Composite solid electrolyte and preparation method and application thereof

Abstract

The application provides a composite solid electrolyte and a preparation method and application thereof. The composite solid electrolyte comprises an electrolyte layer, a Li3PO4 layer and a conductive polymer layer which are sequentially stacked; the composite solid electrolyte has a modification layer composed of the Li3PO4 layer and the conductive polymer layer on the surface, so that lithium ions can be uniformly deposited, lithium dendrite growth is slowed down, lithium powder dispersion is reduced, the probability of lithium metal battery explosion is reduced, interface side reactions can be reduced, the cycle life of the battery is increased, interface gaps are reduced, interface impedance is reduced, and ion transmission capacity is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a composite solid-state electrolyte and a preparation method and application thereof. BACKGROUND

[0002] With the gradual popularization of electric vehicles, the energy density of power batteries is paid more and more attention. The all-solid-state battery is the ultimate goal of the lithium ion battery, and the research and development of the solid-state electrolyte is the key to achieving this goal. The lithium metal negative electrode matched with the solid-state electrolyte has an ultra-high theoretical capacity of 3480 mAh / g. However, the application of the solid-state electrolyte and the lithium metal negative electrode in the lithium ion battery is very difficult, and the main reasons include: firstly, due to the high interfacial reactivity of the lithium metal negative electrode and the solid-state electrolyte, both of them are continuously consumed; secondly, the oxide, sulfide and halide solid-state electrolyte produces a gap between the lithium metal negative electrode due to the high mechanical stress, and the interfacial impedance becomes large; thirdly, the solid-state electrolyte cannot prevent the growth and spread of the interfacial lithium dendrite, and still can pierce the lithium dendrite. Therefore, the application of the solid-state electrolyte still faces many problems.

[0003] The prior art usually generates an SEI layer on the surface of the lithium metal negative electrode in situ or artificially establishes a protective layer to prevent the lithium metal from directly contacting with the electrolyte and reduce the generation of side reactions in order to solve the continuous side reactions of the lithium metal negative electrode and the electrolyte. For example, CN 111063931A discloses a solid-state polymer electrolyte and application thereof. The preparation of the solid-state polymer electrolyte includes: dispersing monomer 1, monomer 2, monomer 3, a crosslinking agent and a lithium salt in a solvent to obtain a mixed solution; and performing thermal initiation polymerization on the mixed solution, that is, performing thermal initiation polymerization on different monomers and a crosslinking agent without an initiator, so that an SEI film can be generated on the electrode surface during the charging and discharging process of the lithium battery. However, the interface protection phase researched at present will continuously age and collapse in the cycle process, finally leading to the capacity reduction and failure of the battery system; on the other hand, the thickness of the artificially established protective layer cannot be stably controlled, leading to the excessively high interfacial impedance of the solid-state electrolyte and the difficulty of normal capacity play; finally, the lithium metal negative electrode is easy to produce dendrites to pierce the protective layer under a high charging current, leading to the failure of the protective layer, the reaction with the solid-state electrolyte layer and even the continuous growth in the solid-state electrolyte layer.

[0004] Based on the above research, it is necessary to provide a composite solid-state electrolyte which can effectively improve the non-uniform deposition of lithium ions on the negative electrode side, make the lithium ions uniformly deposit, avoid the growth of dendrites, also can reduce the interfacial side reaction, increase the cycle life of the battery, reduce the interface gap and improve the ion transmission capacity. SUMMARY

[0005] The application aims to provide a composite solid-state electrolyte and a preparation method and application thereof, the composite solid-state electrolyte has a modification layer on the surface, so that lithium ions are uniformly deposited, the growth of lithium dendrites is slowed down, the dispersion of lithium powder is reduced, the probability of explosion of a lithium metal battery is reduced, the interface side reaction is reduced, the cycle life of the battery is increased, the interface gap is reduced, the interface impedance is reduced, and the ion transmission capacity is improved.

[0006] To achieve the application goal, the application adopts the following technical solutions.

[0007] In a first aspect, the application provides a composite solid-state electrolyte, which comprises an electrolyte layer, a Li3PO4 layer and a conductive polymer layer arranged in sequence.

[0008] The modification layer is arranged on the surface of the electrolyte layer, and the modification layer comprises a Li3PO4 layer and a conductive polymer layer arranged in sequence. On one hand, the modification layer greatly reduces the side reaction between the solid-state electrolyte layer and the negative electrode, increases the lithium ion transmission flux, effectively improves the phenomenon of uneven deposition of lithium ions on the negative electrode side, improves the growth of lithium dendrites, and the high mechanical stress makes it difficult for lithium dendrites to penetrate. On the other hand, the modification layer has a high elastic modulus, can effectively reduce the gap between the solid-state electrolyte layer and the negative electrode, can make the solid-state electrolyte and the negative electrode fully contact under a low pressure, increase the contact area, reduce the interface gap, thereby reduce the impedance and improve the ion transmission capacity.

[0009] Preferably, a lithium metal layer is further arranged between the electrolyte layer and the Li3PO4 layer.

[0010] The lithium metal layer is further arranged between the electrolyte layer and the Li3PO4 layer, which can provide additional lithium ions as a lithium source for the charging and discharging process, play a lithium supplement role, and reduce the interface between the electrolyte layer and the Li3PO4 layer, thereby further improving the electrochemical performance of the composite solid-state electrolyte.

[0011] Preferably, the thickness of the lithium metal layer is 2-15 μm, for example, it can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm or 15 μm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0012] Preferably, the thickness of the Li3PO4 layer is 3-7 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm or 7 μm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0013] The thickness of the Li3PO4 layer in the application is within a reasonable range, which can ensure the comprehensive performance of the composite solid-state electrolyte. If the thickness of the Li3PO4 layer is too small, the diffusion impedance of the electrode sheet will be high, and the transmission of lithium ions will be affected. If the thickness of the Li3PO4 layer is too large, it is easy to break during the cycle of lithium ion battery, and it cannot play the role of long-term protective layer.

[0014] Preferably, the thickness of the conductive polymer layer is 5-15 μm, for example, it can be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm or 15 μm, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0015] Preferably, the thickness of the electrolyte layer is 5-200 μm, for example, it can be 5 μm, 25 μm, 50 μm, 75 μm, 100 μm, 125 μm, 150 μm, 175 μm or 200 μm, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0016] Preferably, the conductive polymer layer comprises a first polymer and a second polymer, the first polymer comprises any one or a combination of at least two of PEO (polyethylene oxide), TPU (thermoplastic polyurethane elastomer), PAA (polyacrylic acid), PAN (polyacrylonitrile), PVMA (polymethyl methacrylate) or polyphosphazine, and the second polymer comprises PVDF (polyvinylidene fluoride) and / or PVDF (polyvinylidene fluoride)-HFP (hexafluoropropylene).

[0017] The conductive polymer in the application uses two different polymers, the first polymer has higher compatibility with lithium metal, no side reaction occurs during the cycle process, and the pulverized lithium can be trapped in the polymer layer, so that the disordered lithium powder will not be distributed in the electrolyte to cause continuous side reactions in the electrolyte; the second polymer serves as the skeleton of the first polymer, so that the structure of the conductive polymer layer will not collapse in long cycle; at the same time, the conductive polymer layer includes the first polymer and the second polymer, which can make the conductive polymer layer have good elasticity, so that the solid-state electrolyte can be fully contacted with the negative electrode under a certain pressure, and the interface impedance is reduced.

[0018] Preferably, the molar ratio of the first polymer to the second polymer is (0.5-2):(0.0025-0.01), for example, it can be 0.5:0.0025, 1:0.1 or 2:0.01, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0019] The second polymer in the conductive polymer layer plays a role of a skeleton, and a small amount of the second polymer is added, that is, when the molar ratio of the first polymer to the second polymer is within the above range, the electrochemical performance of the composite solid-state electrolyte can be further ensured, and if the molar ratio is not within the above range, the structure is prone to collapse in the cycle process, pores are formed, the impedance is increased, the electrochemical cycle performance is greatly reduced, and the side reaction is increased.

[0020] Preferably, the conductive polymer layer further comprises an aluminum salt and / or a magnesium salt.

[0021] The aluminum salt and / or the magnesium salt are further added to the conductive polymer layer, which can guide the uniform deposition of lithium ions on the negative electrode side and reduce the generation of dead lithium in the cycle process, and can form Mg-Li or Al-Li alloy on the surface of lithium metal in the cycle process, guide the uniform deposition of lithium ions, and reduce the generation of lithium dendrites.

[0022] Preferably, the conductive polymer layer further comprises a lithium salt.

[0023] Preferably, the aluminum salt comprises aluminum trifluoromethyl sulfonate.

[0024] Preferably, the magnesium salt comprises magnesium trifluoromethyl sulfonate.

[0025] Preferably, the lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium nitrate or lithium hexafluorophosphate, and a typical but non-limiting combination includes a combination of lithium bisfluorosulfonylimide and lithium nitrate.

[0026] In a second aspect, the application provides a preparation method of the composite solid-state electrolyte according to the first aspect, and the preparation method comprises the following steps:

[0027] (1) preparing a lithium metal layer on the surface of the electrolyte layer, coating a polyphosphoric acid solution on the surface of the lithium metal layer to obtain a Li3PO4 layer;

[0028] (2) coating a conductive polymer layer slurry on the surface of the Li3PO4 layer in step (1) to obtain the composite solid-state electrolyte.

[0029] The Li3PO4 layer is obtained by in-situ reaction of the lithium metal layer and the polyphosphoric acid, so that the uniformity of the Li3PO4 layer is higher, the layer is tightly stacked between other layers, and the conductive polymer layer is directly coated from the slurry, and therefore, the preparation method is simple in process operation and low in material cost.

[0030] Preferably, the concentration of the polyphosphoric acid solution in step (1) is 0.1-2 mol / L, for example, it can be 0.1 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0031] The polyphosphoric acid solution reacts with lithium metal to form lithium phosphate, which can promote the conduction of lithium ions, i.e., provide a protective layer for the solid-state electrolyte to prevent lithium dendrites from penetrating, and both too high and too low concentrations of polyphosphoric acid cannot produce a suitable and effective interface protective phase.

[0032] Preferably, the polyphosphoric acid solution in step (1) is obtained by stirring and mixing polyphosphoric acid and an organic solvent.

[0033] Preferably, the organic solvent includes any one or a combination of at least two of benzene, toluene, ethylbenzene or xylene.

[0034] Preferably, the stirring and mixing time is 60-120 min, for example, it can be 60 min, 80 min, 100 min or 120 min, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0035] Preferably, the coating method in step (1) includes spraying, and the flow rate of the spraying is 1-3 mL / min, for example, it can be 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min or 3 mL / min, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0036] Preferably, after the coating in step (1), a drying step is further performed to obtain the Li3PO4 layer.

[0037] Preferably, the lithium metal layer in step (1) is deposited on the surface of the electrolyte layer by ion deposition.

[0038] Preferably, the electrolyte layer in step (1) is obtained by pressing an electrolyte material into a sheet or preparing a film.

[0039] Preferably, the electrolyte material includes any one or a combination of at least two of a sulfide solid-state electrolyte, an oxide solid-state electrolyte or a halide solid-state electrolyte; for example, the sulfide solid-state electrolyte includes argyrodite (Li6PS5X, X = Cl, Br, I), lithium germanium phosphorus sulfide (LGPS), LPS (Li7P3S 11, any one or a combination of at least two of Li7PS6, P2S5 or Li2S, the oxide solid electrolyte includes any one or a combination of at least two of LiPON type electrolyte, LLZO solid electrolyte or LLZTO, the chloride solid electrolyte Li3InCl6 and / or Li3YCl6.

[0040] Preferably, the conductive polymer layer slurry of step (2) is obtained by mixing the first polymer, the second polymer and the solvent.

[0041] Preferably, the first polymer is added in an amount of 0.5-2 mol, for example, it can be 0.5 mol, 1 mol, 1.5 mol or 2 mol, and the second polymer is added in an amount of 0.0025-0.01 mol, for example, it can be 0.0025 mol, 0.001 mol or 0.01 mol, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0042] Preferably, the first polymer includes any one or a combination of at least two of PEO, TPU, PAA, PAN, PVMA or polyphosphazine, and the second polymer includes PVDF and / or PVDF-HFP.

[0043] Preferably, the weight average molecular weight of the first polymer and the second polymer is independently 2 million or less, for example, it can be 2 million, 1 million, 0.5 million or 0.1 million, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0044] Preferably, the solvent includes any one or a combination of at least two of benzene, toluene, ethylbenzene or xylene.

[0045] Preferably, the temperature of the mixing is 47-60℃, for example, it can be 47℃, 50℃ or 60℃, and the time is 10-14h, for example, it can be 10h, 12h or 14h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0046] Preferably, a lithium salt is further added after the mixing, and the lithium salt is added in an amount of 1-3 mol, for example, it can be 1 mol, 2 mol or 3 mol, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0047] Preferably, 0.01-0.2 mol of an aluminum salt and / or a magnesium salt is further added after the mixing, for example, it can be 0.01 mol, 0.05 mol, 0.1 mol, 0.15 mol or 0.2 mol, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0048] Preferably, after the coating of step (2), vacuum drying is further performed, and the time of the vacuum drying is 6-8h, for example, can be 6h, 7h or 8h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0049] As a preferred technical solution of the preparation method of the application, the preparation method comprises the following steps:

[0050] (1) pressing or preparing an electrolyte material into a sheet or a film to obtain an electrolyte layer, and depositing lithium metal on the surface of the electrolyte layer by ion deposition;

[0051] (2) stirring and mixing polyphosphoric acid and an organic solvent for 60-120min to obtain a polyphosphoric acid solution, and spraying the polyphosphoric acid solution with a concentration of 0.1-2mol / L at a flow rate of 1-3mL / min on the surface of the lithium metal layer of step (1) to obtain a Li3PO4 layer;

[0052] (3) mixing 0.5-2mol of a first polymer, 0.0025-0.01mol of a second polymer and a solvent at a temperature of 47-60℃ for 10-14h, then adding 1-3mol of a lithium salt and 0.01-0.2mol of an aluminum salt and / or a magnesium salt to obtain a conductive polymer layer slurry, coating the conductive polymer slurry on the surface of the Li3PO4 layer of step (2), and then vacuum drying for 6-8h to obtain the composite solid-state electrolyte.

[0053] In a third aspect, the application provides a solid-state battery, comprising a positive electrode sheet, a negative electrode sheet and the composite solid-state electrolyte as described in the first aspect, the negative electrode sheet being arranged on one side of the conductive polymer layer in the composite solid-state electrolyte, and the positive electrode sheet being arranged on one side of the electrolyte layer in the composite solid-state electrolyte.

[0054] Preferably, the negative electrode sheet comprises any one or a combination of at least two of lithium metal, graphite, silicon and silicon-carbon material.

[0055] Compared with the prior art, the application has the following beneficial effects:

[0056] By modifying the surface of the electrolyte layer, setting the Li3PO4 layer and the conductive polymer layer modification layer, the application reduces the side reaction between the solid-state electrolyte layer and the negative electrode, increases the lithium ion transmission flux, improves the lithium ion deposition phenomenon, slows down the growth of lithium dendrites, reduces the gap between the solid-state electrolyte layer and the negative electrode, reduces the impedance and can resist the volume change of the negative electrode, so that the side reaction of the prepared lithium ion battery is significantly reduced, and the cycle performance is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 A schematic diagram of the structure of the composite solid-state electrolyte according to Example 1 of the present application;

[0058] Figure 2 An optical photograph of the composite solid-state electrolyte according to Example 1 of the present application;

[0059] Figure 3 An SEM image of the interface between the composite solid-state electrolyte according to Example 1 of the present application and a lithium metal negative electrode after 50 cycles;

[0060] Figure 4 A cycle performance graph of a solid-state battery made of the composite solid-state electrolyte according to Example 1 of the present application;

[0061] Figure 5 An SEM image of the interface between the solid-state electrolyte according to Comparative Example 1 of the present application and a lithium metal negative electrode after 20 cycles;

[0062] Figure 6 A cycle performance graph of a solid-state battery made of the solid-state electrolyte according to Comparative Example 1 of the present application;

[0063] wherein 1 is an electrolyte layer, 2 is a lithium metal layer, 3 is a Li3PO4 layer, and 4 is a conductive polymer layer. DETAILED DESCRIPTION

[0064] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations on the present application.

[0065] Example 1

[0066] This embodiment provides a composite solid-state electrolyte, a schematic diagram of the structure of the composite solid-state electrolyte is shown in Figure 1 , an optical photograph is shown in Figure 2 , an SEM image of the interface between the composite solid-state electrolyte and a lithium metal negative electrode after 50 cycles is shown in Figure 3 , and a cycle performance graph of a solid-state battery made of the composite solid-state electrolyte is shown in Figure 4 .

[0067] The composite solid-state electrolyte comprises an electrolyte layer 1, a lithium metal layer 2, a Li3PO4 layer 3, and a conductive polymer layer 4 arranged in sequence; the thickness of the lithium metal layer 2 is 5 μm, the thickness of the Li3PO4 layer 3 is 5 μm, the thickness of the conductive polymer layer 4 is 10 μm, and the thickness of the electrolyte layer 1 is 50 μm;

[0068] The conductive polymer layer 4 comprises PEO-PVDF, magnesium trifluoromethyl sulfonate, and lithium bisfluorosulfonylimide, wherein the molar ratio of PEO and PVDF is 1:0.005;

[0069] The preparation method of the composite solid-state electrolyte comprises the following steps:

[0070] (1) 60 mg of Li6PS5Cl is pressed into a sheet under a pressure of 300 MPa to obtain an electrolyte layer 1, and a lithium metal layer 2 is obtained on the surface of the electrolyte layer 1 by ion deposition;

[0071] (2) 1 mol of polyphosphoric acid is heated to 60 degrees, and 1 L of toluene is stirred and mixed at room temperature for 90 min to obtain a polyphosphoric acid solution with a concentration of 1 mol / L. The polyphosphoric acid solution with a concentration of 1 mol / L is sprayed on the surface of the lithium metal layer 2 obtained in step (1) at a flow rate of 2 mL / min, and then dried in a vacuum drying box for 2 h to obtain a Li3PO4 layer 3;

[0072] (3) 1 mol of PEO (weight average molecular weight 300,000), 0.005 mol of PVDF (weight average molecular weight 300,000), and toluene are mixed at a temperature of 50°C for 12 h, then 2 mol of lithium bisfluorosulfonylimide is added and stirred for 20 min, then 0.1 mol of magnesium trifluoromethylsulfonate is added and stirred for 2 h to obtain a conductive polymer layer 4 slurry. The conductive polymer slurry is coated on the surface of the Li3PO4 layer 3 obtained in step (2), and then vacuum dried for 7 h to obtain the composite solid-state electrolyte.

[0073] Example 2

[0074] The composite solid-state electrolyte comprises an electrolyte layer, a lithium metal layer, a Li3PO4 layer and a conductive polymer layer which are sequentially stacked;

[0075] The thickness of the lithium metal layer is 2 μm, the thickness of the Li3PO4 layer is 7 μm, the thickness of the conductive polymer layer is 15 μm, and the thickness of the electrolyte layer is 10 μm;

[0076] The conductive polymer layer comprises PEO-PVDF, aluminum trifluoromethylsulfonate and lithium nitrate, wherein the molar ratio of PEO and PVDF is 0.5:0.0025;

[0077] The preparation method of the composite solid-state electrolyte comprises the following steps:

[0078] (1) 60 mg of Li6PS5Cl is pressed into a sheet under a pressure of 300 MPa to obtain an electrolyte layer, and a lithium metal layer is obtained on the surface of the electrolyte layer by ion deposition;

[0079] (2) 2 mol of polyphosphoric acid is heated to 60 degrees, mixed with 1 L of toluene at room temperature for 120 min to obtain a polyphosphoric acid solution with a concentration of 2 mol / L, and the polyphosphoric acid solution with a concentration of 2 mol / L is sprayed on the surface of the lithium metal layer of step (1) at a flow rate of 1 mL / min, and then dried in a vacuum drying box for 2 h to obtain a Li3PO4 layer;

[0080] (3) 0.5 mol of PEO (weight average molecular weight 1 million), 0.0025 mol of PVDF (weight average molecular weight 1 million), and benzene are mixed at a temperature of 47°C for 14 h, then 3 mol of lithium nitrate is added and stirred for 20 min, then 0.2 mol of aluminum trifluoromethyl sulfonate is added and stirred for 2 h to obtain a conductive polymer layer slurry, and the conductive polymer slurry is coated on the surface of the Li3PO4 layer of step (2), and then vacuum dried for 8 h to obtain the composite solid electrolyte.

[0081] Embodiment 3

[0082] The composite solid electrolyte comprises an electrolyte layer, a lithium metal layer, a Li3PO4 layer and a conductive polymer layer which are sequentially stacked;

[0083] The thickness of the lithium metal layer is 15 μm, the thickness of the Li3PO4 layer is 3 μm, the thickness of the conductive polymer layer is 5 μm, and the thickness of the electrolyte layer is 180 μm;

[0084] The conductive polymer layer comprises PEO-PVDF-HFP, magnesium trifluoromethyl sulfonate and lithium hexafluorophosphate, wherein the molar ratio of PEO and PVDF-HFP is 2:0.01;

[0085] The preparation method of the composite solid electrolyte comprises the following steps:

[0086] (1) 60 mg of Li6PS5Cl is pressed into a sheet under a pressure of 300 Mpa to obtain an electrolyte layer, and a lithium metal layer is obtained on the surface of the electrolyte layer by ion deposition;

[0087] (2) 0.1 mol of polyphosphoric acid is heated to 60 degrees, mixed with 1 L of toluene at room temperature for 60 min to obtain a polyphosphoric acid solution with a concentration of 0.1 mol / L, and the polyphosphoric acid solution with a concentration of 0.1 mol / L is sprayed on the surface of the lithium metal layer of step (1) at a flow rate of 3 mL / min, and then dried in a vacuum drying box for 2 h to obtain a Li3PO4 layer;

[0088] (3) 2 mol of PEO (weight average molecular weight of 300,000), 0.01 mol of PVDF-HFP (weight average molecular weight of 300,000), and toluene were mixed at a temperature of 60°C for 10 h, then 1 mol of lithium hexafluorophosphate was added and stirred for 20 min, 0.01 mol of magnesium trifluoromethylsulfonate was added, and stirring was continued for 2 h to obtain a conductive polymer layer slurry, the conductive polymer slurry was coated on the surface of the Li3PO4 layer of step (2), and then vacuum dried for 6 h to obtain the composite solid electrolyte.

[0089] Example 4

[0090] The composite solid electrolyte of the present embodiment is identical to that of Example 1 except that the lithium metal layer is not included.

[0091] The method for preparing the composite solid electrolyte is identical to that of Example 1 except that the thickness of the lithium metal layer deposited by ion deposition is changed in adaptability, and the lithium metal layer is completely reacted with the polyphosphoric acid.

[0092] Example 5

[0093] The composite solid electrolyte of the present embodiment is identical to that of Example 1 except that the thickness of the Li3PO4 layer is 1 μm.

[0094] The method for preparing the composite solid electrolyte is identical to that of Example 1 except that the concentration of the polyphosphoric acid solution is changed in adaptability, and the thickness of the obtained Li3PO4 layer is 1 μm.

[0095] Example 6

[0096] The composite solid electrolyte of the present embodiment is identical to that of Example 1 except that the thickness of the Li3PO4 layer is 10 μm.

[0097] The method for preparing the composite solid electrolyte is identical to that of Example 1 except that the concentration of the polyphosphoric acid solution is changed in adaptability, and the thickness of the obtained Li3PO4 layer is 10 μm.

[0098] Example 7

[0099] The composite solid electrolyte of the present embodiment is identical to that of Example 1 except that the molar ratio of PEO and PVDF is 1:0.001.

[0100] The method for preparing the composite solid electrolyte is identical to that of Example 1 except that the amount of PEO and PVDF added is changed in adaptability.

[0101] Example 8

[0102] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the molar ratio of PEO and PVDF is 1:0.05.

[0103] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the molar ratio of PEO and PVDF is 1:0.05.

[0104] Example 9

[0105] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the magnesium triflate is not included in the conductive polymer layer.

[0106] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the magnesium triflate is not added in the preparation method of the composite solid-state electrolyte.

[0107] Example 10

[0108] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the concentration of the polyphosphoric acid solution in step (2) of the preparation method is 0.05 mol / L, and the obtained composite solid-state electrolyte is correspondingly changed.

[0109] Example 11

[0110] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the concentration of the polyphosphoric acid solution in step (2) of the preparation method is 2.5 mol / L, and the obtained composite solid-state electrolyte is correspondingly changed.

[0111] Example 12

[0112] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that step (2) of the preparation method is changed to: spraying the Li3PO4 solution on the surface of the lithium metal layer in step (1) at a flow rate of 2 mL / min, and then drying in a vacuum drying box for 2 h to obtain a Li3PO4 layer, and the composite solid-state electrolyte is correspondingly changed.

[0113] Comparative Example 1

[0114] The present example provides a composite solid-state electrolyte, which is the same as that of Example 1 except that the molar ratio of PEO and PVDF is 1:0.05.

[0115] The SEM diagram of the interface between the solid electrolyte of the present comparative example and the lithium metal negative electrode after 20 cycles is shown in Figure 5 The cycle performance diagram of the solid-state battery made of the electrolyte is shown in Figure 6

[0116] Comparative Example 2

[0117] The present comparative example provides a solid-state electrolyte, which is the same as that of Example 1 except that it does not include a Li3PO4 layer.

[0118] The preparation method of the solid-state electrolyte is the same as that of Example 1 except that it does not include step (2).

[0119] Comparative Example 3

[0120] The present comparative example provides a solid-state electrolyte, which is the same as that of Example 1 except that it does not include a conductive polymer layer.

[0121] The preparation method of the solid-state electrolyte is the same as that of Example 1 except that it does not include step (3).

[0122] The composite solid-state electrolyte described in the above examples is pasted with a lithium metal negative electrode sheet with a thickness of 50 microns on the side of the conductive polymer, and is pressed under a pressure of 5Mpa, and then a NCM811 positive electrode is coated on the side of the electrolyte layer, and the positive electrode load is controlled at 0.5g / cm 2 , and then it is put into a test mold for pressure retention at 5Mpa for testing. The test conditions are: charging and discharging test at 25℃ and 0.1C rate; the solid-state electrolyte of the present comparative example is prepared and tested by the same method as above.

[0123] The test results are shown in Table 1:

[0124] Table 1

[0125]

[0126]

[0127] From Table 1, it can be seen that:

[0128] (1) The composite solid-state electrolyte provided by the present application can greatly improve the cycle performance of the solid-state battery through surface modification, and it can be known from Figure 2 that the color after setting the modification layer is basically the same as that of the sulfide electrolyte without setting, and it can be seen that surface modification does not change the properties of the electrolyte sheet; from the comparison of Figure 3 and Figure 5 , it can be known that Figure 5 ​The interface between the solid-state electrolyte and the lithium metal obtained by the comparative example is thick and heavy, and in the cycling process, the lithium metal continuously reacts with the solid-state electrolyte, and the interface continuously deteriorates, resulting in continuous capacity attenuation and a significant reduction in cycle life. The solid-state electrolyte obtained by Example 1 has a lithium metal layer, an interface side reaction layer and a solid-state electrolyte layer in sequence, and the interface between the solid-state electrolyte and the lithium metal obtained by Example 1 is thin and light, and in the cycling process, the lithium metal continuously reacts with the solid-state electrolyte, and the interface continuously deteriorates, resulting in continuous capacity attenuation and a significant reduction in cycle life. Figure 3 The surface has no obvious interface side reaction, and after cycling, the lithium metal negative electrode is still closely attached to the composite solid-state electrolyte layer, and the interface has not deteriorated and the components are distinct.

[0129] (2) Combined Figure 4 and Figure 6 As can be seen, the capacity retention rate of Example 1 is 98.41% after 160 cycles, and the coulombic efficiency is always above 99.9%. This is because the impedance decreases when lithium ions migrate from the solid-state electrolyte to the lithium metal electrode, and the lithium ion conduction flux increases. In addition, there is no side reaction between the solid-state electrolyte and the Li electrode to produce low ion conductors and high electron conductors, and the polymer layer offsets the expansion of the lithium metal layer in the cycling process. In Comparative Example 1, the capacity rapidly attenuates at a rate of 0.1C, and the cycle performance significantly decreases. As can be seen from Example 1 and Comparative Examples 2-3, when the modification layer on the surface of the composite solid-state electrolyte does not include the Li3PO4 layer or the conductive polymer layer, the performance of the obtained solid-state electrolyte decreases. As can be seen from Example 1 and Example 4, the setting of the lithium metal layer can further improve the performance of the solid-state electrolyte. As can be seen from Example 1 and Examples 5-9, the thickness of the Li3PO4 layer and the molar ratio of the two polymers in the conductive polymer layer will affect the performance of the solid-state electrolyte. As can be seen from Example 1 and Examples 10-11, if the concentration of the polyphosphoric acid solution is not within a reasonable range during preparation, it will affect the interface of the Li3PO4 layer. As can be seen from Example 1 and Example 12, the method of using a polyphosphoric acid solution to react with lithium metal to obtain the Li3PO4 layer in the present application can make the interface closely combined and obtain an effective interface protection phase. However, when Li3PO4 is directly used for preparation, Li3PO4 will enter the PEO polymer layer to form a PEO-Li3PO4 composite layer, which cannot protect the lithium metal layer and uniformly deposit lithium ions, and the performance of the obtained composite solid-state electrolyte decreases.

[0130] In summary, the present application provides a composite solid-state electrolyte, a preparation method and application thereof. The surface of the composite solid-state electrolyte has a modification layer, which allows uniform deposition of lithium ions, slows down the growth of lithium dendrites, reduces the dispersion of lithium powder, thereby reducing the probability of explosion of lithium metal batteries, and can reduce interface side reactions, increase battery cycle life, reduce interface voids, thereby reducing interface impedance and improving ion transport capacity.

[0131] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A composite solid-state electrolyte, characterized by, The composite solid-state electrolyte comprises an electrolyte layer, a Li3PO4 layer and a conductive polymer layer which are sequentially stacked; A lithium metal layer is further arranged between the electrolyte layer and the Li3PO4 layer.

2. The composite solid-state electrolyte of claim 1, wherein, The thickness of the lithium metal layer is 2-15 μm.

3. The composite solid-state electrolyte of claim 1, wherein, The thickness of the Li3PO4 layer is 3-7 μm.

4. The composite solid-state electrolyte of claim 1, wherein, The thickness of the conductive polymer layer is 5-15 μm.

5. The composite solid-state electrolyte of claim 1, wherein, The thickness of the electrolyte layer is 5-200 μm.

6. The composite solid-state electrolyte of claim 1, wherein, The conductive polymer layer comprises a first polymer and a second polymer, the first polymer comprises any one or a combination of at least two of PEO, TPU, PAA, PAN, PVMA or polyphosphazine, and the second polymer comprises PVDF and / or PVDF-HFP.

7. The composite solid-state electrolyte of claim 6, wherein, The molar ratio of the first polymer to the second polymer is (0.5-2):(0.0025-0.01).

8. The composite solid-state electrolyte of claim 1, wherein, The conductive polymer layer further comprises an aluminum salt and / or a magnesium salt.

9. The composite solid-state electrolyte of claim 1, wherein, The conductive polymer layer further comprises a lithium salt.

10. The composite solid-state electrolyte of claim 8, wherein, The aluminum salt comprises aluminum trifluoromethyl sulfonate.

11. The composite solid-state electrolyte of claim 8, wherein, The magnesium salt comprises magnesium trifluoromethyl sulfonate.

12. The composite solid-state electrolyte of claim 9, wherein, The lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium nitrate or lithium hexafluorophosphate.

13. A method of producing a composite solid-state electrolyte as claimed in any one of claims 1 to 12, characterized in that, The preparation method comprises the following steps: (1) preparing a lithium metal layer on the surface of an electrolyte layer, coating a polyphosphoric acid solution on the surface of the lithium metal layer to obtain a Li3PO4 layer; (2) coating a conductive polymer layer slurry on the surface of the Li3PO4 layer obtained in step (1) to obtain the composite solid-state electrolyte.

14. The method of claim 13, wherein, The concentration of the polyphosphoric acid solution in step (1) is 0.1-2 mol / L.

15. The preparation method according to claim 13, characterized in that, The polyphosphoric acid solution in step (1) is obtained by stirring and mixing polyphosphoric acid and an organic solvent.

16. The method of claim 15, wherein, The organic solvent comprises any one or a combination of at least two of benzene, toluene, ethylbenzene or xylene.

17. The preparation method according to claim 15, characterized in that, The stirring and mixing time is 60-120 min.

18. The method of claim 13, wherein, The coating mode in step (1) comprises spraying, and the spraying flow rate is 1-3 mL / min.

19. The method of claim 13, wherein, The lithium metal layer in step (1) is deposited on the surface of the electrolyte layer by an ion deposition method.

20. The method of claim 13, wherein, The electrolyte layer in step (1) is obtained by pressing an electrolyte material into a sheet or preparing a film.

21. The method of claim 20, wherein, The electrolyte material comprises any one or a combination of at least two of a sulfide solid-state electrolyte, an oxide solid-state electrolyte or a halide solid-state electrolyte.

22. The method of claim 13, wherein, The conductive polymer layer slurry in step (2) is obtained by mixing a first polymer, a second polymer and a solvent.

23. The method of claim 22, wherein, The addition amount of the first polymer is 0.5-2 mol, and the addition amount of the second polymer is 0.0025-0.01 mol.

24. The method of claim 22, wherein, The first polymer comprises any one or a combination of at least two of PEO, TPU, PAA, PAN, PVMA or polyphosphazine, and the second polymer comprises PVDF and / or PVDF-HFP.

25. The preparation method according to claim 22, characterized in that, The solvent comprises any one or a combination of at least two of benzene, toluene, ethylbenzene or xylene.

26. The method of claim 22, wherein, The mixing temperature is 47-60 ℃, and the mixing time is 10-14 h.

27. The method of claim 22, wherein, The lithium salt is further added after the mixing, and the addition amount of the lithium salt is 1-3 mol.

28. The method of claim 22, wherein, 0.01-0.2 mol of an aluminum salt and / or a magnesium salt is further added after the mixing.

29. The method of claim 13, wherein, The coating in step (2) is further vacuum dried for 6-8 h.

30. The method of claim 13, wherein, The preparation method comprises the following steps: (1) pressing the electrolyte material into a sheet or preparing it into a film to obtain an electrolyte layer, and depositing lithium metal on the surface of the electrolyte layer by ion; (2) stirring and mixing polyphosphoric acid and an organic solvent for 60-120 min to obtain a polyphosphoric acid solution, spraying the polyphosphoric acid solution with a concentration of 0.1-2 mol / L on the surface of the lithium metal layer in step (1) at a flow rate of 1-3 mL / min to obtain a Li3PO4 layer; (3) mixing 0.5-2 mol of a first polymer, 0.0025-0.01 mol of a second polymer, and a solvent at a temperature of 47-60 ℃ for 10-14 h, then adding 1-3 mol of a lithium salt and 0.01-0.2 mol of an aluminum salt and / or a magnesium salt to obtain a conductive polymer layer slurry, coating the conductive polymer layer slurry on the surface of the Li3PO4 layer in step (2), and then vacuum drying for 6-8 h to obtain the composite solid-state electrolyte.

31. A solid state battery, characterized by The solid-state battery comprises a positive electrode sheet, a negative electrode sheet, and the composite solid-state electrolyte according to any one of claims 1-12, the negative electrode sheet is arranged on one side of the conductive polymer layer in the composite solid-state electrolyte, and the positive electrode sheet is arranged on one side of the electrolyte layer in the composite solid-state electrolyte.

32. The solid-state battery of claim 31, wherein, The negative electrode sheet comprises any one or a combination of at least two of lithium metal, graphite, silicon, and silicon-carbon material.

Images