Solid-state electrolyte and method of preparation

Abstract

The application belongs to the field of batteries, and particularly relates to a solid-state electrolyte and a preparation method thereof. The application replaces Ti site elements in LLTO by high-valence element donor doping, and induces segregation of the doping elements at the grain boundaries by a rapid cooling process, so that the atomic structure and the charge distribution characteristics of the grain boundaries are changed, and finally high grain boundary ionic conductivity is realized.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a solid electrolyte and its preparation method. Background Technology

[0002] Solid-state electrolytes are the core component of all-solid-state batteries, and their performance is crucial. Among various oxide solid-state electrolytes, perovskite-type lithium lanthanum titanate (LLTO) stands out due to its excellent bulk ionic conductivity (approximately 10⁻⁶ Ω·cm). -3 Lithium-ion per cubic centimeter (LLTO) is considered a highly promising candidate material. However, in the polycrystalline ceramic morphology, the grain boundary ionic conductivity of LLTO is typically 1–2 orders of magnitude lower than that of the bulk phase, making it difficult for the total ionic conductivity of the material to meet the requirements of practical applications, thus becoming a key bottleneck restricting its industrialization. The physical root of this problem lies in the fact that the particles in the sintered body form a solid-solid interface in the form of point contact, and the resulting high interfacial impedance severely hinders the transgrain boundary transport of lithium ions.

[0003] To overcome this bottleneck, existing technologies generally employ a modification strategy of introducing a second-phase material between grains. Related patents and literature report various schemes, such as: introducing an amorphous nano-silicon oxide layer at the LLTO grain boundaries (CN101325094), composite garnet-type LLZO (CN110556570A), or anti-perovskite Li3OCl (CN110556571A); some studies have also attempted to introduce various glassy oxides at the LLZO and LLTO grain boundaries (see K. Tadanaga et al., Electrochem. Commun. 2013, 33, 51-54; H. Zhang et al., J. Alloy. Compd. 2017, 704, 109-116; K. Yuet al., J. Alloy. Compd. 2018, 739, 892-896). However, this method of "introducing an exogenous second phase" has inherent limitations: the introduced second phase may form new impurity phases during sintering, thereby increasing impedance; more importantly, this strategy is an intrinsic modification and cannot fundamentally optimize the intrinsic structure and space charge layer of grain boundaries. Furthermore, the additional steps complicate the preparation process, hindering large-scale production. Due to these constraints, its grain boundary resistance reduction effect has reached a bottleneck, and the grain boundary ionic conductivity of LLTO generally remains at ~10. -5 Low level, on the order of S / cm.

[0004] Therefore, for LLTO electrolytes, there is an urgent need to develop a new control technology and process route that can achieve intrinsic optimization of grain boundaries without the introduction of exogenous second phases, so as to fundamentally break through the bottleneck of its interface transport performance. Summary of the Invention

[0005] To address the problem that existing technologies rely on introducing exogenous second phases with limited effectiveness, this invention proposes a technical solution for intrinsic grain boundary optimization without introducing an external phase. The core of this solution lies in combining donor doping and rapid thermal processing. Through their synergistic effect, the grain boundary structure and its transport properties are fundamentally controlled and enhanced from within the material.

[0006] Specifically, the present invention solves the above-mentioned technical problems through the following means:

[0007] First, precise elemental doping is used to ensure the uniformity of the composition at the atomic scale, thus suppressing the formation of impurity phases at the source.

[0008] Subsequently, through the synergy of donor doping and rapid cooling processes, intrinsic optimization of grain boundary microstructure and interfacial charge distribution is achieved.

[0009] Ultimately, this invention successfully achieved an order-of-magnitude leap in the grain boundary lithium-ion conductivity of the material, reaching 10. -4 The advanced S / cm level provides a key material foundation for the development of high-performance solid-state batteries.

[0010] This invention provides a perovskite-structured solid electrolyte, lithium lanthanum titanate (LLTO), with low grain boundary impedance and its preparation method. The aim is to solve the key problem that restricts its application: the grain boundary ionic conductivity is much lower than the bulk conductivity, resulting in a low total ionic conductivity.

[0011] Ceramic solid electrolytes consist of grains and grain boundaries. The internal grains exhibit anisotropy, and the atomic arrangement and interface properties differ across different crystal planes. This invention utilizes high-valence element donor doping to partially replace the Ti sites in LLTO, and employs a rapid cooling process to induce segregation of the dopant elements at the grain boundaries. This alters the atomic structure and charge distribution characteristics of the grain boundaries, ultimately achieving high grain boundary ionic conductivity.

[0012] On the one hand, the present invention provides a solid electrolyte with the following chemical formula:

[0013] Li 3x La 2 / 3–x Ti 1–my / 4 M m+ y O3, of which:

[0014] The range of x is: 0.03 ≤ x ≤ 0.167;

[0015] The range of values ​​for y is: 0.005 ≤ y ≤ 0.2;

[0016] m is the absolute value of the valence state of M, m≥5;

[0017] R is the ionic radius of M, 0.55Å≤R(M) m+ ≤0.70Å;

[0018] M represents a dopant element.

[0019] In some implementations, M is selected from one or more of Ta, Nb, V, W, and Mo.

[0020] To maintain the total charge provided by Ti / M ions consistent with the charge provided by Ti ions alone before doping, the total occupancy number of Ti and M ions must be less than 1 (i.e., 1-my / 4+y<1) after incorporating higher valence M ions. This results in a higher lithium-ion concentration in LLTO, thereby increasing the number of mobile lithium ions. Combined with a rapid cooling process that induces segregation of dopant elements at grain boundaries, the atomic structure and charge distribution characteristics of the grain boundaries are altered, ultimately achieving high grain boundary ionic conductivity. Therefore, the donor-doped LLTO provided in this application exhibits better ionic conductivity than undoped LLTO, which is beneficial for its practical application in all-solid-state batteries.

[0021] In some embodiments, the density of the solid electrolyte is ≥95%; optionally, the density of the solid electrolyte is 95%-100%; further optionally, the density of the solid electrolyte is 95%-98%.

[0022] In some embodiments, the bulk conductivity of the solid electrolyte is ≤1 mS / cm; optionally, the bulk conductivity of the solid electrolyte is 0.1-1 mS / cm; further optionally, the bulk conductivity of the solid electrolyte is 0.15-0.95 mS / cm.

[0023] In some embodiments, the solid electrolyte has a grain boundary conductivity ≥ 0.1 mS / cm; optionally, the solid electrolyte has a grain boundary conductivity of 0.1-0.6 mS / cm; further preferably, the solid electrolyte has a grain boundary conductivity of 0.14-0.5 mS / cm.

[0024] The donor-doped LLTO has an ionic conductivity of 0.1-1 mS / cm; preferably, the donor-doped LLTO has an ionic conductivity of 0.2-0.8 mS / cm.

[0025] On one hand, the present invention provides a method for preparing the solid electrolyte, comprising the following steps:

[0026] The lithium source, lanthanum source, titanium source and M source are mixed in proportion, calcined, mixed again, pressed, sintered and rapidly cooled to obtain the perovskite structure solid electrolyte with low grain boundary resistance.

[0027] In some implementations, the primary mixing satisfies at least one of a1-a5:

[0028] a1. The mixing is a wet milling mixture;

[0029] a2. The wet grinding mixture is either wet ball milling or wet sand milling;

[0030] a3. The wet milling solvent used in the wet milling mixture is selected from one or more of water, ethanol, propanol, ethylene glycol, propylene glycol, allyl alcohol, isopropanol, dimethyl carbonate, diethyl carbonate, propylene carbonate, and ethylene carbonate;

[0031] a4. The parameters for wet milling are 400-800 r / min and 3-24 h; preferably, the parameters for wet milling are 500-700 r / min and 6-18 h.

[0032] a5. The lithium source is in 5-50% excess relative to the stoichiometry of the reaction. In some embodiments, the lithium source is in 10-40% excess relative to the stoichiometry of the reaction.

[0033] In some implementations, the method satisfies at least one of b1-b3:

[0034] b1. The calcination conditions are: heating to 700-1400℃ and holding for 3-24 h; preferably, heating to 900-1200℃ and holding for 6-18 h.

[0035] b2. The conditions for secondary mixing are the same as those for primary mixing;

[0036] b3. The average particle size D50 of the powder after secondary mixing is 0.1-1 μm; preferably, the average particle size D50 of the powder after secondary mixing is 0.3-0.8 μm.

[0037] In some embodiments, the pressing conditions are as follows: pressing the secondary mixed powder under a pressure of 200-500 MPa for a holding time of 10-60 minutes to obtain a disc-shaped green body; and / or

[0038] The pressing method is dry pressing or isostatic pressing.

[0039] In some implementations, the method satisfies at least one of c1-c3:

[0040] c1. The sintering conditions are: heating to 1200-1500℃ and holding for 3-36 hours; preferably, heating to 1200-1500℃ and holding for 6-24 hours.

[0041] c2. The secondary calcination method is selected from one or more of the following: solid-state reaction sintering, liquid-state sintering, hot pressing sintering, hot isostatic pressing sintering, microwave sintering, spark plasma sintering, high-pressure sintering, vacuum sintering, atmosphere sintering, and in-situ pressure sintering.

[0042] c3. The rapid cooling is selected from one or more of liquid nitrogen quenching, water immersion quenching, and air quenching.

[0043] In some implementations, the method satisfies at least one of d1-d4:

[0044] d1. The lithium source is selected from one or more of lithium carbonate, lithium oxide, lithium hydroxide, lithium nitrate, lithium acetate, and lithium oxalate;

[0045] d2. The lanthanum source is selected from one or more of lanthanum carbonate, lanthanum oxide, lanthanum hydroxide, and lanthanum nitrate;

[0046] d3. The titanium source is selected from one or more of titanium oxide, titanium hydroxide, and titanium nitrate;

[0047] d4. The source M is selected from one or both of the oxides and hydroxides of M.

[0048] On one hand, the present invention provides a secondary battery, including the solid electrolyte or the solid electrolyte prepared by the preparation method described above.

[0049] On one hand, the present invention provides an electrical device, including the solid electrolyte, the solid electrolyte prepared by the preparation method, or the secondary battery.

[0050] This invention reveals the synergistic mechanism between donor doping and rapid cooling, and based on this, constructs a method that differs from the existing "introduction of exogenous second phase" approach. Specifically, it is manifested as follows:

[0051] New lattice donor doping: selecting ionic radii similar to Ti 4+ The substitution of the B site (Ti site) of LLTO with similar high-valence dopants not only effectively improves the sintering density of the material, but also optimizes its microstructure, laying the foundation for subsequent grain boundary control.

[0052] A novel active modulation of grain boundary structure: By introducing a rapid cooling process, the aforementioned donor dopants are actively induced to selectively segregate at the grain boundaries. This process reconstructs the atomic arrangement in the grain boundary region and effectively modulates the unfavorable space charge layer, thereby significantly reducing grain boundary impedance.

[0053] Construction of a universal approach: By integrating the above doping design with the cooling process, a universal technical solution has been formed that does not rely on the introduction of an "exogenous second phase" and focuses on the intrinsic optimization of grain boundaries. This provides a new and fundamental solution for overcoming the high grain boundary impedance bottleneck of perovskite electrolytes.

[0054] This invention achieves a fundamental improvement in the grain boundary properties of perovskite-structured LLTO solid electrolytes through an innovative process combining high-valence element doping with rapid thermal treatment. The beneficial effects are specifically reflected in the following three aspects:

[0055] 1. Synergistic optimization of grain boundary structure and ion transport performance

[0056] By introducing with Ti 4+ High-valence dopants with similar radii (such as Ta) 5+ 、Nb 5+ (etc.), while achieving precise substitution at B-sites (Ti-sites), a rapid cooling process is combined to actively induce controlled segregation of dopants at grain boundaries. This process not only significantly improves the sintering density and microstructure uniformity of the material, but also more effectively suppresses La... 3+ The unintended segregation of cations at grain boundaries weakens the unfavorable space charge layer effect, thus creating a continuous, low-resistance transgrain boundary transport channel for lithium ions.

[0057] 2. Grain boundary ionic conductivity achieves an order-of-magnitude leap.

[0058] After process optimization according to the present invention, the grain boundary lithium-ion conductivity of LLTO electrolyte is reduced from ~10% by traditional methods. -5 The S / cm magnitude was significantly increased to 0.48 mS / cm (4.8 × 10⁻⁶ mS / cm). -4 The improvement in S / cm is approximately an order of magnitude. This successfully moves the grain boundary conductivity of LLTO electrolyte from a "bottleneck" restricting full-cell performance to a range with "practical application potential".

[0059] 3. The process flow is simple and has excellent scalability.

[0060] The doping and heat treatment steps employed in this invention can be seamlessly integrated with mainstream solid-state sintering processes, eliminating the need to introduce any exogenous second phase or construct complex interface structures, thus simplifying the process flow from the outset. This technical approach demonstrates significant cost advantages and scalable production potential while ensuring product performance repeatability and process controllability. (See attached figures.)

[0061] Figure 1 The XRD patterns are for comparative examples 1-2.

[0062] Figure 2 The XRD patterns are those of Examples 1-4.

[0063] Figure 3 EIS spectra of Comparative Example 1, Comparative Example 2 and Example 1.

[0064] Figure 4 The STEM image and atomic integral intensity at the grain boundary are shown in Comparative Example 1, where (b) and (c) correspond to the atomic integral intensity of the yellow box in Figure a, respectively.

[0065] Figure 5 Figure 1 shows the STEM image and atomic integral intensity at the grain boundary in Example 1, where (b) and (c) correspond to the atomic integral intensity of the red box in Figure a, respectively. Detailed Implementation

[0066] The above embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of protection of this application. Any non-substantial changes and substitutions made by those skilled in the art based on this application shall fall within the scope of protection claimed by this application.

[0067] As used herein, all features or conditions defined by numerical ranges or percentage ranges mentioned by endpoints are for the sake of brevity and convenience only. Therefore, descriptions of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and all individual integer and fractional values ​​within those ranges, particularly integer values. For example, a description of a range “1 to 8” should be considered to specifically disclose all subranges such as 1 to 7, 2 to 8, 3 to 6, 3 to 6, 4 to 8, 3 to 8… etc., particularly subranges defined by all integer values, and should be considered to specifically disclose individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc., regardless of whether these ranges or individual values ​​are explicitly stated. Similarly, a description of a range “between 1 and 8” should also be considered to specifically disclose all ranges such as 1 to 8, 1 to 7, 2 to 8, 3 to 6, 3 to 6, 4 to 8, 3 to 8, etc., and include the endpoint values ​​of these ranges, such as individual values ​​1, 2, 3, 4, 5, 6, 7, 8, etc. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] As used herein, the term “about” refers to an approximation, within approximately or near a range. When the term “about” is used in conjunction with a numerical range, it modifies the range by extending the limits above or below the provided numerical value. Generally, the term “about” is used herein to mean a numerical value that varies by 10% above or below the provided value. On the other hand, the term “about” refers to adding or subtracting 20% ​​of the value of the number it modifies. For example, “about 50%” means within the range of 45%–55%. It should also be understood that all integers and fractions are considered to be modified by the term “about.” In this document, numerical values ​​are to be understood to have the precision of the stated numerical value in significant digits, to the extent that the inventive purpose may be achieved. For example, the number 40.0 can be understood to cover a range from 39.50 to 40.49.

[0069] As used herein, the terms "first," "second," "third," etc., ordinal numbers, unless otherwise stated or further limited, are merely used to distinguish objects with the same attributes by name, and are not used to describe a specific order or sequence, nor to further limit these objects through the ordinal numbers themselves. It should be understood that these ordinal numbers can be interchanged where appropriate without affecting the understanding of this application. Furthermore, it should be understood that disclosures of embodiments without any further limitations imposed by ordinal numbers in this application should also be considered disclosures of embodiments with any further limitations imposed by these ordinal numbers. It should also be understood that the use of a later ordinal number to define an object in this application does not necessarily mean that the same object defined by a earlier ordinal number must also be included in the same embodiment. More importantly, it should be understood that multiple elements with the same name but different ordinal numbers in this application do not imply that they must be different elements; unless otherwise specified, they may be the same or different elements.

[0070] As used herein, the terms “comprising,” “including,” or “containing” are non-exclusive or open-ended terms intended to indicate that a combination (e.g., an apparatus, composition, method, etc.) includes the listed elements (e.g., units of an apparatus, components of a composition, substantial steps of a method, etc.) but does not exclude other elements.

[0071] As used herein, the term "and / or" ("and / or") means and covers any and all possible combinations of one or more of the associated listed items. When used in a list of two or more items, the term "and / or" ("and / or") indicates that any one of the listed items may be included alone, or may include any combination of two or more listed items. For example, if a group, combination, or composition is described as including components A, B, and / or C, then the composition may include A alone, include B alone, include C alone, include a combination of A and B, include a combination of A and C, include a combination of B and C, or include a combination of A, B, and C.

[0072] Unless otherwise specified, the battery components, material types or contents mentioned apply to both lithium-ion and sodium-ion secondary batteries.

[0073] In one embodiment of this application, a secondary battery is provided.

[0074] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. In some embodiments, the electrolyte is a solid-state electrolyte as described in this invention.

[0075]

Positive Electrode

[0076] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0077] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0078] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may be a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0079] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0080] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] [Negative electrode plate]

[0082] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0083] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0084] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0085] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0086] As an example, the negative electrode active material of a secondary battery includes silicon-based materials, and may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries may also be used.

[0087] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0088] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] Electrolytes

[0090] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0091]

Isolation Film

[0092] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0093] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and PI separator with ceramic coating. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0094] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0095] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0096] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0097] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0098] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0099] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0100] An example of an electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this type of device, a battery pack or battery module can be used.

[0101] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0102] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0103] Example 1

[0104] This embodiment provides a low grain boundary resistance perovskite structure lithium lanthanum titanate (Li) 0.33 La 0.56 Ti 0.95 Ta 0.04 The preparation method of O3 solid electrolyte is as follows:

[0105] Raw material weighing and preliminary mixing:

[0106] Accurately weigh the following raw materials and place them in a zirconia ball mill jar:

[0107] Weigh out the following amounts according to the molar ratio of Li₂CO₃, La₂O₃, TiO₂, and Ta₂O₅: 0.165 : 0.28 : 0.95 : 0.02:

[0108] Lithium carbonate (Li₂CO₃) 1.463 g

[0109] Lanthanum trioxide (La₂O₃) 9.123 g

[0110] Titanium dioxide (TiO2) 7.587 g

[0111] 0.884 g of tantalum pentoxide (Ta₂O₅)

[0112] The molecular weight of lithium carbonate is 73.89, that of lanthanum trioxide is 325.809, that of titanium dioxide is 79.866, and that of tantalum pentoxide is 441.89.

[0113] The molecular formula of this embodiment is Li. 0.33 La 0.56 Ti 0.95 Ta 0.04 O3:

[0114] 0.33 / 2 * 73.89 = 12.19g

[0115] 0.56 / 2 * 325.809 = 91.23g

[0116] 0.95 * 79.866 = 75.87g

[0117] 0.04 / 2 * 441.89 = 8.84g

[0118] In this embodiment, 1 / 10 of the amount is used to compensate for the volatilization of the lithium source. The lithium carbonate is in 20% excess relative to the stoichiometric ratio of the reaction, which is 1.463 g.

[0119] Add anhydrous ethanol as a dispersion medium to the jar, and add an appropriate amount of zirconia grinding beads. Place the jar on a ball mill and ball mill at 600 r / min for 12 h to ensure the raw materials are thoroughly mixed.

[0120] Primary calcination and secondary mixing:

[0121] The ball-milled slurry was transferred to an alumina crucible and dried in a vacuum drying oven at 120°C for 12 h to completely remove the ethanol solvent. The dried mixed powder was then placed in a muffle furnace and calcined at 950°C for 12 h to complete the initial solid-phase reaction calcination, followed by furnace cooling to room temperature. The calcined bulk material was then crushed again, placed in a ball mill jar, and anhydrous ethanol was added. A second ball milling was performed for 12 h under the same conditions as the initial mixing, and the resulting slurry was dried in the same manner to obtain a uniformly composed, finely sized initial calcined powder with an average particle size D50 of 0.4 μm.

[0122] Compression molding:

[0123] Accurately weigh an appropriate amount of the above powder, put it into a mold, and press it into a green disc using cold isostatic pressing at 300 MPa. Hold the pressure for 30 minutes to ensure the density of the disc.

[0124] Secondary sintering and rapid cooling:

[0125] The green blank was placed in a muffle furnace and sintered at 1350℃ in air for 9 hours to promote grain growth and densification. Immediately after sintering, the sample was removed and rapidly quenched in liquid nitrogen to induce segregation of dopant elements at the grain boundaries, ultimately obtaining a dense perovskite-structured Li with low grain boundary resistance. 3x La 2 / 3- x Ti 0.95 Ta 0.04 O3 solid electrolyte (where x = 0.11).

[0126] Performance Characterization

[0127] The performance of the LLTO solid electrolyte prepared in this embodiment was tested, and its grain boundary ionic conductivity reached 0.48 mS / cm. Compared with the undoped (Comparative Example 1) control sample, the performance was improved by about 6 times, which effectively solved the problem of high grain boundary impedance. Moreover, the phase was pure and the density was high, which met the requirements of practical applications.

[0128] Example 2:

[0129] The only difference from Example 1 is:

[0130] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tantalum pentoxide is 0.165:0.28:0.975:0.01. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.975 Ta 0.02 O3 (x=0.11).

[0131] Example 3:

[0132] The only difference from Example 1 is:

[0133] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tantalum pentoxide is 0.165:0.28:0.925:0.03. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.925 Ta 0.06 O3 (x=0.11).

[0134] Example 4:

[0135] The only difference from Example 1 is:

[0136] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tantalum pentoxide is 0.165:0.28:0.90:0.04. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.90 Ta 0.08 O3 (x=0.11).

[0137] Example 5:

[0138] The only difference from Example 1 is:

[0139] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tantalum pentoxide is 0.045:0.32:0.95:0.02. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti0.95 Ta 0.04 O3 (x=0.03).

[0140] Example 6:

[0141] The only difference from Example 1 is:

[0142] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tantalum pentoxide is 0.25:0.25:0.95:0.02. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.95 Ta 0.04 O3 (x=0.167).

[0143] Example 7:

[0144] The only difference from Example 1 is:

[0145] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and niobium oxide is 0.165:0.28:0.95:0.02. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.95 Nb 0.04 O3 (x=0.11).

[0146] Example 8:

[0147] The only difference from Example 1 is that,

[0148] The molar ratio of lithium carbonate, lanthanum trioxide, titanium dioxide, and tungsten oxide is 0.165:0.28:0.97:0.02. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x Ti 0.97 W 0.02 O3 (x=0.11).

[0149] Comparative Example 1:

[0150] The only difference from Example 1 is that,

[0151] The molar ratio of lithium carbonate, lanthanum trioxide, and titanium dioxide is 0.165:0.28:1. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x La 2 / 3-x TiO3 (x=0.11), meaning no doping elements were introduced.

[0152] Comparative Example 2:

[0153] The only difference from Example 1 is that,

[0154] The molar ratio of lithium carbonate, strontium oxide, lanthanum trioxide, and titanium dioxide is 0.165:0.03:0.285:1. The chemical composition of the prepared perovskite-structured solid electrolyte is Li 3x Sr 0.03 La 0.57 TiO3 (x=0.11) was doped at the A site instead of the B site doping strategy described in this invention (see Liao, Yu‐Long, et al. "Ultrafast Li‐Rich Transportin Composite Solid‐State Electrolytes." Advanced Materials 37.10(2025).).

[0155] Phase analysis:

[0156] Phase analysis results ( Figure 1 This indicates that the Li prepared in the comparative example... 0.33 La 0.56 TiO3 and Li 0.33 Sr 0.03 La 0.57 All TiO3 samples exhibited a pure-phase perovskite structure, with no impurity phase diffraction peaks observed. Further consolidation... Figure 2 It can be seen that even when using high-valence elements (such as Ta) 5+ Donor doping of LLTO resulted in ceramic samples that still maintained a pure phase structure, indicating that the doping process did not introduce any additional impurity phases, effectively avoiding the problem of increased grain boundary impedance caused by impurity phase precipitation at the phase level.

[0157] Performance testing:

[0158] The ionic conductivity of the perovskite-structured oxide solid electrolyte prepared in this invention was tested using the AC impedance method. The specific steps are as follows:

[0159] Sample preparation: The prepared LLTO ceramic sheets were mechanically ground to a thickness of approximately 1 mm and then polished on both sides. Subsequently, they were ultrasonically cleaned with ethanol and dried in a vacuum oven at 120°C for 12 hours to completely remove surface adsorbates.

[0160] Electrode fabrication: Gold (Au) electrodes were fabricated on both sides of a polished LLTO ceramic wafer using a magnetron sputtering apparatus. The Au layer thickness was approximately 500 nm to form good ohmic contact.

[0161] Impedance testing: The prepared sample was placed in a special fixture and connected to a Solartron 1260 impedance analyzer. AC impedance testing was performed under constant temperature conditions of 25°C, with a frequency range of 1 Hz-10 MHz and a voltage amplitude of 50 mV.

[0162] Data Analysis: The measured electrochemical impedance spectroscopy data were imported into Zview software, and an appropriate equivalent circuit was selected for fitting to obtain the bulk resistance (R0) of the sample. bulk ) and grain boundary resistance (R gb The ionic conductivity is then calculated using the formula σ = L / (R × A), where:

[0163] L is the sample thickness (cm).

[0164] A represents the effective area of ​​the electrode (cm²).

[0165] R is the resistance value (Ω) obtained by fitting.

[0166] The bulk ionic conductivity and grain boundary ionic conductivity of the sample can be calculated using the above methods, thereby comprehensively evaluating its electrochemical performance.

[0167] Table 1

[0168] Group Bulk conductivity mS / cm Grain boundary conductivity mS / cm Density / % Example 1 0.94 0.48 97.3 Example 2 0.83 0.33 96.3 Example 3 0.33 0.28 96.2 Example 4 0.16 0.19 95.8 Example 5 0.41 0.14 95.1 Example 6 0.85 0.34 96.4 Example 7 0.72 0.39 96.8 Example 8 0.63 0.28 95.3 Comparative Example 1 1.2 0.08 94.6 Comparative Example 2 1.4 0.06 94.2

[0169] Figure 3 Room temperature impedance spectra of different samples are shown, including Comparative Example 1, Comparative Example 2, and several examples. From Figure 3 A comparison with the performance data in Table 1 clearly shows that the grain boundary ionic conductivity of Comparative Example 1 (undoped) is only 0.08 mS / cm, and its density is also low, reflecting that its overall performance is significantly constrained by the grain boundary bottleneck. The test results of Comparative Example 2 (Sr-doped) indicate that although conventional doping strategies can improve bulk conductivity to some extent, they fail to improve grain boundary ionic conductivity and density, and even cause further deterioration of grain boundary performance, proving that this method cannot fundamentally solve the problem.

[0170] In stark contrast, all the sample examples prepared according to the technical solution of this invention (i.e., the synergistic process of high-valence element doping and rapid cooling) simultaneously achieved significant improvements in densification and grain boundary ionic conductivity. In particular, Example 1 exhibited a grain boundary ionic conductivity as high as 0.48 mS / cm, approximately six times higher than Comparative Example 1, and its overall conductivity was also optimized due to the breakthrough of the grain boundary bottleneck. This result fully demonstrates that this invention, through intrinsic grain boundary modification, has achieved significant results in opening up ion transport channels across grain boundaries.

[0171] To study the evolution of grain boundary structures at the atomic scale, this invention employs high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). This technique utilizes the atomic number contrast (Z-contrast) imaging principle, where the contrast intensity of the obtained image is directly proportional to the atomic number (Z) of the corresponding element in the sample, thus enabling direct observation and analysis of the atomic-level structure and chemical composition of grain boundary regions. Given that the atomic number of Ta (Z = 73) is much higher than that of Ti (Z = 22), Ta atoms should exhibit brighter contrast in the HAADF-STEM image. In the sample of Comparative Example 1 ( Figure 4 a) The contrast of B-site atoms in the outermost layer of the region near the grain boundary is similar to that in the bulk phase region; Figure 4 Linear integral intensity analysis of b and 4c further confirms that there is no significant difference in the distribution of Ti atoms near the grain boundaries compared to the bulk region. This result indicates that Ti atoms do not undergo elemental segregation at the grain boundaries.

[0172] However, in the Ta-doped example samples ( Figure 5 (a) It can be clearly observed that the contrast of the outermost B-site atoms in the region near the grain boundary is significantly enhanced. Figure 5 The integrated intensity analysis results of b and 5c clearly show that the signal intensity at this location is significantly higher than that in the bulk region. This quantitative evidence confirms that Ta successfully occupies the B site (Ti site) and undergoes selective segregation at the grain boundary.

[0173] The electrochemical performance and microstructure characterization results of the above system corroborate each other, jointly revealing the mechanism of action of the present invention: by doping with high-valence elements and inducing their selective segregation at grain boundaries, the atomic configuration and space charge distribution of the grain boundary region can be intrinsically optimized, thereby significantly reducing grain boundary impedance and ultimately achieving a leapfrog improvement in the overall ion transport performance of the material.

Claims

1. A solid electrolyte, characterized in that, Its chemical formula is: Li 3x La 2 / 3–x Ti 1–my / 4 M m+ y O3, of which: The range of x is: 0.03 ≤ x ≤ 0.167; The range of values ​​for y is: 0.005 ≤ y ≤ 0.2; m is the absolute value of the valence state of M, m≥5; R is the ionic radius of M, 0.55Å≤R(M) m+ ≤0.70Å; M represents a dopant element.

2. The solid electrolyte as described in claim 1, characterized in that, M is selected from one or more of Ta, Nb, V, W, and Mo.

3. The solid electrolyte as described in claim 1, characterized in that, The density of the solid electrolyte is ≥95%; optionally, the density of the solid electrolyte is 95%-100%; further optionally, the density of the solid electrolyte is 95%-98%.

4. The solid electrolyte as described in claim 1, characterized in that, The bulk conductivity of the solid electrolyte is ≤1 mS / cm; optionally, the bulk conductivity of the solid electrolyte is 0.1-1 mS / cm; further optionally, the bulk conductivity of the solid electrolyte is 0.15-0.95 mS / cm.

5. The solid electrolyte as described in claim 1, characterized in that, The solid electrolyte has a grain boundary conductivity ≥ 0.1 mS / cm; optionally, the solid electrolyte has a grain boundary conductivity of 0.1-0.6 mS / cm; further preferably, the solid electrolyte has a grain boundary conductivity of 0.14-0.5 mS / cm.

6. The method for preparing a solid electrolyte as described in claim 1, characterized in that, Includes the following steps: The lithium source, lanthanum source, titanium source and M source are mixed in proportion, calcined, mixed again, pressed, sintered and rapidly cooled to obtain the perovskite structure solid electrolyte with low grain boundary resistance.

7. The preparation method according to claim 6, characterized in that, The first mixing satisfies at least one of a1-a5: a1. The mixing is a wet milling mixture; a2. The wet grinding and mixing process is either wet ball milling or wet sand milling; a3. The wet milling solvent used in the wet milling mixture is selected from one or more of water, ethanol, propanol, ethylene glycol, propylene glycol, allyl alcohol, isopropanol, dimethyl carbonate, diethyl carbonate, propylene carbonate, and ethylene carbonate; a4. The parameters for the wet milling are 400-800 r / min, and the wet milling time is 3-24 h; a5. The lithium source is in 5-50% excess relative to the stoichiometry of the reaction.

8. The preparation method according to claim 6, characterized in that, The method satisfies at least one of b1-b4: b1. The calcination conditions are: heat to 700-1400℃ and hold for 3-24 hours; b2. The conditions for secondary mixing are the same as those for primary mixing; b3. The average particle size D50 of the powder obtained from the secondary mixing is 0.1-1 μm; b4. The average particle size D50 of the powder obtained from the secondary mixing is 0.3-0.8 μm.

9. The preparation method according to claim 6, characterized in that, The pressing conditions are as follows: the secondary mixed powder is pressed at a pressure of 200-500 MPa for a holding time of 10-60 minutes to obtain a round green sheet; and / or The pressing method is dry pressing or isostatic pressing.

10. The preparation method according to claim 6, characterized in that, The method satisfies at least one of c1-c3: c1. The sintering conditions are: heat to 1200-1500℃ and hold for 3-36 hours; c2. The sintering method is selected from one or more of the following: solid-state reaction sintering, liquid-state sintering, hot pressing sintering, hot isostatic pressing sintering, microwave sintering, spark plasma sintering, high-pressure sintering, vacuum sintering, atmosphere sintering, and in-situ pressure sintering; c3. The rapid cooling is selected from one or more of liquid nitrogen quenching, water immersion quenching, and air quenching.

11. The preparation method according to claim 6, characterized in that, The method satisfies at least one of d1-d4: d1. The lithium source is selected from one or more of lithium carbonate, lithium oxide, lithium hydroxide, lithium nitrate, lithium acetate, and lithium oxalate; d2. The lanthanum source is selected from one or more of lanthanum carbonate, lanthanum oxide, lanthanum hydroxide, and lanthanum nitrate; d3. The titanium source is selected from one or more of titanium oxide, titanium hydroxide, and titanium nitrate; d4. The source M is selected from one or both of the oxides and hydroxides of M.

12. A secondary battery, characterized in that, This includes the solid electrolyte as described in any one of claims 1-5 or the solid electrolyte prepared by the preparation method described in any one of claims 6-8.

13. An electrical appliance, characterized in that, Includes the solid electrolyte as described in any one of claims 1-5, the solid electrolyte prepared by the preparation method described in any one of claims 6-8, or the secondary battery as described in claim 12.

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