Graphite Negative Electrode Material for Li-Ion Batteries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high energy density and rapid charge/discharge characteristics due to the trade-off between suppressing excessive reactivity with electrolytes and maintaining high-capacity performance, particularly with graphite-based materials, which often result in increased irreversible capacity and poor rollability.
Innovation Solution
A carbon material with specific physical properties, including a tap density ≥ 0.75 g/cm³, Raman R value ≥ 0.23, and a BET specific surface area between 4 m²/g and 11 m²/g, is developed through heat treatment of natural graphite particles, enhancing both rapid charge/discharge capabilities and reducing irreversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the end face of graphite particle is inactivated to suppress excessive reaction with electrolytic solution, then irreversible capacity is reduced, but rapid charge acceptance characteristics are deteriorated
Solution Approach 1:
The invention applies different surface treatments to different regions of the graphite particle. The end faces are inactivated through heat treatment to reduce irreversible capacity, while the lateral surfaces maintain higher reactivity to enable rapid charge acceptance. This local differentiation resolves the contradiction by allowing each surface region to serve its specific function.
Solution Approach 2:
The invention changes the surface properties of graphite particles by controlling heat treatment parameters (temperature, atmosphere, duration) to achieve specific surface area and surface functional group concentrations. By adjusting these parameters, the particle surface is modified to have reduced reactivity at end faces while maintaining adequate reactivity on lateral surfaces for rapid charging.
2Speed
If specific surface area is increased to enhance rapid charge acceptance characteristics, then charge/discharge characteristics are improved, but electrolytic solution consumption increases leading to electrolyte depletion
Solution Approach 1:
The invention creates non-uniform surface properties where end faces have reduced surface area and reactivity, while lateral surfaces maintain adequate surface area for charge transfer. This local quality differentiation allows the particle to achieve rapid charge acceptance without requiring excessive total surface area, thereby reducing electrolytic solution consumption.
3Quantity of substance
If graphite material is highly densified to obtain high capacity, then energy density is improved, but charge/discharge irreversible capacity increases due to material fracture
Solution Approach 1:
The invention performs preliminary heat treatment of graphite particles before electrode fabrication to inactivate end faces and reduce surface defects. This preliminary action strengthens the particle structure and reduces susceptibility to fracture during subsequent high-density electrode formation, thereby maintaining low irreversible capacity even when the electrode is highly densified for high capacity.
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 carbon material effectively reduces irreversible capacity and maintains high-density, high-capacity performance while ensuring rapid charge/discharge characteristics, supporting the production of high-capacity lithium ion secondary batteries with improved rollability and ease of production.
Implementation Method 1
a negative electrode sheet having a specific surface area (S BET) of not less than 4 m 2/g and not more than 11 m 2/g measured by a BET method... capable of occluding/releasing lithium
Implementation Method 2
heat-treating the graphite material is known. Patent Document 1 discloses heat-treating scale graphite at 400 to 1,800°C in an argon atmosphere
Data Source
AI summary
To provide a carbon material capable of suppressing excessive reactivity with an electrolytic solution and excellent in a rapid charge/discharge characteristics. A carbon material for lithium ion secondary batteries, which satisfies: (i) a tap density ≥ 0.75 g/cm3; (ii) a Raman R value ≥ 0.23 and a half width of D band ΔvD < 45 cm-1, in which the D band appears in the vicinity of 1,358 cm-1 of the Raman spectrum; and (iii) 4 m2/g ≤ BET specific surface area (SA) ≤ 11 m2/g.