Niobium Titanium Composite Oxide Electrode for High-Rate Battery
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Solution Overview
Problem
Nonaqueous electrolyte batteries face challenges with low energy density and rapid charge/discharge limitations due to the use of titanium oxide as a negative electrode material, which results in internal short circuits and reduced capacity compared to carbon-based electrodes.
Innovation Solution
The development of a niobium titanium composite oxide (TiNb2O7) with a monoclinic crystal structure, where secondary particles with a compression fracture strength of 10 MPa or more are coated with a carbon material phase, enhancing lithium ion conductivity and stability, thereby improving energy density and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If titanium oxide is used as negative electrode active material, then rapid charge and discharge performance is improved, but energy density decreases due to higher potential and lower capacity per weight
Solution Approach 1:
The patent uses a composite oxide material containing both titanium and niobium (Ti-Nb composite oxide) instead of pure titanium oxide. The niobium substitution creates additional lithium absorption sites in the crystal structure while maintaining the rapid ion conductivity characteristics of titanium oxide, thereby improving capacity density without sacrificing rate performance
Solution Approach 2:
The patent modifies the crystal structure parameters by substituting niobium for some titanium atoms in the TiNb2O7 structure. This changes the electrochemical properties by creating mixed valence states (Ti3+/Ti4+ and Nb4+/Nb5+) that provide more lithium absorption sites, increasing the theoretical capacity from 175 mAh/g of pure Li4Ti5O12 to higher values in the composite structure
2Quantity of substance
If carbonaceous material is used in negative electrode, then energy density is improved due to lower potential and higher capacity per weight, but dendrite precipitation occurs during rapid charge and discharge
Solution Approach 1:
The patent introduces a carbon coating layer as an intermediary between the composite oxide particles and the electrolyte. This carbon layer serves multiple functions: it prevents direct contact between lithium ions and the oxide surface that would cause dendrite formation, while still allowing rapid lithium ion transport through its conductive structure, thus eliminating the harmful effects of carbonaceous materials while retaining their high capacity benefits
3Quantity of substance
If titanium oxide electrode potential is lowered to improve energy density, then capacity increases, but rapid absorption and release of lithium ion becomes unstable
Solution Approach 1:
The patent creates local variations in the electrode structure by forming composite oxide particles with specific crystallographic orientations and surface characteristics. The TiNb2O7 structure provides localized regions with optimized lithium ion diffusion pathways and stable potential platforms, allowing high capacity utilization while maintaining stable rapid charge-discharge performance at the local particle level
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 niobium titanium composite oxide enables stable rapid charge and discharge with increased energy density and cycle life, maintaining high capacity and high-current performance without impairing rate performance, suitable for use in both negative and positive electrodes.
Implementation Method 1
enhancing lithium ion conductivity and stability
Implementation Method 2
The potential of titanium oxide is due to the redox reaction between Ti3+ and Ti4+ when lithium is electrochemically absorbed and released
Data Source
AI summary
According to one embodiment, there is provided an active substance. The active substance includes secondary particles and a carbon material phase formed on at least a part of a surface of each of the secondary particles. Each of the secondary particles is constructed by aggregated primary particles of an active material. The primary particles of the active material includes a niobium composite oxide represented by LixM(1−y)NbyNb2O(7+δ), wherein M is at least one selected from the group consisting of Ti and Zr, and x, y, and δ respectively satisfy 0≦x≦6, 0≦y≦1, and −1≦δ≦1. The secondary particles have a compression fracture strength of 10 MPa or more.