CN102867988B - A B3+, Al3+, Ti4+, Y3+, F- co-doped solid electrolyte Li7La3Zr2O12 - Google Patents

Abstract

A B ³⁺ , Al ³⁺ , Ti ⁴⁺ , Y ³⁺ , F ^- co-doped lithium ion solid electrolyte Li ₇ La ₃ Zr ₂ O ₁₂ , characterized in that the stoichiometric formula is Li _{7+y1+y2 -m} Y _x La _3-x B _y1 Al _y2 Ti _y3 Zr _2-y1-y2-y3 O _12-m F _m where: x=0.1-0.3; y1=0.1-0.2; y2=0.1-0.2; y3= 0.1-0.2; m=0.1-0.3; Li ₂ CO ₃ : _{Y 2} O ₃ : La ₂ O ₃ : B ₂ O ₃ : Al ₂ O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.15-3.55: 0.05-0.15: 1.35-1.45: 0.05-0.1: 0.05-0.1: 0.1-0.2: 1.4-1.7: 0.1-0.3 (molar ratio) uniformly mixed in the ratio, after ball milling, pressing, sintering; can obtain more than 5× Li-ion conductivity at room temperature of 10 ^-4 S/cm.

Description

A B3+, Al3+, Ti4+, Y3+, F- co-doped solid electrolyte Li7La3Zr2O12

technical field

The invention relates to the field of manufacturing a solid lithium ion electrolyte.

Background technique

Lithium-ion batteries have absolute advantages such as high volume, high weight-to-energy ratio, high voltage, low self-discharge rate, no memory effect, long cycle life, and high power density. They have an annual share of more than 30 billion US dollars in the global mobile power market and far exceed other The market share of the battery is the most promising chemical power source [Wu Yuping, Wan Chunrong, Jiang Changyin, Lithium-ion secondary battery, Beijing: Chemical Industry Press, 2002.]. At present, most lithium-ion secondary batteries at home and abroad use liquid electrolytes. Liquid lithium-ion batteries have some unfavorable factors, such as: liquid organic electrolytes may leak, and may explode at too high a temperature, causing safety accidents, and cannot be used in some applications. Occasions with high safety requirements; liquid electrolyte lithium-ion batteries generally have the problem of cycle capacity fading, and gradually fail due to the dissolution and reaction of electrode active materials in the electrolyte after a period of use [Z.R.Zhang, Z.L.Gong, and Y.Yang, J.Phys.Chem.B, 108, 2004, 17546.]. The all-solid-state battery has high safety and basically no cycle capacity decay. The solid electrolyte also acts as a diaphragm, which simplifies the structure of the battery. In addition, because there is no need to isolate the air, it also simplifies the requirements for equipment in the production process. The appearance of the battery The design is also more convenient and flexible [Wen Zhaoyin, Zhu Xiujian, Xu Xiaoxiong, etc., Research on All-Solid Secondary Batteries, Proceedings of the Twelfth Chinese Academic Conference on Solid State Ionics, 2004. ].

In all-solid-state lithium-ion batteries, the mobility of carriers in the solid-state electrolyte is often much lower than the charge transfer on the electrode surface and the ion diffusion rate in the positive electrode material, which becomes the rate-controlling step in the entire electrode reaction kinetics. Therefore, the development of Inorganic solid-state electrolytes with high lithium-ion conductivity are the core key to constructing high-performance lithium-ion batteries. In addition, it is necessary to develop a solid lithium-ion electrolyte with practical significance, and it is required to have good stability in the environment (stable to carbon dioxide and moisture), in order to enable the composition of the all-solid-state battery to use metal lithium as the negative electrode. Density, it is also hoped that the solid electrolyte can be stable to metal lithium and have a high decomposition voltage. Judging from the lithium-ion solid electrolytes that have been reported so far: LLTO (Li, La) TiO ₃ solid electrolytes have very high intragranular conductivity (about 10 ^-3 S/cm) and relatively high total conductivity at room temperature ( 10 ^-4 S/cm-10 ^-5 S/cm), but the LLTO decomposition voltage is low, unable to form an all-solid-state battery with a discharge voltage above 3.7V and unstable to metallic lithium anodes; LiM ₂ (PO ₄ ) ₃ (M=Ti, Ge, Zr) is a network structure composed of tetrahedral PO ₄ and octahedral MO ₆ , which produces structural holes and fillable coordination, making it possible to control a large number of Li ions , is a promising solid-state electrolyte with high Li-ion conductivity. The ionic conductivity can be further improved by introducing holes or interstitial lithium ions into the structure through the substitution of aliovalent ions [Xiaoxiong Xu, Zhaoyin Wen, ZhonghuaGu, et al., Solid State Ionics, 171, 2004, 207-212.] . Li _1+x Ti _2-x Ga _x P ₃ O ₁₂ , Li _1+2x Ti _{2 -x} MgxP ₃ O ₁₂ , Li _1+x Ge _2-x CrxP ₃ O ₁₂ , Li _1+x Ge _2-x Al _x P ₃ O ₁₂ , Li _1+x Ti _2-x In _x P ₃ O ₁₂ etc. system or others such as Li _1+2x+2y Al _x Mg _y Ti _2-xy Si _x P _3-x O ₁₂ , Li _1+x+y Al _x Ti _2-x Si _y P _3-y O ₁₂ , Li ₁ Systems such as _+x Al _x Ti _2-x P ₃ O ₁₂ have high lithium ion conductivity. However, the normal temperature lithium ion conductivity of these systems is usually between 10 ^-4 S/cm-10 ^-6 S/cm, which cannot well meet the requirements of non-thin film lithium ion batteries for electrolyte conductivity. In addition, the NASICON system is also unstable to metallic lithium anodes. In 2007, Ramaswamy Murugan et al. reported a new type of lithium ion solid electrolyte Li ₇ La ₃ Zr ₂ O ₁₂ in the German Journal of Applied Chemistry. Its lithium ion conductivity at room temperature exceeds 1×10 ^-4 S.cm ^-1 , Decomposition voltage exceeds 5.5V, can use metal lithium as negative electrode, stable to air and moisture, is a kind of lithium fast ion solid electrolyte material (Ramaswamy Murugan, Venkataraman Thangadurai, Werner Weppner, (2007). "Fast lithium ion conduction in garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ . "Angewandte Chemie-International Edition 46(41): 7778-7781.). However, in the case of high current requirements, the conductivity often needs to reach about 5.0×10 ^-4 S/cm to meet the needs of the normal operation of the battery. In addition, the synthesis temperature of the solid electrolyte is about 1350°C, which is high temperature and consumes a lot of energy.

Ion doping is a very effective way to improve the conductivity of solid-state lithium-ion electrolytes, but the interaction between doped ions and the matrix is very complicated, and the size, electronic structure, and electronegativity of the doped ions all affect the ionic conductivity of the matrix. The ability has a great influence, and there will be interaction between different dopant ions, whether to promote lithium ion migration or inhibit lithium ion migration and the degree of promotion and inhibition will vary greatly with the type and concentration of doped ions . In principle, the selection of dopant ions should meet the three conditions of matching the transport bottleneck with the size of the Li ⁺ radius, weak bonding between Li ⁺ and the framework ions, and a moderate ratio of vacancy concentration to Li ⁺ concentration. The lithium ion migration mechanism of this solid electrolyte has not yet been fully understood by researchers. In addition, if ion doping can form a eutectic solid solution, it can reduce the synthesis temperature to a certain extent. Therefore, further research on the type and content of dopant ions is of great significance for the development of solid electrolytes with high lithium ion conductivity.

Contents of the invention

The technical problem to be solved by the present invention is to provide a B ³⁺ , Al ³⁺ , Ti ⁴⁺ , Y ³⁺ , F ^- ion co-doped lithium ion solid electrolyte Li ₇ La ₃ Zr for the existing background technology ₂ O ₁₂ . Y ³⁺ partially replaces La ³⁺ , the two have similar electronic structures, but Y ³⁺ has a smaller radius, Ti ⁴⁺ with a smaller radius also partially replaces Zr ⁴⁺ , and Al ³⁺ with a smaller radius partially replaces Zr ^{4 +} and the partial substitution of Zr ⁴⁺ by B ³⁺ with a smaller radius makes La-O octahedron and Zr-O octahedron produce certain shrinkage distortion, and the size of the migration channel is more matched with the radius of lithium ions to improve the conductivity of lithium ions; while low Valence B ³⁺ and Al ³⁺ partially replace Zr ⁴⁺ to generate additional interstitial lithium ions, increase the number of lithium ion migration in the lattice and improve lithium ion conductivity; F ^- partially replaces O ^2- , F ^- and O ^{2 -The} radius is close, but the electronegativity is strong, and the crystal lattice shrinks, which further increases the lithium ion migration channel cross section and increases the lithium ion migration rate; the synergistic effect of these factors makes the normal temperature ionic conductivity of the solid electrolyte exceed 5.0×10 ^-4 S /cm, which is closer to the ionic conductivity of the liquid electrolyte. At the same time, the boron oxide forms a solid solution with other components, which can reduce the synthesis temperature of the solid electrolyte by 100-150°C.

The present invention is achieved through the following technical solution, which provides a lithium ion solid electrolyte with a lithium ion conductivity exceeding 5.0×10 ^-4 S/cm, and its stoichiometric formula is Li _7+y1+y2-m Y _x La _3-x By 1Al _y2 Ti _y3 Zr _2-y1-y2-y3 O _{12-m F m} where: x=0.1-0.3; y1=0.1-0.2; y2=0.1-0.2; y3=0.1-0.2; m = 0.1-0.3.

In this technical scheme, Li ₂ CO ₃ : _{Y 2} O ₃ : La ₂ O ₃ : B ₂ O ₃ : Al ₂ O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.15-3.55: 0.05-0.15: 1.35-1.45: 0.05-0.1: 0.05-0.1: 0.1-0.2: 1.4-1.7: 0.1-0.3 (molar ratio) ratio uniform mixing, add 2% -6% of 95% ethanol, in the ball mill with 200-400 Ball mill for 10-30 hours at a speed of revolution per minute. After ball milling, dry in a vacuum oven at 60°C-80°C (vacuum degree 10Pa-100Pa) for 10-20 hours. Take it out and re-grind it in an agate mortar for 10-30 minutes. The ground powder is heated to 750-900°C at a rate of 5-10°C/min and kept for 5-10 hours, and then heated to 1150-1250°C at a rate of 2-10°C/min and kept for 10-30 hours. Solid electrolyte powder. The powder is mixed with 1-5wt% as a binding agent (the binding agent is PVC or PVA) and kept under a pressure of 300-500MPa under a press for 2-6 minutes to form a thin sheet. Raise the temperature at a rate of °C/min to 1200-1300 °C for 10-20 hours to prepare a lithium-ion solid electrolyte sheet. As shown in Figure 1, the AC impedance diagram of the solid electrolyte sheet with the composition of Li _7.1 Y _0.1 La _2.9 B _0.1 Al _0.1 Ti _0.1 Zr _1.7 O _11.9 F _0.1 under the electrochemical workstation is calculated from the figure. The conductivity is 8.5×10 ^-4 S /cm.

Compared with the prior art, the present invention has the advantage of adopting B ³⁺ , Al ³⁺ , Ti ⁴⁺ , Y ³⁺ , F ^- ion co-doped lithium ion solid electrolyte Li ₇ La ₃ Zr ₂ O ₁₂ . Partial replacement of La ³⁺ by smaller radius Y ³⁺ , smaller radius Ti ⁴⁺ partial replacement of Zr ⁴⁺ , smaller radius Al ³⁺ partial replacement of Zr ⁴⁺ and smaller radius B ³⁺ partial replacement of Zr ⁴⁺ causes La-O octahedron and Zr-O octahedron to produce a certain shrinkage distortion, and the size of the migration channel better matches the radius of lithium ions to improve the conductivity of lithium ions; low-priced B ³⁺ and Al ³⁺ partially replace Zr ⁴⁺ Generate additional interstitial lithium ions, increase the number of lithium ions migrating in the lattice and improve the conductivity of lithium ions; F ^- partially replaces O ^2- , F ^- has a radius close to O ^2- , but has strong electronegativity and lattice shrinkage , to further increase the lithium ion migration channel cross section and increase the lithium ion migration rate; the synergistic effect of these factors makes the normal temperature ionic conductivity of the solid electrolyte exceed 5.0×10 ^-4 S/cm. At the same time, the boron oxide forms a solid solution with other components, which can reduce the synthesis temperature of the solid electrolyte by 100-150°C.

Description of drawings

Figure 1 is the AC impedance diagram, frequency-impedance and frequency-phase diagram of the lithium-ion solid electrolyte sheet under the electrochemical workstation.

Detailed ways

The present invention will be described in further detail below in conjunction with the implementation examples.

Example 1: Li ₂ CO ₃ : _{Y 2} O ₃ : _{La 2} O ₃ : B ₂ O ₃ : _Al 2 O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.45: 0.05: 1.45: 0.05: 0.05: The ratio of 0.1: 1.7: 0.1 (molar ratio) is evenly mixed, and 2% of 95% ethanol is added, and ball milled at a speed of 250 rpm in a ball mill for 12 hours, and after the ball milling is finished, place in a vacuum oven (vacuum degree 20Pa) at 60°C Dry for 10 hours, take it out and re-grind in an agate mortar for 30 minutes, heat the ground powder to 850°C at a rate of 5°C/min and keep it for 6 hours, then raise the temperature to 1150°C at a rate of 8°C/min and keep it for 22 hours to make solid electrolyte powder. The powder is mixed with 2wt% binder PVC and kept under a pressure of 300MPa under a press for 5 minutes to form a thin sheet. The thin sheet is heated to 1220°C at a rate of 12°C/min and kept for 20 hours in an air atmosphere to make a lithium ion solid Electrolyte sheets.

Example 2: Li ₂ CO ₃ : _{Y 2} O ₃ : _{La 2} O ₃ : B ₂ O ₃ : _Al 2 O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.25: 0.15: 1.35: 0.1: 0.1: The ratio of 0.2: 1.4: 0.3 (molar ratio) is evenly mixed, and 6% of 95% ethanol is added, and ball milled for 15 hours at a speed of 380 rpm in a ball mill. Dry for 15 hours, take it out and re-grind in an agate mortar for 20 minutes, heat the ground powder to 780°C at a rate of 6°C/min and keep it for 10 hours, then heat it up to 1200°C at a rate of 6°C/min and keep it for 15 minutes hours to make solid electrolyte powder. The powder is mixed with 5wt% binder PVC and kept under a pressure of 450MPa under a press for 2 minutes to form a thin sheet. The thin sheet is heated to 1280°C at a rate of 15°C/min and kept for 10 hours in an air atmosphere to make a lithium-ion solid electrolyte. Flakes.

Example 3: Li ₂ CO ₃ : Y ₂ O ₃ : La ₂ O ₃ : B ₂ O ₃ : _Al 2 O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.35: 0.1: 1.4: 0.075: 0.075: The ratio of 0.15: 1.55: 0.2 (molar ratio) is evenly mixed, and 3% of 95% ethanol is added, and ball milled for 20 hours at a speed of 300 revolutions per minute in a ball mill. Dry for 20 hours, take it out and re-grind in an agate mortar for 10 minutes, heat the ground powder to 800°C at a rate of 9°C/min and keep it for 7 hours, then heat it up to 1250°C at a rate of 2°C/min and keep it for 11 hours to make solid electrolyte powder. The powder is mixed with 1wt% binder PVA and kept under a pressure of 300MPa under a press for 6 minutes to form a thin sheet, which is heated to 1300°C at a rate of 15°C/min and kept for 18 hours in an air atmosphere to make a lithium ion solid Electrolyte sheets.

Example 4: Li ₂ CO ₃ : _{Y 2} O ₃ : La ₂ O ₃ : B ₂ O ₃ : _Al 2 O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.2: 0.07: 1.43: 0.06: 0.09: The ratio of 0.12: 1.58: 0.3 (molar ratio) is evenly mixed, and 5.5% of 95% ethanol is added, and ball milled for 29 hours at a speed of 200 rpm in a ball mill. Dry for 10 hours, take it out and re-grind in an agate mortar for 20 minutes, heat the ground powder to 900°C at a rate of 5°C/min and keep it for 5 hours, then heat it up to 1230°C at a rate of 9°C/min and keep it for 20 minutes hours to make solid electrolyte powder. The powder is mixed with 2.8wt% binder PVA and kept under a pressure of 400MPa under a press for 4 minutes to form a thin sheet. The thin sheet is heated to 1250°C at a rate of 20°C/min and kept for 12 hours in an air atmosphere to produce lithium ion. Solid Electrolyte Sheets.

Example 5: Li ₂ CO ₃ : _{Y 2} O ₃ : _{La 2} O ₃ : B ₂ O ₃ : _Al 2 O ₃ : TiO ₂ : ZrO ₂ : Li ₂ F is 3.36: 0.11: 1.39: 0.08: 0.08: The ratio of 0.1: 1.58: 0.2 (molar ratio) is evenly mixed, and 4% of 95% ethanol is added, and ball milled at a speed of 210 rpm for 10 hours in a ball mill. Dry for 18 hours, take it out and re-grind in an agate mortar for 30 minutes, heat the ground powder to 760°C at a rate of 10°C/min and keep it for 10 hours, then heat it up to 1170°C at a rate of 7°C/min and keep it for 28 hours to make solid electrolyte powder. The powder is mixed with 4.6wt% binder PVC and kept under a pressure of 500MPa under a press for 2 minutes to form a thin sheet. The thin sheet is heated to 1200°C at a rate of 10°C/min and kept for 15 hours in an air atmosphere to form a lithium ion Solid Electrolyte Sheets.

Claims (3)

1. A B ³⁺ , Al ³⁺ , Ti ⁴⁺ , Y ³⁺ , F ^- co-doped lithium ion solid electrolyte, characterized in that the stoichiometric formula is Li _{7+ y1+y2-m} Y _x La _{3 -x} B _y1 Al _y2 Ti _y3 Zr _2-y1-y2-y3 O _12-m F _m , where: x=0.1-0.3; y1=0.1-0.2; y2=0.1-0.2; y3=0.1-0.2; m = 0.1-0.3. 2. The lithium ion solid electrolyte according to claim 1, characterized in that Li ₂ CO ₃ : _{Y 2} O ₃ : La ₂ O ₃ : B 2 O 3 : _{Al 2 O 3} : TiO ₂ : ZrO ₂ : _Li The molar ratio of ₂ F is 3.15-3.55: 0.05-0.15: 1.35-1.45: 0.05-0.1: 0.05-0.1: 0.1-0.2: 1.4-1.7: 0.1-0.3. Mix evenly, add 2%-6% of 95% Ethanol is ball milled for 10-30 hours at a speed of 200-400 rpm in a ball mill. 3. The lithium ion solid electrolyte according to claim 1, characterized in that the lithium ion conductivity at room temperature of the prepared solid electrolyte sheet is greater than 5×10 ^-4 S/cm.