A high-pressure-resistant gel electrolyte stable to lithium negative electrode and a preparation method thereof

Abstract

The present application relates to a kind of high-pressure-resistant gel electrolyte stable to lithium negative electrode and preparation method thereof, belong to gel polymer electrolyte technical field.The electrolyte is composed of PVDF-HFP film and electrolyte;The electrolyte is composed of lithium salt I, ester organic solvent, ether organic solvent and lithium salt II;The ester organic solvent is composed of DEC and FEC or is composed of EMC and FEC;The ether organic solvent is 18-crown ether-6, 15-crown ether-5 or 12-crown ether-4;The lithium salt II is lithium nitrate, and lithium salt I is different from lithium salt II.Ether organic solvent and lithium salt II are added to the mixed solution composed of lithium salt I and ester organic solvent, and electrolyte is obtained by heating and stirring, the electrolyte is obtained by soaking PVDF-HFP film in electrolyte, and the interface compatibility of the electrolyte with high-nickel positive electrode and lithium negative electrode is good, can inhibit lithium dendrite growth, and improve the cycle performance of battery.

Description

Technical Field

[0001] This invention relates to a high-voltage resistant gel electrolyte that is stable for lithium anodes and its preparation method, belonging to the field of gel polymer electrolyte technology. Background Technology

[0002] Lithium-ion batteries have made significant contributions to the development of mobile electronics, electric vehicles, and energy storage grids. Currently, improving the safety and energy density of lithium batteries remains a challenge. Gel polymer electrolytes, with their high ionic conductivity and flexibility, have become an important research direction in solid-state electrolyte systems. Furthermore, gel electrolytes avoid the leakage problems of liquid electrolytes, offering higher safety performance, and eliminate the need for inert materials such as separators, thus increasing battery energy density.

[0003] Polyvinylidene chloride-hexafluoropropylene copolymer (PVDF-HFP) has a two-phase structure, consisting of crystalline PVDF and amorphous HFP. The crystalline PVDF provides mechanical support, while the amorphous HFP offers more space, allowing for the trapping of a large amount of liquid. Therefore, PVDF-HFP is often compounded with plasticizers to obtain gel electrolytes with certain mechanical strength and ionic conductivity. Common gel electrolyte plasticizers often consist of carbonate-based organic solvents and lithium salts, similar to the composition of commercial electrolytes, allowing the resulting gel electrolyte to be matched with high-voltage positive electrodes.

[0004] Lithium metal has a capacity of 3860 mAh g. -1 The high specific capacity and low voltage of -3.04V can improve the energy density of the battery. When lithium metal is used as the negative electrode and matched with a gel electrolyte, some problems in the liquid system cannot be avoided during cycling, such as the growth of lithium dendrites and side reactions, which leads to a decrease in the cycle performance of the battery.

[0005] Lithium nitrate (LiNO3) can form an interface layer rich in lithium nitride, which is beneficial for regulating lithium-ion transport and protecting the lithium anode. At the same time, the addition of lithium nitrate can change the deposition morphology of lithium, transforming it from dendritic to spherical, which greatly alleviates the growth of lithium dendrites.

[0006] Lithium nitrate is often used in ether-based electrolytes to stabilize the negative electrode interface. However, ether-based electrolytes are generally only compatible with low-voltage (<4V) positive electrodes (such as LiFePO4). Lithium nitrate has very low solubility in carbonate electrolytes, which means that it cannot be used in high-voltage batteries composed of high-voltage positive electrodes (such as high-nickel positive electrodes) and lithium negative electrodes. Consequently, it cannot solve the problems of poor interface compatibility, lithium dendrite growth, and low coulombic efficiency in such high-voltage batteries. Summary of the Invention

[0007] In view of this, in order to solve the problem that lithium nitrate cannot dissolve in ester organic solvents, and thus cannot solve the problems of poor interfacial compatibility, lithium dendrite growth, and low coulombic efficiency in high-voltage batteries composed of high-voltage positive electrodes and lithium negative electrodes, the purpose of this invention is to provide a high-voltage resistant gel electrolyte that is stable for lithium negative electrodes and its preparation method. In the gel electrolyte, lithium nitrate is introduced into the gel electrolyte containing ester organic solvents, which improves the interfacial compatibility between the gel electrolyte and the high-nickel (NCM) positive electrode, as well as between the gel electrolyte and the lithium negative electrode, while inhibiting the growth of lithium dendrites and improving the cycle performance of the battery.

[0008] To achieve the objectives of this invention, the following technical solutions are provided.

[0009] A high-voltage resistant gel electrolyte that is stable against lithium anodes, the electrolyte being composed of a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) membrane and an electrolyte solution;

[0010] The electrolyte is composed of lithium salt I, ester organic solvent, ether organic solvent and lithium salt II;

[0011] The lithium salt I is the lithium salt used in lithium-ion battery electrolytes in the prior art; and lithium salt I is not lithium nitrate (LiNO3);

[0012] The ester organic solvent is composed of ester organic solvent I and ester organic solvent II in a volume ratio of (1-3):1; ester organic solvent I is diethyl carbonate (DEC) or methyl ethyl carbonate (EMC); ester organic solvent II is fluoroethylene carbonate (FEC).

[0013] The ether organic solvent is 18-crown ether-6, 15-crown ether-5, or 12-crown ether-4;

[0014] The lithium salt II is lithium nitrate (LiNO3).

[0015] Preferably, in the electrolyte, the concentration of lithium salt I is 0.5 mol / L to 5 mol / L, the concentration of ether organic solvent is 0.05 mol / L to 0.2 mol / L, and the concentration of lithium salt II is 0.05 mol / L to 0.5 mol / L.

[0016] More preferably, the molar ratio of the ether organic solvent to lithium salt II in the electrolyte is 2:1.

[0017] Preferably, the ether organic solvent is 18-crown ether-6 or 15-crown ether-5.

[0018] Preferably, the ester organic solvent is composed of ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC) in a volume ratio of 7:3.

[0019] Preferably, the weight-average molecular weight of the PVDF-HFP in the PVDF-HFP membrane is 30w to 50w.

[0020] More preferably, the weight-average molecular weight of PVDF-HFP in the PVDF-HFP membrane is 45.5w.

[0021] Preferably, the lithium salt I is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorooxalateborate (LiDFOB), and lithium hexafluorophosphate (LiPF6).

[0022] A method for preparing a high-voltage resistant gel electrolyte that is stable for lithium anodes, as described in this invention, comprises the following steps:

[0023] (1) The lithium salt I is completely dissolved in the ester organic solvent to obtain a mixed solution;

[0024] (2) Add the ether organic solvent and the lithium salt II to the mixed solution and stir at 30℃~60℃ until the lithium salt II is completely dissolved to obtain the electrolyte;

[0025] (3) The PVDF-HFP membrane is immersed in the electrolyte for 12h to 36h to allow the PVDF-HFP membrane to fully absorb the electrolyte and be composited to obtain the high-voltage resistant gel electrolyte that is stable for lithium anode.

[0026] The PVDF-HFP membrane can be prepared according to the methods described in the prior art.

[0027] Beneficial effects

[0028] (1) This invention provides a high-voltage resistant gel electrolyte that is stable against a lithium anode. The introduction of a fluorinated component (fluoroethylene carbonate) into the gel electrolyte improves its electrochemical window, thereby enabling it to be matched with a high-voltage cathode. Simultaneously, lithium nitrate is introduced into the ester-based gel electrolyte using an ether-based organic solvent, improving its interfacial compatibility with the lithium anode and enhancing the morphology of lithium-ion deposition, thus inhibiting lithium dendrite growth. Batteries assembled from this gel electrolyte, such as NCM811 batteries, exhibit high coulombic efficiency. The gel electrolyte also possesses high ionic conductivity and good interfacial contact properties. Semi-solid-state button batteries or pouch batteries assembled from this gel electrolyte exhibit excellent electrochemical and safety performance.

[0029] (2) This invention provides a high-voltage resistant gel electrolyte that is stable against lithium anodes. In the electrolyte, the molar ratio of ether organic solvent to LiNO3 is 2:1. Under these conditions, the interface between the gel electrolyte and the lithium anode is more stable, exhibiting a smaller overpotential and a longer cycle life, resulting in the best application performance. If there is less ether organic solvent, it will hinder the dissolution of LiNO3, thus affecting the performance of the resulting gel electrolyte; if there is more ether organic solvent, it will increase the interfacial polarization between the gel electrolyte and the lithium anode.

[0030] (3) The present invention provides a method for preparing a high-voltage resistant gel electrolyte that is stable for lithium anodes. The method involves adding an ether organic solvent and the lithium salt II to a mixed solution composed of lithium salt I and an ester organic solvent, and heating at a certain temperature to promote the dissolution of lithium salt II. The electrolyte can be prepared in three steps, and the method is simple. Attached Figure Description

[0031] Figure 1 The images show actual pictures of the electrolytes prepared for Comparative Example 1, Comparative Example 2, and Example 2, respectively.

[0032] Figure 2 The Raman spectra of the gel electrolytes prepared in Example 2 and Comparative Example 1 are shown.

[0033] Figure 3 The figure shows the results of constant current charge-discharge cycle tests of lithium-lithium symmetric batteries assembled from gel electrolytes prepared in Comparative Example 1 and Comparative Example 3, respectively.

[0034] Figure 4 The figure shows the constant current charge-discharge cycle test results of the lithium-lithium symmetric battery assembled from the gel electrolyte prepared in Comparative Example 2.

[0035] Figure 5 The graph shows the constant current charge-discharge cycle test results of the lithium-lithium symmetric battery assembled from the gel electrolyte prepared in Example 2.

[0036] Figure 6 The image shows the SEM image of the lithium anode after constant current charge-discharge cycling of the lithium-lithium symmetric battery assembled from the gel electrolyte prepared in Comparative Example 2.

[0037] Figure 7 SEM image of the lithium anode after constant current charge-discharge cycle of the lithium-lithium symmetric battery assembled from the gel electrolyte prepared in Example 2.

[0038] Figure 8 The graph shows the linear voltammetric scan results of the gel electrolyte prepared in Example 3.

[0039] Figure 9The graph shows the constant current charge-discharge cycle test results of lithium-lithium symmetric batteries composed of the gel electrolytes prepared in Examples 1 and 3, respectively.

[0040] Figure 10 The graph shows the test results of NCM-Li metal batteries assembled from the gel electrolytes prepared in Example 2 and Comparative Example 1, respectively, under charge-discharge cycles at a current density of 0.5C.

[0041] Figure 11 The image shows the SEM image of the NCM cathode after cycling of the NCM-Li metal battery assembled with the gel electrolyte prepared in Example 2.

[0042] Figure 12 The image shows the SEM image of the NCM cathode after cycling of the NCM-Li metal battery assembled from the gel electrolyte prepared in Comparative Example 1.

[0043] Figure 13 The N1s spectra of the NCM cathodes after cycling are shown in the NCM-Li metal batteries assembled from the gel electrolytes prepared in Example 2 and Comparative Example 1, respectively.

[0044] Figure 14 The image shows the Ni 2p spectra of the NCM cathode after cycling in NCM-Li metal batteries assembled from the gel electrolytes prepared in Example 2 and Comparative Example 1, respectively.

[0045] Figure 15 The N1s spectra of the lithium anodes of NCM-Li metal batteries assembled from the gel electrolytes prepared in Example 2 and Comparative Example 1 after cycling are shown, where (a) is the N1s spectrum of Example 2; and (b) is the N1s spectrum of Comparative Example 1.

[0046] Figure 16 Impedance diagram of a blocking battery assembled from the gel electrolyte prepared in Example 2.

[0047] Figure 17 The image shows the cyclic voltammogram of the NCM-Li metal battery assembled from the gel electrolyte prepared in Example 4. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments. Unless otherwise specified, the methods described are conventional methods, and the raw materials described are available from publicly available commercial sources or prepared according to literature.

[0049] In the following embodiments:

[0050] The Raman spectroscopy test was performed using an in-Via Raman spectrometer from Renishaw, UK, with an excitation wavelength of 785 cm⁻¹. -1 .

[0051] The constant current charge-discharge cycle test involves assembling a Li / gel electrolyte / Li lithium-lithium symmetric battery in an argon-filled glove box, and then using a CT3002A Land test system from Wuhan Landian Electronics Co., Ltd. to perform constant current charge-discharge cycle tests on the assembled lithium-lithium symmetric battery.

[0052] Microscopic morphology was observed using a Hitachi FESEM (S-4800, HITACHI) field emission scanning electron microscope.

[0053] The linear sweep voltammetry (LSV) test involved assembling a stainless steel / gel electrolyte / lithium anode battery by sandwiching the gel electrolyte between a stainless steel and a lithium electrode. The oxidation decomposition voltage of the electrolyte was measured using a CHI 660E electrochemical workstation from Shanghai Chenhua Instrument Co., Ltd. (hereinafter referred to as "Shanghai Chenhua"). The test conditions were: scan from open-circuit voltage to 6V at a scan rate of 0.1 mV / s. -1 .

[0054] The charge-discharge cycle test involved dissolving PVDF in N-methylpyrrolidone to obtain a PVDF binder. NCM811 positive electrode powder, conductive carbon, and the PVDF binder were ground uniformly in a mortar at a mass ratio of 8:1:1 to obtain a slurry. The slurry was then uniformly coated onto aluminum foil using a 150μm scraper, placed in a constant temperature drying oven, and dried at 80℃ for 24 hours. After drying, the foil was removed and cut into circular electrode sheets with a diameter of 11mm, which were the NCM811 positive electrode sheets. The gel electrolyte was then assembled with the NCM811 positive electrode sheets, lithium foil, gaskets, and spring contacts to form a CR2032 button battery. The battery was subjected to charge-discharge cycles using a Land testing system. At 30℃, the charge-discharge voltage range was 2.75V–4.3V. After three cycles at 0.1C, the battery was cycled again at a current density of 0.5C.

[0055] The X-ray photoelectron spectroscopy (XPS) test was performed using a Thermo Scientific K-Alpha instrument to analyze the composition of the NCM cathode and gel electrolyte interface. An Ulvac-Phi PHI QUANTERA-II SXM instrument was used to perform Ar phase measurements at 0s, 60s, and 120s. + Sputtering was used to analyze the composition of the interface between the lithium anode and the gel electrolyte.

[0056] The impedance testing method for the electrolyte is as follows: the electrolyte is sandwiched between two stainless steel inert electrodes to assemble a blocking battery; using a Shanghai Chenhua CHI 660E electrochemical workstation, and employing AC impedance spectroscopy at 1Hz to 10Hz... 5The test was conducted at a test frequency of Hz; then the ionic conductivity (abbreviated as conductivity) of the electrolyte was calculated according to formula (i):

[0057]

[0058] In equation (i), σ is the conductivity, L is the thickness of the PVDF-HFP film, R is the intrinsic resistance of the blocking battery, and S is the area of ​​the stainless steel electrode.

[0059] The cyclic voltammetry (CV) test was performed by assembling the gel electrolyte to be tested between the NCM811 positive electrode and the lithium electrode into a battery. The test was conducted using a CHI 660E electrochemical workstation from Shanghai Chenhua, under the following conditions: scan rate of 0.1 mV / s. -1 The voltage range is 2.75V to 4.5V.

[0060] The PVDF-HFP membrane can be prepared according to the methods described in the prior art; the weight-average molecular weight of PVDF-HFP in the PVDF-HFP membrane is 45.5w.

[0061] Example 1

[0062] (1) Add LiTFSI to an ester organic solvent and stir until LiTFSI is completely dissolved in the ester organic solvent to obtain a transparent mixed solution; the ester organic solvent is composed of EMC and FEC in a volume ratio of 7:3.

[0063] (2) Add 18-crown ether-6 and LiNO3 to the mixed solution and stir at 60°C. After the LiNO3 is completely dissolved, the electrolyte is obtained.

[0064] The electrolyte contains 1 mol / L LiTFSI, 0.05 mol / L 18-crown ether-6, and 0.05 mol / L LiNO3.

[0065] (3) The PVDF-HFP membrane is immersed in the electrolyte for 24 hours to allow the PVDF-HFP membrane to fully absorb the electrolyte and be composited, thereby obtaining a high-voltage resistant gel electrolyte that is stable for lithium anode.

[0066] Example 2

[0067] Unlike Example 1, the concentration of 18-crown ether-6 in the electrolyte obtained in step (2) is 0.1 mol / L, while the rest are the same as in Example 1, resulting in a high-voltage resistant gel electrolyte that is stable to the lithium anode.

[0068] Example 3

[0069] Unlike Example 1, the concentration of 18-crown ether-6 in the electrolyte obtained in step (2) is 0.2 mol / L, while the rest are the same as in Example 1, resulting in a high-voltage resistant gel electrolyte that is stable to the lithium anode.

[0070] Example 4

[0071] Unlike Example 1, the ether organic solvent in the electrolyte obtained in step (2) is 15-crown ether-5; the concentration of 15-crown ether-5 in the electrolyte is 0.1 mol / L, and the rest are the same as in Example 1, thus obtaining a high-voltage resistant gel electrolyte that is stable to the lithium anode.

[0072] Comparative Example 1

[0073] (1) Add LiTFSI to an ester organic solvent and stir to completely dissolve LiTFSI in the ester organic solvent to obtain a transparent electrolyte; the ester organic solvent is composed of EMC and FEC in a volume ratio of 7:3; the concentration of LiTFSI in the electrolyte is 1 mol / L.

[0074] (2) The PVDF-HFP membrane is immersed in the electrolyte for 24 hours to allow the PVDF-HFP membrane to fully absorb the electrolyte and undergo composite formation, thereby obtaining a gel electrolyte.

[0075] Comparative Example 2

[0076] (1) Add LiTFSI to an ester organic solvent and stir until LiTFSI is completely dissolved in the ester organic solvent to obtain a transparent mixed solution; the ester organic solvent is composed of EMC and FEC in a volume ratio of 7:3.

[0077] (2) Assuming that LiNO3 dissolves in the mixed solution prepared in this comparative example, and that the concentration of LiNO3 in the resulting electrolyte is 0.05 mol / L, LiNO3 is added to the mixed solution at this concentration, and the mixture is stirred at 30°C for 12 hours to obtain the electrolyte. The concentration of LiTFSI in the electrolyte is 1 mol / L.

[0078] (3) The PVDF-HFP membrane is immersed in the electrolyte for 24 hours to allow the PVDF-HFP membrane to fully absorb the electrolyte and undergo composite formation, thereby obtaining a gel electrolyte.

[0079] Figure 1 The images show actual samples before adding PVDF-HFP membranes to the electrolytes prepared in Comparative Example 1, Comparative Example 2, and Example 2, respectively. Figure 1The white substance in the three bottles is a magnetic particle. It can be seen that the electrolytes prepared in Comparative Example 1 and Example 2 are clear and transparent, while the electrolyte obtained by adding LiNO3 to the mixed solution in Comparative Example 2 is turbid. This shows that lithium nitrate cannot be completely dissolved in the electrolyte without ether reagents; while the solubility of lithium nitrate in the electrolyte with added ether reagents will be greatly increased.

[0080] Comparative Example 3

[0081] (1) Add LiTFSI to an ester organic solvent and stir until LiTFSI is completely dissolved in the ester organic solvent to obtain a transparent mixed solution; the ester organic solvent is composed of EMC and FEC in a volume ratio of 7:3.

[0082] (2) Add 18-crown ether-6 to the mixed solution and stir until homogeneous to obtain an electrolyte.

[0083] The electrolyte contains 1 mol / L LiTFSI and 0.1 mol / L 18-crown ether-6.

[0084] (3) The PVDF-HFP membrane is immersed in the electrolyte for 24 hours to allow the PVDF-HFP membrane to fully absorb the electrolyte and undergo composite formation, thereby obtaining a gel electrolyte.

[0085] Test Example 1

[0086] Raman spectroscopy was performed on the gel electrolytes prepared in Example 2 and Comparative Example 1 to elucidate the chemical composition of the electrolytes. The test results are shown in [Figure number missing]. Figure 2 .right Figure 2 Fitting the Raman spectrum shows that 738 cm⁻¹ -1 ~752cm -1 The peak indicates that Li + -FSI - The solvent cluster has three different coordination structures: at 741.07 cm⁻¹ -1 The place indicates the freedom of TFSI - A type of telescopic design, 744.99cm -1 The location indicates TFSI - Coordinated with a single lithium ion, 750.73 cm -1 The location indicates TFSI - With two or more Li + Fit, 731.24cm -1 The peak of the symmetric ring deformation of FEC is 735.56 cm⁻¹. -1 The peak represents the complexation of FEC with lithium ions.

[0087] Compared to Comparative Example 1, the gel electrolyte prepared in Example 2 showed an increase in free FECs, indicating a good coordination ability between 18-crown ether-6 and lithium ions, further demonstrating that 18-crown ether-6 promotes the dissolution of lithium nitrate in the electrolyte; this experimental result also explains Figure 1 The electrolyte in Example 2 is clear and transparent.

[0088] Test Example 2

[0089] The gel electrolytes prepared in Comparative Examples 1, 2, 3, and 2 were assembled into lithium-lithium symmetric batteries, respectively, and tested at 0.3 mA cm⁻¹. -2 The areal capacity was determined by constant current charge-discharge cycle testing at the areal current density for 20 minutes of charging and 20 minutes of discharging, resulting in a measured areal capacity of 0.1 mAh cm⁻¹. -2 The test results are shown below. Figures 3 to 5 ,Depend on Figure 3 It can be seen that the first-cycle overpotential of the symmetric battery assembled with the gel electrolyte of Comparative Example 3 is 67mV, which is greater than the overpotential of Comparative Example 1 (53.9mV in the first cycle). This indicates that the addition of 18-crown ether-6 will increase the overpotential between the electrolyte and the lithium metal anode, making the interfacial compatibility between the electrolyte and the lithium metal anode worse and increasing the polarization of the battery.

[0090] Depend on Figure 4 It can be seen that the symmetric battery assembled with the gel electrolyte of Comparative Example 2 has an overpotential of 59.5mV during cycling and a cycle life of less than 30h. This indicates that simply adding lithium nitrate does not significantly improve the battery performance. Although the overpotential does not increase significantly, it reduces the cycle life of the battery.

[0091] Depend on Figure 5 It can be seen that the symmetric battery assembled from the gel electrolyte of Example 2, with crown ether and lithium nitrate added simultaneously, can not only cycle stably for more than 400 hours, but also has an overpotential of less than 40mV per cycle.

[0092] In summary, the results show that adding either ether-based organic solvents or lithium nitrate to the electrolyte of gel electrolytes increases the overpotential of the gel electrolyte. However, when both ether-based organic solvents and lithium nitrate are added to the electrolyte, the resulting gel electrolyte not only does not increase the overpotential between the electrolyte and the lithium anode, but actually reduces the overpotential and exhibits a long cycle life of up to 200 hours. This further indicates that the reduced overpotential of the gel electrolyte obtained by adding ether and lithium nitrate to the ester-based organic solvent suggests improved interfacial compatibility with the lithium anode. The longer cycle time also indicates that the gel electrolyte with added ether and lithium nitrate can suppress dendrite growth, preventing lithium dendrites from penetrating the separator and causing short-circuit failure of the battery.

[0093] Test Example 3

[0094] The gel electrolytes prepared in Example 2 and Comparative Example 1 were respectively assembled into lithium-lithium symmetric batteries, and tested at 0.3 mA / cm². -2 A constant current charge-discharge cycle test was performed at the surface current density, with a charge-discharge cycle of 1 hour and a discharge cycle of 1 hour. Therefore, the tested surface capacity is 0.3 mAh cm⁻¹. -2 The cycle number was set to 10 revolutions. After the cycle was completed, the symmetrical battery was disassembled, and the microstructure of the lithium anode in the battery was observed. The observation results are as follows: Figure 6 and Figure 7 As shown, from Figure 7 It can be seen that the lithium anode in Comparative Example 1 formed a relatively thick solid electrolyte interphase (SEI) film after cycling, and broken lithium fibers and a large amount of dead lithium were deposited on the surface of the lithium anode. From... Figure 8 It can be seen that after cycling, the lithium anode surface of Example 2 is smooth and dense, which indicates that the lithium nitrate dissolved in the electrolyte was successfully introduced into the gel electrolyte, which played an important role in improving the SEI film on the anode side, enabling stable deposition and extraction of lithium ions and avoiding the formation of lithium dendrites.

[0095] Test Example 4

[0096] The gel electrolyte prepared in Example 3 was subjected to linear sweep voltammetry (LSV) testing, and the test results are shown in [Figure 1]. Figure 8 Therefore, it can be seen that the current of the gel electrolyte does not increase significantly at 4.5V, indicating that the gel electrolyte has a wide electrochemical window and can be matched with high nickel cathodes, such as NCM811 cathodes.

[0097] The gel electrolytes prepared in Examples 1, 2 and 4 were tested according to this test example. All three had a wide electrochemical window and could be matched with high-nickel cathodes.

[0098] Test Example 5

[0099] The gel electrolytes obtained in Examples 1 and 3 were assembled into lithium-lithium symmetric batteries, respectively, and tested at 0.3 mA / cm². -2 The areal capacity was determined by constant current charge-discharge cycle testing at the areal current density for 20 minutes of charging and 20 minutes of discharging, resulting in a measured areal capacity of 0.1 mAh cm⁻¹. -2 The test results are shown below. Figure 9 Therefore, it can be seen that the molar ratio of 18-crown ether-6 to lithium nitrate in Example 1 is 1:1, and the lithium-lithium symmetric battery assembled with the electrolyte prepared in Example 1 can achieve a cycle time of 100 hours. However, compared with Example 3 and... Figure 5The test results of Example 2 shown in the figure indicate that the battery of Example 1 is prone to short circuits, suggesting that the electrolyte of Example 1 is less effective at suppressing lithium dendrite growth than that of Examples 3 and 2. In Example 3, the molar ratio of 18-crown ether-6 to lithium nitrate is 4:1. The figure shows that Example 3 has a larger overpotential, suggesting that a higher content of ethers increases the interfacial polarization between the gel electrolyte and the lithium anode. Furthermore, through the above... Figure 5 It can be seen that in Example 2, when the molar ratio of 18-crown ether-6 to lithium nitrate is 2:1, the interface phase between the gel electrolyte and the lithium anode obtained in Example 2 is more stable, with a smaller overpotential and a longer cycle life.

[0100] Test Example 6

[0101] The gel electrolytes prepared in Example 2 and Comparative Example 1 were assembled into NCM-Li metal batteries, and then charge-discharge cycle tests were conducted at a current density of 0.5C. The test results are shown in [Figure number missing]. Figure 10 Therefore, it can be seen that the NCM-Li metal battery assembled from the gel electrolyte of Example 2 has an initial discharge specific capacity of 183.3 mAh g. -1 After 120 cycles, the battery has a discharge specific capacity of 160.3 mAh g. -1 The capacity retention rate was 87.5%; the NCM-Li metal battery assembled from the gel electrolyte of Comparative Example 1 had an initial discharge specific capacity of 172.3 mAh g⁻¹. -1 Furthermore, after 120 cycles, the discharge specific capacity decayed to 71.7 mAh g. -1 The capacity retention rate was only 41.6%. This indicates that the electrolyte with added ether-based organic solvents and lithium nitrate can make the NCM-Li metal battery cycle stably and have a high coulombic efficiency. Furthermore, it shows that the addition of ether-based organic solvents and lithium nitrate to the gel electrolyte can generate a stable interfacial layer and reduce side reactions between the NCM cathode and the electrolyte.

[0102] Test Example 7

[0103] The gel electrolytes prepared in Example 2 and Comparative Example 1 were assembled into NCM-Li metal batteries, and then subjected to charge-discharge cycle tests at a current density of 0.5C for 50 cycles. After the cycle was completed, the batteries were disassembled, and the microstructure of the NCM positive electrode was observed. The observation results are shown in […]. Figure 11 and Figure 12As can be seen, the surface of the NCM cathode in Example 2 is smooth and intact, while the surface of the NCM cathode in Comparative Example 1 is cracked and has a thick layer of byproducts. This indicates that the cathode structure of Example 2 maintains good integrity, resulting in fewer side reactions. The formation of a thin cathode-electrolyte interface phase (CEI) can suppress side reactions between the cathode and the electrolyte, preventing the cathode from continuously cracking and coming into contact with the electrolyte, thus avoiding side reactions.

[0104] Test Example 8

[0105] The gel electrolytes prepared in Example 2 and Comparative Example 1 were assembled into NCM-Li metal batteries, and then subjected to charge-discharge cycle tests at a current density of 0.5C for 50 cycles. After the cycles were completed, the batteries were disassembled, and XPS tests were performed on the NCM positive electrode and the lithium negative electrode, respectively. The test results are shown in [Figure number missing]. Figures 13-15 .

[0106] from Figure 13 As can be seen, compared with Comparative Example 1, the battery assembled in Example 2 generated more nitrides at the positive electrode interface, had higher conductivity, and promoted the rapid transport of lithium ions. This may be due to the decomposition of dissolved lithium nitrate at the interface.

[0107] from Figure 14 It can be seen that, compared with Comparative Example 1, the battery assembled in Example 2 generates less NiF2 at the positive electrode interface, that is, there are fewer byproducts at the interface. This indicates that the addition of 18-crown ether-6 and lithium nitrate makes the electrolyte and the CEI generated on the positive electrode side more stable, protects the inner NCM particles, and reduces side reactions at the interface.

[0108] Figure 15 XPS N 1s spectra can characterize the composition of the lithium anode / electrolyte interface, and it can be seen from them that in Ar + After sputtering for 0s, 60s, and 120s, compared to Comparative Example 1, Example 2 showed more LiNO2 and LiN in the interface. x O y The SEI film, rich in highly conductive Li3N, provides rapid ion transport, enabling uniform deposition of lithium ions, avoiding the growth of lithium dendrites, and improving the morphology of lithium ion deposition.

[0109] Test Example 9

[0110] The gel electrolyte prepared in Example 2 was assembled into a blocking battery, and the impedance of the gel electrolyte was tested. The test results are shown in [Figure 1]. Figure 16Therefore, the impedance of the gel electrolyte at room temperature is 5.89 Ω, and the thickness of the electrolyte is 46 μm as determined by a micrometer. The conductivity of the gel electrolyte is calculated to be 0.284 mS / cm. -1 More than 10 -3 S cm -1 This indicates that it has a high ionic conductivity and meets the conditions for cycling at room temperature.

[0111] The gel electrolytes prepared in Examples 1, 3, and 4 were tested according to the test method of this test example. The test results showed that the gel electrolytes of these examples all had high ionic conductivity.

[0112] Test Case 10

[0113] The gel electrolyte prepared in Example 4 was assembled into an NCM-Li metal battery, and cyclic voltammetry tests were performed on the battery for 3 cycles. The test results are shown in [Figure 4]. Figure 17 Therefore, it can be seen that the battery assembled in Example 4 has the typical oxidation and reduction peaks of high-nickel materials. Moreover, after activation in the first week, the cycling curves in the following two weeks show a high degree of overlap, indicating high reversibility. This further demonstrates that the gel electrolyte prepared in Example 4 is well-matched with the high-nickel cathode.

[0114] The gel electrolytes prepared in Examples 1 to 3 were tested according to the test method of this test example. The test results showed that the gel electrolytes prepared in Examples 1 to 3 all had typical oxidation and reduction peaks of high nickel materials, and the cycling curves of the last two weeks had a high degree of overlap. This further illustrates that the gel electrolytes with added ether reagents and lithium nitrate can still match the high nickel cathode, and the matching degree is good.

[0115] This invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the scope of protection of this invention.

Claims

1. A high-pressure resistant gel electrolyte stable to lithium negative electrode, characterized by: The electrolyte is composed of a PVDF-HFP film and an electrolyte solution; The electrolyte solution is composed of lithium salt I, ester organic solvent, ether organic solvent and lithium salt II; The ester organic solvent is composed of ester organic solvent I and ester organic solvent II in a volume ratio of (1-3):1; the ester organic solvent I is diethyl carbonate or methyl ethyl carbonate; the ester organic solvent II is fluoroethylene carbonate; The ether organic solvent is 18-crown-6, 15-crown-5 or 12-crown-4; The lithium salt II is lithium nitrate, and the lithium salt I is different from the lithium salt II.

2. The high voltage resistant gel electrolyte stable to lithium negative electrode according to claim 1, characterized by: In the electrolyte solution, the concentration of lithium salt I is 0.5-5 mol / L, the concentration of ether organic solvent is 0.05-0.2 mol / L, and the concentration of lithium salt II is 0.05-0.5 mol / L.

3. The high voltage resistant gel electrolyte stable to lithium negative electrode according to claim 2, characterized by: In the electrolyte solution, the molar ratio of ether organic solvent to lithium salt II is 2:

1.

4. The high voltage resistant gel electrolyte stable to lithium negative electrode according to any one of claims 1 to 3, characterized by: The lithium salt I is one or more of lithium bistrifluoromethylsulfonylimide, lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate and lithium hexafluorophosphate; The ester organic solvent is composed of methyl ethyl carbonate and fluoroethylene carbonate in a volume ratio of 7:3; The ether organic solvent is 18-crown-6 or 15-crown-5; The weight average molecular weight of PVDF-HFP in the PVDF-HFP film is 30-50 w.

5. The high voltage resistant gel electrolyte stable to lithium negative electrode according to claim 4, characterized by: The weight average molecular weight of PVDF-HFP in the PVDF-HFP film is 45.5 w.

6. A method of producing a high-pressure-resistant gel electrolyte stable to a lithium negative electrode according to any one of claims 1 to 5, characterized by: The method steps are as follows: (1) completely dissolving the lithium salt I in the ester organic solvent to obtain a mixed solution; (2) adding the ether organic solvent and the lithium salt II to the mixed solution and stirring at 30-60°C until the lithium salt II is completely dissolved to obtain the electrolyte solution; (3) soaking the PVDF-HFP film in the electrolyte solution for 12-36 h to obtain the high-pressure-resistant gel electrolyte stable to lithium negative electrode.

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