Phosphorus-based additive-containing local high-concentration electrolyte, preparation method and application thereof, and lithium metal battery
By introducing lithium difluorooxalate phosphate (LiDFBOP) into lithium-ion batteries to regulate the solvation structure of locally high-concentration electrolytes, the problem of interfacial instability of positive electrode materials in lithium-ion batteries was solved, achieving oxidation resistance and interfacial stability under high voltage and improving the cycle performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-09
- Publication Date
- 2026-04-07
AI Technical Summary
The cathode materials of existing lithium-ion batteries are interfacially unstable in multi-electron redox reactions, leading to a decrease in battery capacity. Furthermore, high-concentration electrolytes have problems such as high viscosity and poor wettability, which limit their application.
The lithium salt additive lithium difluorooxalate phosphate (LiDFBOP) is introduced to regulate the solvation structure of locally high-concentration electrolytes, forming an electrode-electrolyte interface rich in F/P inorganic components, thereby improving interface stability.
It improves the battery's oxidation resistance under high voltage, enhances the stability of the lithium metal interface, improves the cycle stability and capacity retention of FeF3/Li batteries, and significantly improves the battery's charge and discharge performance.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of high-energy-density secondary battery technology, specifically to a locally high-concentration electrolyte containing phosphorus-based additives, its preparation method and application, and lithium metal batteries. Background Technology
[0002] Batteries are the preferred choice for energy storage systems and a key technology driving modern societal development. Among them, lithium-ion batteries, as the most advanced and practical representative of rechargeable power sources, are widely used in various portable electronic products and electric vehicles. However, with the iterative updates of electronic devices and the rapid development of new energy vehicles, lithium-ion batteries face severe challenges in terms of energy density and manufacturing costs. Commercially available intercalated cathode materials are gradually approaching their theoretical capacity limits, failing to meet the aforementioned demands. Therefore, it is necessary to explore and develop new cathode materials. Conversion-type cathode materials achieve lithium storage through multi-electron redox reactions and possess high theoretical specific capacity. Conversion-type iron fluoride (FeF3) cathodes have attracted widespread attention due to their moderate operating voltage, high specific capacity, high energy density, low cost, and abundant resources. When matched with lithium metal anodes, which have extremely high theoretical specific capacity (up to 3860 mAh g⁻¹), FeF3's mass / volume energy density is higher than that of traditional intercalated cathode materials, thus possessing extremely high development potential and making it an ideal cathode material for next-generation lithium and lithium-ion batteries.
[0003] The liquid-solid interface between transition metal fluorides and organic electrolytes is unstable (resulting in numerous side reactions). With increasing charge-discharge cycles, the organic electrolyte continuously decomposes, and an SEI layer accumulates on the electrode surface, hindering lithium-ion transport. After multiple cycles, the battery capacity gradually decreases, making it unsuitable for application. The use of a suitable electrolyte can provide a favorable reaction environment, better utilizing the performance of iron fluoride cathode materials.
[0004] Introducing appropriate functionalized additives into the electrolyte and specifically regulating the composition of the CEI layer can further stabilize the iron fluoride cathode interface, reducing the dissolution of active materials and the occurrence of side reactions. However, film-forming additives can sometimes form a relatively thick SEI on the electrode surface. An excessively thick SEI film may increase the internal resistance of the battery, leading to limited cathode kinetic performance. High-concentration electrolytes (HCEs) possess a unique solvation structure that endows the system with excellent electrochemical stability, but HCEs suffer from high viscosity and poor wettability, thus limiting their practical applications. Locally high-concentration electrolytes (LHCEs) retain the solvation structure of HCEs while overcoming their inherent drawbacks. LHCEs are beneficial for constructing CEIs rich in inorganic substances, stabilizing structural changes in conversion cathode materials, and suppressing the dissolution of active materials and the occurrence of side reactions. Summary of the Invention
[0005] The purpose of this invention is to provide a locally high-concentration electrolyte containing phosphorus-based additives. By introducing the lithium salt additive lithium difluorooxalate phosphate (LiDFBOP), the solvation structure of the locally high-concentration electrolyte is controlled, forming an electrode-electrolyte interface rich in F / P inorganic components. The locally high-concentration electrolyte containing LiDFBOP of this invention exhibits excellent physicochemical properties (antioxidant properties, high ion transport number, wettability, etc.) and good compatibility with both positive and negative electrodes, thus solving the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a locally high-concentration electrolyte containing phosphorus-based additives, comprising the following components: lithium salt, ether solvent, fluoroether diluent, and lithium difluorodioxarate phosphate;
[0007] The molar ratio of the lithium salt to the ether solvent is 1:1 to 1.5;
[0008] The molar ratio of the lithium salt to the fluoroether diluent is 1:2.5~3;
[0009] The amount of lithium difluorodioxalate phosphate added is 1~3 wt% of the total mass of the electrolyte.
[0010] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.
[0011] Preferably, the ether solvent is at least one of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.
[0012] Preferably, the fluoroether diluent is at least one of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.
[0013] A method for preparing the above-described high-concentration electrolyte containing phosphorus-based additives, characterized by comprising the following steps:
[0014] (1) In an argon atmosphere with water and oxygen levels below 0.1 ppm, lithium salt was added to a sample vial containing a mixture of ether-based solvent and fluorinated ether diluent, and stirred thoroughly until the lithium salt was completely dissolved (12 h) to obtain the basic electrolyte.
[0015] (2) In an argon atmosphere with water and oxygen levels below 0.1 ppm, the phosphorus-based additive is added to the electrolyte in step (1) by mass ratio and stirred thoroughly until the additive is completely dissolved (12h-24h) to obtain a locally high-concentration electrolyte containing the phosphorus-based additive.
[0016] Application of a locally high-concentration electrolyte containing phosphorus-based additives in conversion lithium metal batteries.
[0017] A conversion-type lithium metal battery includes a positive electrode, a negative electrode, an electrolyte, a separator, and a battery casing assembly, wherein the electrolyte is a locally high-concentration electrolyte containing phosphorus-based additives prepared by the method of claim 5.
[0018] Preferably, the positive electrode material is a conversion-type positive electrode FeF3, lithium metal, carbon-coated aluminum foil, or copper foil; the negative electrode material is lithium metal; and the separator is polypropylene or glass fiber.
[0019] Compared with the prior art, the beneficial effects of the present invention are:
[0020] (1) The present invention uses a local high-concentration electrolyte with LiFSI, TTE, DME and 3%LiDFBOP with a voltage window >4.5V to improve the oxidation resistance of FeF3 cathode under high voltage.
[0021] (2) The electrolyte provided by the present invention uses a small amount of LiDFBOP, which contains oxalic acid groups and phosphate groups that can preferentially decompose at high voltage (~4.5V) to form a CEI interface rich in P / F inorganic components; and reduce and decompose on the lithium metal side (~1.9V) to form a stable SEI interface, thereby improving the stability of the lithium metal interface.
[0022] (3) The present invention uses a locally high-concentration electrolyte containing 3% LiDFBOP. The charge and discharge working potential range of the FeF3 / Li battery is 1-4.5V. After 200 cycles at 0.2C rate, the discharge specific capacity is as high as 444 mAh g-1, and the capacity retention rate is 72.5%. After 400 cycles at 1C rate, the discharge specific capacity is as high as 371 mAh g-1, and the capacity retention rate is 82%, which improves the cycle stability of FeF3 / Li battery.
[0023] (4) LiDFBOP additive can be directly added to the electrolyte of lithium salts such as LiPF6, LiFSI, and LiTFSI. It has strong compatibility with mainstream systems. Adding 1-3wt% can significantly improve performance and the cost is controllable. Attached Figure Description
[0024] Figure 1 This is a comparison chart of the electrochemical stability windows of the two electrolytes in Example 3 (3%-LHCE) and the comparative example (LHCE).
[0025] Figure 2 The graph shows the cycle performance of Li / Cu batteries assembled using two electrolytes: Example 3 (3%-LHCE) and the comparative example (LHCE).
[0026] Figure 3The graph shows the cycling performance of FeF3 / Li batteries assembled with electrolytes from Examples 1 (1%-LHCE), 2 (2%-LHCE), 3 (3%-LHCE), and the comparative example (LHCE) at 1C rate.
[0027] Figure 4 The first three charge-discharge curves of the FeF3 / Li battery assembled with the electrolyte of Example 3 (3%-LHCE) at 0.2 C rate.
[0028] Figure 5 This is a graph showing the cycling performance of the FeF3 / Li battery assembled with the electrolyte of Example 3 (3%-LHCE) at a rate of 0.2 C. Detailed Implementation
[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] Please see Figures 1-5 All raw materials used in this invention can be purchased from the market, and the methods in the following embodiments are conventional methods in the field.
[0031] In this embodiment of the invention, the lithium salt is LiFSI, the ether solvent is DME, the diluent is TTE, and the phosphorus-based additive is LiDFBOP.
[0032] In this embodiment of the invention, the molar ratio of lithium salt to ether solvent is 1:1.2, and the molar ratio of lithium salt to diluent in the locally high-concentration electrolyte is 1:3.
[0033] In the embodiments of the present invention, the content of LiDFBOP in the locally high-concentration electrolyte containing LiDFBOP additive is 1~3wt% of the total electrolyte mass.
[0034] This invention introduces a phosphorus-based additive, LiDFBOP, which contains oxalic acid and phosphate groups. The presence of fluorine atoms lowers the lowest unoccupied molecular orbital (LUMO) energy level of the molecule, causing it to preferentially decompose on the electrode surface and form a stable interfacial film. On the FeF3 cathode surface, the inorganic components (such as LiF and LixPOyFz) generated by the decomposition of LiDFBOP can inhibit transition metal dissolution and electrolyte oxidation, thereby improving the cycle stability of the battery at a high voltage of 4.5 V.
[0035] The following is a specific example of the preparation of a locally high-concentration electrolyte containing phosphorus-based additives:
[0036] Example 1
[0037] (1) In an argon atmosphere with water and oxygen concentrations below 0.1 ppm, 1.87 g LiFSI was weighed and placed in a sample vial. Then, 6.96 g TTE and 1.08 g DME were added sequentially. After mixing, the mixture was magnetically stirred for 12 h to obtain a clear and transparent electrolyte.
[0038] (2) Add 1 wt% LiDFBOP to the electrolyte in step (1) and stir thoroughly until all the additives are dissolved. Record this as 1%-LHCE.
[0039] Example 2
[0040] (1) In an argon atmosphere with water and oxygen concentrations below 0.1 ppm, 1.87 g of LiFSI was weighed and placed in a sample bottle. Then, 6.96 g of TTE and 1.08 g of DME were added sequentially. After mixing, the mixture was magnetically stirred for 12 h to obtain a clear and transparent electrolyte.
[0041] (2) Add 2wt% LiDFBOP to the electrolyte in step (1) and stir thoroughly until all the additives are dissolved. Record this as 2%-LHCE.
[0042] Example 3
[0043] (1) In an argon atmosphere with water and oxygen concentrations below 0.1 ppm, 1.87 g of LiFSI was weighed and placed in a sample bottle. Then, 6.96 g of TTE and 1.08 g of DME were added sequentially. After mixing, the mixture was magnetically stirred for 12 h to obtain a clear and transparent electrolyte.
[0044] (2) Add 3wt% LiDFBOP to the electrolyte in step (1) and stir thoroughly until all the additives are dissolved. Record this as 3%-LHCE.
[0045] Comparative Example
[0046] In an argon atmosphere with water and oxygen concentrations below 0.1 ppm, 1.87 g of LiFSI was weighed and placed in a sample vial. Then, 6.96 g of TTE and 1.08 g of DME were added sequentially. After mixing, the mixture was magnetically stirred for 12 hours to obtain a clear and transparent electrolyte, denoted as LHCE.
[0047] The following describes the application and performance testing of a locally concentrated electrolyte containing phosphorus-based additives in a conversion-type lithium metal battery:
[0048] The linear sweep voltammetry test method involved in the following application example 1 is as follows: Under the constant temperature condition of 25°C, the oxidation stability of different electrolyte systems was determined by LSV test using a CHI660E electrochemical workstation. The cutoff voltage was 5.0 V and the scan rate was 0.2 mV / s.
[0049] The coulombic efficiency test method involved in the following application example 2 is as follows: Under constant temperature conditions of 25°C, a Li / Cu half-cell is used for testing at the LAND electrochemical workstation. A portion of lithium is deposited on the copper foil by constant current discharge (the areal capacity of the deposit is controlled according to the discharge time); then, constant current charging is performed to completely remove the deposited lithium on the copper foil, with voltage as the cutoff condition (usually 1 V); the ratio of the areal capacity of the removed lithium to the areal capacity of the deposited lithium during this process is the coulombic efficiency per turn.
[0050] The constant current charge-discharge test method in Example 3 is as follows: The electrochemical performance of the FeF3 cathode in different electrolyte systems was tested using a LAND electrochemical workstation to evaluate the compatibility of the electrolyte system with FeF3. The FeF3 voltage range was 1-4.5 V, and the 1C current density was 712 mA g-1.
[0051] Application Example 1:
[0052] The electrolytes prepared in Example 3 (3%-LHCE) and the comparative example (LHCE) were used with lithium metal as the counter electrode, carbon-coated aluminum foil as the working electrode, and polypropylene as the separator. The batteries were assembled into a battery with the following components: negative electrode shell, lithium metal, separator, electrolyte, carbon-coated aluminum foil, gasket, spring sheet, and positive electrode shell. The batteries were left to stand for 4 hours and then subjected to LSV testing.
[0053] Figure 1 This is a comparison chart of the electrochemical stability windows of the two electrolytes in Example 3 and the Comparative Example. As can be seen from the chart, the electrochemical window of the 3%-LHCE electrolyte is >4.5V, indicating that the locally high-concentration electrolyte containing LiDFBOP has higher oxidation stability under high voltage.
[0054] Application Example 2
[0055] The electrolytes prepared in Example 3 (3%-LHCE) and the comparative example (LHCE) were assembled into batteries according to the following steps: negative electrode shell, lithium metal, separator, electrolyte, copper foil, gasket, spring sheet, and positive electrode shell. After standing for 4 hours, the coulombic efficiency was tested. The areal capacity of the deposited lithium metal was 1 mAh cm-2, and the current density was 0.5 mA cm-2.
[0056] Figure 2The graph shows the cycling performance of Li / Cu batteries assembled with the two electrolytes from Example 3 and the comparative example. As can be seen from the graph, the Li / Cu battery assembled with LHCE electrolyte shows obvious fluctuations after 110 cycles, while the Li / Cu battery assembled with 3%-LHCE electrolyte maintains stable cycling for 200 cycles and has a higher coulombic efficiency than the LHCE electrolyte. This indicates that the locally high-concentration electrolyte containing LiDFBOP has better compatibility with lithium metal and has significant advantages in terms of stability and reversibility.
[0057] Application Example 3
[0058] The four electrolytes prepared in Examples 1 (1%-LHCE), 2 (2%-LHCE), 3 (3%-LHCE), and the comparative example (LHCE) were assembled into batteries according to the following steps: negative electrode shell, lithium metal, separator, electrolyte, FeF3, gasket, spring sheet, and positive electrode shell. After standing for 8 hours, constant current charge and discharge tests were performed.
[0059] Figure 3 The graph shows the cycle performance of FeF3 / Li batteries assembled with electrolytes from Examples 1, 2, 3 and the comparative example at 1C rate. As can be seen from the graph, adding LiDFBOP can significantly improve the cycle performance of the battery. The optimal addition amount is 3wt%. After 400 charge-discharge cycles at 1C current density, the battery capacity in 3% LiDFBOP-LHCE electrolyte is 371 mAh g-1, and the capacity retention rate is 82%.
[0060] Figure 4 The graph shows the charge-discharge curves of the FeF3 / Li battery assembled with the electrolyte of Example 3 at a rate of 0.2C for the first three cycles. As can be seen from the graph, the FeF3 cathode exhibits its typical charge-discharge plateau in the 3%-LHCE electrolyte. During the first discharge cycle, the plateau of about 1.9V belongs to the reduction and decomposition of LiDFBOP.
[0061] Figure 5 The graph shows the cycling performance of the FeF3 / Li battery assembled with the electrolyte of Example 3 at a rate of 0.2 C. As can be seen from the graph, after 200 charge-discharge cycles at a current density of 0.2 C, the battery capacity in the 3% LiDFBOP-LHCE electrolyte is as high as 444 mAh g-1, with a capacity retention rate of 72.5%.
[0062] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A locally concentrated electrolyte containing phosphorus-based additives, characterized in that: It includes the following components: lithium salt, ether solvent, fluoroether diluent, and lithium difluorodioxanol phosphate; The molar ratio of the lithium salt to the ether solvent is 1:1 to 1.5; The molar ratio of the lithium salt to the fluoroether diluent is 1:2.5~3; The amount of lithium difluorodioxalate phosphate added is 1~3 wt% of the total mass of the electrolyte.
2. The locally concentrated electrolyte containing phosphorus-based additives according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.
3. The locally concentrated electrolyte containing phosphorus-based additives according to claim 1, characterized in that: The ether solvent is at least one of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.
4. The locally concentrated electrolyte containing phosphorus-based additives according to claim 1, characterized in that: The fluoroether diluent is at least one of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.
5. A method for preparing a locally high-concentration electrolyte containing a phosphorus-based additive as described in any one of claims 1-4, characterized in that: Includes the following steps: (1) In an argon atmosphere with water and oxygen levels below 0.1 ppm, lithium salt was added to a sample vial containing a mixture of ether-based solvent and fluorinated ether diluent, and stirred thoroughly until the lithium salt was completely dissolved (12 h) to obtain the basic electrolyte. (2) In an argon atmosphere with water and oxygen levels below 0.1 ppm, the phosphorus-based additive is added to the electrolyte in step (1) by mass ratio and stirred thoroughly until the additive is completely dissolved (12h-24h) to obtain a locally high-concentration electrolyte containing the phosphorus-based additive.
6. The application of the locally high-concentration electrolyte containing phosphorus-based additives as described in claim 1 in a conversion lithium metal battery.
7. A conversion-type lithium metal battery, characterized in that: The battery includes a positive electrode, a negative electrode, an electrolyte, a separator, and a battery casing assembly, wherein the electrolyte is a locally high-concentration electrolyte containing phosphorus-based additives prepared by the method described in claim 5.
8. A conversion-type lithium metal battery according to claim 7, characterized in that: The positive electrode material is a conversion-type positive electrode FeF3, lithium metal, carbon-coated aluminum foil, and copper foil; the negative electrode material is lithium metal; and the separator is polypropylene and glass fiber.