Negative Electrode Material for Li-Ion Battery
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high-density electrodes while maintaining charge and discharge efficiency and preventing an increase in irreversible capacity, particularly due to the limitations of spheroidal graphite materials which can be damaged by pressing, leading to reduced performance and shorter battery life.
Innovation Solution
A negative electrode material with an oil absorption capacity of 50 ml/100 g or more and a post-pressurization density of 1.70 g/cm3 or more, featuring specific surface area, degree of circularity, R value, and tap density within defined ranges, and comprising aggregated or bonded flat graphite particles to minimize voids and reduce the risk of cracking during densification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If spheroidal graphite is used to increase density, then bulk density is improved, but charge and discharge efficiency deteriorates when pressed
Solution Approach 1:
The invention uses a composite particle structure consisting of spheroidal graphite particles combined with flake graphite particles. The spheroidal graphite provides high bulk density, while the flake graphite particles fill voids and prevent excessive orientation during pressing, maintaining electrolyte permeability and charge/discharge efficiency. This composite approach resolves the contradiction by combining the advantages of both particle types.
Solution Approach 2:
The invention applies local quality by creating a heterogeneous particle size distribution within the graphite material. Small particles are used to fill voids between larger spheroidal particles, while larger particles maintain the overall density. This local variation in particle size and shape allows the electrode to achieve high density without compromising the electrolyte pathways needed for efficient charge and discharge.
2Volume of stationary object
If pressing pressure is increased to densify the negative electrode, then space is reduced, but cracks in particles increase leading to more side reactions
Solution Approach 1:
The invention employs beforehand cushioning by using a composite particle structure with flake graphite particles that act as a cushioning matrix around spheroidal graphite particles. This structure absorbs and distributes pressing pressure, preventing crack formation in the spheroidal particles while still achieving the desired electrode density. The flake particles serve as a protective framework that mitigates the harmful effects of high pressing pressure.
3Quantity of substance
If flat graphite particles are used, then capacity is maintained, but bulk density is low
Solution Approach 1:
The invention merges the advantages of flat graphite particles (high capacity) with spheroidal graphite particles (high density) by creating a composite structure. The flat graphite particles maintain lithium ion capacity, while the spheroidal particles increase bulk density. The combination allows the electrode to achieve both high capacity and high density simultaneously, resolving the contradiction between these two parameters.
Data Source
AI summary
A negative electrode material for lithium ion secondary batteries has an oil absorption capacity of 50 ml/100 g or more, and a post-pressurization density of 1.70 g/cm3 or more.