A class of lithium-ion solid-state electrolytes based on β-eucryptite derivatives

Abstract

The present invention discloses a class of lithium-ion solid electrolytes based on β-eucryptite derivatives, and their composition includes Li y , 4‑y , 1‑ , y AlSi 1‑x P x O4 or Li 1‑y AlSiO 4‑y X y . By adjusting the content ratio of P and Si elements in the β-Li 1‑ x AlSi 1‑x P x O4 (0 < x ≤ 1) material and replacing the O atoms in Li 1‑y AlSiO 4‑y X [[ID= 24]] y (0 < y ≤ 1, X = F, Cl, Br, I) with F, Cl, Br, I atoms, the present invention reduces the activation energy barrier for lithium-ion diffusion and improves the lithium-ion conductivity of the solid electrolyte in the all-solid-state battery of β-Li 1‑x AlSi 1‑x P x O4 and Li 1‑ y AlSiO 4‑y X y (X = F, Cl, Br, I).

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to a type of lithium ion solid electrolyte based on β-eucryptite derivatives. Background Art

[0002] Solid-state lithium batteries are a new generation of energy storage devices with high energy density and high safety. To develop high-performance solid-state lithium batteries, solid electrolytes, as a crucial component of all-solid-state batteries, still face many unresolved challenges. One of these challenges is the need to improve ionic conductivity at room temperature. Decades of extensive research have explored a variety of solid-state lithium-ion conductors, including lisicon, argentite, garnet, nasion, lithium nitride, hydride, and perovskite lithium halide materials. However, these materials still struggle to meet the required conductivity and stability requirements. For example, inorganic compound solid electrolytes such as LLZO, LLZTO, and LATP suffer from high interfacial impedance with electrodes and high preparation and processing costs, hindering their commercialization. LISICON-like sulfide materials exhibit excellent lithium-ion conductivity, even exceeding the 10 mS / cm of commercial liquid electrolytes. However, sulfide materials are sensitive to moisture and have a narrow electrochemical window, making them difficult to operate in air and unstable at high-voltage cathodes. Garnet materials generally exhibit good stability, but their room temperature conductivity is typically well below 1ms / cm, making them unsuitable for high-energy, high-rate solid-state batteries. Therefore, developing new solid-state lithium-ion conductors with high lithium conductivity and superior mechanical, thermal, chemical, and electrochemical stability has become a key research priority and a challenge.

[0003] Silicon-based materials are potential candidates for lithium conductors. Silicate-based materials are widely found on Earth and have diverse structures. They exhibit very good mechanical, thermal, chemical and electrochemical stability. In recent years, silicate materials have once again attracted attention as lithium ion conductors. For example, β-lithium garnet MAlSi2O6 (M=Li, Na, K, Rb or Cs) was synthesized as an alkali metal ion conductor with a diffusion barrier between 0.56eV-0.83eV. Mo et al. found through ab initio molecular dynamics (AIMD) calculations and experiments that LiTaSiO5, LiAlSiO4 and Li2ZnSiO4 may have high Li conductivity at room temperature. The results show that Li 1.125 Ta 0.875 Zr 0.125 The theoretical value of the diffusion barrier of SiO5 is 0.21eV, and the experimental value is 0.38eV. By doping, the Li diffusion barrier in Li2ZnSiO4 can be significantly reduced. If the diffusion barrier of silicate materials can be greatly reduced, silicate materials will become extremely promising solid-state lithium ion conductors.

[0004] Due to the extensive application of silicon-based materials and their excellent electrochemical stability, there is no need to pay much attention to their stability issues, but only to focus on how to improve the ionic conductivity of lithium ions. In particular, understanding the diffusion mechanism of Li in silicate materials from both theoretical and experimental aspects will help to rationally design silicate-based Li conductors with significantly reduced diffusion barriers and high RT ionic conductivity.

[0005] β-euryptite (lithium nepheline) LiAlSiO4 has a hexagonal structure with the space group P6222. LiAlSiO4 exhibits very small thermal expansion, even an anisotropic negative thermal expansion (NTE) behavior. The original LiAlSiO4 is a one-dimensional (1D) lithium-ion conductor along the c-axis, with a typical diffusion barrier of 0.6 - 0.95 eV and cannot be used as a lithium-ion conductor at room temperature. Summary of the Invention

[0006] The present invention provides a class of lithium-ion solid electrolytes based on β-lithium nepheline derivatives, aiming to reduce the activation energy barrier of lithium-ion diffusion and improve the lithium-ion conductivity of β-Li 1-x AlSi 1-x P x O4 (0 < x ≤ 1) materials by adjusting the content ratio of P and Si elements and replacing O atoms in Li 1- y AlSiO 4-y X y (0 < y ≤ 1, X = F, Cl, Br, I), and Li 1- x AlSi 1-x P x O4 and Li 1-y AlSiO 4-y X y (X = F, Cl, Br, I) materials.

[0007] The present invention adopts the following technical solutions:

[0008] A class of lithium-ion solid electrolytes based on β-lithium nepheline derivatives, the composition of which includes Li 1-x AlSi 1-x P x O4 or Li 1-y AlSiO 4-y X y .

[0009] Furthermore, x in the Li 1-x AlSi 1-x P x O4 satisfies: 0 < x ≤ 1.

[0010] Furthermore, the Li 1-x AlSi 1-x P x O4 is Li 0.75 AlSi 0.75 P 0.25 O4, Li 0.5 AlSi 0.5 P 0.5 O4, Li 0.25 AlSi 0.25 P 0.75 O4, Li 0.25 -AlPO4.

[0011] Furthermore, the y in the Li 1-y AlSiO 4-y X y satisfies: 0 < y ≤ 1.

[0012] Furthermore, the X in the Li 1-y AlSiO 4-y X y is X = F, Cl, Br, I.

[0013] Furthermore, the Li 1-y AlSiO 4-y X y is Li 0.5 AlSiO 3.5 F 0.5 、Li 0.5 AlSiO 3.5 Cl 0.5 、Li 0.5 AlSiO 3.5 Br 0.5 以及Li 0.5 AlSiO 3.5 I 0.5 .

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] (1) The elements such as P, F, Cl, Br, I added in the present invention are widely sourced, low-cost, and the prediction calculation methods are mature.

[0016] (2) The present invention adjusts the content ratio of P and Si elements in the β-Li 1-x AlSi 1-x P x O4 (0 < x ≤ 1) material and replaces Li with F, Cl, Br, I atoms in the Li 1-y AlSiO 4-y X yThe O atom in (0 < y ≤ 1, X = F, Cl, Br, I) reduces the activation energy barrier for lithium-ion diffusion and increases β-Li 1-x AlSi 1-x P x O4 and Li 1-y AlSiO 4-y X y (X = F, Cl, Br, I) The lithium-ion conductivity of the solid electrolyte in all-solid-state batteries.

[0017] (3) The present invention adds many new all-solid-state electrolytes with high Li-ion conductivity, further promoting the development of all-solid-state lithium-ion batteries.

[0018] (4) This method of the present invention has the potential to predict more high-lithium-ion electrolyte materials.

[0019] (5) In the energy field, the present invention is used as an all-solid-state lithium-ion battery, which includes primary batteries and secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 In (a) and (b) are Li 1-x AlSi 1-x P x O4 (0 < x ≤ 1) Typical optimized structural diagrams, (c) and (d) are Li 1- y AlSiO 4-y X y (y = 0 - 1, X = F, Cl, Br, I) Optimized structural diagrams.

[0021] Figure 2 For Li 1-x AlSi 1-x P x O4's lithium-ion conductivity (a), diffusion barrier (b), volume of different unit cells (c), and a, c axis side lengths of different unit cells (d) diagrams.

[0022] Figure 3 For Li 1-y AlSiO 4-y X y 's lithium-ion conductivity (a), diffusion barrier (b), volume of different unit cells (c), and a, c axis side lengths of different unit cells (d) diagrams.

[0023] Figure 4 For Li 1-x AlSi 1-x P x O4 after optimization to obtain Li 0.75 AlSi 0.75 P 0.25Li of O4 with LiBSiO4, LiAlSiO4, LiGaSiO4, and LiAlGeO4 + Fitting curve graph (a) of the relationship between Li conductivity and temperature and broken line graph (b) of diffusion barrier. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. However, the implementation manners of the present invention are not limited thereto.

[0025] A research method for a class of lithium-ion solid electrolytes based on β-eucryptite derivatives, comprising the following steps:

[0026] (1) At different temperatures, ab initio molecular dynamics (AIMD) simulations were performed on β-euryptite Li 1-x AlSi 1-x P x O4 (0 < x ≤ 1) and Li 1-y AlSiO 4-y X y (y = 0 - 1, X = F, Cl, Br, I). The Vienna ab initio simulation package (VASP) was used for structure optimization and kinetic analysis. The projector augmented wave (PAW) pseudopotential and the generalized gradient approximation (GGA) parameterized by Perdew, Burke, and Ernzerhof (PBE) were used for all simulations. The PAW pseudopotential cutoff energy for structure optimization was 520 eV, and the cutoff energy for AIMD simulations was 400 eV. Structure optimization was performed by using a Monkhorst k-point mesh with a size of 3×3×3 to sample the integration of the Brillouin zone. The force convergence criterion was For AIMD simulations, the NVT ensemble time step with a Nosé-Hoover thermostat was set to 2 fs, and the total time of AIMD simulations was in the range of 50 - 200 ps.

[0027] (2) According to the Einstein-Smoluchowski equation, the Li diffusion coefficient was obtained from the mean square displacement (MSD) data obtained by AIMD simulations.

[0028] (3) The AIMD calculation method was used to study Li in β-euryptite Li 1-x AlSi 1-x P x O4 and Li 1-y AlSiO 4-y X y(Diffusion in (y = 0 - 1, X = F, Cl, Br, I)). The results show that by changing the Li / P ratio, the Li diffusion barrier in LiAlSiO4 decreases significantly from 2.04 eV in Li 0.25 -AlPO4 to 0.18 eV in Li 0.75 AlSi 0.75 P 0.25 O4; By replacing the O element with the X (F, Cl, Br, I) element, the obtained Li 0.5 AlSiO 0.35 Br 0.5 electrolyte has the lowest Li + diffusion barrier, which is 0.33 eV.

[0029] (4) The structure of Li 1-x AlSi 1-x P x O4 is the same as that of LiAlSiO4. The P element replaces part of the Si element, and the Li content can be adjusted by the Li / P ratio. At other Li / P ratios, the optimized structure of Li 1-x AlSi 1-x P x O4 (x = 0 - 1). With the change of the lithium-phosphorus ratio, the β-spodumene structure changes little. With the increase of x, the lattice parameters a, c and the unit cell volume all increase because there are more P atoms in the unit cell. The structure of Li 1-y AlSiO 4-y X y (y = 0 - 1, X = F, Cl, Br, I) is also the same as that of LiAlSiO4. Different from the former, part of the O atoms are replaced by the halogen element X. In the LiAlSiO4 unit cell, there are 12 Li atoms, 12 Al atoms, 12 Si atoms and 48 O atoms. When the Li / P ratio decreases from 3 to 1 / 4, the change range of Li atoms in the unit cell is (0 - 24). There are 4 Li diffusion channels along the c direction. The diffusion channels are formed by the edge-sharing connection of Si - O tetrahedra and Al - O tetrahedra to form a double - helix structure. With the change of the number of Li atoms in the cell, the number of Li atoms in each diffusion channel can vary from 0 to 6. The diffusion channels containing one Li atom, two Li atoms and four Li atoms are called 1Li channel, 3Li channel and 4Li channel respectively. With the change of the number of Li atoms in the diffusion channel, the Li - Li distance is also different.

[0030] [[ID=4​​​​​​​​​​4-y X y (y = 0 - 1, X = F, Cl, Br, I) optimized structural diagram.

[0031] Figure 1 In (a, b) and (c, d), they are the side view and top view of the 3Li channel and the (i) 4Li channel respectively. The Li diffusion channels in the figure are formed by Si - O and Al - O tetrahedral chains shared by double helices. The arrows indicate the Li diffusion direction. The Li - Li distance changes with the number of Li in the diffusion channels. The balls of light gray (large balls), dark black (inside the tetrahedron), dark gray (inside the tetrahedron), gray (small balls), dark black (tetrahedron), and dark black (medium - sized balls) represent Li, Si, Al, O, P, and (F, Cl, Br, I) atoms respectively. The dark black and dark gray tetrahedrons represent Si - O and Al - O tetrahedrons respectively.

[0032] According to the Nernst - Einstein equation, a linear fit is performed on the relationship curve between lg(σT) and 1000 / T to obtain the Li diffusion barrier. The diffusion barrier data is shown in Figure b. When x = 1, the original Li 0.25- The diffusion barrier of AlPO4 is the highest, at 2.04 eV. When 0 < x < 1, the diffusion barrier is lower than the original value of LiAlSiO4. When x = 0.25, Li 0.75 AlSi 0.75 P 0.25 O4 has the smallest diffusion barrier of 0.18 eV. As x increases from 0 to 1, the diffusion barrier first decreases and then increases. Especially when x > 0.75, the diffusion barrier of Li 0.25- AlPO4 (when AlPO4 is exactly the electrically neutral atomic ratio according to the element valence ratio. There is no Li ion or atom in it. To conduct Li, it needs to be introduced from the outside. Here, Li0.25 - means that the Li here is foreign) rapidly increases to 2.04 V.

[0033] Figure 2 For Li 1-x AlSi 1-x P x O4, graphs of lithium ion conductivity (a), diffusion barrier (b), volume of different unit cells (c), and a, c - axis side lengths of different unit cells (d).

[0034] From Figure 2 It can be concluded that when x = 0.25, for the all - solid - state electrolyte Li 0.75 AlSi 0.75 P 0.25 O4, Li +The diffusion barrier is the lowest, at 0.18 eV. The ionic conductivity σ = 1.17 S / cm. Regardless of the value of x within the range 0 < x ≤ 1, the unit cell volume is smaller than that of LiAlSiO4. This is mainly because as x gradually increases, the length of the a-axis gradually becomes shorter, and the length of the c-axis first decreases and then increases, but the overall volume remains smaller than that of LiAlSiO4.

[0035] Figure 3 for Li 1-y AlSiO 4-y X y Graphs of the lithium-ion conductivity (a), diffusion barrier (b), volumes of different unit cells (c), and lengths of the a and c axes of different unit cells (d) of Li 0.5 AlSiO 3.5 F 0.5 、Li 0.5 AlSiO 3.5 Cl<{ 0.5 、Li 0.5 AlSiO 3.5 Br 0.5 and Li 0.5 AlSiO 3.5 I 0.5 electrolytes.

[0036] From [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​0.25 Li of O4 + The conductivity is more than 5 orders of magnitude higher than that of LiAlSiO4, and the lower the temperature, the more obvious the advantage. At the same time, in Li 0.75 AlSi 0.75 P 0.25 O4, the diffusion barrier of Li + is also the lowest, with Ea = 0.18 eV. More detailed data are listed in Table 1.

[0039] Table 1 Composition, lithium ion diffusion barrier and predicted room temperature conductivity of solid state electrolytes

[0040]

[0041]

[0042] Table 1 contains the composition of the predicted solid state electrolyte and the diffusion barrier of Li + in it, as well as the predicted values of its room temperature conductivity. Moreover, the corresponding values of LiBSiO4, LiAlSiO4, LiGaSiO4 and LiAlGeO4 are also listed in the table.

[0043] This invention studies the molecular dynamics of Li 1-x AlSi 1-x P x O4 and Li 1-y AlSiO 4-y X y in Li, and different values of x in the range of (0 - 1) are used to adjust the Li / P ratio in Li 1-x AlSi 1-x P x O4. Halogen elements F, Cl, Br, I are respectively used to replace the O element in Li 1- y AlSiO 4-y X y (0 < y ≤ 1), so as to reduce the diffusion barrier of Li and improve the conductivity of lithium ions. The predicted all-solid-state electrolyte contains the following components: Li 0.75 AlSi 0.75 P 0.25 O4, Li 0.5 AlSi 0.5 P 0.5 O4, Li 0.25 AlSi 0.25 P 0.75 O4, Li 0.25 -AlPO4, Li 0.5 AlSiO 3.5 F 0.5 、Li 0.5AlSiO 3.5 Cl 0.5 、Li 0.5 AlSiO 3.5 Br 0.5 and Li 0.5 AlSiO 3.5 I 0.5 wait.

[0044] In this embodiment, the various components added are widely available, low in cost, and the prediction calculation method is mature. 1-x AlSi 1-x P x Optimal Li / P ratio and Li in O4 electrolyte 1-y AlSiO 4-y X y Chinese envoy Li + Halogen elements with lower energy barriers can significantly improve the performance of solid electrolyte Li in all-solid-state batteries. 1-x AlSi 1-x P x O4 and Li 1-y AlSiO 4-y X y Lithium ion conductivity.

Claims

1. A lithium-ion solid electrolyte based on a β-eucryptite derivative, characterized in that: Its composition includes Li 1- x AlSi 1-x P x O4 or Li 1-y AlSiO 4-y X y； said it 1-x AlSi 1-x P x O4 is for Him 0.75 AlSi 0.75 P 0.25 O4、He 0.5 AlSi 0.5 P 0.5 O4、He 0.25 AlSi 0.25 P 0.75 O4、He 0.25 -AlPO4.

2. The lithium-ion solid electrolyte based on a β-eucryptite derivative according to claim 1, characterized in that: The Li 1-y AlSiO 4-y X y The y in satisfies: 0 <y≤1。 3. The lithium-ion solid electrolyte based on a β-eucryptite derivative according to claim 1 or 2, characterized in that: The Li 1-y AlSiO 4-y X y Where X=F,Cl,Br,I.

4. The lithium-ion solid electrolyte based on a β-eucryptite derivative according to claim 3, characterized in that: The Li 1-y AlSiO 4-y X y For Li 0.5 AlSiO 3.5 F 0.5 、Li 0.5 AlSiO 3.5 Cl 0.5 、Li 0.5 AlSiO 3.5 Br 0.5 and Li 0.5 AlSiO 3.5 I 0.5 .

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