Electrolyte for sodium ion battery

Abstract

The invention discloses an electrolyte for a sodium-ion battery. The electrolyte is prepared from three parts, namely an organic solvent, sodium salt and an additive, the organic solvent is composed of cyclic carbonate, chain carbonate and chain ether; the cyclic carbonate is one or two of ethylene carbonate and propylene carbonate. The additive trifluoroethyl acrylate and the nitrile compound have extremely remarkable characteristics and can efficiently form a protective film on a positive electrode, the oxidation activity of a positive electrode material to an electrolyte can be effectively reduced by forming the film on the positive electrode, and especially under the high-temperature condition, the oxidation activity of the positive electrode material to the electrolyte can be effectively reduced. The lithium ion battery cathode material has a strong inhibition effect on the oxidation of an electrolyte, so that the condition that transition metals such as nickel and iron are subjected to reduction reaction at the cathode and are dissolved out can be inhibited to a great extent, the high-temperature cycle life of a lithium ion battery is practically improved, and a solid guarantee is provided for stable operation of the lithium ion battery in a high-temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolytes, and in particular to an electrolyte for sodium ion batteries. Background Art

[0002] Since the 21st century, lithium batteries have been widely used in many fields such as mobile phones, computers, wearable devices, electric vehicles, two-wheeled bicycles, power tools, street lights, etc. In recent years, the consumption of lithium resources has shown the characteristics of large usage and fast consumption, and at the same time, the growth of lithium production cannot meet the growth of consumption. The reason is that, on the one hand, lithium resources are limited, mainly in the form of spodumene ore and salt lake lithium; on the other hand, lithium extraction operations cannot be carried out in salt lakes in winter.

[0003] In contrast, sodium is widely available and has abundant reserves, with reserves 420 times that of lithium and a price far lower than lithium. In recent years, as lithium prices have skyrocketed, sodium-ion batteries have attracted widespread attention because they are expected to cost 30% to 50% less than lithium-ion batteries. In the fields of energy storage, hybrid power, and replacement of lead-acid batteries, sodium-ion batteries have extremely attractive application prospects.

[0004] According to the positive electrode material, sodium ion batteries can be divided into three types: Na3V2(PO4)3, NaFe1 / 3Ni1 / 3Mn1 / 3O3, and Prussian blue. Among them, NaFe1 / 3Ni1 / 3Mn1 / 3O3 sodium ion batteries are favored by people because they have higher energy density than Na3V2(PO4)3 sodium ion batteries and longer cycle life than Prussian blue sodium ion batteries.

[0005] However, during use, it was found that the material has the following disadvantages: First, the Fe and Ni in the material are highly oxidizing. When they are in direct contact with the electrolyte at high temperature or high voltage, they will catalyze the decomposition of the electrolyte, accelerate the consumption of the electrolyte, and cause the positive electrode CEI film to thicken and the impedance to increase; second, Fe and Ni can easily enter the negative electrode with the migration of charges, destroy the negative electrode SEI film, and lead to a decrease in cycle life. Summary of the invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes an electrolyte for a sodium ion battery, wherein the additive forms a film at the positive electrode to prevent the occurrence of side reactions between the positive electrode material and the electrolyte; the additive forms a film at the negative electrode to prevent the electrolyte from being further reduced at the negative electrode, thereby effectively improving the cycle life of the sodium ion battery.

[0007] The present invention provides an electrolyte for a sodium ion battery, which comprises an organic solvent, a sodium salt and an additive. The organic solvent is composed of three parts: cyclic carbonate, chain carbonate and chain ether; The cyclic carbonate is one or both of ethylene carbonate and propylene carbonate; The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and methyl propyl carbonate; The chain ether is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; The additive is composed of trifluoroethyl acrylate and nicotinonitrile compounds, wherein the nicotinonitrile compounds are one or more of 2-amino-5-bromo-nicotinonitrile, 6-amino-2-methylnicotinonitrile, 4,6-amino-2-bromonicotinonitrile, and 2-chloro-4-methoxynicotinonitrile; The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate and sodium tetrafluoroborate.

[0008] Preferably, the mass ratio of the sodium salt, cyclic carbonate, chain carbonate, chain ether, trifluoroethyl acrylate, and nicotinonitrile compounds in the electrolyte is 5-25:5-30:20-60:5-20:0.1-3:0.1-3.

[0009] The additives of trifluoroethyl acrylate and nitrile compounds involved in the present invention have extremely remarkable characteristics. They can efficiently form a protective film on the positive electrode. This process plays a vital role in promoting the migration of lithium ions at the positive electrode interface. By forming a film on the positive electrode, the oxidation activity of the positive electrode material on the electrolyte can be effectively reduced, especially under high temperature conditions, the oxidation of the electrolyte is strongly inhibited. In this way, the reduction reaction and subsequent dissolution of transition metals such as nickel and iron at the negative electrode can be greatly inhibited, which effectively improves the high-temperature cycle life of the lithium-ion battery and provides a solid guarantee for the stable operation of the lithium-ion battery in a high-temperature environment. DETAILED DESCRIPTION

[0010] The present invention will be further explained below in conjunction with specific embodiments.

[0011] The present invention provides an electrolyte for a sodium ion battery, which comprises an organic solvent, a sodium salt and an additive. The organic solvent is composed of three parts: cyclic carbonate, chain carbonate and chain ether; The cyclic carbonate is one or both of ethylene carbonate and propylene carbonate; The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and methyl propyl carbonate; The chain ether is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; The additive is composed of trifluoroethyl acrylate and nicotinonitrile compounds, wherein the nicotinonitrile compounds are one or more of 2-amino-5-bromo-nicotinonitrile, 6-amino-2-methylnicotinonitrile, 4,6-amino-2-bromonicotinonitrile, and 2-chloro-4-methoxynicotinonitrile; The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate and sodium tetrafluoroborate.

[0012] In this embodiment, the mass proportions of the sodium salt, cyclic carbonate, chain carbonate, chain ether, trifluoroethyl acrylate, and nicotinonitrile compounds in the electrolyte are 5-25:5-30:20-60:5-20:0.1-3:0.1-3. Example

[0013] 15g of sodium hexafluorophosphate, 25g of ethylene carbonate, 50g of dimethyl carbonate, 9g of diethylene glycol dimethyl ether, 0.5g of trifluoroethyl acrylate, and 0.5g of 2-amino-5-bromo-nicotinoyl nitrile are mixed evenly to prepare an electrolyte. Example

[0014] 20g of sodium hexafluorophosphate, 24g of propylene carbonate, 40g of dimethyl carbonate, 14g of tetraethylene glycol dimethyl ether, 1.0g of trifluoroethyl acrylate, and 1.0g of hexanetrinitrile are mixed evenly to prepare an electrolyte. Example

[0015] 15g of sodium hexafluorophosphate, 20g of ethylene carbonate, 50g of dimethyl carbonate, 12g of ethylene glycol dimethyl ether, 2.0g of trifluoroethyl acrylate, and 1.0g of adiponitrile were mixed evenly to prepare an electrolyte.

[0016] Comparative Example 1 On the basis of Example 1, no additives are added.

[0017] Comparative Example 2 Based on Example 1, 2-amino-5-bromo-nicotinonitrile was not added.

[0018] Comparative Example 3 The method was similar to that of Example 1 except that trifluoroethyl acrylate was not added.

[0019] The electrolytes prepared in the examples and comparative examples were injected into 26700-3.0Ah sodium ion battery cells (positive electrode NaFe1 / 3Ni1 / 3Mn1 / 3O3, negative electrode hard carbon) to prepare batteries.

[0020] The prepared battery was subjected to a cycle test at 45° C. for 1000 cycles, and the first and 1000th discharge capacities of the battery were recorded. The discharge retention rate was calculated, and the discharge retention rate = the first discharge capacity / the 1000th discharge capacity*100%.

[0021] As can be seen from the table below, the sodium ion battery containing trifluoroethyl acrylate and nicotinonitrile compound additives has the best cycle life, and the battery internal resistance increases by about 1mΩ before and after the cycle; the sodium ion battery without additives has a poor cycle life, and the battery internal resistance increases significantly before and after the cycle; project Discharge retention rate Internal resistance before circulation Internal resistance after cycle Example 1 85.8% 13.36 14.10 Example 2 86.1% 13.58 14.37 Example 3 87.6% 13.43 14.31 Comparative Example 1 23.3% 14.35 20.19 Comparative Example 2 70.3% 13.92 15.66 Comparative Example 3 63.6% 14.03 15.79 The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An electrolyte for a sodium ion battery, characterized in that: It consists of three parts: organic solvent, sodium salt and additives; The organic solvent is composed of three parts: cyclic carbonate, chain carbonate and chain ether; The cyclic carbonate is one or both of ethylene carbonate and propylene carbonate; The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and methyl propyl carbonate; The chain ether is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; The additive is composed of trifluoroethyl acrylate and nicotinonitrile compounds, wherein the nicotinonitrile compounds are one or more of 2-amino-5-bromo-nicotinonitrile, 6-amino-2-methylnicotinonitrile, 4,6-amino-2-bromonicotinonitrile, and 2-chloro-4-methoxynicotinonitrile; The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate and sodium tetrafluoroborate.

2. The electrolyte for sodium ion battery according to claim 1, characterized in that: The mass proportions of the sodium salt, cyclic carbonate, chain carbonate, chain ether, trifluoroethyl acrylate, and nicotinonitrile compounds in the electrolyte are 5-25:5-30:20-60:5-20:0.1-3:0.1-3.