Ether electrolyte additive and application thereof in sodium-ion battery

Abstract

The ether electrolyte additive can efficiently improve the first circle coulomb efficiency of the negative electrode side, and can also accelerate the low-temperature sodium storage kinetics of the electrolyte, thereby improving the battery capacity, low-temperature performance and expanding the use range. The application of ether electrolyte (EBEs) in the field of sodium ion batteries is gradually increasing, and it has outstanding advantages in improving the performance of the negative electrode side. Compared with ester electrolyte, the stable solvation structure can realize highly reversible solvent-co-intercalation reaction and form a thin and stable SEI, which is beneficial to the stable cycle and fast sodium storage kinetics of the negative electrode. However, the low first circle coulomb efficiency and low-temperature performance still need further research.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a sodium-ion battery electrolyte additive and its application in ether-based electrolyte. BACKGROUND

[0002] Ether-based electrolytes (EBEs) are gradually increasing in application in the field of sodium-ion batteries, and have outstanding advantages in improving the performance of the negative electrode. Compared with ester-based electrolytes, its stable solvation structure can realize highly reversible solvent-co-intercalation reaction and form a thin and stable SEI, which is beneficial to the stable cycle and fast sodium storage kinetics of the negative electrode. However, its low first-cycle coulombic efficiency and low-temperature performance still need further research.

[0003] Therefore, it is of great significance to reasonably design a new type of ether-based electrolyte for expanding the application of ether-based electrolyte and improving the first-cycle coulombic efficiency, capacity and low-temperature performance of the battery. SUMMARY

[0004] To solve the above technical problems, the present application aims to provide a sodium-ion battery electrolyte additive which can effectively improve the first-cycle coulombic efficiency, capacity and low-temperature performance of the negative electrode and expand its application range.

[0005] The present application provides a sodium-ion battery electrolyte, comprising:

[0006] sodium salt, ether-based solvent, additive.

[0007] Preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate, sodium trifluoromethylsulfonate, sodium bis(trifluoromethanesulfonyl)imide and sodium bis(fluorosulfonyl)imide.

[0008] Preferably, the ether-based solvent is selected from one or more of dimethoxymethane (DMM), diethylene glycol dimethyl ether (DEGDME), dimethyl ether (DME), tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (METHF), 1,3-dioxolane (DOL).

[0009] Preferably, the concentration of sodium salt in the electrolyte is 0.5-2 mol L -1 , preferably 1-1.5 mol L -1 .

[0010] Preferably, the (fluorinated) phenyl-containing quaternary ammonium / phosphonium salt is selected from one or more of methyltriphenylphosphonium bromide, methyltriphenylphosphonium iodide, methyltriphenylphosphonium chloride, pentyltriphenylphosphonium bromide, tetradecyltriphenylphosphonium bromide, methyltriphenylphosphonium bromide, methyltriphenylphosphonium iodide, methyltriphenylphosphonium chloride, pentyltriphenylphosphonium bromide, tetradecyltriphenylphosphonium bromide. The (fluorinated) phenyl-containing organophosphorus / boron / amine / silicon is selected from one or more of triphenylphosphine, triphenylboron, triphenylamine, triphenylsilane.

[0011] Preferably, the volume percentage of the additive in the composite electrolyte is 0.2-2%, preferably 0.2-0.5%.

[0012] The application provides an ether electrolyte additive for sodium ion batteries and application thereof in sodium ion batteries.

[0013] The sodium ion battery is composed of a negative electrode, a separator and a polyanion positive electrode, which are sequentially arranged in the electrolyte; the polyanion positive electrode refers to a polyanion compound as an active material, and the polyanion compound includes one or two or more of Na3V2(PO4)3, Na3V2(PO4)2F3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na2FeP2O, Na4Fe3(PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, Na2FeSiO4, preferably Na3V2(PO4)3.

[0014] The negative electrode is a carbon-based material negative electrode, and the carbon-based material is one or two or more of graphene, hard carbon and soft carbon, preferably hard carbon; the membrane material is selected from one or two or more of glass fiber membrane and celgard membrane, preferably celgard.

[0015] Advantages:

[0016] The ether electrolyte additive of the application can efficiently improve the first circle coulombic efficiency and capacity of the negative electrode side and also accelerate the low-temperature sodium storage kinetics of the electrolyte, thereby improving the battery capacity and low-temperature performance and expanding the use range. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 : Example 1 and Comparative Example 1 Pt||Na electrolytic cell LSV reduction curve.

[0018] Figure 2 : Example 1 and Comparative Example 1 HC||Na half-cell first circle coulombic efficiency at room temperature.

[0019] Figure 3 : First cycle coulombic efficiency of HC||Na half-cell at room temperature for Example 2 and Comparative Example 2.

[0020] Figure 4 : Rate capability of HC||Na half-cell at room temperature for Example 1 and Comparative Example 1.

[0021] Figure 5 : Rate capability of HC||Na half-cell at room temperature for Example 2 and Comparative Example 2.

[0022] Figure 6 : First cycle coulombic efficiency of HC||Na half-cell at -10°C for Example 2 and Comparative Example 2.

[0023] Figure 7 : First cycle coulombic efficiency of HC||Na half-cell at -20°C for Example 2 and Comparative Example 2.

[0024] Figure 8 : Rate capability of HC||Na half-cell at -10°C for Example 2 and Comparative Example 2.

[0025] Figure 9 : Rate capability of HC||Na half-cell at -20°C for Example 2 and Comparative Example 2.

[0026] Figure 10 : First cycle coulombic efficiency of NPFF||HC full cell at room temperature for Example 1 and Comparative Example 1.

[0027] Figure 11 : Rate capability of NPFF||HC full cell at room temperature for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0028] To characterize the performance of ether electrolyte additives, half-cells, electrolytic cells without active material participation, and soft package full cells were assembled as test objects.

[0029] Among them, the half-cell is only used to study the electrochemical performance of different electrolytes in the carbon-based negative electrode material of the battery, so in the carbon-based material||metal half-cell, metal Na is used as the counter electrode, i.e. the negative electrode, and the positive electrode selects the carbon-based material. For example, the glass fiber membrane is selected as the separator. Its theoretical specific capacity is 300 mAh / g, the rate test selects the capacity change under different currents (0.1C / 0.2C / 0.5C / 1C / 2C / 5C / 10C, 1C=300 mA / g), the cycle test selects the capacity retention under a fixed current, and the voltage range is selected as 0-2.5V. The room temperature rate and cycle test temperature are selected as 25°C, the low temperature test temperature is selected as -10°C / -20°C, the electrode diameter is 14mm, and the effective area is 1.5386cm 2 .

[0030] Electrolyte solution was prepared by dissolving NaPF6 in solvent DEGDME. The half-cell (HC||Na), Pt||Na electrolyte cell and NFPP||HC pouch full cell were assembled and tested in Ar glove box (water content <0.01 ppm, oxygen content <0.01 ppm) at 25℃. The Pt and metal electrode area was 1 cm2. 2 ;

[0031] The positive electrode in full cell was selected as Na4Fe3(PO4)2P2O7, the negative electrode was selected as hard carbon, the separator was selected as celgard membrane, the voltage range was selected as 1.5-3.6 V, the test temperature was 25℃, and the effective electrode area was 106*74 mm2. 2 The battery was assembled as four positive and five negative, and the electrolyte solution was 4 ml.

[0032] Example 1

[0033] The additive was selected as methyltriphenylphosphonium bromide MTPPB, the additive mass concentration was selected as 0.25%, and the solvent was selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.25% MTPPB was prepared, and the half-cell (HC||Na), Pt||Na electrolyte cell and NFPP||HC pouch full cell were assembled and tested.

[0034] Example 2

[0035] The additive was selected as methyltriphenylphosphonium bromide MTPPB, the additive mass concentration was selected as 0.25%, and the solvent was selected as diglycol dimethyl ether DEGDME. A mixed solution of 0.6 mol / L NaPF6-DEGDME+0.25% MTPPB was prepared, and the half-cell (HC||Na), Pt||Na electrolyte cell and NFPP||HC pouch full cell were assembled and tested.

[0036] Example 3

[0037] The additive was selected as methyltriphenylphosphonium bromide MTPPB, the additive concentration was selected as 0.5%, and the solvent was selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.5% MTPPB was prepared, and the half-cell (HC||Na), Pt||Na electrolyte cell and NFPP||HC pouch full cell were assembled and tested.

[0038] Example 4

[0039] The additive is also a quaternary phosphonium salt, tetradecyltriphenylphosphonium bromide TTPPB with different groups, the additive mass concentration is selected as 0.25%, and the solvent is selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.25% TTPPB is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0040] Example 5:

[0041] The additive is also a quaternary phosphonium salt, tetradecyltriphenylphosphonium bromide TTPPB with different groups, the additive mass concentration is selected as 0.25%, and the solvent is selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.25% TTPPB is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0042] Example 6:

[0043] The additive is also a quaternary phosphonium salt, tetradecyltriphenylphosphonium bromide TTPPB with different groups, the additive mass concentration is selected as 0.25%, and the solvent is selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.25% TTPPB is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0044] Comparative Example 1:

[0045] A mixed solution of 1 mol / L NaPF6-DEGDME is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0046] Comparative Example 2:

[0047] A mixed solution of 0.6 mol / L NaPF6-DEGDME is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0048] Comparative Example 3:

[0049] The additive is also a quaternary phosphonium salt, tetradecyltriphenylphosphonium bromide TTPPB with different groups, the additive mass concentration is selected as 0.25%, and the solvent is selected as diglycol dimethyl ether DEGDME. A mixed solution of 1 mol / L NaPF6-DEGDME+0.25% TTPPB is prepared, and half cells (HC||Na), Pt||Na electrolytic cells and NFPP||HC soft package full cells are respectively assembled for testing.

[0050] Comparative Example 4:

[0051] Additive tetrapropylammonium bromide TPAB with similar function was selected to prepare a mixed solution of 0.6 mol / L NaPF6-DEGDME + 0.25% TPAB, and a half-cell (HC||Na), a Pt||Na electrolytic cell and a NFPP||HC soft-pack full cell were respectively assembled and tested.

[0052] Table 1 Reduction current value of LSV of Pt||Na electrolytic cell of Examples 2-6 and Comparative Example 2 at 0.8 V

[0053] Current value at 0.8V Example 2 -0.06 mA Example 3 -0.05 mA Example 4 -0.03 mA Example 5 -0.04 mA Example 6 -0.07 mA Comparative Example 2 -0.5 mA Comparative Example 3 -0.6 mA Comparative Example 4 -0.8 mA

[0054] Figure 1 Table 1 is the LSV reduction curve and reduction current value of the examples and comparative examples in the Pt||Na electrolytic cell, and it is found that Figure 1 the reduction peak of the additive MTPPB appears significantly in the middle, and it is obvious that MTPPB has a reduction inhibition effect on the solvent DEGDEME, which makes the reduction reaction current smaller, indicating that the addition of a certain concentration of the additive can effectively inhibit the reduction decomposition of the ether electrolyte and improve the stability of the ether electrolyte.

[0055] Table 2 First cycle coulombic efficiency of HC||Na half-cell at room temperature of Examples 3-6

[0056] Coulombic efficiency for the first cycle Example 3 97％ Example 4 98％ Example 5 97.5％ Example 6 98.5％ Comparative Example 3 80％ Comparative Example 4 81％

[0057] Figure 2 , Figure 3 Table 2 is the first cycle coulombic efficiency of the examples and comparative examples HC||Na half-cell at room temperature, and the ICE value can be used to judge the reversible sodium capacity consumed by the formation of SEI of the electrolyte at the HC interface. The higher the ICE, the thinner the SEI formed, and the less the effective sodium capacity consumed. It is found from the chart that under the conditions of different sodium salt solubility and different types of additives, the ICE of HC||Na is higher than 95% (close to 100%), which proves that the additive has a significant beneficial effect on the formation of SEI, greatly reducing the consumption of effective sodium capacity.

[0058] Table 3 Capacity of HC||Na half-cell at room temperature of Examples 3-6 under different rates

[0059]

[0060] Figure 4 , Figure 5Table 3 is the rate performance of the HC||Na half-cells of the examples and the comparative examples at room temperature. The kinetics of different electrolytes in HC were tested by changing the current. The rates were 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 10C, respectively. It was found from the graph that the capacity and rate performance of HC||Na were obviously improved under the conditions of different sodium salt concentrations and different types of additives, which verified that the additives could effectively reduce sodium loss, thereby improving the capacity, and the good SEI formed by the additives accelerated the sodium storage kinetics.

[0061] Table 4 is the first cycle coulombic efficiency of the HC||Na half-cells of examples 3-6 at low temperature.

[0062]

[0063]

[0064] Figure 6 、 Figure 7 Table 4 is the first cycle coulombic efficiency of the HC||Na half-cells of examples 3-6 at low temperature. It was found from the graph that the ICE of HC||Na was higher than 90% under the low-temperature conditions of different types of additives, which proved that the results at low temperature were consistent with those at room temperature, and an effective SEI could be formed to reduce the consumption of effective sodium capacity.

[0065] Table 5 is the capacity of the HC||Na half-cells of examples 3-6 at low temperature under different rates. The rates were 0.1C, 0.2C, 0.5C, 1C, 2C and 5C at -10℃, and the rates were 0.1C, 0.2C, 0.5C, 1C, 2C and 5C at -20℃.

[0066]

[0067] Figure 8 、 Figure 9 Table 5 is the rate performance of the HC||Na half-cells of examples 3-6 at low temperature. The rates were 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 10C at -10℃, and the rates were 0.1C, 0.2C, 0.5C, 1C, 2C and 5C at -20℃. It was found from the graph that the capacity and rate performance of HC||Na were also obviously improved under the conditions of different types of additives.

[0068] Table 6 is the first cycle coulombic efficiency of the NPFF||HC full cells of examples 2-6 and comparative examples 2-4 at room temperature.

[0069]

[0070]

[0071] Table 7 is the capacity of the NPFF||HC full cells of examples 2-6 and comparative examples 2-4 at room temperature under different rates.

[0072]

[0073] Figure 10 、 Figure 11 Table 6 and Table 7 are the first circle coulomb efficiency and rate performance of the example and comparative example NPFF||HC full cell at room temperature, the rate is selected as 0.1C, 0.2C, 0.5C, 1C, 2C and 5C respectively. It is found from the chart that under the condition of different sodium salt solubility and different additive types, the first circle coulomb efficiency, capacity and rate performance of the NFPP||HC full cell have obvious increase, which proves that the additive has good application in the full cell.

Claims

1. An electrolyte, characterized in that: The solute is sodium salt, the solvent is an ether solvent, and one or more of methyltriphenylphosphonium bromide, methyltriphenylphosphonium chloride, amyltriphenylphosphonium bromide, tetradecyltriphenylphosphonium bromide, and triphenylphosphine are used as additives. The mass concentration of the additives in the solvent is 0.2% to 0.5%.

2. The electrolyte according to claim 1, characterized in that: The sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl imide) and sodium bis(fluorosulfonyl imide).

3. The electrolyte according to claim 1, characterized in that: The ether solvent is selected from one or more of dimethoxymethane (DMM), diethylene glycol dimethyl ether (DEGDME), dimethyl ether (DME), tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (METHF), and 1,3-dioxolane (DOL).

4. The electrolyte according to claim 1 or 2, characterized in that: The concentration of sodium salt in the electrolyte is 0.5-2 mol L -1 .

5. The electrolyte according to claim 4, characterized in that: The concentration of sodium salt in the electrolyte is 1-1.5 mol / L.

6. Use of the electrolyte according to claim 1 as an electrolyte in a sodium ion battery.

7. The use according to claim 6, characterized in that: The sodium ion battery is composed of a negative electrode, a separator and a polyanionic positive electrode, which are arranged in sequence in the electrolyte; wherein the polyanionic positive electrode refers to a polyanionic compound as an active material, and the polyanionic compound includes one or more of Na3V2(PO4)3, Na3V2(PO4)2F3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na2FeP2O, Na4Fe3(PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, and Na2FeSiO4.

8. The use according to claim 7, characterized in that: The negative electrode is a carbon-based material negative electrode, and the carbon-based material is one or more of graphene, hard carbon, and soft carbon; The membrane material of the diaphragm is selected from one or two of glass fiber membrane and celgard membrane.

9. The use according to claim 6, characterized in that: The electrolyte has a positive electrode potential range of 0-2.5 V in sodium ion batteries.

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