Sodium-ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a sodium-ion battery electrolyte as well as a preparation method and application thereof, and belongs to the technical field of sodium-ion batteries. The electrolyte comprises an electrolyte salt, a carbonic ester organic solvent and an additive. The sodium salt comprises sodium perchlorate and sodium hexafluorophosphate, the carbonic ester organic solvent comprises ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and the additive comprises trimethyl borate, triethyl borate, trimethoxy boroxane and (2, 2, 2-trifluoroethyl) borate. Under the condition of not changing the existing process, the additive is introduced into the carbonic ester electrolyte, and the electrolyte is good in conductivity and fast in ion transmission. After the battery is assembled, the electrode interface performance is stable, the cycle life of the battery under normal-temperature and high-temperature conditions is remarkably prolonged, meanwhile, the growth of sodium dendrites is inhibited, and the gas production phenomenon is reduced. The additive is wide in raw material source, low in cost and suitable for commercial development.

Description

Technical Field

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

[0002] The low content and uneven distribution of lithium resources in the earth's crust have limited the further development of lithium-ion batteries. In this context, sodium-ion batteries are abundant in resources and low in cost, and have great market prospects and development potential. However, the cycle life of existing sodium-ion batteries under room and high temperature conditions still needs to be improved. At the same time, the growth of sodium dendrites and gas production inside the battery also limit its performance and safety.

[0003] In recent years, hard carbon has been considered the most promising negative electrode material for sodium-ion batteries due to its advantages such as abundant sodium storage sites and high reversible specific capacity. However, when carbonate electrolytes are applied to the hard carbon system of sodium-ion batteries, they exhibit poor cycle performance, poor kinetic performance, and safety issues such as sodium precipitation and gas production. The problems of hard carbon electrodes in sodium-ion batteries are highly related to the formed interface. The ideal interface effectively isolates electrons and passivates the hard carbon electrode. In the actual process, the interface composition and structure of hard carbon generated in carbonate electrolytes are unstable, the electrolyte is continuously consumed, the interfacial impedance increases, and the battery exhibits poor kinetic and cycle performance. High temperature exacerbates the occurrence of undesirable reactions inside the battery, further causing safety problems for the battery.

[0004] Therefore, it is necessary to optimize the sodium ion battery electrolyte and design a stable interface to improve the sodium ion battery problem. Interface regulation belongs to the nanometer size. In the existing technology, Publication No. CN117497852A discloses fluoroethylene carbonate as a film-forming additive for the negative electrode of sodium ion batteries, which preferentially undergoes reduction decomposition to form a stable interface and improves the capacity retention rate of sodium ion batteries. However, the interface energy barrier of fluoroethylene carbonate increases at high temperatures, and there is easy oxidation decomposition, which causes dissolution of the interface, resulting in increased acidity of the electrolyte, high gas production, and worsening of high-temperature storage problems. Publication No. CN118554007A discloses that by introducing additives such as vinylene carbonate into the sodium ion battery electrolyte, the ionic conductivity and cycle performance of the sodium ion battery electrolyte are effectively improved. However, studies have found that more vinylene carbonate additives will cause a significant increase in impedance and affect the positive electrode interface, which is not conducive to the cycle life of the battery. Summary of the invention

[0005] In view of the above problems, the present invention optimizes the sodium ion battery electrolyte, significantly improves the cycle life of the battery under normal temperature and high temperature conditions, and inhibits the growth of sodium dendrites and reduces gas production.

[0006] One of the purposes of the present invention is to provide a sodium ion battery electrolyte.

[0007] A second object of the present invention is to provide a method for preparing a boron-containing electrolyte for a sodium ion battery.

[0008] A third object of the present invention is to provide a high temperature application of a sodium ion battery electrolyte.

[0009] A fourth object of the present invention is to provide a sodium ion battery electrolyte for use in a hard carbon negative electrode.

[0010] A fifth object of the present invention is to provide an application of a sodium ion battery electrolyte in different precursor negative electrodes.

[0011] The sixth object of the present invention is to provide an application of a sodium ion battery electrolyte in a sodium iron pyrophosphate-hard carbon system soft-pack battery.

[0012] The seventh object of the present invention is to provide a sodium ion battery electrolyte with low cost and suitable for commercial development.

[0013] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0014] A sodium ion battery electrolyte, comprising a sodium salt, a solvent and an additive;

[0015] The sodium salt is any one of sodium perchlorate and sodium hexafluorophosphate;

[0016] The solvent is any one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or a mixture of several thereof;

[0017] The additive is any one of trimethyl borate, triethyl borate, trimethoxyboroxine, (2,2,2-trifluoroethyl) borate or a mixture of several of them.

[0018] Furthermore, the molar concentration of the sodium salt in the solvent is 0.5 mol / L to 3 mol / L

[0019] Furthermore, the volume percentage of the additive in the solvent is 0.5 vol% to 5 vol%.

[0020] A method for preparing a sodium ion battery electrolyte comprises the following steps: adding a certain amount of sodium salt into a solvent, stirring the mixture thoroughly until the mixture is uniform and transparent, adding a proper amount of additives until the mixture is dissolved, and standing the mixture for 12 hours to obtain an electrolyte.

[0021] Application of a sodium ion battery electrolyte in a hard carbon negative electrode.

[0022] Application of a sodium ion battery electrolyte in different precursor negative electrodes.

[0023] Application of a sodium ion battery electrolyte in a sodium iron pyrophosphate-hard carbon system soft-pack battery.

[0024] The structure and composition of the interface determine the electrochemical performance and safety performance of the sodium ion battery. The present invention introduces any one or a mixture of trimethyl borate, triethyl borate, trimethoxyboroxine, (2,2,2-trifluoroethyl) borate into the carbonate electrolyte to optimize the interface composition, reduce the ion transfer impedance and interface energy barrier, improve the conductivity and kinetic performance, and extend the cycle life of the sodium ion battery.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The present invention discloses a sodium ion battery electrolyte, which is composed of a sodium salt, a carbonate solvent, and an additive. The electrolyte contains a functional boron-containing additive, which significantly improves the stability and conductivity of the electrolyte. At the same time, the additive decomposes to form boron-containing organic and inorganic species, forming a stable interface with low impedance, low energy barrier, high electronic insulation, and high kinetics, which significantly improves the cycle life of the sodium ion battery.

[0027] 2. In view of the above-mentioned advantages of sodium ion battery electrolyte, the prepared sodium ion battery can significantly improve the cycle stability and kinetic performance of the battery under extreme high temperature conditions of 65°C.

[0028] 3. The sodium ion battery electrolyte provided by the present invention is universal in different precursor negative electrode materials.

[0029] 4. The sodium ion battery electrolyte provided by the present invention effectively inhibits the decomposition of the electrolyte and significantly improves the safety performance of the battery such as gas production and sodium precipitation.

[0030] 5. The sodium ion battery electrolyte provided by the present invention has a simple preparation process, low cost, and is suitable for industrial production and commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 The cycle performance diagram of the battery in different electrolytes;

[0033] Figure 2 The morphology of the battery in different electrolytes;

[0034] Figure 3 Electrochemical impedance diagram of the battery in different electrolytes. DETAILED DESCRIPTION

[0035] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0036] Example 1

[0037] An electrolyte of this embodiment includes a sodium salt, a solvent and an additive, wherein the sodium salt is sodium perchlorate, the solvent is a mixture of ethylene carbonate and diethyl carbonate, and the additive is (2,2,2-trifluoroethyl) borate.

[0038] The molar concentration of the sodium perchlorate in the mixture of ethylene carbonate and diethyl carbonate is 1 mol / L, and the volume percentage of the additive in the mixture of ethylene carbonate and diethyl carbonate is 0.5 vol%.

[0039] The preparation method comprises the following steps:

[0040] 1 mol / L sodium perchlorate was added to the mixture of ethylene carbonate and diethyl carbonate, and the mixture was stirred thoroughly until dissolved. After adding (2,2,2-trifluoroethyl) borate additive, the mixture was stirred and allowed to stand for 12 hours.

[0041] Example 2

[0042] The only difference between this embodiment and embodiment 1 is that the volume percentage of the additive (2,2,2-trifluoroethyl) borate in the electrolyte is 1 vol%.

[0043] Example 3

[0044] The only difference between this embodiment and embodiment 1 is that the volume percentage of the additive (2,2,2-trifluoroethyl) borate in the electrolyte is 2 vol%.

[0045] Example 4

[0046] The only difference between this embodiment and embodiment 1 is that the volume percentage of the additive (2,2,2-trifluoroethyl) borate in the electrolyte is 5 vol%.

[0047] Example 5

[0048] An electrolyte of this embodiment includes a sodium salt, a solvent and an additive. The sodium salt is sodium perchlorate, the solvent is a mixture of ethylene carbonate and diethyl carbonate, and the additive is trimethoxyboroxine.

[0049] The molar concentration of the sodium perchlorate in the mixture of ethylene carbonate and diethyl carbonate is 1 mol / L, and the volume percentage of the additive in the mixture of ethylene carbonate and diethyl carbonate is 0.5 vol%.

[0050] The preparation method comprises the following steps:

[0051] 1 mol / L sodium perchlorate was added to the mixture of ethylene carbonate and diethyl carbonate, and the mixture was stirred thoroughly until dissolved. After the trimethoxyboroxine additive was added, the mixture was stirred and allowed to stand for 12 hours.

[0052] Example 6

[0053] The only difference between this embodiment and embodiment 5 is that the volume percentage of the additive trimethoxyboroxine in the electrolyte is 1 vol%.

[0054] Example 7

[0055] The only difference between this embodiment and embodiment 5 is that the volume percentage of the additive trimethoxyboroxine in the electrolyte is 2 vol%.

[0056] Example 8

[0057] The only difference between this embodiment and embodiment 5 is that the volume percentage of the additive trimethoxyboroxine in the electrolyte is 5 vol%.

[0058] Comparative Example 1

[0059] In this example, an existing commercial electrolysis was used to assemble the cell hard carbon / Na.

[0060] The electrolyte obtained above was applied to the following batteries, and various electrochemical physical and electrochemical performance tests were carried out:

[0061] like Figure 1 As shown, the electrolyte samples of Examples 2, 6, 8 and comparative cases of the present invention are cycled in different electrolytes. It can be seen from the figure that the use of additives significantly improves the reversible capacity of the cycle. The initial cycle capacities of Examples 2, 6, 8 and comparative cases are 276.15mAh / g, 271.59mAh / g, 256.51mAh / g and 261.0mAh / g, respectively. Optimizing the electrolyte reduces impedance and reduces interfacial energy barriers, allowing more sodium ions to be embedded. According to the calculation based on capacity retention rate = reversible capacity after cycle / first charge capacity, the capacity retention rates of Examples 2, 6, 8 and comparative cases are 83.24%, 102.33%, 101.31% and 82.05%, respectively. Examples 2, 6 and 8 effectively improve the cycle stability of the battery, so that the capacity of the battery can be effectively utilized.

[0062] like Figure 2As shown, the hard carbon electrode interface diagram in the electrolyte samples of Examples 1, 2, 6 and Comparative Example 1 of the present invention. (a is Example 1, b is Example 2, c is Example 6, and d is Comparative Example 1). It can be seen from the figure that the use of additives (Examples 1, 2, 6) is conducive to the formation of a thinner and more uniform SEI film, which can shorten the sodium ion transmission path and is conducive to high rate and long cycle. In the battery without adding additives (Comparative Example 1), the hard carbon electrode interface is uneven in thickness and cannot effectively protect the electrode. The interface is constantly regenerated, which is not conducive to the cycle performance of the battery.

[0063] like Figure 3 As shown, the electrochemical impedance diagrams of the electrolyte samples of Examples 2, 6, 7 of the present invention and the comparative case in the battery, it can be intuitively seen from the figure that the impedance of the electrolyte of Example 6, the impedance of the interface and the charge transfer impedance are significantly reduced, and the low impedance is conducive to the transmission of sodium ions in the battery and accelerates the ion transmission kinetics.

[0064] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A sodium ion battery electrolyte, characterized in that: The electrolyte comprises a sodium salt, a solvent and an additive; The sodium salt is any one of sodium perchlorate and sodium hexafluorophosphate; The solvent is any one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, or a mixture of several thereof; The additive is any one of trimethyl borate, triethyl borate, trimethoxyboroxine, (2,2,2-trifluoroethyl) borate or a mixture of several of them.

2. A sodium ion battery electrolyte according to claim 1, characterized in that: The molar concentration of the sodium salt in the solvent is 0.5 mol / L to 3 mol / L.

3. A sodium ion battery electrolyte according to claim 1, characterized in that: The volume percentage of the additive in the solvent is 0.5 vol% to 5 vol%.

4. A method for preparing a sodium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: A certain amount of sodium salt is added to the solvent and stirred thoroughly until it is uniform and transparent, and an appropriate amount of additive is added until it is dissolved. The mixture is allowed to stand for 12 hours to obtain a sodium ion battery electrolyte.

5. Use of the sodium ion battery electrolyte according to any one of claims 1 to 3 in a hard carbon negative electrode.

6. Application of the sodium ion battery electrolyte according to any one of claims 1 to 3 in different precursor negative electrodes.

7. Use of the sodium ion battery electrolyte according to any one of claims 1 to 3 in a sodium iron pyrophosphate-hard carbon system soft-pack battery.

8. Use of the sodium ion battery electrolyte according to any one of claims 1 to 3 at high temperatures.

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