Ionic gel and preparation method thereof, and application of ionic gel in sulfide all-solid-state battery positive electrode material

Abstract

The invention provides an ionic gel and a preparation method thereof, and an application of the ionic gel in a sulfide all-solid-state battery positive electrode material, the ionic gel is composed of an ionic liquid polymer and a plasticizer, a lithium salt 1 is dissolved in the ionic liquid polymer, and a lithium salt 2 is dissolved in the plasticizer. The ionic gel provided by the invention is composed of an ionic liquid polymer with good thermal stability and a plasticizer, by reasonably optimizing the proportion of the ionic liquid polymer, the plasticizer and the lithium salt, the ionic gel has high-pressure stability and high ionic conductivity, and keeps thermodynamic compatibility with sulfide electrolyte; when being applied, the material can be matched with a high-voltage and high-capacity high-nickel positive electrode material, and meanwhile, lithium ion transmission paths in the electrode are enriched; the ionic gel has a solid-state characteristic, has certain adhesion, can be stabilized on an internal interface of the positive electrode, and effectively inhibits side reactions; and under relatively high packaging pressure, the positive electrode solid-solid interface can be optimized for a long time, the interface impedance is reduced, and the rate capability of the all-solid-state battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to an ion gel and its preparation method, and its application in sulfide all-solid-state battery cathode materials. Background Technology

[0002] Currently, lithium-ion batteries are widely used in energy storage devices, electric vehicles, and portable communication devices. However, due to the use of flammable and toxic organic solvents as electrolytes, lithium-ion batteries pose safety hazards and cannot be matched with high-energy-density lithium metal anodes. In order to further improve the safety and energy density of lithium batteries, researchers have focused on solid-state battery research in recent years, among which sulfide all-solid-state batteries show the most promising development prospects.

[0003] However, sulfide-based all-solid-state batteries also face several challenges. For example, the significant difference in Young's modulus between the cathode material and the sulfide electrolyte means that even though the sulfide electrolyte is relatively soft, good interfacial contact cannot be achieved between solid powders through cold pressing alone, leading to high interfacial impedance. Furthermore, the positive electrode active material undergoes volume deformation during charge and discharge, causing particle breakage and interfacial contact failure. Thermodynamic instability exists between the sulfide solid-state electrolyte and conventional oxide cathodes. Additionally, the narrow electrochemical window of the sulfide solid-state electrolyte makes it difficult to match with high-voltage, high-capacity, high-nickel cathode materials. Therefore, it is necessary to improve the solid-solid interface of the sulfide all-solid-state battery cathode to enhance its electrochemical performance.

[0004] To optimize the solid-solid interface of the cathode in sulfide all-solid batteries, existing technologies have introduced solutions that incorporate liquid electrolyte components to optimize the solid-solid interface. However, these solutions pose a risk of flammability and are prone to migration under long-term cycling and high-voltage packaging conditions, leading to a deterioration of the solid-solid interface contact. Furthermore, they may cause new problems after seeping into the electrolyte or anode side. Solutions that introduce solid polymers such as polyethylene oxide are also available, but their high-voltage stability is limited, making it difficult to match with high-voltage, high-capacity, high-nickel cathode materials, thus limiting further improvements in battery energy density. Summary of the Invention

[0005] The purpose of this invention is to provide an ionic gel, its preparation method, and its application in the cathode material of sulfide all-solid-state batteries, aiming to solve the problems of poor battery cycle capacity, short cycle life, and poor rate performance caused by solid-solid interface contact failure during charge-discharge cycles in sulfide all-solid-state battery cathodes. This invention discloses an ionic gel with excellent overall performance, composed of a thermally stable ionic liquid polymer and a plasticizer; by rationally optimizing the ratio of the ionic liquid polymer, plasticizer, and lithium salt, this ionic gel possesses both high-voltage stability and high ionic conductivity (10⁻⁶ Ω·cm). -3 -10-4 (mS / cm), while maintaining thermodynamic compatibility with sulfide electrolytes. By matching with high-voltage, high-capacity high-nickel cathode materials, the ion gel with certain adhesion is stabilized at the cathode interface of sulfide solid-state batteries, effectively optimizing the solid-solid contact interface of the cathode in the long term, reducing interface impedance, further enriching the lithium-ion transport path inside the electrode, and improving the cycle stability and rate performance of sulfide all-solid-state batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An ionic gel is disclosed, comprising an ionic liquid polymer and a plasticizer. The ionic liquid polymer contains dissolved lithium salt 1, and the plasticizer contains dissolved lithium salt 2.

[0008] The cation of the ionic liquid polymer is polydimethyldiallylammonium, and the anion is at least one of bis(trifluoromethylsulfonylimide) anion, bis(trifluoromethylsulfonylimide) anion, hexafluorophosphate anion, difluorooxalateborate anion, and tetrafluoroborate anion.

[0009] The weight-average molecular weight of the ionic liquid polymer is one of less than 100,000, 100,000-200,000, or 200,000-350,000.

[0010] Even better, the weight-average molecular weight of the ionic liquid polymer is less than 100,000.

[0011] Further, the plasticizer is at least one selected from N-methyl-N-butylpyrrole bis(fluorosulfonyl)imide, N-methyl-N-butylpyrrole bis(trifluoromethylsulfonyl)imide, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, and vinylene carbonate.

[0012] Furthermore, lithium salt 1 and lithium salt 2 are independently selected from at least one of lithium bis(trifluoromethylsulfonylimide), lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium nitrate, or lithium difluorophosphate.

[0013] The aforementioned ionic gel has the following mass ratio of components: 5%-95% ionic liquid polymer and 5%-95% plasticizer. Specifically, the mass ratio of lithium salt 1 to ionic liquid polymer is 15-60:100, and the mass ratio of lithium salt 2 to plasticizer is 10-50:100.

[0014] The above-mentioned method for preparing ionic gel includes mixing the ionic liquid polymer with lithium salt 1 and plasticizer with lithium salt 2 in a solvent to obtain mixture 1 and mixture 2, then mixing mixture 1 and mixture 2 in an appropriate ratio, removing the solvent, and thus obtaining the ionic gel.

[0015] Further, the solvent is at least one selected from cyclohexane, p-xylene, acetonitrile, dichloromethane, ethyl acetate, diethyl ether, toluene, tetrahydrofuran, N-methylpyrrolidone, and acetone.

[0016] The mass ratio of each component in the positive electrode of the sulfide all-solid-state battery using the above-mentioned ion gel is 0.5%-10%, positive electrode active material 60%-80%, conductive agent 1%-5%, and sulfide solid electrolyte 20%-35%.

[0017] Furthermore, an ion gel for a sulfide all-solid-state battery and its application in the positive electrode includes the following steps:

[0018] S1. Dissolve the ionic liquid polymer, lithium salt, and plasticizer in an appropriate amount of solvent in a certain proportion to prepare a solution of 0.1 g / ml, and stir at 25-80 ℃ for 0.5-10 h to obtain a homogeneous solvent, wherein the number of lithium salt types is at least one.

[0019] S2. Weigh 60-80 mg of positive electrode active material, 20-35 mg of sulfide solid electrolyte, and 0.5-5 mg of conductive agent, and add 5-50 μL of the above homogeneous solution to it. Add the solvent used in S1 to the mixture to obtain a solution with a solid content of about 10%, and stir at 25-60 ℃ for 0.5-4 h to obtain a homogeneous suspension.

[0020] S3. Remove the solvent from the suspension by vacuuming at a temperature of 25-60 ℃ to obtain a dry cathode material;

[0021] S4. Place the obtained solid powder in an agate mortar and grind it for 10-60 min to obtain a uniform sulfide solid battery cathode material.

[0022] Furthermore, a sulfide all-solid-state battery was assembled using the aforementioned positive electrode material, Li6PS5Cl sulfide solid electrolyte, and lithium indium alloy negative electrode.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) This invention discloses an ionic gel with excellent comprehensive performance, which is composed of an ionic liquid polymer with good thermal stability and a plasticizer; by rationally optimizing the ratio of ionic liquid polymer, plasticizer and lithium salt, the ionic gel has both high pressure stability and high ionic conductivity (10). -3 -10 -4 (mS / cm), while maintaining thermodynamic compatibility with sulfide electrolytes;

[0025] (2) When this high-performance ion gel is applied to the cathode of a sulfide all-solid-state battery, it can be matched with high-voltage, high-capacity high-nickel cathode materials, while enriching the lithium-ion transport path inside the electrode, which helps to realize a high-energy-density sulfide all-solid-state battery.

[0026] (3) The ion gel is solid and does not have the fluidity of a liquid; it also has a certain degree of adhesion, which can stabilize it at the internal interface of the positive electrode and effectively suppress the side reaction between the sulfide electrolyte and the high nickel positive electrode material; under high packaging pressure, it can optimize the solid-solid interface of the positive electrode for a long time, reduce the interface impedance, and improve the rate performance of the sulfide all-solid battery.

[0027] (4) In addition, the raw materials for this ion gel are readily available, the preparation process is simple, it is environmentally friendly and safe.

[0028] Based on the above advantages, the present invention significantly improves the electrochemical performance of sulfide solid-state batteries. Attached Figure Description

[0029] Figure 1 This is a graph showing the oxidative stability of the ionogel prepared in Example 1;

[0030] Figure 2 Thermogravimetric analysis (TGA) results of the ionogel prepared in Example 1;

[0031] Figure 3 Example 1: Sulfide Solid State Mold Battery (3wt% Py) 14 Long-cycle performance of FSI+PDADMAFSI)NMC811|Li6PS5Cl|LiIn at 100MPa packaging pressure and 0.5C / 0.5C charge / discharge rate;

[0032] Figure 4 Example 1: Sulfide Solid State Mold Battery (3wt% Py) 14 Rate performance of FSI+PDADMAFSI)NMC811|Li6PS5Cl|LiIn and NMC811|Li6PS5Cl|LiIn under 100MPa packaging pressure. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0034] The following detailed description, in conjunction with specific embodiments and comparative examples, illustrates the process. Unless otherwise specified, all conditions in the following embodiments are performed under standard conditions or conditions recommended by the manufacturer. Reagents and instruments used, unless otherwise stated, are commercially available, standard products.

[0035] Example 1

[0036] This embodiment provides an ion gel for sulfide all-solid-state batteries, its application in the cathode, and the sulfide all-solid-state battery itself. The implementation steps are as follows:

[0037] (1) Preparation of ionogel: First, in the ionogel, the mass ratio of plasticizer to ionic liquid polymer is 60:40. Lithium salt is selected as LiFSI, and plasticizer is Py. 14 FSI, the polymeric ionic liquid is PDADMAFSI (M w <100,000). Lithium salt LiFSI in Py 14 The mass fraction of FSI is 12.5%, and the mass fraction of LiFSI in PDADMAFSI is 20%. Weigh out PDADMAFSI, LiFSI, and Py according to the above proportions. 14 FSI was mixed in acetonitrile solvent and magnetically stirred at 25 °C for 10 h to obtain a homogeneous solution with a concentration of 0.1 g / ml.

[0038] (2) The mass ratio of positive electrode active material, sulfide electrolyte, conductive agent, and ion gel is 70:26:1:3. Acetonitrile solvent is added to obtain a solution with a solid content of about 10%. The solution is magnetically stirred at 25 °C for 1 h to obtain a uniform suspension. The acetonitrile solvent in the suspension is removed by vacuum at 40 °C, and then the solution is hand-ground in a mortar for 1 h to obtain a dry positive electrode material.

[0039] (3) Assemble a sulfide all-solid-state battery using the above positive electrode material, Li6PS5Cl sulfide solid electrolyte, and lithium indium alloy negative electrode.

[0040] Figure 1 The oxidation stability of the ion gel prepared in Example 1 was tested, and the ion gel exhibited an oxidation stability of >5 V. Figure 2 Thermogravimetric analysis of the prepared ionogel showed that it exhibited thermal stability below 245 °C; the ionogel also demonstrated high oxidative stability and good thermal stability. Figure 3 For sulfide solid-state mold batteries (3wt% Py 14 The long-cycle performance of FSI+PDADMAFSI)NMC811|Li6PS5Cl|LiIn at 0.5C / 0.5C is shown in the figure. Figure 3 It can be seen that the battery capacity does not decrease after 50 cycles; Figure 4 For sulfide solid-state mold batteries (3wt% Py 14 The rate performance graphs of FSI+PDADMAFSI)NMC811|Li6PS5Cl|LiIn and NMC811|Li6PS5Cl|LiIn are presented by... Figure 4It can be seen that the battery with ion gel introduced exhibits a discharge specific capacity exceeding 100 mAh / g at 5C, significantly higher than that of the blank sample. Therefore, the introduction of ion gel into the cathode material of sulfide solid-state batteries significantly improves the electrochemical performance of sulfide solid-state batteries.

[0041] Example 2

[0042] This embodiment provides an ion gel for sulfide all-solid-state batteries and its application in the cathode and sulfide all-solid-state batteries. The main difference from Embodiment 1 is that the mass ratio of polymeric ionic liquid to plasticizer in the ion gel is different.

[0043] (1) Preparation of ionogel: First, the mass ratio of plasticizer to polymeric ionic liquid in the ionogel is 40:60. Lithium salt is selected as LiFSI, and plasticizer is Py. 14 FSI, the polymeric ionic liquid is PDADMAFSI (M w <100,000). Lithium salt LiFSI in Py 14 The mass fraction of FSI is 12.5%, and the mass fraction of LiFSI in PDADMAFSI is 20%. PDADMAFSI, LiFSI, and Py are weighed according to the above proportions. 14 FSI was mixed in acetonitrile solvent and magnetically stirred at 25 °C for 10 h to obtain a homogeneous solution with a concentration of 0.1 g / ml.

[0044] (2) The mass ratio of positive electrode active material, sulfide electrolyte, conductive agent and ion gel is 70:26:1:3. Acetonitrile solvent is added to obtain a solution with a solid content of about 10%. The solution is magnetically stirred at 25 °C for 1 h to obtain a uniform suspension. The acetonitrile solvent in the suspension is removed by vacuum at 40 °C, and then the solution is hand-ground in a mortar for 1 h to obtain a dry positive electrode material.

[0045] (3) Assemble a sulfide all-solid-state battery using the above positive electrode material, Li6PS5Cl sulfide solid electrolyte, and lithium indium alloy negative electrode.

[0046] Example 3

[0047] This embodiment provides an ion gel for sulfide all-solid-state batteries and its application in the cathode, and a sulfide all-solid-state battery. The main difference from Embodiment 1 is that the mass fraction of the ion gel introduced into the cathode material is different.

[0048] (1) Preparation of ionogel: First, the mass ratio of plasticizer to polymeric ionic liquid in the ionogel is 60:40. Lithium salt is selected as LiFSI, and plasticizer is Py. 14 FSI, the polymeric ionic liquid is PDADMAFSI (M w <100,000). Lithium salt LiFSI in Py14 The mass fraction of FSI is 12.5%, and the mass fraction of LiFSI in PDADMAFSI is 20%. PDADMAFSI, LiFSI, and Py are weighed according to the above proportions. 14 FSI was mixed in acetonitrile solvent and magnetically stirred at 25 °C for 10 h to obtain a homogeneous solution with a concentration of 0.1 g / ml.

[0049] (2) The mass ratio of positive electrode active material, sulfide electrolyte, conductive agent and ion gel is 70:28:1:1. Acetonitrile solvent is added to obtain a solution with a solid content of about 10%. The solution is stirred at 25 °C for 1 h to obtain a uniform suspension. The acetonitrile solvent in the suspension is removed by vacuum at 40 °C. The solution is then placed in a mortar and ground by hand for 1 h to obtain a dry positive electrode material.

[0050] (3) Assemble a sulfide all-solid-state battery using the above positive electrode material, Li6PS5Cl sulfide solid electrolyte, and lithium indium alloy negative electrode.

[0051] Example 4

[0052] This embodiment provides an ion gel for sulfide all-solid-state batteries and its application in the cathode, as well as the sulfide all-solid-state battery itself. The main difference from Embodiment 1 is the choice of plasticizer in the ion gel.

[0053] (1) Preparation of ionogel: First, in the ionogel, the mass ratio of plasticizer to polymeric ionic liquid is 60:40. LiFSI is selected as the lithium salt, Py14TFSI as the plasticizer, and PDADMAFSI (M...) as the polymeric ionic liquid. w <100,000). Lithium salt LiFSI in Py 14 The mass fraction of TFSI is 11.9%, and the mass fraction of LiFSI in PDADMAFSI is 20%. PDADMAFSI, LiFSI, and Py are weighed according to the above proportions. 14 TFSI was dissolved in acetonitrile solvent and magnetically stirred at 25 °C for 10 h to obtain a homogeneous solution with a concentration of 0.1 g / ml.

[0054] (2) The mass ratio of positive electrode active material, sulfide electrolyte, conductive agent and ion gel is 70:26:1:3. Acetonitrile solvent is added to obtain a solution with a solid content of about 10%. The solution is magnetically stirred at 25°C for 1 h to obtain a uniform suspension. The acetonitrile solvent in the suspension is removed by vacuum at 40°C, and then the solution is hand-ground in a mortar for 1 h to obtain a dry positive electrode material.

[0055] (3) Assemble a sulfide all-solid-state battery using the above positive electrode material, Li6PS5Cl sulfide solid electrolyte, and lithium indium alloy negative electrode.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An ionogel, characterized in that, The ionogel is composed of an ionic liquid polymer and a plasticizer, wherein lithium salt 1 is dissolved in the ionic liquid polymer and lithium salt 2 is dissolved in the plasticizer.

2. The ionogel according to claim 1, characterized in that, The cation of the ionic liquid polymer is polydimethyldiallylammonium, and the anion is at least one of bis(trifluoromethylsulfonylimide) anion, bis(trifluoromethylsulfonylimide) anion, hexafluorophosphate anion, difluorooxalateborate anion, and tetrafluoroborate anion. The weight-average molecular weight of the ionic liquid polymer is one of less than 100,000, 100,000-200,000, or 200,000-350,000.

3. The ionogel according to claim 1, characterized in that, The plasticizer is at least one of N-methyl-N-butylpyrrole bis(fluorosulfonyl)imide, N-methyl-N-butylpyrrole bis(trifluoromethylsulfonyl)imide, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, and vinylene carbonate.

4. The ionogel according to claim 1, characterized in that, Lithium salt 1 and lithium salt 2 are independently selected from at least one of lithium bis(trifluoromethylsulfonylimide), lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium nitrate, or lithium difluorophosphate.

5. The ionogel according to claim 1, characterized in that, The mass ratio of each component in the ionic gel is as follows: 5%-95% ionic liquid polymer and 5%-95% plasticizer; wherein, the mass ratio of lithium salt 1 to ionic liquid polymer is 15-60:100, and the mass ratio of lithium salt 2 to plasticizer is 10-50:

100.

6. A method for preparing an ion gel according to any one of claims 1 to 5, the method comprising: The ionic liquid polymer and lithium salt 1, plasticizer and lithium salt 2 are mixed evenly in a solvent to obtain mixture 1 and mixture 2. Then, mixture 1 and mixture 2 are blended in an appropriate ratio and the solvent is removed to obtain the ionic gel. The solvent is at least one selected from cyclohexane, p-xylene, acetonitrile, dichloromethane, ethyl acetate, diethyl ether, toluene, tetrahydrofuran, N-methylpyrrolidone, and acetone.

7. The application of the ion gel according to any one of claims 1 to 5 in the positive electrode of a sulfide all-solid-state battery, characterized in that, The cathode of a sulfide-based all-solid-state battery includes an ion gel. The mass ratio of each component in the cathode of a sulfide-based all-solid-state battery is as follows: ion gel 0.5%-10%, cathode active material 60%-80%, conductive agent 1%-5%, and sulfide solid electrolyte 20%-35%.

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