A modified porous-dense solid-state electrolyte and a method for preparing the same

Abstract

This invention belongs to the field of solid-state electrolyte preparation technology, and discloses a modified porous-dense solid-state electrolyte and its preparation method, comprising: spreading molten salt material onto the porous layer surface of the porous-dense solid-state electrolyte, and heating it for the first time until the molten salt material melts; wherein, the porous-dense solid-state electrolyte comprises a porous layer and a dense layer composed of solid electrolyte powder; after the molten salt material melts, it is heated for the second time to decompose the molten salt material, and the decomposition products of the molten salt material adhere to the surface of the porous layer to obtain the modified porous-dense solid-state electrolyte. This invention provides a simple and easily scalable surface modification method based on molten salt, avoiding the use of expensive and complex surface coating technology, significantly improving the non-wetting problem between the ion-conducting network and the alkali metal, achieving the goal of improving the utilization rate of the alkali metal in the negative electrode, thereby realizing stable cycling of solid-state alkali metal batteries under high current density and large area capacity.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte preparation technology, and more specifically, relates to a modified porous-dense solid electrolyte and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in mobile electronic devices due to their long cycle life, low cost, and fast response. However, the energy density of lithium-ion batteries has gradually reached its theoretical limit, and their use of flammable organic electrolytes significantly compromises their safety. Solid-state alkali metal batteries, using alkali metals as the negative electrode and solid ionic conductors as the electrolyte, offer high energy density and safety, and are expected to replace lithium-ion batteries as the next-generation electrochemical energy storage technology. However, at high current densities (≥1.0 mA cm⁻¹), they face challenges. -2 Under these conditions, the volume change of the alkali metal anode is drastic, resulting in large stress / strain at the electrolyte / electrode interface, making it difficult to maintain good interfacial wettability and increasing interfacial resistance. At the same time, the anode bulk phase lacks a continuous ion permeation path, resulting in low ion migration efficiency and few effective reaction interfaces. These factors lead to low alkali metal utilization of the anode and poor battery rate performance.

[0003] Existing technologies have proposed a porous-dense bilayer electrolyte that can construct a continuous ion permeation path to a certain extent and improve ion migration efficiency. However, the interface wettability of this porous-dense bilayer electrolyte / alkali metal anode interface is poor, which cannot truly improve the problem of low alkali metal utilization of the anode and poor battery rate performance. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a modified porous-dense solid electrolyte and its preparation method, the purpose of which is to improve the utilization rate of alkali metals in the negative electrode so as to improve the rate performance of the battery.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing a modified porous-dense solid electrolyte is provided, comprising:

[0006] Molten salt material is spread evenly on the surface of the porous layer of the porous-dense solid electrolyte, and then heated for the first time until the molten salt material melts; wherein, the porous-dense solid electrolyte comprises a porous layer and a dense layer composed of solid electrolyte powder;

[0007] After the molten salt material is melted, it is heated a second time to decompose the molten salt material. The decomposition products of the molten salt material adhere to the surface of the porous layer to obtain a modified porous-dense solid electrolyte.

[0008] Furthermore, the molten salt material has a melting point of 50℃ to 500℃ and a decomposition temperature of 100℃ to 700℃.

[0009] Furthermore, the preparation process of the porous-dense solid electrolyte includes:

[0010] Solid electrolyte powder and pore-forming agent are stirred and mixed in an organic inert solvent, and then the organic inert solvent is evaporated to obtain a mixed powder;

[0011] Solid electrolyte powder is added to a tableting mold and pressed into a tablet as a dense layer precursor; the mixed powder is evenly spread on the surface of the dense layer precursor and integrally pressed into a preform; wherein, the mixed powder forms a porous layer precursor during the pressing process;

[0012] The green blank is sintered to form a porous-dense solid electrolyte consisting of a porous layer and a dense layer.

[0013] Furthermore, the proportion of the pore-forming agent in the mixed powder is 10wt% to 33.3wt%.

[0014] Furthermore, the amount of porous layer powder used is 50mg to 100mg, and the amount of dense layer powder used is 100mg to 500mg.

[0015] Furthermore, the solid electrolyte is a garnet-type oxide, β″-alumina, NASICON-type, argentite-germanium ore-type, alkali metal nitride, or LiPON-type solid electrolyte;

[0016] The pore-forming agent is polyethylene oxide, polymethyl methacrylate, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, chitosan, methylcellulose, starch, FeCl3, AlCl3, BiCl3, SbF3, SbCl3, S or SeS2.

[0017] According to a second aspect of the present invention, a modified porous-dense solid electrolyte is provided, which is prepared by the modified porous-dense solid electrolyte preparation method according to any one of the first aspects.

[0018] According to a third aspect of the present invention, a method for preparing a composite alkali metal anode is provided, comprising:

[0019] An alkali metal is heated to a molten state and cast onto the surface of a porous layer of a modified porous-dense solid electrolyte to obtain a composite alkali metal anode.

[0020] The modified porous-dense solid electrolyte is prepared by the modified porous-dense solid electrolyte preparation method described in any one of the first aspects, or is the modified porous-dense solid electrolyte described in the second aspect.

[0021] Furthermore, the alkali metal is lithium, sodium, or potassium.

[0022] According to a fourth aspect of the present invention, a composite alkali metal anode is provided, which is prepared by the composite alkali metal anode preparation method described in the third aspect.

[0023] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0024] (1) This invention found that directly using the prepared porous-dense solid electrolyte as the electrolyte for a solid-state alkali metal battery results in poor wettability at the interface between the electrolyte and the alkali metal anode. Specifically, this is because the surface energy of molten alkali metal is very high, resulting in a very large contact angle if it directly contacts the porous-dense solid electrolyte. Based on this, the modified porous-dense solid electrolyte preparation method of this invention uses a molten salt with low surface energy (which has a low contact angle with the porous-dense solid electrolyte) to modify the surface of the porous-dense solid electrolyte. The molten salt material is spread evenly on the porous layer surface of the porous-dense solid electrolyte and heated until it melts. The molten salt material then penetrates into the porous layer of the porous-dense solid electrolyte through capillary force. Upon further heating, the molten salt material decomposes, and the decomposition products adhere to the surface of the porous layer, thereby improving the wettability between the porous layer and the alkali metal anode. In this way, the utilization rate of the alkali metal at the anode can be improved, thus improving the rate performance of the battery.

[0025] (2) The present invention uses a method of uniformly modifying the surface of porous-dense solid electrolytes with molten salt, which avoids the use of complex and expensive surface modification technologies such as magnetron sputtering, atomic layer deposition, and vapor deposition. It improves the wettability of porous solid electrolytes with alkali metals in a simple and low-cost way.

[0026] (3) When the molten alkali metal negative electrode is combined with the modified porous-dense solid electrolyte, on the one hand, the molten alkali metal is uniformly adsorbed into the porous layer of the modified porous-dense solid electrolyte under the action of capillary force. On the other hand, the molten alkali metal will also react with the products of the decomposition of the molten salt material attached to the surface of the porous layer during modification. The chemically induced molten alkali metal uniformly fills the porous structure. Under this combined physical and chemical action, the contact / reaction area between the alkali metal and the solid electrolyte is effectively increased, which is conducive to improving the charge transfer rate and the utilization rate of the alkali metal, so as to improve the rate performance of the battery.

[0027] (4) Preferably, at the set melting point and decomposition temperature of the molten salt material, the molten salt material can obtain a low melt viscosity to penetrate into the porous solid electrolyte for uniform surface modification, and a sufficient decomposition rate to form active nanoparticles to induce subsequent molten alkali metal injection into the porous electrolyte layer.

[0028] (5) Furthermore, in this invention, the solid electrolyte powder containing the pore-forming agent is integrally pressed into a blank and the pore-forming agent is removed by sintering. Sintering ensures that there is a high bonding strength between the porous layer and the dense layer. Therefore, a three-dimensional continuous ion-conducting network is formed inside the porous-dense solid electrolyte. Using it as an ion permeation path can improve the ion migration efficiency inside the alkali metal anode and increase the electrochemical reaction active interface. Therefore, it alleviates the stress / strain caused by the volume change of the alkali metal anode, enhances the electrode reaction kinetics, and reduces battery polarization.

[0029] (6) Preferably, the proportion of the pore-forming agent in the mixed powder is set in a way that can form an open porous structure while ensuring the integrity of the formed porous structure.

[0030] (7) Preferably, the powder quality of the porous layer and the dense layer is set so that the molten lithium can completely fill the porous layer without any residue on the surface; and the battery internal resistance can be reduced as much as possible while maintaining the strength of the porous structure. Attached Figure Description

[0031] Figure 1 This is a flowchart of the modified porous-dense solid electrolyte preparation method in an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the porous-dense solid electrolyte preparation method in an embodiment of the present invention.

[0033] Figure 3 SEM images of porous-dense LLZTO (PD-LLZTO) electrolytes prepared from mixed powders with different pore-forming agent mass ratios.

[0034] Figure 4 SEM images of molten lithium injected into porous LLZTO electrolyte with different amounts of porous layer powder.

[0035] Figure 5 The images show SEM images of porous-dense LLZTO at different sizes in Example 1; where (a) and (b) are SEM images at 500 μm and 50 μm, respectively.

[0036] Figure 6 This is a schematic diagram of the AgNO3 molten salt modified porous LLZTO layer in Example 1.

[0037] Figure 7 This is an optical schematic diagram of AgNO3 molten salt permeating into porous LLZTO in Example 1.

[0038] Figure 8 This is an optical schematic diagram of the high-temperature decomposition of AgNO3 in the porous LLZTO layer in Example 1.

[0039] Figure 9 This is an optical schematic diagram of the porous LLZTO layer modified with AgNO3 infiltrated with molten Li metal in Example 1.

[0040] Figure 10 The images shown are SEM images and EDX results of molten Li infiltrating into the porous LLZTO layer in Example 1. Among them, (a) is the SEM result of the porous / dense LLZTO interface after molten Li filling, (b)-(d) are the corresponding EDX results of Ag, La and O, respectively; (e) and (f) are the SEM results and locally magnified SEM results of the porous layer after molten Li filling, respectively, and (g) and (h) are the corresponding EDX results of Ag and La, respectively.

[0041] Figure 11 Cyclic performance and critical current density of a Li-Ag|PDP-LLZTO|Li-Ag lithium symmetric battery prepared and assembled according to Example 1 were tested; where (a)-(c) represent 0.5 mA / cm², respectively. -2 @0.5mAh cm -2 1.0mAcm -2 @0.5mAh cm -2 and 1.5mAcm -2 @0.75mAh cm -2 (d) shows the cycle performance of the Li symmetric cell; (d) shows the critical current density test of the Li symmetric cell.

[0042] Figure 12 The cycling performance of the Li-Ag|DP-LLZTO|LFP lithium iron phosphate solid lithium metal battery assembled according to Example 1, as well as the Li-Ag|LLZTO|LFP and Li|LLZTO|LFP lithium iron phosphate solid lithium metal batteries without porous structure, are shown in (a)-(b), which represent the cycling performance of the lithium iron phosphate full cell at 0.5C and 1.0C, respectively. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] In this invention, the terms "first," "second," etc., used in the invention and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0045] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a modified porous-dense solid electrolyte, comprising:

[0046] Molten salt material is spread evenly on the surface of the porous layer of the porous-dense solid electrolyte, and then heated for the first time until the molten salt material melts; then heated for the second time to decompose the molten salt material, and the decomposition products of the molten salt material adhere to the surface of the porous layer to obtain the modified porous-dense solid electrolyte; wherein, the above-mentioned porous-dense solid electrolyte includes a porous layer composed of solid electrolyte powder and a dense layer composed of solid electrolyte powder.

[0047] Preferably, the molten salt material has a melting point of 50℃ to 500℃ and a decomposition temperature of 100℃ to 700℃. The molten salt material with these melting points and decomposition temperatures can achieve a low melt viscosity to penetrate into the porous solid electrolyte for uniform surface modification, and a sufficient decomposition rate to form active nanoparticles to induce subsequent molten alkali metal injection into the porous electrolyte layer.

[0048] In embodiments of the present invention, such as Figure 2 As shown, the preparation of the above-mentioned porous-dense solid electrolyte includes:

[0049] Solid electrolyte powder and pore-forming agent are stirred and mixed in an organic inert solvent, and then the solvent is evaporated to obtain a mixed powder;

[0050] Solid electrolyte powder is added to a tableting mold and pressed into a tablet as a dense layer precursor. Then, the pressing head is removed, and mixed powder is added and spread evenly on the surface of the dense layer precursor. The pressing head is reinserted and pressed into a preform in one piece. The preform consists of a porous layer precursor and a dense layer precursor.

[0051] The above-mentioned green blank is sintered in a ceramic crucible to form a porous-dense solid electrolyte consisting of a porous layer and a dense layer.

[0052] Preferably, the solid electrolyte powder is a chemically stable solid electrolyte with alkali metals. This prevents it from reacting with the subsequently molten alkali metal anode, thus improving the stability of the porous structure. Examples of suitable solid electrolytes include garnet-type oxides, β″-alumina, NASICON-type, argentite-germanium sulfide-type, alkali metal nitrides, and LiPON-type solid electrolytes that are chemically stable with alkali metals.

[0053] Pore-forming agents are artificially synthesized organic, natural polymers, or inorganic substances that can form open porous structures after heating by burning, volatilizing, or sublimating, and whose remaining substances after sintering do not affect the conductivity of solid electrolytes. Artificially synthesized organic substances, such as polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), are organic substances that can be removed by oxidation and combustion. Natural polymers, such as chitosan, methylcellulose, and starch, are organic substances that can be removed by oxidation and combustion. Inorganic substances, such as FeCl3, AlCl3, BiCl3, SbF3, SbCl3, S, and SeS2, are inorganic substances that are easily sublimated / volatilized by heating.

[0054] Preferably, the proportion of the pore-forming agent in the porous layer precursor (or mixed powder) is 10wt% to 33.3wt%; at this ratio, an open porous structure can be formed while ensuring the integrity of the formed porous structure. Figure 3 As shown, porous solid electrolytes prepared with 5% pore-forming agent have low porosity and many closed pores, which may prevent molten alkali metal from being fully injected into the porous structure. Porous solid electrolytes prepared with 50% pore-forming agent cannot maintain structural integrity. Pore-forming agent ratios from 10% to 33.3% can simultaneously maintain open-pore structures and structural integrity, with a 33.3% ratio maximizing porosity to increase the loading of alkali metal in the porous structure.

[0055] Preferably, the sintering temperature of the green body in the ceramic crucible is 100℃~1700℃, the heating rate during sintering is 1℃ / min~10℃ / min, the holding time after sintering is 10min~10h, and the cooling rate is 1℃ / min~10℃ / min.

[0056] Preferably, the porous layer powder has a mass of 50mg to 100mg, and the dense layer powder has a mass of 100mg to 500mg. For example... Figure 4 As shown, when the porous layer powder dosage is 30mg, the porous layer is relatively thin, and a large amount of molten lithium remains on the surface of the porous layer. When the porous layer powder dosage is 200mg, the porous layer is relatively thick, and molten lithium cannot completely fill the porous layer. When the porous layer powder dosage is 50mg–100mg, molten lithium can completely fill the porous layer without surface residue. For the dense layer, too little powder cannot maintain the strength of the entire structure, while too much powder can easily lead to excessive internal resistance in the battery; therefore, a dosage of 100mg–500mg is chosen.

[0057] In this embodiment of the invention, a modified porous-dense solid electrolyte is also provided, which is prepared by the above-described method for preparing a modified porous-dense solid electrolyte.

[0058] In this embodiment of the invention, a method for preparing a composite alkali metal anode is also provided, comprising:

[0059] The alkali metal is heated to a molten state and poured onto the porous layer surface of the modified porous-dense solid electrolyte prepared above to obtain a composite alkali metal anode.

[0060] Alkali metals include lithium, sodium, potassium, and other alkali metals.

[0061] In this embodiment of the invention, a composite alkali metal anode is also provided, which is prepared by the above-described composite alkali metal anode preparation method.

[0062] This invention reveals that directly using the prepared porous-dense solid electrolyte as the electrolyte in a solid-state alkali metal battery results in poor wettability at the interface between the electrolyte and the alkali metal anode. Specifically, this is because the surface energy of molten alkali metal is very high, leading to a very large contact angle when it directly contacts the porous-dense solid electrolyte. Therefore, this invention provides a modified porous-dense solid electrolyte preparation method. This method uses a molten salt with low surface energy (which has a lower contact angle with the porous-dense solid electrolyte) to modify the surface of the electrolyte. The molten salt material is spread evenly on the porous layer surface of the porous-dense solid electrolyte and heated until it melts. The molten salt material then penetrates into the porous layer of the porous-dense solid electrolyte through capillary force. Upon further heating, the molten salt material decomposes, and the decomposition products adhere to the surface of the porous layer, thereby improving the wettability between the porous layer and the alkali metal anode. This improves the utilization rate of the alkali metal at the anode, thus enhancing the battery's rate performance.

[0063] This invention uses a method based on molten salt to uniformly modify the surface of porous-dense solid electrolytes, avoiding complex and costly surface modification techniques such as magnetron sputtering, atomic layer deposition, and vapor deposition. This method improves the wettability of porous solid electrolytes with alkali metals in a simple and low-cost manner.

[0064] When a molten alkali metal anode is combined with a modified porous-dense solid electrolyte, the molten alkali metal is uniformly adsorbed into the porous layer of the modified porous-dense solid electrolyte under the action of capillary force. On the other hand, the molten alkali metal also reacts with the decomposition products of the molten salt material attached to the surface of the porous layer during modification. The chemically induced molten alkali metal uniformly fills the porous structure. Under this combined physical and chemical action, the contact / reaction area between the alkali metal and the solid electrolyte is effectively increased, which is beneficial to improving the charge transfer rate and the utilization rate of the alkali metal, thereby improving the rate performance of the battery.

[0065] In preparing a porous-dense solid electrolyte, this invention integrates solid electrolyte powder containing a pore-forming agent with solid electrolyte powder to form a blank, and then removes the pore-forming agent by sintering. Sintering ensures a high bonding strength between the porous layer and the dense layer, thus forming a three-dimensional continuous ion-conducting network as an ion permeation pathway. This improves the ion migration efficiency inside the alkali metal anode, increases the electrochemical reaction activity interface, alleviates the stress / strain caused by the volume change of the alkali metal anode, enhances electrode reaction kinetics, and reduces battery polarization.

[0066] The method of the present invention will be further described below with specific embodiments.

[0067] Example 1

[0068] Preparation of garnet-type Li superionic conductor LLZTO (lithium lanthanum zirconium tantalum oxide, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Powder was used as the solid electrolyte powder, and 10 μm diameter polymethyl methacrylate (PMMA) spheres were used as pore-forming agents, with a solid electrolyte to pore-forming agent mass ratio of 2:1. The mixture was stirred and mixed in isopropanol solvent at 700 rpm, and then dried to remove the solvent, yielding a mixed precursor powder. 0.05 g of this powder and 0.1 g of LLZTO powder were sequentially added to a tableting mold and pressed into a preform at 300 MPa. Subsequently, it was sintered in a magnesium oxide crucible at 1250 °C for 20 min, with a heating / cooling rate of 10 °C / min, to obtain a porous-dense LLZTO (PD-LLZTO) solid electrolyte; wherein the mass of the porous layer and the dense layer powder were 50 mg and 100 mg, respectively. Figure 3 The image shown is a SEM image of porous-dense LLZTO at different sizes. Figure 5(a) and (b) are SEM images at 500 μm and 50 μm, respectively. AgNO3 was used as a surface modification material for the porous layer. After melting at 250 °C, it diffused into the porous layer and was further heated to 550 °C to decompose, forming nano-Ag particles loaded on the surface of the porous layer to improve its lithiophilicity. Subsequently, lithium metal was heated to 220 °C to melt and alloy with the nano-Ag particles in the porous layer. Under capillary force, the molten lithium diffused into the porous layer to form a composite Li-Ag@LLZTO electrode, as shown in the image. Figures 6-9 As shown.

[0069] The decomposition reaction process of AgNO3 is as follows:

[0070]

[0071] The alloying reaction process is as follows:

[0072] xLi + Ag → Li x Ag

[0073] In Example 1, the SEM images and EDX results of molten Li infiltrating into the porous LLZTO layer are as follows: Figure 10 As shown, (a) is the SEM result of the porous / dense LLZTO interface after molten Li filling, (b)-(d) are the EDX results of Ag, La and O respectively; (e) and (f) are the SEM results of the porous layer after molten Li filling and the SEM results after local magnification, respectively; (g) and (h) are the EDX results of Ag and La respectively. The EDX result of Ag is used to reflect the distribution of the negative electrode, and the EDX result of La is used to reflect the distribution of the solid electrolyte. It can be seen that molten Li can penetrate to the interface between the porous layer and the dense layer and fill the pores of the porous layer, showing an interpenetrating morphology with the porous LLZTO. At the same time, no Ag nanoparticles were observed, indicating that molten Li may have undergone a solid solution reaction with it. The EDX results show that the distribution of Ag and O elements is almost the same (the O element is mainly caused by the oxidation of Li during the sample transfer process, and to a certain extent represents the distribution of Li), proving that the continuous phase filling the pores is composed of Ag and Li, and is speculated to be a Li-Ag solid solution alloy. The magnified SEM image of the porous layer shows that the Li-Ag alloy has good wettability with LLZTO.

[0074] Figure 11 To test the cycle performance and critical current density of the porous-dense-porous LLZTO (PDP-LLZTO) and assembled Li-Ag|PDP-LLZTO|Li-Ag lithium symmetric battery according to Example 1, Figure 11 In this context, (a)-(c) represent 0.5 mAcm. -2 @0.5mAh cm -21.0mAcm -2 @0.5mAh cm -2 and 1.5mAcm -2 @0.75mAh cm -2 The cycling performance of the Li-symmetric cell is shown in (d); the critical current density of the Li-symmetric cell is measured. It can be seen that at 0.5 mA / cm², the cell exhibits good performance. -2 @0.5mAh cm -2 Under these conditions, the polarization of the Li-Ag|LLZTO|Li-Ag battery continuously increases, leading to short-circuit failure after 120 hours of cycling. Conversely, the Li-Ag|PDP-LLZTO|Li-Ag battery can cycle stably for over 6500 hours; when the current density increases to 1.0 mA cm⁻¹... -2 Even at 1.5 mA cm⁻¹, the battery still maintained stable cycling for 1600 hours, demonstrating the excellent long-term cycling stability of the PDP-LLZTO. -2 High current density and 0.75mAh cm⁻¹ -2 Even with a large capacity, the battery can still cycle stably for over 300 hours, indicating that the ion-conducting network constructed by porous LLZTO significantly increases the lithium-ion migration depth, improves electrode reaction kinetics, alleviates negative electrode stress / strain, and improves the utilization rate of active materials, thus achieving stable cycling of the battery under high current / high capacity. The critical current density (CCD) of the Li-Ag|PDP-LLZTO|Li-Ag battery reaches 2.1 mAcm. -2 .

[0075] Figure 12 To evaluate the cycle performance of the Li-Ag|PD-LLZTO|LFP lithium iron phosphate (LFP) solid lithium metal battery assembled according to Example 1, as well as the non-porous Li-Ag|LLZTO|LFP and Li|LLZTO|LFP batteries, Figure 12 In the figure, (a)-(b) represent the cycle performance of lithium iron phosphate full cells at 0.5C and 1.0C, respectively; it can be seen that the Li|LLZTO|LFP battery can only cycle 60 and 12 times at 0.5C and 1.0C, respectively, with an initial capacity of 123.5 mAh g. -1 and 18.5mAh g -1 The Li-Ag|LLZTO|LFP battery has a capacity of 147.0 mAh g at 0.5C. -1 Furthermore, after 83 cycles, the capacity rapidly decreased, leading to battery failure. At a higher rate of 1.0C, the battery capacity continued to decline, reaching only 7.1 mAh g after 90 cycles. -1 In contrast, the Li-Ag|PD-LLZTO|LFP full cell with a porous solid electrolyte structure exhibits a discharge specific capacity of 150.3 mAh g⁻¹ at 0.5C.-1 After 400 stable cycles, the capacity retention rate was 98.7%. Even at 1.0C, the Li-Ag|PD-LLZTO|LFP full cell exhibited a capacity of 130.2 mAh g⁻¹. -1 The high capacity, and the fact that it retains 91.3% of its initial capacity after 350 cycles, indicates that the porous electrolyte provides a stable ion permeation pathway, increases the ion migration depth at the negative electrode, improves electrode reaction kinetics, and alleviates the stress / strain at the negative electrode, thus achieving excellent cycling performance.

[0076] Example 2

[0077] Unlike Example 1, Example 2 uses Na3Zr2Si2PO4. 12 As a solid electrolyte, PVDF-HFP was used as the pore-forming agent at a mass ratio of 3:1. SnF2 was used as the molten salt material to modify the porous layer. The powder masses of the porous layer and the dense layer were 50 mg and 150 mg, respectively, resulting in a critical current density of 1.5 mA cm⁻¹ for the sodium-symmetric battery. -2 The relevant experimental data are shown in Table 1.

[0078] Example 3

[0079] In Example 3, β″-alumina was used as the solid electrolyte, starch as the pore-forming agent (mass ratio 2:1), and SnCl4 was used as the molten salt material to modify the porous layer. The powder masses of the porous layer and the dense layer were 70 mg and 150 mg, respectively, resulting in a critical current density of 1.8 mA cm⁻¹ for the potassium symmetric cell. -2 The relevant experimental data are shown in Table 1. It should be noted that other solid electrolyte powders and pore-forming agents can also be used in other embodiments. The mass of the porous layer powder can also be 80 mg, 100 mg, etc. The mass of the dense layer powder can also be 200 mg, 300 mg, 500 mg, etc.

[0080] Other commonly used molten salt materials can also be selected, as long as they meet the required melting point and decomposition temperature.

[0081] Comparative Example 1

[0082] Unlike Example 1, Comparative Example 1 only used conventional Li 6.4 La3Zr 1.4 Ta 0.6 O 12 As a solid electrolyte, the relevant experimental data are shown in Table 1 and... Figure 11 As shown.

[0083] Table 1. Experimental data of the examples and comparative examples.

[0084]

[0085] It can be seen that the solid-state alkali metal battery constructed in the embodiments of the present invention can significantly improve the diffusion rate and utilization rate of the alkali metal anode, achieving high current density (>1.0 mA cm⁻¹) -2 Large area capacity (>0.5mAh cm⁻¹) -2 Stable cycle (>1600h) under the following conditions, such as Figure 11 As shown in (b) of the diagram.

[0086] In summary, this invention solves the problems of discontinuous ionic conductive network inside the alkali metal anode and low bonding strength with the solid electrolyte. It also provides a simple and easily scalable surface modification method based on molten salt, avoiding the use of expensive and complex surface coating technology. This significantly improves the non-wetting problem between the ionic conductive network and the alkali metal, thereby increasing the utilization rate of the alkali metal in the anode and achieving stable cycling of solid alkali metal batteries under high current density and large area capacity.

[0087] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a modified porous-dense solid electrolyte, characterized in that, include: Molten salt material is spread evenly on the surface of the porous layer of the porous-dense solid electrolyte, and then heated for the first time until the molten salt material melts. The molten salt material penetrates into the porous layer of the porous-dense solid electrolyte through capillary force. The porous-dense solid electrolyte includes a porous layer and a dense layer composed of solid electrolyte powder. After the molten salt material is melted, it is heated a second time to decompose the molten salt material. The decomposition products of the molten salt material adhere to the surface of the porous layer to obtain a modified porous-dense solid electrolyte. The molten salt material has a melting point of 50℃ to 500℃ and a decomposition temperature of 100℃ to 700℃.

2. The method for preparing modified porous-dense solid electrolyte according to claim 1, characterized in that, The preparation process of the porous-dense solid electrolyte includes: Solid electrolyte powder and pore-forming agent are stirred and mixed in an organic inert solvent, and then the organic inert solvent is evaporated to obtain a mixed powder; Solid electrolyte powder is added to a tableting mold and pressed into a tablet as a dense layer precursor; the mixed powder is evenly spread on the surface of the dense layer precursor and integrally pressed into a preform; wherein, the mixed powder forms a porous layer precursor during the pressing process; The green blank is sintered to form a porous-dense solid electrolyte consisting of a porous layer and a dense layer.

3. The method for preparing modified porous-dense solid electrolyte according to claim 2, characterized in that, The proportion of the pore-forming agent in the mixed powder is 10 wt% to 33.3 wt%.

4. The method for preparing modified porous-dense solid electrolyte according to claim 2, characterized in that, The amount of porous layer powder used is 50 mg ~ 100 mg, and the amount of dense layer powder used is 100 mg ~ 500 mg.

5. The method for preparing modified porous-dense solid electrolyte according to claim 2, characterized in that, The solid electrolyte is a garnet-type oxide, β″-alumina, NASICON-type, argentite-germanium ore-type, alkali metal nitride, or LiPON-type solid electrolyte. The pore-forming agent is polyethylene oxide, polymethyl methacrylate, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, chitosan, methylcellulose, starch, FeCl3, AlCl3, BiCl3, SbF3, SbCl3, S or SeS2.

6. A modified porous-dense solid electrolyte, characterized in that, The modified porous-dense solid electrolyte is prepared by the modified porous-dense solid electrolyte preparation method according to any one of claims 1-5.

7. A method for preparing a composite alkali metal anode, characterized in that, include: An alkali metal is heated to a molten state and cast onto the surface of a porous layer of a modified porous-dense solid electrolyte to obtain a composite alkali metal anode. The modified porous-dense solid electrolyte is prepared by the modified porous-dense solid electrolyte preparation method according to any one of claims 1-5, or is the modified porous-dense solid electrolyte according to claim 6.

8. The method for preparing the composite alkali metal anode according to claim 7, characterized in that, The alkali metal is lithium, sodium, or potassium.

9. A composite alkali metal anode, characterized in that, The composite alkali metal anode is prepared by the composite alkali metal anode preparation method according to claim 7 or 8.

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