metal phosphide and a metal oxide or a metal phosphide.
3. The negative electrode material according to claim 2, characterized in that, Calculated by mass percentage, its components include: 10% to 90% of the carbon substrate and 10% to 90% of the metal compound.
4. The negative electrode material according to claim 1, wherein The flatness value F of the flat strip-shaped fiber satisfies: 0 < F = W / T - 1 < 10, where W is the radial cross-sectional width of the flat strip-shaped fiber, 800 nm ≤ W ≤ 2000 nm; T is the radial cross-sectional thickness of the flat strip-shaped fiber, 100 nm ≤ T ≤ 800 nm.
5. The negative electrode material according to any one of claims 1 to 4, characterized in that The particle size of the metal compound is 20 nm to 100 nm; and / or, the diameter of the carbon substrate is 800 nm to 2000 nm.
6. The method for preparing the negative electrode material according to any one of claims 1 to 5, characterized in that, It includes the following steps: S1. Mix a raw material including a phosphorus-containing heteropolyacid, a metal salt, a phosphorus supplement material, a conductive polymer monomer, and a high molecular polymer with a solvent to prepare a spinning solution; S2. Perform electrospinning using the spinning solution to obtain spun fibers; S3. Perform pre-oxidation treatment and sintering treatment on the spun fibers in sequence to obtain the negative electrode material.
7. The method for preparing the negative electrode material according to claim 6, wherein, In step S1, the components of the raw material satisfy at least one of the following conditions: The mass ratio of the phosphorus-containing heteropolyacid to the phosphorus supplement material is 1:3 to 1:8; The dosage of the metal salt accounts for 10% to 50% of the mass of the phosphorus supplement material; The phosphorus-containing heteropolyacid is selected from at least one of phosphotungstic heteropolyacid, phosphomolybdic heteropolyacid, and phosphotungstomolybdic heteropolyacid; The conductive polymer monomer is selected from at least one of pyrrole, thiophene, and aniline; The high molecular polymer is selected from at least one of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol, and polymethyl methacrylate; The phosphorus supplement material is selected from at least one of phosphoric acid, phosphate, phytic acid, and phytate; 8. The preparation method of the negative electrode material according to claim 6, characterized in that, In step S2, the humidity during the electrospinning process is controlled at 20% to 70%; And / or, in step S3, the pre-oxidation treatment is carried out by heating pre-oxidation in an air atmosphere at 150 to 300 °C; the sintering treatment is carried out in an inert atmosphere at 500 °C to 1000 °C.
9. A negative electrode sheet, characterized in that, It includes the negative electrode material according to any one of claims 1 to 5, or the negative electrode material prepared by the preparation method of the negative electrode material according to any one of claims 6 to 8.
10. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, a separator, and the negative electrode sheet according to claim 9; the separator is clamped between the positive electrode sheet and the negative electrode sheet.