Electrolyte, method for preparing the same, and use thereof

Abstract

The application provides an electrolyte, a preparation method and use thereof. The electrolyte comprises a ferrous salt, an alcohol amine compound, an ether additive, a lithium salt and a solvent. The electrolyte provided by the application can effectively alleviate the gas production problem in the formation stage through the synergistic effect among the ferrous salt, the alcohol amine compound and the ether compound, avoids the occurrence of the bulging phenomenon of the battery cell, effectively avoids the occurrence of the side reaction between the electrolyte and the electrode, improves the stability of the SEI film, prevents the generation and puncture of lithium dendrites, and further improves the electrochemical performance and safety performance of the battery. In addition, the electrolyte provided by the application is simple and easy to operate and is easy to be applied to actual production.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, and particularly relates to an electrolyte, its preparation method, and its uses. Background Technology

[0002] During the first charge and discharge cycle of a lithium-ion battery, the electrolyte undergoes reduction and decomposition on the surface of the negative electrode material, forming a solid electrolyte interphase (SEI) film. This SEI film formation is an irreversible process, leading to reduced lithium content, lower coulombic efficiency, and poor cycle performance. Currently, these problems can be addressed by replenishing lithium ions into the battery through both positive and negative electrode lithium replenishment. Among these methods, adding a small amount of high-capacity material during the positive electrode slurry preparation to compensate for the irreversible capacity loss during the first charge and discharge cycle has gained widespread attention due to its high safety and simple manufacturing process.

[0003] Adding lithium replenishing agents to the positive electrode slurry can compensate for the lithium consumed during the initial charge to form the SEI film, thereby improving the battery's capacity, energy density, and cycle performance. However, lithium replenishing agents readily react with moisture and carbon dioxide in the air, producing large amounts of gases such as O2 and CO2. This phenomenon is particularly pronounced during the formation stage, which can easily lead to cell rupture due to gas buildup, causing safety issues.

[0004] To address the above problems, common solutions include: (1) coating the surface of the lithium replenishing agent with LiCoO2, Li2MoO3, Mo2N, ZrO2, or activated carbon to stabilize the structure of the lithium replenishing agent and slow down its reaction with air; (2) under a certain humidity environment, the positive electrode lithium replenishing agent reacts with water and carbon dioxide to form stable lithium carbonate on the surface of the positive electrode lithium replenishing agent, thus isolating the air from the reaction with the inner layer lithium replenishing agent; (3) extending the formation gas extraction time, but this method is not conducive to improving production efficiency, and incomplete gas removal can easily cause brown spots at the interface. At the same time, the above methods (1) and (2) can only slow down the reaction between the lithium replenishing agent and air, but cannot effectively avoid the problem of a large amount of gas generation caused by the reaction of the lithium replenishing agent with water in the electrolyte due to the electrolyte wetting the electrode during the formation stage.

[0005] CN106505250A discloses a method for suppressing gas generation during battery formation. The method includes the following steps: (1) pre-charging a lithium-ion battery at a predetermined voltage; (2) placing the pre-charged lithium-ion battery in a vacuum device and performing a low-vacuum evacuation process; (3) filling the lithium-ion battery with a protective gas; (5) charging the lithium-ion battery after filling with the protective gas under constant temperature conditions; (6) placing the charged lithium-ion battery in a vacuum device and performing a high-vacuum evacuation process. This method alleviates the gas generation during the formation process by continuously evacuating the vacuum device, but it is not conducive to improving production efficiency, and incomplete gas removal can easily cause brown spots at the interface.

[0006] Currently, by optimizing the electrolyte, it is hoped that production efficiency can be improved while alleviating gas generation during the formation stage. CN105261791A discloses an ultra-high temperature high-voltage lithium-ion battery electrolyte, which includes a non-aqueous organic solvent, lithium hexafluorophosphate, a gas generation inhibitor, and a low-resistance additive. The non-aqueous organic solvent includes a carbonate solvent and a high-boiling-point carboxylic acid ester solvent. The gas generation inhibitor is a sulfonyl lactone compound. The low-resistance additive is any one or a mixture of two of lithium fluorosulfonylimide and cyclic sulfate. It uses a sulfonyl lactone compound to suppress gas generation during the high-temperature storage of lithium-ion batteries, rather than targeting gas generation during formation, and does not consider the impact of the sulfonyl lactone compound on low-temperature performance.

[0007] Therefore, there is an urgent need to develop an electrolyte that can effectively alleviate gas generation during battery formation while improving production efficiency and reducing costs, thereby further enhancing the electrochemical and safety performance of the battery. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte, its preparation method, and its applications. Through the synergistic effect among ferrous salts, alkanolamine compounds, and ether compounds, the gas generation problem during the formation stage can be effectively alleviated, preventing cell bulging and swelling. Furthermore, it can effectively prevent side reactions between the electrolyte and the electrode, improve the stability of the SEI film, and prevent the formation and puncture of lithium dendrites, thereby further enhancing the electrochemical and safety performance of the battery.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides an electrolyte comprising ferrous salt, an alkanolamine compound, an ether additive, a lithium salt, and a solvent.

[0011] During the battery formation stage, the electrolyte wets the electrode sheets, and the water in the electrolyte comes into direct contact with the lithium replenishing agent, causing the lithium replenishing agent to react with the water in the electrolyte and generate a large amount of gas, mainly O2 and CO2. The electrolyte provided in this invention contains ferrous salt, alkanolamine compounds, and ether additives. The ferrous salt can react with the generated O2, that is, the ferrous salt in the electrolyte absorbs O2 impurity gas; the alkanolamine compounds can react with the generated CO2, that is, the alkanolamine compounds in the electrolyte absorb CO2 impurity gas. Therefore, the electrolyte provided in this invention can effectively absorb the gas generated during the formation stage, avoiding the degradation of battery performance and safety. The ether additives, as excellent negative electrode film-forming additives, can stably adhere to the negative electrode surface, isolating the electrolyte from contact with the negative electrode surface, avoiding the occurrence of side reactions, improving the stability of the SEI film, preventing the formation and puncture of lithium dendrites, thereby improving the cycle performance of the battery.

[0012] The electrolyte provided by this invention effectively alleviates gas generation during the formation stage through the synergistic effect among ferrous salts, alkanolamine compounds, and ether compounds, preventing cell bulging and swelling. Furthermore, it effectively avoids side reactions between the electrolyte and electrodes, improving the stability of the SEI film and preventing lithium dendrite formation and puncture, thereby further enhancing the electrochemical and safety performance of the battery. In addition, using the electrolyte provided by this invention to alleviate gas generation during the formation stage is simple, easy to operate, and readily applicable to actual production.

[0013] As a preferred embodiment of the present invention, with the electrolyte having a mass fraction of 100 wt%, the total mass fraction of the ferrous salt, the alkanolamine compound, and the ether additive is 0.5 to 10 wt%, for example, it can be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] This invention limits the total mass fraction of ferrous salts, alkanolamine compounds, and ether additives to 0.5–10 wt%. When the total mass fraction is below 0.5 wt%, the electrical and safety performance of the battery cell will degrade rapidly. This is because the low additive content leads to bulging and swelling of the battery cell, hindering ion transport and affecting its electrical and safety performance. When the total mass fraction is above 10 wt%, the battery cell will experience long-term electrical performance degradation. This is because the reduced proportion of lithium salts and solvents reduces the electrolyte wetting effect, which is detrimental to the battery cell's storage, cycling, and other electrical performance characteristics.

[0015] As a preferred embodiment of the present invention, with the total mass fraction of the ferrous salt, the alkanolamine compound, and the ether additive being 100 wt%, the mass fraction of the ferrous salt is 20-30 wt%, for example, it can be 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] This invention limits the mass fraction of ferrous salt to 20-30 wt%. When the mass fraction is below 20 wt%, it will cause the battery cell to bulge. This is because, on the one hand, Fe 3+ It reacts chemically with a small amount of impurity gas O2; on the other hand, a small amount of Fe... 3+ It can undergo coordination reactions with alkanolamine compounds, resulting in residual gaseous impurities (O2) in the system; when the mass fraction exceeds 30 wt%, it can cause cell bulging due to excessive Fe. 3+ It can undergo coordination reactions with alcohol amine compounds, resulting in some residual gaseous impurities such as CO2 remaining inside.

[0017] Preferably, based on a total mass fraction of 100 wt% for the ferrous salt, the alkanolamine compound, and the ether additive, the mass fraction of the alkanolamine compound is 50-70 wt%, for example, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt%, 60 wt%, 62 wt%, 64 wt%, 66 wt%, 68 wt%, or 70 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0018] This invention limits the mass fraction of the alkanolamine compound to 50–70 wt%. When the mass fraction is below 50 wt%, it will cause the battery cell to bulge. This is because only a portion of the alkanolamine compound reacts with the gaseous impurity CO2, while the other portion reacts with Fe. 3+ Coordination reactions occur, resulting in some residual gaseous impurities (CO2) in the system. When the mass fraction is higher than 70 wt%, it can cause cell bulging. This is because the presence of residual gaseous impurities (O2) in the system is detrimental to lithium-ion transport.

[0019] Furthermore, the content of alcohol amine compounds in this invention is higher than that of ferrous salts. This is because alcohol amine compounds can react with ferrous ions to absorb the Fe generated from O2 impurity gas. 3+ The coordination reaction occurs, and the resulting complex product has no effect on other components of the electrolyte.

[0020] Preferably, based on a total mass fraction of 100 wt% for the ferrous salt, the alkanolamine compound, and the ether additive, the mass fraction of the ether additive is 10-20 wt%, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0021] This invention limits the mass fraction of ether additives to 10-20 wt%. When the mass fraction is below 10 wt%, the battery cell's electrical performance weakens. This is because ether additives, as excellent negative electrode film-forming additives, can stably adhere to the negative electrode surface, isolating the electrolyte from contact with the negative electrode surface, avoiding side reactions, improving the stability of the SEI film, preventing the formation and puncture of lithium dendrites, and effectively improving the battery cell's cycle performance. When the mass fraction is above 20 wt%, the battery cell bulges. This is because the content of ferrous salts and alkanolamine compounds is too low to completely absorb gaseous impurities O2 and CO2 in the system.

[0022] Therefore, this invention controls the mass fraction of ferrous salt to 20-30 wt%, the mass fraction of alkanolamine compounds to 50-70 wt%, and the mass fraction of ether additives to 10-20 wt%, which is more conducive to leveraging the synergistic effect among ferrous salt, alkanolamine compounds, and ether compounds. This can better alleviate gas generation during the formation stage, improve SEI film stability, and further enhance the electrochemical and safety performance of the battery.

[0023] As a preferred embodiment of the present invention, with the electrolyte having a mass fraction of 100 wt%, the solvent has a mass fraction of 81-90 wt%, for example, it can be 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, or 90 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0024] Preferably, based on a mass fraction of 100 wt% for the electrolyte, the mass fraction of the lithium salt is 8 to 15 wt%, for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] As a preferred embodiment of the present invention, the ferrous salt includes any one or a combination of at least two of ferrous chloride, ferrous sulfate, or ferrous carbonate.

[0026] Preferably, the alkanolamine compound includes any one or a combination of at least two of monoethanolamine, diethanolamine, diisopropanolamine, or methyldiethanolamine.

[0027] Preferably, the ether additive includes any one or a combination of at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether.

[0028] As a preferred embodiment of the present invention, the solvent includes any one or a combination of at least two of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, or vinyl propionate.

[0029] Preferably, the lithium salt comprises any one or a combination of at least two of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium fluoroalkyl sulfonate, lithium dioxaborate, or lithium difluorooxaborate; preferably lithium hexafluorophosphate.

[0030] In a second aspect, the present invention provides a method for preparing the electrolyte described in the first aspect, the method comprising:

[0031] The electrolyte is obtained by mixing ferrous salt, alkanolamine compound, ether additive, lithium salt and solvent.

[0032] As a preferred embodiment of the present invention, the preparation method includes:

[0033] The lithium salt is mixed with the solvent, and then the ferrous salt, the alkanolamine compound, and the ether additive are added to obtain the electrolyte.

[0034] In this invention, ferrous salts, alkanolamine compounds, and ether additives can be added simultaneously or separately, and this invention does not limit the order in which they are added.

[0035] In a preferred embodiment of the present invention, all mixing is carried out under stirring conditions.

[0036] Preferably, the stirring speed is 1000 to 3000 rpm, for example, it can be 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm or 3000 rpm, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] Preferably, the temperature of the electrolyte preparation process is 20 to 40°C, for example, 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C or 40°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the humidity during the preparation of the electrolyte is 0-10%, for example, it can be 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the electrolyte described in the first aspect.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] The electrolyte provided by this invention effectively alleviates gas generation during the formation stage through the synergistic effect among ferrous salts, alkanolamine compounds, and ether compounds, preventing cell bulging and swelling. Furthermore, it effectively avoids side reactions between the electrolyte and electrodes, improving the stability of the SEI film and preventing lithium dendrite formation and puncture, thereby further enhancing the electrochemical and safety performance of the battery. In addition, using the electrolyte provided by this invention to alleviate gas generation during the formation stage is simple, easy to operate, and readily applicable to actual production. Detailed Implementation

[0042] 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.

[0043] Example 1

[0044] This embodiment provides an electrolyte comprising ferrous chloride, diethanolamine, ethylene glycol dimethyl ether, lithium hexafluorophosphate, and a mixture of ethylene carbonate and diethyl carbonate; based on a mass fraction of 100 wt% for the electrolyte, the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether is 5 wt%, the mass fraction of lithium hexafluorophosphate is 11 wt%, and the mass fraction of the mixture of ethylene carbonate and diethyl carbonate is 84 wt%.

[0045] Of which, based on a total mass fraction of ferrous chloride, diethanolamine and ethylene glycol dimethyl ether of 100 wt%, the mass fraction of ferrous chloride is 25 wt%, the mass fraction of diethanolamine is 60 wt%, and the mass fraction of ethylene glycol dimethyl ether is 15 wt%.

[0046] This embodiment also provides a method for preparing an electrolyte, the method comprising:

[0047] At a temperature of 30°C and a humidity of 5%, 11 wt% lithium hexafluorophosphate was added to a mixture of 84 wt% ethylene carbonate and diethyl carbonate, with the electrolyte having a mass fraction of 100 wt%. The mixture was stirred at 2000 rpm until homogeneous. Subsequently, 25 wt% ferrous chloride, 60 wt% diethanolamine, and 15 wt% ethylene glycol dimethyl ether were added, with the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether being 100 wt%. The mixture was stirred at 2000 rpm until homogeneous to obtain the electrolyte.

[0048] Example 2

[0049] This embodiment provides an electrolyte comprising ferrous sulfate, diisopropanolamine, diethylene glycol dimethyl ether, lithium hexafluorophosphate, and a mixture of ethylene carbonate and methyl ethyl carbonate; based on a mass fraction of 100 wt% for the electrolyte, the total mass fraction of ferrous sulfate, diisopropanolamine, and diethylene glycol dimethyl ether is 10 wt%, the mass fraction of lithium hexafluorophosphate is 8 wt%, and the mass fraction of the mixture of ethylene carbonate and methyl ethyl carbonate is 82 wt%.

[0050] Of which, based on a total mass fraction of ferrous sulfate, diisopropanolamine, and diethylene glycol dimethyl ether of 100 wt%, the mass fraction of ferrous sulfate is 20 wt%, the mass fraction of diisopropanolamine is 70 wt%, and the mass fraction of diethylene glycol dimethyl ether is 10 wt%.

[0051] This embodiment also provides a method for preparing an electrolyte, the method comprising:

[0052] At a temperature of 20°C and a humidity of 10%, 8 wt% lithium hexafluorophosphate was added to a mixture of 82 wt% ethylene carbonate and methyl ethyl carbonate, with the electrolyte mass fraction being 100 wt%. The mixture was stirred at 1000 rpm until homogeneous. Subsequently, 20 wt% ferrous sulfate, 70 wt% diisopropanolamine, and 10 wt% diethylene glycol dimethyl ether were added, with the total mass fraction of ferrous sulfate, diisopropanolamine, and diethylene glycol dimethyl ether being 100 wt%. The mixture was stirred at 1000 rpm until homogeneous to obtain the electrolyte.

[0053] Example 3

[0054] This embodiment provides an electrolyte comprising ferrous carbonate, methyl diethanolamine, tetraethylene glycol dimethyl ether, lithium hexafluorophosphate, and acrylate; based on a mass fraction of 100 wt% for the electrolyte, the total mass fraction of ferrous carbonate, methyl diethanolamine, and tetraethylene glycol dimethyl ether is 0.5 wt%, the mass fraction of lithium hexafluorophosphate is 15 wt%, and the mass fraction of acrylate is 84.5 wt%.

[0055] Of which, based on a total mass fraction of ferrous carbonate, methyl diethanolamine, and tetraethylene glycol dimethyl ether of 100 wt%, the mass fraction of ferrous carbonate is 30 wt%, the mass fraction of methyl diethanolamine is 50 wt%, and the mass fraction of tetraethylene glycol dimethyl ether is 20 wt%.

[0056] This embodiment also provides a method for preparing an electrolyte, the method comprising:

[0057] At a temperature of 40°C and a humidity of 0%, 15 wt% lithium hexafluorophosphate was added to 84.5 wt% acrylate, with the electrolyte being 100 wt% by mass. The mixture was stirred at 3000 rpm until homogeneous. Subsequently, 30 wt% ferrous carbonate, 50 wt% methyldiethanolamine, and 20 wt% tetraethylene glycol dimethyl ether were added, with the total mass fraction of ferrous carbonate, methyldiethanolamine, and tetraethylene glycol dimethyl ether being 100 wt% by mass. The mixture was stirred at 3000 rpm until homogeneous to obtain the electrolyte.

[0058] Example 4

[0059] The difference between this embodiment and Example 1 is that, based on an electrolyte mass fraction of 100 wt%, the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether in the electrolyte is 0.2 wt%. The total mass reduction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether is allocated to the mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0060] Example 5

[0061] The difference between this embodiment and Embodiment 1 is that, based on an electrolyte mass fraction of 100 wt%, the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether in the electrolyte is 15 wt%, and the total increase in mass of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether is equal to the total decrease in mass of the mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Embodiment 1.

[0062] Example 6

[0063] The difference between this embodiment and Example 1 is that, with a total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether of 100 wt%, the mass fraction of ferrous chloride is 15 wt%, and the reduced mass of ferrous chloride is allocated to diethanolamine and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0064] Example 7

[0065] The difference between this embodiment and Example 1 is that, with the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether being 100 wt%, the mass fraction of ferrous chloride is 35 wt%, and the increase in mass of ferrous chloride is equal to the total decrease in mass of diethanolamine and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0066] Example 8

[0067] The difference between this embodiment and Example 1 is that, based on a total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether of 100 wt%, the mass fraction of diethanolamine is 45 wt%, and the reduced mass of diethanolamine is allocated to ferrous chloride and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0068] Example 9

[0069] The difference between this embodiment and Example 1 is that, with the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether being 100 wt%, the mass fraction of diethanolamine is 75 wt%, and the increase in mass of diethanolamine is equal to the total decrease in mass of ferrous chloride and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0070] Example 10

[0071] The difference between this embodiment and Example 1 is that, with a total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether of 100 wt%, the mass fraction of ethylene glycol dimethyl ether is 5 wt%, and the reduced mass of ethylene glycol dimethyl ether is allocated to ferrous chloride and ethylene glycolamine according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0072] Example 11

[0073] The difference between this embodiment and Example 1 is that, with the total mass fraction of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether being 100 wt%, the mass fraction of ethylene glycol dimethyl ether is 25 wt%, and the increase in mass of ethylene glycol dimethyl ether is equal to the total decrease in mass of ferrous chloride and diethanolamine according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that ferrous chloride is omitted from the electrolyte, and the mass of ferrous chloride is allocated to diethanolamine and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that diethanolamine is omitted from the electrolyte, and the mass of diethanolamine is allocated to ferrous chloride and ethylene glycol dimethyl ether according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is that ethylene glycol dimethyl ether is omitted from the electrolyte, and the mass of ethylene glycol dimethyl ether is allocated to ferrous chloride and diethanolamine according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0080] Comparative Example 4

[0081] The difference between this comparative example and Example 1 is that ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether are omitted from the electrolyte, and the total mass of ferrous chloride, diethanolamine, and ethylene glycol dimethyl ether is allocated to the mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate according to the electrolyte formulation ratio. The remaining process parameters and operating conditions are the same as in Example 1.

[0082] Batteries were assembled using the electrolytes prepared in Examples 1-11 and Comparative Examples 1-4, respectively. The assembly process is as follows:

[0083] (1) Preparation of positive electrode sheet: Based on the mass fraction of the coating on the positive electrode sheet being 100wt%, 93% lithium iron phosphate (LFP), 2.5% lithium supplementer (Li5FeO4), 3% conductive agent (carbon nanotube), 1% binder (polytetrafluoroethylene) and 0.5% dispersant (PVP) are mixed and stirred evenly, and a solvent (NMP) is added to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated on aluminum foil, dried, cold pressed, and die-cut into strips to prepare a positive electrode sheet.

[0084] (2) Preparation of negative electrode sheet: Based on the mass fraction of the coating on the negative electrode sheet being 100wt%, 94% of graphite, 2% of conductive agent (carbon black), 2% of adhesive (sodium carboxymethyl cellulose) and 2% of binder (styrene-butadiene rubber) are mixed and stirred evenly, and deionized water is added to prepare a negative electrode slurry. Then, the negative electrode slurry is evenly coated on copper foil, cold-pressed, baked and die-cut into strips to prepare a negative electrode sheet.

[0085] (3) The positive electrode, the separator and the negative electrode are wound into a core under a certain pressure and the core is placed in an aluminum shell; among them, the separator is PP film.

[0086] (4) Under negative pressure, the electrolytes obtained in Examples 1-11 and Comparative Examples 1-4 are injected respectively. After the electrolytes have been allowed to stand for a while, they are then encapsulated and subjected to subsequent processes such as formation and capacity testing to obtain the battery.

[0087] The batteries assembled using the electrolytes in Examples 1-11 and Comparative Examples 1-4 were subjected to performance tests under the following conditions:

[0088] (1) Gas generation test using the water displacement method: Prepare a beaker filled with 3 / 4 pure water, a piece of insulating tape about 50cm long, and a weighing balance; take 3 formed batteries and seal the battery tabs with insulating tape; take 1 battery, wrap it with insulating tape, and immerse the battery in water while maintaining the same pulling force, ensuring that the battery tabs are level with the water surface. Record the weight after the balance stabilizes; during the test, try to keep the pulling force and the battery immersion position consistent.

[0089] (2) Cyclic performance test: ① Charge and discharge the battery at a temperature of 25±2℃; ② Charge: 0.33C~0.5C current, constant current and constant voltage charging to 3.65V, cut-off current: 0.05C; ③ Discharge: 0.33C~0.5C current, constant current discharging to 2.5V; ④ Perform cell charge and discharge cycle test using the above process, and compare its capacity retention rate after 100 cycles / 500 cycles / 2000 cycles. The calculation formula is: X-cycle capacity retention rate = X-cycle capacity / first cycle discharge capacity × 100%.

[0090] The test results of the batteries prepared using the electrolytes in Example 1 and Comparative Example 4 are shown in Table 1.

[0091] Table 1

[0092]

[0093] The test results of the batteries prepared using the electrolytes in Examples 2-11 and Comparative Examples 1-3 are shown in Table 2.

[0094] Table 2

[0095]

[0096]

[0097] Analysis of the data in Tables 1 and 2 shows that:

[0098] A comparison of Examples 1 and 4-5 shows that when the total mass fraction of ferrous salts, alkanolamine compounds, and ether additives is less than 0.5 wt%, it will lead to accelerated degradation of the battery cell's electrical and safety performance; when the total mass fraction of ferrous salts, alkanolamine compounds, and ether additives is greater than 10 wt%, it will lead to long-term degradation of the battery cell's electrical performance.

[0099] A comparison of Examples 1 and 6-7 shows that when the mass fraction of ferrous salt is less than 20 wt%, it will cause the battery cell to bulge; when the mass fraction of ferrous salt is greater than 30 wt%, it will cause the battery cell to bulge.

[0100] A comparison of Examples 1 and 8-9 shows that when the mass fraction of the alkanolamine compound is less than 50 wt%, it will cause the battery cell to bulge; when the mass fraction of the alkanolamine compound is greater than 70 wt%, it will cause the battery cell to bulge.

[0101] A comparison of Example 1 and Examples 10-11 shows that when the mass fraction of ether additives is less than 10 wt%, it will lead to a weakening of the battery cell's electrical performance; when the mass fraction is greater than 20 wt%, it will lead to bulging of the battery cell.

[0102] A comparison of Example 1 and Comparative Examples 1-4 shows that in this invention, the synergistic effect of ferrous salts, alkanolamine compounds, and ether additives effectively alleviates gas generation during the formation stage, preventing cell bulging and swelling. Furthermore, it effectively prevents side reactions between the electrolyte and electrodes, improves the stability of the SEI film, and prevents lithium dendrite formation and puncture, thereby further enhancing the electrochemical and safety performance of the battery. The absence of any one of these additives will reduce the aforementioned improvements.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 lithium-ion batteries, characterized in that, The electrolyte comprises ferrous salts, alkanolamine compounds, ether additives, lithium salts, and solvents; Based on a mass fraction of 100 wt% for the electrolyte, the total mass fraction of the ferrous salt, the alkanolamine compound, and the ether additive is 0.5~10 wt%. Based on a total mass fraction of 100 wt% for the ferrous salt, the alkanolamine compound, and the ether additive, the mass fraction of the ferrous salt is 20-30 wt%. Based on a total mass fraction of 100 wt% for the ferrous salt, the alkanolamine compound, and the ether additive, the mass fraction of the alkanolamine compound is 50-70 wt%. Based on a total mass fraction of 100 wt% for the ferrous salt, the alkanolamine compound, and the ether additive, the mass fraction of the ether additive is 10-20 wt%. The alkanolamine compounds include any one or a combination of at least two of monoethanolamine, diethanolamine, diisopropanolamine or methyldiethanolamine; The ether additives include any one or a combination of at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether.

2. The electrolyte according to claim 1, characterized in that, With the electrolyte having a mass fraction of 100 wt%, the solvent has a mass fraction of 81-90 wt%.

3. The electrolyte according to claim 1, characterized in that, Based on a mass fraction of 100 wt% for the electrolyte, the mass fraction of the lithium salt is 8-15 wt%.

4. The electrolyte according to claim 1, characterized in that, The ferrous salt includes any one or a combination of at least two of ferrous chloride, ferrous sulfate, or ferrous carbonate.

5. The electrolyte according to claim 1, characterized in that, The solvent includes any one or a combination of at least two of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, or vinyl propionate.

6. The electrolyte according to claim 1, characterized in that, The lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium fluoroalkyl sulfonate, lithium dioxaborate, or lithium difluorooxaborate.

7. A method for preparing the electrolyte according to any one of claims 1-6, characterized in that, The preparation method includes: The electrolyte is obtained by mixing ferrous salt, alkanolamine compound, ether additive, lithium salt and solvent.

8. The preparation method according to claim 7, characterized in that, The preparation method includes: The lithium salt is mixed with the solvent, and then the ferrous salt, the alkanolamine compound, and the ether additive are added to obtain the electrolyte.

9. The preparation method according to claim 7, characterized in that, All mixing was carried out under stirring conditions.

10. The preparation method according to claim 9, characterized in that, The stirring speed is 1000~3000 rpm.

11. The preparation method according to claim 8, characterized in that, The electrolyte is prepared at a temperature of 20~40℃.

12. The preparation method according to claim 8, characterized in that, The humidity during the preparation of the electrolyte is 0-10%.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte for lithium-ion batteries as described in any one of claims 1-6.

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