Low-temperature sodium-ion battery containing modified negative electrode and preparation method and application thereof

Abstract

The application provides a low-temperature sodium ion battery containing a modified negative electrode and a preparation method and application thereof, and the low-temperature sodium ion battery comprises a positive electrode, a negative electrode and an electrolyte; the negative electrode comprises a negative electrode slurry, and the negative electrode slurry comprises an active material, conductive carbon, sodium carboxymethyl cellulose and butadiene styrene rubber; the active material comprises modified hard carbon; the modified hard carbon is prepared by oscillating and mixing hard carbon, single-walled carbon nanotubes, graphite carbon and soft carbon to achieve physical coating, and then oscillating and mixing the physical coating with doped modification precursor powder to achieve element doping and chemical coating through high-temperature calcination; and the electrolyte comprises an additive selected from trimethylsilyl nicotinate, 4-hydroxy-3-methoxycinnamic acid methyl ester and the like. The application improves the adhesion of the negative electrode slurry on the current collector, optimizes the solvent formula to improve the desolvation capacity of sodium ions in the electrolyte and reduce the viscosity, and adds an additive to modify the electrode surface interface film, so that the charge-discharge performance of the battery at low temperature is improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a low-temperature sodium-ion battery with a modified negative electrode, its preparation method, and its application. Background Technology

[0002] The development of large-scale electrical energy storage systems (EESs) is crucial for storing wind, solar, and other intermittent renewable energy sources. Rechargeable lithium-ion batteries (LIBs), with their high energy density, high conversion efficiency, long cycle life, and environmental friendliness, have become the preferred choice for energy storage devices. However, the low abundance, uneven distribution, and rising price of lithium reserves, coupled with its unsatisfactory low-temperature performance, inevitably hinder the application of lithium batteries in extreme low-temperature environments. Therefore, sodium-ion batteries (SIBs) are considered the most promising candidates for EESs because sodium resources are inexpensive, abundant, and share similar physicochemical properties with lithium. Furthermore, compared to lithium... + In comparison, Na + With weaker Lewis acidity and a smaller Stokes radius (4.6 vs. 4.8 Å), sodium-based electrolytes exhibit higher ionic conductivity. However, under extreme low-temperature conditions, the charge transfer kinetics of SIBs deteriorate significantly, leading to a severe decline in electrochemical performance. Electrode materials and electrolytes, as key components of SIBs, are closely related to their charge transfer kinetics, thus profoundly affecting their low-temperature (LT) performance.

[0003] Hard carbon (HC) has attracted widespread attention as a preferred anode material for SIBs. It has been reported that the microstructure of hard carbon changes during continuous charge-discharge processes, leading to alterations in its electrochemical behavior. Hard carbon is an amorphous carbon material composed of short-range ordered but randomly oriented graphite-like crystals and amorphous regions with abundant nanopores and defect sites. By selecting precursors, doping with metals or non-metals, and adjusting pyrolysis temperature or time, the interlayer spacing and size of pseudo-graphite crystallites, the volume and size of nanopores, and the degree of defects in hard carbon can be controlled to some extent, thereby enabling the structural design and electrochemical customization of hard carbon electrodes. However, the electrochemical performance of HC is influenced by a combination of factors, including its volumetric structure, the solvation structure of the electrolyte, and the SEI composition. Therefore, adjusting or designing the electrolyte composition, as well as optimizing the structure of the anode material and the composition of the anode interfacial film, is a viable strategy.

[0004] Experimental and theoretical simulation results show that Na +HC-modified materials can be easily inserted into carbon materials through large interlayer distances and appropriate defects. For example, M-Nx-C and M-Nx-S coordination structures (where M, N, C, and S represent metal, nitrogen, carbon, and sulfur atoms, respectively) can easily modulate the local carbon structure of HC. This has been extensively studied in the field of electrocatalysis. However, the preparation process of HC-modified materials is complex, energy-intensive, and has poor yields. It also needs to be compatible with other auxiliary materials and electrolytes, inevitably leading to problems such as high electrode brittleness, easy cracking, poor adhesion, and poor cycle life at low temperatures. Therefore, developing a negative electrode with good low-temperature adaptability for large-scale industrial application poses a significant challenge to researchers.

[0005] Therefore, a low-temperature sodium-ion battery with a high-performance negative electrode sheet was developed to improve the problems of high brittleness, easy cracking, and poor adhesion of the negative electrode sheet, and to provide a possible way to further improve the LT performance of the battery. Summary of the Invention

[0006] To address the issues of high rigidity, brittleness, and poor adhesion of negative electrode sheets in existing technologies, this invention provides a low-temperature sodium-ion battery with a modified negative electrode, its preparation method, and its application. On one hand, it improves the adhesion of the negative electrode slurry to the current collector; on the other hand, it optimizes the solvent formulation to enhance the desolvation capability of sodium ions in the electrolyte and reduce viscosity; and it adds additives to modify the interface film on the electrode surface, thereby improving the battery's charge-discharge performance (including cycle and first-efficiency performance) at low temperatures.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a low-temperature sodium-ion battery with a modified negative electrode, comprising a positive electrode, a negative electrode and an electrolyte;

[0009] The negative electrode includes a negative electrode slurry, which includes an active material, conductive carbon, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0010] The active material is modified hard carbon, which is prepared by physically coating hard carbon by mixing hard carbon with single-walled carbon nanotubes, graphite carbon and soft carbon in a vortex, and then further mixing and calcining it with doped modified precursor powder to complete element doping modification; the doped modified precursor powder is selected from at least one of tryptone powder, sunflower seed powder, sulfur-containing precursor powder and zinc-rich yeast powder.

[0011] The electrolyte includes a base electrolyte and additives;

[0012] The additive is selected from at least one of trimethylsilyl nicotinate, methyl 4-hydroxy-3-methoxycinnamate, acetazolamide, and tert-butyl (2,5-difluoropyridin-4-yl)carbamate.

[0013] In some embodiments, the negative electrode slurry comprises, by weight percentage, 90-96% active material, 1-5% conductive carbon, 1-5% sodium carboxymethyl cellulose, and 1-5% styrene-butadiene rubber.

[0014] In some embodiments, the mass ratio of the active material, conductive carbon, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in the negative electrode slurry is 94:2:1.5:2.5.

[0015] In some embodiments, the active material is prepared from at least one of the following components: hard carbon, single-walled carbon nanotubes (SWNTs), graphite carbon (GC), and soft carbon (SC). In some embodiments, the active material is prepared from at least one of the following components, by weight percentage: hard carbon 90-96%, single-walled carbon nanotubes 1-5%, graphite carbon 1-5%, and soft carbon 1-5%. In some embodiments, the modified hard carbon is prepared from at least one of the following components: hard carbon, single-walled carbon nanotubes (SWNTs), graphite carbon (GC), and soft carbon (SC). In some embodiments, the modified hard carbon is prepared from at least one of the following components, by weight percentage: hard carbon 90-96%, single-walled carbon nanotubes 1-5%, graphite carbon 1-5%, and soft carbon 1-5%.

[0016] In some embodiments, the hard carbon, regardless of brand, is a type of conventional industrial hard carbon.

[0017] In some embodiments, the single-walled carbon nanotubes (SWNTs) may be any one or two of the following three types: armchair type, serrated type, and chiral type (or spiral type).

[0018] In some embodiments, the graphite carbon (GC) may be either artificial graphite or natural graphite.

[0019] In some embodiments, the soft carbon (SC) may be one or more of petroleum coke, needle coke, carbon fiber, coke, carbon microspheres, pitch, etc.

[0020] In some embodiments, the modified hard carbon preparation process includes: physically coated hard carbon is prepared by oscillating and mixing hard carbon with single-walled carbon nanotubes, graphite carbon and soft carbon, and then further oscillating and mixing with doped modified precursor powder and calcining to complete element doping modification.

[0021] In some embodiments, the calcination temperature is 400~800℃, preferably 400℃, 500℃, 600℃, 700℃, 800℃, or any two of the above values ​​forming a range.

[0022] In some embodiments, the calcination holding time is 1 to 4 hours, preferably 1 hour, 2 hours, 3 hours, 4 hours, or any two of the above values ​​forming a range.

[0023] In some embodiments, the mass ratio of the physically coated hard carbon to the doped modified precursor powder is (10-25):1, preferably 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, and any two of the above values ​​constitute any range.

[0024] In some embodiments, the doped and modified precursor powder is selected from at least one of tryptone powder, sunflower seed powder, sulfur-containing precursor powder, and zinc-rich yeast powder. In some embodiments, the sulfur-containing precursor powder is prepared by mixing and grinding dried scallions, garlic leaves, and onions. In some embodiments, the sulfur-containing precursor powder is prepared by mixing and grinding dried scallions, garlic leaves, and onions in a mass ratio of 1:1:1. In some embodiments, the sunflower seed powder is prepared by mixing and grinding germinated sunflower seeds and pumpkin seeds in a mass ratio of 1:1.

[0025] In some embodiments, the doped modified precursor powder is selected from one of the following combinations: (1) a combination of tryptone powder and sunflower seed powder, (2) a combination of tryptone powder and zinc-rich yeast powder, and (3) a combination of tryptone powder, sunflower seed powder and sulfur-containing precursor powder.

[0026] In some embodiments, the doped modified precursor powder is selected from one of the following combinations: (1) a combination of tryptone powder and sunflower seed powder in a mass ratio of 1:1; (2) a combination of tryptone powder and zinc-rich yeast powder in a mass ratio of 1:1; (3) a combination of tryptone powder, sunflower seed powder and sulfur-containing precursor powder in a mass ratio of 1:1:1.

[0027] In some embodiments, the conductive carbon may be at least one of conductive graphite, conductive carbon black, conductive carbon fiber, and graphene.

[0028] In some embodiments, the conductive carbon is a combination of SP, Kappa100 and single-walled carbon nanotubes in a mass ratio of 1:0.5:0.5.

[0029] In some embodiments, the negative electrode preparation process is as follows: active material, conductive carbon, sodium carboxymethyl cellulose and deionized water are mixed and dispersed, styrene-butadiene rubber is added, degassing is performed, and dispersion is carried out to obtain a negative electrode slurry;

[0030] The negative electrode slurry is coated onto the current collector to obtain the negative electrode.

[0031] In some embodiments, the base electrolyte includes a solvent and a solute.

[0032] In some embodiments, the solvent is selected from at least one of carbonate solvents, organic ether solvents, and carboxylic acid ester solvents. In some embodiments, the carbonate solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). In some embodiments, the organic ether solvent is selected from at least one of chain ethers such as 1,2-dimethoxypropane (DMP), dimethoxymethane (DMM), and ethylene glycol dimethyl ether (DME), and cyclic ethers such as tetrahydrofuran (THF). In some embodiments, the carboxylic acid ester solvent is selected from at least one of methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), and ethyl propionate (EP). In some embodiments, the solvent is a mixture of EMC, PC, EC, and EP in a mass ratio of 60:20:10:10. In some embodiments, the solute is a sodium salt, including but not limited to at least one selected from NaPF6, NaClO4, NaSO3CF3, NaBF4, NaNO3, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4. In some embodiments, the solute is a mixed sodium salt of NaPF6 and NaSO3CF3, with a molar ratio of (6-8):3, preferably 6:3, 7:3, 8:3, or any two of the above values ​​forming a range. In some embodiments, the basic electrolyte uses EMC, PC, EC, and EP as a mixed solvent, and the solute is a mixed sodium salt of NaPF6 and NaSO3CF3. In some embodiments, the base electrolyte uses EMC, PC, EC and EP as mixed solvents in a mass ratio of at least one of 60:20:10:10, 30:30:30:10 or 50:20:20:10, and the solute is a mixed sodium salt of NaPF6 and NaSO3CF3, with NaPF6 concentration of 0.6 M and NaSO3CF3 concentration of 0.3 M.

[0033] In some embodiments, 1 to 6% additives are added to the electrolyte based on the total mass of the base electrolyte, preferably 1%, 2%, 3%, 4%, 5%, 6%, or any two of the above values ​​forming a range.

[0034] In some embodiments, the electrolyte contains an additive that is one of the following combinations: a combination of trimethylsilyl nicotinate and methyl 4-hydroxy-3-methoxycinnamate, a combination of trimethylsilyl nicotinate and acetazolamide, a combination of trimethylsilyl nicotinate and tert-butyl (2,5-difluoropyridin-4-yl)carbamate, a combination of methyl 4-hydroxy-3-methoxycinnamate and acetazolamide, a combination of methyl 4-hydroxy-3-methoxycinnamate and tert-butyl (2,5-difluoropyridin-4-yl)carbamate, or a combination of acetazolamide and tert-butyl (2,5-difluoropyridin-4-yl)carbamate.

[0035] In some embodiments, the additive is one of the following combinations:

[0036] The combination of trimethylsilyl nicotinate and methyl 4-hydroxy-3-methoxycinnamate in a mass ratio of 1:1;

[0037] The combination of trimethylsilyl nicotinate and acetazolamide in a mass ratio of 1:1;

[0038] The combination of trimethylsilyl nicotinate and (2,5-difluoropyridin-4-yl) tert-butyl carbamate in a mass ratio of 1:1;

[0039] A combination of methyl 4-hydroxy-3-methoxycinnamate and acetazolamide in a mass ratio of 1:1;

[0040] A combination of methyl 4-hydroxy-3-methoxycinnamate and tert-butyl (2,5-difluoropyridin-4-yl)carbamate in a mass ratio of 1:1;

[0041] The combination of acetazolamide and (2,5-difluoropyridin-4-yl) tert-butyl carbamate in a mass ratio of 1:1.

[0042] In some embodiments, the active material in the negative electrode slurry accounts for 90-96% by weight, preferably 90%, 92%, 93%, 94%, 95%, 96%, or any two of the above values ​​forming a range.

[0043] In some embodiments, the negative electrode slurry contains 1 to 5% conductive carbon by weight, preferably 1%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming a range.

[0044] In some embodiments, the negative electrode slurry contains 1 to 5% sodium carboxymethyl cellulose by weight percentage, preferably 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming a range.

[0045] In some embodiments, the negative electrode slurry contains styrene-butadiene rubber at a weight percentage of 1-5%, preferably 1%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming a range.

[0046] In some embodiments, the active material / modified hard carbon contains 90-96% hard carbon by weight percentage, preferably 90%, 92%, 93%, 94%, 95%, 96%, or any two of the above values ​​forming a range.

[0047] In some embodiments, the active material / modified hard carbon contains 1 to 5% single-walled carbon nanotubes by weight percentage, preferably 1%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming a range.

[0048] In some embodiments, the active material / modified hard carbon contains 1 to 5% graphite carbon by weight percentage, preferably 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming any range.

[0049] In some embodiments, the active material / modified hard carbon contains 1 to 5% soft carbon by weight percentage, preferably 1%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or any two of the above values ​​forming a range.

[0050] Secondly, the present invention provides a method for preparing the low-temperature sodium-ion battery described herein, wherein,

[0051] (1) Mix the solvent and solute to prepare the basic electrolyte;

[0052] (2) Add additives to the basic electrolyte and mix them evenly to obtain the electrolyte;

[0053] (3) Hard carbon is physically coated by mixing hard carbon with single-walled carbon nanotubes, graphite carbon and soft carbon by vibration. Then, it is further mixed with doped and modified precursor powder by vibration and high temperature calcination to complete element doping and chemical coating, thus obtaining modified hard carbon.

[0054] (4) Modified hard carbon is mixed with conductive carbon, sodium carboxymethyl cellulose and styrene-butadiene rubber to prepare negative electrode slurry;

[0055] (5) Coat the negative electrode slurry onto the current collector, dry it, and form it into a sheet to obtain the negative electrode;

[0056] (6) The obtained electrolyte, positive electrode and negative electrode are used to prepare a low-temperature sodium-ion battery.

[0057] Thirdly, the present invention provides an application of the low-temperature sodium-ion battery described herein in an energy storage device.

[0058] In this invention, "low temperature" means that it can be between -60°C and 0°C, preferably between -40°C and 0°C or between -20°C and 0°C.

[0059] "Low-temperature sodium-ion battery" refers to a sodium-ion battery that can be charged and discharged at temperatures ranging from -60°C to 80°C. In this invention, the preferred temperatures are -40°C to 60°C or -20°C to 60°C.

[0060] In the embodiments, "room temperature" refers to room temperature of 10~40℃, preferably 20~30℃ or 25℃.

[0061] Based on the different hybridization orbitals of carbon atoms (sp, sp) 2 and sp 3 Carbon materials can be broadly classified into several types: graphite carbon (GC), soft carbon (SC), and hard carbon (HC). Hard carbon is typically produced from a fully cross-linked precursor material. Unfortunately, this precursor cannot form a semi-fluid state during pyrolysis. 3 -C bonded graphene sheets lose their sliding ability, making HC extremely rigid yet brittle. GC and SC materials are primarily composed of sp... 2 Composed of carbon atoms, with each layer consisting of hexagonal rings arranged parallel to each other in an ordered, overlapping crystal structure, this ensures excellent conductivity and flexibility. Flexible interlayer connections, linked by covalent bonds or van der Waals forces, endow the three-dimensional network with superelasticity and the ability to deform under extremely low loads, which helps buffer HC lattice deformation at low temperatures and improves the material's adhesion to current collectors. Single-walled carbon nanotubes (SWNTs), formed by rolling up a single layer of graphene, further enhance the electron delocalization ability of carbon materials, reduce internal resistance of powders, and minimize energy loss at low temperatures.

[0062] This invention first physically coats hard carbon with single-walled carbon nanotubes, graphitic carbon, and soft carbon, then mixes it with doping-modified precursor powders, and further completes elemental doping and chemical coating modification through high-temperature calcination. The resulting anode effectively improves the hardness and brittleness of the electrode sheet and enhances adhesion. Doping-modified precursor powders containing P, Zn, N, S, and K are readily available, resulting in low material modification costs. The P-Nx-C, Zn-Nx-C, and P-Nx-S structures obtained after high-temperature doping are beneficial for enriched microporous structures and for Na+ concentration in electrochemical experiments. +By increasing the interlayer distance, reducing defects caused by atomic doping, and achieving appropriate specific surface area and pore volume, the modified HC can simultaneously exhibit high Na+ content in low-temperature electrochemical tests. + With high storage capacity and high ICE, the local electric field (LEF) formed by P-Nx-C, Zn-Nx-C, and P-Nx-S within the graphite domains provides a non-deterministic Coulomb force that attracts the foil, thereby improving the adhesion of the material to the current collector.

[0063] Beneficial effects:

[0064] This invention modifies hard carbon in at least two ways. First, it uses single-walled carbon nanotubes, graphite carbon, and soft carbon for physical coating. Second, it mixes with doped precursor powders and further completes chemical coating and atomic doping through high-temperature calcination, thereby improving the conductivity and flexibility of hard carbon. In the modified negative electrode, the sodium ion diffusion barrier is lowered, the charge transfer resistance of the negative electrode is reduced, promoting ion transport and thus alleviating the capacity decay of the battery at low temperatures, making sodium-ion batteries more suitable for low-temperature applications. The modified negative electrode has higher capacity, first-efficiency, and discharge voltage. The adhesion of the negative electrode material to the current collector and its resistance to external force damage are improved. The electron delocalization ability of the active material is improved, the internal resistance of the powder is reduced, and energy loss is reduced at low temperatures.

[0065] This invention optimizes the solvent system to ensure that the electrolyte does not solidify at -60°C, further improving the desolvation ability of sodium ions in the electrolyte. Trimethylsilyl nicotinate and methyl 4-hydroxy-3-methoxycinnamate are used as additives in the electrolyte to form a thin, inorganic-rich SEI and a rapid interfacial Na+. + Storage kinetics, simultaneously triggering local electric fields (LEF) formed by P-Nx-C, Zn-Nx-C, and P-Nx-S within the graphite domains, provides a non-deterministic Coulomb force, accelerating the Na₂O₅ mass. + Storage kinetics, reducing diffusion barriers and thus improving cycling at low temperatures.

[0066] This invention improves the electrolyte and negative electrode, enabling sodium-ion batteries to have better low-temperature charge-discharge capabilities, namely, cycle life and first-efficiency performance. Attached Figure Description

[0067] Figure 1 The following are the results of the adhesion test of the negative electrode sheet in Example 2. (a) is the HC negative electrode sheet; (b) is the HC-1 negative electrode sheet; (c) is the HC-2 negative electrode sheet; and (d) is the HC-3 negative electrode sheet.

[0068] Figure 2 The graph shows the viscosity test results of the electrolyte in Example 3 at different temperatures. (a) is 25℃; (b) is -20℃; and (c) is -60℃.

[0069] Figure 3 The graph shows the capacity retention rate of the half-cell prepared by the negative electrode sheet in Example 4 at -10°C.

[0070] Figure 4 The following are the appearance diagrams of the negative electrode sheet in Example 5. (a) Negative electrode sheet without cracks, (b) Negative electrode sheet with cracks.

[0071] Figure 5 This is a graph showing the first charge-discharge capacity-voltage curve of the battery prepared from the crack-free negative electrode sheet in Example 5.

[0072] Figure 6 This is a charge-discharge curve of the battery prepared with a cracked negative electrode sheet in Example 5.

[0073] Figure 7 This is a diagram showing the percentage of constant current and constant voltage in the battery prepared from the crack-free negative electrode sheet in Example 5.

[0074] Figure 8 This is a graph showing the percentage of constant current and constant voltage in the battery prepared with a cracked negative electrode sheet in Example 5.

[0075] Figure 9 This is a comparison chart of the ramp capacity and plateau capacity ratio during the first charge and discharge of the battery prepared from the crack-free negative electrode sheet in Example 5.

[0076] Figure 10 This is a comparison chart of the ramp capacity and plateau capacity ratio during the first charge and discharge of the battery prepared with the cracked negative electrode sheet in Example 5.

[0077] Figure 11 The Nyquist plot of the negative electrode half-cell prepared in Example 5 at -20°C.

[0078] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Detailed Implementation

[0079] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0080] I. Chemicals and Instruments

[0081] Dimethyl carbonate (DMC, 99.9%) was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; ethylene carbonate (EC, 99%) and propylene carbonate (PC, 99.5%) were purchased from Shanghai E. En Chemical Technology Co., Ltd.; sodium hexafluorophosphate (NaPF6, 99.9%), ethyl propionate (EP, 99.5%), sodium trifluoromethanesulfonate (NaSO3CF3, 98%), ethyl methyl carbonate (EMC, 98%), polyvinylidene fluoride (PVDF, melt viscosity (K Poise): 23.5~29.5), sodium carboxymethyl cellulose (CMC, viscosity: 600-3000 mPa s), and polystyrene-butadiene copolymer (SBR) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; tryptone was purchased from Beijing Bairddi Biotechnology Co., Ltd. (OXOID). LP0042B); Zinc-enriched yeast powder was purchased at https: / / e.tb.cn / h.SspQMn2NKPG8Ajo?tk=7cLCf82HLI1 CZ057 "Zinc-enriched yeast powder"; scallions, garlic leaves, onions, sunflower seeds, and pumpkin seeds were purchased at the local market.

[0082] The following equipment was purchased: Vortex mixer (LC-Vortex-P2E) from Zhejiang Lichen Scientific Instruments Co., Ltd.; Battery tester (CT-4008-5VA-SI) from Shenzhen Xinwei Electronics Co., Ltd.; Electrochemical workstation (CHI660E) from Shanghai Chenhua Instrument Technology Co., Ltd.; Vacuum mixer (SFM) and electrode punching machine (JK20140311) from Hefei Kejing Materials Technology Co., Ltd.; Vacuum oven (DZF-6020BZ) from Shanghai Yixin Scientific Instruments Co., Ltd.; Super (1220 / 750 / 900) super cleanroom glove box from Shanghai Mikelona Electromechanical Technology Co., Ltd.; Button battery hydraulic sealing machine PX-HS-20 from Shenzhen Pengxiang Yunda Co., Ltd.; High and low temperature test chamber (LRHS-800B-L) from Shanghai Linpin Instrument Co., Ltd.

[0083] II. General operations are as follows:

[0084] 1. Preparation of electrode sheets

[0085] 1) Preparation of element-doped modified precursor powder

[0086] Nitrogen: Tryptone is a dried yeast autolysate, rich in nitrogen. Take an appropriate amount and dry it in a vacuum drying oven at 50-65℃ for 5-7 days, then grind it into powder to obtain tryptone powder for later use.

[0087] Zinc: Biogenic zinc, also known as protein zinc, is, as the name suggests, a combination of protein and zinc. The bond between them can be a covalent compound or a chelate compound primarily composed of coordinate bonds. Zinc-enriched yeast powder is dried in a vacuum drying oven at 50-65℃ for 5-7 days, then ground into powder to obtain zinc-enriched yeast powder for later use.

[0088] Sulfur elements, such as allyl sulfide in onions and garlic, allicin mainly found in garlic and onions, and diallyl disulfide, an oily liquid with a distinctive garlic-like odor, are all readily available organic sulfur sources from nature. After washing onions, garlic leaves, and onions with deionized water, they are cut into small pieces with scissors and air-dried at room temperature for 7 days. Then, they are dried in a vacuum drying oven at 45°C for 48 hours. The mixture is weighed in a 1:1:1 ratio and ground into powder in a mortar to obtain sulfur-containing precursor powder for later use.

[0089] Phosphorus: Sunflower seeds or pumpkin seeds contain about 45% phosphorus. Soak sunflower seeds and pumpkin seeds in clean water for 3-5 days until the seeds germinate, then wash them with deionized water 3-5 times, air dry them at room temperature for 7 days, and then dry them under vacuum at 45-65℃ for 3-5 days. Then mix them in a 1:1 mass ratio and grind them into powder to make sunflower seed powder as a natural phosphorus supplement.

[0090] 2) Preparation of physically coated hard carbon

[0091] Take hard carbon, single-walled carbon nanotubes (SWNT), graphite carbon (GC), and soft carbon (SC) in a mass ratio of 95:1:2:2. Among them, the hard carbon material is not limited to any brand and is a type of conventional industrial hard carbon; the single-walled carbon nanotubes (SWNT) can be any one or two of the three types: armchair type, serrated type, and chiral type (or spiral type); the graphite carbon (GC) can be any one of artificial graphite and natural graphite; the soft carbon (SC) can be one or more of the following: petroleum coke, needle coke, carbon fiber, coke, carbon microspheres, asphalt, etc.

[0092] After weighing the above materials according to the proportions, they can be sealed in centrifuge tubes and shaken on a vortex mixer for 10-30 minutes to ensure that the powder is mixed evenly to obtain physically coated hard carbon (PCHC).

[0093] 3) Preparation of modified hard carbon

[0094] ① According to experimental needs, tryptone powder and sunflower seed powder in a 1:1 mass ratio were ground in a mortar to obtain NP precursor powder. 50 mg of NP precursor powder and 950 mg of physically coated hard carbon (PCHC) were weighed into a centrifuge tube and mixed by vortex mixing for 5 min. The mixture was then placed in a porcelain boat and placed in a muffle furnace. Using nitrogen as a protective gas, the furnace was calcined at a rate of 1-5 °C / min at a temperature of 400-800 °C for 1-4 h. Once the furnace temperature dropped to 40-60 °C, the calcined carbon was removed for later use, yielding modified hard carbon HC-1. The nitrogen source is tryptone powder, and the phosphorus source is sunflower seed powder. Obtaining nitrogen or phosphorus sources from organisms or plants results in high enrichment rates, is harmless to the human body, and is green and pollution-free. It can convert inorganic N and P elements into organic forms, making the elements stable.

[0095] ② According to experimental requirements, tryptone powder and zinc-enriched yeast powder in a 1:1 mass ratio were ground in a mortar to obtain N-Zn precursor powder. 50 mg of N-Zn precursor powder and 950 mg of PCHC were weighed into a centrifuge tube and mixed by vortex mixing for 5 min. The mixture was then placed in a ceramic boat and placed in a muffle furnace with nitrogen as the protective gas. The heating rate was 1-5 °C / min, the high-temperature calcination temperature was 400-800 °C, and the holding time was 1-4 h. Once the furnace temperature dropped to 40-60 °C, the mixture was removed for later use, yielding modified hard carbon HC-2. The nitrogen source is tryptone powder, and the zinc source is zinc-enriched yeast powder. Bio-based organic N and Zn can better flow onto the surface of carbon materials or penetrate into crevices at high temperatures. Furthermore, compared to inorganic nitrogen-containing compounds and zinc-containing compounds, which require higher activation and bond energies for ionic bond breaking, organic N and Zn compounds facilitate elemental doping reactions.

[0096] ③ According to experimental requirements, tryptone powder, sunflower seed powder, and sulfur-containing precursor powder in a mass ratio of 1:1:1 were ground in a mortar to obtain NPS precursor powder. 50 mg of NPS precursor powder and 950 mg of PCHC were weighed into a centrifuge tube and mixed in a vortex mixer for 5 min. The mixture was then placed in a porcelain boat and placed in a muffle furnace with nitrogen as the protective gas. The heating rate was 1~5℃ / min, the high-temperature calcination temperature was 400~800℃, and the holding time was 1~4h. When the temperature in the furnace dropped to 40~60℃, it could be taken out for use to obtain carbon-coated PNS-doped modified hard carbon HC-3.

[0097] In this embodiment, a simple initial oscillation is used to achieve physical coating, followed by high-temperature chemical coating and atomic doping to improve the conductivity and flexibility of the hard carbon powder.

[0098] The unmodified active material is hard carbon.

[0099] 4) Preparation of negative electrode slurry

[0100] Take the active material, conductive carbon, CMC, and SBR, and weigh them according to the mass ratio of active material: conductive carbon: CMC: SBR = 94:2:1.5:2.5. The amount of active material can be adjusted appropriately according to experimental requirements. Pour the weighed negative electrode powder active material, conductive carbon, and CMC into the mixing tank of a vacuum mixer, add deionized water as solvent, disperse to a solid content of 40-45%, disperse for 100-150 min, and disperse at 10 rpm. Then adjust the viscosity by adding deionized water as solvent, to a solid content of 30-35%, disperse for 10-30 min, and disperse at 10 rpm. Then add SBR and degas for 10-15 min at a dispersion speed of 2-5 rpm to obtain the slurry.

[0101] The conductive carbon can be one or more of conductive graphite, conductive carbon black, conductive carbon fiber and graphene, preferably a combination of SP, Kappa100 and single-walled carbon nanotubes.

[0102] 5) Preparation of negative electrode sheet

[0103] The slurry is scraped onto the current collector. The slurry can be scraped once or twice. Modified negative electrode slurry can be scraped first, and then unmodified negative electrode slurry can be scraped after it dries. There are no restrictions on drying time and drying temperature. The current collector can be aluminum foil or copper foil, and there are no restrictions on thickness. Preferably, it is 6 µm copper foil.

[0104] When performing electrode adhesion tests, the electrodes are cut to a width of 6 cm and a length of 15 cm.

[0105] When assembling batteries, electrode punching machines are used to punch electrodes into round pieces with a diameter of 1.2 cm.

[0106] 2. Preparation of electrolyte

[0107] The electrolyte includes sodium salts, solvents, and additives. Sodium salts include, but are not limited to, NaPF6, NaClO4, NaSO3CF3, NaBF4, NaNO3, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4; preferably, a mixture of NaPF6 and NaSO3CF3 sodium salts in a molar ratio of 6:3; the solvent can be a carbonate solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc., or... It is an organic ether solvent, such as chain ethers like 1,2-dimethoxypropane (DMP), dimethoxymethane (DMM), and ethylene glycol dimethyl ether (DME), and cyclic ethers like tetrahydrofuran (THF), or a carboxylic acid ester solvent, such as methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), and ethyl propionate (EP). The preferred solvent is a mixture of EMC, PC, EC, and EP in a mass ratio of 60:20:10:10. The additive is selected from one or a mixture of two of the following: trimethylsilyl nicotinate, methyl 4-hydroxy-3-methoxycinnamate, acetazolamide, and tert-butyl (2,5-difluoropyridin-4-yl)carbamate.

[0108] All electrolyte preparations were completed in a glove box with an oxygen content of less than 0.1 ppm. Solid powders were dried in the glove box for 7 to 10 days, and liquid reagents were dehydrated by adding molecular sieves for 2 to 3 days.

[0109] The battery assembly followed standard procedures. The basic electrolyte formulation was a mixed solvent of EMC, PC, EC, and EP in a mass ratio of 60:20:10:10. The sodium salt in the solvent was a mixture of NaPF6 and NaSO3CF3, with NaPF6 concentration at 0.6 M and NaSO3CF3 concentration at 0.3 M. This was designated Electrolyte No. 1. The control electrolyte was a mixed solvent of EMC, PC, EC, and EP in a mass ratio of 30:30:30:10. The sodium salt in this solvent was also a mixture of NaPF6 and NaSO3CF3, with NaPF6 concentration at 0.6 M and NaSO3CF3 concentration at 0.3 M. M is named Electrolyte No. 2; the electrolyte comparison sample is a mixed solvent with the following formula: EMC, PC, EC and EP, with a mass ratio of 50:20:20:10. The sodium salt in the solvent is a mixed sodium salt of NaPF6 and NaSO3CF3, with the concentration of NaPF6 being 0.6M and the concentration of NaSO3CF3 being 0.3M. This is named Electrolyte No. 3.

[0110] When assembling the battery, an electrode punching machine is used to punch it into a disc with a diameter of 1.2 cm. The mass of active material is 2.1 mg, the standard specific capacity is 300 mAh / g, the charging current is 0.063 mA, and the cutoff voltage is 2 V. The discharge process adopts constant current and constant voltage. The discharge current in the constant current stage is 0.063 mA, and the voltage cutoff voltage is 0.02 V.

[0111] Example 1:

[0112] (1) Take hard carbon (HC), single-walled carbon nanotubes (SWNT), graphite carbon (GC), and soft carbon (SC) in a mass ratio of 95:1:2:2. The single-walled carbon nanotubes (SWNT) are armchair type; the graphite carbon (GC) is artificial graphite; and the soft carbon (SC) is petroleum coke. After weighing the above powders according to the proportions, package them in centrifuge tubes and shake them on a vortex mixer for 20 minutes to ensure that the powders are mixed evenly to obtain a mixed powder, so as to achieve a simple physical coating purpose.

[0113] ① According to experimental requirements, tryptone powder and sunflower seed powder in a mass ratio of 1:1 were ground in a mortar to obtain NP precursor powder; 50 mg of NP precursor powder and 950 mg of PCHC were weighed into a centrifuge tube, and mixed by vortex mixing for 5 min. The mixture was then placed into a porcelain boat and placed in a muffle furnace with nitrogen as the protective gas. The heating rate was 5℃ / min, the high-temperature calcination temperature was 600℃, and the holding time was 2 h. When the temperature inside the furnace dropped to 60℃, it could be taken out for use to obtain modified hard carbon HC-1.

[0114] ② According to experimental requirements, tryptone powder and zinc-enriched yeast powder in a mortar were ground in a 1:1 mass ratio to obtain N-Zn precursor powder. 50 mg of N-Zn precursor powder and 950 mg of PCHC were weighed into a centrifuge tube and mixed in a vortex mixer for 5 min. The mixture was then placed in a porcelain boat and placed in a muffle furnace with nitrogen as the protective gas. The heating rate was 3 °C / min, the high-temperature calcination temperature was 600 °C, and the holding time was 3 h. When the temperature inside the furnace dropped to 50 °C, it could be taken out for use to obtain modified hard carbon HC-2.

[0115] ③ According to experimental requirements, tryptone powder, sunflower seed powder, and sulfur-containing precursor powder in a mass ratio of 1:1:1 were ground in a mortar to obtain NPS precursor powder. 50 mg of NPS precursor powder and 950 mg of PCHC were weighed into a centrifuge tube and mixed by vortex mixing for 5 min. The mixture was then placed in a porcelain boat and placed in a muffle furnace with nitrogen as the protective gas. The heating rate was 2℃ / min, the high-temperature calcination temperature was 600℃, and the holding time was 4 h. When the temperature in the furnace dropped to 40℃, it could be taken out for use to obtain carbon-coated PNS-doped modified hard carbon HC-3.

[0116] The modified active substances obtained by modification are modified hard carbon 1 (hard carbon HC-1), modified hard carbon 2 (hard carbon HC-2), and modified hard carbon 3 (hard carbon HC-3).

[0117] The unmodified active material is hard carbon (HC).

[0118] (2) Slurry preparation: Take active material, conductive carbon, CMC and SBR, and weigh them according to the mass ratio of active material: conductive carbon: CMC: SBR = 94: 2: 1.5: 2.5. The conductive carbon is a mixture of SP, Kappa100 and single-walled carbon nanotubes, with a mass ratio of 1: 0.5: 0.5.

[0119] The weighed active material, conductive carbon, and CMC were poured into the mixing tank of a vacuum mixer. Deionized water was added as solvent to disperse the solids content to 42%, with a dispersion time of 120 min and a dispersion speed of 10 rpm. The viscosity was then adjusted by adding more deionized water to achieve a solids content of 33%, with a dispersion time of 20 min and a dispersion speed of 10 rpm. SBR was then added for degassing, with a degassing time of 12 min and a dispersion speed of 3 rpm, resulting in the slurry.

[0120] Based on the different active substances, the prepared slurries are named as shown in Table 1 below:

[0121]

[0122] (3) Electrode preparation

[0123] The slurry was applied in one pass onto a 6 µm current collector. For the electrode adhesion test, the electrode was cut to a width of 6 cm and a length of 15 cm. The electrode was thus obtained.

[0124] (4) Electrolyte preparation

[0125] All electrolyte preparations were completed in a glove box with an oxygen content of less than 0.1 ppm. Solid powders were dried in the glove box for 7-10 days, and liquid reagents were dehydrated by adding molecular sieves for 2-3 days.

[0126] The basic electrolyte formulation is a mixed solvent of EMC, PC, EC and EP in a mass ratio of 60:20:10:10. The sodium salt in the solvent is a mixed sodium salt of NaPF6 and NaSO3CF3, with a NaPF6 concentration of 0.6 M and a NaSO3CF3 concentration of 0.3 M. This is named electrolyte No. 1.

[0127] The electrolyte comparison sample was a mixed solvent with the following formulation: EMC, PC, EC and EP in a mass ratio of 30:30:30:10. The sodium salt in the solvent was a mixed sodium salt of NaPF6 and NaSO3CF3, with a NaPF6 concentration of 0.6 M and a NaSO3CF3 concentration of 0.3 M. This was named electrolyte No. 2.

[0128] The electrolyte comparison sample was a mixed solvent with the following formulation: EMC, PC, EC and EP in a mass ratio of 50:20:20:10. The sodium salt in the solvent was a mixed sodium salt of NaPF6 and NaSO3CF3, with a concentration of 0.6 M for NaPF6 and 0.3 M for NaSO3CF3. This was named electrolyte No. 3.

[0129] (5) Battery assembly

[0130] The button cell assembly followed standard procedures. During assembly, the electrodes and sodium plates prepared in Example 1 were used. The electrodes were punched into 1.2 cm diameter discs using a punching machine. The active material mass was 2.1 mg, the standard specific capacity was 300 mAh / g, the charging current was 0.063 mA, cutoff at 2 V, and the discharge process employed constant current and constant voltage. During the constant current phase, the discharge current was 0.063 mA, and the voltage cutoff was 0.02 V.

[0131] Example 2: Electrode Adhesion Test

[0132] The cross-cut adhesion test, based on a physical destructive method, assesses the adhesion between the current collector and the active electrode material of a battery. The procedure involves using a specialized cross-cutting tool to create a uniform grid on the coating surface, covering it with pressure-sensitive adhesive tape, and then quickly peeling it off. The percentage of the coating area that has detached is observed. A smaller detached area indicates a higher adhesion grade. Results are determined according to ISO standards: Grade 0 (no detachment), Grade 1 (detachment ≤ 5%), Grade 2 (detachment 5%–15%), Grade 3 (detachment 15%–35%), Grade 4 (detachment 35%–65%), and Grade 5 (detachment > 65%). For squares with blurred boundaries, they are treated as complete squares. Test results are as follows: Figure 1 As shown.

[0133] Figure 1 The images show the adhesion tests for HC, HC-1, HC-2, and HC-3 negative electrode sheets, respectively. The left side shows the scratches left by a cross-cut adhesion tester on the negative electrode sheet, and the right side shows the adhesion after transparent tape was applied and then removed. Clearly, the adhesion of the untreated HC electrode sheet, after being scratched by the cross-cut adhesion tester... Figure 1(See left image a). Level 1 detachment had already occurred, while electrodes prepared with other modified carbon materials did not show detachment. When the pressure-sensitive tape was peeled off the electrode, HC showed Level 4 detachment. The detachment rates of electrodes HC-1, HC-2, and HC-3 were Level 2, Level 1, and Level 2 detachment, respectively, indicating that the modification treatment of the carbon material was effective. It is possible that the local electric field (LEF) formed by P-Nx-C, Zn-Nx-C, and P-Nx-S within the graphite domains provides a non-deterministic Coulomb force, attracting the foil and improving the adhesion of the material to the current collector.

[0134] Example 3 Electrolyte viscosity test:

[0135] In selecting the electrolyte solvent, the solvent needs to have a high dielectric constant and relatively high polarity of its molecules to ensure complete dissolution of the sodium salt, allowing it to dissociate into sodium ions and the corresponding anions. The solvent viscosity should be as low as possible to ensure conductivity; high viscosity reduces the fluidity of the liquid. It should also be compatible with all phases / components of the sodium-ion battery. The liquid temperature range of the electrolyte is largely determined by the solvent. Therefore, EMC (low viscosity and melting point), EP (low viscosity, melting point, and density), EC (high dielectric constant), and PC (wide temperature range and high dielectric constant) were selected. The specific physicochemical properties of the solvents are shown in Table 2.

[0136]

[0137] To analyze the effect of different solvent ratios on the rheological properties of electrolytes at different temperatures, viscosity tests were conducted on electrolytes prepared with the same solvent in different ratios.

[0138] Electrolyte viscosity test at different temperatures: After standing for 4 hours at 25 ℃, -20 ℃, and -60 ℃ respectively, the reagent bottles were removed, the surface of the bottles was wiped clean of water droplets, and photographed for comparison. Figure 2 As shown.

[0139] Depend on Figure 2 As can be seen from this, electrolytes 1, 2, and 3 all exhibit good fluidity at room temperature (25℃).

[0140] Figure 2 b shows that at -20℃, no scraping occurred when the reagent bottle was inverted. This may be because the ratio of high-viscosity, high-melting-point PC and EC, each at 30%, led to a decrease in the overall solvent viscosity, resulting in poor flowability.

[0141] but Figure 2The data shows that at -60℃, electrolyte #2 exhibited severe crystallization, almost completely reducing it to a liquid state. Electrolyte #3 showed bottom wall scraping, with the supernatant becoming turbid and showing some micro-crystals. This indicates that the solvent ratios for electrolytes #2 and #3 are unsuitable at the extremely low temperature of -60℃. However, electrolyte #1 did not exhibit crystallization or wall scraping at -60℃ and remained liquid, which is beneficial for the dissociation of sodium salts and the desolvation of sodium ions, demonstrating that electrolyte #1 is adaptable to extremely low temperatures.

[0142] In summary, by optimizing the electrolyte solvent formulation, the problem of crystallization or loss of fluidity in sodium-ion batteries at low temperatures was effectively improved. Experiments have demonstrated that the No. 1 electrolyte provided in this embodiment does not solidify at -60°C, exhibiting excellent low-temperature adaptability.

[0143] Example 4: Comparative Test of Low-Temperature Performance of Electrolytes

[0144] To further improve the low-temperature performance of the electrolyte, electrolyte No. 1, which already exhibited good fluidity at low temperatures, was modified. The additives included one or more of the following: trimethylsilyl nicotinate (2% by weight of electrolyte No. 1), methyl 4-hydroxy-3-methoxycinnamate (2% by weight of electrolyte No. 1), acetazolamide (2% by weight of electrolyte No. 1), and tert-butyl (2,5-difluoropyridin-4-yl)carbamate (2% by weight of electrolyte No. 1). Specific combinations are detailed in Table 3. The battery was assembled according to the method described in Example 1, using HC-1 electrodes. The single variable factor in the experiment was the electrolyte.

[0145]

[0146] The corresponding electrolyte was then injected into the coin cell, and HC-1 electrodes were assembled. The cells were cycled 100 times at a rate of 0.05C within a voltage range of 0-2V at -10℃. The cycle capacity retention was recorded. Figure 3 .

[0147] Depend on Figure 3It is evident that the presence of a single additive can effectively improve battery capacity retention. Adding two additives together does not necessarily yield better results than adding a single additive. However, the combined effects of 2% trimethylsilyl nicotinate and 2% methyl 4-hydroxy-3-methoxycinnamate, and 2% trimethylsilyl nicotinate and 2% acetazolamide, are superior to those of single additives. Specifically, for the additive-free No. 1 battery, after 100 cycles at a rate of 0.05 within a voltage range of 0-2V at -10℃, its capacity retention was only 82.37%. The capacity retention rates for No. 1-1, No. 1-2, No. 1-3, and No. 1-4 batteries were 92.74%, 89.96%, 87.78%, and 90.09%, respectively. The capacity retention rates of batteries 1-5 and 1-6 were 96.91% and 95.04%, respectively, indicating that silane, nicotinic acid ester, aminosulfonyl, acetamide, etc., can synergistically optimize the composition of the negative electrode interface film in carbonate and carboxylic acid ester solvents. The use of additives also needs to consider their compatibility with other reagents in the electrolyte and negative electrode materials. It is not that adding two reagents with good single effects will achieve better results. For example, the capacity retention rates of batteries 1-7, 1-8, 1-9, and 1-10 are not as good as those added alone. Only two compatible additives can achieve better results.

[0148] The above electrolyte formulation experiment is not limited to an additive mass ratio of 1:1, not limited to an addition amount of 2% of the total electrolyte mass, and not limited to an HC-1 negative electrode.

[0149] As can be seen from Example 4, the electrolyte obtained by this invention improves the compatibility with electrode materials and also improves the capacity retention of the battery after low-temperature cycling. By introducing suitable additives into the base electrolyte and optimizing the composition of the electrode surface interface film, the interfacial ion transport kinetics are effectively improved. The synergistic effect between the various components also slows down the capacity decay of the battery during charge-discharge at -10℃. An optimal electrolyte formulation with good low-temperature adaptability, good electrode interface stability, and good compatibility with electrode materials has been developed, and it is effectively compatible with the negative electrode sheet prepared in Example 1.

[0150] Example 5 Electrochemical performance test of electrode with or without cracks

[0151] (1) Prepare smooth HC negative electrode sheets, HC-1 negative electrode sheets, HC-2 negative electrode sheets, and HC-3 negative electrode sheets according to the normal coating process. Cut half of the electrode sheets into 1.2 cm round pieces. Then shake the remaining half of the electrode sheet up and down and left and right 5 times in the air. Wrinkles will appear in the current collector, and cracks will appear in the electrode sheet. The collected electrode sheets are as follows: Figure 4 As shown.

[0152] Figure 4a, from left to right, are HC negative electrode, HC-1 negative electrode, HC-2 negative electrode, and HC-3 negative electrode. Figure 4 b represents the corresponding cracked electrode. After being damaged by external force, the surface of the electrode shows uneven marks of varying degrees. This may be due to the fact that the copper foil of the negative current collector is particularly thin and soft. When the electrode is shaken, it deforms. This may be caused by uneven stress on the material coated on the electrode.

[0153] (2) Assemble them into button cells. The electrolyte used is electrolyte No. 1-5 selected in Example 4. In the voltage range of 0-2V, charge at a constant current rate of 0.1C and discharge at a constant current and constant voltage rate of 0.1C. Obtain charge and discharge curves respectively.

[0154] Figure 5 , Figure 6 The figures show the initial charge-discharge capacity-voltage curves for the HC negative electrode, HC-1 negative electrode, HC-2 negative electrode, and HC-3 negative electrode with and without cracks.

[0155]

[0156] Figure 5 As shown in Table 4, the reversible capacity of the battery prepared with the unmodified HC anode under flat and healthy electrode conditions is 301.44 mAh / g, and the initial discharge efficiency is 90.3%. The reversible capacities of the batteries prepared with HC-1, HC-2, and HC-3 anode electrodes are 309.32 mAh / g, 321.46 mAh / g, and 318.73 mAh / g, respectively; the initial discharge efficiencies are 90.78%, 91.75%, and 91.02%, respectively. It is evident that the anode capacity of the batteries prepared with the treated anode electrodes all shows a certain increase. This may be because atoms such as N, S, P, and Zn have larger atomic radii than C, which can increase the interlayer spacing of carbon materials, facilitating the insertion and extraction of sodium ions and improving their electrochemical performance.

[0157] When the unmodified HC negative electrode sheet is damaged and deformed by external force, the material is subjected to stress in different directions, resulting in wrinkles of varying degrees, accompanied by cracks that are invisible to the naked eye. Figure 6The reversible capacities of batteries prepared from HC, HC-1, HC-2, and HC-3 anode electrodes with cracks were 253.25 mAh / g, 264.18 mAh / g, 302.55 mAh / g, and 276.39 mAh / g, respectively, with initial discharge efficiencies of 88.03%, 89.18%, 91.29%, and 90.61%, respectively. This indicates a decrease in both capacity and initial efficiency of the anode. The batteries prepared with HC anodes showed the largest reductions in capacity and initial efficiency, at 48.19 mAh / g and 2.75%, respectively; the batteries prepared with HC-2 anodes showed the smallest reduction in capacity, at 18.91 mAh / g, while the initial efficiency remained almost unchanged. Electrodes made from unmodified hard carbon exhibited significant contact resistance due to the rigidity and brittleness of the hard carbon itself, leading to substantial degradation in electrochemical performance when subjected to external forces between materials or between the material and the current collector. In contrast to the negative electrode of HC, the electrode made of modified carbon material, although also damaged by external forces, may only experience deformation of the current collector. The modified carbon material adheres tightly to the current collector, likely due to the introduction of N / S / P / Zn atoms, which alters the electronic state of the carbon material surface and promotes better adhesion to the copper foil current collector. Although... Figure 6 Charging curve and Figure 5 The curves are similar, but Figure 6 The discharge curves of each negative electrode all exhibit varying degrees of wavy behavior. The most obvious example is the charging curve of the battery prepared with the HC negative electrode, where the initial discharge voltage inflection point drops sharply from 0.94V to 0.66V, indicating severe voltage polarization.

[0158] Test results show that batteries prepared with modified negative electrodes exhibit higher capacity, higher initial efficiency, higher discharge voltage, and stronger resistance to external damage than batteries prepared with unmodified negative electrodes.

[0159] (3) In order to further investigate the charge-discharge behavior of the hard carbon anode, we studied its discharge curve, and the results are as follows: Figure 7-8 As shown in Table 5. Figure 7 A graph showing the percentage of constant current and constant voltage during the first charge and discharge cycle of a battery prepared with a crack-free negative electrode. Figure 8The graph shows the percentage of constant current and constant voltage capacity in the first charge-discharge cycle of batteries prepared with cracked negative electrode sheets. The discharge curve plateau voltage of hard carbon during sodium intercalation is very close to 0V, and a large portion of the capacity is near the overpotential. This portion of the capacity is particularly sensitive to polarization. When the electrode loading or current is too high, the discharge process will terminate prematurely due to polarization. To reduce the impact of polarization on capacity utilization, constant voltage discharge is further performed in addition to constant current discharge. The percentages of constant current capacity in batteries prepared with crack-free negative electrodes (HC negative electrode sheet, HC-1 negative electrode sheet, HC-2 negative electrode sheet, HC-3 negative electrode sheet) are 94.74%, 96.37%, 97.32%, and 97.47%, respectively. Figure 7 The constant current capacity percentages of batteries prepared with cracked negative electrodes (HC negative electrode sheet, HC-1 negative electrode sheet, HC-2 negative electrode sheet, HC-3 negative electrode sheet) are 70.29%, 79.91%, 96.87%, and 83.11%, respectively. Figure 8 This situation may occur due to the presence of overpotential. Before the sodium insertion potential of the HC negative electrode reaches the sodium deposition potential, the half-cell discharge cutoff voltage is prematurely triggered. At this point, the HC negative electrode stops sodium insertion, so near 0V, a portion of the HC negative electrode's capacity needs to be released through constant voltage. However, the HC-1, HC-2, and HC-3 negative electrode sheets, due to the alteration of the electron cloud state on the HC surface by N, S, P, and Zn atoms, and the increased interlayer spacing, weaken the influence of polarization during discharge. Even if cracks appear in the negative electrode sheet, the corresponding batteries prepared can still maintain good discharge performance, especially the batteries prepared with the HC-2 negative electrode.

[0160]

[0161] Figure 9 A comparison of the percentages of ramp capacity (0.1-2V) and plateau capacity (0.02V-0.1V) in the first charge-discharge cycle of batteries prepared with crack-free negative electrode sheets. Figure 10A comparison of the percentage of ramp capacity (0.1-2V) and plateau capacity (0.02V-0.1V) during the first charge-discharge cycle of a battery prepared with a cracked negative electrode. The sodiumization curve of the hard carbon negative electrode changes with voltage and is divided into two parts: the first part (0.1-2V) is the discharge ramp region, and the second part is the discharge plateau region (0.02V-0.1V). Since sodium ions are more preferentially adsorbed at the edge graphite domains and surface defects, and the intercalation between graphite layers requires overcoming electrostatic repulsion, the ramp capacity may originate from the adsorption of sodium ions at the edges and defect sites of the randomly stacked graphite microcrystals. Defect sites include vacancies, carbon layer edges, and freely bonded carbides. The plateau capacity may originate from the intercalation of sodium ions between graphite microcrystal layers and the filling of pores formed by the interlacing of graphite microcrystals. Compared to batteries fabricated with crack-free HC negative electrode sheets, batteries fabricated with crack-free HC-1, HC-2, and HC-3 negative electrode sheets all showed improved ramp capacity and plateau capacity. Figure 9 Compared to batteries fabricated with crack-free HC anode sheets, batteries fabricated with cracked HC-1, HC-2, and HC-3 anode sheets exhibit higher ramp and plateau capacities. This is likely due to the alteration of the electron cloud state on the HC surface by N / S / P / Zn atoms, which enhances the adsorption process of sodium ions. These adsorption processes may include physical and chemical adsorption, with adsorption sites located on the surface, edges, or defects of the carbon material. However, due to the poor crystallinity of hard carbon, its internal microstructure is relatively complex, and its surface state is difficult to determine. Whether the sodium storage mechanism in the plateau region is intercalation between carbon layers, adsorption or filling in nanopores, or both, further verification requires more precise research methods and more systematic experimental designs. However, it is clear that the modification of the hard carbon material surface by N / S / P / Zn atoms is beneficial to improving the plateau capacity.

[0162] (4) To further investigate its low-temperature performance, low-temperature cycling tests and low-temperature impedance tests were conducted on the battery. Table 6 shows the 0.1C charge-discharge data of the prepared battery at 0℃, -10℃, and -20℃. It can be seen that as the temperature decreases, the capacity of the hard carbon anode gradually decreases. This may be because the low temperature increases the polarization of the electrode during charge-discharge and reduces the activation energy of the reaction, thus leading to capacity decay. Among them, the battery prepared with HC anode is most affected by temperature. Specifically, the discharge capacity at 0℃ is 268.32 mAh / g, and the discharge capacity at -20℃ is 96.43 mAh / g. The capacity difference under such temperature difference is 181.89 mAh / g. At -20℃, the capacity retention rate drops to 80% after only 146 cycles. This indicates that decreasing temperature significantly impacts the reversible capacity and cycle stability of hard carbon. However, the reversible capacity differences of batteries prepared with HC-1, HC-2, and HC-3 anodes at the same temperature difference are 174.15 mAh / g, 111.2 mAh / g, and 132.04 mAh / g, respectively. At -20℃, the number of cycles required to retain 80% of the capacity is 426, 859, and 598, respectively. This may be due to the alteration of the electron cloud state on the HC surface by N / S / P / Zn atoms, which enhances the adsorption process of sodium ions. Additionally, the additives trimethylsilyl nicotinate and methyl 4-hydroxy-3-methoxycinnamate synergistically optimize the composition of the anode interface film. Therefore, the modification of hard carbon effectively mitigates the rapid capacity decay of batteries prepared with hard carbon anodes at low temperatures.

[0163]

[0164] (5) Impedance test of the negative electrode half-cell:

[0165] Impedance testing of the negative electrode half-cell was performed on an electrochemical workstation. The initial voltage was the cell's open-circuit voltage. The high-frequency range was 100 kHz, and the low-frequency range was 10 mHz. The perturbation amplitude was set to an appropriate sinusoidal amplitude of 10 mV, and the integration time and AC settling time were both 2 s.

[0166] Figure 11This is a comparison of the impedance of a negative electrode half-cell at -20℃ after five charge-discharge cycles at a rate of 0.1C. The Nyquist plot includes the equivalent series resistance (Rs) and charge transfer resistance (Rct) in the high-frequency region, and the Warburg process (ZW) in the low-frequency region. The diameter of the irregular semicircle represents the charge transfer resistance (Rct), and the irregular semicircle of the negative electrode half-cell prepared with the HC negative electrode is the largest. The decrease in the negative electrode charge transfer resistance of the negative electrode half-cell prepared with the modified negative electrode confirms the reduction of the sodium ion diffusion barrier after surface modification with N / S / P / Zn atoms. Therefore, although the insertion and deintercalation of sodium ions in the electrode material becomes more difficult at -20℃, the decrease in kinetic performance weakens the active material participating in the discharge process, making it more difficult for sodium ions to diffuse from the electrode surface to the interior, which greatly affects the cycle performance of the battery. The decrease in temperature requires a larger activation energy for the electrochemical reaction, and the thermodynamic effects provide greater reaction resistance for charge-discharge. However, in hard carbon anodes modified with N / S / P / Zn atoms, the increased interlayer spacing can reduce the inhibition of electron transport by shielding the electrostatic interactions between layers. Furthermore, the introduction of N / S / P / Zn atoms provides more active sites, and the carbon coating further reduces the internal resistance between powder particles, thus promoting ion transport.

[0167] In summary, the negative electrode sheet of the battery of this invention, through atomic surface modification and chemical coating with carbon materials, and the electrolyte, through solvent optimization and additive improvement, effectively improves the electrochemical performance of the hard carbon negative electrode at low temperatures, reduces the battery charge transfer resistance, and promotes sodium ion transport. The multi-atom surface modification of hard carbon materials using N / S / P / Zn and chemical carbon coating is an effective modification strategy of this invention. This strategy significantly improves the adhesion of the negative electrode material to the current collector through microstructure regulation (increasing interlayer spacing and providing active sites), interface optimization (reducing contact resistance), and enhancing the electron delocalization between powders. It also improves the interfacial ion transport kinetics of the negative electrode material under harsh low-temperature environments, thus partially offsetting the negative effects of low temperature. The electrolyte, after solvent optimization, can remain liquid at -60℃. The combined use of additives such as trimethylsilyl nicotinate, methyl 4-hydroxy-3-methoxycinnamate, acetazolamide, and tert-butyl (2,5-difluoropyridin-4-yl)carbamate can modify the interfacial film on the electrode surface, providing an effective reference for improving the low-temperature performance of sodium-ion batteries.

[0168] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low temperature sodium-ion battery comprising a modified negative electrode, characterized in that, The battery comprises a positive electrode, a negative electrode and an electrolyte. The negative electrode comprises a negative electrode slurry, and the negative electrode slurry comprises an active material, conductive carbon, sodium carboxymethyl cellulose and styrene-butadiene rubber. The active material is modified hard carbon, which is prepared by mixing hard carbon, single-walled carbon nanotubes, graphite carbon and soft carbon to obtain physically coated hard carbon, and then further mixing and calcining a doping modification precursor powder to complete element doping and chemical coating. The electrolyte comprises a base electrolyte and an additive, and the additive is at least one of trimethylsilane nicotinic acid ester, 4-hydroxy-3-methoxycinnamic acid methyl ester, acetazolamide and (2,5-difluoropyridine-4-yl) tert-butyl carbamate.

2. The low temperature sodium-ion battery of claim 1, wherein, The calcination temperature is 400-800 DEG C, the holding time is 1-4 h, the mass ratio of the physically coated hard carbon and the doping modification precursor powder is (10-25):1, and the sulfur-containing precursor powder is prepared by mixing and grinding onion, garlic leaves and dried onion.

3. The low temperature sodium-ion battery of claim 1, wherein, The sulfur-containing precursor powder is prepared by mixing and grinding onion, garlic leaves and dried onion at a mass ratio of 1:1:1; the melon seed powder is prepared by mixing and powdering germinated sunflower seeds and pumpkin seeds at a mass ratio of 1:1; and the doping modification precursor powder is selected from one of the following combinations: (1) a combination of tryptone powder and melon seed powder, (2) a combination of tryptone powder and zinc-rich yeast powder, and (3) a combination of tryptone powder, melon seed powder and sulfur-containing precursor powder.

4. The low temperature sodium-ion battery of claim 1, wherein, The doping modification precursor powder is selected from one of the following combinations: (1) a combination of tryptone powder and melon seed powder at a mass ratio of 1:1, (2) a combination of tryptone powder and zinc-rich yeast powder at a mass ratio of 1:1, and (3) a combination of tryptone powder, melon seed powder and sulfur-containing precursor powder at a mass ratio of 1:1:

1.

5. The low temperature sodium-ion battery of claim 1, wherein, In the negative electrode slurry, the active material accounts for 90-96%, the conductive carbon accounts for 1-5%, the sodium carboxymethyl cellulose accounts for 1-5% and the styrene-butadiene rubber accounts for 1-5% by weight percentage. The active material is prepared from at least the following components, wherein the hard carbon accounts for 90-96%, the single-walled carbon nanotubes account for 1-5%, the graphite carbon accounts for 1-5% and the soft carbon accounts for 1-5% by weight percentage. The conductive carbon is a combination of SP, Kappa100 and single-walled carbon nanotubes at a mass ratio of 1:0.5:0.

5.

6. The low temperature sodium-ion battery of claim 1, wherein, The negative electrode is prepared by mixing and dispersing the active material, the conductive carbon, the sodium carboxymethyl cellulose and deionized water, adding the styrene-butadiene rubber, degassing and dispersing to obtain the negative electrode slurry. The negative electrode slurry is coated on the current collector to obtain the negative electrode.

7. The low temperature sodium-ion battery of claim 1, wherein, The base electrolyte comprises a solvent and a solute. The solvent is at least one of a carbonate solvent, an organic ether solvent and a carboxylic acid ester solvent. The solute is at least one of NaPF6, NaClO4, NaSO3CF3, NaBF4, NaNO3, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4.

8. The low temperature sodium-ion battery of claim 7, wherein, In the base electrolyte, EMC, PC, EC, and EP are mixed solvents, and the mass ratio is at least one of 60:20:10:10, 30:30:30:10, or 50:20:20:10; The solute is a mixed sodium salt of NaPF6 and NaSO3CF3, and the molar ratio of the two is (6-8):3; In the electrolyte, 1-6% of an additive is added based on the total mass of the base electrolyte; The additive in the electrolyte is one of the following combinations: a combination of trimethylsilyl nicotinic acid ester and 4-hydroxy-3-methoxycinnamic acid methyl ester, a combination of trimethylsilyl nicotinic acid ester and acetazolamide, a combination of trimethylsilyl nicotinic acid ester and (2,5-difluoropyridin-4-yl) tert-butyl carbamate, a combination of 4-hydroxy-3-methoxycinnamic acid methyl ester and acetazolamide, a combination of 4-hydroxy-3-methoxycinnamic acid methyl ester and (2,5-difluoropyridin-4-yl) tert-butyl carbamate, and a combination of acetazolamide and (2,5-difluoropyridin-4-yl) tert-butyl carbamate.

9. A method of preparing the low-temperature sodium-ion battery according to any one of claims 1 to 8, characterized in that, The method comprises (1) mixing the solvent and the solute to prepare a base electrolyte; (2) adding an additive to the base electrolyte and mixing uniformly to prepare an electrolyte; (3) mixing hard carbon with single-walled carbon nanotubes, graphite carbon, and soft carbon to prepare physically coated hard carbon, further mixing and calcining the physically coated hard carbon with a doped and modified precursor powder to complete element doping and chemical coating and prepare modified hard carbon; (4) mixing the modified hard carbon with conductive carbon, sodium carboxymethyl cellulose, and styrene-butadiene rubber to prepare a negative electrode slurry; (5) coating the negative electrode slurry on a current collector, drying, and tabletting to prepare a negative electrode; (6) preparing a low-temperature sodium ion battery using the obtained electrolyte, the positive electrode, and the negative electrode.

10. Use of the low-temperature sodium ion battery according to any one of claims 1-8 in an energy storage device.

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