Positive Electrode Layer With CNT-Filled Voids for Cycle Stability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in maintaining favorable cycle characteristics due to cracking of positive electrode active materials during charging and discharging, leading to increased resistance and potential loss of electron conduction paths.
Innovation Solution
A positive electrode layer is developed containing tungsten-based secondary particles with primary particles and voids, where first carbon nanotubes are included within the voids of the secondary particles, and the tungsten valence is optimized to satisfy a specific X-ray absorption fine structure analysis condition, ensuring effective electron conduction even if cracks occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nanotubes are applied on the surface of positive electrode active material, then electrical conductivity is improved, but cycle characteristics deteriorate due to cracking of active material particles
Solution Approach 1:
Carbon nanotubes are nested inside the voids of secondary particles formed by aggregated primary particles. This internal placement ensures that conductive pathways are maintained within the particle structure even when external cracks occur during charging and discharging cycles, thereby improving cycle characteristics while maintaining electrical conductivity.
Solution Approach 2:
The secondary particles are designed with a porous structure containing voids between primary particles. These voids serve as reservoirs to accommodate carbon nanotubes, allowing the material to maintain structural flexibility and conductive pathways during volume changes associated with lithium insertion and extraction, thus improving cycle stability.
2Reliability
If tungsten oxide coating is applied to positive electrode active material, then initial resistance is reduced, but resistance increases during charging and discharging cycles
Solution Approach 1:
The positive electrode active material is designed as a composite structure with lithium composite oxide primary particles, tungsten oxide coating, and embedded carbon nanotubes. This composite structure combines the low resistance properties of tungsten oxide with the structural stability and conductive network provided by carbon nanotubes, maintaining resistance stability during charging and discharging cycles.
Solution Approach 2:
The valence of tungsten in the tungsten oxide coating is controlled to be +4 or a mixture of +4 and +6. This specific parameter control optimizes the electronic conductivity and structural stability of the coating, reducing initial resistance and preventing excessive resistance increase during cycling by maintaining appropriate oxidation states during lithium insertion and extraction.
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 reduces battery resistance and improves cycle characteristics by maintaining electron conduction paths and lowering active energy, thereby enhancing the performance of lithium ion secondary batteries.
Implementation Method 1
the positive electrode layer contains, as the carbon nanotubes, first carbon nanotubes of which at least some are included in the voids of the secondary particles... ensuring effective electron conduction even if cracks occur
Implementation Method 2
spectrums at rising positions (10,195 eV to 10,206 eV) of peaks of L absorption edges of tungsten measured by X-ray absorption fine structure analysis (XAFS)
Data Source
AI summary
In the present disclosure, the above problem can be addressed by providing a positive electrode layer used in a lithium ion secondary battery, wherein the positive electrode layer contains a positive electrode active material and carbon nanotubes, wherein the positive electrode active material contains tungsten and is secondary particles including a plurality of primary particles and voids formed between the plurality of primary particles, wherein the positive electrode layer contains, as the carbon nanotubes, first carbon nanotubes of which at least some are included in the voids of the secondary particles, and wherein spectrums at rising positions (10,195 eV to 10,206 eV) of peaks of L absorption edges of tungsten measured by X-ray absorption fine structure analysis (XAFS) satisfy:(a-b)/(c-b)≤0.79.Formula (1)