Electrolyte for graphite negative electrode sodium-ion battery
By using sodium dicyanoguanidine and sodium cyanourea as additives in a graphite anode sodium-ion battery, a stable SEI film is formed, which solves the problems of interfacial film instability and interlayer structure collapse in traditional electrolyte systems. This achieves high initial capacity and long cycle life, improves battery safety and high rate performance, and is suitable for cost-sensitive large-scale application scenarios.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING DAXIN NEW ENERGY AUTOMOBILE IND CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-23
AI Technical Summary
Traditional graphite anode sodium-ion battery electrolytes suffer from problems such as loose and porous interfacial film, poor cycle stability, safety risks caused by sodium dendrite growth, poor high-rate performance, and easy collapse of graphite interlayer structure, which seriously restrict their commercial application.
Sodium dicyanididine (NaDCG) and sodium cyanourea (NaCU) are used as additives to form a dense solid electrolyte interphase (SEI) membrane. By combining the strong interlayer anchoring ability of NaDCG with the interfacial film-forming advantages of NaCU, a synergistic effect of interlayer stability and interfacial protection is achieved.
At a current density of 300 mA g⁻¹, the initial charging capacity reaches 108~112 mAh g⁻¹, and the capacity retention rate after 3000 cycles is ≥94%. The discharge capacity at 0.5C rate is ≥110 mAh g⁻¹, the capacity retention rate at 1C is ≥95%, the capacity retention rate at 3C rate is ≥88%, the capacity retention rate at 5C rate is ≥90%, the discharge capacity at 5C rate is ≥88%, the capacity retention rate at 5C rate is ≥88%, and the capacity retention rate after 3000 cycles is ≥94%. This effectively reduces sodium ion intercalation resistance, suppresses interlayer collapse, improves the cycle stability and high-rate performance of the battery, and enhances thermal stability.
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Figure CN122267302A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of new energy battery technology, and specifically to an electrolyte for a graphite anode sodium-ion battery. Background Technology
[0002] Sodium-ion batteries, as an important supplement and alternative to lithium-ion batteries, have shown broad application prospects in large-scale energy storage due to their advantages such as abundant sodium resources, low cost, and environmental friendliness. Graphite, as a negative electrode material for sodium-ion batteries, has advantages such as low cost, good conductivity, and moderate theoretical capacity, and is considered one of the most commercially promising negative electrode materials. However, due to the larger radius of sodium ions, the insertion / extraction process between graphite layers is more difficult than that of lithium ions, placing higher demands on the electrolyte system. Sodium-ion battery electrolytes typically consist of organic solvents, sodium salts, and additives. Although the additives are used in small amounts, they have a crucial impact on battery performance. Currently, the commercialization of graphite negative electrode sodium-ion batteries is constrained by the bottleneck of electrolyte technology, and there is an urgent need to develop high-performance electrolyte systems to promote large-scale industrial applications.
[0003] Traditional graphite anode sodium-ion battery electrolytes suffer from core technical challenges such as a porous interfacial film and poor cycle stability. Without additives or with an imperfect additive system, the solid electrolyte interfacial film structure formed by the electrolyte on the graphite anode surface is unstable, failing to effectively prevent the continuous decomposition of the electrolyte and uneven deposition of sodium ions, leading to rapid capacity decay during battery cycling. Experimental data shows that after 100 cycles, the capacity retention rate of graphite anode sodium-ion batteries using traditional electrolyte systems can plummet to below 50%, and after 3000 cycles, it is even less than 30%, far from meeting the industry requirement of a lifespan of over 10 years for energy storage batteries. Simultaneously, the unstable interfacial film easily induces sodium dendrite growth. These dendrites extend continuously during repeated charge and discharge, potentially piercing the separator, causing internal short circuits, thermal runaway, or even fire and explosion, posing serious safety hazards. This problem is particularly pronounced in low-temperature environments or under high-rate charge and discharge conditions, severely restricting the application and promotion of sodium-ion batteries in key areas such as electric vehicles and grid energy storage.
[0004] Furthermore, traditional electrolyte systems perform poorly under high-rate charge-discharge conditions, with 5C-rate capacity retention typically below 70%, failing to meet the demands of high-power applications. More critically, repeated sodium ion insertion and extraction can lead to the collapse of the graphite interlayer structure, resulting in unstable interlayer spacing and further exacerbating capacity decay. The graphite interlayer spacing gradually shrinks from its initial 0.37 nm during cycling, increasing resistance to sodium ion insertion and worsening diffusion kinetics. Existing additive technologies often struggle to balance the relationship between additive dosage and overall performance. Insufficient dosage results in inadequate interlayer support and interface protection, with a capacity retention of only about 75% after 3000 cycles; excessive dosage increases electrolyte viscosity, reduces ion migration rate, and lowers 5C-rate capacity retention to below 70%. Moreover, the problem of insufficient thermal stability remains unresolved. Traditional electrolyte systems have low thermal decomposition initiation temperatures, with battery exothermic reaction temperatures typically below 200°C, posing thermal safety risks under extreme conditions. The aforementioned technical bottlenecks are intertwined and mutually restrictive, severely hindering the commercial application of graphite anode sodium-ion batteries. There is an urgent need to develop new electrolyte additive systems to achieve a breakthrough in overall performance. Summary of the Invention
[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an electrolyte for a graphite anode sodium-ion battery, which solves the problems of traditional electrolytes such as loose and porous interfacial film, poor cycle stability, safety risks caused by sodium dendrite growth, poor high-rate performance, and easy collapse of graphite interlayer structure.
[0006] To achieve the above objectives, the present invention provides the following technical solution: An electrolyte for a graphite negative electrode sodium-ion battery is composed of an organic solvent, sodium salt, and additives.
[0007] Preferably, the organic solvent is one or more of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
[0008] Preferably, the sodium salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium difluorosulfonamide.
[0009] Preferably, the additive is one or more of sodium dicyanoguanidine and sodium cyanourea.
[0010] Preferably, the additive compound is compounded in a mass ratio of sodium dicyanoguanidine to sodium cyanourea = 1~2:1.
[0011] Preferably, the electrolyte is composed of 10-20 parts by weight of sodium salt, 77-89.8 parts by weight of organic solvent, and 0.2-3.0 parts by weight of additives.
[0012] Preferably, the water content of the electrolyte is ≤10ppm.
[0013] Preferably, the electrolyte in the graphite negative electrode sodium-ion battery is at 300 mA·g -1 Initial charging capacity at current density ≥200mAh·g -1 After 3000 cycles, the capacity retention rate is ≥94%.
[0014] Preferably, the electrolyte has a discharge capacity ≥ 110 mAh·g at a 0.5C rate. -1 1C capacity retention rate ≥95%, 3C capacity retention rate ≥90%, 5C capacity retention rate ≥88%.
[0015] The technical effects and advantages of the electrolyte for a graphite negative electrode sodium-ion battery of the present invention are as follows: 1. The electrolyte prepared by this invention has a pH of 300 mAg. -1 The initial charging capacity of the battery at the given current density can reach 108~112 mAh g. -1 After 3,000 charging cycles, the capacity retention rate can reach 94%.
[0016] 2. The electrolyte prepared by this invention has a battery capacity retention rate of more than 85% in the range of 1C-5C, and the discharge capacity at 5C rate can reach 88% of that at 0.5C rate.
[0017] 3. When the additive dosage is too low, the interlayer support and interface protection effects are insufficient, and the capacity retention rate is only 75.3% after 3000 cycles; when the dosage is too high, the electrolyte viscosity increases, the ion migration rate decreases, the battery polarization intensifies, and some unreacted additive molecules are easily adsorbed on the electrode surface, which damages the stability of the interface film, resulting in the 5C rate capacity retention rate dropping to 72.1%.
[0018] 4. When NaDCG and NaCU are used in combination, this invention can combine the strong interlayer anchoring ability of NaDCG with the interfacial film-forming advantages of NaCU to achieve a synergistic effect of interlayer stability and interfacial protection.
[0019] 5. In this invention, the DCG in sodium dicyanoguanidine (NaDCG) is used. - Anions and Cu in sodium cyanourea (NaCu) - All anions have a polycyano conjugated structure, and their molecular size and charge distribution are adapted to the graphite interlayer environment. Multiple nitrogen atoms can serve as strong coordination sites, embedding into the graphite interlayer after the first discharge, and anchoring to the interlayer structure through the synergistic effect of coordination bonds and π bonds, forming a persistent and stable ligand channel. This expands the graphite interlayer spacing to 0.41~0.42 nm, effectively reducing the sodium ion embedding energy barrier, inhibiting interlayer collapse, and ensuring structural integrity during cycling.
[0020] 6. In this invention, the NaDCG and NaCU additives do not interfere with the main coordination layer of the electrolyte. They interact with the molecules of the outer solvation layer, promoting the efficient desolvation and embedding of sodium ions into the graphite layer while maintaining high ionic conductivity.
[0021] 7. In this invention, the additives stabilize the interlayer structure of graphite while participating in the electrode interface reaction to form a dense and highly ionicly conductive SEI film, thereby inhibiting electrolyte decomposition and electrode corrosion.
[0022] 8. In this invention, the electrolyte improves thermal stability through the conjugated system in its molecular structure, achieving a triple effect of interlayer stability, interface protection, and enhanced thermal safety when the battery exothermic reaction temperature is increased to 25~30℃. Attached Figure Description
[0023] Figure 1 This is a flowchart of an electrolyte for a graphite negative electrode sodium-ion battery proposed in this invention. Detailed Implementation
[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0025] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0026] Example 1 This embodiment provides an electrolyte for a graphite negative electrode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6); Bridging-donor-ligand: Sodium dicyanoguanidine (NaDCG).
[0027] Experimental objective: Prepare an electrolyte for a graphite anode sodium-ion battery with NaDCG as the sole additive.
[0028] Experimental steps: S1: Weigh 84.5 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain an organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: Add 0.5 parts by weight of sodium dicyanoguanidine (NaDCG) additive to the basic electrolyte prepared in S2, controlling the added mass to be 0.5% of the total mass of the electrolyte, and then continue stirring for 6 hours to make the additive evenly dispersed, thus obtaining an electrolyte containing the additive. S4: The electrolyte containing additives prepared in S3 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0029] Experimental results: See Table 1 for details.
[0030] In Example 1, sodium dicyanidate guanidine (NaDCG) was used as a bridging-donor-ligand additive. The cyano group in its molecular structure has strong coordination ability, allowing it to form a stable solvation sheath structure with sodium ions. During charging, it preferentially undergoes reduction and decomposition on the graphite anode surface before solvent molecules, forming a dense solid electrolyte interphase (SEI) film rich in Na-CN / Na-N bonds. This SEI film exhibits high ion conductivity, excellent electronic insulation, and strong mechanical stability, promoting rapid desolvation of sodium ions, preventing continuous electrolyte decomposition, and adapting to changes in the graphite anode volume. Therefore, a capacity of 210.2 mAh·g was achieved. -1 It boasts a high initial capacity and a long cycle retention rate of 94.5%, with a coulomb efficiency of 99.83%.
[0031] Example 2 This embodiment provides an electrolyte for a graphite negative electrode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6); Bridging-donor-ligand: Sodium cyanurate (NaCu).
[0032] Experimental objective: To investigate the effect of a single NaCu additive on the electrolyte.
[0033] Experimental steps: S1: Weigh 84 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain a mixed organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the mixed organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: Add 1 part by weight of sodium cyanourea (NaCu) additive to the basic electrolyte prepared in S2, and control the added mass to be 0.5% of the total mass of the electrolyte. Then continue stirring for 6 hours to make the additive evenly dispersed, and obtain an electrolyte containing the additive. S4: The electrolyte containing additives prepared in S3 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0034] Experimental results: See Table 2 for details.
[0035] In Example 2, the sodium cyanourea molecule contains dual functional groups of cyano and urea. The urea group can enhance the interaction with solvent molecules through hydrogen bonding, while the cyano group provides coordination sites for sodium ions. Through the synergistic coordination effect, the urea group and ether solvent form a hydrogen bond network to stabilize the solvation structure. The urea group decomposition products and the cyano group decomposition products jointly construct a composite SEI film and inhibit solvent co-intercalation. However, the single cyano group coordination effect is more advantageous in sodium-ion battery systems.
[0036] Example 3 This embodiment provides an electrolyte for a graphite negative electrode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6); Bridging-donor-ligand: Sodium dicyanoguanidine (NaDCG) and sodium cyanourea (NaCU).
[0037] Experimental objective: To investigate the effect of compound NaDCG and NaCu on the electrolyte.
[0038] Experimental steps: S1: Weigh 83 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain an organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: Add 1.2 parts by weight of sodium dicyanoguanidine (NaDCG) and 0.8 parts by weight of sodium cyanourea to the basic electrolyte prepared in S2, controlling the added mass to be 2% of the total mass of the electrolyte. Then continue stirring for 6 hours to ensure uniform dispersion of the additives, and obtain an electrolyte containing the additives. S4: The electrolyte containing additives prepared in S3 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0039] Experimental results: See Table 3 for details.
[0040] In Example 3, the combination of NaDCG and NaCu produces a synergistic enhancement effect. NaDCG provides high ion conductivity, while NaCu provides film flexibility. Together, they form a gradient SEI structure, with the inner layer rich in NaDCG decomposition products and the outer layer rich in NaCu decomposition products. The mass ratio of 1.2:0.8 achieves the best balance between functional group density and film thickness. Therefore, Example 3 achieves the best performance, proving that the combination strategy can give full play to the complementary advantages of the two additives.
[0041] Comparative Example 1 This embodiment provides an electrolyte for a graphite negative electrode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6).
[0042] Experimental objective: Prepare an additive-free electrolyte for a graphite anode sodium-ion battery.
[0043] Experimental steps: S1: Weigh 85 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain an organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: The basic electrolyte prepared in S2 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0044] Experimental results: See Table 4 for details.
[0045] In Comparative Example 1, the diethylene glycol dimethyl ether in the electrolyte without additives is unstable on the graphite anode surface and preferentially decomposes and consumes active sodium. The resulting interfacial film is loose and porous, which cannot effectively prevent electrolyte penetration, leading to uneven sodium deposition and sodium dendrite growth. Dendrites may pierce the diaphragm and cause a short circuit. Therefore, Comparative Example 1 has the worst performance, highlighting the necessity of additives.
[0046] Comparative Example 2 This embodiment provides an electrolyte for a graphite negative electrode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6); Bridging-donor-ligand: Sodium dicyanoguanidine (NaDCG).
[0047] Experimental objective: To investigate the effect of low-dosage NaDCG addition on electrolyte performance.
[0048] Experimental steps: S1: Weigh 84.9 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain an organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: Add 0.1 parts by weight of sodium dicyanoguanidine (NaDCG) additive to the basic electrolyte prepared in S2, controlling the added mass to be 0.1% of the total mass of the electrolyte, and then continue stirring for 6 hours to make the additive evenly dispersed, thus obtaining an electrolyte containing the additive. S4: The electrolyte containing additives prepared in S3 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0049] Experimental results: See Table 5 for details.
[0050] In Comparative Example 2, the insufficient additive content resulted in a low NaDCG concentration, which prevented the formation of a continuous and dense SEI film on the negative electrode surface. The exposed graphite surface caused the electrolyte to decompose continuously. The incomplete film layer was prone to breakage and exposure of fresh surface during cycling, leading to accelerated cycle decay. Therefore, the performance of Comparative Example 2 was significantly lower than that of Example 1, proving that 0.5% is the optimal addition threshold for NaDCG.
[0051] Comparative Example 3 This embodiment provides an electrolyte for a conventional graphite anode sodium-ion battery, and the specific implementation steps include: Experimental materials: Organic solvent: diethylene glycol dimethyl ether G2; Sodium salt: Sodium hexafluorophosphate (NaPF6); Bridging-donor-ligand: Sodium cyanurate (NaCu).
[0052] Experimental objective: A high-dosage NaCu additive was provided to investigate the effect of high dosage on electrolyte performance.
[0053] Experimental steps: S1: Weigh 81.5 parts by weight of diethylene glycol dimethyl ether G2, then place it in a dry glove box and dehydrate it using a molecular sieve for 48 hours while controlling the moisture content to <10ppm, to obtain an organic solvent for later use. S2: In an argon-protected glove box, weigh 15 parts by weight of sodium hexafluorophosphate (NaPF6), then add it to the organic solvent prepared in step S1, and finally stir magnetically for 12 hours to completely dissolve the sodium salt and obtain the basic electrolyte. S3: Add 3.5 parts by weight of sodium cyanourea (NaCu) additive to the basic electrolyte prepared in S2, controlling the added mass to be 3.5% of the total mass of the electrolyte, and then continue stirring for 6 hours to make the additive evenly dispersed, thus obtaining an electrolyte containing the additive. S4: The electrolyte containing additives prepared in S3 was allowed to stand for 24 hours to mature, then filtered to remove insoluble matter, and then installed in a sodium-ion battery for electrochemical performance testing.
[0054] Experimental results: See Table 6 for details.
[0055] In Comparative Example 3, the excessive amount of additives led to the decomposition of excess NaCu, forming an excessively thick SEI film, which increased the diffusion resistance of sodium ions. At the same time, the high concentration of additives increased the viscosity of the electrolyte and reduced the ion mobility. The excessive additives themselves decomposed and consumed active sodium and reduced the first efficiency. Therefore, the performance of Comparative Example 3 decreased, proving that there is an optimal concentration window for the additives.
[0056] Based on the comparative embodiments and comparative examples, and referring to Figure 1 The flowchart illustrates how Example 1, through an optimal balance of additive types and amounts, cleverly improved the long-cycle stability and high-rate performance of graphite anode sodium-ion batteries by using a single NaDCG additive (0.5%) with cyano coordination film formation mechanism. This makes it suitable for cost-sensitive, high-cycle-life-demand large-scale applications. Example 2, while also achieving a 94.2% capacity retention rate using sodium cyanourea (NaCu) as a single additive, showed slightly weaker hydrogen bonding between the urea groups compared to the coordination effect of the cyano groups, resulting in slightly inferior performance compared to Example 1. Example 3, employing a NaDCG and NaCu combination strategy, achieved an optimal 95.1% capacity retention rate, but increased process complexity and cost. Comparative Example 1 used an additive-free base electrolyte, but the initial capacity was only 108.3 mAh·g. -1 After 100 cycles, the capacity retention rate plummeted to 48.2%, proving that a stable SEI film cannot be formed without additives. Comparative Example 2 used a low amount of NaDCG, but the capacity retention rate was only 75.3%, proving that too low an additive concentration cannot form a continuous and dense protective film layer. Comparative Example 3 highlighted the functional limitations of the traditional high-addition strategy, but excessive additives led to an excessively thick film layer, increased viscosity, and a decrease in capacity retention rate to 82.1%. Therefore, this invention, through the molecular design and dosage optimization of bridging-donor-ligand additives, achieves the optimal balance between SEI film density and ion conductivity at an addition amount of 0.5%. A single additive can meet most application requirements, while a compounding strategy can further explore performance potential in high-end scenarios. The overall technical solution has significant innovation and practical value.
[0057] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.
[0058] In conclusion, 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. An electrolyte for a graphite negative electrode sodium-ion battery, characterized in that, It consists of organic solvents, sodium salts, and additives.
2. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The organic solvent is one or more of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
3. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The sodium salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium difluorosulfonamide.
4. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The additive is one or more of sodium dicyanoguanidine and sodium cyanourea.
5. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 4, characterized in that, The additive compound is formulated with sodium dicyanoguanidine and sodium cyanourea in a mass ratio of 1 to 2:
1.
6. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The electrolyte is composed of 10-20 parts by weight of sodium salt, 77-89.8 parts by weight of organic solvent, and 0.2-3.0 parts by weight of additives.
7. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The water content of the electrolyte is ≤10ppm.
8. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The electrolyte is used in a graphite anode sodium-ion battery at 300 mA·g -1 Initial charging capacity at current density ≥200mAh·g -1 After 3000 cycles, the capacity retention rate is ≥94%.
9. The electrolyte for a graphite negative electrode sodium-ion battery as described in claim 1, characterized in that, The electrolyte has a discharge capacity ≥110 mAh·g at a 0.5C rate. -1 1C capacity retention rate ≥95%, 3C capacity retention rate ≥90%, 5C capacity retention rate ≥88%.