Preparation method of modified black phosphorus quantum dots, non-aqueous electrolyte and sodium ion battery thereof

Abstract

The application provides a preparation method of modified black phosphorus quantum dots, a nonaqueous electrolyte and a sodium ion battery thereof. The preparation method of the modified black phosphorus quantum dots comprises the following steps: S1, adding ground black phosphorus and nitrogen-containing heterocyclic ionic liquid into a solvent to obtain a reaction solution; and S2, refluxing the reaction solution in an inert atmosphere. The modified black phosphorus quantum dots are obtained by modifying the black phosphorus quantum dots by using the nitrogen-containing heterocyclic ionic liquid. When the modified black phosphorus quantum dots are applied to the nonaqueous electrolyte, the impedance of the sodium ion battery in the cycle process can be reduced, and the high-rate cycle performance and high-temperature cycle performance of the sodium ion battery can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a method for preparing modified black phosphorus quantum dots, a non-aqueous electrolyte, and a sodium-ion battery thereof. Background Technology

[0002] The SEI (solid electrolyte interphase) film is a passivation layer formed by the reaction between the electrode material and the electrolyte at the solid-liquid interface. This layer effectively prevents solvent molecules in the electrolyte from damaging the electrode material. The composition of the electrolyte is closely related to the SEI film on the electrode surface; a suitable electrolyte can generate a stable SEI film on the electrode surface, improving the battery's cycle performance. Various functional additives are important components of the electrolyte and can improve the SEI film, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), propylene-1,3-propanesulfonate lactone (PES), and ethylene sulfite (PS). However, under high voltage conditions, these additives can cause oxidative decomposition of the electrolyte at the electrode interface, leading to rapid degradation of battery performance.

[0003] Black phosphorus is a novel direct bandgap two-dimensional material with a bandgap ranging from 0.3 eV (bulk state) to 1.5 eV (monolayer), adjustable by the number of layers. Therefore, it can absorb light from the visible spectrum to infrared wavelengths used in communications, and it also boasts high carrier mobility (up to 1000 cm⁻¹ at a thickness of 10 nm). 2 ˙v -1 ˙s -1 ) and a higher on / off ratio (10 4 Black phosphorus quantum dots (MPDs) have shown great potential advantages in the fields of semiconductors, optoelectronics, and photothermal energy. Current literature reports the application of MPDs in combination with other materials in the electrodes of energy batteries to improve the charge / discharge performance and cycle stability of the negative electrode material. However, there are few reports on the technology of modifying MPDs and using them as additives in non-aqueous electrolytes.

[0004] Based on this, a method for preparing modified black phosphorus quantum dots, a non-aqueous electrolyte, and a sodium-ion battery thereof are provided. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing modified black phosphorus quantum dots, a non-aqueous electrolyte, and a sodium-ion battery thereof. The method of this invention can effectively prepare modified black phosphorus quantum dots. When these modified black phosphorus quantum dots are applied to a non-aqueous electrolyte, the impedance of the sodium-ion battery during cycling can be reduced, effectively improving the high-rate cycling performance and high-temperature cycling performance of the sodium-ion battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing modified black phosphorus quantum dots, comprising the steps of:

[0007] S1 involves grinding blocky black phosphorus and a nitrogen-containing heterocyclic ionic liquid, then adding a solvent to obtain a reaction solution;

[0008] S2 involves refluxing the reaction solution under an inert atmosphere.

[0009] Compared with existing technologies, the preparation process of this invention is simple, and the method of this invention can effectively synthesize modified black phosphorus quantum dots. The modified black phosphorus quantum dots of this invention are black phosphorus quantum dots coated with a nitrogen-containing heterocyclic ionic liquid. When applied to non-aqueous electrolytes, the black phosphorus quantum dots make the non-aqueous electrolyte more stable during storage. Furthermore, due to the high carrier mobility of the black phosphorus quantum dots themselves, they adhere to the surfaces of the positive and negative electrodes, reducing impedance during cycling. During cycling, the black phosphorus quantum dots decompose, forming fluorinated phosphides in situ. The resulting SEI and CEI films also have low impedance, improving the fast-charging performance of sodium-ion batteries. Simultaneously, during battery cycling, the CEI film formed by the nitrogen-containing heterocyclic structure of the nitrogen-containing heterocyclic ionic liquid coating the black phosphorus quantum dots can suppress the growth of DCR during high-temperature cycling, thereby improving the high-temperature cycling performance of sodium-ion batteries.

[0010] Preferably, the nitrogen-containing heterocyclic ionic liquid comprises 1-ethyl-3-methylimidazolium dinitrile amine salt.

[0011] Preferably, in S1, the mass ratio of the blocky black phosphorus to the nitrogen-containing heterocyclic ionic liquid is 1:15 to 30, specifically, but not limited to, 1:15, 1:18, 1:20, 1:22, 1:24, 1:26, 1:28, and 1:30, with 1:20 being the most preferred. The solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with diethyl carbonate (DEC) being the most preferred.

[0012] Preferably, in S2, the reflux reaction temperature is 130℃~150℃, specifically but not limited to 130℃, 135℃, 140℃, 145℃, 150℃, preferably 140℃, and the time is 4~8h, specifically but not limited to 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, preferably 6h, and the protective atmosphere is nitrogen or argon.

[0013] Preferably, the nitrogen-containing heterocyclic ionic liquid is vacuum dried before grinding, and its moisture content is 15-25 ppm after drying.

[0014] Specifically, the grinding is mechanical grinding, the grinding time is 0.5 to 1 hour, and the particle size of the black phosphorus after grinding is 3-15 nm. The drying is vacuum drying, the vacuum drying temperature is 40 to 50°C, specifically but not limited to 40°C, 42°C, 43°C, 45°C, 46°C, 48°C, 50°C, preferably 45°C, and the drying time is 36 hours to 72 hours, preferably 36 hours, 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 65 hours, 70 hours, 72 hours, preferably 48 hours.

[0015] Preferably, after the reflux reaction is completed, the reaction solution is centrifuged at a speed of 10000 r / min to 15000 r / min.

[0016] A second aspect of the present invention provides a non-aqueous electrolyte comprising a sodium salt, a non-aqueous organic solvent, and an additive, wherein the additive comprises modified black phosphorus quantum dots prepared by the above preparation method, wherein the particle size of the modified black phosphorus quantum dots is 3 nm to 15 nm, specifically but not limited to 3 nm, 4 nm, 5 nm, 8 nm, 10 nm, 12 nm, 14 nm, and 15 nm.

[0017] Preferably, the modified black phosphorus quantum dots in the non-aqueous electrolyte are 0.005% to 0.15% by mass, and more preferably 0.005%, 0.008%, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, or 0.15%.

[0018] Preferably, the sodium salt comprises at least one of sodium hexafluorophosphate (NaPF6), sodium difluorooxalate borate (NaDFOP), sodium tetrafluoroborate (NaDFOP), sodium bis(oxalate borate) (NaBOB), sodium perchlorate (NaClO), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaCF3SO3), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0019] Preferably, the sodium salt in the non-aqueous electrolyte is 7% to 21% by mass, specifically, but not limited to, 7%, 10%, 12%, 14%, 15%, 16%, 18%, and 21%.

[0020] Preferably, the non-aqueous organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), amyl carbonate, vinyl carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-PP), ethyl propionate (EP), ethyl butyrate (Eb), diethylene glycol dimethyl ether (DME), diethylene glycol diethyl ether (ECS), diethylene glycol dimethyl ether (DEGME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), methyltetrahydrofuran (MTHF), diphenyl ether (DPE), and crown ether (CE).

[0021] Preferably, the non-aqueous solvent accounts for 60% to 90% by mass in the non-aqueous electrolyte, specifically, but not limited to, 60%, 65%, 70%, 72%, 74%, 75%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, and 90%.

[0022] Preferably, the additive further includes at least one selected from tris(trimethylsilane)borate (TMSB), tris(trimethylsilane)phosphate (TMSP), 4,4'-bi-1,3-dioxolane-2,2'-dione (BDC), ethylene 3,3-diisothiazolate (BDTD), triallyl phosphate (TAP), tris(trimethylsilane)phosphite (TMSPi), triargyl phosphate (TPP), vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), diethyl pyrocarbonate (DEPC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), and 1,3-propanediol cyclosulfonate (PCS), wherein the mass percentage of the above additives in the non-aqueous electrolyte is 0% to 15%, specifically, but not limited to, 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, and 15%.

[0023] A third aspect of the present invention provides a non-aqueous electrolyte, comprising a positive electrode and a negative electrode, and further comprising the aforementioned non-aqueous electrolyte.

[0024] Preferably, the positive electrode comprises a positive electrode active material, wherein the positive electrode active material is selected from α-NaFeO2, NaCoO2, Na 0.7 [Fe 0.7 Mn 0.3 O2, Na(Mn) 0.25 Fe 0.25 Co 0.25 Ni 0.25O2, NaMnO2, Na x [Fe 1 / 2 Mn 1 / 2 ]O2 (x=0.5 or 0.67), Na[Ni 0.75-x Fe x Mn 0.25 O2 (x = 0.4, 0.45, 0.5, or 0.55), Na 0.67 [Mn 0.6 Ni 0.15 Fe 0.25 O2, Na[Li 0.05 (Ni 0.25 Fe 0.25 Mn 0.5 ) 0.95 ]O2, Na2FePO4F, Na4Fe2(CN)6, NaNi 0.33 Fe 0.33 Mn 0.33 At least one of O2, NaFePO4, Na2FeP2O7, Na2MnPO4F, NaCoPO4, Na3V2(PO4)3, NaCrO2, and Na2Fe2(SO4)3.

[0025] Preferably, the negative electrode comprises a negative electrode material selected from at least one of soft carbon, hard carbon, sodium titanate, MoS2, Fe2O3, Fe3O4, ZnS, Sb, and SbSn. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0027] Example A

[0028] This embodiment provides a method for preparing modified black phosphorus quantum dots, including the following steps:

[0029] S1 dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) at 45°C under vacuum for 48 h. 25 mg of black phosphorus and 500 mg of the dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) were added to an agate mortar and mechanically ground for 40 min. The black phosphorus / 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) complex was then transferred to a round-bottom flask containing 180 mL of DEC to obtain the reaction solution.

[0030] S2 deoxygenated the reaction solution by argon bubbling for 40 min, and then reacted at 140℃ for 6 h under argon atmosphere, cooling water reflux, and vigorous stirring. After the reaction was completed, the reaction solution was cooled to room temperature and centrifuged in a centrifuge at 10000 r / min to obtain modified black phosphorus quantum dots, denoted as compound A.

[0031] Example B

[0032] This embodiment provides a method for preparing modified black phosphorus quantum dots, including the following steps:

[0033] S1 dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) at 40°C under vacuum for 70 h. 25 mg of black phosphorus and 380 mg of the dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) were added to an agate mortar and mechanically ground for 30 min. After grinding, the black phosphorus / 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) complex was transferred to a round-bottom flask containing 180 mL of DEC to obtain the reaction solution.

[0034] S2 subjected the reaction solution to argon bubbling for 40 min to remove oxygen, and then reacted at 145℃ for 5 h under argon atmosphere, cooling water reflux, and vigorous stirring. After the reaction was completed, the reaction solution was cooled to room temperature and centrifuged at 12000 r / min to obtain modified black phosphorus quantum dots, denoted as compound B.

[0035] Example C

[0036] This embodiment provides a method for preparing modified black phosphorus quantum dots, including the following steps:

[0037] S1 dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) at 50°C under vacuum for 38 hours. 25 mg of black phosphorus and 750 mg of the dried 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) were added to an agate mortar and mechanically ground for 60 minutes. After grinding, the black phosphorus / 1-ethyl-3-methylimidazolium dinitrile (1-ethyl-3-methylimidazolium dinitrile) complex was transferred to a round-bottom flask containing 180 mL of DEC to obtain the reaction solution.

[0038] S2 deoxygenated the reaction solution by argon bubbling for 40 min, and then reacted at 150℃ for 7 h under argon atmosphere, cooling water reflux, and vigorous stirring. After the reaction was completed, the reaction solution was cooled to room temperature and centrifuged at 15000 r / min to obtain modified black phosphorus quantum dots, denoted as compound C.

[0039] Example 1

[0040] In a nitrogen-filled glove box (O2 ≤ 5 ppm, H2O ≤ 5 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 1:2:1 to obtain 85.98 g of a non-aqueous organic solvent. Then, 0.1 g of compound A prepared in Example A was added to obtain a mixed solution. The mixed solution was sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 14 g of sodium hexafluorophosphate was slowly added to the mixed solution in a nitrogen-filled glove box (O2 ≤ 5 ppm, H2O ≤ 5 ppm). After mixing thoroughly, the electrolyte was prepared.

[0041] The electrolyte formulations for Examples 2-16 and Comparative Examples 1-4 are shown in Table 1. The steps for preparing the non-aqueous electrolyte are the same as in Example 1.

[0042] Table 1

[0043]

[0044]

[0045] The preparation method of BPQDs in Comparative Example 3 includes ball milling of block black phosphorus with N-methylpyrrolidone, followed by ultrasonication and centrifugation, and then freeze-drying of the supernatant. The specific preparation method is the same as in the prior art, and will not be repeated here.

[0046] NaNi with a maximum charging voltage of 4.2V 0.33 Fe 0.33 Mn 0.33 O2 was used as the positive electrode material and hard carbon as the negative electrode material. Sodium-ion batteries with a theoretical capacity of 1000mAh were prepared using the samples from Examples 1-16 and Comparative Examples 1-4 according to the conventional sodium battery preparation method. High-temperature cycle performance test and high-temperature storage internal resistance change rate test were conducted respectively. The test results are shown in Table 2.

[0047] High-rate cycling performance test :

[0048] The sodium-ion battery was charged at a constant current of 4C to 4.2V in an environment of 25℃, then charged at a constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 4C to 1.5V. This cycle was repeated, and the discharge capacity of the first cycle and the discharge capacity of the last cycle were recorded. The capacity retention rate was calculated using the following formula.

[0049] Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%

[0050] High-Temperature Storage Internal Resistance Change Rate Test :

[0051] The sodium-ion battery was subjected to 5 charge-discharge cycles at a charge-discharge rate of 1C at room temperature. Finally, it was charged to full capacity at a rate of 1C. The internal resistance T0 of the sodium-ion battery was recorded. The fully charged battery was stored at 60℃ for 15 days, and the internal resistance T of the sodium-ion battery was recorded. The experimental data such as the rate of change of the battery internal resistance were calculated. The results are shown in Table 2.

[0052] Internal resistance change rate = (T-T0) / T*100%

[0053] Table 2

[0054]

[0055]

[0056] As shown in Table 2, the overall performance of Examples 1-14 of this invention is superior to that of Comparative Examples 1-4. This may be because the non-aqueous electrolyte contains the modified black phosphorus quantum dots prepared in this invention. Applying the modified black phosphorus quantum dots prepared in this invention to the non-aqueous electrolyte can reduce the impedance of the sodium-ion battery during cycling, effectively improving the high-rate cycling performance and high-temperature cycling performance of the sodium-ion battery. This may be due to the high carrier mobility of the black phosphorus quantum dots themselves. Their attachment to the positive and negative electrode surfaces can reduce the impedance during cycling. During cycling, the black phosphorus quantum dots decompose and form fluorinated phosphides in situ. The resulting SEI and CEI films also have low impedance, which can improve the fast-charging performance of the sodium-ion battery. At the same time, the CEI film formed by the nitrogen-containing heterocycles of the 1-ethyl-3-methylimidazolium dinitrile ammonium salt coated with black phosphorus quantum dots during battery cycling can inhibit the growth of DCR during high-temperature cycling, thereby improving the high-temperature performance of the sodium-ion battery.

[0057] See Examples 1-16 for further details. Example 10 exhibits the best 4C cycle performance and the smallest impedance increase at 60°C. This may be because the sodium salt in this example also contains NaDFOP. NaDFOP adsorbs on the negative electrode and synergistically modifies the black phosphorus quantum dots, resulting in a SEI layer with relatively low impedance. As shown in Example 13, adding DTD to compound A can also improve the 4C cycle performance of the battery.

[0058] Comparative Example 1 contains no additives or auxiliaries, and therefore has the worst performance. Comparative Example 2 contains only additives, and its performance is better than that of Comparative Example 1, but worse than that of Examples 1-16. Comparative Examples 3 and 4 contain only unmodified black phosphorus quantum dots or only 1-ethyl-3-methylimidazolium dinitrile, and their performance is better than that of Comparative Examples 1 and 2, but worse than that of Examples 1-16.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A nonaqueous electrolyte comprising a sodium salt, a nonaqueous organic solvent, and an additive, characterized in that, The additive comprises modified black phosphorus quantum dots; The preparation method of the modified black phosphorus quantum dots comprises the steps of: S1 adding block black phosphorus and nitrogen-containing heterocyclic ionic liquid after grinding into a solvent to obtain a reaction solution, wherein the nitrogen-containing heterocyclic ionic liquid comprises 1-ethyl-3-methyl imidazole dicyanamide salt; S2 performing a reflux reaction on the reaction solution under an inert atmosphere.

2. The nonaqueous electrolyte according to claim 1, characterized by In S1, the mass ratio of the block black phosphorus to the nitrogen-containing heterocyclic ionic liquid is 1:15-30, and the solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate.

3. The nonaqueous electrolyte according to claim 1, characterized by In S2, the reflux reaction is performed at a temperature of 130-150°C for 4-8 hours, and the inert atmosphere is nitrogen or argon.

4. The nonaqueous electrolyte according to claim 1, characterized by The nitrogen-containing heterocyclic ionic liquid is vacuum dried before being ground, and the moisture content of the dried nitrogen-containing heterocyclic ionic liquid is 15-25 ppm.

5. The nonaqueous electrolyte according to claim 1, wherein After the reflux reaction is completed, the reaction solution is centrifuged at a speed of 10,000-15,000 r / min.

6. The nonaqueous electrolyte according to claim 1, wherein The modified black phosphorus quantum dots have a particle size of 3-15 nm.

7. The nonaqueous electrolyte according to claim 1, wherein The mass percentage of the modified black phosphorus quantum dots in the non-aqueous electrolyte is 0.005%-0.15%.

8. The nonaqueous electrolyte according to claim 1, wherein The additive further comprises at least one of tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, 4,4'-bi-1,3-dioxolane-2,2'-dione, 3,3-bisvinyl disulfate, triallyl phosphate, tris(trimethylsilyl) phosphite, tripropargyl phosphate, vinylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, diethyl pyrocarbonate, 1,3-propane sultone, vinyl sulfate and 1,3-propanediol cyclic sulfate.

9. A sodium-ion battery comprising a positive electrode and a negative electrode, characterized in that, The non-aqueous electrolyte according to any one of claims 1-8 is also provided.

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