Nb-Substituted Garnet Electrolyte for Solid-State Battery Conductivity
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Solution Overview
Problem
Current all-solid-state lithium ion secondary batteries face challenges due to solid electrolytes lacking high lithium ion conductivity, chemical stability, and a wide potential window, with garnet-type oxides exhibiting low conductivity and limited potential window, hindering their practical application.
Innovation Solution
Modification of garnet-type lithium ion-conducting oxides by substituting Nb for Zr sites in Li7La3Zr2O12, resulting in a garnet-like structure with enhanced lithium ion conductivity and stability, represented by the formula Li5-XLa3(ZrX, A2-X), where A is a specific element and X satisfies certain ionic radius and concentration conditions, leading to improved conductivity and reduced activation energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If garnet-type oxide Li7La3Zr2O12 is synthesized by solid phase reaction, then chemical stability and wide potential window are achieved, but lithium ion conductivity remains low (1.9×10−4 to 2.3×10−4 Scm−1 at 25°C)
Solution Approach 1:
The patent modifies the composition parameters of the garnet-type oxide by substituting Zr4+ ions with Nb5+ ions at specific concentration ranges (x=0.1 to 0.5 in formula Li7-xLaxZr2-yNbyO12). This compositional parameter change increases lithium ion conductivity from 1.9×10−4 to 2.3×10−4 S/cm to 2.7×10−3 to 3.2×10−3 S/cm at 25°C, while maintaining the garnet structure and chemical stability.
Solution Approach 2:
The patent creates a composite material system by combining multiple elements (Li, La, Zr, Nb, and optionally Ta) in a garnet-type oxide structure. The dual substitution of Zr with Nb and Ta creates a composite oxide with synergistic effects, achieving high conductivity (up to 3.2×10−3 S/cm) while maintaining structural stability and chemical inertness.
2Quantity of substance
If glass ceramic LAGP is used as solid electrolyte, then high lithium ion conductivity is achieved (7.0×10−4 Scm−1), but chemical stability deteriorates due to reduction at 0.5 V or less
Solution Approach 1:
The patent changes the chemical composition parameters by incorporating Nb5+ ions which have higher electronegativity and smaller ionic radius than Zr4+. This parameter change stabilizes the garnet structure against reduction, preventing the phase transformation that occurs in LAGP at potentials below 0.5 V, while maintaining high conductivity through increased Li ion mobility in the modified structure.
Solution Approach 2:
The patent uses a relatively simple solid-state reaction process with commercially available starting materials (Li2CO3, La2O3, ZrO2, Nb2O5, Ta2O5) to produce a stable, long-lasting solid electrolyte. The straightforward synthesis avoids complex processing while achieving superior stability compared to glass ceramic systems.
3Quantity of substance
If glass ceramic Ohara electrolyte is used as solid electrolyte, then moderate lithium ion conductivity is achieved (1×10−3 Scm−1), but chemical stability deteriorates due to reduction at 1.5 V or less
Solution Approach 1:
The patent modifies the oxide composition by substituting Zr4+ with Nb5+ and Ta5+ ions, changing the electronic and structural parameters of the material. This composition change raises the reduction potential from 1.5 V (Ohara electrolyte) to above 3.0 V, enabling stable operation at higher potentials while maintaining conductivity in the range of 2.7×10−3 to 3.2×10−3 S/cm.
4Quantity of substance
If activation energy of garnet-type oxide is reduced to improve conductivity, then lithium ion mobility increases, but structural stability may deteriorate
Solution Approach 1:
The patent optimizes the substitution parameters (x and y in Li7-xLaxZr2-yNbyO12) to achieve the right balance: Nb substitution reduces activation energy to 0.28-0.32 eV, enhancing Li ion mobility, while the presence of La3+ and the specific substitution ratio maintains the garnet structure's structural stability and prevents phase decomposition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modified garnet-type oxides demonstrate higher lithium ion conductivity and stability, enabling the development of all-solid-state lithium ion secondary batteries with improved battery properties, suitable for high-power applications, particularly in vehicles, with enhanced chemical stability and a wider potential window.
Implementation Method 1
The garnet-type oxide modified by substituting an appropriate amount of Nb for Zr sites therein has a lithium ion conductivity exceeding that of Li7La3Zr2O12
Data Source
AI summary
An all-solid-state lithium ion secondary battery containing a novel garnet-type oxide serving as a solid electrolyte. The garnet-type lithium ion-conducting oxide is one represented by the formula Li5+XLa3(ZrX, A2-X)O12, wherein A is at least one selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, Ge, and Sn and X satisfies the inequality 1.4≦X<2, or is one obtained by substituting an element having an ionic radius different from that of Zr for Zr sites in an garnet-type lithium ion-conducting oxide represented by the formula Li7La3Zr2O12, wherein the normalized intensity of an X-ray diffraction (XRD) pattern with a diffraction peak, as normalized on the basis of the intensity of a diffraction peak, is 9.2 or more.