Dry-method solid electrolyte membrane and preparation method and application thereof

Abstract

The invention discloses a dry-method solid-state electrolyte membrane as well as a preparation method and application thereof, belongs to the technical field of dry-method solid-state electrolyte membranes, and overcomes the defects that in the prior art, a relatively thin dry-method solid-state electrolyte membrane is easy to crack, cannot be self-supported and is low in ionic conductivity, and the solid-state electrolyte membrane is in poor contact with a solid-solid interface of an electrode. The dry-method solid electrolyte membrane comprises the following components in percentage by mass: 90%-96% of a solid electrolyte material, 1.5%-3% of polytetrafluoroethylene and 1%-8.5% of a lithiated polymer, the lithiated polymer comprises a lithium salt and a non-polar polymer; the number-average molecular weight of the non-polar polymer is less than or equal to 105, the melting point of the non-polar polymer is less than or equal to 55 DEG C, and the ionic conductivity of the non-polar polymer is greater than or equal to 10 <-6 > S / cm. The transverse tensile strength, the longitudinal tensile strength, the ionic conductivity and the cycle performance of the dry-method solid electrolyte membrane are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of dry-process solid-state electrolyte membranes, and in particular relates to a dry-process solid-state electrolyte membrane and a preparation method and application thereof. Background Art

[0002] Solid-state electrolyte membranes are categorized into dry-process and wet-process. To avoid side reactions during the preparation of wet-process solid-state electrolyte membranes, non-polar solvents are required. However, most non-polar solvents are expensive and highly toxic, making dry-process solid-state electrolyte membranes a current research hotspot.

[0003] In the existing dry-process solid-state electrolyte membrane preparation process, PTFE (polytetrafluoroethylene) is generally used as a binder. The PTFE emulsion is demulsified, dried, and crushed to form pre-fiberized PTFE dry powder with a fiber diameter of about 50-200nm. The solid electrolyte material is then directly mixed with the PTFE dry powder. The PTFE dry powder is more likely to form a three-dimensional continuous network structure during mixing. The PTFE fibers are tightly entangled with the solid electrolyte material particles through mechanical shearing, providing mechanical support and reducing interfacial pores while maintaining the flexibility of the electrolyte. However, since the current strength of PTFE fibers does not meet the demand, the electrolyte membrane needs to be made thicker (greater than 50μm), which affects the energy density of the all-solid-state battery. However, if the dry solid electrolyte membrane is made into a thinner membrane (less than 50μm), the obtained dry solid electrolyte membrane is prone to cracking and cannot form a self-supporting membrane, which eventually leads to the problem of short circuit of the solid-state battery; and the current dry solid electrolyte membrane using only PTFE (polytetrafluoroethylene) as a binder has a high porosity and blocked ion channels, resulting in a serious decrease in ion conductivity; and after forming a solid-state battery, the solid electrolyte membrane has poor contact with the solid-solid interface of the electrode, affecting the battery's electrochemical performance and cycle life.

[0004] The prior art discloses a solution of adding lithiated polyacrylic acid (Li-PAA) with a certain conductivity to a dry solid electrolyte membrane. Although this solution can improve the ionic conductivity to a certain extent, the problems of cracking and poor solid-solid interface contact remain unsolved. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the thinner dry solid electrolyte membrane in the prior art, such as easy cracking, inability to be self-supporting, low ionic conductivity, and poor contact between the solid electrolyte membrane and the solid-solid interface of the electrode, thereby providing a dry solid electrolyte membrane and its preparation method and application.

[0006] To this end, the present invention provides the following technical solutions.

[0007] In a first aspect, the application provides a dry solid-state electrolyte film, comprising 90-96% of a solid-state electrolyte material, 1.5-3% of polytetrafluoroethylene and 1-8.5% of a lithiated polymer, by mass percentage;

[0008] The lithiated polymer comprises a lithium salt and a non-polar polymer;

[0009] The non-polar polymer has a number average molecular weight ≤10 5 The non-polar polymer has a melting point ≤55℃, and an ionic conductivity ≥10 -6 S / cm.

[0010] In a possible implementation, the ratio of the molar amount of the repeating unit in the non-polar polymer to the molar amount of lithium ion in the lithium salt is 8:1-20:1, preferably 9:1.

[0011] For example, the ratio of the molar amount of ethylene oxide unit (EO) in PEO to the molar amount of lithium ion in the lithium salt is 8:1-20:1.

[0012] In a possible implementation, the non-polar polymer comprises one or more of polyethylene oxide (PEO), polyethylene glycol (PEG), polypropylene oxide (PPO), polytetrahydrofuran (PTHF, polytetramethylene ether), polypropylene glycol (PPG);

[0013] When the non-polar polymer is PEO, lithium ion (Li+) forms a complex with ether oxygen atom (-O-) in the PEO chain through coordination, which inhibits the ordered arrangement of PEO molecular chain, resulting in a decrease in crystalline region and a decrease in melting point. The lithiated polymer has a certain flowability under slightly heated conditions, which can play a wetting effect.

[0014] In a possible implementation, the lithium salt comprises one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiSO3CF3), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium bis(pentafluorophenylsulfonyl)imide (LiN(SO2C6F5)2), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2);

[0015] In a possible implementation, the solid-state electrolyte material comprises one or more of sulfide solid-state electrolyte, halide solid-state electrolyte, oxide solid-state electrolyte;

[0016] Optionally, the sulfide solid-state electrolyte comprises LiP6S5Cl, Li 10 GeP2S 12 , Li7P3S11 one or more of lithium zirconium chloride (LZCl), lithium yttrium chloride (LYCl), lithium indium bromide (LIB);

[0017] Optionally, the halide solid-state electrolyte comprises one or more of lithium zirconium chloride (LZCl), lithium yttrium chloride (LYCl), lithium indium bromide (LIB);

[0018] Optionally, the oxide solid-state electrolyte comprises one or more of lithium lanthanum titanate (LLTO), lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO).

[0019] In a possible implementation, the thickness of the dry-state solid electrolyte film is ≤ 50 μm.

[0020] In a second aspect, the present application provides a method for preparing the dry-state solid electrolyte film, comprising the following steps:

[0021] S1, mixing the solid-state electrolyte material, polytetrafluoroethylene, and lithiated polymer;

[0022] S2, pre-fiberization treatment;

[0023] S3, hot-pressing into a film.

[0024] In a possible implementation, in the S1, the method for preparing the lithiated polymer comprises:

[0025] heating and melting the non-polar polymer, then adding lithium salt, mixing uniformly, and then freezing, drying, and crushing to obtain lithiated polymer particles;

[0026] In a possible implementation, the freezing is performed in a liquid nitrogen or liquid carbon dioxide environment.

[0027] In a possible implementation, in the S1, the stirring speed during mixing is 30-50 rpm, and the stirring time is 1.5-2 h.

[0028] In a possible implementation, the S2 comprises: stirring the product of the S1 at 100-200 °C for 5-30 min, and the stirring speed is ≥ 1000 rpm; optionally, the stirring speed is 1000-5000 rpm.

[0029] In a possible implementation, the S3 comprises:

[0030] pressing the product of the S2 into a thin film, and then hot-pressing the thin film;

[0031] In a possible implementation, the hot-pressing comprises a first-stage hot-pressing and a second-stage hot-pressing.

[0032] The first stage hot pressing has a pressure of 5-20 MPa, a temperature of 90-120 DEG C, and a maintaining time of 5-10 min.

[0033] The second stage hot pressing has a pressure of 50-200 MPa, a temperature of 50-60 DEG C, and a maintaining time of 5-10 min.

[0034] Optionally, in S3, the film is formed by roller pressing at 50-55 DEG C.

[0035] Optionally, the drying in S1 is low-temperature vacuum drying, for example, vacuum drying at -30 DEG C to -40 DEG C.

[0036] Optionally, the raw materials are mixed uniformly by using a V-type mixer in S1.

[0037] The V-type mixer has a slow mixing speed, and S1 uses a relatively mild mixing method to avoid the fiberization of PTFE in the mixing process, which causes the material to form a ball. The uniformity of the mixed material is greater than or equal to 99.9%, the breaking rate of the material in the mixing process is less than 0.1%, and there is no local overheating (no mechanical friction heat generation).

[0038] Optionally, the breaking in S1 is low-temperature grinding; optionally, a low-temperature ball mill is used, the ball-to-material ratio is 8:1 to 15:1, the rotation speed is 10 to 30 rpm, and the ball milling time is 10 to 20 min. Optionally, the temperature of the low-temperature grinding is -10 DEG C to -20 DEG C.

[0039] In a third aspect, the application provides a full solid-state battery, which comprises the dry solid-state electrolyte film or the dry solid-state electrolyte film prepared according to the method. The technical scheme of the application has the following advantages:

[0040] 1. The dry solid-state electrolyte film comprises, in mass percentage, 90% to 96% of a solid-state electrolyte material, 1.5% to 3% of polytetrafluoroethylene, and 1% to 8.5% of a lithiated polymer; the lithiated polymer comprises a lithium salt and a non-polar polymer; the number average molecular weight of the non-polar polymer is less than or equal to 10 5 -6 S / cm.

[0041] Conventional dry solid-state electrolyte films are difficult to completely avoid micro defects (such as micro cracks and pores) due to the limited fiber strength of PTFE, the infinite extension of the material, and the intrinsic brittleness of the material after compression, and the defects will become stress concentration points and accelerate crack propagation.

[0042] The application adds a lithiated polymer, which comprises a lithium salt and a non-polar polymer, and the number average molecular weight of the non-polar polymer is less than or equal to 10 5 ​The low-molecular-weight non-polar polymer has a low melting point, and the addition of the lithium salt can destroy the crystalline structure of the polymer, reduce the crystallinity, and make the lithiated polymer be in a gel state at room temperature. The addition of the lithiated polymer is equivalent to introducing flexible links, which can fill defects and strengthen the toughness of the entire material, thereby avoiding the cracking of the electrolyte film with low thickness. Moreover, the gel-state lithiated polymer fills the gaps between the solid-state electrolytes, provides a dual-ion channel, and is beneficial to improving the ionic conductivity of the electrolyte film. At the same time, due to the soft characteristics of the gel state, the solid-solid contact problem between the electrode and the solid-state electrolyte film is greatly improved, and the battery performance and the battery life are improved.

[0043] In the present application, the content of the lithiated polymer is controlled to be 1% to 8.5%, so that the dry-state solid-state electrolyte film has good self-supporting property, ionic conductivity, and solid-solid interface contact property. If the content of the lithiated polymer is too low, the optimization effects mentioned in the present application cannot be achieved, and if the content of the lithiated polymer is too high, the dry-state electrolyte film will be too soft and viscous, and the ionic conductivity will be affected.

[0044] 2. The ratio of the molar amount of the repeating unit in the non-polar polymer to the molar amount of lithium ions in the lithium salt is 8:1 to 20:1.

[0045] In the present application, the ratio of the molar amount of the repeating unit in the non-polar polymer to the molar amount of lithium ions in the lithium salt is controlled within the range of the present application, which can reduce the crystallinity, expand the amorphous region, and ensure the ionic conductivity.

[0046] 3. The preparation method of the dry-state solid-state electrolyte film of the present application comprises the following steps: S1, mixing the solid-state electrolyte material, polytetrafluoroethylene, and lithiated polymer; S2, pre-fiberization treatment; and S3, hot pressing into a film.

[0047] The preparation method of the present application does not need the step of hot isostatic pressing, and ordinary hot pressing can be used, thereby avoiding the problem of slow production rhythm and high equipment investment caused by hot isostatic pressing, and being beneficial to the subsequent industrialization of the solid-state battery.

[0048] 4. The preparation method of the lithiated polymer of the present application comprises: heating and melting the non-polar polymer, then adding lithium salt, mixing uniformly, and then freezing, drying, and crushing to obtain lithiated polymer particles.

[0049] The non-polar polymer and the lithium salt are mixed uniformly and then rapidly frozen, which can destroy the crystalline structure. The freezing, drying, and crushing form a powder, which can be uniformly distributed between the solid-state electrolyte films in the mixing process, effectively solving the problem that the coating or spraying scheme can only be added on the surface layer and forming a group, so that the lithiated polymer is uniformly distributed in the finally obtained dry-state solid-state electrolyte film.

[0050] Freeze-drying avoids thermal degradation of polymer chains caused by high temperatures, maintains the amorphous structure of the electrolyte, and inhibits the formation of crystallization peaks. At the same time, the chemical stability is improved, and the chemical composition of the battery cell (such as lithium salt) does not decompose at low temperatures, avoiding side reactions caused by high temperatures.

[0051] 5. The hot pressing of this application includes the first stage hot pressing and the second stage hot pressing; the pressure of the first stage hot pressing is 5~20Mpa, the temperature is 90~120℃, and it is maintained for 5~10min; the pressure of the second stage hot pressing is 50~200Mpa, the temperature is 50~60℃, and it is maintained for 5~10min.

[0052] During the first stage of hot pressing, the lithium polymer particles will gradually melt to form a gel, the membrane layer will gradually become thinner and complete densification. In the second stage, the temperature is reduced and the pressure is increased. This process realizes the densification of the grain boundaries, reduces the interface impedance, and completes the production of the composite solid-state dry electrolyte membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0054] Figure 1 Schematic diagram of the dry solid electrolyte membrane of Comparative Example 1;

[0055] Figure 2 This is a schematic diagram of the dry solid electrolyte membrane of Example 1;

[0056] Figure 3 This is the SEM image of the dry solid electrolyte membrane of Comparative Example 1;

[0057] Figure 4 This is the SEM image of the dry solid electrolyte membrane of Example 1. DETAILED DESCRIPTION

[0058] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0059] Unless otherwise indicated, the experimental procedures and conditions in the examples were carried out according to conventional procedures described in the literature. Unless otherwise indicated, the reagents and instruments used were commercially available conventional reagent products.

[0060] Example 1

[0061] The present example provides a method for preparing a dry-state solid electrolyte film, comprising the following steps:

[0062] S1, preparing a lithiated polymer: 5.8 g of PEO (Mn = 10 5 , ionic conductivity ≥ 10 -6 S / cm, melting point 50℃) was heated and melted at 80℃, then 4.2 g of lithium salt LiTFSI was added, stirred and mixed uniformly, then quickly frozen in a liquid nitrogen environment, vacuum dried at-30℃, and ground at low temperature (-10℃) to obtain PEO / Li salt composite particles. Low-temperature ball milling was used, the ball-to-material ratio was 10:1, the rotation speed was 20 rpm, and the ball milling time was 15 min.

[0063] Mix 96 g of solid-state electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene, and 2.5 g of the PEO / Li salt composite particles prepared above, mix uniformly by a V-type mixer, the rotation speed is 40 rpm, and the stirring time is 1 h.

[0064] S2, pre-fibrillation treatment of the product of S1 by mechanical shearing: stirring at 150℃ for 15 min, stirring speed 3000 rpm.

[0065] S3, roll the product of S2 into a thin film at 50℃, then heat press the film; the heat pressing includes a first stage heat pressing and a second stage heat pressing; the first stage heat pressing has a pressure of 20 Mpa and a temperature of 100℃, and is maintained for 5 min; the second stage heat pressing has a pressure of 100 Mpa and a temperature of 50℃, and is maintained for 10 min, to obtain a dry-state solid electrolyte film with a thickness of 30 μm.

[0066] Example 2

[0067] The present example provides a method for preparing a dry-state solid electrolyte film, comprising the following steps:

[0068] S1, preparing a lithiated polymer: 5.8 g of PEO (Mn = 10 5 , ionic conductivity ≥ 10 -6S1, Preparation of PEO / Li salt composite particles: 90 g of solid electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene, and 8.5 g of the PEO / Li salt composite particles prepared above were mixed and uniformly mixed by a V-type mixer at a speed of 40 rpm for 1 h.

[0069] S1, Preparation of PEO / Li salt composite particles: 90 g of solid electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene, and 8.5 g of the PEO / Li salt composite particles prepared above were mixed and uniformly mixed by a V-type mixer at a speed of 40 rpm for 1 h.

[0070] S2, Pre-fibrillation treatment of the product of S1 by mechanical shearing: stirring at 150°C for 15 min at a stirring speed of 3000 rpm.

[0071] S3, Rolling the product of S2 into a thin film at 50°C, and then hot pressing the film; the hot pressing includes a first stage hot pressing and a second stage hot pressing; the first stage hot pressing is at a pressure of 20 MPa and a temperature of 100°C for 5 min; the second stage hot pressing is at a pressure of 100 MPa and a temperature of 50°C for 10 min, to obtain a dry solid electrolyte film with a thickness of 30 μm.

[0072] Example 3

[0073] The present example provides a method for preparing a dry solid electrolyte film, comprising the following steps:

[0074] S1, Preparation of a lithiated polymer: 5.8 g of PEO (Mn = 10 5 , ionic conductivity ≥ 10 -6 S / cm, melting point 50°C) was heated and melted at 80°C, then 4.2 g of lithium salt LiTFSI was added, and the mixture was stirred and mixed uniformly, then rapidly frozen in a liquid nitrogen environment, vacuum dried, and ground at a low temperature (-10°C) to obtain PEO / Li salt composite particles. Low-temperature grinding was performed using a low-temperature ball mill at a ball-to-material ratio of 10:1, a rotation speed of 20 rpm, and a ball milling time of 15 min.

[0075] S1, Preparation of PEO / Li salt composite particles: 90 g of solid electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene, and 8.5 g of the PEO / Li salt composite particles prepared above were mixed and uniformly mixed by a V-type mixer at a speed of 40 rpm for 1 h.

[0076] S2, Pre-fibrillation treatment of the product of S1 by mechanical shearing: stirring at 150°C for 15 min at a stirring speed of 3000 rpm.

[0077] S3. Roll the product of S2 into a thin film at 50°C, and then hot press the thin film; the hot pressing includes a first stage hot pressing and a second stage hot pressing; the pressure of the first stage hot pressing is 20 MPa, the temperature is 100°C, and the maintenance time is 5 minutes; the pressure of the second stage hot pressing is 100 MPa, the temperature is 50°C, and the maintenance time is 10 minutes, to obtain a dry solid electrolyte membrane with a thickness of 30 μm.

[0078] Example 4

[0079] This embodiment is basically the same as embodiment 1, except that, in S1, PEO is 5.51 g and LiTFSI is 4.49 g, that is, EO / Li+ in the PEO / Li salt composite particles of this embodiment is 8:1.

[0080] Example 5

[0081] This embodiment is basically the same as Example 1, except that PEO is 7.54 g and LiTFSI is 2.46 g, that is, EO / Li+ in the PEO / Li salt composite particles of this embodiment is 20:1.

[0082] Example 6

[0083] This embodiment provides a method for preparing a dry solid electrolyte membrane, comprising the following steps:

[0084] S1, preparation of lithiated polymer: 5.8g PEG (Mn = 7*10 4 , ionic conductivity ≥10 -5 50-55°C) was melted at 80°C, and then 4.2g of lithium salt LiTFSI was added and stirred to mix thoroughly. The mixture was then rapidly frozen in liquid nitrogen, vacuum dried, and ground at low temperature (-10°C) to produce PEG / Li salt composite particles. This was performed using a cryogenic ball mill with a ball-to-material ratio of 10:1, a rotation speed of 20 rpm, and a ball milling time of 15 minutes.

[0085] 96 g of solid electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene and 2.5 g of the PEG / Li salt composite particles prepared above were mixed and uniformly mixed using a V-type mixer at a speed of 40 rpm for 1 hour.

[0086] S2. Pre-fiberize the product of S1 by mechanical shearing: stirring at 150° C. for 15 min, with a stirring speed of 3000 rpm.

[0087] S3, roll the product of S2 into a film at 50℃, and then hot-press the film; the hot-pressing includes a first-stage hot-pressing and a second-stage hot-pressing; the first-stage hot-pressing has a pressure of 20 MPa and a temperature of 100℃, and is maintained for 5 min; the second-stage hot-pressing has a pressure of 100 MPa and a temperature of 50℃, and is maintained for 10 min, to obtain a dry-state electrolyte film with a thickness of 30 μm.

[0088] Example 7

[0089] The present example provides a method for preparing a dry-state electrolyte film, including the following steps:

[0090] S1, preparing a lithiated polymer: 5.8 g of PEO (Mn = 10 5 , ionic conductivity ≥ 10 -6 S / cm, melting point 50℃) is heated and melted at 80℃, then 4.2 g of lithium salt LiTFSI is added, stirred and mixed uniformly, then rapidly frozen in a liquid nitrogen environment, vacuum dried, and ground at low temperature (-10℃) to obtain PEO / Li salt composite particles. Low-temperature grinding is performed using a low-temperature ball mill, with a ball-to-material ratio of 10:1, a rotation speed of 20 rpm, and a ball milling time of 15 min.

[0091] Mix 96 g of solid-state electrolyte material Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO), 1.5 g of polytetrafluoroethylene, and 2.5 g of the PEO / Li salt composite particles prepared above, mix uniformly by a V-type mixer, with a rotation speed of 40 rpm and stirring for 1 h.

[0092] S2, pre-fibrillation treatment of the product of S1 by mechanical shearing: stirring at 150℃ for 15 min, with a stirring rotation speed of 3000 rpm.

[0093] S3, roll the product of S2 into a film at 50℃, and then hot-press the film; the hot-pressing includes a first-stage hot-pressing and a second-stage hot-pressing; the first-stage hot-pressing has a pressure of 20 MPa and a temperature of 100℃, and is maintained for 5 min; the second-stage hot-pressing has a pressure of 100 MPa and a temperature of 50℃, and is maintained for 10 min, to obtain a dry-state electrolyte film with a thickness of 30 μm.

[0094] Comparative Example 1

[0095] The present comparative example is basically the same as Example 1, except that no lithiated polymer is added in the present comparative example, specifically including:

[0096] S1, 96 g of solid electrolyte material LiP6S5Cl, 4 g of polytetrafluoroethylene were mixed and uniformly mixed by a V-type mixer at a speed of 40 rpm for 1 h.

[0097] S2, the product of S1 was pre-fibrillated by mechanical shearing: stirring at 150 °C for 15 min at a stirring speed of 3000 rpm.

[0098] S3, the product of S2 was rolled into a thin film at 50 °C, and then the film was hot-pressed; the hot-pressing included a first-stage hot-pressing and a second-stage hot-pressing; the first-stage hot-pressing was at a pressure of 20 MPa and a temperature of 100 °C for 5 min; the second-stage hot-pressing was at a pressure of 100 MPa and a temperature of 50 °C for 10 min, to obtain a dry solid electrolyte film with a thickness of 30 pm.

[0099] Comparative Example 2

[0100] This comparative example was basically the same as Example 1, except that 88 g of solid electrolyte material LiP6S5Cl, 1.5 g of polytetrafluoroethylene and 10.5 g of PEO / Li salt composite particles were mixed.

[0101] Comparative Example 3

[0102] This comparative example was basically the same as Example 1, except that the Mn of PEO was 10 6 , the ionic conductivity was ≥10 -7 S / cm, and the melting point was 80 °C.

[0103] Figure 1 This is a structural schematic diagram of a conventional dry electrolyte film (Comparative Example 1), and after the PTFE is fibrillated, a network is formed, connecting the solid electrolyte material particles to form an electrolyte film, but there are still gaps between the intermediate sulfide solid electrolyte / sulfide solid electrolyte, resulting in insufficient ion transport channels, which leads to poor ion transport and a significant reduction in conductivity.

[0104] Figure 2 This is a structural schematic diagram of a composite dry electrolyte film used in the application, and after the PTFE is fibrillated, a network is formed, connecting the solid electrolyte powder particles to form an electrolyte sheet, and then due to the incorporation of the freeze-dried PEO / lithium salt polymer solid electrolyte powder, the PEO / lithium salt polymer solid electrolyte powder is then melted by heating to become a gel state Figure 2The green part in the middle is filled with the interstices between the sulfide solid electrolyte / sulfide solid electrolyte, provides a dual-ion channel, and is beneficial to improving the ionic conductivity of the electrolyte film. At the same time, due to the soft characteristics of the gel state, when assembling the positive electrode / complex dry electrolyte film / negative electrode solid-state battery, the solid-solid interface contact can also be significantly improved by 50°C flat plate hot pressing, thereby improving the battery performance and cycle life, so that the hot isostatic pressing process which seriously drags the production rhythm and requires high equipment investment can be avoided.

[0105] Figure 3 SEM image of the dry solid electrolyte film prepared for Comparative Example 1, Figure 4 SEM image of the dry solid electrolyte film prepared for Example 1 of the present application. It is consistent with the theoretical structure.

[0106] The PEO / lithium salt polymer solid electrolyte uniformly distributed in the dry electrolyte film of the present application is in a molten state during subsequent hot pressing treatment, which can solve the problem that the sulfide electrolyte particles in the traditional composite dry electrolyte film using PTFE as the binder still have gaps between them, resulting in insufficient ion transmission channels and poor ion transmission, thereby causing a serious reduction in ionic conductivity. The PEO / lithium salt polymer solid electrolyte uniformly distributed in the dry electrolyte film of the present application itself has a certain ion conduction ability, and at the same time fills the interstices of the sulfide solid electrolyte particles, thereby greatly improving the ionic conductivity compared with the pure PTFE solid-state scheme.

[0107] Test Example

[0108] 1) The ionic conductivity of the dry solid electrolyte film is calculated using the following formula:

[0109] σ Li = L / RS = L / R(πr 2 )

[0110] Where, σ Li - ionic conductivity, L - electrolyte wafer thickness, R - bulk resistance in the impedance spectrum of the electrolyte wafer, S - electrolyte wafer surface area, r - electrolyte wafer radius.

[0111] The dry solid electrolyte film supports the electrolyte wafer, and the bulk resistance R in the impedance spectrum is tested. The test instrument used is CHI600E of Shanghai Chenhua Instrument Co., Ltd., the alternating voltage signal amplitude is 5mV, and the test frequency range is 10 5 ~ 10 -2 Hz.

[0112] 2) Tensile strength test:

[0113] The dry solid electrolyte films obtained from the examples and comparative examples were subjected to tensile strength test. The tensile strength test was performed according to the provisions in GB13022-91.

[0114] 3) Cycle life test method:

[0115] The dry solid electrolyte films obtained from the examples and comparative examples were respectively used to make symmetric batteries (lithium metal sheet / solid electrolyte film / lithium metal sheet), which were loaded into button cells for testing:

[0116] In the form of constant current charge and discharge, the test current density was 1 mA·cm -2 The cycle stability of the dry solid electrolyte film was characterized by judging the cycle number of the stable polarization voltage. The symmetric battery was tested by using Wuhan Lan electric test system to characterize the cycle stability of the solid electrolyte film / Li + The test environment was constant temperature 25℃ to exclude interference.

[0117] The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] From Table 1, it can be seen that the transverse and longitudinal tensile strength of the dry solid electrolyte film of the present application is significantly improved, the crack resistance is obviously improved, and the ionic conductivity and cycle performance of the present application are also significantly improved.

[0122] Obviously, the above examples are only examples for clearly illustrating, but not limitation to the embodiments. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A dry solid electrolyte membrane, characterized in that: Calculated by mass percentage, it includes 90% to 96% of solid electrolyte material, 1.5% to 3% of polytetrafluoroethylene and 1% to 8.5% of lithiated polymer; The lithiated polymer includes a lithium salt and a non-polar polymer; The number average molecular weight of the non-polar polymer is ≤10 5 The melting point of the non-polar polymer is ≤55°C, and the ionic conductivity of the non-polar polymer is ≥10 -6 S / cm.

2. The dry solid electrolyte membrane according to claim 1, characterized in that The ratio of the molar amount of the repeating units in the non-polar polymer to the molar amount of the lithium ions in the lithium salt is 8:1 to 20:1, preferably 9:

1.

3. The dry solid electrolyte membrane according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The non-polar polymer includes one or more of polyethylene oxide, polyethylene glycol, polypropylene oxide, polytetrahydrofuran, and polypropylene glycol; (2) The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(pentafluorophenylsulfonyl)imide, lithium bis(oxalatoborate), and lithium difluorophosphate; (3) The solid electrolyte material includes one or more of a sulfide solid electrolyte, a halide solid electrolyte, and an oxide solid electrolyte; Optionally, the sulfide solid electrolyte includes LiP6S5Cl, Li 10 GeP2S 12 、Li7P3S 11 One or more of; Optionally, the halide solid electrolyte includes one or more of lithium zirconium chloride, lithium yttrium chloride, and lithium indium bromide; Optionally, the oxide solid electrolyte includes one or more of lithium lanthanum titanate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium tantalum oxide.

4. The dry solid electrolyte membrane according to claim 1 or 2, characterized in that: The thickness of the dry solid electrolyte membrane is ≤50 μm.

5. A method for preparing a dry solid electrolyte membrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, mixing the solid electrolyte material, polytetrafluoroethylene and lithiated polymer; S2, prefibrosis treatment; S3, hot pressing film forming.

6. The method for preparing a dry solid electrolyte membrane according to claim 5, characterized in that: In S1, the preparation method of the lithiated polymer includes: The non-polar polymer is heated and melted, and then lithium salt is added, mixed evenly, and then frozen, dried, and crushed to obtain lithiated polymer particles; Optionally, the freezing is performed in a liquid nitrogen or liquid carbon dioxide environment.

7. The method for preparing a dry solid electrolyte membrane according to claim 5 or 6, characterized in that: In the above S1, the stirring speed during mixing is 30 to 50 rpm, and the stirring time is 1.5 to 2 hours.

8. The method for preparing a dry solid electrolyte membrane according to claim 5 or 6, characterized in that: The S2 comprises: stirring the product of the S1 at 100-200° C. for 5-30 minutes, with a stirring speed of ≥1000 rpm.

9. The method for preparing a dry solid electrolyte membrane according to claim 5 or 6, characterized in that: The S3 includes: Pressing the product of S2 into a film, and then hot-pressing the film; Optionally, the hot pressing includes a first stage hot pressing and a second stage hot pressing; The first stage of hot pressing has a pressure of 5-20 MPa and a temperature of 90-120°C, and is maintained for 5-10 minutes; The second stage hot pressing has a pressure of 50-200 MPa and a temperature of 50-60° C., and is maintained for 5-10 minutes.

10. An all-solid-state battery, characterized in that: The invention comprises the dry solid electrolyte membrane according to any one of claims 1 to 4 or the dry solid electrolyte membrane prepared according to the method according to any one of claims 5 to 9.

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