CN102456917B - A NASICON-type solid lithium-ion electrolyte co-doped with F- and Zn2+ ions - Google Patents

Abstract

The invention relates to an F<-> and Zn<2+> co-doped NASICON type solid lithium ion electrolyte. The electrolyte is characterized in that: the electrolyte has a stoichiometric formula of Li1+2x-yZnxM2-xP3O12-yFy, wherein x=0.1-0.5; y=0.1-0.2; and M is one of Ti, Ge, and Zr. According to the invention, materials are well mixed according to a molar ratio that ZnO:LiF:MO2(M=Ti, Ge, Zr):NH4H2PO4:Li2CO3=0.1-0.5:0.1-0.2:1.5-1.9:3.0:0.4-0.9; the mixture is ball-milled, compacted, and sintered, such that the electrolyte is obtained. With the electrolyte, a room temperature lithium ion conductivity is higher than 10<-4>S/cm.

Description

A NASICON-type solid lithium-ion electrolyte co-doped with F- and Zn2+ ions

technical field

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

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. ]. the

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. LiM ₂ (PO ₄ ) ₃ (M=Ti, Ge, Zr) with NASICON polycrystal is a grid structure composed of tetrahedral PO ₄ and octahedral MO ₆ (such as M=Ti), resulting in a structural The hole and fillable coordination, which allow the regulation of a large number of Li ions, is a promising solid 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 [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} Mg _x P 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 and other systems all have high lithium ion conductivity. At present, researchers have tried Ga ³⁺ , Cr ³⁺ , Sc ³⁺ , In ³⁺ , Al ³⁺ , La ³⁺ , Fe ³⁺ , Tl ³⁺ , Lu ³⁺ , Y ³⁺ , Eu ³⁺ , In ³⁺ , Si ⁴⁺ , V ⁵⁺ , Ta ⁵⁺ , Nb ⁵⁺ , S ⁶⁺ and other high or low price cations partially replace Ti ⁴⁺ (Ge ⁴⁺ , Zr ⁴⁺ ) or P ⁵⁺ , which improves the ionic conductivity of the NASICON matrix LiM ₂ (PO ₄ ) ₃ (M=Ti, Ge, Zr) to a certain extent. 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. The interaction between dopant ions and the matrix is very complicated. In principle, the selection of dopant ions should satisfy the transmission bottleneck and the matching of the Li ⁺ radius, the weak bonding force between Li ⁺ and the framework ions, and the moderate ratio of vacancy concentration to Li ⁺ concentration. condition. Lithium ion migration in the NASICON solid electrolyte exists in two ways: Li(I) vacancies-Li(II) vacancies, Li(II) vacancies-Li(II) vacancies, and one group of Li(II) vacancies-Li( II) The vacancy migration mode is blocked by oxygen atoms to reduce the ionic conductivity. Therefore, it is of great significance to further study the type and content of dopant ions to improve the conductivity of NASICON-type lithium-ion solid-state electrolytes.

Contents of the invention

The technical problem to be solved by the present invention is to provide a NASICON type lithium ion solid electrolyte LiM ₂ (PO ₄ ) ₃ co-doped with F ^- , Zn ²⁺ anions and cations in view of the existing background technology. Zn ²⁺ partially replaces Mi ⁴⁺ , and a unit mole of Zn ²⁺ can produce 2 mol interstitial lithium ions, avoiding the distortion of the octahedral structure caused by the introduction of a large number of low-valent ions and making up for the reduction in the number of interstitial lithium ions caused by F ^- doping Small. And F ^- partially replaces the oxygen ion in the MO octahedron, which has the following effects: (1) F ^- is an anion with extremely strong electronegativity. After partially replacing O ^2- , the stability of the structure is increased, and the Li- O bond energy weakens the bonding force between lithium ions and the skeleton, and enhances Li ⁺ mobility; (2) F ^- ion radius is smaller than O ^2- , so it can reduce a group of Li(II) vacancy-Li(II) vacancy migration The steric hindrance caused by middle oxygen ions; (3) The transport bottleneck formed by anions is reduced, making it more compatible with the size of Li ⁺ . The synergistic effect of the two makes 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, which provides a lithium ion solid electrolyte with a lithium ion conductivity exceeding 10 ^-4 S/cm, and its stoichiometric formula is Li _1+2x-y Zn _x M _2-x P ₃ O _12-y F _y , wherein: x=0.1-0.5; y=0.1-0.2; M is one of Ti, Ge, Zr.

In this technical scheme, ZnO: LiF: MO ₂ (M=Ti, Ge, Zr): NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ is 0.1-0.5: 0.1-0.2: 1.5-1.9: 3.0: 0.4 Mix evenly at a ratio of -0.9 (molar ratio), add 3%-9% of 95% ethanol, ball mill in a ball mill at a speed of 100-500 rpm for 10-50 hours, and vacuum at 60°C-80°C after ball milling Dry in an oven (vacuum degree 10Pa-100Pa) for 2-10 hours, take it out and re-grind in an agate mortar for 10-30 minutes, and the ground powder is heated to 700-1000℃ at a rate of 5-30℃/min Heat preservation for 5-16 hours to make solid electrolyte powder. The powder is mixed with 1-5wt% as a binding agent (the binding agent can be PVC, a kind of PVA) under the pressure of 200-500MPa under the press to keep the pressure for 2-6 minutes to form a thin sheet, the thin sheet in a nitrogen atmosphere Then, the temperature is raised to 800-1000° C. at a rate of 10-30° C./minute and kept for 3-10 hours to prepare a lithium-ion solid electrolyte sheet. Figure 1 is the AC impedance diagram of the solid electrolyte sheet with the composition of Li _1.1 Zn _0.1 Ti _1.9 P _3.0 O _11.9 F _0.1 under the electrochemical workstation, and the calculated conductivity is 2.3x10 ^-4 S/cm from the diagram.

Compared with the prior art, the present invention has the advantages of co-doping with F ^- and Zn ²⁺ anions and cations, Zn ²⁺ partially replaces M ⁴⁺ , and a small amount of doping can greatly increase the number of interstitial lithium ions , avoiding the distortion of the octahedral structure caused by the introduction of a large number of low-valent ions. The F ^- part replaces the oxygen ions in the MO octahedron, and its strong electronegativity reduces the steric hindrance caused by oxygen ions in the migration of a group of Li(II) vacancies-Li(II) vacancies, and weakens the relationship between lithium ions and Li(II) vacancies. The bonding force of the skeleton enhances the mobility of Li ⁺ , reduces the transport bottleneck formed by anions, and makes it more compatible with the size of Li ⁺ , which greatly improves the conductivity of the NASICON solid lithium 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. the

Detailed ways

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

Example 1: Mix ZnO: LiF: TiO ₂ : NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ in a ratio of 0.1: 0.1: 1.9: 3.0: 0.5 (molar ratio), and add 3% of 95% ethanol, Ball milling in a ball mill at a speed of 100 rpm for 15 hours, after ball milling, dry in a 60°C vacuum oven (vacuum degree 20Pa) for 3 hours, take it out and regrind in an agate mortar for 30 minutes, the powder after grinding is Raise the temperature at a rate of 6°C/min to 700°C for 6 hours to prepare a solid electrolyte powder. The powder is mixed with 2wt% binder (PVC) and kept under a pressure of 250MPa for 2 minutes under a press to form a thin sheet, which is heated to 800°C at a rate of 10°C/min and kept for 10 hours under a nitrogen atmosphere to make lithium Ionic solid electrolyte sheets.

Example 2: Mix ZnO: LiF: GeO ₂ : NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ in a ratio of 0.3: 0.1: 1.7: 3.0: 0.7 (molar ratio), and add 9% of 95% ethanol, In the ball mill, ball mill at a speed of 450 rev/min for 45 hours. After ball milling, dry in an 80°C vacuum oven (vacuum degree 95Pa) for 9 hours. After taking it out, re-grind in an agate mortar for 30 minutes. The powder after grinding is Raise the temperature at a rate of 25°C/min to 950°C for 15 hours to prepare a solid electrolyte powder. The powder is mixed with 5wt% binder (PVC) and kept under a pressure of 450MPa for 6 minutes under a press to form a thin sheet, which is heated to 1000°C at a rate of 25°C/min and kept for 10 hours under a nitrogen atmosphere to make lithium Ionic solid electrolyte sheets.

Example 3: Mix ZnO: LiF: ZrO ₂ : NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ in a ratio of 0.5: 0.2: 1.5: 3.0: 0.8 (molar ratio), and add 5% of 95% ethanol, In the ball mill, ball mill at a speed of 300 rev/min for 30 hours. After ball milling, dry in a 75°C vacuum oven (vacuum degree 50Pa) for 6 hours. After taking it out, re-grind in an agate mortar for 20 minutes. The powder after grinding is Raise the temperature at a rate of 10°C/min to 850°C for 12 hours to prepare a solid electrolyte powder. The powder is mixed with 2.6wt% binder (PVA) and kept under a pressure of 400 MPa under a press for 4 minutes to form a thin sheet. The thin sheet is heated to 900°C at a rate of 15°C/min and kept for 7 hours under a nitrogen atmosphere. Lithium ion solid electrolyte sheet.

Example 4: Mix ZnO: LiF: TiO ₂ : NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ in a ratio of 0.4: 0.1: 1.6: 3.0: 0.8 (molar ratio), and add 6% of 95% ethanol, In the ball mill, ball mill at a speed of 350 rev/min for 20 hours. After ball milling, dry in a 70°C vacuum oven (vacuum degree 50Pa) for 8 hours. After taking it out, re-grind in an agate mortar for 10 minutes. The powder after grinding is Raise the temperature at a rate of 8°C/min to 800°C for 15 hours to prepare a solid electrolyte powder. The powder is mixed with 2.6wt% binder (PVA) and kept under a pressure of 400 MPa under a press for 4 minutes to form a thin sheet, which is made by heating up to 900°C at a rate of 15°C/min for 3 hours under a nitrogen atmosphere. Lithium ion solid electrolyte sheet.

Example 5: Mix ZnO: LiF: GeO ₂ : NH ₄ H ₂ PO ₄ : Li ₂ CO ₃ in a ratio of 0.4: 0.2: 1.6: 3.0: 0.7 (molar ratio), and add 7% of 95% ethanol, In the ball mill, ball mill at a speed of 300 rev/min for 35 hours. After ball milling, dry in a 75°C vacuum oven (vacuum degree 60Pa) for 6 hours. After taking it out, regrind in an agate mortar for 26 minutes. The powder after grinding is Raise the temperature at a rate of 10°C/min to 850°C for 12 hours to prepare a solid electrolyte powder. The powder is mixed with 2.6wt% binder (PVC) and kept under a pressure of 400MPa under a press for 4 minutes to form a thin sheet. The thin sheet is heated to 900°C at a rate of 15°C/min and kept for 7 hours under a nitrogen atmosphere. Lithium ion solid electrolyte sheet.

Claims (3)

1. one kind adopts F ^-, Zn ²⁺ion co-doped NASICON type lithium ion solid electrolyte, its stoichiometric equation is Li _1+2x-yzn _xm _2-xp ₃o _12-yf _y, wherein: x=0.1-0.5; Y=0.1-0.2, M are the one in Ti, Ge, Zr.

2. lithium ion solid electrolyte according to claim 1, is characterized in that ZnO: LiF: MO ₂: NH ₄h ₂pO ₄: Li ₂cO ₃for the ratio uniform mixing of 0.1-0.5: 0.1-0.2: 1.5-1.9: 3.0: 0.4-0.9, wherein M is one in Ti, Ge, Zr and aforementioned proportion is all mol ratio, add 95% ethanol of 3%-9%, with the rotating speed ball milling 10-50 hour of 100-500 rev/min in ball mill.

3. lithium ion solid electrolyte according to claim 1, is characterized in that, the normal temperature lithium ion conductivity of obtained solid electrolyte flake is greater than 10 ^-4s/cm.