Ester electrolyte suitable for lithium-rich manganese-based positive electrode and lithium metal battery based on ester electrolyte
By using ester electrolytes containing fluorine-containing lithium salts and fluorine-containing solvents in lithium metal batteries, the problem of poor interface stability of lithium-rich manganese-based lithium metal batteries is solved, and the battery cycle stability and safety is improved.
Patent Information
- Application Number
- CN202510355582.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-25
- Publication Date
- 2025-05-13
AI Technical Summary
The practical application of lithium-rich manganese-based lithium metal batteries faces the problem of poor interface stability between the electrolyte and the positive and negative electrodes, resulting in a decrease in battery coulomb efficiency and safety hazards.
Ester electrolytes with fluorine-containing lithium salts and fluorine-containing solvents are used to regulate the electrolyte components to build a stable interface layer on the surface of lithium metal negative electrodes and lithium-rich manganese-based positive electrodes to inhibit interface side reactions.
It significantly improves the cycle stability of lithium metal batteries, reduces the growth of lithium dendrites, extends the service life of the battery, and improves the safety of the battery.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium metal batteries, and in particular to an ester electrolyte suitable for a lithium-rich manganese-based positive electrode and a lithium metal battery based thereon. Background Art
[0002] In recent years, the rapid development of portable electronic devices and electric vehicles has put forward higher requirements on the energy density and cycle life of energy storage batteries, and it is urgent to develop high specific energy battery systems. Compared with traditional lithium-ion batteries with graphite as the negative electrode, lithium metal batteries with metallic lithium as the negative electrode have higher theoretical energy density (>500Wh kg -1 ), so it has a wide range of application prospects. At present, lithium iron phosphate (LiFeO4), lithium nickel cobalt manganese oxide (LiNi x Mn y Co z O2, x+y+z=1) and lithium cobalt oxide (LiCoO2) as the positive electrode of lithium metal battery system have been widely used in commercial applications, achieving a high energy density. With the widespread use of drones, the consumer market has put forward higher requirements for the energy density of lithium metal batteries (> 600Wh kg -1 ). Therefore, it is necessary to use high nickel positive electrode and lithium-rich manganese-based positive electrode materials to improve the energy density of lithium metal batteries. Among them, lithium-rich manganese-based positive electrode has a higher working voltage and theoretical specific capacity, and is regarded as a positive electrode material with application prospects.
[0003] However, the practical application of lithium-rich manganese-based lithium metal batteries faces the challenge of poor interfacial stability between the electrolyte and the positive and negative electrodes. On the one hand, lithium metal has strong chemical activity, and the solid electrolyte interface layer (SEI) formed by the intense chemical and electrochemical coupling reaction between it and the electrolyte has poor stability. It breaks, reorganizes and dynamically evolves during the battery charge and discharge cycle, causing continuous consumption of the electrolyte and rapid growth of the interface impedance, resulting in a decrease in the battery's Coulombic efficiency. At the same time, the growth of lithium dendrites can easily cause battery short circuits, posing a safety hazard. On the other hand, lithium-rich manganese-based positive electrode materials are at a higher operating voltage, and the electrolyte decomposes more violently, which greatly aggravates the instability of the positive electrode / electrolyte interface layer (CEI), thereby causing a decrease in the structural stability of the positive electrode material. Therefore, improving the stability of the electrode interface is crucial to improving the cycle stability of lithium metal batteries.
[0004] Reasonable design of electrolyte components is the key to improving the stability of the electrode interface of lithium metal batteries. By regulating the electrolyte components, the composition and structure of the electrode interface film can be significantly improved, thereby affecting the cycle stability of lithium metal batteries. The traditional lithium-ion battery electrolyte system commonly found on the market has poor compatibility with the lithium metal negative electrode, and it is difficult to stabilize the lithium metal negative electrode and the lithium-rich manganese-based positive electrode at the same time. Therefore, it is necessary to develop a high-performance electrolyte suitable for lithium-rich manganese-based lithium metal batteries. Summary of the invention
[0005] In order to improve the cycle stability of lithium-rich manganese-based lithium metal batteries, the present invention provides an ester electrolyte suitable for lithium-rich manganese-based positive electrodes and a lithium metal battery based thereon. By selecting suitable lithium salts and solvents, the electrolyte can construct a stable interface layer on the surface of the lithium metal negative electrode and the lithium-rich manganese-based positive electrode, significantly inhibiting the interface side reactions existing in the charging and discharging process under high-voltage environment, thereby achieving the cycle stability of lithium-rich manganese-based lithium metal batteries.
[0006] To achieve the above object, the present invention adopts the following technical solution:
[0007] The present invention provides an ester electrolyte suitable for a lithium-rich manganese-based positive electrode, comprising a lithium salt and an ester solvent, wherein the lithium salt is a fluorine-containing lithium salt, and the ester solvent comprises a fluorine-containing solvent.
[0008] According to some embodiments of the present invention, the fluorine-containing lithium salt comprises one or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(fluoromethanesulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide), and the ester solvent comprises one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, and methyl trifluoroethyl carbonate.
[0009] According to some embodiments of the present invention, the fluorine-containing lithium salt contains at least lithium tetrafluoroborate.
[0010] According to some embodiments of the present invention, the ester solvent contains at least one or two of fluorine-containing solvents such as fluoroethylene carbonate and methyl trifluoroethyl carbonate.
[0011] According to some embodiments of the present invention, the concentration of the fluorine-containing lithium salt in the electrolyte is controlled to be 0.5M to 3M.
[0012] According to some embodiments of the present invention, based on the total volume of the electrolyte, the volume fraction of the fluorine-containing solvent in the solvent is 80-100% in all solvents.
[0013] The present invention also provides a lithium metal battery, comprising a lithium metal negative electrode, an electrolyte, a lithium-rich manganese-based positive electrode and a separator, wherein the electrolyte is the ester electrolyte described in the present invention.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0015] 1. The present invention adds a combination of fluorine-containing lithium salt and fluorine-containing solvent to the lithium metal battery electrolyte, which can regulate the interfacial stability of the lithium metal negative electrode and inhibit the growth of lithium dendrites, thereby significantly reducing the coulombic efficiency drop and dead lithium problems caused by the growth of lithium dendrites. The electrolyte of the present invention contains more fluorine-containing components, which can form an inorganic-rich interface layer at the interface of the lithium metal negative electrode, improve the interface kinetics problem, and achieve the improvement of the cycle stability of the lithium metal negative electrode.
[0016] 2. The ester electrolyte in the present invention has good compatibility with lithium-rich manganese-based positive electrode materials, can achieve relatively stable circulation of lithium-rich manganese-based lithium metal batteries under high voltage conditions, and is expected to achieve high energy density lithium metal batteries.
[0017] 3. The lithium salt and solvent used in the present invention are both industrial products, which are low in price, easy to prepare, and the amount of electrolyte used is relatively low.
[0018] 4. The ester electrolyte provided by the present invention has far-reaching significance for improving the development of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 The Li||Li symmetric battery assembled with the electrolytes in Example 1 and Comparative Example 1 at 0.5 mA cm -2 and 1mAhcm -2 Constant current charge and discharge cycle results under conditions;
[0020] Figure 2 The Li||Cu half-cell assembled with the electrolyte in Comparative Example 1 was -2 Deposition at a current density of 0.5 mAh cm -2 SEM image of lithium metal capacity;
[0021] Figure 3 The Li||Cu half-cell assembled with the electrolyte in Comparative Example 1 was -2 Deposition at a current density of 1 mAh cm -2 SEM image of lithium metal capacity;
[0022] Figure 4 The Li||Cu half-cell assembled with the electrolyte in Example 1 was -2 Deposition at a current density of 0.5 mAh cm -2 SEM image of lithium metal capacity;
[0023] Figure 5 The Li||Cu half-cell assembled with the electrolyte in Example 1 was tested at 0.5 mA cm-2 Deposition at a current density of 1 mAh cm -2 SEM image of lithium metal capacity;
[0024] Figure 6 Cycling results of Li (450 μm)||LRMO battery assembled with the electrolyte in Example 1 and Comparative Example 1 when charged at a rate of 0.2C and discharged at a rate of 0.5C in the voltage range of 2V to 4.7V;
[0025] Figure 7 Cycling results of Li (50 μm)||LRMO battery assembled with the electrolyte in Example 1 and Comparative Example 1 when charged at a rate of 0.2C and discharged at a rate of 0.5C in the voltage range of 2V to 4.7V;
[0026] Figure 8 The surface morphology of the lithium metal negative electrode of the Li (450 μm)||LRMO battery assembled with the electrolyte in Comparative Example 1 after 50 cycles at a charge rate of 0.2C and a discharge rate of 0.5C in the voltage range of 2V to 4.7V;
[0027] Fig. 9 The surface morphology of the lithium-rich manganese-based positive electrode material of the Li (450 μm)||LRMO battery assembled with the electrolyte in Comparative Example 1 after 50 cycles at a charge rate of 0.2C and a discharge rate of 0.5C in the voltage range of 2V to 4.7V;
[0028] Fig.10 The surface structure of the lithium metal negative electrode of the Li (450 μm)||LRMO battery assembled with the electrolyte in Example 1 after 50 cycles at a charge rate of 0.2C and a discharge rate of 0.5C in the voltage range of 2V to 4.7V;
[0029] Fig.11 Surface structure of lithium-rich manganese-based positive electrode material of Li(450 μm)||LRMO battery assembled with the electrolyte in Example 1 after 50 cycles at a charge rate of 0.2C and a discharge rate of 0.5C in the voltage range of 2V to 4.7V. DETAILED DESCRIPTION
[0030] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. The protection scope of the present invention is not limited to the following examples.
[0031] Example 1
[0032] The present embodiment provides an ester electrolyte having a fluorine-containing lithium salt and a fluorine-containing solvent, and the specific preparation method thereof is: dissolving lithium tetrafluoroborate (LiBF4) in a mixed solution of fluoroethylene carbonate (FEC) and methyl trifluoroethyl carbonate (FEMC) to obtain an electrolyte after dissolution; specifically, the concentration of LiBF4 in the electrolyte is 2M, and the volume ratio of FEC and FEMC is 1:1.
[0033] Comparative Example 1
[0034] This comparative example provides an electrolyte, and its specific preparation method is: dissolving lithium tetrafluoroborate (LiBF4) in a mixed solution of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) to obtain an electrolyte after dissolution; specifically, the concentration of LiBF4 in the electrolyte is 2M, and the volume ratio of FEC and DEC is 1:1.
[0035] The electrolytes prepared in Example 1 and Comparative Example 1 were subjected to the following performance tests:
[0036] Step 1: Use the two electrolytes of Example 1 and Comparative Example 1 to assemble a Li||Li symmetrical battery, with the lithium metal anode as the working electrode and the counter electrode, and use a commercial PE separator to assemble the battery. -2 , 1mAh cm -2 Charge and discharge test.
[0037] Figure 1 The Li||Li symmetric battery assembled with the electrolytes in Example 1 and Comparative Example 1 at 0.5 mA cm -2 At a current density of 1 mAh cm -2 The performance comparison of the capacity density of the battery was carried out. The results showed that the Li||Li symmetric battery assembled with the electrolyte of Comparative Example 1 had a significant overpotential increase after about 250 hours of cycling, and a short circuit occurred after about 330 hours, accompanied by a relatively serious voltage fluctuation; in contrast, the Li||Li symmetric battery assembled with the electrolyte of Example 1 was able to achieve a stable cycle of about 700 hours without a significant overpotential increase.
[0038] Step 2: Use the two electrolytes of Example 1 and Comparative Example 1 to assemble a Li||Cu half-cell at 0.5 mA cm -2 The deposition was carried out at a constant current density of .
[0039] Figure 2 The Li||Cu half-cell assembled with the electrolyte in Comparative Example 1 was -2 The deposition current density was 0.5 mAh cm -2Deposition image of lithium metal deposition. It can be observed that there are more dendritic lithium on the surface of the copper substrate, and the coverage on the substrate surface is relatively low.
[0040] Figure 3 The Li||Cu half-cell assembled with the electrolyte in Comparative Example 1 was -2 1 mAh cm was deposited at a current density of -2 Deposition image of lithium metal deposition capacity. It can be observed that compared with 0.5 mAh cm -2 During the deposition capacity, the size of the deposited lithium metal increased significantly, but relatively significant dendritic lithium was still observed, indicating that the compatibility between the electrolyte and the lithium metal anode was relatively poor.
[0041] Figure 4 The Li||Cu half-cell assembled with the electrolyte in Example 1 was -2 The deposition current density was 0.5 mAh cm -2 Deposition image of lithium metal deposition. The results show that the bulk lithium metal deposited in Example 1 evenly covers the surface of the copper substrate, presenting a relatively flat morphology as a whole, without obvious dendrite growth.
[0042] Figure 5 The Li||Cu half-cell assembled with the electrolyte in Example 1 was -2 1 mAh cm was deposited at a current density of -2 Deposition image of lithium metal deposition capacity. The results show that compared with 0.5 mAh cm -2 When depositing capacity, the lithium metal in Example 1 is 1 mAh cm -2 The deposition capacity can evenly cover the entire substrate.
[0043] Step 3: Use the two electrolytes of Example 1 and Comparative Example 1 to assemble a lithium metal battery. In this step, a 450 μm thick lithium metal is used as the negative electrode, and the surface loading is 1 mAh cm -2 The lithium-rich manganese-based material is used as the positive electrode and PE is used as the separator to assemble a lithium metal battery. At the same time, the battery is charged at 0.2C in the voltage range of 2V to 4.7V and discharged at 0.5C.
[0044] Figure 6The charge and discharge cycle performance of the Li||LRMO battery assembled with the electrolyte in Example 1 and Comparative Example 1 in the voltage range of 2V to 4.7V. The results show that when charged at a rate of 0.2C and discharged at a rate of 0.5C, the Li||LRMO battery assembled with the electrolyte in Comparative Example 1 exhibits a faster capacity decay, and only maintains about 51.7% of the discharge capacity after 400 cycles. In Example 1, the Li||LRMO battery still has a capacity retention rate of about 80% after 400 cycles.
[0045] Step 4: Assemble lithium metal batteries using the electrolytes of Example 1 and Comparative Example 1. Different from step 3, in order to further compare the compatibility between the electrolyte and the lithium metal negative electrode and the lithium-rich manganese-based positive electrode, this step uses lithium metal with a thickness of only 50 microns as the negative electrode and a surface loading of 1 mAh cm -2 The lithium-rich manganese-based material is used as the positive electrode and PE is used as the separator to assemble a lithium metal battery. The battery is also charged at 0.2C in the voltage range of 2V to 4.7V and discharged at 0.5C.
[0046] Figure 7 The charge and discharge cycle performance of the Li||LRMO battery assembled with the electrolyte in Example 1 and Comparative Example 1 in the voltage range of 2V to 4.7V. The results show that when charged at a rate of 0.2C and discharged at a rate of 0.5C, the Li||LRMO battery in Comparative Example 1 only maintained a discharge capacity of about 61.3% after 350 cycles. In Example 1, after the same number of cycles, the Li||LRMO battery still had a capacity retention rate of about 81.6%. This further illustrates that the electrolyte in the present invention promotes the cycle stability of lithium metal batteries.
[0047] Step 5: Use the two electrolytes of Example 1 and Comparative Example 1 to assemble the Li||LRMO battery in Step 3. After 50 cycles under the above-mentioned charge and discharge conditions, disassemble the battery in the discharged state and perform SEM characterization on the positive and negative electrodes respectively.
[0048] Figure 8 The morphology of the lithium metal negative electrode side of the Li||LRMO battery assembled with the electrolyte of Comparative Example 1 after 50 cycles of charge and discharge in the voltage range of 2V to 4.7V. The results show that after 50 cycles of charge and discharge, the surface structure of the lithium metal negative electrode in Comparative Example 1 is relatively uneven, and very significant cracks are observed.
[0049] Fig. 9The side morphology of the lithium-rich manganese-based positive electrode material of the Li||LRMO battery assembled with the electrolyte of Comparative Example 1 after 50 cycles of charge and discharge in the voltage range of 2V to 4.7V. It can be observed from the figure that after 50 cycles of charge and discharge, there are obvious cracks on the surface of the lithium-rich manganese-based positive electrode material in Comparative Example 1, which indicates that the interface reaction between the electrode material and the electrolyte is relatively serious, which significantly affects the structural stability of the electrode material.
[0050] Fig.10 The morphology of the lithium metal negative electrode side of the Li||LRMO battery assembled with the electrolyte of Example 1 after 50 cycles of charge and discharge in the voltage range of 2V to 4.7V. The results show that, unlike the test results of Comparative Example 1, the electrolyte in Example 1 has better compatibility with the lithium metal negative electrode, and after 50 cycles, the surface morphology of the lithium metal negative electrode is still relatively complete, and there are no significant cracks. This shows that the electrolyte can significantly improve the interfacial stability of the lithium metal negative electrode.
[0051] Fig.11 The side morphology of the lithium-rich manganese-based positive electrode material of the Li||LRMO battery assembled with the electrolyte of Example 1 after 50 cycles of charge and discharge in the voltage range of 2V to 4.7V. It can be observed from the figure that after 50 cycles of charge and discharge, the electrolyte in Example 1 has better compatibility with the lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material after the cycle maintains a relatively complete surface result without obvious cracks.
[0052] The specific embodiments of the present invention are described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, the equalization changes and modifications made without departing from the spirit and scope of the present invention should be included in the scope of the present invention.
Claims
1. An ester electrolyte suitable for lithium-rich manganese-based positive electrode, characterized in that: It includes a lithium salt and an ester solvent, wherein the lithium salt is a fluorine-containing lithium salt, and the ester solvent includes a fluorine-containing solvent.
2. The ester electrolyte according to claim 1, characterized in that The lithium salt is selected from one or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(fluoromethanesulfonyl imide) and lithium bis(trifluoromethanesulfonyl imide).
3. The ester electrolyte according to claim 1, characterized in that The ester solvent is selected from one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, and methyl trifluoroethyl carbonate.
4. The ester electrolyte according to claim 1 or 2, characterized in that: The concentration of the fluorine-containing lithium salt in the electrolyte is 0.5M to 3M.
5. The ester electrolyte according to claim 1 or 3, characterized in that: The volume fraction of the fluorine-containing solvent in all solvents in the electrolyte is 80-100%.
6. A lithium metal battery comprising a lithium metal negative electrode, an electrolyte, a lithium-rich manganese-based positive electrode and a separator, characterized in that: The electrolyte is the ester electrolyte according to any one of claims 1 to 5.
7. The lithium metal battery according to claim 6, characterized in that The positive electrode is a lithium-rich manganese-based positive electrode, and the positive electrode uses a carbon-coated aluminum foil as a current collector.