Directional solvation type local high-concentration electrolyte and application thereof in lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery electrolytes, and discloses a directional solvation type local high-concentration electrolyte and an application thereof in a lithium ion battery. The electrolyte contains a lithium salt, a solvent, a diluent and a directional solvation component, the directional solvation component is neutral molecules; the molecular dipole moment of the directional solvation component is greater than or equal to 1.5 D, the main shaft length is greater than or equal to 0.6 nm, and the length-width ratio is greater than or equal to 2.0; the directional solvation component is selected from at least one of a linear fluoro-ether compound, a linear fluoro-ester compound and a linear boron-containing ether compound; and in the electrolyte, the concentration of the directional solvation component is 0.05 to 2 weight percent. The electrolyte provided by the invention has higher orientation parameter, conductivity and lithium ion transference number, the prepared lithium ion battery has better cycle performance, and the ion transmission efficiency and the interface stability are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery electrolyte, and particularly relates to a directional solvation type local high-concentration electrolyte and application thereof in lithium ion batteries. BACKGROUND

[0002] Lithium ion batteries are widely used in energy storage power stations, electric transportation and portable electronic devices due to their high energy density and long cycle life. However, the traditional carbonate electrolyte is prone to problems such as limited ion transport, unstable interface and dendrite formation during high-rate charging and discharging or long-term cycling, which limits the safety and life of the battery.

[0003] In recent years, the local high-concentration electrolyte (LHCE) has been proposed by introducing inert diluents into the high-concentration salt solution, which takes into account the solvation structure and lower viscosity characteristics of the high-concentration electrolyte, and has made significant progress in improving thermal stability and suppressing side reactions. However, the solvation shell molecules in the existing LHCE system are still randomly oriented, the lithium ion migration directionality is poor, the interface electric field distribution is uneven, and local electric field concentration is easily formed under high current density, leading to dendrite growth and interface film rupture.

[0004] Therefore, it is urgent to propose a solvation structure that can form oriented arrangement under the action of electric field, to regulate ion migration channels and interface electric field distribution from the level of solvent molecular orientation, so as to further improve the ion transport efficiency and interface stability of the electrolyte. SUMMARY

[0005] The purpose of the present application is to overcome the problems of slow ion migration and insufficient interface stability of the existing local high-concentration electrolyte.

[0006] The inventors of the present application provide the present application based on the following inventive idea: Under the framework of traditional LHCE, solvents or diluents with molecular anisotropy and high dipole moment are introduced, which are oriented under the action of electric field, so that the Li + The directional solvation layer is formed around the anion-rich cluster, and an ordered ion migration channel and uniform interface electric field distribution are established. When polar molecules (such as linear fluorinated ether, aromatic ether or siloxane) are introduced into the local high-concentration system, the molecular dipole moment interacts with the electric field of the salt-rich domain, and the molecular main axis is oriented along the direction of the electric field, forming a "directional solvation layer". This oriented structure can enhance the Li +The migration directionality is reduced, the desolvation barrier is lowered, and a continuous polarization layer is established at the electrode-electrolyte interface, homogenizing the interface electric field, suppressing local overcurrent and dendrite formation. From a microscopic mechanism, the introduction of molecular anisotropy component is equivalent to constructing an "ordered electric field response network" in the electrolyte. Through molecular orientation, the spatial controllability of solvation structure and the directionalization of ion migration path are realized, thereby realizing the synergistic optimization of electrolyte conductivity and interface stability without changing the chemical composition of the system.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a local high-concentration electrolyte of directional solvation type, which contains a lithium salt, a solvent, a diluent and a directional solvation component. The directional solvation component is a neutral molecule; the molecular dipole moment of the directional solvation component is ≥1.5 D, the major axis length is ≥0.6 nm, and the aspect ratio is ≥2.0; the directional solvation component is selected from at least one of linear fluorinated ether compounds, linear fluorinated ester compounds and linear boron-containing ether compounds; In the electrolyte, the concentration of the directional solvation component is 0.05-2 wt%.

[0008] The second aspect of the present application provides the application of the electrolyte of the first aspect in a lithium ion battery.

[0009] The third aspect of the present application provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte. The electrolyte is the local high-concentration electrolyte of directional solvation type according to the first aspect of the present application.

[0010] Through the above technical solution, the present application has at least the following advantages: (1) The present application introduces a neutral molecule with molecular anisotropy and high dipole moment into a local high-concentration electrolyte system, which forms a solvation layer with consistent orientation under the action of an electric field, thereby significantly improving the migration directionality and efficiency of lithium ions and reducing the ion transmission impedance; (2) The oriented solvation structure formed by the present application can establish a continuous ordered molecular layer at the electrode-electrolyte interface, effectively homogenize the local electric field distribution, suppress dendrite formation and improve the electrode interface stability; (3) The present application constructs a solvation network driven by molecular orientation, making the electrolyte ion transmission and interface reaction process more orderly controllable, thereby realizing the synergistic optimization of high-efficiency conduction and interface stability; (4) The present application does not change the main chemical composition of the local high-concentration electrolyte system, and only by introducing a small amount of directional solvation component can the performance be improved, which has good universality and engineering adaptability. DETAILED DESCRIPTION

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Each integer value within the stated ranges is incorporated into this disclosure as if each value is individually recited. The endpoints of the ranges of values (as well as the parameters) are not exclusive; the scope of ranges encompasses values from the lower and upper limits of the range if the context of the range indicates that such a range is intended. The disclosure of ranges includes endpoints.

[0012] As previously described, the first aspect of the present application provides a directional solvation type local high-concentration electrolyte, which contains a lithium salt, a solvent, a diluent and a directional solvation component; The directional solvation component is a neutral molecule; the directional solvation component has a molecular dipole moment ≥ 1.5 D, a major axis length ≥ 0.6 nm and an aspect ratio ≥ 2.0; the directional solvation component is selected from at least one of a linear fluoroether compound, a linear fluoroester compound and a linear boron-containing ether compound; In the electrolyte, the concentration of the directional solvation component is 0.05-2 wt%.

[0013] Preferably, the directional solvation component is selected from at least one of 1,1,2,2-tetrafluoroethyl isopropyl ether, bis-trifluoromethoxy ether, trifluoroethyl carbonate, difluorobisdimethoxyborane and 1,2-bis(trifluoroethoxy)ethane.

[0014] Preferably, the electrolyte has a parallel absorption intensity to vertical absorption intensity ratio R ≥ 1.5 under a polarized infrared spectrum test at 25°C, an applied electric field of 10 4 V / m, and an orientation parameter S calculated according to the formula S = (R 1) / (R+2) ≥ 0.20.

[0015] Preferably, the lithium salt is selected from at least one of lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0016] Preferably, the solvent is selected from at least one of a fluoro-phosphate compound, a fluoro-carbonate compound and an ether compound.

[0017] Further preferably, the fluoro-phosphate compound is selected from at least one of trifluoroethyl phosphate (TFEP), difluoromethyl phosphate (DFMP), trifluoropropyl phosphate (TFPP); the fluoro-carbonate compound is selected from at least one of trifluoroethyl carbonate (TFEC), difluoropropyl carbonate (DFPC), trifluoromethyl carbonate (TFMC); and the ether compound is selected from at least one of ethylene glycol dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane.

[0018] Preferably, the diluent is selected from at least one of trifluoromethoxybenzene, bis-trifluoroethyl ether, perfluorohexyldimethyl ether.

[0019] Preferably, the lithium salt, the solvent and the diluent are in a molar ratio of 1:2-6:4-8.

[0020] Further preferably, in the electrolyte, the concentration of the lithium salt is 1.5-4.0 mol / L.

[0021] As mentioned before, the second aspect of the present application provides the electrolyte of the first aspect for use in a lithium ion battery.

[0022] As mentioned before, the third aspect of the present application provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte; The electrolyte is the directed solvation type local high concentration electrolyte of the first aspect of the present application.

[0023] Preferably, the positive electrode material of the battery comprises LiFePO4, and the negative electrode of the battery is formed of graphite.

[0024] The present application will be described in detail below by way of examples. In the following examples, the raw materials and equipment used are commercially available, and the solvents used are of analytical purity.

[0025] Lithium salt: Lithium difluoro(oxalato)borate (LiDFOB) was purchased from Duoduo Reagent Co., Ltd. Lithium bis(fluorosulfonyl)imide (LiFSI) was purchased from Duoduo Reagent Co., Ltd. Solvent: Trifluoroethyl carbonate (TFEC) was purchased from Duoduo Reagent Co., Ltd. Triethyl phosphate (TEP) was purchased from Duoduo Reagent Co., Ltd. Diluent: Trifluoromethoxybenzene (TFMB) was purchased from Macklin Reagent Co., Ltd. Bis-trifluoroethyl ether (BTFE) was purchased from Macklin Reagent Co., Ltd. 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) was purchased from Macklin Reagent Co., Ltd. Directed solvation component: 1,1,2,2-Tetrafluoroethyl isopropyl ether, with a molecular dipole moment of 1.9 D, a major axis length of 0.72 nm, and an aspect ratio of 2.3, was purchased from Macklin Reagent Co., Ltd. Bis-trifluoromethoxy ether, with a molecular dipole moment of 2.1 D, a major axis length of 0.78 nm, and an aspect ratio of 2.4, was purchased from Macklin Reagent Co., Ltd. Difluoroborondimethoxide, 1.8 D of molecular dipole moment, 0.70 nm of major axis length, 2.1 of aspect ratio, purchased from Macklin Reagent Co., Ltd.; Methoxybenzene, 1.2 D of molecular dipole moment, 0.48 nm of major axis length, 1.6 of aspect ratio, purchased from Macklin Reagent Co., Ltd.

[0026] The following preparation examples are used to illustrate the preparation method of the electrolyte of the present application Preparation Example 1 (1) In an argon glove box (H2O and O2 are both <0.1 ppm), lithium salt, solvent, diluent were mixed according to the molar ratio of 1:4:6, so that the concentration of lithium salt in the electrolyte was 2 mol / L, and stirred at 25℃ for 12 h to form a uniform local high-concentration electrolyte mother liquor.

[0027] (2) The local high-concentration electrolyte mother liquor obtained in step (1) was added with a directional solvation component, so that the concentration of the directional solvation component in the electrolyte was 0.3 wt%, and continued to be stirred for 6 h to obtain a directional solvation type local high-concentration electrolyte, named S1.

[0028] The specific process parameters of the rest of the preparation example are shown in Table 1.

[0029] Preparation Example 2-Preparation Example 8 Preparation Example 2-Preparation Example 8 were all prepared by the similar method of Preparation Example 1, the difference was listed in Table 1, and the prepared electrolytes were named as S2-S8 in turn.

[0030] Comparative Preparation Example 1, Comparative Preparation Example 2 Comparative Preparation Example 1, Comparative Preparation Example 2 were all prepared by the similar method of Preparation Example 1, the difference was listed in Table 1, and the prepared electrolytes were named as DS1, DS2 in turn.

[0031] Table 1

[0032] The following application examples are used to illustrate the preparation method of the lithium ion battery of the present application Application Example 1 The commercial LiFePO4 cathode, commercial graphite anode, commercial separator and electrolyte S1 were assembled into a battery to obtain a lithium ion battery.

[0033] Application Example 2-Application Example 8 Application Example 2-Application Example 8 were all prepared by the similar method of Application Example 1, the difference was that the electrolyte S1 in Application Example 1 was replaced by electrolytes S2-S8 respectively.

[0034] Comparative Application Example 1, Comparative Application Example 2 Comparative Application Example 1 and Comparative Application Example 2 were carried out in a similar manner to Application Example 1, except that electrolyte S1 in Application Example 1 was replaced by electrolyte DS1 and DS2, respectively.

[0035] Test Example The performance test data of the electrolytes prepared in Preparation Example and Comparative Preparation Example are shown in Table 2.

[0036] Electrolyte orientation property test: the molecular orientation parameters of each electrolyte were tested by a polarized infrared spectrometer. The test conditions were: temperature 25℃, applied electric field 10 4 V / m, electrode spacing 1.0 mm. The characteristic absorption peak of the oriented solvated component was used as the detection signal, and the absorption intensities in the parallel (I ∥ ) and perpendicular (I ⊥ ) directions were recorded, respectively, and the absorption ratio R=I ∥ / I ⊥ and the orientation parameter S=(R 1) / (R+2) were calculated.

[0037] The ionic conductivity of the electrolyte was tested by an alternating current impedance analyzer (CHI760E), and each electrolyte was injected into a stainless steel | stainless steel symmetrical battery, and tested at 25℃, and the calculation formula was σ=L / (R·S).

[0038] The lithium ion transference number (t Li + ) was determined by the steady-state current method, and the formula was t Li + =(I ss ·(ΔV I0R0)) / (I0·(ΔV I ss R ss ), where I0, I ss were the currents before and after polarization, and R0, R ss were the impedances before and after polarization.

[0039] Table 2

[0040] The performance test data of the lithium ion batteries prepared in Application Example and Comparative Application Example are shown in Table 3.

[0041] Battery cycle performance test: Land charge-discharge tester of Wuhan Lan electric is used for charge-discharge test, and the battery structure is LiFePO4 positive electrode, graphite negative electrode.Testing conditions are as follows: in 2.5-3.65 V voltage range, first activate three times at 0.1 C rate, and then charge-discharge cycle is carried out 100 times at 0.5 C rate.Calculation formula is as follows: room temperature cycle 100 times capacity retention rate (%)=(100th cycle discharge capacity / first cycle discharge capacity) x 100%, and room temperature refers to 25±2 ℃.

[0042] Table 3

[0043] It can be seen from the above results that the electrolyte provided by the application has a higher orientation parameter, can produce ordered arrangement under the action of an electric field, thereby constructing a directional solvation layer; meanwhile, the electrolyte has higher electrical conductivity and lithium ion transference number, and the lithium ion battery prepared has better cycle performance, and ion transmission efficiency and interface stability are significantly improved.

[0044] The above describes the preferred embodiments of the application, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application and belong to the protection scope of the application.

Claims

1. A directional solvation type local high-concentration electrolyte, characterized by, The electrolyte contains a lithium salt, a solvent, a diluent and a directional solvation component; The directional solvation component is a neutral molecule; the directional solvation component has a molecular dipole moment ≥ 1.5 D, a major axis length ≥ 0.6 nm and an aspect ratio ≥ 2.0; the directional solvation component is selected from at least one of linear fluoroether compounds, linear fluoroester compounds and linear boron-containing ether compounds; In the electrolyte, the concentration of the directional solvation component is 0.05-2 wt%.

2. The electrolyte according to claim 1, characterized in that, The directional solvation component is selected from at least one of 1,1,2,2-tetrafluoroethyl isopropyl ether, bis-trifluoromethoxy ether, trifluoroethyl carbonate, difluoro dimethoxy borane and 1,2-bis(trifluoroethoxy)ethane.

3. The electrolyte of claim 1, wherein The electrolyte has a ratio R of parallel absorption intensity to vertical absorption intensity ≥1.5 by polarization infrared spectrum test under the condition of 25℃, 10 4 V / m external electric field, and an orientation parameter S calculated by formula S=(R 1) / (R+2) ≥0.

20.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt is selected from at least one of lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

5. The electrolyte according to any one of claims 1 to 3, wherein The solvent is selected from at least one of fluoro phosphate compounds, fluoro carbonate compounds and ether compounds.

6. The electrolyte according to any one of claims 1 to 3, wherein The diluent is selected from at least one of trifluoromethoxy benzene, bis-trifluoroethyl ether and perfluorohexyl dimethyl ether.

7. The electrolyte according to any one of claims 1 to 3, wherein The molar ratio of the lithium salt, the solvent and the diluent is 1:2-6:4-8; And / or, in the electrolyte, the concentration of the lithium salt is 1.5-4.0 mol / L.

8. Use of the electrolyte of any one of claims 1-7 in a lithium ion battery.

9. A lithium-ion battery, characterized by The battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; The electrolyte is the directional solvation type partial high concentration electrolyte of any one of claims 1-7.

10. The battery of claim 9, wherein, The positive electrode material of the battery contains LiFePO4, and the negative electrode of the battery is formed of graphite. The battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; The electrolyte is the directional solvation type partial high concentration electrolyte of any one of claims 1-7. The positive electrode material of the battery contains LiFePO4, and the negative electrode of the battery is formed of graphite.

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