Ion polarization enhanced local high-concentration electrolyte and application thereof in lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery electrolyte, and discloses ion polarization enhanced local high-concentration electrolyte and application thereof in a lithium ion battery. The electrolyte contains a lithium salt, a solvent, a diluent and a polarization enhancing component, the polarization enhancing component is neutral molecules, and the molecular polarizability is greater than or equal to 15; the polarization enhancing component is selected from at least one of an aromatic sulfone compound, a conjugated amine oxide, a silyl-containing ether compound and an aromatic amide compound; and in the electrolyte, the concentration of the polarization enhancing component is 0.05 to 2 weight percent. The electrolyte provided by the invention has higher conductivity and lithium ion transference number, the capacity retention ratio of the prepared lithium ion battery is higher, and the high-voltage adaptability is obviously enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery electrolyte, and particularly relates to an ion polarization enhanced 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 vehicles and power grid frequency modulation scenarios. However, the traditional carbonate electrolyte system has the problems of strong flammability, poor thermal stability and serious interface side reactions under high voltage conditions, which limits its application in high safety and high energy density energy storage systems.

[0003] To improve such problems, researchers have proposed the concepts of "high-concentration electrolyte (HCE)" and "local high-concentration electrolyte (LHCE)". LHCE introduces inert diluents into high-concentration salt solutions, which reduces the viscosity and cost of the system while maintaining the solvation structure of high-concentration electrolyte, significantly improving the safety and electrode interface stability of the electrolyte.

[0004] However, the existing LHCE system still has the following deficiencies: (1) under high salt concentration, the strong coordination between Li + and anions leads to limited ion migration, slow Li + desolvation kinetics and large ion transport resistance; (2) the internal electric field strength of the solvation cluster is limited, and the coordination structure of the anion and the solvent is still susceptible to uneven polarization on the electrode surface, forming uneven SEI films or side reaction products; (3) under high voltage (>4.5 V), the overall dielectric stability and electron shielding ability of the electrolyte are insufficient, leading to problems such as oxidation side reactions and solvent decomposition.

[0005] Therefore, it is urgent to propose a new electrolyte regulation strategy to improve ion migration, solvation kinetics and interface stability from the perspective of electric field distribution and polarization behavior of the solvation structure, in order to further improve the high-voltage adaptability and cycle stability of the electrolyte. SUMMARY

[0006] The purpose of the present application is to overcome the problems of limited ion migration, poor interface stability and insufficient high-voltage adaptability of the existing local high-concentration electrolyte.

[0007] The inventors of the present application provide the present application based on the following invention idea: Under the framework of traditional LHCE, neutral molecules with high molecular polarization rate or high dielectric polarization ability are introduced, which are locally induced by the electric field in the Li + -anion solvation cluster or at the boundary of the cluster, thereby forming a locally enhanced dipole field to achieve fine regulation of the solvation structure and interface behavior. High-polarization-rate molecules can be locally induced by the electric field in the Li +- under the strong electric field of anion, induced dipoles are generated, which cooperates with original solvent molecules to change the Li + - the coordination distance and orientation of anion weaken the local binding energy and reduce the desolvation barrier, thus improving the Li + migration number and conductivity; meanwhile, these polarized molecules are arranged in a continuous polarization layer at the electrode-electrolyte interface, which can enhance the uniformity of local electric field, inhibit the distortion of ion flow density, promote the uniform deposition of lithium ions and reduce the generation of dendrites; in addition, the induced dipoles are opposite to the direction of the interface electric field, which can effectively buffer the solvent oxidation electron flow channel, improve the dielectric stability of the electrolyte under high pressure, and inhibit the autocatalytic decomposition under high temperature by enhancing the electron shielding ability.

[0008] To achieve the above-mentioned purposes, the first aspect of the present application provides an ion polarization enhanced local high-concentration electrolyte, which contains a lithium salt, a solvent, a diluent and a polarization enhancing component; The polarization enhancing component is a neutral molecule, and the molecular polarizability is ≥ 15 ų; the polarization enhancing component is selected from at least one of aromatic sulfone compounds, conjugated amine oxides, silicon-containing ether compounds and aromatic amide compounds; In the electrolyte, the concentration of the polarization enhancing component is 0.05-2 wt%.

[0009] The second aspect of the present application provides the application of the electrolyte of the first aspect in a lithium ion battery.

[0010] 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 ion polarization enhanced local high-concentration electrolyte of the first aspect of the present application.

[0011] Through the above technical solution, the present application has at least the following advantages: (1) By introducing a neutral molecule with high molecular polarizability into a local high-concentration electrolyte system, the present application can form a directional dipole layer in the solvation cluster by using induced polarization effect, which can enhance the local electric field strength and promote the directional migration of lithium ions, thereby significantly improving the ion conductivity of the electrolyte; (2) The polarization enhancing component of the present application forms a uniform polarization layer at the electrode-electrolyte interface, which can effectively improve the interface electric field distribution, inhibit the generation of lithium dendrites, and significantly improve the electrode interface stability; (3) The electrolyte system of the present application has stronger dielectric stability and electron shielding ability under high pressure, which can inhibit the occurrence of solvent oxidation and side reactions, thereby improving the high-pressure resistance and cycle life of the battery; (4) The present application does not change the main chemical composition of the local high-concentration electrolyte, and only by introducing a trace amount of a high-polarizability component, the performance optimization can be achieved, and good universality and industrial adaptability are obtained. DETAILED DESCRIPTION

[0012] 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 present application. Any numerical values need not be a precision value, unless expressly indicated as such. In this application, any numerical values include all values from the lower numerical limit to the upper numerical limit, inclusive of the endpoints in range in combination with other certain values. For ranges, the endpoints are included within the range.

[0013] As described above, the first aspect of the present application provides an ion polarization enhanced local high-concentration electrolyte, which contains a lithium salt, a solvent, a diluent and a polarization enhancement component; The polarization enhancement component is a neutral molecule, and the molecular polarizability is greater than or equal to 15 ų; the polarization enhancement component is selected from at least one of an aromatic sulfone compound, a conjugated amine oxide, a silicon-containing ether compound and an aromatic amide compound; In the electrolyte, the concentration of the polarization enhancement component is 0.05-2 wt%.

[0014] In the present application, the molecular polarizability is a microscopic parameter for characterizing the polarization degree of a dielectric under the action of an electric field, and is defined as the ratio of the molecular induced dipole moment to the effective electric field intensity.

[0015] Preferably, the polarization enhancement component is selected from at least one of diphenyl sulfone, benzothiophene sulfone, N-oxidized pyridine, N,N-dimethyl benzamide and methoxy trimethyl silane.

[0016] Preferably, the polarization enhancement component forms a directional dipole layer in the electrolyte system through induced polarization, and the dipole layer has an orientation ratio greater than or equal to 0.6 under an external electric field of 10 4 -10 5 V / m.

[0017] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate or lithium difluoro(oxalato)borate.

[0018] Preferably, the solvent is selected from at least one of a phosphate compound, a carbonate compound, an ether compound and a sulfone compound.

[0019] Further preferably, the phosphate compound is selected from at least one of triethyl phosphate, trimethyl phosphate, and triphenyl phosphate; the carbonate compound is selected from at least one of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate; the ether compound is selected from at least one of ethylene glycol dimethyl ether, tetrahydrofuran, and dioxolane; and the sulfone compound is selected from at least one of dimethyl sulfoxide, sulfolane, and sulfoxonium.

[0020] Preferably, the diluent is selected from at least one of fluorobenzene, trifluoromethoxybenzene, bistrifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0021] Preferably, the molar ratio of the lithium salt, the solvent, and the diluent is 1:1-6:4-8.

[0022] Preferably, the concentration of the lithium salt in the electrolyte is 1.5-4.5 mol / L.

[0023] As described above, the second aspect of the present application provides the electrolyte of the first aspect for use in a lithium ion battery.

[0024] As described above, 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 ionically polarized enhanced local high-concentration electrolyte of the first aspect of the present application.

[0025] Preferably, the positive electrode of the battery comprises a LiFePO4 positive electrode or a LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode, and the negative electrode of the battery is formed of graphite.

[0026] The present application will be described in detail below through examples. In the following examples, the raw materials and equipment used are commercially available, and the solvents used are of analytical purity.

[0027] Lithium salt: lithium bis(fluorosulfonyl)imide (LiFSI), purchased from Dofarm New Material Co., Ltd.; Solvent: triethyl phosphate (TEP), purchased from Macklin Reagent Co., Ltd.; Diluent: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), purchased from Macklin Reagent Co., Ltd.; Polarization-enhancing component: Diphenyl sulfone, with a molecular polarizability of 22.1 ų, purchased from Macklin Reagent Co., Ltd.; N-oxidized pyridine, with a molecular polarizability of 17.8 ų, purchased from Macklin Reagent Co., Ltd.; Methoxytrimethylsilane, molecular polarizability of 16.5 Å3, purchased from Macklin Reagent Co., Ltd.

[0028] 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 in a molar ratio of 1:3:6, so that the concentration of lithium salt in the electrolyte was 2.5 mol / L, and stirred for 12 h to form a uniform local high-concentration solvated structure; (2) The polarizability-enhancing component was added to the local high-concentration solvated structure obtained in step (1) to make the concentration of the polarizability-enhancing component in the electrolyte 0.3 wt%, and continue to stir for 6 h to obtain an ionic polarizability-enhancing local high-concentration electrolyte, named S1.

[0029] The remaining specific process parameters of the present preparation example are shown in Table 1.

[0030] Preparation Examples 2-8 Preparation Examples 2-8 were all prepared by a method similar to that of Preparation Example 1, with the differences listed in Table 1, and the prepared electrolytes were named S2-S8 in turn.

[0031] Comparative Preparation Example 1 and Comparative Preparation Example 2 Comparative Preparation Example 1 and Comparative Preparation Example 2 were both prepared by a method similar to that of Preparation Example 1, with the differences listed in Table 1, and the prepared electrolytes were named DS1 and DS2 in turn.

[0032] Table 1

[0033] The following application examples are used to illustrate the preparation method of the lithium ion battery of the present application Application Example 1 A commercial LiFePO4 cathode or LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode, a commercial graphite anode, a commercial separator, and the electrolyte S1 were assembled into a battery, to obtain a lithium ion battery.

[0034] Application Examples 2-8 Application Examples 2-8 were all prepared by a method similar to that of Application Example 1, except that the electrolyte S1 in Application Example 1 was replaced by electrolytes S2-S8, respectively.

[0035] Comparative Application Example 1 and 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.

[0036] Test Example The performance test data of the electrolytes prepared in the Preparation Examples and Comparative Preparation Examples are shown in Table 2.

[0037] The ionic conductivity (σ) was tested by an impedance analyzer (Shanghai Chenhua CHI760E). The electrolyte was injected into a stainless steel | stainless steel symmetrical battery, and the alternating current impedance measurement was carried out at 25°C under constant temperature conditions. L is the electrode spacing, R is the impedance, and S is the electrode area. The calculation formula is: σ = L / (R·S).

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

[0039] Table 2

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

[0041] Battery cycle performance test: The Land charge-discharge tester of Wuhan Blue Electric was used for charge-discharge test. The battery structure was LiFePO4 positive electrode and graphite negative electrode. The test conditions were: in the voltage range of 2.5-3.65 V, first activated three times at 0.1C rate, and then charged and discharged at 0.5C rate for 100 cycles. The calculation formula is: capacity retention rate (%) after 100 cycles at room temperature = (100th cycle discharge capacity ÷ initial cycle discharge capacity) × 100%, and room temperature refers to 25±2°C.

[0042] Battery high-voltage cycle performance test: The Land charge-discharge tester of Wuhan Blue Electric was used for charge-discharge test. The battery structure was LiNi 0.8 Co 0.1 Mn 0.1O2 cathode, graphite anode. Test conditions: in the voltage range of 2.5-4.6 V, first activate three times at 0.1C rate, then charge and discharge at 0.5C rate for 100 cycles. The calculation formula is: capacity retention rate (%) of 100 high-voltage cycles = (discharge capacity of the 100th high-voltage cycle ÷ discharge capacity of the first high-voltage cycle) x 100%.

[0043] Table 3

[0044] It can be seen from the above results that the electrolyte provided by the application has higher electrical conductivity and lithium ion transference number, the capacity retention rate of the prepared lithium ion battery is higher, and the high-voltage adaptability is obviously enhanced.

[0045] 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. An ion-polarization-enhanced locally high-concentration electrolyte, characterized in that, The electrolyte contains lithium salt, solvent, diluent, and polarization-enhancing components; The polarization-enhancing component is a neutral molecule with a molecular polarizability ≥ 15 ų. The polarization-enhancing component is selected from at least one of aromatic sulfone compounds, conjugated amine oxides, silicone-containing ether compounds, and aromatic amide compounds; In the electrolyte, the concentration of the polarization-enhancing component is 0.05-2 wt%.

2. The electrolyte according to claim 1, characterized in that, The polarization enhancement component is selected from at least one of diphenyl sulfone, benzothiophene sulfone, N-pyridine oxide, N,N-dimethylbenzamide, and methoxytrimethylsilane.

3. The electrolyte according to claim 1 or 2, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, or lithium difluorooxalate borate.

4. The electrolyte according to claim 1 or 2, characterized in that, The solvent is selected from at least one of phosphate esters, carbonates, ethers, and sulfones.

5. The electrolyte according to claim 1 or 2, characterized in that, The diluent is selected from at least one of fluorobenzene, trifluoromethoxybenzene, bis(trifluoroethyl) ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

6. The electrolyte according to claim 1 or 2, characterized in that, The molar ratio of the lithium salt, the solvent, and the diluent is 1:1-6:4-8.

7. The electrolyte according to claim 1 or 2, characterized in that, The concentration of the lithium salt in the electrolyte is 1.5-4.5 mol / L.

8. The application of the electrolyte according to any one of claims 1-7 in a lithium-ion battery.

9. A lithium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The electrolyte is the ion polarization enhanced local high-concentration electrolyte as described in any one of claims 1-7.

10. The battery according to claim 9, characterized in that, The positive electrode of this battery includes either LiFePO4 or LiNi. 0.8 Co 0.1 Mn 0.1 The battery uses an O2 ternary cathode and a graphite-based anode.

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