Electrolyte, preparation method thereof and lithium ion battery

Abstract

The invention provides an electrolyte, a preparation method thereof and a lithium ion battery. The electrolyte comprises a solvent, a lithium salt and an additive; the additive has a lithium-philic group; the solvation ability of the additive to the lithium salt is lower than that of the solvent to the lithium salt. The additive with the lithium-loving group is introduced into the electrolyte and is adsorbed on the surface of the electrode, so that coordination of the solvent is occupied in a solvation structure of lithium ions at an electrode-electrolyte interface, and the lithium ion solvation capability of the additive is lower than that of the solvent to the lithium ions; according to the invention, a solvation structure of lithium ions rich in anions at an interface is realized, so that the stability of an electrode-electrolyte interface is further improved, uniform distribution and deposition of lithium ions are promoted, and an electrochemical window is widened, so that the capacity expression and cycling stability of the lithium ion battery at a relatively high current rate can be effectively promoted; and the development of lithium ion batteries with high energy density, high power density and high safety is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials, relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a preparation method thereof, and a lithium ion battery. Background Art

[0002] High specific energy power batteries have become one of the most important research directions in the current energy storage field. However, simply relying on optimizing the structure and preparation process of traditional lithium-ion batteries is difficult to meet the current market demand for energy density. Therefore, the development of the next generation of battery chemistry has become a necessary path for the preparation of high specific energy batteries. Among them, the use of a battery with a higher charging voltage limit (>4.3V vsLi + / Li) and a low-reduction-potential lithium metal anode (-3.04V vs SHE) are paired together to form a high-voltage lithium battery, which has become one of the most promising next-generation high-energy-density power battery systems for practical use. However, traditional ester electrolytes are difficult to adapt to this battery system. The main reasons include: (1) Low electrochemical window (<4Vv.s.Li + / Li) causes the electrolyte to continuously decompose at the high voltage positive electrode interface during charging, affecting the battery cycle performance; (2) the high saturated vapor pressure makes ester electrolytes have safety hazards such as combustion or even explosion; (3) the uneven nucleation and growth of lithium metal negative electrodes in traditional electrolytes reduce their stability and safety. Therefore, it is crucial to find an electrolyte system that can adapt to both high voltage positive electrodes and lithium metal negative electrodes to achieve safe high specific energy power batteries.

[0003] To this end, the existing technology adopts the method of increasing the concentration of lithium salts, but the cost of the electrolyte is expensive, which limits its large-scale commercial application, and it usually has disadvantages such as high viscosity, poor battery wettability and low ion conductivity; researchers also usually adopt a high fluorination strategy for lithium salts, solvents and diluent molecules in high-concentration electrolytes and local high-concentration electrolytes. The fluorinated electrolyte components help to generate lithium metal negative electrode solid electrolyte interface (SEI) rich in lithium fluoride, which is generally considered to help inhibit lithium dendrite formation, reduce interfacial side reactions and improve the cycle life of lithium negative electrodes. However, a high degree of fluorination has greatly increased the cost of the electrolyte, and the defluorination phenomenon is serious under high temperature and impurities such as water, which also brings environmental hazards. The local high-concentration lithium ion solvation structure makes the ion conductivity of the system lower than the lithium ion migration number compared with commercial ester electrolytes. And the lithium ion conductivity of lithium fluoride itself is not high, which limits the rate of electrode interface reaction.

[0004] In addition, the electrode-electrolyte interface (EEI) is a key site for the exchange of ions and electrons inside the battery. A stable and efficient interface can significantly improve the ion transfer efficiency, reduce internal resistance, prevent further reaction between the electrolyte and the electrode, inhibit the growth of lithium dendrites, etc., which is crucial to improving the performance of lithium metal batteries. However, the EEI formed in the current traditional ester and ether electrolytes is prone to rupture and recombination, which not only consumes a large amount of lithium metal and electrolyte, but also leads to an increase in the internal resistance of the battery and a decrease in performance.

[0005] Therefore, there is an urgent need to provide an electrolyte that can solve the problems of high dissociation of lithium salts and occupation of the solvation sheath by solvent molecules in traditional electrolytes at the electrode-electrolyte interface, thereby improving the stability of the electrode-electrolyte interface and improving the capacity performance and cycle performance of lithium-ion batteries. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention aims to provide an electrolyte, a preparation method thereof and a lithium ion battery. The present invention introduces an additive with a lithium-philic group into the electrolyte so that the additive is adsorbed on the electrode surface, thereby occupying the coordination of the solvent in the solvation structure of lithium ions at the electrode-electrolyte interface, and utilizing the characteristic that the solvation ability of the additive to lithium ions is lower than that of the solvent to lithium ions, thereby realizing the solvation structure of lithium ions rich in anions at the interface, thereby improving the stability of the electrode-electrolyte interface, promoting the uniform distribution and deposition of lithium ions, and widening the electrochemical window, which can effectively promote the capacity performance and cycle stability of lithium ion batteries at higher current rates, and has a promoting effect on the development of high energy density, high power density and high safety lithium ion batteries.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte comprising a solvent, a lithium salt and an additive.

[0009] The additive has a lithiophilic group.

[0010] The solvating ability of the additive for the lithium salt is lower than the solvating ability of the solvent for the lithium salt.

[0011] The invention solves the problems of high dissociation of lithium salts and occupation of the solvation sheath by solvent molecules in traditional electrolytes by introducing an additive with a lithiophilic group into the electrolyte without affecting the ionic conductivity and solvation structure of the whole system, so as to adsorb the additive on the electrode surface and occupy the coordination of the solvent in the solvation structure of lithium ions at the electrode-electrolyte interface (EEI), thereby solving the problems of high dissociation of lithium salts and occupation of the solvation sheath by solvent molecules in traditional electrolytes, and forming an anion-derived inorganic-rich and uniform high-stability solid electrolyte interface (SEI) by utilizing the characteristic that the solvation capacity of the additive for lithium ions is lower than that of the solvent for lithium ions, which is beneficial to promoting the uniform distribution and deposition of lithium ions, broadening the electrochemical window, and realizing the stable and long cycle of the lithium metal negative electrode.

[0012] The electrolyte provided by the present invention can effectively promote the capacity performance and cycle stability of lithium-ion batteries at higher current rates, and has a promoting effect on the development of high energy density, high power density and high safety lithium-ion batteries.

[0013] Preferably, the lithium-philic group includes any one of a mercapto group, an amine group, a carboxyl group or a phosphate group, or a combination of at least two of them. Exemplarily, when the chemically active mercapto group encounters lithium metal, it will form a Li-S bond with the lithium metal, so that the additive is externally connected to the surface of the lithium metal in a bonded form, thereby achieving the enrichment of the additive on the surface of the lithium metal, and because the additive has a lower solvation ability, the solvation structure of the lithium ions at the interface is richer in anions without affecting the ionic conductivity and solvation structure of the entire system, thereby forming a SEI richer in inorganic components, thereby achieving a stable and long cycle of the lithium metal negative electrode and the high-voltage lithium metal battery.

[0014] Preferably, the additive comprises a silicone additive, preferably a fluorine-free silicone additive.

[0015] In the present invention, fluorine-free siloxane additives are preferred for the following reasons: (1) The increase in fluorine content will lead to relatively high production costs and greater environmental burden; (2) The reduction of fluorinated inorganic salts only produces inorganic EEI (electrode-electrolyte interface), while the reduction of fluorinated organic solvents will produce unstable and fragile organic EEI components, which are easily decomposed during the electrochemical cycle, resulting in decreased interface stability and increased internal impedance of the battery, affecting the performance and life of the battery. Therefore, it is very necessary to design a new low-fluorine electrolyte that is environmentally friendly, low-cost, and has good compatibility with both lithium metal and high-voltage positive electrodes.

[0016] Preferably, the additive includes any one of mercaptopropylmethyldimethoxysilane (3MDS), aminopropylmethyldimethoxysilane, and propionic acid methyldimethoxysilanol, or a combination of at least two thereof, but is not limited thereto. For example, the chemical structure of 3MDS is:

[0017] Preferably, in the electrolyte, the concentration of the additive is 0.01-0.15 mol / L, for example, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L or 0.15 mol / L, but not limited thereto.

[0018] In the present invention, the concentration of suitable additives can realize anion-rich lithium ion solvation structure at the electrode-electrolyte interface, promote the reduction of more anions on the lithium metal surface, thereby forming an inorganic-rich and more stable SEI, which is stable to lithium metal, and the average coulombic efficiency of the resulting battery is also significantly improved.

[0019] Preferably, the solvation energy of the additive to the lithium salt is 0.01-10 kJ / mol, for example, 0.01 kJ / mol, 0.1 kJ / mol, 1 kJ / mol, 5 kJ / mol or 10 kJ / mol, but is not limited thereto.

[0020] In the present invention, the solvation energy of the additives in the above range for lithium salts is lower than that of the solvent for lithium salts, so that the lithium ion solvation structure rich in additives can be rich in more anions and more easily desolvated at the electrode interface.

[0021] Preferably, the limiting solubility of the lithium salt in the additive is 0.01-10 mol / L, for example, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 5 mol / L, 8 mol / L or 10 mol / L, etc., but is not limited thereto.

[0022] In the present invention, the solvation capacity can be characterized by the parameter of limiting solubility. A low limiting solubility means a weak solvation capacity, that is, the limiting solubility of the lithium salt in the additive is lower than the limiting solubility of the lithium salt in the solvent, which means that the solvation capacity of the additive for the lithium salt is lower than the solvation capacity of the solvent for the lithium salt.

[0023] Preferably, the solvent is a siloxane solvent, preferably a fluorine-free siloxane solvent.

[0024] Preferably, the siloxane solvent includes any one or a combination of at least two of ethyltrimethoxysilane (ETMS), tetraethyl orthosilicate (TEOS), methyltriethoxysilane (MTES), dimethyldiethoxysilane (DMES) or dimethyldimethoxysilane (DMMS), preferably any two or a combination of at least three of ethyltrimethoxysilane, tetraethyl orthosilicate, methyltriethoxysilane, dimethyldiethoxysilane or dimethyldimethoxysilane, but is not limited thereto. Exemplarily, the chemical formula of ETMS is:

[0025] Preferably, the lithium salt includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3) or lithium difluoroborate oxalate (LiDFOB), but is not limited thereto.

[0026] Preferably, the molar ratio of the lithium salt to the solvent is 1:(0.5-5), for example, 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5, etc., but is not limited thereto.

[0027] Preferably, the molar ratio of the lithium salt to the additive is 1:(0.01-10), for example, it can be 1:0.01, 1:0.02, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:1, 1:3, 1:5, 1:7, 1:9 or 1:10, but is not limited thereto, and is preferably 1:(1-5).

[0028] In the present invention, the lithium salt and the additive in a suitable molar ratio can ensure the high ionic conductivity of the electrolyte, which is conducive to the rapid transmission of ions inside the battery and improves the charge and discharge efficiency of the battery; at the same time, it can ensure the formation of EEI with excellent electrochemical properties.

[0029] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising the following steps:

[0030] The electrolyte is obtained by mixing a solvent, a lithium salt and an additive, wherein the additive has a lithium-philic group and the solvating ability of the additive to the lithium salt is lower than the solvating ability of the solvent to the lithium salt.

[0031] Preferably, the mixing method comprises:

[0032] Add the additive to the solvent and stir once, then add the lithium salt and stir a second time.

[0033] Preferably, the secondary stirring time is ≥12 h, for example, it can be 12 h, 15 h, 18 h or 20 h.

[0034] In a third aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte as described in the first aspect.

[0035] Preferably, the material of the negative electrode plate includes lithium metal or lithium alloy.

[0036] Exemplarily, in the positive electrode plate, the positive electrode active material is a high-nickel layered oxide material (such as NCM811), a lithium iron phosphate material or a lithium cobalt oxide material, etc., and the separator can be homemade or purchased from a lithium battery separator produced by Celgard.

[0037] Preferably, the surface of the positive electrode sheet and / or the negative electrode sheet is modified with an additive, and the additive is the additive in the electrolyte described in the first aspect.

[0038] In the present invention, additives are used to pre-modify the surface of the positive electrode and / or negative electrode, which helps to enrich the additives on the electrode surface, construct solvation differences at the electrode-electrolyte interface, and thus realize anion-rich solvation structure at the interface.

[0039] It should be noted that the present invention does not limit the modification method of the positive electrode sheet and / or the negative electrode sheet with additives, for example, immersing the conventional positive electrode sheet / negative electrode sheet in a solution containing the additives.

[0040] The present invention is not limited to the above-listed numerical values, and other unlisted numerical values ​​within the numerical range are also applicable. However, due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention introduces an additive with a lithiophilic group into the electrolyte without affecting the ionic conductivity and solvation structure of the entire system, so that the additive is adsorbed on the electrode surface, thereby squeezing out the coordination of the solvent in the solvation structure of lithium ions at the electrode-electrolyte interface, thereby solving the problems of high dissociation of lithium salts and occupation of the solvation sheath by solvent molecules in traditional electrolytes. In addition, the present invention utilizes the characteristic that the solvation ability of lithium salts for lithium ions is lower than that of the solvent for lithium ions, thereby forming an anion-derived inorganic-rich and uniform high-stability solid electrolyte interface (SEI), which is beneficial to promoting the uniform distribution and deposition of lithium ions, widening the electrochemical window, and realizing the stable long-term cycle of the lithium metal negative electrode.

[0043] (2) The electrolyte provided by the present invention can effectively promote the capacity performance and cycle stability of lithium-ion batteries at higher current rates, and has a promoting effect on the development of high energy density, high power density and high safety lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the difference in solvation structure at the interface constructed between the electrolyte provided in Example 1 of the present invention and the lithium metal negative electrode.

[0045] Figure 2 A schematic diagram comparing the solubility of lithium salts in the solvents and additives provided by the present invention.

[0046] Figure 3 The linear sweep voltammetry curve of the siloxane electrolyte provided by the present invention.

[0047] Figure 4 This is the charge and discharge curve of the lithium metal button battery provided in Example 3 of the present invention.

[0048] Figure 5 This is the charge and discharge curve of the lithium metal button battery provided in Comparative Example 1 of the present invention.

[0049] Figure 6 The cycle curves of the lithium metal button cells provided in Example 1 and Comparative Example 1 of the present invention.

[0050] Figure 7 Schematic diagram for comparing Raman spectral curves of the electrolytes provided in Example 2, Example 3 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The technical scheme of the present invention is further described below by specific implementation methods. For ease of understanding the present invention, the present invention lists the following embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Example 1

[0053] This embodiment provides an electrolyte, which includes a solvent, a lithium salt and an additive; wherein the additive is 3MDS, and the lithium-philic group in 3MDS is a thiol group; the solvent is ETMS; the lithium salt is LiFSI; in the electrolyte, the concentration of 3MDS is 0.1 mol / L, the concentration of LiFSI is 1.5 mol / L, and the molar ratio of LiFSI to ETMS is 1:4.178.

[0054] The solvation capacity of 3MDS for LiFSI is lower than that of ETMS. The limiting solubility of LiFSI in 3MDS is lower than that in ETMS, and the limiting solubility of LiFSI in 3MDS is 4.5 mol / L.

[0055] This embodiment also provides a method for preparing the above electrolyte, the preparation method comprising the following steps:

[0056] 3MDS was added to ETMS, and after being stirred evenly, LiFSI was added and stirred for 12 hours to obtain the electrolyte.

[0057] This embodiment also provides a lithium metal button battery, including a positive electrode plate, a lithium metal negative electrode plate, a separator and the electrolyte as described above.

[0058] Among them, the positive electrode plate includes a current collector aluminum foil and a lithium iron phosphate material coated on the surface of the current collector aluminum foil, and the diaphragm is purchased from Celgard.

[0059] This embodiment also provides an assembly method of the lithium metal button battery, comprising the following steps:

[0060] In a glove box filled with inert gas, first place the spring gasket at the bottom of the battery shell, then place the gasket, lithium metal negative electrode sheet, diaphragm, and positive electrode sheet in turn, then inject the electrolyte, and finally put the battery cover on and use a tablet press to press the battery together.

[0061] Figure 1 The schematic diagram of the difference in solvation structure at the interface constructed between the electrolyte provided by Example 1 of the present invention and the lithium metal negative electrode is shown. As can be seen from the figure, 3MDS contains chemically active thiol groups. When encountering lithium metal, it forms a Li-S bond with lithium metal and connects to the surface of lithium metal. 3MDS is enriched on the surface of lithium metal, and 3MDS has a lower solvation ability. Under the condition of not affecting the ionic conductivity and solvation structure of the entire system, the solvation structure of lithium ions at the interface is richer in anions, thereby forming a SEI richer in inorganic components, thereby achieving stable long-term circulation of lithium metal negative electrodes and high-voltage lithium metal batteries.

[0062] The present invention explores the limiting solubility of solvents and additives for lithium salts. The specific test steps include: adding LiFSI to ETMS and 3MDS respectively, and when the concentration of LiFSI increases to 4.5 mol / L, the following is obtained: Figure 2 As shown in the solubility comparison diagram, it can be seen that the solution after the solvent ETMS dissolves LiFSI is clear and transparent, showing a solvation ability higher than that of 3MDS.

[0063] The present invention also explores the oxidation resistance of siloxane solvents. The specific method includes: adding LiFSI to the solvent ETMS to obtain a siloxane electrolyte with a LiFSI concentration of 1.5 mol / L; testing the siloxane electrolyte using linear scanning voltammetry, and the test curve is as follows: Figure 3 As shown in the figure, it can be seen that siloxane electrolytes have good chemical stability, are resistant to oxidation, are low in cost, and are environmentally friendly.

[0064] Example 2

[0065] The difference between this embodiment and embodiment 1 is that the amount of 3MDS added is adjusted so that the concentration of 3MDS in the electrolyte is 0.02 mol / L.

[0066] The rest of the preparation methods and parameters were the same as those in Example 1.

[0067] Example 3

[0068] The difference between this embodiment and embodiment 1 is that the amount of 3MDS added is adjusted so that the concentration of 3MDS in the electrolyte is 0.1 mol / L.

[0069] The rest of the preparation methods and parameters were the same as those in Example 1.

[0070] Example 4

[0071] The difference between this embodiment and embodiment 1 is that the amount of 3MDS added is adjusted so that the concentration of 3MDS in the electrolyte is 0.15 mol / L.

[0072] The rest of the preparation methods and parameters were the same as those in Example 1.

[0073] Example 5

[0074] The difference between this embodiment and embodiment 1 is that the additive is aminopropylmethyldimethoxysilane, and the lithium-philic group in aminopropylmethyldimethoxysilane is an amine group.

[0075] The rest of the preparation methods and parameters were the same as those in Example 1.

[0076] Example 6

[0077] The difference between this embodiment and embodiment 1 is that the additive is methyl dimethoxy silanol propionate, and the lithium-philic group in methyl dimethoxy silanol propionate is a carboxylic acid group.

[0078] The rest of the preparation methods and parameters were the same as those in Example 1.

[0079] Example 7

[0080] The difference between this embodiment and embodiment 1 is that the amount of 3MDS added is adjusted so that the concentration of 3MDS in the electrolyte is 0.005 mol / L.

[0081] The rest of the preparation methods and parameters were the same as those in Example 1.

[0082] Example 8

[0083] The difference between this embodiment and embodiment 1 is that the amount of 3MDS added is adjusted so that the concentration of 3MDS in the electrolyte is 0.2 mol / L.

[0084] The rest of the preparation methods and parameters were the same as those in Example 1.

[0085] Example 9

[0086] The difference between this embodiment and embodiment 1 is that the additive is a fluorine-containing silicone additive, and the fluorine-containing silicone additive is a fluorinated polyether silicone.

[0087] The rest of the preparation methods and parameters were the same as those in Example 1.

[0088] Example 10

[0089] The difference between this embodiment and embodiment 1 is that the surface of the positive electrode plate is modified with 3MDS.

[0090] The rest of the preparation methods and parameters were the same as those in Example 1.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that no additive is introduced into the electrolyte.

[0093] The rest of the preparation methods and parameters were the same as those in Example 1.

[0094] Figure 4 and Figure 5 The charge and discharge curves of the lithium metal button cell provided in Example 3 and Comparative Example 1 of the present invention are shown respectively, Figure 6 The cycle curves of the lithium metal button cells provided in Example 1 and Comparative Example 1 of the present invention are shown. By comparison, it can be seen that the polarization of the lithium metal button cells protected by the present invention is significantly reduced during the charge and discharge process, and the cycle life is significantly improved, indicating that the design of the interface solvation structure difference makes the electrolyte-electrode interface more stable.

[0095] Figure 7 The Raman spectrum curves of the electrolytes provided in Example 2, Example 3 and Comparative Example 1 of the present invention are compared. As can be seen from the figure, after the additive is added to the electrolyte, the solvation structure in the electrolyte liquid phase does not change.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that the additive is mercaptopropoxytrimethoxysilane, and the solvating ability of the additive to LiFSI is higher than that of ETMS to LiFSI.

[0098] The rest of the preparation methods and parameters were the same as those in Example 1.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that the additive is propylmethyldimethoxysilane which does not have a lithiophilic group.

[0101] The rest of the preparation methods and parameters were the same as those in Example 1.

[0102] Performance Testing

[0103] 1. The ionic conductivity of the electrolytes provided in the above embodiments and comparative examples was tested by using the AC impedance method and the Raman spectroscopy-assisted method. The calculation formula of the ionic conductivity is:

[0104] Where σ represents ionic conductivity, in mS·cm -2 ; Rs is the resistance value of the electrolyte obtained by the test, in Ω; A is the electrode area, in cm 2 ; d is the distance between the electrodes, in cm.

[0105] 2. The Aurbach method was used to test the lithium metal button cells and Xining coulombic efficiency provided in the above embodiments and comparative examples. The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] analyze:

[0110] As can be seen from the above table, the electrolyte provided by the present invention is applied to lithium metal batteries, and the difference in the interface solvation structure constructed does not affect the solvation structure and ionic conductivity in the electrolyte liquid phase. In addition, the coulombic efficiency of lithium metal batteries has also been significantly improved, and the lithium metal negative electrode is more stable.

[0111] It can be seen from Example 1 and Examples 2-4 that within a suitable concentration range, as the concentration of the additive increases, the average coulombic efficiency increases accordingly, indicating that the prepared electrolyte helps to improve the stability of the lithium metal battery.

[0112] It can be seen from Example 1 and Examples 5-6 that when additives with different types of lithiophilic groups are applied to lithium metal batteries, the differences in the constructed interfacial solvation structures do not affect the solvation structure and ionic conductivity in the electrolyte liquid phase, and can both improve the average coulombic efficiency and operating stability of lithium metal batteries.

[0113] It can be seen from Example 1 and Examples 7-8 that if the concentration of 3MDS in the electrolyte is too low, the interfacial solvation difference is not obvious and the improvement of coulombic efficiency is limited; if the concentration of 3MDS in the electrolyte is too high, the ionic conductivity of the entire electrolyte is affected.

[0114] It can be seen from Examples 1 and 9 that if the additive is a fluorine-containing siloxane additive, compared with a fluorine-free siloxane additive, the desolvation energy barrier is large due to the strong electron-withdrawing ability of fluorine atoms and the strong lithium ion solvation ability, resulting in low coulombic efficiency.

[0115] It can be seen from Example 1 and Example 10 that pre-modifying the surface of the positive electrode with 3MDS is beneficial to better constructing the interface solvation difference, making the lithium ion solvation structure richer in anions.

[0116] It can be seen from Example 1 and Comparative Example 1 that if no additive is introduced into the electrolyte, the problem of high dissociation of lithium salt and occupation of the solvation sheath by solvent molecules at the electrode-electrolyte interface cannot be solved, resulting in poor performance of the lithium metal battery.

[0117] It can be seen from Example 1 and Comparative Example 2 that if the solvation ability of the additive to LiFSI is higher than that of ETMS to LiFSI, the difference in solvation ability cannot be used to make the solvation structure of lithium ions at the interface rich in anions, thereby forming an inorganic component-rich SEI. Therefore, the introduction of the additive will lead to poor performance of lithium metal batteries.

[0118] It can be seen from Example 1 and Comparative Example 3 that if the additive is propylmethyldimethoxysilane which does not have a lithiophilic group, it is difficult for the additive to form a bond with the lithium metal negative electrode, resulting in the inability of the additive to be enriched on the lithium metal surface, thereby making it impossible to enrich anions in the solvation structure of lithium ions at the interface, causing the performance of the lithium metal battery to deteriorate.

[0119] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a solvent, a lithium salt and an additive; The additive has a lithium-philic group; The solvating ability of the additive for the lithium salt is lower than the solvating ability of the solvent for the lithium salt.

2. The electrolyte according to claim 1, characterized in that The lithium-philic group includes any one or a combination of at least two of a thiol group, an amine group, a carboxyl group or a phosphate group; Preferably, the additive comprises a siloxane additive, preferably a fluorine-free siloxane additive; Preferably, the additive includes any one of mercaptopropylmethyldimethoxysilane, aminopropylmethyldimethoxysilane, and propionic acid methyldimethoxysilanol, or a combination of at least two thereof.

3. The electrolyte according to claim 1 or 2, characterized in that In the electrolyte, the concentration of the additive is 0.01-0.15 mol / L.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The limiting solubility of the lithium salt in the additive is 0.01-10 mol / L.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The solvent is a siloxane solvent, preferably a fluorine-free siloxane solvent; Preferably, the siloxane solvent includes any one of ethyltrimethoxysilane, tetraethyl orthosilicate, methyltriethoxysilane, dimethyldiethoxysilane or dimethyldimethoxysilane, or a combination of at least two of them, preferably a combination of any two of ethyltrimethoxysilane, tetraethyl orthosilicate, methyltriethoxysilane, dimethyldiethoxysilane or dimethyldimethoxysilane, or a combination of at least three of them.

6. The electrolyte according to any one of claims 1 to 5, characterized in that: The molar ratio of the lithium salt to the solvent is 1:(0.5-5); Preferably, the molar ratio of the lithium salt to the additive is 1:(0.001-10), preferably 1:(1-5).

7. A method for preparing an electrolyte according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: The electrolyte is obtained by mixing a solvent, a lithium salt and an additive; wherein the additive has a lithium-philic group; and the solvating ability of the additive to the lithium salt is lower than the solvating ability of the solvent to the lithium salt.

8. The preparation method according to claim 7, characterized in that: The mixing method includes: Add the additive to the solvent, stir once, then add the lithium salt, stir a second time; Preferably, the secondary stirring time is ≥12 h.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 6.

10. The lithium ion battery according to claim 9, characterized in that: The material of the negative electrode plate includes lithium metal or lithium alloy; Preferably, the surface of the positive electrode sheet and / or the negative electrode sheet is modified with an additive, and the additive is the additive in the electrolyte according to any one of claims 1-6.

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