A lithium-niobium-tungsten oxide solid electrolyte material, its design method and its application

Abstract

This invention discloses a novel lithium-niobium-tungsten oxide solid electrolyte material, its design method, and its application as an electrolyte or positive electrode interface modification layer in all-solid-state lithium batteries; the chemical formula of the material is Li5NbWO8; the method uses Li2WO4 as the structural unit, designs doping sites through topological structure analysis, and employs Nb... 5+ For W 6+ The material undergoes heterovalent substitution at specific sites and is combined with lithium-ion concentration adjustment to maintain electroneutrality. The material of this invention has high thermodynamic stability, high theoretical oxidation limit, high ionic conductivity, and good interfacial compatibility. As a bulk electrolyte or cathode interface modification layer, this material can significantly improve the cycle life and energy density of all-solid-state lithium batteries, especially those using high-voltage cathode systems, providing a new material solution for solving the interface problem of solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state lithium battery technology, specifically to a novel lithium-niobium-tungsten oxide solid electrolyte material, its design method, and its application as an electrolyte or positive electrode interface modification layer in all-solid-state lithium batteries. Background Technology

[0002] All-solid-state lithium batteries have become a research hotspot for next-generation energy storage devices due to their potential for high safety and high energy density. Solid-state electrolytes are one of the core components of all-solid-state batteries. Oxide solid-state electrolytes, such as garnet-type Li7La9Zr2O... 12 LLZO has attracted widespread attention due to its high room-temperature ionic conductivity and good chemical stability. However, the stabilization of LLZO usually depends on high-temperature sintering and doping, which can easily lead to problems such as high grain boundary resistance and poor contact with the electrode interface. In particular, under the operating voltage of high-voltage layered oxide cathodes (such as LiCoO2 and LiNiO2), most solid electrolytes suffer from severe interfacial side reactions and insufficient stability, resulting in battery capacity decay and impedance increase.

[0003] In existing technologies, coating the cathode with materials such as LiNbO3 can improve the interface, but its intrinsic ionic conductivity is low, limiting rate performance. While tungsten-containing compounds (such as Li2WO4) exhibit better ion conduction potential and interface protection, their single composition has limitations in terms of structural stability and overall performance optimization. Therefore, there is an urgent need to develop a novel solid-state electrolyte material that combines high ionic conductivity, a wide electrochemical window, and excellent interfacial compatibility with high-voltage cathodes. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel lithium-niobium-tungsten oxide solid electrolyte material. This material, through the synergistic design of niobium (Nb) and tungsten (W) elements, achieves high thermodynamic stability, a wide electrochemical stability window, excellent lithium-ion conductivity, and good intrinsic chemical compatibility with high-voltage cathodes.

[0005] Specifically, the technical solution provided by this invention is as follows: A lithium-niobium-tungsten oxide solid electrolyte material, the general chemical formula of which is Li5NbWO8; the crystal structure of which has a three-dimensional inorganic framework composed of [NbO6] octahedrons and [WO6] octahedrons connected by shared edges, wherein a three-dimensional continuous diffusion channel for lithium ion migration is formed within the three-dimensional inorganic framework.

[0006] The present invention also discloses its design method, which includes the following steps: S1. Using Li2WO4 crystal as the structural unit, topological analysis of its crystal structure was performed to identify lithium-ion storage sites and lithium-ion migration channels in the interstitial space of its framework. S2. Based on the principles of ionic radius matching and charge compensation, Nb is used. 5+ W in Li2WO4 6+ By performing heterovalent substitution at the sites and adjusting the lithium ion concentration in the system to maintain electroneutrality, a material system with the general chemical formula Li5NbWO8 was constructed. S3. Enumerate the configurations of the Li5NbWO8 material system to generate all atomic arrangement configurations with unequal symmetry, and perform preliminary screening using Ewald energy calculations to obtain candidate configurations; S4. Perform first-principles structural relaxation on the candidate configurations, select the structure with the lowest total energy as the basic model of the target material, and calculate the energy above hull (E). hull The thermodynamic stability of the material was evaluated and verified.

[0007] Preferably, in step S1, the Voronoi partitioning method is used for topological analysis; in step S3, after initial screening by Ewald energy calculation, the 50 configurations with the lowest energy are selected for first-principles structural relaxation in step S4.

[0008] The present invention also discloses the application of the above-mentioned lithium-niobium-tungsten oxide solid electrolyte material in all-solid-state lithium batteries, wherein the material is used as a solid electrolyte in all-solid-state lithium batteries or as a surface coating modification layer for high-voltage layered oxide cathode materials.

[0009] Preferably, the high-voltage layered oxide cathode material is LiCoO2 or LiNiO2.

[0010] The advantages of this invention compared to the prior art are: (1) Composition and structural innovation: This invention is the first to propose and theoretically verify a specific lithium-niobium-tungsten oxide with the chemical formula Li5NbWO8 as a solid electrolyte. Among them, Nb and W elements play a synergistic role: Nb 5+ It helps stabilize the crystal structure and buffer lattice stress; while W 6+ The high valence state characteristics play a key role in improving ionic conductivity and high voltage stability.

[0011] (2) Excellent comprehensive performance: Based on first-principles calculations, the material is predicted to have the following outstanding properties: High thermodynamic stability: its E hull The value is approximately 36 meV / atom, indicating that it is a thermodynamically stable metastable phase.

[0012] (3) High theoretical oxidation limit: Its intrinsic electrochemical stability window is approximately 3.61V (vs. Li + / Li), the oxidation limit is significantly higher than that of conventional Li7La3Zr2O. 12 (LLZO) electrolyte (~2.9V), capable of withstanding high voltage positive electrode.

[0013] (4) High ionic conductivity: The predicted room temperature ionic conductivity can reach 3.39 mS / cm, and the activation energy is approximately 0.26 eV, meeting the requirements of high-performance solid electrolytes. Its rapid conduction mechanism originates from W 6+ / Nb 5+ Co-doping-induced lithium-ion "co-migration".

[0014] (5) Good interfacial compatibility: Thermodynamic analysis shows that the material has an interfacial decomposition energy close to zero with fully lithiated layered oxide cathodes such as LiCoO2 and LiNiO2, and the interfacial reaction driving force is also low under high voltage charging state, exhibiting excellent intrinsic chemical compatibility. This is attributed to its unique design of "highest valence state cation framework + lithium-rich matrix".

[0015] (6) Broad application prospects: As a bulk electrolyte or positive electrode interface modification layer, this material can significantly improve the cycle life and energy density of all solid-state lithium batteries, especially those using high-voltage positive electrode systems, providing a new material solution for solving the interface problem of solid-state batteries. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the crystal structure of Li5NbWO8 of the present invention.

[0017] Figure 2 This is a spatial probability density distribution diagram of lithium ion diffusion in Li5NbWO8 in this invention.

[0018] Figure 3 This is a schematic diagram of the Arrhenius fitting of lithium ion diffusion in Li5NbWO8 at different temperatures according to the present invention.

[0019] Figure 4 This is a schematic diagram showing the change in reaction energy of Li5NbWO8 under different lithium chemical potentials according to the present invention.

[0020] Figure 5 This is a schematic diagram of the DOS of Li5NbWO8 calculated by the present invention.

[0021] Figure 6 This is a schematic diagram of the van Hough correlation function for lithium ion diffusion in Li5NbWO8 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] In the following embodiments of the present invention, the crystal structure data used are from the Inorganic Crystal Structure Database (ICSD). Configuration enumeration and thermodynamic stability calculations are performed using the Pymatgen software package. First-principles calculations are performed using the VASP software package. The generalized gradient approximation PBE functional of the projected fused wave method is selected. The plane wave cutoff energy is uniformly set to 520 eV. The Brillouin zone K-point grid is divided using the Monkhorst-Pack method. The structural relaxation convergence criterion is that the interatomic interaction force is less than 0.01 eV / Å. The total energy convergence threshold of the system is 10. -5 eV.

[0024] Example 1: Design and thermodynamic stability verification of Li5NbWO8 solid electrolyte material This embodiment is used to verify the design method of the lithium-niobium-tungsten oxide solid electrolyte material of the present invention, and the thermodynamic stability of the obtained material. The specific steps are as follows: (1) Matrix selection and topology analysis The Li2WO4 crystal with the number ICSD-1044 in the inorganic crystal structure database was selected as the doping matrix. The crystal structure of Li2WO4 was analyzed by Voronoi segmentation topology analysis method, which clarified that its inorganic framework structure is composed of [WO6] octahedral basic units. Sites that can be used for lithium-ion storage in the framework interstitial space and a three-dimensional continuous channel network that can be used for lithium-ion migration were identified, providing a structural basis for subsequent doping site design.

[0025] (2) Construction of doping model Based on the principles of ionic radius matching and charge compensation, a heterovalent doping scheme was designed: using Nb 5+ W in the Li2WO4 lattice 6+ By substituting sites and simultaneously adjusting the lithium ion content in the lattice to maintain the system's electrical neutrality, a material system with the chemical composition Li5NbWO8 was finally constructed. In this system, lithium ions are randomly distributed, providing the structural basis for a fast ion conductor.

[0026] (3) Configuration enumeration and initial screening The configurations of the Li5NbWO8 chemical system were enumerated using the Pymatgen software package to generate all Nb, W, and Li atomic arrangements with inequivalent symmetry under this general chemical formula. The Ewald energies of all enumerated configurations were calculated, and the 50 configurations with the lowest Ewald energies were selected as candidate configurations for subsequent structure optimization.

[0027] (4) First-principles structural relaxation and ground-state structure determination For the 50 candidate configurations obtained from the initial screening, first-principles geometric relaxation was performed using the VASP software package. After relaxation, the total energy of each configuration was calculated, and the configuration with the lowest total energy was finally selected as the ground-state stable structure of Li5NbWO8 material. Structural analysis revealed that in this ground-state structure, [NbO6] octahedrons and [WO6] octahedrons are connected by shared edges to form a three-dimensional inorganic framework. The framework contains three-dimensional continuous diffusion channels for lithium ion migration, perfectly matching the structural features designed in this invention.

[0028] (5) Verification of thermodynamic stability Based on the Li-Nb-WO quaternary phase diagram, the energy above hull (E) of the above ground-state structure was calculated using the Pymatgen software package. hull The calculated value shows that the E value of this material is... hull The value is 36 meV / atom, which meets the criteria for the stable existence of metastable phases, proving that the Li5NbWO8 material designed in this invention has good thermodynamic stability and is feasible for experimental synthesis.

[0029] Example 2: Verification of the electronic structure and electrochemical stability window of Li5NbWO8 solid electrolyte material This embodiment is used to verify the electronic insulation properties and electrochemical stability window of the material described in this invention. The specific operation is as follows: (1) Electronic structure calculation Based on the ground-state stable structure of Li5NbWO8 obtained in Example 1, the density of states (DOS) was calculated using the VASP software package. The calculation results show that the material has an electronic bandgap of 3.84 eV, exhibiting wide bandgap semiconductor characteristics and significant electronic insulation properties, which can effectively avoid internal short circuits caused by electrons passing through the electrolyte during solid-state battery use. Further orbital analysis shows that the conduction band bottom of the material is mainly contributed by W5d orbitals and Nb4d orbitals, while the valence band top is mainly contributed by O2p orbitals.

[0030] (2) Calculation of electrochemical stability window Based on thermodynamic data obtained from first-principles calculations, a Gibbs free energy phase diagram for the Li5NbWO8 system was constructed. The lithiation / delithiation reaction pathways of the material under different lithium chemical potentials were simulated, and its redox limiting potential was calculated. The calculation results show that, relative to Li... + The reduction potential of / Li is 2.08V (corresponding to the reduction products being NbW intermetallic compounds and Li₂O), and the oxidation limiting potential is 3.61V (corresponding to the oxidation reaction being lattice oxygen evolution). Therefore, the electrochemical stability window of the material described in this invention is 2.08V~3.61V (vs. Li). + Li), whose oxidation limit is significantly higher than that of traditional LLZO oxide solid electrolytes, has the ability to be used in conjunction with high-voltage cathode materials.

[0031] Example 3: Verification of ion transport performance of Li5NbWO8 solid electrolyte material This embodiment is used to verify the lithium-ion conductivity and transport mechanism of the material described in this invention. The specific operation is as follows: (1) Ab initio molecular dynamics simulation Based on the ground-state stable structure of Li5NbWO8 obtained in Example 1, a supercell model was constructed, and ab initio molecular dynamics (AIMD) simulations were performed using the VASP software package in the range of 900K-1400K. (2) Calculation of ionic conductivity and activation energy The mean square displacement (MSD) data of lithium ions were extracted from the AIMD simulation trajectories at various temperatures, and the self-diffusion coefficient of lithium ions at different temperatures was calculated. The relationship between the diffusion coefficient and temperature was fitted based on the Arrhenius equation, and the activation energy Ea of lithium ion diffusion was found to be 0.26 eV. The fitting result was extrapolated to 300 K (room temperature), and the room temperature lithium ion conductivity of the material was predicted to reach 3.39 mS / cm, which meets the requirements of high-performance all-solid-state lithium batteries for the ionic conductivity of solid electrolytes.

[0032] (3) Analysis of lithium-ion transport mechanism Based on AIMD simulations, the spatial probability density distribution of lithium ions in the Li5NbWO8 system was plotted, visualizing the three-dimensional diffusion path of lithium ions in the lattice. This confirmed that lithium ions can rapidly migrate within the three-dimensional continuous channels formed by the [NbO6] / [WO6] octahedral framework. Further calculation of the van Hough correlation function for lithium ion diffusion revealed that the diffusion of lithium ions in this system is mainly characterized by the simultaneous and cooperative migration of multiple lithium ions, confirming the W... 6+ / Nb 5+ The co-doping-induced lithium-ion "co-migration" mechanism is the microscopic origin of the material's high room-temperature ionic conductivity.

[0033] Example 4: Verification of interfacial compatibility between Li5NbWO8 solid electrolyte material and high-voltage cathode This embodiment is used to verify the intrinsic chemical compatibility of the material described in this invention with the high-voltage layered oxide cathode. The specific operation is as follows: (1) Construction of interfacial thermodynamic calculation model The Li5NbWO8 material obtained in Example 1 was respectively reacted with the high-voltage cathode materials LiCoO2 and LiNiO2 in the discharge state, and the high-voltage cathode material Li in the charge state. 0.5 CoO2, Li 0.5 NiO2 is used for pairing, and each pairing system is regarded as a pseudo-binary system. Based on the thermodynamic phase data of the Materials Project database, a pseudo-binary phase diagram of each pairing system is constructed.

[0034] (2) Calculation of interface decomposition energy and compatibility analysis The interfacial decomposition energy (ΔE_D) of each paired system under thermodynamic equilibrium was calculated. The absolute value of the interfacial decomposition energy was used to determine the driving force of interfacial side reactions; the smaller the absolute value, the better the interfacial chemical compatibility. The calculation results show that: The interfacial decomposition energy ΔE_D between Li5NbWO8 and discharged LiCoO2 and LiNiO2 is >-10meV / atom. The absolute value of the interfacial decomposition energy is extremely low, indicating that there are almost no interfacial side reactions between the two in the discharged state. Li5NbWO8 and Li in the charged state 0.5 CoO2, Li 0.5 The interfacial decomposition energy of NiO2, ΔE_D > -2meV / atom, indicates that under high-voltage charging conditions, the driving force of interfacial side reactions is extremely low, and there is no risk of violent interfacial reactions.

[0035] The above results confirm that the Li5NbWO8 material described in this invention has excellent intrinsic chemical compatibility with high-voltage layered oxide cathode materials, which can effectively solve the problem of interfacial side reactions between high-voltage cathodes and electrolytes in all-solid-state lithium batteries.

[0036] This invention seeks protection for a lithium-niobium-tungsten oxide solid-state electrolyte material with the general chemical formula Li5NbWO8. Based on the same inventive concept, derivative materials with similar three-dimensional fast-ion conductor structures and high voltage interface stability obtained by using similar topological analysis and heterovalent doping strategies, through trace element substitution (e.g., partially replacing Nb or W with Ta, Mo, etc.) or non-stoichiometric fine-tuning, should all fall within the scope of protection of this invention. This invention also seeks protection for the application of this material as an electrolyte or positive electrode interface modification layer in all-solid-state lithium batteries.

Claims

1. A lithium-niobium-tungsten oxide solid electrolyte material, characterized in that, The chemical formula of the material is Li5NbWO8; the crystal structure of the material has a three-dimensional inorganic framework composed of [NbO6] octahedrons and [WO6] octahedrons connected by shared edges, and a three-dimensional continuous diffusion channel for lithium ion migration is formed within the three-dimensional inorganic framework.

2. A design method for the lithium-niobium-tungsten oxide solid electrolyte material as described in claim 1, characterized in that, Includes the following steps: S1. Using Li2WO4 crystal as the structural unit, topological analysis of its crystal structure was performed to identify lithium-ion storage sites and lithium-ion migration channels in the interstitial space of its framework. S2. Based on the principles of ionic radius matching and charge compensation, Nb is used. 5+ W in Li2WO4 6+ By performing heterovalent substitution at the sites and adjusting the lithium ion concentration in the system to maintain electroneutrality, a material system with the general chemical formula Li5NbWO8 was constructed. S3. Enumerate the configurations of the Li5NbWO8 material system to generate all atomic arrangement configurations with unequal symmetry, and perform preliminary screening using Ewald energy calculations to obtain candidate configurations; S4. Perform first-principles structural relaxation on the candidate configurations, select the structure with the lowest total energy as the basic model of the target material, and evaluate and verify its thermodynamic stability by calculating the energy above hull value.

3. The design method according to claim 2, characterized in that, In step S1, the Voronoi partitioning method is used for topological analysis; in step S3, after initial screening by Ewald energy calculation, the 50 configurations with the lowest energy are selected for first-principles structural relaxation in step S4.

4. The application of the lithium-niobium-tungsten oxide solid electrolyte material according to any one of claims 1 to 3 in all-solid-state lithium batteries, characterized in that, The material is used as a solid electrolyte in all-solid-state lithium batteries, or as a surface coating modification layer for high-voltage layered oxide cathode materials.

5. The application according to claim 4, characterized in that, The high-voltage layered oxide cathode material is LiCoO2 or LiNiO2.

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