Lithium ion electrolyte, preparation method thereof and lithium ion capacitor
By designing the lithium-ion electrolyte, controlling the molar ratio of lithium ions to solvents and solvent composition, the problem of performance attenuation of lithium ion batteries in extremely low temperature environments is solved, and stable performance and excellent capacitor performance are achieved at temperatures below -40℃.
Patent Information
- Application Number
- CN202510034102.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-09
- Publication Date
- 2025-04-15
AI Technical Summary
Existing lithium-ion batteries are difficult to maintain satisfactory performance in temperature environments of -20°C and below, especially at lower temperatures (≤-40°C).
By designing a lithium-ion electrolyte, which consists of lithium salt and solvent, the molar ratio of lithium ions to carbonyl groups in the solvent is less than 1:3, and only one or two solvents are used to regulate the chemical interaction in the electrolyte to improve the low-temperature performance.
The lithium-ion electrolyte maintains stable performance at temperatures of -40°C and below, and the lithium-ion capacitor exhibits higher specific capacity, better rate performance and more stable cycle life at -40°C.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a lithium ion electrolyte and a preparation method thereof, and a lithium ion capacitor. Background Art
[0002] As the application of rechargeable mobile power sources expands, higher requirements are placed on the ability of electrochemical energy storage devices to cope with extremely low temperature environments. Currently, the most commercially mature lithium-ion batteries generally have difficulty maintaining satisfactory performance in temperatures of -20°C or below.
[0003] Therefore, it is necessary to develop lithium-ion electrolytes that can maintain the stable performance of lithium-ion electrochemical energy storage devices at lower temperatures (≤-40°C). Summary of the invention
[0004] In view of the above problems, the present invention provides a lithium ion electrolyte which can maintain stable performance at low temperatures (≤-40° C.).
[0005] Another object of the present invention is to provide a method for preparing the above-mentioned lithium ion electrolyte.
[0006] The present invention also provides a lithium ion capacitor using the lithium ion electrolyte.
[0007] In order to achieve the above object, the present invention adopts the following technical scheme:
[0008] A lithium ion electrolyte is composed of a lithium salt and a solvent, wherein the molar ratio of lithium ions in the lithium salt to carbonyl groups in the solvent is less than 1:3, and the number of the solvents is at most two.
[0009] The inventors found that kinetic hysteresis is the main factor causing the low-temperature performance degradation of lithium-ion energy storage devices. Therefore, the inventors found that improving kinetics through electrolyte design is a feasible way to develop the low-temperature performance of lithium-ion energy storage devices.
[0010] Electrolytes are generally composed of lithium salts and solvents. Depending on the molecular structure and molar ratio, they exhibit quantifiable physical and chemical properties at the macro level, such as solubility, conductivity, viscosity, freezing point, etc., and maintain a stable solvation structure at the micro level, which widely affects the charge transfer process at the electrode-electrolyte interface and the interfacial solid electrolyte membrane characteristics. Studies have found that the regulation of the electrolyte solvation structure can significantly improve the performance of the electrolyte, especially promoting the kinetic process of lithium ions at the electrode-electrolyte interface under low temperature conditions. The key to regulation is the three chemical interactions between the components of the electrolyte: ion-ion interaction, ion-dipole interaction, and dipole-dipole interaction. Therefore, regulating the specific chemical interaction environment between the components to change the performance of lithium-ion electrolytes is a high-performance lithium-ion electrolyte design idea worthy of research and promotion. However, in conventional electrolyte design, more than two lithium salts or solvents are often used, and additional additives are introduced, which not only leads to inefficient design but also causes waste of electrolyte components.
[0011] The inventors of the present invention have found that when the molar ratio of lithium ions to carbonyl groups in the solvent is less than 1:3, the lithium ion electrolyte can maintain stable performance at temperatures of -40°C and below. Moreover, the present invention only requires one or two solvents, and is a simple and efficient electrolyte.
[0012] Wherein, the lithium salt is selected from fluorosulfonyl imide lithium salts, including lithium bis(fluorosulfonyl imide) or lithium bis(trifluoromethylsulfonyl imide).
[0013] Wherein, the solvent is a cyclic carbonate solvent, and the molar ratio of the lithium salt to the cyclic carbonate solvent is less than 1:3.
[0014] In order to further improve the low-temperature conductivity and promote the interface dynamics, the solvent is a mixture of cyclic carbonate and linear carbonate.
[0015] Wherein, the molar ratio of the cyclic carbonate solvent to the linear carbonate solvent is 1:1 to 1:3.
[0016] Wherein, the cyclic carbonate solvent is propylene carbonate.
[0017] Wherein, the linear carbonate solvent is 2,2,2-trifluoroethyl methyl carbonate or ethyl methyl carbonate.
[0018] The molar ratio of lithium ions in the lithium salt to carbonyl groups in the solvent is 1:4 to 1:11.
[0019] Among them, the concentration of lithium salt in the electrolyte is between 0.8M and 5M.
[0020] The preparation method of the lithium ion electrolyte is as follows: in an argon atmosphere, a certain proportion of lithium salt and solvent are mixed evenly.
[0021] A low-temperature lithium-ion capacitor uses the low-temperature lithium-ion electrolyte.
[0022] The beneficial effects of the present invention are as follows:
[0023] (1) The lithium ion electrolyte of the present invention can remain in liquid state at extremely low temperatures (<-100°C), has high conductivity and low viscosity, and has good wettability on the surface of carbon material pole pieces.
[0024] (2) Lithium-ion electrolytes have a low desolvation energy barrier and derive a stable and strong SEI layer on the negative electrode side, promoting the kinetic processes at the electrode-electrolyte interface.
[0025] (3) Low-temperature lithium-ion electrolyte is used in lithium-ion capacitors. The devices have higher specific capacity, better rate performance and more stable cycle life at -40°C, and maintain stable operation at -60°C. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 This is a data graph showing the change in conductivity of the lithium ion electrolyte prepared in Example 7 with temperature.
[0027] Figure 2 This is a data graph showing the change in conductivity of the lithium ion electrolyte prepared in Comparative Example 1 with temperature.
[0028] Figure 3 The low temperature capacity retention rate of the lithium ion capacitors assembled with the electrolytes obtained in Example 7 and Comparative Example 1. DETAILED DESCRIPTION
[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0030] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.
[0031] The raw materials used in the examples are as follows (the raw materials used in the experiments in this example were purchased from Suzhou Duoduo Chemical Technology Co., Ltd.):
[0032] 1. Lithium difluorosulfonyl imide - LiFSI; the molecular formula is:
[0033] ;
[0034] 2. Propylene carbonate-PC, its molecular formula is:
[0035] ;
[0036] 3. 2,2,2-Trifluoroethyl methyl carbonate - FEMC, the molecular formula is:
[0037] ;
[0038] 4. Ethyl methyl carbonate -EMC, the molecular formula is:
[0039] .
[0040] Example 1
[0041] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0042] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0043] Weigh 0.404 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0044] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0045] Example 2
[0046] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0047] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0048] Weigh 0.808 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0049] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0050] Embodiment 3:
[0051] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0052] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0053] Weigh 1.212 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0054] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0055] Embodiment 4:
[0056] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0057] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0058] Weigh 1.616 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0059] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0060] Embodiment 5:
[0061] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0062] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0063] Weigh 2.02 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0064] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0065] Embodiment 6:
[0066] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0067] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0068] Weigh 2.424 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0069] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0070] Embodiment 7:
[0071] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0072] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0073] Weigh 2.828 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0074] The prepared electrolyte was transferred into an aluminum bottle, sealed and set aside for later use, and recorded as FEP.
[0075] Embodiment 8:
[0076] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0077] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0078] Weigh 3.232 g of the second solvent FEMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0079] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0080] Embodiment 9:
[0081] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0082] Weigh 2.61 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0083] Transfer the prepared electrolyte into an aluminum bottle and seal it for later use.
[0084] Embodiment 10:
[0085] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0086] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0087] Weigh 1.862 g of the second solvent EMC, add it to the obtained uniform solution, place the preparation bottle on a magnetic stirrer, and stir at room temperature for 5 min until the mixture is completely mixed;
[0088] Transfer the prepared electrolyte into an aluminum bottle and seal it.
[0089] Comparative Example 1:
[0090] Weigh 0.478 g of lithium salt LiFSI and place it in a clean electrolyte preparation bottle;
[0091] Weigh 0.783 g of the first solvent PC, add it to the preparation bottle, add a magnet, place it on a magnetic stirrer, and stir at room temperature for 5 minutes until the lithium salt is fully dissolved;
[0092] Transfer the prepared electrolyte into an aluminum bottle, seal it and set it aside for later use, record it as HP.
[0093] Figure 1 The conductivity of the FEP sample corresponding to Example 7 changes with temperature. The conductivity decreases with decreasing temperature. At -50°C, the conductivity is 0.5 mS cm -1 ;
[0094] Figure 2 This is the data graph of the conductivity of sample HP corresponding to Comparative Example 1 as a function of temperature. As the temperature decreases, the conductivity decreases. At -50°C, the conductivity is 0.005 mS cm -1 .
[0095] contrast Figure 1 and Figure 2 , further illustrating that when the molar ratio of lithium ions to carbonyl groups in the solvent is less than 1:3, the lithium ion electrolyte of the present invention maintains a higher conductivity at -50°C, wherein the conductivity of Example 7 is 100 times that of Comparative Example 1.
[0096] Lithium-ion capacitor performance test:
[0097] The samples obtained in Examples 1 to 10 and Comparative Example 1 were used as lithium ion electrolytes in lithium ion capacitors to test their electrochemical properties in the following steps:
[0098] Activated carbon was used as the positive electrode, a metal lithium sheet (thickness of 450 μm) was used as the negative electrode, and the above-prepared electrolyte (Examples 1 to 10 and Comparative Example) was assembled into a CR2032 type button battery; the assembled button battery was placed on a blue electric charge and discharge tester for constant current charge and discharge test, with a voltage window of 2.0 to 3.8 V and a current density of 0.05 A g -1 , and tested its specific capacity in different temperature environments.
[0099] Table 1 shows the discharge specific capacity of the lithium ion capacitors assembled with the electrolytes obtained in Examples 1 to 10 and Comparative Example 1 at -40°C based on the mass of the activated carbon positive electrode active material.
[0100] Table 1
[0101]
[0102] From the comparison of the specific capacities of the embodiments and the comparative examples in Table 1, it can be seen that when the molar ratio of lithium ions to carbonyl groups in the solvent is less than 1:3, the performance can still be kept stable at -40°C.
[0103] At the same time, the comparison between Example 7 and Example 10 shows that the performance of the fluorinated linear carbonate is more stable.
[0104] Figure 3 The low temperature capacity retention rate of the lithium ion capacitor assembled with the electrolyte obtained in Example 7 and Comparative Example 1. By comparing Example 1 to Example 8 in Table 1, it can be seen that in the lithium ion electrolyte of the cyclic carbonate system, adding fluorinated linear carbonate as the second solvent effectively improves the low temperature performance of the lithium ion capacitor.
[0105] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
[0106] The parts not described in detail in the present description belong to the known technology in the art. The above embodiments are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be included within the scope of the present invention.
Claims
1. A lithium ion electrolyte, characterized in that: The lithium ion electrolyte consists of a lithium salt and a solvent, the molar ratio of lithium ions in the lithium salt to carbonyl groups in the solvent is less than 1:3, and there are at most two solvents.
2. The lithium ion electrolyte according to claim 1, characterized in that The lithium salt is selected from fluorosulfonyl imide lithium salts, including lithium bis(fluorosulfonyl imide) or lithium bis(trifluoromethylsulfonyl imide).
3. The lithium ion electrolyte according to claim 1, characterized in that The solvent is a cyclic carbonate solvent, and the molar ratio of the lithium salt to the cyclic carbonate solvent is less than 1:
3.
4. The lithium ion electrolyte according to claim 1, characterized in that The solvent is a mixture of a cyclic carbonate solvent and a linear carbonate solvent.
5. The lithium ion electrolyte according to claim 4, characterized in that The molar ratio of the cyclic carbonate solvent to the linear carbonate solvent is 1:1 to 1:
3.
6. The lithium ion electrolyte according to claim 1 or 4, characterized in that: The cyclic carbonate solvent is propylene carbonate.
7. The lithium ion electrolyte according to claim 4, characterized in that The linear carbonate solvent is 2,2,2-trifluoroethyl methyl carbonate or ethyl methyl carbonate.
8. The lithium ion electrolyte according to claim 1, characterized in that The molar ratio of lithium ions of the lithium salt to carbonyl groups in the solvent is 1:4 to 1:
11.
9. The method for preparing a lithium ion electrolyte according to any one of claims 1 to 8, characterized in that: The preparation method comprises the steps of uniformly mixing a certain proportion of lithium salt and a solvent in an argon atmosphere.
10. A low temperature lithium ion capacitor, characterized in that: Use the low-temperature lithium ion electrolyte described in any one of claims 1 to 8.