Silicon-Graphite Core Shell Battery Anode
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Solution Overview
Problem
Lithium rechargeable batteries face challenges with low energy density and capacity due to the use of graphite as a negative active material, which reacts with organic electrolytes and experiences volume changes during charge and discharge, leading to capacity deterioration and conductivity issues.
Innovation Solution
A negative active material for lithium rechargeable batteries is developed, comprising a core with a lithium-doping material coated with an oxide layer and a carbon layer, which suppresses volume expansion and improves conductivity, formed through heat-treating and etching processes to create a porous structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If graphite is used as a negative active material, then excellent reversibility and long cycle life are achieved, but low density results in low capacity and low energy density per unit volume
Solution Approach 1:
The invention uses a composite structure combining silicon core (for high capacity) with graphite shell (for stability and conductivity). This composite material approach allows the battery to achieve both high capacity from silicon and excellent cycle life from graphite, resolving the contradiction between capacity and reliability
2Reliability
If graphite is used as a negative active material, then long cycle life is guaranteed, but graphite reacts with organic electrolyte at high discharge voltage causing battery swelling and decreased capacity
Solution Approach 1:
The invention introduces an artificial protective film (intermediary layer) between the graphite and organic electrolyte. This film acts as a barrier that prevents harmful side reactions between graphite and electrolyte, while still allowing lithium ion transport, thus eliminating the harmful effects while maintaining the benefits of graphite
3Quantity of substance
If silicon-based negative active material is used, then high capacity is achieved, but volume change of greater than or equal to about 300% during charge and discharge causes weak contact with current collector and deteriorating capacity
Solution Approach 1:
The invention uses a graphite shell (flexible protective layer) that can accommodate the volume expansion and contraction of the silicon core during charge and discharge cycles. This flexible shell maintains structural integrity and prevents pulverization, allowing the silicon to achieve high capacity while maintaining volume stability
4Quantity of substance
If silicon-based negative active material is used, then high capacity is realized, but low electrical conductivity results in no smooth charge transfer reaction when intercalating/deintercalating lithium
Solution Approach 1:
The invention creates a composite structure where graphite (with high electrical conductivity) surrounds the silicon core. The graphite shell provides excellent electrical conductivity pathways, enabling smooth charge transfer reactions, while the silicon core provides high capacity. This composite approach resolves the contradiction between capacity and conductivity
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 solution enhances the battery's capacity and cycle-life characteristics by preventing material pulverization and side reactions, while improving electrical conductivity and high-rate capability.
Implementation Method 1
an oxide layer of the material being capable of doping and dedoping lithium formed on the exterior of the core including a material being capable of doping and dedoping lithium
Implementation Method 2
a carbon layer formed on the exterior of the oxide layer of the material being capable of doping and dedoping lithium
Implementation Method 3
heat-treating and etching processes to create a porous structure
Data Source
AI summary
Disclosed are a negative active material for a rechargeable lithium battery that includes a core including a material being capable of doping and dedoping lithium, an oxide layer of the material being capable of doping and dedoping lithium formed on the exterior of the core including a material being capable of doping and dedoping lithium, and a carbon layer formed on the exterior of the oxide layer of the material being capable of doping and dedoping lithium, a method for preparing a negative active material for a rechargeable lithium battery, and a rechargeable lithium battery including the same.