A sulfide composite electrolyte and its preparation method and application

Abstract

The present invention discloses a sulfide composite electrolyte and a preparation method and application thereof, which relates to the technical field of solid-state batteries. An organic coating agent and an organic solvent are mixed, oxide nanoparticles are dispersed therein, a precipitate is extracted and dried to obtain an oxide@organic coating agent composite material, and then the sulfide electrolyte is subjected to ball milling treatment to obtain the sulfide composite electrolyte, which solves the above-mentioned lithium dendrite and self-discharge problems existing in sulfide all-solid-state batteries. The prepared sulfide composite electrolyte can smoothly transmit lithium ions, while blocking the electron transfer between the sulfide electrolyte interface, reducing the electronic conductivity, and helping to inhibit the growth of lithium dendrites along the gaps of the sulfide electrolyte, which can reduce the lithium dendrite problem in solid-state batteries. The preparation method provided by the present invention has a simple process, low equipment requirements, and is easy to scale up.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a sulfide composite electrolyte and a preparation method and application thereof. Background Art

[0002] Sulfide all-solid-state lithium batteries have attracted widespread attention due to their safety and potential high energy density. Among various SSE systems, sulfide electrolytes have high ionic conductivity compared to polymer solid electrolytes and better electrode / electrolyte interface compatibility than rigid oxide solid electrolytes. Sulfide electrolytes can react with the electrode interface to form a solid electrolyte interface (SEI), producing an ionic conductivity interface. This interface can ensure that Li + The smooth transport of sulfide electrolytes and the suppression of further side reactions between electrode materials are achieved.

[0003] Although sulfide solid electrolytes have high compatibility between high ionic conductivity and electrode / electrolyte interface, the lithium dendrite problem also hinders the industrial development of sulfide all-solid-state batteries. In early studies, some researchers attributed the cause to the mismatch of the Li / SSE interface, which caused Li dendrites to grow from the interface and then gradually penetrated into the bulk of the sulfide electrolyte, causing battery short circuit. However, recent research results show that the growth of Li dendrites starts from the inside of the sulfide electrolyte, and Li metal is directly deposited in the gap between the sulfide electrolyte interface and gradually spreads and grows. The cause of this problem is the neglected electronic conductivity of the sulfide solid electrolyte. Among them, Li+ is preferentially reduced by electrons in the sulfide solid electrolyte to form local Li filaments, which can well explain the phenomenon of Li dendrites growing along the gap between the sulfide electrolyte. Based on this phenomenon, blocking electron transfer on the sulfide electrolyte can be considered as an effective strategy to inhibit the formation of Li dendrites in sulfide all-solid-state batteries. In addition, the high electronic conductivity of the sulfide electrolyte will lead to electron transfer inside the sulfide all-solid-state battery, resulting in severe self-discharge. However, the self-discharge problem has been neglected.

[0004] For the performance of lithium-ion batteries, the ionic conductivity and electronic conductivity of sulfide electrolytes play a vital role. High ionic conductivity can ensure the rapid migration of lithium ions during the battery charging and discharging process, realize high-rate charging and discharging of the battery, and improve the power performance of the battery; while low electronic conductivity effectively prevents battery self-discharge and improves the battery's energy retention capacity and safety. However, existing technologies face many challenges in regulating the ionic conductivity and electronic conductivity of sulfide electrolytes. On the one hand, in the process of improving ionic conductivity, electronic conductivity often increases, increasing the risk of battery self-discharge. For example, when lithium ion channels are increased by optimizing the crystal structure, the structure will be more open and disordered, providing more transmission paths for electrons; for example, when ionic conductivity is increased by introducing impurities or defects, it will become a capture or scattering center for electrons, increasing the electron conduction pathway. On the other hand, when reducing electronic conductivity, ionic conductivity will be greatly sacrificed, which seriously affects the charging and discharging effect of the battery. For example, by adjusting the ratio of elements to increase the localization of electrons, it makes it more difficult for electrons to conduct in the crystal, but this change in chemical bonds can easily affect the interaction between lithium ions and surrounding atoms, making the migration of lithium ions more difficult; for example, some interface layers are formed at the electrode / electrolyte interface to reduce electronic conductivity, but these interface layers often have high resistance, which will hinder the transmission of lithium ions between the electrode and the electrolyte. At present, there are few reports on achieving a good balance between the two. This dilemma also limits the widespread application and performance improvement of sulfide electrolytes in lithium-ion batteries. An innovative method is urgently needed to break through this technical bottleneck. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a sulfide composite electrolyte and a preparation method and application thereof, by improving the preparation method of the electrolyte, the electronic conductivity is greatly reduced under the premise of slightly reducing the ionic conductivity.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] <First aspect>

[0008] The present invention provides a method for preparing a sulfide composite electrolyte, comprising the following steps:

[0009] S1, mixing an organic coating agent and an organic solvent to obtain a mixed solution;

[0010] S2, dispersing oxide nanoparticles in the mixed solution to obtain a dispersed solution;

[0011] S3, extracting the precipitate in the dispersed solution, and drying it to obtain an oxide@organic coating agent composite material;

[0012] S4, mixing the sulfide electrolyte with the oxide@organic coating agent composite material, performing a mixing treatment, and obtaining the sulfide composite electrolyte.

[0013] As an embodiment, the organic coating agent includes one or more of polyvinylidene fluoride, 1,3-propylene glycol, polyimide, polyacrylonitrile, and polyetherimide.

[0014] In some embodiments, the organic coating agent is selected from one or more of polyvinylidene fluoride, polyetherimide, polyimide, and 1,3-propylene glycol.

[0015] In some embodiments, the organic coating agent is polyvinylidene fluoride or polyetherimide.

[0016] As one embodiment, the oxide includes one or more of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, silicon oxide, zinc oxide, titanium oxide, and barium titanate.

[0017] In some embodiments, the oxide is selected from lithium lanthanum titanium oxide or silicon oxide.

[0018] As an embodiment, the sulfide electrolyte includes one or more of LiGePS, LiPS, LiPSCl, LiPSBr and LiPSI.

[0019] In some embodiments, the sulfide electrolyte is Li6PS5Cl.

[0020] As an embodiment, the mass ratio of the organic coating agent to the oxide is 1: (10~35).

[0021] In some embodiments, the mass ratio of the organic capping agent to the oxide is 1 to 32.33.

[0022] In some embodiments, the mass ratio of the organic capping agent to the oxide is 1:10.78.

[0023] As an embodiment, the mass ratio of the sulfide electrolyte and the oxide@organic coating agent composite material is (45~55):1.

[0024] In some embodiments, the mass ratio of the sulfide electrolyte to the oxide@organic coating agent composite material is 49:1.

[0025] As an embodiment, the organic solvent includes one or more of methanol, ethanol, N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, and tetrahydrofuran.

[0026] In some embodiments, the organic solvent is N-methylpyrrolidone or acetonitrile.

[0027] As an embodiment, the dispersion solution is dispersed by one or more of ultrasound, stirring, and shaking.

[0028] In some embodiments, the dispersion solution is dispersed by ultrasound.

[0029] As an embodiment, the precipitate is extracted from the dispersed solution by one or more of rotary evaporation, centrifugation, and suction filtration.

[0030] In some embodiments, the extraction is performed by suction filtration.

[0031] As an embodiment, the precipitate is dried by vacuum drying.

[0032] As an embodiment, the drying temperature of the precipitate is 60-100°C.

[0033] As an embodiment, the drying time of the precipitate is 6 to 24 hours.

[0034] As an embodiment, in step S4, the mixing process is performed by ball milling.

[0035] As an embodiment, the ball mill uses two grinding balls with different specifications.

[0036] In some embodiments, the diameter sizes are 3 mm and 5 mm, respectively, with a mass ratio of 2:1.

[0037] As an embodiment, the ball-to-material ratio of the ball mill is 1-1.5:1.

[0038] In some embodiments, the ball-to-material ratio of the ball mill is 1.3: 1. As an embodiment, the rotation speed of the ball mill is 150-250 rpm, and the time is 3-5 h.

[0039] In some embodiments, the ball milling speed is 200 rpm and the time is 4 hours.

[0040] <Second Aspect>

[0041] The invention provides a sulfide composite electrolyte, which is prepared by adopting the preparation method of the sulfide composite electrolyte.

[0042] <Third Aspect>

[0043] The present invention provides an application of a sulfide composite electrolyte in a solid-state battery.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] In view of the lithium dendrite and self-discharge problems existing in the sulfide all-solid-state battery described in the background technology, the present invention provides a method for preparing a sulfide composite electrolyte, wherein oxide particles with a high dielectric constant and an organic coating agent can provide an electronic insulating layer well, and after being composited with the sulfide electrolyte, the organic coating agent has good deformation adaptability, effectively alleviates the rigid interface contact between the sulfide electrolyte particles and the oxide particles, can form a good interface bonding with the sulfide electrolyte, hinders the migration of electrons, reduces the electronic conductivity of the sulfide composite electrolyte (the decrease rate exceeds 95%), while still maintaining a good ionic conductivity (the decrease rate is less than 25%), therefore, can inhibit the electron transfer inside the sulfide all-solid-state battery, thereby reducing the self-discharge effect of the battery and improving the voltage stability of the solid-state sulfide battery.

[0046] The sulfide electrolyte in this composite material can smoothly transmit lithium ions, while blocking the electron transfer between the sulfide electrolyte interfaces, reducing electronic conductivity, helping to inhibit the growth of lithium dendrites along the sulfide electrolyte gaps, and reducing the lithium dendrite problem in solid-state batteries.

[0047] The method for preparing a sulfide composite electrolyte provided by the present invention has simple process, low requirements on equipment and is easy to scale up. DETAILED DESCRIPTION

[0048] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for preparing a sulfide composite electrolyte, comprising the following steps:

[0051] S1, adding 6 mg of an organic coating agent (polyvinylidene fluoride PVDF in this embodiment, with a molecular weight of 40W) into 400 mg of an organic solvent (N-methylpyrrolidone NMP in this embodiment) to dissolve and obtain a mixed solution;

[0052] S2, 194 mg of oxide nanoparticles (lithium titanium oxide (Li 3x La 2 / 3-x TiO3, x=0.11) powder, 200 nm particle size, marked as LLTO) is added to the above mixed solution and ultrasonically dispersed to obtain a dispersed solution;

[0053] S3, filtering the dispersed solution, collecting the precipitate, and vacuum drying the precipitate at 60-80° C. to obtain a composite material of an oxide-coated organic coating agent (expressed as oxide@organic coating agent). In this embodiment, a composite material of lithium lanthanum titanate coated with PVDF is obtained, named LLTO@PVDF;

[0054] S4. 294 mg of sulfide electrolyte powder (Li6PS5Cl, D50 particle size of 2μm) and 6 mg of LLTO@PVDF composite material were ball-milled together. The grinding balls were 3mm and 5mm zirconium balls, with a mass ratio of 2:1, a ball-to-material ratio of 1.3:1, a ball-milling speed of 200 rpm, and a time of 4 h to obtain a sulfide composite electrolyte.

[0055] Example 2

[0056] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0057] In step S2, the oxide is silicon dioxide powder with a particle size D50 of 50 nm;

[0058] In step S3, a composite material of PVDF coated on the surface of silicon dioxide is obtained, named SiO2@PVDF, and is used for subsequent treatment in step S4.

[0059] Example 3

[0060] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0061] In step S1, the organic coating agent is polyetherimide PEI, and the organic solvent is acetonitrile;

[0062] In step S3, a composite material of lithium lanthanum titanate coated with PEI is obtained, named LLTO@PEI, and used for subsequent treatment in step S4.

[0063] Example 4

[0064] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0065] In step S1, the organic coating agent is 1,3-propylene glycol (PEO), and the organic solvent is acetonitrile;

[0066] In step S3, a composite material of lithium lanthanum titanate coated with PEO is obtained, named LLTO@PEO, and used for subsequent treatment in step S4.

[0067] Example 5

[0068] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0069] In step S1, the organic coating agent is PEO;

[0070] In step S3, a composite material of lithium lanthanum titanate coated with PEO is obtained, named LLTO@PEO, and used for subsequent treatment in step S4.

[0071] Example 6

[0072] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0073] In step S1, the organic coating agent is polyimide particles (DuPont, USA, model SP-202);

[0074] In step S3, a composite material of lithium lanthanum titanate coated with PEO is obtained, named LLTO@PI, and used for subsequent treatment in step S4.

[0075] Example 7

[0076] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0077] In step S1, the mass of PVDF is 18 mg.

[0078] Comparative Example 1

[0079] The electrolyte material of this comparative example is Li6PS5Cl, and the D50 particle size is 2 μm.

[0080] Comparative Example 2

[0081] This comparative example provides a method for preparing a sulfide composite electrolyte that does not contain oxides, and the steps are:

[0082] S1. Add 6 mg of an organic coating agent (PEI in this comparative example) into 400 mg of an organic solvent (acetonitrile) and dissolve to obtain a mixed solution;

[0083] S2, adding 294 mg of sulfide electrolyte to the mixed solution, and performing ultrasonic dispersion to obtain a dispersed solution;

[0084] S3. Extract the precipitate from the dispersed solution obtained in step S2, and dry it under vacuum at 60-80° C. to obtain a composite material of sulfide electrolyte coated with PEI, named LiPSCl@PEI.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing a sulfide composite electrolyte that does not contain oxides, and the steps are:

[0087] S1. Add 6 mg of an organic coating agent (PEO in this comparative example) into 400 mg of an organic solvent (acetonitrile) and dissolve to obtain a mixed solution;

[0088] S2, adding 294 mg of sulfide electrolyte to the mixed solution, and performing ultrasonic dispersion to obtain a dispersed solution;

[0089] S3. Extract the precipitate from the dispersed solution obtained in step S2, and dry it under vacuum at 60-80° C. to obtain a composite material of sulfide electrolyte coated with PEO, named LiPSCl@PEO.

[0090] Comparative Example 4

[0091] This comparative example provides a method for preparing a sulfide composite electrolyte without an organic coating agent, the steps being:

[0092] 294 mg of sulfide electrolyte and 194 mg of LLTO were ball-milled at a speed of 200 rpm for 4 h to obtain a sulfide composite electrolyte named LiPSCl / LLTO.

[0093] Comparative Example 5

[0094] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0095] In step S1, the mass of PVDF is 50 mg.

[0096] Comparative Example 6

[0097] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0098] S4. 200 mg of sulfide electrolyte powder (Li6PS5Cl, D50 particle size of 2 μm) and 100 mg of LLTO@PVDF composite were ball milled together.

[0099] Comparative Example 7

[0100] This embodiment provides a method for preparing a sulfide composite electrolyte, and the steps are basically the same as those in Embodiment 1, except that:

[0101] In step S1, the organic solvent is acetonitrile.

[0102] Application and performance testing:

[0103] The electrolyte materials obtained in the above-mentioned embodiments and comparative examples were placed in all-solid-state battery molds, respectively, and maintained at a pressure of 50 Mbar for 3 min. Blocking electrodes were matched at both ends, and the ionic conductivity and electronic conductivity were tested and analyzed using the AC impedance method. The results after detection are shown in Table 1. The ionic conductivity and electronic conductivity of Comparative Example 1 are used as the standard. The decrease rates of the corresponding performances of the embodiments and comparative examples are compared and analyzed. The results are shown in Table 2.

[0104] The formula for calculating ionic conductivity is as follows:

[0105]

[0106] In the formula, is the ionic conductivity of the solid electrolyte, in ms / cm;

[0107] L is the thickness of the solid electrolyte in cm;

[0108] R is the intrinsic resistance of the solid electrolyte, in Ω;

[0109] S is the cross-sectional area of ​​the solid electrolyte, in cm 2 .

[0110] The electronic conductivity parameter is measured by it chronoamperometry, and the calculation formula is as follows:

[0111]

[0112] In the formula,

[0113] is the electronic conductivity of the solid electrolyte, in S / cm;

[0114] is the solid electrolyte volume resistance, in Ω.

[0115] Table 1 Test results of electrolyte membranes of various embodiments and comparative examples

[0116]

[0117] Table 2 Relevant performance degradation rate of electrolyte membranes in various embodiments and comparative examples

[0118]

[0119] It can be seen from the test results of Table 1 and Table 2 that, compared with Comparative Example 1 of pure sulfide electrolyte, the improved sulfide composite electrolyte cleverly balances the conduction characteristics of ions and electrons, and the reduction rate of ion conductivity is stably controlled at a relatively low level (below 25%, especially the reduction rate of Examples 1 to 3 is below 10%), while the reduction rate of electronic conductivity is extremely high (above 95%, especially the reduction rate of Examples 1 to 3 is above 98%), which means that the improved sulfide composite electrolyte can still ensure the efficient transmission of lithium ions in the electrolyte under the premise of slightly reducing the ion conductivity; and the great reduction of electronic conductivity effectively prevents the occurrence of battery self-discharge, and significantly improves the safety and energy retention capacity of the battery.

[0120] In summary, the present invention provides a method for preparing a sulfide composite electrolyte, first dissolving an organic coating agent in an organic solvent to obtain a mixed solution; then dispersing the oxide in the mixed solution, filtering and drying to obtain an oxide@organic coating agent composite material. Through this step, a layer of organic coating agent is coated on the surface of the oxide particles; then it is mixed with a sulfide electrolyte to prepare a composite sulfide electrolyte material with low electronic conductivity; the composite sulfide electrolyte material prepared by this method has the characteristics of simple process and easy mass production. It also has the following advantages:

[0121] (1) The excellent deformation adaptability of the organic coating layer can effectively buffer the rigid interface contact between the oxide particles and the sulfide electrolyte particles. The oxide@organic coating composite material acts as an electronic insulating layer, inhibiting the transfer of electrons in the sulfide electrolyte and effectively inhibiting the growth of Li dendrites along the gaps in the sulfide electrolyte, thereby reducing the problem of lithium dendrites in solid-state batteries.

[0122] (2) The low electronic conductivity of sulfide electrolytes will inhibit electron transfer within sulfide all-solid-state batteries, thereby reducing the self-discharge effect of the battery and improving the voltage stability of solid-state sulfide batteries.

[0123] (3) In particular, in Example 1, when LLTO particles are used as the oxide, due to its unique structure, it is more conducive to the migration and diffusion of lithium ions.

[0124] It can be seen from the comparative examples that a layer of high dielectric constant organic coating agent is directly coated on the surface of the sulfide electrolyte to prepare a sulfide@organic coating agent composite electrolyte material. There are the following problems:

[0125] (1) When sulfide electrolyte is directly mixed with high dielectric constant oxide particles, because both materials are rigid materials and the solid-solid interface is difficult to handle, it is usually difficult to achieve a decrease in electronic conductivity, and lithium ions are easily precipitated in the gaps of the composite material to form lithium dendrites.

[0126] (2) Organic coating agents generally have lower lithium ion conductivity, resulting in lower lithium ion conductivity when the sulfide@organic coating agent composite material is used as an electrolyte.

[0127] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a sulfide composite electrolyte, characterized in that: The following steps are involved: S1, mixing an organic coating agent and an organic solvent to obtain a mixed solution; S2, dispersing oxide nanoparticles in the mixed solution to obtain a dispersed solution; S3, extracting the precipitate in the dispersed solution, and drying it to obtain an oxide@organic coating agent composite material; S4, mixing the sulfide electrolyte with the oxide@organic coating agent composite material, and performing a mixing treatment to obtain the sulfide composite electrolyte; The organic coating agent includes one or more of polyvinylidene fluoride, 1,3-propylene glycol, polyimide, polyacrylonitrile, and polyetherimide; the oxide includes one or more of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, silicon dioxide, zinc oxide, titanium oxide, and barium titanate; the sulfide electrolyte is LiPSCl; the mass ratio of the organic coating agent to the oxide is 1: (10~35); the mass ratio of the sulfide electrolyte to the oxide@organic coating agent composite material is (45~55):

1.

2. The method for preparing a sulfide composite electrolyte according to claim 1, characterized in that: The organic coating agent includes one or more of polyvinylidene fluoride, 1,3-propylene glycol, polyimide, and polyetherimide, and the oxide is lithium lanthanum titanium oxide or silicon dioxide.

3. The method for preparing the sulfide composite electrolyte according to claim 1, characterized in that: The organic solvent includes one or more of methanol, ethanol, N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile and tetrahydrofuran.

4. The method for preparing a sulfide composite electrolyte according to claim 1, characterized in that: The organic solvent is N-methylpyrrolidone or acetonitrile.

5. The method for preparing a sulfide composite electrolyte according to any one of claims 1 to 4, characterized in that: It also includes one or more of the following technical features: A. The dispersion method of the dispersion solution is one or more of ultrasound, stirring, and vibration; B. extracting the precipitate from the dispersed solution by one or more of rotary evaporation, centrifugation, and suction filtration; C. The drying method of the precipitate is vacuum drying; D. The mixing process is carried out by ball milling.

6. A sulfide composite electrolyte, characterized in that: The sulfide composite electrolyte is prepared by the preparation method of any one of claims 1 to 5.

7. The sulfide composite electrolyte according to claim 6, characterized in that Suitable for application in solid-state batteries.

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