An anode-free sodium battery electrolyte, a preparation method and application thereof

Abstract

The application discloses a negative-electrode-free sodium battery electrolyte and a preparation method and application thereof, and belongs to the battery field.The negative-electrode-free sodium battery electrolyte comprises the following raw materials in parts by weight: 50-80 parts of a linear ether main solvent; 10-30 parts of 1,3-dioxolane cosolvent; 10-17 parts of an electrolyte sodium salt; and 0.3-2 parts of a pyridine boronic acid additive.The pyridine boronic acid additive is at least one of pyridine-3-boronic acid, pyridine-3-boronic acid neopentyl glycol ester and pyridine-4-boronic acid neopentyl glycol ester.The linear ether main solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether and diethylene glycol diethyl ether.The negative-electrode-free sodium battery electrolyte can achieve the effects of good first-effect exertion and long cycle life.

Description

Technical Field

[0001] This invention relates to sodium-ion batteries, and more particularly to a negative electrode-free sodium battery electrolyte, its preparation method, and its application. Background Technology

[0002] With the continued depletion of fossil fuels leading to global climate change and energy security challenges, the installed capacity of renewable energy sources, represented by wind and solar power, continues to climb. However, the intermittent nature of renewable energy sources has created an urgent need for grid-scale energy storage technology. Since its commercialization in the 1990s, lithium-ion batteries (LIBs) have dominated the consumer electronics and electric vehicle markets due to their high energy density (300-350 Wh / kg) and cycle stability. However, limited by the 0.0065% lithium abundance in the Earth's crust and uneven resource distribution, the price of LIB raw materials fluctuates wildly, making it difficult to support the sustainable development needs of large-scale energy storage systems.

[0003] Sodium-ion batteries (SIBs) are a potential alternative, with the following core advantages: (1) Sodium resources are far more abundant than lithium, with a crustal content of 2.36%, and the main raw materials, such as sodium chloride and sodium sulfate, can be obtained on a large scale at low cost; (2) Sodium belongs to Group IA elements, just like lithium, and has similar electrochemical properties. However, sodium ions have a larger ionic radius (1.02 Å vs Li). + The molar mass of 0.76 Å and higher (22.99 g / mol vs 6.94 g / mol) has led to a significant reduction in the energy density of SIBs, currently only about 120-160 Wh / kg, which restricts their high-end applications.

[0004] Anode-free sodium batteries (AFSBs) theoretically increase energy density to over 400 Wh / kg by directly depositing metallic sodium on copper current collectors, eliminating the traditional sodium-intercalated anode design. However, this system faces three key challenges: (1) irreversible sodium loss during cycling, including continuous SEI formation, dead sodium formation, and dendrite shedding, leading to rapid capacity decay; (2) decomposition of traditional ester / ether electrolytes before sodium deposition, exacerbating interfacial side reactions; and (3) lack of a stable electrolyte / current collector interface, making it difficult to achieve highly reversible sodium deposition / stripping, with initial coulombic efficiency typically <90%. Summary of the Invention

[0005] Objectives of the invention: The objective of this invention is to provide a sodium-free battery electrolyte with good initial efficiency and long cycle life; another objective of this invention is to provide a method for preparing the above-mentioned sodium-free battery electrolyte; a third objective of this invention is to provide an application of the above-mentioned sodium-free battery electrolyte in batteries.

[0006] Technical solution: The negative electrode-free sodium battery electrolyte of the present invention comprises, by weight, the following raw materials: 50-80 parts of linear ether main solvent; 10-30 parts of 1,3-dioxolane co-solvent; 10-17 parts of electrolyte sodium salt; and 0.3-2 parts of pyridine boric acid additive.

[0007] Preferably, the amount of pyridine boric acid additive added is 0.5-1 part.

[0008] The amount of linear ether main solvent added is 65-70 parts.

[0009] The linear ether primary solvent is at least one of ethylene glycol dimethyl ether (CAS: 110-71-4), diethylene glycol dimethyl ether (CAS: 111-96-6), tetraethylene glycol dimethyl ether (CAS: 143-24-8), ethylene glycol diethyl ether (CAS: 16484-86-9), and diethylene glycol diethyl ether (CAS: 112-36-7).

[0010] The electrolyte sodium salt includes sodium hexafluorophosphate (NaPF6), and also includes one of sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaOTF), and sodium difluorosulfonamide (NaFSI).

[0011] The pyridine boric acid additive is at least one of pyridine-3-boronic acid (CAS: 131534-65-1), neopentyl glycol pyridine-3-boronic acid (CAS: 845885-86-1), and neopentyl glycol pyridine-4-boronic acid (CAS: 869901-52-0).

[0012] The method for preparing the negative electrode-free sodium battery electrolyte of the present invention includes the following steps: (1) Weigh the required components; (2) Mix the main solvent and the co-solvent; (3) Add sodium electrolyte salt; (4) Adding additives will yield the electrolyte.

[0013] The application of the negative electrode-free sodium battery electrolyte of the present invention in the battery includes the following steps: mixing nickel iron manganese, conductive carbon black and polyvinylidene fluoride in a solvent to obtain a slurry; coating the slurry onto the surface of an aluminum current collector and drying it; forming a multi-layer sandwich structure from an NFM positive electrode, a separator and a copper foil current collector through a winding process; after vacuum drying, injecting electrolyte and encapsulating to obtain a negative electrode-free sodium battery.

[0014] Invention Principle: This invention provides a negative electrode-free sodium battery electrolyte, which is a co-solvent electrolyte. Linear ether is used as the main solvent, and 1,3-dioxolane (DOL, CAS: 646-06-0) is used as the co-solvent. The two form a solvent system, which is then combined with disodium salt and pyridine borate as film-forming additives to form the electrolyte.

[0015] Pyridine borate compounds can simultaneously form an interfacial film to protect the positive and negative electrodes of the battery cell, effectively solving the sodium dendrite and interfacial problems associated with sodium-ion batteries without a negative electrode. During cell formation, pyridine borate compounds preferentially decompose over solvents to form a uniform SEI film, preventing sodium ions from preferentially reducing and depositing at surface defects and protrusions, forming initial crystal nuclei. This inhibits rapid sodium accumulation during cycling, reducing the formation of needle-like and dendritic dendrites, and minimizing interfacial side reactions and safety issues caused by sodium dendrite formation. Simultaneously, a condensation reaction occurs in the high-potential operating range of the positive electrode, generating a CEI film containing a BOB covalent network. This effectively inhibits the dissolution of transition metals from the positive electrode, preventing cell membrane puncture and potential cell explosion, while also reducing interfacial impedance and improving cell cycle performance.

[0016] Ethers, as solvents, are beneficial for increasing dielectric constant, promoting ion dissociation, and improving ionic conductivity. Furthermore, ether-based solvents can form a more stable inorganic layer on the anolyte current collector, inhibiting sodium dendrite growth. DOL, as a co-solvent, can significantly weaken cation-anion and solvent-solvent interactions, enabling rapid sodium ion transport in the electrolyte. In addition, the participation of DOL molecules in the solvation sheath structure reduces the binding energy of sodium ions with the linear ether-based main solvent and alters PF6. - The energy level distribution around the anion results in a lower desolvation energy barrier and enables anion-dominated interfacial chemical regulation at lower concentrations.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method uses pyridine boric acid as a film-forming additive, and the resulting electrodeless sodium battery has excellent performance, with a minimum first efficiency of 95.2% and a maximum of 97.3%, and a cycle life of up to 386 cycles; (2) By adjusting the type and ratio of linear ether solvents, the amount of sodium salt added, and the type and amount of pyridine boric acid additives, the synergistic effect between the components significantly improves the performance of the electrodeless sodium battery, with the first efficiency stable at 95.2%-97.3% and the cycle life reaching 304-386 cycles; (3) The application of electrodeless sodium batteries can eliminate the processes of coating and rolling of negative electrode materials, reduce the number of electrode layers and the thickness, and make the cell stacking / winding more efficient, which is conducive to improving the yield of the production line; at the same time, the elimination of negative electrode hard carbon materials can save about 20% of the material cost. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the embodiments.

[0019] Example 1

[0020] The sodium-free electrolyte for a negative electrode described in this invention comprises, by weight, the following raw materials: 65.5 parts of the main solvent diethylene glycol dimethyl ether; 20 parts of the co-solvent 1,3-dioxolane; 12.5 parts of sodium hexafluorophosphate and 1.5 parts of sodium tetrafluoroborate, respectively; and 0.5 parts of pyridine-3-boronic acid additive.

[0021] The method for preparing the negative electrode-free sodium battery electrolyte of the present invention includes the following steps: (1) Weigh each of the above components according to their respective weight parts; (2) Mix the main solvent and the co-solvent and stir to form a homogeneous first solution; (3) Add the sodium salt of electrolyte to the first solution and stir to form a homogeneous second solution; (4) Add the additive to the second solution and stir to form a homogeneous solution to obtain the electrolyte.

[0022] The application of the sodium-free negative electrode battery electrolyte of the present invention in batteries includes the following steps: Nickel-iron-manganese (NFM), Super C65 conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed uniformly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 85:10:5 to obtain an NFM ternary cathode slurry. This slurry was coated onto the surface of an aluminum current collector and then dried in a vacuum oven at 110°C for 12 hours. The anode-free sodium battery adopted a sandwich structure design, consisting of an NFM cathode, a polypropylene (PP) separator, and a copper foil current collector, forming a multilayer structure with 5 positive layers and 6 negative layers through a winding process. After drying the battery under vacuum at 80°C for 12 hours, 0.72 g of pre-prepared electrolyte was injected into an argon-filled glove box. After 1 minute of vacuum immersion, the battery was encapsulated under -95 kPa conditions to obtain the anode-free sodium battery.

[0023] Examples 2-14 and Comparative Examples 2-3 Based on the experimental conditions of Example 1, Examples 2-14 and Comparative Examples 2-3 were constructed by changing only some substances or their addition amounts, and the corresponding negative electrode-free sodium batteries were tested to test their first efficiency and cycle life at room temperature 0.2C / 0.5C 2.0-3.8V. The experimental conditions and test results are shown in Table 1.

[0024] Table 1. Some substances and their amounts added in each experiment experiment main solvent Amount of main solvent added / part DOL / serving Sodium hexafluorophosphate / part additive Additive dosage / serving First-efficacy (%) Cycle life (cycles) Example 1 Diethylene glycol dimethyl ether 65.5 20 12.5 Pyridine-3-boronic acid 0.5 97.3 386 Example 2 Diethylene glycol dimethyl ether 55.5 30 12.5 Pyridine-3-boronic acid 0.5 95.6 304 Example 3 Diethylene glycol dimethyl ether 75.5 10 12.5 Pyridine-3-boronic acid 0.5 95.2 310 Example 4 Diethylene glycol dimethyl ether 70 20 9 Pyridine-3-boronic acid 0.5 96.4 322 Example 5 Diethylene glycol dimethyl ether 65.5 17.5 15 Pyridine-3-boronic acid 0.5 97.0 351 Example 6 Ethylene glycol dimethyl ether 65.5 20 12.5 Pyridine-3-boronic acid 0.5 97.0 377 Example 7 Tetraethylene glycol dimethyl ether 65.5 20 12.5 Pyridine-3-boronic acid 0.5 96.8 368 Example 8 Ethylene glycol diethyl ether 65.5 20 12.5 Pyridine-3-boronic acid 0.5 97.1 380 Example 9 Diethylene glycol diethyl ether 65.5 20 12.5 Pyridine-3-boronic acid 0.5 96.7 375 Example 10 Diethylene glycol dimethyl ether 65.5 20.2 12.5 Pyridine-3-boronic acid 0.3 96.4 322 Example 11 Diethylene glycol dimethyl ether 65.5 19.7 12.5 Pyridine-3-boronic acid 0.8 97.1 350 Example 12 Diethylene glycol dimethyl ether 65.5 19.5 12.5 Pyridine-3-boronic acid 1 96.8 341 Example 13 Diethylene glycol dimethyl ether 65.5 20 12.5 Neopentyl pyridine-3-boronate 0.5 96.8 372 Example 14 Diethylene glycol dimethyl ether 65.5 20 12.5 Neopentyl pyridine-4-boronate 0.5 96.5 368 Comparative Example 2 Diethylene glycol dimethyl ether 66 20 12.5 none 0 94.1 297 Comparative Example 3 Diethylene glycol dimethyl ether 86 0 12.5 none 0 89.8 237 Comparative Example 1 A conventional electrolyte comprises, by weight, the following raw materials: organic solvents propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in 25 parts, 31 parts, and 30 parts, respectively; and sodium electrolyte salts sodium hexafluorophosphate and sodium tetrafluoroborate, in 12.5 parts and 1.5 parts, respectively.

[0025] The preparation method of this conventional electrolyte includes the following steps: (1) Weigh each of the above components according to their respective weight parts; (2) Mix the three organic solvents and stir to form a homogeneous first solution; (3) Add the sodium salts of electrolyte one by one to the first solution to obtain the conventional electrolyte.

[0026] Following the steps of the application of electrolyte in batteries as described in Example 1, batteries were prepared using the conventional electrolyte obtained in Comparative Example 1, and their initial efficiency and cycle life at room temperature (0.2C / 0.5C, 2.0-3.8V) were tested. The initial efficiency was 55.3%, and the cycle life was 3 cycles.

[0027] Experimental results show that by adjusting the type and ratio of linear ether solvents, the amount of sodium salt added, and the type and amount of pyridine boric acid additives, the electrochemical performance of the negative electrode-free sodium batteries obtained using this method is significantly better than that of the comparative examples. The batteries obtained in the examples have a stable initial efficiency of 95.2%-97.3% and a cycle life of 304-386 cycles, which is far superior to the performance of batteries prepared without the addition of pyridine boric acid (Comparative Example 2, initial efficiency 94.1%, 297 cycles; Comparative Example 3, initial efficiency 89.8%, 237 cycles), indicating a significant improvement in overall performance.

[0028] In Examples 1-14, linear ether main solvents and pyridine borate additives were added, while in Comparative Example 2, no pyridine borate additives were added. This indicates that pyridine borate additives and linear ether solvents can synergistically construct stable and dense SEI and CEI films, which can both inhibit sodium dendrite growth and improve electrode interface side reactions, effectively solving the interface defects and dendrite problems of negative electrode-less sodium batteries. Although different additives were used, they did not significantly affect the key indicators, and all achieved excellent initial efficiency and cycle life, indicating that there are many types of pyridine borate additives to choose from. Performance improvements were achieved using different pyridine borate substances (Examples 1, 13, and 14). Pyridine-3-boronic acid (0.5 parts) corresponded to an initial efficiency of 97.3% and 386 cycles, neopentyl glycol pyridine-3-boronic acid achieved an initial efficiency of 96.8% and 372 cycles, and neopentyl glycol pyridine-4-boronic acid achieved an initial efficiency of 96.5% and 368 cycles, all exhibiting excellent interface modification effects.

[0029] The linear ether solvents selected in this method all showed good compatibility. Diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether can all achieve an initial efficiency of over 95% and a cycle life of over 300 cycles, demonstrating high tolerance for solvent structure.

[0030] Example 1 is the optimal formulation, which uses diethylene glycol dimethyl ether and 1,3-dioxolane as a compound solvent, an appropriate sodium salt ratio, and 0.5 parts of pyridine-3-boronic acid additive, achieving an initial efficiency of 97.3% and a cycle life of 386 cycles, with the best overall performance.

Claims

1. A sodium-ion battery electrolyte without a negative electrode, characterized in that, By weight, it includes the following raw materials: 50-80 parts of linear ether main solvent, 10-30 parts of 1,3-dioxolane co-solvent, 10-17 parts of electrolyte sodium salt, and 0.3-2 parts of pyridine boric acid additive.

2. The electrolyte according to claim 1, characterized in that, The amount of the pyridine boric acid additive added is 0.5-1 part.

3. The electrolyte according to claim 1, characterized in that, The amount of the linear ether main solvent added is 65-70 parts.

4. The electrolyte according to claim 1, characterized in that, The linear ether main solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

5. The electrolyte according to claim 1, characterized in that, The electrolyte sodium salt includes sodium hexafluorophosphate, and also includes one of sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium difluorosulfonamide.

6. The electrolyte according to claim 1, characterized in that, The pyridine boric acid additive is at least one of pyridine-3-boronic acid, neopentyl glycol pyridine-3-boronic acid, and neopentyl glycol pyridine-4-boronic acid.

7. A method for preparing the electrolyte according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Weigh the required components; (2) Mix the main solvent and the co-solvent; (3) Add sodium electrolyte salt; (4) Adding additives will yield the electrolyte.

8. The application of a sodium-free battery electrolyte according to any one of claims 1-6 or the electrolyte obtained by the preparation method according to claim 7 in a battery.

9. The application according to claim 8, characterized in that, Includes the following steps: Nickel-iron-manganese, conductive carbon black and polyvinylidene fluoride are mixed evenly in a solvent to obtain a slurry; the slurry is coated on the surface of the current collector and dried; a multilayer structure is formed by the NFM positive electrode, the separator and the current collector; electrolyte is injected and the battery is encapsulated to obtain a negative electrode-free sodium battery.

10. The application according to claim 9, characterized in that, The solvent is N-methylpyrrolidone.