An overcharge-preventing electrolyte, a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion batteries, and relates to an overcharge-preventing electrolyte as well as a preparation method and application thereof. The overcharge-preventing electrolyte comprises a sodium salt, a solvent and an electrolyte additive, and the electrolyte additive comprises sodium tetraphenylborate. By selecting sodium tetraphenylborate as an overcharge-preventing additive and applying it to the electrolyte, the sodium tetraphenylborate can be polymerized into a film at a high voltage of a positive electrode to limit an overcharge current, has a faster response speed, a more complete shutdown effect, can be reduced and decomposed on a negative electrode surface, participates in the formation or optimization of a solid electrolyte interface film, realizes a 'one-dose double-effect', improves the safety boundary and electrochemical performance of a battery, and avoids the negative influence of adding a conventional inert molecular additive on the ionic conductivity and solvation structure of the battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to an overcharge-resistant electrolyte, its preparation method, and its application. Background Technology

[0002] With the deepening of the "dual carbon" concept, the intermittent nature of renewable energy sources (such as solar and wind power) has created an urgent need for large-scale energy storage technologies. Sodium-ion batteries, due to their abundant resources (sodium's cost is far lower than lithium), environmental friendliness, and relatively high safety, are considered strong candidates for next-generation large-scale energy storage technologies. However, in practical applications, especially in large-scale battery packs, inconsistencies between individual battery cells and potential management system failures can lead to battery overcharging. Overcharging can trigger a series of side reactions, including increased internal pressure, soaring temperature, electrolyte decomposition, and damage to electrode materials, ultimately potentially leading to thermal runaway, or even fire and explosion, posing a significant safety threat to people and property.

[0003] Currently, the mainstream methods for improving the safety of sodium-ion batteries include improving electrode materials, optimizing battery management systems, and adding functional electrolyte additives. Among these, electrolyte additives have attracted widespread attention due to their low cost, minimal modification, and ease of industrialization. Traditional overcharge protection electrolyte additives (such as biphenyl) are mainly small-molecule substances. Their mechanism of action is that when the voltage is too high, electrochemical polymerization occurs on the surface of the electrode (especially the positive electrode), forming a non-conductive or low-conductive film, which limits the overcharge current by drastically increasing the internal resistance.

[0004] However, existing overcharge protection additives have the following main problems: ① They only react at the positive electrode when the voltage is too high, forming a non-conductive film to limit the current. This passive protection may not react quickly enough, or the insulating film formed may be uneven, leading to local current concentration and overheating risks; ② Most traditional overcharge protection additives are electrochemically inert small organic molecules. Adding them to the electrolyte will dilute the effective ion-conducting components, degrade the ionic conductivity of the electrolyte and the solvation structure of sodium ions, and thus affect the normal charge and discharge performance of the battery; ③ The synthesis process of some special overcharge protection additives is complex and the cost is high, which is not conducive to large-scale application in sodium-ion batteries where low cost is an important advantage.

[0005] Therefore, in view of the above-mentioned technical problems, developing an overcharge-resistant electrolyte that can actively, quickly and completely block overcharging without affecting the electrochemical performance of the battery is an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an anti-overcharge electrolyte, its preparation method, and its application. The anti-overcharge electrolyte can actively, quickly, and completely block battery overcharging without affecting the normal electrochemical performance of the battery (such as cycle life and rate performance), and is also low in cost and easy to industrialize.

[0007] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides an overcharge protection electrolyte, the overcharge protection electrolyte comprising a sodium salt, a solvent, and an electrolyte additive; The electrolyte additive includes sodium tetraphenylborate.

[0008] The overcharge protection electrolyte provided by this invention creatively uses sodium tetraphenylborate as an electrolyte additive, utilizing its differentiated reaction at the positive and negative electrode interfaces to achieve "dual effects with one additive," simultaneously improving the battery's safety margin and electrochemical performance. Specifically, unlike traditional overcharge protection electrolyte additives (such as biphenyl), which only passively react under high voltage, the sodium tetraphenylborate anion BPh4... ⁻ At overcharge potential, it acts as both a "sacrificial agent" and a "film-forming monomer." On the one hand, under high voltage at the positive electrode, it can undergo a polymerization reaction, oxidizing and polymerizing on the surface of the battery's positive electrode to form a high-barrier film to limit overcharge current. Moreover, the generated high-barrier film is a conductive polymer film. This film can cover the positive electrode surface more uniformly and quickly in the early stages of formation, resulting in a faster response speed and a more thorough turn-off effect. At the same time, the conductivity of this film avoids uneven current distribution and local overheating caused by local insulation, thus enhancing safety. On the other hand, at low potential at the negative electrode, it can undergo reduction and decomposition, participating in the formation or optimization of the solid electrolyte interface film. This design cleverly combines the sodium ion carrier with the safety function unit, avoiding the negative impact of adding inert molecules (traditional electrolyte additives) on the electrolyte's ionic conductivity and solvation structure. Consequently, it is harmless or even beneficial to the battery's electrochemical performance (such as cycle life and rate performance).

[0009] Furthermore, the sodium tetraphenylborate added to the overcharge protection electrolyte provided by this invention is inexpensive and does not require a complex synthesis process, making it easy to scale up for industrial applications.

[0010] Preferably, the solvent includes any one or a combination of at least two of the following: carbonate solvents, ether solvents, or phosphate solvents.

[0011] Preferably, the carbonate solvent includes any one or a combination of at least two of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC).

[0012] Preferably, the ether solvent includes any one or a combination of at least two of diethylene glycol dimethyl ether (G2), ethylene glycol dimethyl ether (DME), tetraethylene glycol dimethyl ether (G4), or tetrahydrofuran (THF).

[0013] Preferably, the phosphate ester solvent includes trimethyl phosphate (TMP) and / or triethyl phosphate (TEP).

[0014] Preferably, based on 1 L of solvent, the amount of sodium salt used is 0.5 to 2 mol, for example, 0.5 mol, 0.7 mol, 0.9 mol, 1.1 mol, 1.2 mol, 1.3 mol, 1.4 mol, 1.5 mol, 1.6 mol, 1.7 mol, 1.8 mol, 1.9 mol or 2 mol, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0015] Preferably, the sodium salt comprises any one or a combination of at least two of sodium difluorooxalate borate (NaDFOB), sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium dioxalate borate (NaBOB), or sodium nitrate (NaNO3).

[0016] Preferably, the amount of sodium tetraphenylborate used is 0.5-40% based on the total mass of the sodium salt and solvent as 100%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and more preferably, it is 1-10%.

[0017] In a second aspect, the present invention provides a method for preparing an overcharge-resistant electrolyte as described in the first aspect, the method comprising: first mixing a sodium salt and a solvent, then adding an electrolyte additive and mixing to obtain the overcharge-resistant electrolyte.

[0018] Preferably, the mixing temperature for adding electrolyte additives is 50~70℃, such as 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an overcharge-resistant electrolyte as described in the first aspect.

[0020] Preferably, the active material of the positive electrode includes any one or a combination of at least two of layered oxides, polyanionic compounds, or Prussian blue analogues.

[0021] Preferably, the active material of the negative electrode includes any one or a combination of at least two of hard carbon, soft carbon, or titanium-based oxides.

[0022] Preferably, the diaphragm comprises a glass fiber diaphragm or a polyolefin porous membrane.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The overcharge protection electrolyte provided by the present invention includes sodium salt, solvent and electrolyte additive, and the electrolyte additive includes sodium tetraphenylborate; by applying sodium tetraphenylborate as an overcharge protection additive to the electrolyte, the differential reaction of sodium tetraphenylborate at the positive and negative electrode interfaces is utilized to polymerize into a film under high voltage at the positive electrode to limit the overcharge current, the response speed is faster, the turn-off effect is more thorough, and it can be reduced and decomposed on the negative electrode surface to participate in the formation or optimization of the solid electrolyte interface film, thus achieving "one agent with two effects", while improving the safety boundary and electrochemical performance of the battery, and avoiding the negative impact of adding inert molecular additives on the electrolyte ionic conductivity and solvation structure; (2) The sodium tetraphenylborate added to the overcharge protection electrolyte provided by the present invention is a commercially mature reagent with low cost and no complicated synthesis process, making it easy to scale up to industrial scale. Attached Figure Description

[0024] Figure 1 These are charge-discharge curves of batteries made from the electrolytes provided in Example 2 and Comparative Example 1. Detailed Implementation

[0025] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0026] Unless otherwise specified, the overcharge protection electrolytes described in the following embodiments are all prepared in a glove box filled with argon atmosphere.

[0027] Example 1 An overcharge protection electrolyte comprises sodium hexafluorophosphate, ethylene carbonate, diethyl carbonate, and sodium tetraphenylborate; The volume ratio of ethylene carbonate to diethyl carbonate is 3:7. Based on a total volume of ethylene carbonate and diethyl carbonate of 1 L, the amount of sodium hexafluorophosphate used is 1 mol; Based on the total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate being 100%, the mass of sodium tetraphenylborate is 1%. The preparation method of the overcharge protection electrolyte provided in this embodiment 1 includes: mixing a mixture of ethylene carbonate and diethyl carbonate, first adding sodium hexafluorophosphate and mixing evenly, then adding sodium tetraphenylborate powder, and heating at 60°C until completely dissolved to obtain the overcharge protection electrolyte.

[0028] Example 2 An overcharge protection electrolyte comprises sodium difluorooxalate borate, diethylene glycol dimethyl ether, and sodium tetraphenylborate; Wherein, based on a volume of 1 L of diethylene glycol dimethyl ether, the amount of sodium difluorooxalate borate is 1 mol; Based on the total mass of diethylene glycol dimethyl ether and sodium difluorooxalate borate being 100%, the mass of sodium tetraphenylborate is 2%. The preparation method of the overcharge protection electrolyte provided in this embodiment 2 includes: adding sodium difluorooxalate borate to diethylene glycol dimethyl ether and mixing evenly, then adding sodium tetraphenylborate powder, and heating at 50°C until completely dissolved to obtain the overcharge protection electrolyte.

[0029] Example 3 An overcharge protection electrolyte comprises sodium difluorooxalate borate, ethylene carbonate, diethyl carbonate, propylene carbonate, and sodium tetraphenylborate. The volume ratio of ethylene carbonate, diethyl carbonate, and propylene carbonate is 1:4:5. Based on a total volume of ethylene carbonate, diethyl carbonate, and propylene carbonate of 1 L, the amount of sodium difluorooxalate borate used is 1 mol. Based on the total mass of sodium difluorooxalate borate, ethylene carbonate, diethyl carbonate, and propylene carbonate being 100%, the mass of sodium tetraphenylborate is 7%. The preparation method of the overcharge protection electrolyte provided in this embodiment 3 includes: mixing ethylene carbonate, diethyl carbonate and propylene carbonate as solvents, first adding sodium difluorooxalate borate and mixing evenly, then adding sodium tetraphenylborate powder, and heating at 70°C until completely dissolved to obtain the overcharge protection electrolyte.

[0030] Example 4 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 3%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0031] Example 5 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 5%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0032] Example 6 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 8%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0033] Example 7 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 10%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0034] Example 8 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 0.5%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0035] Example 9 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 20%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0036] Example 10 An overcharge protection electrolyte differs from Example 1 only in that, based on a total mass of sodium hexafluorophosphate, ethylene carbonate, and diethyl carbonate of 100%, the mass of sodium tetraphenylborate is 40%, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0037] Example 11 An overcharge protection electrolyte differs from Example 1 only in that an equimolar amount of sodium tetrafluoroborate is used instead of sodium hexafluorophosphate; all other substances, amounts, and preparation methods are the same as in Example 1.

[0038] Example 12 An overcharge protection electrolyte differs from Example 1 only in that an equimolar amount of sodium nitrate is used instead of sodium hexafluorophosphate; all other substances, amounts, and preparation methods are the same as in Example 1.

[0039] Comparative Example 1 An electrolyte is provided that differs from that of Example 1 only in that sodium tetraphenylborate is not added; all other substances, amounts, and preparation methods are the same as in Example 1.

[0040] Comparative Example 2 An overcharge protection electrolyte differs from Example 1 only in that it uses an equal mass of biphenyl instead of sodium tetraphenylborate; all other substances, amounts, and preparation methods are the same as in Example 1.

[0041] Comparative Example 3 An overcharge protection electrolyte differs from Example 1 only in that diethyl carbonate of equal mass is used instead of sodium tetraphenylborate; all other substances, amounts, and preparation methods are the same as in Example 1.

[0042] Performance testing: (1) Using polyanionic polypropylene (NFPP) as the positive electrode, sodium sheet as the negative electrode, and glass fiber membrane as the separator, and combining the overcharge protection electrolyte provided in Example 2 and the electrolyte provided in Comparative Example 1, CR2032 type button batteries were assembled respectively. Then, a forced overcharge test was performed at 25°C, and the battery was charged to the set capacity (150% SOC) at a constant rate (0.5 C). Then, a normal discharge test was performed, and the charge-discharge curves were obtained as shown in the figure. Figure 1 As shown; The voltage of the battery made with the electrolyte provided in Comparative Example 1 rose sharply to over 5 V in the later stage of overcharging. In contrast, the voltage of the battery made with the overcharge protection electrolyte provided in Example 2 reached a threshold of about 4.3 V when charged to about 150% SOC, and a clear voltage "plateau" appeared. The voltage was effectively clamped and no longer continued to rise. This proves that the overcharge protection electrolyte with 2% sodium tetraphenylborate by mass can achieve efficient and reliable battery-level overcharge protection and reduce the risk of battery overcharging.

[0043] (2) Using polyanionic poly(NFPP) as the positive electrode, sodium sheet as the negative electrode, and glass fiber as the separator, and combining the anti-overcharge electrolyte provided in Examples 1-12 and the electrolyte provided in Comparative Examples 1-3, CR2032 button batteries were assembled respectively. Then, a forced overcharge test was performed at 25°C. The battery was charged to the set capacity (150% SOC) at a constant rate (0.5 C). The voltage threshold was obtained as the turn-off voltage. Then, a normal discharge test was performed. The number of times the battery's limit voltage was not exceeded was obtained as the effective anti-overcharge cycle. The data obtained from the above tests were recorded in Table 1. Table 1 According to the data in Table 1: The overcharge protection electrolytes provided in Examples 1-12 use sodium tetraphenylborate as an overcharge protection additive, which can respond promptly and make the battery's shutdown voltage 4.3-4.4 V. Under the above shutdown voltage conditions, the battery can be given an effective overcharge protection cycle of 70-100 cycles. Among them, Example 2 performs the best, with an effective overcharge protection cycle of nearly 100 cycles.

[0044] Comparing Example 1 and Comparative Examples 1-3, it can be seen that the electrolytes provided by Comparative Example 1 (without overcharge protection additive) and Comparative Example 3 (with a different type of additive) were further processed into batteries, resulting in a turn-off voltage of 5.0 V and an effective overcharge protection cycle of 0. However, the electrolyte provided by Comparative Example 2, which used biphenyl as an overcharge protection additive, was further processed into batteries, resulting in an effective overcharge protection cycle of only 9 weeks under a turn-off voltage of 4.5 V, indicating a poor overcharge protection effect.

[0045] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An overcharge-resistant electrolyte, characterized in that, The overcharge protection electrolyte includes sodium salt, solvent, and electrolyte additives; The electrolyte additive includes sodium tetraphenylborate.

2. The overcharge protection electrolyte according to claim 1, characterized in that, The solvent includes any one or a combination of at least two of the following: carbonate solvents, ether solvents, or phosphate solvents.

3. The overcharge protection electrolyte according to claim 2, characterized in that, The carbonate solvents include any one or a combination of at least two of ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, or methyl ethyl carbonate. Preferably, the ether solvent includes any one or a combination of at least two of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or tetrahydrofuran; Preferably, the phosphate ester solvent includes trimethyl phosphate and / or triethyl phosphate.

4. The overcharge protection electrolyte according to any one of claims 1 to 3, characterized in that, Based on a solvent volume of 1L, the sodium salt volume is 0.5~2 mol.

5. The overcharge protection electrolyte according to any one of claims 1 to 4, characterized in that, The sodium salt includes any one or a combination of at least two of sodium difluorooxalate borate, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium dioxalate borate, or sodium nitrate.

6. The overcharge protection electrolyte according to any one of claims 1 to 5, characterized in that, The amount of sodium tetraphenylborate used is 0.5-40%, preferably 1-10%, based on the total mass of the sodium salt and solvent as 100%.

7. A method for preparing the overcharge protection electrolyte as described in any one of claims 1 to 6, characterized in that, The preparation method includes: first mixing sodium salt and solvent, then adding electrolyte additives and mixing to obtain the overcharge protection electrolyte.

8. The preparation method according to claim 7, characterized in that, The mixing temperature for adding electrolyte additives is 50~70℃.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an overcharge-resistant electrolyte as described in any one of claims 1 to 5.

10. The sodium-ion battery according to claim 9, characterized in that, The active material of the positive electrode includes any one or a combination of at least two of layered oxides, polyanionic compounds, or Prussian blue analogues. Preferably, the active material of the negative electrode includes any one or a combination of at least two of hard carbon, soft carbon, or titanium-based oxides; Preferably, the diaphragm comprises a glass fiber diaphragm or a polyolefin porous membrane.

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