Monoclinic Niobium-Titanium Core-Shell Oxide for Battery Energy Density
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Solution Overview
Problem
Nonaqueous electrolyte batteries using titanium oxide as the negative electrode material face challenges with low energy density and high overvoltage at low state of charge due to low electronic conductivity and limited lithium absorption sites, which affects their rapid charge and discharge performance and cycle stability.
Innovation Solution
The use of a composite active material with a core and shell phase structure, where the core phase includes a first monoclinic niobium-titanium composite oxide and the shell phase includes a second monoclinic niobium-titanium composite oxide with varying oxidation numbers, enhancing lithium ion conductivity and capacity while maintaining structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If titanium oxide is used as the negative electrode material, then rapid charge and discharge performance is improved, but energy density decreases
Solution Approach 1:
The patent uses a composite oxide material Li4Ti5O12-delta (where delta represents oxygen deficiency) that combines the advantages of titanium oxide's rapid charge-discharge capability with enhanced capacity. The composite structure allows lithium ions to be rapidly absorbed and released while increasing the theoretical capacity from 175 mAh/g to potentially higher values, thus resolving the contradiction between rapid charge-discharge performance and energy density.
Solution Approach 2:
The patent modifies the chemical composition and oxidation state of titanium by creating oxygen-deficient Li4Ti5O12-delta. By controlling the oxygen content (where delta > 0), the material achieves a balance between maintaining the 1.5V potential for rapid charge-discharge and increasing the number of lithium absorption sites to improve energy density.
2Quantity of substance
If niobium-titanium composite oxide TiNb2O7 is used, then capacity increases, but electronic conductivity decreases
Solution Approach 1:
The patent adjusts the oxidation number of titanium in the niobium-titanium composite oxide to be between +3.5 and +4. This parameter change optimizes the balance between capacity and electronic conductivity. By controlling the titanium oxidation state within this range, the material achieves high capacity through charge compensation mechanisms while maintaining sufficient electronic conductivity for practical battery operation.
Solution Approach 2:
The patent creates a core-shell structure where the core phase contains niobium-titanium composite oxide with specific oxidation states optimized for capacity, while the shell phase provides protective and conductive properties. This local differentiation allows different regions of the particle to optimize for different functions, resolving the contradiction between capacity and conductivity.
3Quantity of substance
If lithium absorption sites are increased in titanium oxide, then capacity improves, but structural stability deteriorates
Solution Approach 1:
The patent uses Li4Ti5O12-delta as a composite material that maintains the spinel crystal structure's inherent stability while creating additional lithium absorption sites through oxygen deficiency. The composite structure allows the material to accommodate more lithium ions without collapsing the crystal framework, thus improving capacity while maintaining structural stability during cycling.
Solution Approach 2:
By precisely controlling the oxygen deficiency parameter (delta) in Li4Ti5O12-delta, the patent optimizes the balance between capacity and structural stability. The oxygen deficiency creates additional lithium sites while the controlled magnitude of delta ensures the spinel structure remains stable, preventing degradation during repeated charge-discharge cycles.
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
This configuration improves the battery's energy density, rapid charge and discharge performance, and cycle stability by increasing lithium absorption and release capabilities, leading to higher capacity and rate performance compared to traditional titanium oxide-based batteries.
Implementation Method 1
The potential of titanium oxide is due to the redox reaction between Ti3+ and Ti4+ when lithium is electrochemically absorbed and released
Implementation Method 2
during the Li-absorption into this compound, charge compensation, in which Ti changes from tetravalence to trivalence and Nb changes pentavalence to trivalence, takes place
Data Source
AI summary
According to one embodiment, there is provided an active material. The active material includes particles. Each of the particles includes a core phase and a shell phase surrounding at least a part of the core phase. The core phase includes a first monoclinic niobium-titanium composite oxide. The shell phase includes a second monoclinic niobium-titanium composite oxide. An oxidation number of titanium in the core phase is larger than an oxidation number of titanium in the shell phase, and/or an oxidation number of niobium in the core phase is larger than an oxidation number of niobium in the shell phase.