Spherical Graphite Anode Structure for Cycle Life and Rate Capability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for preparing spherical graphite particles as anode active materials for lithium secondary batteries face limitations in charge/discharge characteristics and cycle life-span due to instability and irreversible reactions with the electrolyte, as the bonding force of flaky graphite fragments is reduced, leading to poor contact with the electrolyte and excessive solid-electrolyte interphase film formation.
Innovation Solution
A method involving a mechanochemical reaction to spheroidize and coat flaky graphite particles with amorphous carbon, using composite particles like silicon, tin, or their oxides, to enhance the formation of gaps between particles and improve stability, resulting in improved charge/discharge characteristics and cycle life-span.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If flaky graphite particles are granulated into spherical particles without gaps between fragments, then particle density is improved, but charge/discharge characteristics deteriorate due to limited electrolyte contact
Solution Approach 1:
The spherical graphite particle is segmented into multiple flaky graphite fragments that are bonded together. This segmentation creates internal gaps and void spaces between the fragments, allowing electrolyte penetration while maintaining the overall spherical shape and density needed for good manufacturing properties.
Solution Approach 2:
The surface structure of the spherical particle is designed with local variations - the outer surface maintains spherical integrity for good contact, while the internal structure between fragments creates gaps for electrolyte access. This local quality differentiation resolves the contradiction between density and reactivity.
2Ease of manufacture
If conventional granulation is used to form spherical particles, then manufacturing simplicity is maintained, but particle stability deteriorates due to reduced bonding force of flaky fragments
Solution Approach 1:
The flaky graphite fragments are subjected to ultrasonic treatment before granulation to pre-expand gaps and create defects on the fragment surfaces. This preliminary action enhances the bonding interfaces between fragments during subsequent granulation, improving particle stability while maintaining manufacturing simplicity.
Solution Approach 2:
Ultrasonic vibration is applied to the flaky graphite particles to induce mechanical effects that expand gaps between fragments and create surface defects. This mechanical vibration enhances the bonding characteristics of fragments during granulation, resolving the stability issue without complicating the manufacturing process.
3Duration of action of moving object
If repeated charging/discharging is performed with conventional particles, then battery capacity is utilized, but harmful effects increase due to irreversible reactions and excessive solid-electrolyte interphase film formation
Solution Approach 1:
The surface of the spherical graphite particles is pre-coated with amorphous carbon before battery assembly. This preliminary protective layer prevents direct contact between the graphite surface and electrolyte, blocking irreversible reactions and excessive solid-electrolyte interphase film formation during subsequent charging/discharging cycles while still allowing lithium ion transport.
Solution Approach 2:
The amorphous carbon coating, which could be seen as an additional layer potentially blocking ion transport, actually benefits the system by preventing harmful irreversible reactions. The coating converts the potential harm of direct graphite-electrolyte contact into a protective barrier that enhances long-term battery performance and stability.
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 method effectively enhances high-rate charge/discharge characteristics and cycle life-span of secondary batteries by forming stable spherical graphite particles with improved bonding and reduced irreversible reactions, leading to higher charge/discharge efficiency and capacity retention.
Implementation Method 1
preparing coated particles by mixing the intermediate-stage spheroidized particles with composite particles and performing a mechanochemical reaction thereon to coat the surface of the intermediate-stage spheroidized particles with the composite particles
Implementation Method 2
spheroidizing the coated particles and coating the surface thereof with amorphous carbon to prepare spherical graphite
Implementation Method 3
during charging and discharging processes in which lithium ions are repeatedly intercalated and deintercalated
Data Source
AI summary
The present invention relates to a method for preparing an anode active material and a secondary battery including the anode active material. The anode active material may be prepared by including the steps of: preparing intermediate-stage spheroidized particles by pulverizing and spheroidizing flaky graphite particles; preparing coated particles by mixing the intermediate-stage spheroidized particles with composite particles and performing a mechanochemical reaction thereon to coat the surface of the intermediate-stage spheroidized particles with the composite particles; and spheroidizing the coated particles and coating the surface thereof with amorphous carbon to prepare spherical graphite.