Electrolyte of lithium ion battery and lithium ion battery
By adding additives such as nonafluorohexyltrimethoxysilane to the lithium battery electrolyte, a high-voltage resistance interface film is formed, which solves the problems of positive electrode structure collapse and electrolyte decomposition at high voltage of lithium batteries, and improves the comprehensive performance and cycle stability of lithium-ion batteries.
Patent Information
- Application Number
- CN202510630210.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-16
- Publication Date
- 2025-08-15
AI Technical Summary
In the high temperature, high-rate charging and discharging of charge and discharge and long-term cycles, traditional lithium battery electrolytes have problems such as poor electrode interface stability and rapid attenuation of battery capacity. Especially under high charging voltage, the positive electrode structure is prone to collapse, and the side reaction between transition metal dissolution and electrolyte is intensified, affecting the cycle life and safety of lithium batteries.
Nonafluorohexyltrimethoxysilane, tridecafluorooctyltrimethoxysilane or heptadecyltrimethoxysilane are used as additives to form a high voltage-resistant interface film, which is preferentially adsorbed on the positive electrode and oxidized into an interface film, inhibiting electrolyte decomposition and transition metal ions crosstalk, and promoting the storage and transmission of lithium ions.
It improves the high voltage cycle, high temperature cycle and high surface load cycle performance of lithium-ion batteries under high voltage, improves the operating safety performance and long cycle stability of lithium-ion batteries, and extends the life of lithium-ion batteries.
Smart Images
Figure CN120497450A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of secondary batteries, and in particular to an electrolyte of a lithium ion battery and a lithium ion battery. Background Art
[0002] With the rapid development of new energy vehicles and portable electronic devices, lithium-ion batteries have been widely used as efficient energy storage devices. As a core component of lithium batteries, the electrolyte has a significant impact on the battery's performance, safety, and lifespan. Currently, traditional electrolyte systems still have many problems during high temperatures, high-rate charge and discharge, and long-term cycling, such as electrolyte decomposition, poor electrode interface stability, and rapid battery capacity decay. Therefore, the development of high-performance electrolyte additives to improve the overall performance of the electrolyte has become a hot topic in current lithium battery research.
[0003] According to the formula for calculating volumetric energy density, the design of high-energy-density lithium-ion batteries can be achieved by increasing the operating voltage and the positive electrode surface load. At higher operating voltages, the positive electrode material releases a higher capacity, increasing the energy density of the lithium-ion battery. A higher positive electrode surface load also increases the energy density of the lithium-ion battery.
[0004] The charging voltage of the lithium battery commonly used at present is 4.2V. When the charging voltage is increased to 4.3V or above, the positive electrode structure is prone to collapse, resulting in the dissolution of transition metals, and the side reactions with the electrolyte are intensified. The electrolyte is continuously oxidized and deposited on the surface of the positive electrode, increasing the internal resistance of the positive electrode side, which will reduce the rate performance and cycle stability of the lithium battery. The electrolyte itself will also undergo oxidative degradation under high voltage conditions, producing harmful gases, further reducing the cycle life of the lithium battery until it fails. When operating under high temperature conditions, the activity of the positive electrode material increases, the energy barrier of the chemical reaction is further reduced, and various side reactions further damage the cycle life of the lithium battery, reducing the safety and stability of the lithium battery.
[0005] It should be noted that the information disclosed in the above background technology section is only used to understand the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention
[0006] In order to make up for the deficiencies of the prior art, the present invention provides an electrolyte for a lithium ion battery and a lithium ion battery.
[0007] The present invention adopts the following technical solutions:
[0008] In a first aspect, an electrolyte for a lithium-ion battery is provided, comprising a lithium salt, an additive, and an organic solvent, wherein the additive is at least one of nonafluorohexyltrimethoxysilane (NFTMS), tridecafluorooctyltrimethoxysilane (PFOTMS), and heptadecafluorodecyltrimethoxysilane (HFTMS).
[0009] Preferably, based on the total volume of the electrolyte, the volume percentage of the additive is a%, 0<a≤20.
[0010] Preferably, 0<a<5.
[0011] Preferably, in the electrolyte, the concentration of the lithium salt is b mol / L, 0<b≤2.
[0012] Preferably, the lithium salt is a fluorine-containing lithium salt; the fluorine-containing lithium salt is at least one of hexafluorophosphate, hexafluoroarsenate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, lithium tetrafluoroborate, lithium hexafluoroantimonate, and lithium hexafluoroantimonate.
[0013] Preferably, the organic solvent is at least one of a carbonate solvent and a carboxylate solvent.
[0014] Preferably, the carbonate solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl propyl carbonate; the carboxylate solvent is at least one of ethyl propionate, propyl propionate and ethyl acetate.
[0015] Preferably, in the electrolyte, the lithium salt is lithium hexafluorophosphate, the additive is tridecafluorooctyltrimethoxysilane (PFOTMS), and the organic solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate.
[0016] Preferably, in the electrolyte, the concentration of lithium hexafluorophosphate is 1 mol / L, the volume of tridecafluorooctyltrimethoxysilane (PFOTMS) accounts for 2% of the volume of the electrolyte, and the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:7.
[0017] In a second aspect, a lithium-ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described in the first aspect.
[0018] Preferably, the positive electrode active material on the positive electrode sheet is LiNi x Co y Mn z O2 or LiCoO2, wherein: x+y+z=1 and x>0.6.
[0019] The present invention has the following beneficial effects:
[0020] The electrolyte provided by the present invention can improve the comprehensive performance of lithium-ion batteries such as high voltage cycle, high temperature cycle and high surface load cycle discharge performance at high charging voltage. The lithium-ion battery obtained thereby can simultaneously have good high voltage cycle, high temperature cycle and high surface load (positive electrode surface load ≥ 20mg / cm2) at high charging voltage (4.3-4.7V). 2 ) cycle performance, the maximum storage temperature can reach 60℃.
[0021] In the preferred technical solution, the present invention aims at the capacity attenuation and safety performance problems caused by irreversible phase change, interface film thickening, electrolyte decomposition and transition metal ion crosstalk caused by lattice distortion of high nickel manganese lithium batteries or lithium cobalt oxide batteries under high voltage and high surface load. By making the silicon-oxygen bonds in the additives resistant to high voltage and weakening the interaction between lithium ions and solvent molecules, the additives are preferentially adsorbed on the electrodes and oxidized into interface films at high voltage, which can protect the positive and negative electrode structures (especially, the additives are preferentially adsorbed on the positive electrode and oxidized into interface films at high voltage, which can protect the positive electrode structure), thereby promoting the storage and transmission of lithium ions; especially, by the electrodes Due to the synergistic effect of lithium hexafluorophosphate (more preferably at a concentration of 1 mol / L), tridecafluorooctyltrimethoxysilane (PFOTMS) (more preferably at a volume fraction of 2%), and an organic solvent of ethylene carbonate and ethyl methyl carbonate (more preferably at a volume ratio of 3:7) in the electrolyte, PFOTMS will be preferentially adsorbed on the positive electrode and can inhibit the decomposition of ethylene carbonate, so that the high-nickel-cobalt-manganese ternary positive electrode battery or lithium cobalt oxide battery has good high-voltage cycle, high-temperature cycle and high-area load cycle performance at high charging voltage, thereby improving the operating safety performance of high-nickel-cobalt-manganese lithium batteries and lithium cobalt oxide batteries as well as high-voltage, high-area load and long-cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 2 is a cycle diagram of the Li||NCM811 battery of Examples 1, 3, 4 of the present invention and Comparative Example 1 at 4.3V.
[0023] Figure 2 These are photos of the electrolytes obtained in Examples 1, 3, and 4.
[0024] Figure 3a Schematic diagram of the adsorption configuration of PFOTMS and EC on NCM811.
[0025] Figure 3b Schematic diagram of the adsorption energy of PFOTMS and EC on NCM811 respectively.
[0026] Figure 3c Schematic diagram of the binding energy of PFOTMS and EC with lithium ions respectively.
[0027] Figure 4 These are LSV (Linear Sweep Voltammetry) test graphs of the electrolytes of Control Example 1 and Example 1.
[0028] Figure 5a These are SEM images of the positive electrode of the Li||NCM811 battery of control example 2 at different magnifications.
[0029] Figure 5b These are SEM images of the positive electrode of the Li||NCM811 battery of Example 2 at different magnifications.
[0030] Figure 6 SEM images of the negative electrodes of the Li||NCM811 batteries of Example 2 of the present invention (right figure) and Comparative Example 2 (left figure).
[0031] Figure 7 This is a cycle diagram of the Li||NCM811 battery of Example 1 of the present invention at 4.7V.
[0032] Figure 8 2 is a cycle diagram of the Li||NCM811 battery of Example 2 of the present invention and Comparative Example 2 at 4.5V.
[0033] Figure 9 2 is a cycle diagram of the Li||LCO battery of Example 5 of the present invention and Comparative Example 3 at 4.6V.
[0034] Figure 10a and 10b Cycle diagrams of the Li||LCO batteries of Control Example 4 and Example 6 at 4.4 V, respectively.
[0035] Figure 11 1 is a cycle diagram of the Li||NCM811 battery of Example 1 of the present invention and Comparative Example 1 at 4.5V and 60°C.
[0036] Figure 12 Impedance diagrams of the Li||NCM811 batteries of Example 1 of the present invention and Comparative Example 1 after 500 cycles at 4.5 V. DETAILED DESCRIPTION
[0037] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is merely illustrative and is not intended to limit the scope and application of the present invention. In the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.
[0038] A specific embodiment of the present invention provides an electrolyte for a lithium ion battery, comprising a lithium salt, an additive, and an organic solvent, wherein the additive is at least one of nonafluorohexyltrimethoxysilane (NFTMS) shown in formula I, tridecafluorooctyltrimethoxysilane (PFOTMS) shown in formula II, and heptafluorodecyltrimethoxysilane (HFTMS) shown in formula III.
[0039]
[0040] In some embodiments, the volume percentage of the additive is a%, based on the total volume of the electrolyte, where 0<a≤20.
[0041] In some embodiments, 0<a<5.
[0042] In some embodiments, in the electrolyte, the concentration of the lithium salt is b mol / L, 0<b≤2.
[0043] In some embodiments, the lithium salt is a fluorine-containing lithium salt; the fluorine-containing lithium salt is at least one of hexafluorophosphate, hexafluoroarsenate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, lithium tetrafluoroborate, lithium hexafluoroantimonate, and lithium hexafluoroantimonate.
[0044] In some embodiments, the organic solvent is at least one of a carbonate solvent and a carboxylate solvent.
[0045] In some embodiments, the carbonate solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl propyl carbonate; the carboxylate solvent is at least one of ethyl propionate, propyl propionate and ethyl acetate.
[0046] In some embodiments, in the electrolyte, the lithium salt is lithium hexafluorophosphate, the additive is tridecafluorooctyltrimethoxysilane (PFOTMS), and the organic solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate.
[0047] In some embodiments, in the electrolyte, the concentration of lithium hexafluorophosphate is 1 mol / L, the volume of tridecafluorooctyltrimethoxysilane (PFOTMS) accounts for 2% of the volume of the electrolyte, and the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:7.
[0048] The specific embodiment of the present invention also provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte. The separator and the electrolyte are placed between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises an aluminum foil current collector and a positive electrode membrane, the positive electrode membrane comprises a positive electrode active material, preferably, the positive electrode active material on the positive electrode sheet is LiNi x Co y Mn z O2 or LiCoO2, wherein: x+y+z=1 and x>0.6. The material of the negative electrode plate is at least one of lithium metal, graphite, silicon carbon, silicon oxide, and silicon.
[0049] Preferably, the material of the negative electrode plate is lithium metal, and the addition of the additive PFOTMS in the electrolyte can inhibit the growth of lithium dendrites on the surface of the lithium metal negative electrode under high voltage.
[0050] In a preferred embodiment, in order to address the irreversible phase change caused by lattice distortion, thickening of the interface film, electrolyte decomposition and capacity attenuation and safety performance problems caused by transition metal ion crosstalk in high nickel cobalt manganese lithium batteries or lithium cobalt oxide batteries under high voltage and high surface load, the silicon-oxygen bond in the additive is resistant to high voltage and weakens the interaction between lithium ions and solvent molecules. The additive is preferentially adsorbed on the electrode and oxidized into an interface film at high voltage, which can protect the positive and negative electrode structures and promote the storage and transmission of lithium ions; in particular, through the synergistic effect of lithium hexafluorophosphate (more preferably at a concentration of 1 mol / L), tridecafluorooctyltrimethoxysilane (PFOTMS) (more preferably at a volume fraction of 2%), and an organic solvent of ethylene carbonate and ethyl methyl carbonate (more preferably at a volume ratio of 3:7) in the electrolyte, the high nickel cobalt manganese ternary positive electrode battery or lithium cobalt oxide battery simultaneously has good high voltage cycle, high temperature cycle and high surface load cycle performance at high charging voltage, thereby improving the operating safety performance of high nickel cobalt manganese lithium batteries and lithium cobalt oxide batteries and high voltage and high surface load long cycle stability.
[0051] Specific embodiments of the present invention are further described below.
[0052] Example 1
[0053] A lithium-ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode material is lithium nickel cobalt manganese oxide (NCM811, i.e. LiNi 0.8 Co 0.1 Mn 0.1 O2) material; the negative electrode material is lithium metal, and the preparation process of the lithium ion battery is as follows:
[0054] The positive electrode material NCM811, conductive carbon black, and binder polyvinylidene fluoride were mixed in a mass ratio of 80:10:10 and dispersed with N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil current collector, dried, rolled, and punched to obtain a positive electrode. In this example, the positive electrode surface loading was 2.5 mg / cm 2 or 3.5 mg / cm 2 .
[0055] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3:7, and then 1 mol / L lithium hexafluorophosphate and 2 vol% of tridecafluorooctyltrimethoxysilane (PFOTMS) were added to prepare an electrolyte.
[0056] Celgard 2400 is used as the battery separator.
[0057] In a glove box with a protective atmosphere of high-purity argon, the prepared positive electrode, separator, electrolyte, and negative electrode were placed in a 2032 battery case in a certain order to complete the preparation of a button cell (Li||NCM811 battery). The battery prepared in this example can be written as Li||2%PFOTMS||NCM811.
[0058] Example 2
[0059] The difference from Example 1 is that the mass ratio of the positive electrode material NCM811, the conductive carbon black and the binder polyvinylidene fluoride in the positive electrode slurry is 94:3:3, so that a lithium-ion battery with a high positive electrode surface load can be obtained. The loading amount of the positive electrode active material can be adjusted by the coating thickness on the aluminum foil current collector to make the positive electrode surface load 20-30 mg / cm 2 The battery prepared in this example can be written as Li||2%PFOTMS||NCM811. In this example, the positive electrode surface loading is 20 mg / cm 2 or 30 mg / cm 2 .
[0060] Example 3
[0061] The experimental method is the same as that of Example 1, except that the volume fraction of the additive tridecafluorooctyltrimethoxysilane (PFOTMS) in the electrolyte is 1%. The battery prepared in this example can be written as Li||1%PFOTMS||NCM811.
[0062] Example 4
[0063] The experimental method is the same as that of Example 1, except that the volume fraction of the additive tridecafluorooctyltrimethoxysilane (PFOTMS) in the electrolyte is 5%. The battery prepared in this example can be written as Li||5%PFOTMS||NCM811.
[0064] Example 5
[0065] The experimental method is the same as that of Example 1, except that the positive electrode material used is lithium cobalt oxide. The battery prepared in this example can be written as Li||2%PFOTMS||LCO.
[0066] Example 6
[0067] The experimental method is the same as that of Example 2, except that the positive electrode material used is lithium cobalt oxide.
[0068] Comparative Example 1
[0069] The experimental method is the same as that of Example 1, except that the electrolyte does not contain any additives. That is, the electrolyte in the control example is prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 and then adding 1 mol / L lithium hexafluorophosphate. This electrolyte is named CCE in this article, and the battery prepared in this example can be written as Li||CCE||NCM811.
[0070] Comparative Example 2
[0071] The experimental method is the same as that of Example 2, except that the electrolyte is the same as that of Control Example 1. The battery prepared in this example can be written as Li||CCE||NCM811.
[0072] Comparative Example 3
[0073] The experimental method is the same as that of Example 5, except that the electrolyte is the same as that of Control Example 1. The battery prepared in this example can be written as Li||CCE||LCO.
[0074] Comparative Example 4
[0075] The experimental method is the same as that of Example 6, except that the electrolyte is the same as that of Control Example 1. The battery prepared in this example can be written as Li||CCE||LCO.
[0076] The above embodiments and reference examples were subjected to performance tests, and the results were as follows:
[0077] Figure 1 The Li||NCM811 battery (positive electrode surface loading of 2.5 mg / cm2) of Examples 1, 3, 4 and Comparative Example 1 of the present invention 2) Cycling diagram at 4.3 V. As can be seen from the figure, at 4.3 V, the cycling stability of the Li||2%PFOTMS||NCM811 battery is significantly higher than that of the Li||CCE||NCM811 battery, Li||1%PFOTMS||NCM811, and Li||5%PFOTMS||NCM811. After 300 cycles, the capacity retention rate is 82.3%, while the capacity retention rate of the Li||CCE||NCM811 battery is only 71.6%.
[0078] Figure 2 Photos of the electrolytes obtained in Examples 1, 3, and 4 show that the electrolyte containing 5% PFOTMS exhibits a slight emulsification, presumably due to the poor compatibility of the siloxane additive with CCE. Therefore, it is best to add less than 5 vol% PFOTMS to the electrolyte.
[0079] Figure 3a is the adsorption configuration diagram of PFOTMS and EC on NCM811, Figure 3b is the adsorption energy of PFOTMS and EC on NCM811, Figure 3c is the binding energy of PFOTMS and EC with lithium ions respectively. Figures 3a-3c The adsorption energy of PFOTMS on NCM811 (-2.09 eV) is greater than that of EC on NCM811 (-1.13 eV), indicating that PFOTMS preferentially adsorbs on the NCM811 cathode surface, thereby reducing solvent decomposition and forming a Si-rich interface. Furthermore, the unique Si–O bond with a large internal cavity enhances PFOTMS's binding affinity for Li+. Computational chemical characterization of the Li+ binding energies of PFOTMS and EC in the electrolyte revealed a PFOTMS-Li+ binding energy of -0.34 eV, while the EC-Li+ binding energy was -0.11 eV. This significantly enhanced lithium ion binding energy theoretically mitigates EC decomposition in the solvent.
[0080] Figure 4 The LSV test graphs of the electrolytes of Control Example 1 and Example 1 show that the electrolyte containing 2% PFOTMS undergoes oxidation at around 3.4V, which is higher than that of CCE.
[0081] Figure 5a The SEM images of the positive electrode of the Li||NCM811 battery of control example 2 at different magnifications are as follows: Figure 5bSEM images of the positive electrode of the Li||NCM811 battery from Example 2 at different magnifications are shown. Drastic fluctuations in lattice parameters during charge and discharge significantly exacerbate mechanical failure of the material, accelerating the propagation of microcracks within the material. Microcracks generated within the high-nickel ternary cathode particles create channels through which electrolyte penetrates into the interior of the CCE cathode particles, increasing the surface area exposed to electrolyte attack. SEM analysis demonstrates the protective effect of 2% PFOTMS on the cathode structure.
[0082] Figure 6 The following are SEM images of the negative electrode of the Li||NCM811 battery of Example 2 of the present invention (right figure, the "fluorosilicone additive" in the figure refers to PFOTMS) and Control Example 2 (left figure, the "basic electrolyte" in the figure refers to CCE). It can be seen that the surface of the lithium metal negative electrode in Control Example 2 is severely broken, and the lithium metal on the negative electrode side is distributed in the form of moss-like dendrites. The surface of the lithium metal in Example 2 is flat and smooth, and no obvious lithium dendrites are seen. The above data show that the addition of PFOTMS can inhibit the growth of lithium dendrites on the surface of the lithium metal negative electrode under high voltage.
[0083] Figure 7 Example 1 of the present invention (positive electrode surface loading is 3.5 mg / cm 2 ) Cycling diagram at 4.7 V. The effectiveness of the Li||2%PFOTMS||NCM811 battery was verified at 4.7 V. At a rate of 0.5C, the capacity retention rate of the Li||2%PFOTMS||NCM811 battery reached 80.80% after 600 cycles.
[0084] Figure 8 The Li||NCM811 battery of Example 2 and Comparative Example 2 (positive electrode surface loading of 30 mg / cm 2 ) Cycling graph at 4.5V. Increasing the charge voltage to 4.5V reveals a more pronounced difference between the 2% PFOTMS and CCE batteries. After 100 cycles, the Li||2% PFOTMS||NCM811 battery exhibits a capacity retention of 92.35%, while the Li||CCE||NCM811 battery exhibits a capacity retention of only 64.16%.
[0085] The Li||LCO batteries assembled in Example 5 and Comparative Example 3 were subjected to electrochemical cycling performance tests at room temperature within a voltage range of 3-4.6V. Figure 9 The Li||LCO battery of Example 5 of the present invention and Comparative Example 3 (positive electrode surface loading is 2.5 mg / cm 2) Cycling graph at 4.6V. When the cutoff voltage is increased to 4.6V, the cycling performance difference between the Li||2%PFOTMS||LCO battery and the Li||CCE||LCO battery becomes more pronounced. After 500 cycles, the capacity retention rates of the two batteries are 89.75% and 73.79%, respectively, demonstrating that 2% PFOTMS at 4.6V significantly stabilizes the layered cathode structure of lithium cobalt oxide and improves the cycling stability of lithium cobalt oxide batteries.
[0086] The Li||LCO batteries assembled in Example 6 and Comparative Example 4 were subjected to room temperature electrochemical cycling performance tests in a voltage range of 3-4.4V. Figure 10a and 10b The Li||LCO batteries of Control Example 4 and Example 6 (positive electrode surface loading of 20 mg / cm 2 ) Cycle diagram at 4.4 V. The experimental results show that when the surface loading is increased to 20 mg / cm 2 The improvement of PFOTMS on the performance of Li||LCO battery is more obvious. The discharge capacity of Li||2%PFOTMS||LCO battery after 500 cycles is 166.17mAhg -1 The capacity retention rate is 92.79%, with almost no attenuation, while the Li||CCE||LCO battery has a short circuit at around 40 cycles.
[0087] Figure 11 The Li||NCM811 battery of Example 1 and Comparative Example 1 (positive electrode surface loading of 2.5 mg / cm 2 ) Cycling diagram at 4.5V and 60°C. At 60°C, after 275 cycles, the capacity retention of the Li||2%PFOTMS||NCM811 battery reached 84.80%, while the capacity retention of the Li||CCE||NCM811 battery was only 61.45%, indicating that 2%PFOTMS significantly stabilizes the NCM811 cathode structure and improves the cycling stability of NCM811 batteries at high temperatures.
[0088] Figure 12 The impedance diagram of the Li||NCM811 battery of Example 1 of the present invention and Comparative Example 1 after 500 cycles at 4.5V. After 500 cycles at 4.5V, the interfacial impedance R CEI =533.7Ω, which is much smaller than the interface impedance R of Li||CCE||NCM811 battery CEI =1132.0Ω, indicating that the CEI interface layer formed by PFOTMS has smaller impedance and can better protect the high-nickel ternary positive electrode structure. Figure 12In the figure, CPE1 and CPE2 are capacitors, W1 is the diffusion impedance, and R1-R3 are resistors.
[0089] In summary, in the embodiment of the present invention, PFOTMS is used as an electrolyte additive to form a weak coordination structure that excludes part of the solvent, and preferentially oxidizes to derive an interface layer rich in LiF and Si-O, which can inhibit the severe solvent decomposition under high voltage and high surface load and the crosstalk effect caused by the migration of transition metal ions, and promote Li + Conductive and uniform deposition can significantly improve the cycling stability of the NCM811 cathode structure under high voltage and high surface load conditions. At 4.7V, after 600 cycles, the capacity retention rate of the Li||2%PFOTMS||NCM811 battery was 80.80%. At the same time, PFOTMS can improve the cycling stability of high surface load commercial lithium cobalt oxide cathodes. The discharge specific capacity of the Li||2%PFOTMS||LCO battery after 500 cycles was 166.17mAh g -1 , the capacity retention rate is 92.79% (4.4V, 20mg / cm 2 ). Therefore, the electrolyte of the present invention helps to improve the normal temperature and high temperature cycle life of the lithium ion battery, and also helps to reduce the impedance of the lithium ion battery. The lithium ion battery using the electrolyte of the present invention has a longer cycle life at high voltage and high surface load.
[0090] The above description further details the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be construed as being limited to these descriptions. Persons skilled in the art will appreciate that, without departing from the spirit of the present invention, they may make various substitutions or modifications to the described embodiments, and these substitutions or modifications should be considered to fall within the scope of protection of the present invention. Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "preferred embodiments," "examples," "specific examples," or "some examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with such embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Persons skilled in the art may combine and assemble the different embodiments or examples described in this specification, as well as features of different embodiments or examples, without conflicting opinions. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications may be made herein without departing from the scope of protection of the patent application.
Claims
1. An electrolyte for a lithium ion battery, characterized in that The invention comprises a lithium salt, an additive and an organic solvent, wherein the additive is at least one of nonafluorohexyltrimethoxysilane (NFTMS), tridecafluorooctyltrimethoxysilane (PFOTMS) and heptadecafluorodecyltrimethoxysilane (HFTMS).
2. The electrolyte according to claim 1, wherein Based on the total volume of the electrolyte, the volume percentage of the additive is a%, 0<a≤20, preferably, 0<a<5.
3. The electrolyte according to claim 1, wherein In the electrolyte, the concentration of the lithium salt is b mol / L, 0<b≤2.
4. The electrolyte according to claim 1, wherein The lithium salt is a fluorine-containing lithium salt; the fluorine-containing lithium salt is at least one of hexafluorophosphate, hexafluoroarsenate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, lithium tetrafluoroborate, lithium hexafluoroantimonate, and lithium hexafluoroantimonate.
5. The electrolyte according to claim 1, wherein The organic solvent is at least one of a carbonate solvent and a carboxylate solvent.
6. The electrolyte according to claim 5, wherein The carbonate solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl propyl carbonate; the carboxylate solvent is at least one of ethyl propionate, propyl propionate and ethyl acetate.
7. The electrolyte according to claim 1, wherein In the electrolyte, the lithium salt is lithium hexafluorophosphate, the additive is tridecafluorooctyltrimethoxysilane (PFOTMS), and the organic solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate.
8. The electrolyte according to claim 7, wherein In the electrolyte, the concentration of lithium hexafluorophosphate is 1 mol / L, the volume of tridecafluorooctyltrimethoxysilane (PFOTMS) accounts for 2% of the volume of the electrolyte, and the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:
7.
9. A lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 8.
10. The lithium-ion battery according to claim 9, wherein The positive active material on the positive electrode plate is LiNi x Co y Mn z O2 or LiCoO2, wherein: x+y+z=1 and x>0.6.