Electrolyte matched with layered oxide positive electrode material of sodium ion battery

Abstract

The invention discloses an electrolyte matched with a layered oxide positive electrode material of a sodium-ion battery, which comprises a carbonate solvent, an electrolyte salt and an electrolyte additive, the carbonate solvent is one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoro dimethyl carbonate, fluoro ethylene carbonate and fluoro methyl ethyl carbonate; the electrolyte salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate and sodium difluoro (oxalato) borate; and the electrolyte additive is inorganic acid or inorganic salt containing chalcogenide elements and cyanogens. According to the present invention, the electrochemical window of the electrolyte is widened, the CEI film containing the sulfur element and the cyanide group can be generated, the redox couple of S2-and SO3 < 2-> participates in the redox reaction, the active oxygen generated when the redox positive electrode system is charged to the high voltage is captured, the dissolution of the transition metal ions is reduced, and the electrochemical performance of the sodium ion battery is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries and relates to an electrolyte for a sodium ion battery, and in particular to an electrolyte matching a layered oxide positive electrode material for a sodium ion battery. Background Art

[0002] Currently, secondary batteries represented by lithium-ion batteries have been widely used, but with the depletion of lithium resources, future energy storage has been challenged. In recent years, sodium-ion batteries (SIBs) have become one of the main candidate batteries for grid-scale energy storage systems (ESSs) due to their abundant sodium resources and environmental friendliness. In order to convert and store renewable energy more efficiently, a large number of studies have been devoted to improving the energy density of sodium-ion batteries. Materials with high specific capacity often have good prospects in improving battery energy density, but high capacity often needs to be obtained by widening the voltage range.

[0003] A wide voltage range often means greater structural damage. When the charge cut-off voltage is increased, the positive electrode material will be accompanied by oxygen release problems, which will not only cause structural damage to the material, but the oxidized oxygen ions and even oxygen will catalyze the decomposition of the electrolyte, exacerbating the side reactions between the electrode and the electrolyte. When the discharge cut-off voltage is further reduced, the common element Mn in the transition metal position will be reduced to Mn 3+ , and Mn 3+ It has a serious Jan-Taylor effect, which causes the crystal structure to be distorted and affects the structural stability of the material. These problems combined will cause the transition metal in the positive electrode material to dissolve, seriously affecting the electrochemical performance. In order to solve the above problems, modification methods for positive electrode materials such as bulk doping and surface coating have been widely used, but they often lead to capacity loss and reduced rate performance. Summary of the invention

[0004] In order to solve the above-mentioned problems existing in the background technology, the present invention provides an electrolyte that matches the layered oxide positive electrode material of the sodium ion battery. The electrolyte introduces a bifunctional additive - chalcogen and cyanide. The chalcogen acts as a deoxygenating component, and combines with the superoxide group generated by the positive electrode material when charged to a high voltage to avoid catalytic electrolyte decomposition, and releases oxygen anions during subsequent discharge, and regenerates the deoxygenating additive, and continues to enter the subsequent redox process to ensure the stable circulation of the battery at high voltage. Cyanide can effectively combine with transition metals to prevent transition metals from dissolving. The electrolyte of the present invention can not only effectively broaden the electrochemical window of the electrolyte, but also produce a CEI membrane containing sulfur and cyanide groups, so that S 2- and SO3 2-The redox couple participates in the redox reaction, captures the active oxygen generated when the redox positive electrode system is charged to a high voltage, reduces the dissolution of transition metal ions, and effectively improves the electrochemical performance of the sodium ion battery.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] An electrolyte matching a sodium ion battery layered oxide positive electrode material, comprising a carbonate solvent, an electrolyte salt and an electrolyte additive, wherein:

[0007] The carbonate solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluorodimethyl carbonate, fluoroethylene carbonate, and fluoroethyl methyl carbonate;

[0008] The electrolyte salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, and sodium difluorooxalatoborate, and the concentration of the electrolyte salt in the electrolyte is 0.8 to 1.2 mol / L;

[0009] The electrolyte additive is an inorganic acid or inorganic salt containing a chalcogen element and cyanide, namely, one of sodium thiocyanate, sodium selenocyanate, thiocyanic acid and polonium cyanic acid, and has the following structure:

[0010]

[0011] Wherein, A is a chalcogen element, specifically one of S, Se, Te and Po, and the concentration of the electrolyte additive in the electrolyte is 0.005-0.05 mol / L.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] (1) The electrolyte of the present invention is an electrolyte that has both high-voltage stability and safety. It uses a bifunctional electrolyte additive to capture the active oxygen released by the material, reduce the dissolution of transition metals, reduce the oxidative decomposition of the electrolyte, and improve the stability of the battery.

[0014] (2) The electrolyte of the present invention has multiple synergistic effects. The electrolyte additives decompose preferentially before other solvents, and a stable CEI film containing sulfur and cyanide can be formed on the surface of the positive electrode. The S in CEI 2- Can react with superoxide groups to generate SO3 2- , protecting the electrolyte from catalytic oxidation and reducing the side reactions between the positive electrode material and the electrolyte. The cyanide can combine with the transition metal ions and reduce the dissolution of the transition metal ions.

[0015] (3) The electrolyte of the present invention can effectively capture the active oxygen released by the positive electrode material, reduce the nucleophilic attack of the active oxygen on the electrolyte, reduce the gas production of the battery, and improve the safety performance.

[0016] (4) The additive used in the electrolyte of the present invention has regeneration ability and belongs to a redox couple. The reduced component S 2- Absorbs superoxide groups generated by the positive electrode material to generate oxidized components SO3 2- ; During discharge, the oxidized component SO3 2- Reduction occurs, oxygen anions are released, and the reduced components are regenerated, continuing to play a role in the subsequent charge and discharge process.

[0017] (5) The electrolyte of the present invention can expand the voltage range to 1.5-4.5 V, meeting the application of different types of layered oxide positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the LSV curve diagram of the electrolyte of comparative example 1 and examples 1-2;

[0019] Figure 2 The graph is a cycle performance curve of the electrolytes of Examples 4 to 5 and Comparative Example 1 after 300 cycles at a high voltage of 4.5 V. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0021] Example 1

[0022] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, ethylene carbonate (EC) and propylene carbonate (PC) after dehydration are uniformly mixed in a volume ratio of 1:1, and then 1 mol / L of sodium perchlorate and 0.03 mol / L of sodium thiocyanate additives are added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0023] Example 2

[0024] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, ethylene carbonate (EC) and propylene carbonate (PC) after dehydration are uniformly mixed in a volume ratio of 1:1, and then 1 mol / L of sodium perchlorate and 0.03 mol / L of sodium selenocyanate additives are added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0025] Example 3

[0026] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, fluoroethyl methyl carbonate (FEMC) and propylene carbonate (PC) are uniformly mixed at a volume ratio of 1:1 after dehydration, and then 1 mol / L of sodium perchlorate and 0.01 mol / L of thiocyanate additives are added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0027] Example 4

[0028] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, ethylene carbonate (EC), dimethyl carbonate (DMC) and propylene carbonate (PC) after dehydration are uniformly mixed in a volume ratio of 1:1:1, and then 1 mol / L of sodium hexafluorophosphate and 0.01 mol / L of polonium cyanate additives are added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0029] Example 5

[0030] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, ethylene carbonate (EC), dimethyl carbonate (DMC) and propylene carbonate (PC) are uniformly mixed at a volume ratio of 1:1:1 after dehydration, and then 5% by volume of fluoroethylene carbonate (FEC) is added, and then 1 mol / L of sodium hexafluorophosphate and 0.03 mol / L of sodium thiocyanate additives are added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0031] Comparative Example 1

[0032] An electrolyte matching a layered oxide positive electrode material for a sodium ion battery is prepared according to the following steps: in a glove box, ethylene carbonate (EC) and propylene carbonate (PC) after dehydration are uniformly mixed in a volume ratio of 1:1, and then 1 mol / L sodium perchlorate is added, and the mixture is stirred in the glove box for 3 to 5 hours to prepare an electrolyte.

[0033] The high-voltage electrolytes of the above-mentioned embodiments and comparative examples of the present invention were tested.

[0034] Half-cell assembly with Na 0.72 Li 0.24 Mn 0.76The O2 positive electrode material is the active material, which is mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1, and N-methylpyrrolidone (NMP) is used as the solvent. The mixture is placed in a weighing bottle and stirred for 12 hours to obtain a slurry. The slurry is coated on the current collector aluminum foil using a coater, transferred to a vacuum drying oven at 120°C and dried for 12 hours. After punching the sheet into a pole piece with a diameter of 14 mm and accurately weighing the pole piece mass, the metal sodium sheet is used as the negative electrode, the electrolyte in the above embodiment and the comparative example is used, and a glass fiber diaphragm is used to assemble a CR2032 button battery half-cell in an argon glove box.

[0035] Charge and discharge test: The voltage range of button cell charge and discharge is 2.0~4.5V. Before the cycle test, the battery was activated three times with a small current density of 20mA / g (0.1C), and then cycled at a rate of 1C in the same voltage range. All electrochemical performance tests were conducted at room temperature.

[0036] The electrolyte of Example 1 and the electrolyte of the comparative example were used to perform LSV test. Figure 1 It can be seen that the electrolyte of the present invention will decompose into a film at around 3.7V. The cycle curves of the electrolytes of Examples 1 and 2 and the electrolyte of the comparative example for 100 charge and discharge cycles at 2 to 4.5V are as follows: Figure 2 As shown, Examples 1 to 2 all exhibited better cycle stability.

[0037] The capacity retention results of the half-cells assembled from Examples 1 to 5 and Comparative Example 1 after 100 cycles at a rate of 1C are shown in Table 1.

[0038] Table 1

[0039] Sample name 0.1C capacity (mAh / g) Capacity retention after 100 cycles Example 1 205 87％ Example 2 195 82％ Example 3 202 79.8％ Example 4 196 76.3％ Example 5 186 75％ Comparative Example 1 185 48.9％

[0040] By comparing Examples 1 to 5 with Comparative Example 1, the electrolyte of the present invention has a more excellent cycle life, can maintain the stability of the positive electrode material and the electrolyte, and has certain advantages in exerting the capacity of the positive electrode material.

Claims

1. An electrolyte matching a sodium ion battery layered oxide positive electrode material, characterized in that The electrolyte comprises a carbonate solvent, an electrolyte salt and an electrolyte additive, wherein the electrolyte additive is an inorganic acid or inorganic salt containing a chalcogen element and a cyanide, and the concentration of the electrolyte additive in the electrolyte is 0.005-0.05 mol / L.

2. The electrolyte matching the layered oxide positive electrode material of the sodium ion battery according to claim 1, characterized in that The carbonate solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluorodimethyl carbonate, fluoroethylene carbonate, and fluoroethyl methyl carbonate.

3. The electrolyte matching the layered oxide positive electrode material of the sodium ion battery according to claim 1, characterized in that The electrolyte salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, and sodium difluorooxalatoborate.

4. The electrolyte matching the sodium ion battery layered oxide positive electrode material according to claim 1 or 3, characterized in that The concentration of the electrolyte salt in the electrolyte is 0.8 to 1.2 mol / L.

5. The electrolyte matching the layered oxide positive electrode material of sodium ion battery according to claim 1, characterized in that The electrolyte additive is one of sodium thiocyanate, sodium selenocyanate, thiocyanic acid and polonium cyanic acid.

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