Organic electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium batteries, and particularly discloses an organic electrolyte and a preparation method and application thereof, the organic electrolyte comprises an inorganic oxide additive, a lithium salt and an organic solvent, the mass percentage content of the inorganic oxide additive is 0.01-3.0 wt%, and the concentration of the lithium salt is 0.1-6 mol / L. The specific inorganic oxide is selected as the film-forming additive of the lithium battery, so that stable interface films can be formed on the surfaces of the positive electrode and the negative electrode at the same time, the interface impedance of the battery is reduced, side reactions in the battery and dissolution of transition metal ions are inhibited, the cycling stability of the lithium battery in a high-voltage and wide-temperature range is effectively improved, and the service life of the lithium battery is prolonged. Meanwhile, good economic benefits are also shown.

Description

Technical Field

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

[0002] Lithium batteries have been widely used in electric vehicles, portable electronic devices and other fields due to their high energy density and long cycle life. However, with the development of society, the power and consumer battery industries have put forward higher requirements on the energy density, safety, life and other performance of lithium batteries.

[0003] As an important component of lithium batteries, electrolyte has an important influence on the stability of the positive and negative electrode interfaces. Improving battery performance by introducing additives is a very simple, economical and efficient way. The electrodes of lithium batteries are composed of positive and negative electrodes. For metal oxide positive electrodes, metal ions in a higher valence state during the cycle will catalyze the decomposition of the electrolyte, resulting in a large amount of electrolyte consumption and the generation of harmful substances, which in turn causes the degradation of the positive electrode structure. At the same time, the dissolved metal ions migrate to the negative electrode under the action of the electric field and also destroy the solid electrolyte interface film (SEI) on its surface. For the negative electrode, a poor SEI film makes it difficult to suppress the side reactions on the negative electrode surface, reducing the Coulomb efficiency. At the same time, the continuous and uneven deposition / stripping of lithium ions will also lead to the generation of lithium dendrites and dead lithium, thereby significantly reducing the electrochemical performance and safety of lithium batteries. Therefore, it is crucial to construct a stable and durable electrode interface protective layer in situ through electrolyte additives to improve the electrochemical performance and safety of batteries. The electrolytes currently in use contain mainly organic solvents and lithium salt additives, which result in problems such as high cost, insufficient high-voltage stability, and difficulty in effectively improving the stability of the positive and negative electrode interfaces at the same time. Some additives are also toxic.

[0004] Therefore, it is very necessary to develop a new high-efficiency organic electrolyte to improve the interface stability between the electrode and the electrolyte. Summary of the invention

[0005] The purpose of the present invention is to provide an organic electrolyte to address the problems existing in the prior art. By adopting low-cost, non-toxic inorganic oxides as film-forming additives for lithium batteries, the problems of high additive costs, strong toxicity of some additives, and difficulty in effectively improving the positive and negative electrode interface stability at the same time in the existing electrolytes are solved. In addition, the performance of lithium batteries at room temperature, high and low temperature cycles, etc. are significantly improved.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned organic electrolyte.

[0007] Another object of the present invention is to provide a lithium battery comprising the above-mentioned organic electrolyte.

[0008] In order to achieve the above purpose, the technical solution of the present invention is:

[0009] An organic electrolyte comprises an inorganic oxide additive, a lithium salt and an organic solvent, wherein the mass percentage content of the inorganic oxide additive is 0.01wt% to 3.0wt% and the concentration of the lithium salt is 0.1-6mol / L.

[0010] Inorganic oxide additives are used as electrode film-forming additives.

[0011] In a preferred embodiment of the present invention, the inorganic oxide additive includes at least one of magnesium oxide (MgO), aluminum oxide (Al2O3), silicon oxide (SiO), silicon dioxide (SiO2), boron oxide (B2O3), phosphorus trioxide (P2O3), phosphorus pentoxide (P2O5), sulfur trioxide (SO3), and disulfur trioxide (S2O3).

[0012] In a preferred embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium tetrafluoroborate, and lithium perchlorate.

[0013] In a preferred embodiment of the present invention, the organic solvent is at least one of cyclic or linear carbonate organic solvents.

[0014] More preferably, the cyclic carbonate organic solvent is at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, propylene carbonate and trifluoromethylethylene carbonate.

[0015] More preferably, the linear carbonate organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, ethyl methyl carbonate, and methyl trifluoroethyl carbonate.

[0016] The method for preparing the organic electrolyte comprises the following steps: adding lithium salt and inorganic oxide additive into an organic solvent, stirring and mixing to obtain the organic electrolyte.

[0017] A lithium battery comprising the organic electrolyte.

[0018] Lithium batteries include lithium-ion batteries or lithium metal batteries.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the organic electrolyte of the present invention adopts inorganic oxide as an additive, which can participate in the formation of the interface film between the electrode / electrolyte, improve the stability of the interface film, and thus effectively inhibit the degradation of the electrode material structure and the decomposition of the organic electrolyte during long cycles, thereby improving the room temperature and high and low temperature electrochemical performance of the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a normal temperature cycle performance diagram of lithium batteries containing the electrolytes in Example 1 of the present invention and Comparative Example 1;

[0021] Figure 2 It is a high temperature cycle performance diagram of lithium batteries containing the electrolytes in Example 1 of the present invention and Comparative Example 1;

[0022] Figure 3 The graph is a low temperature cycle performance graph of lithium batteries containing the electrolytes in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0024] An organic electrolyte comprises an inorganic oxide additive, a lithium salt and an organic solvent, wherein the mass percentage content of the inorganic oxide additive is 0.01wt% to 3.0wt% and the concentration of the lithium salt is 0.1-6mol / L.

[0025] The inorganic oxide additive includes at least one of magnesium oxide (MgO), aluminum oxide (Al2O3), silicon oxide (SiO), silicon dioxide (SiO2), boron oxide (B2O3), phosphorus trioxide (P2O3), phosphorus pentoxide (P2O5), sulfur trioxide (SO3), and disulfur trioxide (S2O3).

[0026] The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium tetrafluoroborate, and lithium perchlorate.

[0027] The organic solvent is at least one of cyclic or chain carbonate organic solvents.

[0028] The cyclic carbonate organic solvent is at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, propylene carbonate and trifluoromethylethylene carbonate.

[0029] The chain carbonate organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, ethyl methyl carbonate and methyl trifluoroethyl carbonate.

[0030] The method for preparing the organic electrolyte comprises the following steps: adding lithium salt and inorganic oxide additive into an organic solvent, stirring and mixing to obtain the organic electrolyte.

[0031] A lithium battery comprising the organic electrolyte.

[0032] The embodiment of the present invention and the comparative example adopt the same battery system, using lithium-rich layered oxide as the positive electrode material, lithium metal as the negative electrode, and a microporous PP film as a separator to assemble a button-type half-cell. The preparation process of the positive electrode is as follows: first, the lithium-rich layered oxide positive electrode particles, conductive carbon and a binder are uniformly mixed in an N-methylpyrrolidone solvent, and then the obtained slurry is coated on an aluminum foil, and then dried, rolled and cut to obtain a positive electrode sheet.

[0033] Example 1

[0034] The lithium salt used in the electrolyte in this embodiment is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L. The organic solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 1:1:1. The inorganic oxide boron oxide (B2O3) is used as an additive, and its addition amount is 0.5wt% of the total mass of the electrolyte.

[0035] The preparation method of the electrolyte comprises the following steps: adding lithium salt and inorganic oxide additives into an organic solvent to obtain a mixture containing various components; stirring and mixing the mixture to obtain the electrolyte.

[0036] Example 2

[0037] The lithium salt used in the electrolyte in this embodiment is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L. The organic solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 1:1:1. The inorganic oxide boron oxide (B2O3) is used as an additive, and its addition amount is 0.25wt% of the total mass of the electrolyte.

[0038] The preparation method of the above electrolyte is the same as that of Example 1.

[0039] Example 3

[0040] The lithium salt used in the electrolyte in this embodiment is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L. The organic solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 1:1:1. The inorganic oxide boron oxide (B2O3) is used as an additive, and its addition amount is 1wt% of the total mass of the electrolyte.

[0041] The preparation method of the above electrolyte is the same as that of Example 1.

[0042] Comparative Example 1

[0043] In the comparative example, the lithium salt used in the electrolyte is lithium hexafluorophosphate, the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, and the organic solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 1:1:1.

[0044] The preparation method of the electrolyte comprises the following steps: adding lithium salt into an organic solvent, stirring and mixing the mixture to obtain the electrolyte.

[0045] Example 4

[0046] A lithium battery comprises the organic electrolyte in embodiment 1.

[0047] Example 5

[0048] A lithium battery comprising the organic electrolyte in Example 2.

[0049] Example 6

[0050] A lithium battery comprising the organic electrolyte in Example 3.

[0051] Comparative Example 2

[0052] A lithium battery comprises the organic electrolyte in Comparative Example 1.

[0053] like Figure 1 As shown in the cycle curve, the button half-cells were assembled and tested using the electrolytes in Comparative Example 1 and Example 1. The discharge capacity after 200 cycles at a voltage range of 2-4.8 V and a current density of 250 mA / g was 221 mAh / g, and the capacity retention rate was as high as 92.1%, showing significantly improved discharge capacity and cycle stability.

[0054] The electrolytes in Comparative Example 1 and Example 2 were used to assemble and test button-type half-cells. After 200 cycles at a voltage range of 2-4.8 V and a current density of 250 mA / g, the discharge capacity was 216 mAh / g, and the capacity retention rate was as high as 91.2%.

[0055] The electrolytes in Comparative Example 1 and Example 3 were used to assemble and test button-type half-cells. After 200 cycles at a voltage range of 2-4.8 V and a current density of 250 mA / g, the discharge capacity was 196 mAh / g, and the capacity retention rate was as high as 85.1%.

[0056] The button cells were assembled with the electrolytes in Comparative Example 1 and Example 1, and cycle tests were performed at a high temperature of 55°C. The results are as follows: Figure 2 As shown in the figure, the electrolyte of Example 1 has better high-temperature cycle stability, indicating that it can improve the high-temperature electrochemical performance of lithium batteries.

[0057] The button cells were assembled with the electrolytes in Comparative Example 1 and Example 1, and cycle tests were performed at a low temperature of -15°C. The results are as follows: Figure 3 As shown, the low temperature cycle performance comparison diagram of the comparative example and Example 1. As can be seen from the figure, Example 1 of the present invention has better low temperature cycle stability, indicating that it can improve the low temperature electrochemical performance of the lithium battery.

[0058] According to the embodiments described above, an inorganic oxide additive is added to the organic electrolyte. The additive can participate in the film-forming reaction at the interface between the positive and negative electrodes to form a stable and durable interface protective layer on the electrode surface, thereby inhibiting the decomposition of the electrolyte and maintaining the stability of the positive electrode structure. Therefore, it can effectively improve the high and low temperature performance of lithium batteries, broaden the application range of electrolytes, and has good application prospects.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An organic electrolyte, characterized in that: The invention comprises an inorganic oxide additive, a lithium salt and an organic solvent. The mass percentage content of the inorganic oxide additive is 0.01wt% to 3.0wt%, and the concentration of the lithium salt is 0.1-6mol / L.

2. The organic electrolyte according to claim 1, characterized in that The inorganic oxide additive includes at least one of magnesium oxide, aluminum oxide, silicon oxide, silicon dioxide, boron oxide, phosphorus trioxide, phosphorus pentoxide, sulfur trioxide, and disulfur trioxide.

3. The organic electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium tetrafluoroborate, and lithium perchlorate.

4. The organic electrolyte according to claim 1, characterized in that The organic solvent is at least one of cyclic or chain carbonate organic solvents.

5. The organic electrolyte according to claim 4, characterized in that The cyclic carbonate organic solvent is at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, propylene carbonate and trifluoromethylethylene carbonate.

6. The organic electrolyte according to claim 4, characterized in that The chain carbonate organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, ethyl methyl carbonate and methyl trifluoroethyl carbonate.

7. A lithium battery, characterized in that: Contains the organic electrolyte as described in any one of claims 1 to 6.

8. The method for preparing an organic electrolyte according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: adding lithium salt and inorganic oxide additive into an organic solvent, stirring and mixing the mixture evenly to obtain the organic electrolyte.

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