Graphite-Hard Carbon Anode Composition for Low-Impedance Fast Charging
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Solution Overview
Problem
Current commercial graphite negative electrodes in electrochemical apparatuses, such as lithium-ion batteries, face limitations in fast charge and discharge performance, rate performance, and cycling performance, necessitating an improvement in these aspects to meet the increasing demands of energy density and safety.
Innovation Solution
A negative electrode comprising a combination of graphite and hard carbon, where the mass ratio of hydrogen to carbon in both materials is optimized, along with specific compacted densities and particle sizes, to enhance the active material's performance, thereby improving current distribution and reducing impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If commercial graphite is used as negative electrode material, then high efficiency and stable charge and discharge plateau are achieved, but fast charge and discharge performance and cycling performance are limited
Solution Approach 1:
The patent uses a composite negative electrode material consisting of graphite and hard carbon. The hard carbon component has a hydrogen-to-carbon mass ratio W1/W2 between 5-19 and compacted density ratio d1/d2 between 0.38-0.55 relative to graphite. This composite structure combines the stable charge-discharge characteristics of graphite with the fast ion transport properties of hard carbon, thereby improving both cycling performance and fast charge performance simultaneously
Solution Approach 2:
The patent optimizes specific parameters of the hard carbon material including the hydrogen-to-carbon mass ratio (W1/W2 = 5-19) and compacted density ratio (d1/d2 = 0.38-0.55). By precisely controlling these parameters, the material achieves optimal balance between structural stability for cycling performance and porosity for fast ion diffusion, resolving the contradiction between reliability and productivity
2Stability of the object's composition
If graphite structure is optimized for stability, then stable charge and discharge plateau is achieved, but rate performance is limited
Solution Approach 1:
The composite of graphite and hard carbon allows the graphite component to maintain stable charge-discharge plateau while the hard carbon component provides fast ion transport channels. The hard carbon's disordered structure with controlled hydrogen content creates pathways for rapid lithium ion diffusion without compromising the overall electrochemical stability provided by graphite
Solution Approach 2:
The patent applies local quality by having different regions with different functions: graphite provides stable electrochemical platform with consistent potential, while hard carbon regions provide fast kinetics. The specific local properties of hard carbon (H/C ratio, compacted density) are optimized to create micro-environments favorable for fast ion transport while maintaining overall compositional stability
Data Source
AI summary
A negative electrode includes: a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, where the negative electrode active material includes graphite and hard carbon. Based on a total mass of the hard carbon, a ratio of a mass of element hydrogen to a mass of element carbon in the hard carbon is W1, and based on a total mass of the graphite, a ratio of a mass of element hydrogen to a mass of element carbon in the graphite is W2, a value of W1/W2 being within a range of 5 to 19. The electrochemical apparatus has reduced impedance and improved rate performance and cycling performance.