Composite Graphite Negative Electrode for Lithium-Ion Battery
Solution Overview
Problem
The challenge lies in developing a negative electrode material for lithium-ion secondary batteries that maintains high-load characteristics while increasing electrode density, without causing peeling from the current collector or deteriorating charge-discharge properties, which is currently hindered by the high crystalline anisotropy and reaction activity of spherical natural graphite with the electrolytic solution.
Innovation Solution
A composite particle structure is introduced, comprising spherical graphite and graphite particles with nonparallel orientation planes, optimized with specific R-value, pore volume, and surface area, to enhance lithium ion migration and reduce lattice defects, thereby improving the electrode's density and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If spherical natural graphite is used to increase negative electrode density, then electrode density is improved, but charge-discharge efficiency deteriorates due to high reaction activity with electrolytic solution
Solution Approach 1:
A low crystallinity carbon coating layer is applied as an intermediary between the spherical natural graphite and the electrolytic solution. This coating layer reduces the direct reaction activity between the graphite surface and electrolyte, thereby improving charge-discharge efficiency while maintaining the high density benefits of spherical graphite particles.
Solution Approach 2:
The invention uses composite particles consisting of spherical natural graphite core combined with low crystallinity carbon coating. This composite structure combines the high density advantage of spherical graphite with the low reaction activity and good electrolyte permeability of low crystallinity carbon, resolving the contradiction between density and charge-discharge efficiency.
2Quantity of substance
If high pressing pressure is applied to increase negative electrode density, then electrode density is improved, but peeling occurs between graphite and current collector
Solution Approach 1:
The invention changes the particle morphology parameter from flake-shaped to spherical shape. This spherical morphology reduces the anisotropic stress distribution during pressing, allowing high density to be achieved with lower pressing pressure, thereby preventing peeling between graphite and current collector while maintaining high electrode density.
3Reliability
If artificial graphite with secondary particle structure is used, then cycling performance is improved, but pressing pressure must be high to achieve desired density
Solution Approach 1:
The invention applies spheroidality by using spherical natural graphite particles instead of flake-shaped graphite. The spherical shape allows particles to pack more efficiently and uniformly under pressure, achieving the desired electrode density with lower pressing pressure while maintaining good cycling performance through the spherical morphology's inherent advantages.
Data Source
AI summary
A negative electrode material for a lithium-ion secondary battery, in which the negative electrode material includes a composite particle including a spherical graphite particle and plural graphite particles that have a compressed shape and that aggregate or are combined so as to have nonparallel orientation planes, and the negative electrode material has an R-value in a Raman measurement of from 0.03 to 0.10, and has a pore volume as obtained by mercury porosimetry of from 0.2 mL/g to 1.0 mL/g in a pore diameter range of from 0.1 μm to 8 μm.