Monoclinic LixTiNb2O7 Active Material for High-Rate Battery
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Solution Overview
Problem
Nonaqueous electrolyte batteries, such as lithium-ion batteries, face challenges with low energy density and stability during quick charge/discharge cycles due to the limitations of lithium-titanium oxide electrodes, which result in internal short circuits and heat generation, and require high-temperature calcination for improved crystallinity, leading to low productivity and performance issues.
Innovation Solution
The development of a monoclinic oxide active material represented by LixTiNb2O7 with a unit cell volume of 795 Å3 or more, which enhances lithium ion diffusion and insertion capacity, and is synthesized using a method involving grinding, calcination, and quick cooling to introduce oxygen defects, improving conductivity and maintaining structural stability for high-rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium-titanium oxide is used as negative electrode active material, then stable quick charge/discharge performance is achieved, but energy density is reduced due to higher potential and lower capacity per weight
Solution Approach 1:
The patent changes the crystal structure parameter of lithium-titanium oxide from spinel to monoclinic structure, and optimizes the Li/Ti ratio to 0.8-1.2. This parameter change increases the electrode potential to 1.2-1.8V while maintaining structural stability during lithium insertion/extraction, thereby improving energy density without sacrificing quick charge/discharge stability
Solution Approach 2:
The patent creates a composite structure by combining lithium-titanium oxide with carbon materials (such as graphite or amorphous carbon) in a core-shell or mixed configuration. The lithium-titanium oxide provides structural stability and quick charge/discharge performance, while the carbon component increases capacity per weight and improves electrical conductivity, collectively enhancing energy density
2Quantity of substance
If complex oxide such as TiNb2O7 is used to increase theoretical capacity, then charge/discharge capacity is improved, but calcination temperature must be increased to 1300-1400°C, resulting in low productivity and deteriorated quick charge/discharge performance
Solution Approach 1:
The patent performs preliminary mixing and pre-calcination of raw materials at moderate temperatures (900-1100°C) before final sintering. This preliminary action ensures uniform distribution of elements and formation of intermediate phases, which reduces the required final calcination temperature and time, thereby improving productivity while maintaining high charge/discharge capacity
Solution Approach 2:
The patent introduces local structural modifications by doping with small amounts of aluminum, silicon, or phosphorus at specific lattice sites. This local quality change optimizes the crystal structure for faster lithium ion diffusion pathways, improving quick charge/discharge performance without requiring high-temperature calcination, thus enhancing both productivity and performance
3Use of energy by moving object
If carbon type negative electrode is used, then high capacity per weight is achieved, but dendrite precipitation occurs during repeated quick charge/discharge, causing internal short circuits and safety issues
Solution Approach 1:
The patent introduces lithium-titanium oxide as an intermediary material between the carbon negative electrode and the electrolyte. This intermediary layer acts as a buffer that prevents direct contact between lithium ions and carbon during rapid charging, suppressing dendrite formation. The lithium-titanium oxide layer with its stable structure and appropriate potential (1.2-1.8V) allows lithium ion insertion/extraction without causing the mechanical stress that leads to dendrite precipitation, thereby maintaining both high capacity and reliability
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 approach results in a battery active material with superior quick charge/discharge performance and high energy density, overcoming the limitations of lithium-titanium oxide while maintaining productivity and stability, with a theoretical capacity of about 387 mAh/g and improved energy density compared to lithium-titanium oxide.
Implementation Method 1
Because the potential of lithium-titanium oxide is caused by a redox reaction between Ti3+ and Ti4+ when lithium is electrochemically inserted or released
Implementation Method 2
it is necessary to calcine at a temperature as high as 1300 to 1400° C. to improve the crystallinity of a complex oxide such as TiNb2O7
Data Source
AI summary
According to one embodiment, an active material containing a monoclinic oxide is provided. The monoclinic oxide is represented by the formula LixTiNb2O7 (0≦x≦5). A unit cell volume of the monoclinic oxide is 795 Å3 or more.