An overcharge-preventing electrolyte additive and application thereof in sodium-ion batteries

Abstract

The application discloses an overcharge-preventing electrolyte additive and application thereof in a sodium ion battery, and relates to the technical field of sodium ion batteries. The specific steps comprise the following steps: a conventional electrolyte with a sodium salt concentration of 0.7-1.4 M is prepared, two or more than two of electrolytes EC, PC and EMC are selected and prepared, and the prepared electrolyte is named as a basic electrolyte; different concentrations of overcharge-preventing electrolyte additives A and additives B are added into the basic electrolyte as electrolyte additives, and sodium ion battery electrolytes containing different concentrations of additives are prepared. The method effectively improves the safety and electrochemical performance of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to an electrolyte additive for preventing overcharging and its application in sodium-ion batteries. Background Technology

[0002] Overcharging seriously threatens the safety of sodium-ion batteries. During overcharging, sodium ions are deintercalated from the positive electrode and gain electrons at the negative electrode. Over-deposited sodium forms sodium dendrites at the negative electrode, which may puncture the separator and cause a short circuit inside the battery. The positive electrode material that has been over-deintercalated has extremely high reactivity in sodium-ion electrolyte and is prone to thermal decomposition at high temperatures, releasing heat. Regardless of the mechanism, a large amount of heat will be released, causing thermal runaway of the sodium-ion battery and leading to safety accidents. To prevent sodium-ion batteries from overcharging during use, the methods currently used in the market are mainly divided into two categories: (1) introducing external components for voltage monitoring. (2) developing anti-overcharge and flame-retardant electrolytes for sodium-ion batteries. External protection methods mainly include installing positive temperature coefficient (PTC) elements, current interruption devices, external overcharge safety protection circuits, or explosion-proof safety valves inside the battery. However, introducing an external system to prevent battery overcharging will increase the weight and volume of the battery module, thereby increasing the cost and complexity of the battery. Once the external system fails, the battery will be in danger. By modifying the electrolyte, a self-protection mechanism can be established inside the battery. This not only simplifies the battery production process and reduces the manufacturing cost, but also improves battery safety in a fundamental way with higher reliability.

[0003] As an overcharge protection additive for sodium-ion batteries, it needs to have the following characteristics: (1) good solubility in the organic solvent of the electrolyte and fast diffusion speed. (2) good stability within the operating temperature and voltage range of the battery, with no side effects on the normal use of sodium-ion batteries. (3) strong protection effect on the battery in the high voltage range. According to the mechanism of action of sodium-ion battery overcharge protection electrolyte, it can be divided into two categories: redox additives and electropolymerization additives. Redox additives are oxidized at the positive electrode of the battery and diffuse to the negative electrode of the battery after the battery is overcharged to the redox reaction potential. The reduction products then pass through the separator back to the positive electrode and are oxidized again. In the process of repeated cycles, the excess charge in the overcharge process is consumed, and the overcharge protection effect is played. When lithium-ion batteries are overcharged, the polymerizable monomers will undergo electropolymerization reaction. The generated electropolymerization products can increase the internal resistance of the battery, limit the current and consume the overcharged energy.

[0004] This work introduces (ortho-, meta-, and para-)fluoroanisole (FA) electrolyte additives, which allow the additives to function at a certain potential. This prevents the voltage of sodium-ion batteries from continuously rising during charging and exceeding the safety threshold, thus fundamentally solving the overcharge safety problem of sodium-ion batteries. At the same time, the electrolyte additives are characterized by small amounts and high efficiency, which can reduce the cost increase caused by the introduction of external overcharge protection structures and reduce the complexity of the battery system. Summary of the Invention

[0005] The purpose of this invention is to provide an anti-overcharge electrolyte additive and a method for its application in sodium-ion batteries. By combining and optimizing the proportion of different additives in the electrolyte, the voltage of sodium-ion batteries is prevented from continuously rising during charging, thereby improving the electrochemical performance and safety of sodium-ion batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An electrolyte additive for preventing overcharging and its application in sodium-ion batteries, characterized in that the electrolyte comprises: sodium salt, electrolyte, additive A and additive B.

[0008] Preferably, additive A is selected from compound o-fluoroanisole (2-FA), m-fluoroanisole (3-FA), and p-fluoroanisole (4-FA).

[0009] Preferably, the preparation method of additive B is as follows:

[0010] By weight, 16-32 parts of 3,4-difluoro-2-methoxyaniline (CAS: 114076-35-6); 6-12 parts of N-allyl-2-pyrimidinamine; 0.002-0.03 parts of 1-allyl-3-methylimidazolium tetrafluoroborate (CAS: 851606-63-8); 3-6 parts of sodium ethoxide; 200-300 parts of toluene; and 3-7 parts of sodium hydroxide are stirred and reacted at 60-70℃ for 100-150 min. Toluene is removed by distillation to obtain additive B.

[0011] Preferably, additives A and B account for 1-20% of the total mass of the electrolyte.

[0012] Preferably, the sodium salt is sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4).

[0013] Preferably, the electrolyte comprises cyclic organic solvents and chain organic solvents. The cyclic organic solvents include one or more of ethylene carbonate, propylene carbonate, and butene carbonate, and the chain organic solvents include one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0014] Preferably, the positive electrode active material of the sodium-ion battery is NaFe. 0.5 Mn 0.5 O2, NaNi 0.3 Fe 0.4 Mn 0.3 O2, NaNi 0.33 Fe 0.34 Mn 0.33 O2, NaNi 0.25 Fe 0.5 Mn 0.25 O2, NaNi 0.2 Cu 0.1 Fe 0.4 Mn 0.3 O2, NaNi 0.25 Fe 0.4 Co 0.1 Mn 0.25 O2, NaNi 0.5 Fe 0.4 Mn 0.4 O 2.4 or NaNi 0.4 Fe 0.2 Mn 0.3 O 1.8 One or at least two of them.

[0015] Preferably, the electrolyte is prepared by the following method:

[0016] (1) Prepare a traditional electrolyte with a sodium salt concentration of 0.7-1.4M by selecting two or more of the electrolytes EC, PC and EMC and naming them as the basic electrolyte;

[0017] (2) Add different concentrations of anti-overcharge electrolyte additive A and additive B to the base electrolyte as electrolyte additives to prepare sodium-ion battery electrolytes with different concentrations of additives.

[0018] The preparation mechanism of additive B is as follows:

[0019] The 3,4-difluoro-2-methoxyaniline reacts with N-allyl-2-pyrimidinylamine and 1-allyl-3-methylimidazolium tetrafluoroborate respectively in an amino-olefin addition reaction to obtain a synergist containing difluoromethoxybenzene, pyrimidinylamine, and tetrafluoroborate, which is used to assist fluoroanisole as an overcharge prevention additive for sodium ion electrolytes.

[0020] The technical effects of additive B:

[0021] 1. Formation of a protective solid electrolyte interface

[0022] Chemical stability: These additives form a stable solid electrolyte interface (SEI) on the electrode surface, which effectively prevents further decomposition of the electrolyte under high voltage, thus preventing battery degradation under overcharge conditions. Selective permeation: The formed SEI film allows sodium ions to pass through but prevents larger organic molecules or dissociated ions from passing through, thereby ensuring battery cycle efficiency and lifespan.

[0023] 2. Promotes thermal stability

[0024] Increased heat capacity: The presence of additives can increase the heat capacity of battery components, slowing down the rate of temperature rise under overcharge conditions and providing time for protection measures to activate. Heat dissipation performance: Tetrafluoroborate is particularly known for its high thermal stability, remaining stable even at high temperatures, which helps prevent thermal runaway caused by overheating.

[0025] 3. Electrochemical activity and consumable protection

[0026] Potential regulation: These additives can undergo electrochemical reactions at specific voltages, thereby forming a protective layer before the battery reaches dangerous charging levels or altering the battery's internal resistance to limit current flow. Sacrificial agent role: In the electrochemical reaction, these additives can be oxidized or reduced first, thus sacrificing themselves to protect critical electrode materials from overcharging damage.

[0027] 4. Affects the properties of the electrolyte

[0028] Solubility and Compatibility: The addition of additives improves the solubility of the electrolyte and the compatibility with electrode materials, which helps stabilize the properties of the electrolyte and reduce the generation of harmful chemicals under overcharge conditions. Increased Ion Mobility: In particular, tetrafluoroborate, as an ionic liquid or additive, can enhance the overall ion mobility of the electrolyte and reduce heat accumulation in the battery under high load.

[0029] In summary, these mechanisms work together to give sodium-ion batteries better stability and safety under overcharge conditions. Further exploration of the applications of these compounds in different battery systems will be very important.

[0030] The technical mechanism of the above solution:

[0031] This invention provides an anti-overcharge electrolyte additive and its application in sodium-ion batteries. During battery overcharging, FA undergoes an electropolymerization reaction, and the generated polymer is initially uniformly deposited on the surface of the positive electrode material and the separator. As the reaction progresses, the deposited polymer increases and further grows along the pores in the separator, eventually penetrating the separator and forming a conductive bridge between the positive and negative electrodes. This creates a micro-short circuit inside the battery, reducing the battery voltage and improving the overcharge safety of the sodium-ion battery.

[0032] Technical effects:

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) This invention provides a method for improving battery safety. By optimizing the proportion of additives in the electrolyte, an overcharge-resistant electrolyte additive and its application in sodium-ion batteries are provided. During battery overcharging, FA undergoes an electropolymerization reaction, and the generated polymer is first uniformly deposited on the surface of the positive electrode material and the separator. As the reaction progresses, the deposited polymer increases and further grows along the pores on the separator, eventually penetrating the separator and forming a conductive bridge between the positive and negative electrodes, causing a micro-short circuit inside the battery, reducing the battery voltage, and improving the overcharge safety of sodium-ion batteries.

[0035] (2) The preparation process provided by this invention is relatively simple and requires less additives, thus improving the overall performance of sodium-ion batteries with a smaller amount of additives. The product has relatively good performance and a certain competitive advantage. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0038] Example 1

[0039] This invention provides a method for improving battery safety, comprising the following components:

[0040] This embodiment provides a sodium-ion battery electrolyte with the following formula: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different amounts of additives o-fluoroanisole (2-FA) and additive B are added according to Table 1. The electrolyte is prepared by mixing all raw materials thoroughly.

[0041] The preparation method of additive B is as follows:

[0042] Additive B is obtained by mixing 16g of 3,4-difluoro-2-methoxyaniline (CAS: 114076-35-6), 6g of N-allyl-2-pyrimidinamine, 0.002g of 1-allyl-3-methylimidazolium tetrafluoroborate (CAS: 851606-63-8), 3g of sodium ethoxide, 200g of toluene, and 3g of sodium hydroxide, stirring at 60℃ for 100min, and then removing the toluene by distillation.

[0043] Table 1

[0044] Formula Name propylene carbonate methyl ethyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> 2-FA Additive B Formula 1 20g 20g 20g 10.08g 3ml 0.05g Formula 2 20g 20g 20g 10.08g 6ml 0.1g Formula 3 20g 20g 20g 10.08g 9ml 0.25g Formula 4 20g 20g 20g 10.08g 12ml 0.4g

[0045] Example 2

[0046] This invention provides a method for improving battery safety, comprising the following components:

[0047] This embodiment provides a sodium-ion battery electrolyte with the following formula: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different amounts of additives m-fluoroanisole (3-FA) and additive B are added. The electrolyte is prepared according to Table 2. All raw materials are mixed thoroughly to form the electrolyte.

[0048] The preparation method of additive B is as follows:

[0049] Additive B is obtained by mixing 24g of 3,4-difluoro-2-methoxyaniline (CAS: 114076-35-6), 9g of N-allyl-2-pyrimidinamine, 0.015g of 1-allyl-3-methylimidazolium tetrafluoroborate (CAS: 851606-63-8), 4.5g of sodium ethoxide, 250g of toluene, and 5g of sodium hydroxide, stirring at 65°C for 125 minutes, and then removing the toluene by distillation.

[0050] Table 2

[0051] Formula Name propylene carbonate methyl ethyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> 3-FA Additive B Formula 1 20g 20g 20g 10.08g 3ml 0.05g Formula 2 20g 20g 20g 10.08g 6ml 0.1g Formula 3 20g 20g 20g 10.08g 9ml 0.25g Formula 4 20g 20g 20g 10.08g 12ml 0.4g

[0052] Example 3

[0053] This invention provides a method for improving battery safety, comprising the following components:

[0054] This embodiment provides a sodium-ion battery electrolyte with the following formula: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different amounts of additives, p-fluoroanisole (4-FA) and additive B, are prepared according to Table 3. The electrolyte is prepared by mixing all raw materials thoroughly.

[0055] The preparation method of additive B is as follows:

[0056] Additive B is obtained by mixing 32g of 3,4-difluoro-2-methoxyaniline (CAS: 114076-35-6), 12g of N-allyl-2-pyrimidinamine, 0.03g of 1-allyl-3-methylimidazolium tetrafluoroborate (CAS: 851606-63-8), 6g of sodium ethoxide, 300g of toluene, and 7g of sodium hydroxide, stirring at 70℃ for 150min, and then removing the toluene by distillation.

[0057] Table 3

[0058] Formula Name propylene carbonate methyl ethyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> 4-FA Additive B Formula 1 20g 20g 20g 10.08g 3ml 0.05g Formula 2 20g 20g 20g 10.08g 6ml 0.1g Formula 3 20g 20g 20g 10.08g 9ml 0.25g Formula 4 20g 20g 20g 10.08g 12ml 0.4g

[0059] Comparative Example 1

[0060] This invention provides a method for improving battery safety, comprising the following components:

[0061] This embodiment provides a sodium-ion battery electrolyte with the following formula: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. The electrolyte is prepared by mixing all raw materials thoroughly.

[0062] Test Example 1: Electrochemical Performance Test

[0063] Battery assembly: The positive electrode materials of Examples 1-3 and Comparative Example 1 were all Prussian blue (PB) positive electrodes. The positive electrode was composed of PB, polyvinylidene fluoride (PVDF) binder, carbon nanotubes and Super P conductive agent in a mass ratio of 90.0:4.0:1.5:4.5. N-methylpyrrolidone (NMP) was added to make a viscous adhesive solution, which was coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain the positive electrode sheet.

[0064] Hard carbon anode material is used as the active material. The anode is composed of HC, sodium alginate binder and Super P conductive agent in a mass ratio of 92:5:3. N-methylpyrrolidone (NMP) is added to make a viscous adhesive solution, which is coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain the anode sheet.

[0065] PE film is used as a separator.

[0066] The Prussian blue (PB)-HC battery was tested within a voltage range of 1.5V-4.5V. It was first discharged at a rate of 0.1C to a voltage of 1.5V, and then charged at a rate of 0.1C to 4.5V.

[0067] Test Example 2: LSV

[0068] After assembling the battery, remove it from the glove box and allow it to stand at room temperature for 2-3 hours. Then, use a Chenhua electrochemical workstation to perform linear scan voltammetry tests. For half-cells without added active materials, the scan voltage range is 1.5-6.0V, and the scan rate is 0.5mV / s. Next, scan the same sodium manganate-HC battery with a 5% 3FA electrolyte system at different scan rates of 0.1, 0.2, 0.5, and 1mV / s, scanning the voltage range of 1.5-6.0V. For the same half-cell, perform low-rate scans first, followed by high-rate scans.

[0069] Test Example 3: Thermal Stability Test

[0070] A fully discharged Prussian blue (PB)-HC battery was disassembled in a glove box to prepare a sodium manganate positive electrode and an HC negative electrode. The sodium manganate positive electrode, HC negative electrode, electrolyte containing (ortho-, meta-, and para-)fluoroanisole (FA), and two sets of basic electrolytes were then removed and immediately subjected to DSC testing. The test temperature range was -50 to 400℃, and the heating rate was 5℃ / s. The exothermic energy was observed.

[0071] Test Example 4: Safety Test at Room Temperature

[0072] To investigate the overcharge protection effect of (ortho-, meta-, para-)fluoroanisole (FA) as an electrolyte additive for sodium-ion batteries, we conducted a room-temperature overcharge safety test using a Prussian blue (PB) full-cell system to examine the effect of 3FA under actual conditions. The assembled Prussian blue (PB)-HC batteries were allowed to stand until the electrolyte fully impregnated the active material. Then, using a battery charge-discharge cycler, the batteries were pre-charged and discharged three times within the 1.5-4.0V range at a charge-discharge rate of 0.2C. The batteries were then rapidly overcharged to 4.5V at 0.2C, and the changes in the charge-discharge plateau after the introduction of the additive were observed. During the preparation process, a pipette was used to ensure that the same volume of electrolyte was added to each half-cell, and to prevent electrolyte leakage throughout the experiment.

[0073] Test results:

[0074] Example 1:

[0075]

[0076] Example 2:

[0077]

[0078] Example 3:

[0079]

[0080] Comparative example:

[0081]

[0082] As can be seen from the test data of the above embodiments and test examples, this method is effective in improving the safety and electrochemical performance of sodium-ion batteries.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An overcharge-resistant electrolyte for sodium-ion batteries, characterized in that, The electrolyte comprises: sodium salt, organic solvent, additive A and additive B; Additive A is selected from o-fluoroanisole, m-fluoroanisole, and p-fluoroanisole; The preparation method of additive B is as follows: By weight, 16-32 parts of 3,4-difluoro-2-methoxyaniline, 6-12 parts of N-allyl-2-pyrimidinamine, 0.002-0.03 parts of 1-allyl-3-methylimidazolium tetrafluoroborate, 3-6 parts of sodium ethoxide, 200-300 parts of toluene, and 3-7 parts of sodium hydroxide are stirred and reacted at 60-70℃ for 100-150 min. Toluene is removed by distillation to obtain additive B. Additives A and B comprise 1-20% of the total mass of the electrolyte.

2. The overcharge-resistant electrolyte for a sodium-ion battery according to claim 1, characterized in that, The sodium salt is sodium hexafluorophosphate or sodium perchlorate.

3. The overcharge-resistant electrolyte for a sodium-ion battery according to claim 1, characterized in that, The organic solvents include cyclic organic solvents and chain organic solvents. Cyclic organic solvents include one or more of ethylene carbonate, propylene carbonate, and butene carbonate. Chain organic solvents include one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

4. The application of the overcharge-resistant electrolyte according to claim 1 in a sodium-ion battery, characterized in that, The positive electrode active material of the sodium-ion battery is NaFe. 0.5 Mn 0.5 O2, NaNi 0.3 Fe 0.4 Mn 0.3 O2, NaNi 0.33 Fe 0.34 Mn 0.33 O2, NaNi 0.25 Fe 0.5 Mn 0.25 O2, NaNi 0.2 Cu 0.1 Fe 0.4 Mn 0.3 O2, NaNi 0.25 Fe 0.4 Co 0.1 Mn 0.25 O2, NaNi 0.5 Fe 0.4 Mn 0.4 O 2.4 or NaNi 0.4 Fe 0.2 Mn 0.3 O 1.8 One or at least two of them.

Images