CN102780031B - A kind of Mg 2+, Al 3+, Zr 4+, F -ion co-doped garnet-type solid electrolyte - Google Patents

Abstract

A Mg ²⁺ , Al ³⁺ , Zr ⁴⁺ , F ^- ion co-doped garnet-type lithium ion solid electrolyte Li ₅ La ₃ Nb ₂ O ₁₂ , characterized in that the stoichiometric formula is Li _{5+x+2y +zm} La _3-x Mg _x Al _y Zr _z Nb _2-yz O _12-m F _m where: x=0.1-0.5; y=0.1-0.2; z=0.1-0.2; m=0.1-0.3; ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.25-2.9: 1.25-1.45: 0.1-0.5: 0.05-0.1: 0.1-0.2: 0.8- The ratio of 0.9:0.1-0.3 (molar ratio) is evenly mixed, and it is made by ball milling, pressing and sintering; it can obtain the lithium ion conductivity at room temperature greater than 10 ^-4 S/cm.

Description

A Mg2+, Al3+, Zr4+, F- ion co-doped garnet-type solid electrolyte

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 batteries is the most promising chemical power source [Wu Yuping, Wan Chunrong, Jiang Changyin, Lithium-ion Secondary Batteries, Beijing: Chemical Industry Press, 2002.]. At present, most of the lithium-ion secondary batteries at home and abroad use liquid electrolytes. Liquid lithium-ion batteries have some disadvantages, 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; 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 introduction of holes or interstitial lithium ions in the structure can further improve the ionic conductivity through the substitution of asymmetric ions [XiaoxiongXu, ZhaoyinWen, 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 0 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. W.Weppner et al. proposed a new garnet-structured solid electrolyte Li ₅ La ₃ M ₂ O ₁₂ (M=Nb, Ta) in 2003 (Thangadurai, V., H.Kaack, et al., Journal of the American Ceramic Society, 86 (3) 2003, 437-440.), this solid electrolyte is very stable to metal lithium negative electrode and even molten metal lithium, and it is a solid electrolyte with great application value for all-solid lithium ion batteries. However, the normal temperature conductivity of pure Li ₅ La ₃ M ₂ O ₁₂ (M=Nb, Ta) is only about 10 ^-6 S/cm. In 2006, W.Weppner et al reported K ⁺ , In ³⁺ single-ion doped Li ₅ La ₃ M ₂ O ₁₂ (M=Nb, Ta) (Thangadurai, V.andW.Weppner, Journal of Solid State Chemistry 179 (4), 2006, 974-984.). The normal temperature ionic conductivity is increased to the order of 10 ^-5 S/cm. But it still can't meet the requirement of electrolyte conductivity for non-thin-film lithium-ion batteries.

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 garnet-type solid electrolyte has not yet been fully understood by researchers. Therefore, further research on the type and content of dopant ions is of great significance for the development of garnet-type 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 Mg ²⁺ , Al ³⁺ , Zr ⁴⁺ , F- ion co ^- doped garnet lithium ion solid electrolyte Li ₅ La ₃ Nb ₂ for the existing background technology O ₁₂ . First, replace La ³⁺ with Mg ²⁺ and replace Nb ⁵⁺ with Al ³⁺ . Low-valent ions replace high-valent ions to generate additional interstitial lithium ions, increasing the number of migrating lithium ions in the lattice; at the same time, the ionic radius of Mg ²⁺ is smaller than La ³⁺ , and the radius of Al ³⁺ ions is smaller than that of Nb ⁵⁺ ions. The synergistic effect of the two makes La-O octahedron and Nb-O octahedron produce a certain shrinkage distortion, which moderately expands the migration channel cross section of lithium ions, thereby Improve the conductivity of lithium ions; F ^- partly replaces O ^2- , F ^- is close to O ² - in radius, but has strong electronegativity and lattice shrinkage, further increases the cross section of lithium ion migration channels, and improves lithium ion migration rate; Zr ^{4 +} Partial substitution of Nb ⁵⁺ helps to reduce the activation energy of lithium ion migration. These synergistic effects make the normal temperature ionic conductivity of the solid electrolyte exceed 10 ^-4 S/cm, which is closer to the ionic conductivity of the liquid electrolyte.

The present invention is achieved through the following technical solution. The technical solution provides a lithium ion solid electrolyte with a lithium ion conductivity exceeding 10 ^-4 S/cm, and its stoichiometric formula is Li _5+x+2y+zm La _3-x Mg _{xAlyZrzNb2 -yzO12-mFm where : x} =0.1-0.5; _y =0.1-0.2; z=0.1-0.2; m=0.1-0.3.

In this technical solution, Li ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.25-2.9: 1.25-1.45: 0.1-0.5: 0.05- 0.1: 0.1-0.2: 0.8-0.9: 0.1-0.3 (molar ratio) and mix evenly, add 3%-10% 95% ethanol, ball mill in a ball mill at a speed of 200-400 rpm for 10-30 hours After ball milling, dry in a vacuum oven at 60°C-80°C (vacuum degree at 10Pa-100Pa) for 10-30 hours, take it out and re-grind it in an agate mortar for 10-30 minutes, and grind the powder with 5- The temperature is raised to 700-800°C at a rate of 10°C/min and kept for 5-10 hours, and then the temperature is raised to 900-1100°C at a rate of 2-10°C/min and kept for 10-30 hours to form a solid electrolyte powder. The powder is mixed with 1-5wt% binder (the binder 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 1/min to 900-1150° C. and keep it warm for 10-30 hours to make a lithium-ion solid electrolyte sheet. Figure 1 is the AC impedance diagram of the solid electrolyte sheet with the composition of Li _5.3 La _2.9 Mg _0.1 Al _0.1 Zr _0.1 Nb _1.8 O _11.9 F _0.1 under the electrochemical workstation, and the calculated conductivity is 3.6x10 ^-4 S/cm from the diagram.

Compared with the prior art, the present invention has the advantages of adopting Mg ²⁺ , Al ³⁺ , Zr ⁴⁺ , and F- ions co ^- doped garnet-type lithium ion solid electrolyte Li ₅ La ₃ Nb ₂ O ₁₂ . By substituting Mg ²⁺ for La ³⁺ and Al ³⁺ for Nb ⁵⁺ , low-valent ions replace high-valent ions to generate additional interstitial lithium ions, increasing the number of migrating lithium ions in the lattice; at the same time, the ionic radius of Mg ²⁺ is less than The radius of La ³⁺ and Al ³⁺ ions is smaller than that of Nb ⁵⁺ ions. The synergistic effect of the two causes a certain shrinkage distortion of the La-O octahedron and Nb-O octahedron, which moderately expands the cross-section of the migration channel of lithium ions, thereby improving Lithium ion conductivity; F ^- partially replaces O ^2- , F ^- is close to O ² - in radius, but has strong electronegativity and lattice shrinkage, which further increases the cross section of lithium ion migration channel and improves lithium ion migration rate; Zr ⁴⁺ Partial substitution of Nb ⁵⁺ helps to reduce the activation energy of lithium ion migration. These synergistic effects greatly enhance the conductivity of the garnet-type solid Li-ion electrolyte. It is very beneficial to the construction of all-solid-state lithium-ion batteries.

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 description

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

Example 1: Li ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.55: 1.41: 0.18: 0.06: 0.13: 0.875: 0.15 (molar ratio ) in a uniform mixing ratio, add 3.2% of 95% ethanol, ball mill with a speed of 250 rev/min for 10 hours in a ball mill, dry in a 60°C vacuum oven (vacuum degree 20Pa) for 10 hours after the ball mill finishes, take it out and place it on agate Re-grind in the mortar for 30 minutes. The ground powder is heated at a rate of 5 °C/min to 720 °C for 10 hours, and then heated at a rate of 3 °C/min to 900 °C for 11 hours to make a 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 1000°C at a rate of 11°C/min and kept for 10 hours in an air atmosphere to make a lithium ion solid Electrolyte sheets.

Example 2: Li ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.66: 1.3: 0.4: 0.07: 0.12: 0.87: 0.16 (molar ratio ) in a uniform mixing ratio, add 8.5% of 95% ethanol, ball mill with a speed of 380 rev/min for 15 hours in a ball mill, dry in a vacuum oven (vacuum degree 95Pa) at 80°C for 30 hours after ball milling, take it out and place it on agate Re-grind in the mortar for 30 minutes, and the ground powder is heated to 780°C at a rate of 8°C/min for 10 hours, and then heated to 950°C at a rate of 7°C/min for 15 hours to make a 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 1050°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 : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.55: 1.45: 0.1: 0.05: 0.1: 0.9: 0.10 (molar ratio ) in a uniform mixing ratio, add 3% 95% ethanol, ball mill with a speed of 300 rev/min for 20 hours in a ball mill, dry in a 70°C vacuum oven (vacuum degree 50Pa) for 20 hours after ball milling, take it out and put it on agate Re-grind in the mortar for 10 minutes. The ground powder is heated at a rate of 10 °C/min to 800 °C for 7 hours, and then heated at a rate of 2 °C/min to 1100 °C for 12 hours to make a 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. The thin sheet is heated to 1150°C at a rate of 15°C/min and kept for 28 hours in an air atmosphere to make a lithium ion solid Electrolyte sheets.

Example 4: Li ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.565: 1.35: 0.3: 0.07: 0.15: 0.855: 0.2 (molar ratio ) ratio evenly mixed, added 9% of 95% ethanol, ball milled at a speed of 390 revs/min for 29 hours in a ball mill, dried in a vacuum oven (vacuum degree 100Pa) at 80° C. for 10 hours after ball milling, and placed on agate Re-grind in the mortar for 20 minutes. The ground powder is heated at a rate of 8 °C/min to 750 °C for 5 hours, and then heated at a rate of 9 °C/min to 1000 °C for 20 hours to make a solid electrolyte powder. The powder is mixed with 2.6wt% 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 1050°C at a rate of 20°C/min and kept for 18 hours in an air atmosphere to produce lithium ion. Solid Electrolyte Sheets.

Example 5: Li ₂ CO ₃ : La ₂ O ₃ : MgO: Al ₂ O ₃ : ZrO ₂ : Nb ₂ O ₅ : Li ₂ F is 2.6: 1.25: 0.5: 0.1: 0.2: 0.8: 0.3 (molar ratio ) was evenly mixed in proportion, added 6% of 95% ethanol, and ball milled for 10 hours at a speed of 210 revs/min in a ball mill. After ball milling, dried in a vacuum oven (vacuum degree 20Pa) at 60°C for 30 hours, and placed on agate after taking out Re-grind in the mortar for 30 minutes. The ground powder is heated to 710°C at a rate of 5°C/min and kept for 10 hours, and then heated to 900°C at a rate of 6°C/min for 28 hours to make a solid electrolyte powder. The powder is mixed with 5wt% binder PVC and kept under a pressure of 500MPa under a press for 2 minutes to form a thin sheet, which is heated to 900°C at a rate of 10°C/min and kept for 10 hours in an air atmosphere to make a lithium ion solid Electrolyte sheets.

Claims (2)

1. a Mg ²⁺, Al ³⁺, Zr ⁴⁺, F ^-ion co-doped carbuncle type lithium ion solid electrolyte, is characterized in that its stoichiometric equation is Li _5+x+2y+z-mla _3-xmg _xal _yzr _znb _2-y-zo _12-mf _m, wherein: x=0.1-0.5; Y=0.1-0.2; Z=0.1-0.2; M=0.1-0.3; Described solid electrolyte is adopted and is prepared with the following method: by Li ₂cO ₃: La ₂o ₃: MgO: Al ₂o ₃: ZrO ₂: Nb ₂o ₅: Li ₂f, with the ratio uniform mixing of mol ratio 2.25-2.9: 1.25-1.45: 0.1-0.5: 0.05-0.1: 0.1-0.2: 0.8-0.9: 0.1-0.3, adds 95% ethanol of 3%-10%, with the rotating speed ball milling 10-30 hour of 200-400 rev/min in ball mill.

2. carbuncle type lithium ion solid electrolyte according to claim 1, is characterized in that the normal temperature lithium ion conductivity of the thin slice of the described solid electrolyte obtained is greater than 10 ^-4s/cm.