Composite Carbon Anodes With Silicon Shells for Stable Li Capacity
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Solution Overview
Problem
Existing lithium-based electrical storage devices, particularly lithium ion batteries, face limitations due to low power performance and limited capacity of graphitic anodes, and silicon and tin alloying electrochemical modifiers suffer from substantial swelling and shrinkage, leading to poor cycle life and capacity.
Innovation Solution
Development of composite carbon materials with optimized lithium alloying electrochemical modifiers, such as silicon, incorporated through methods like copolymerizing polymer precursors with electrochemical modifiers and pyrolyzing to form composite materials with high surface area and tailored pore structures, enhancing first cycle efficiency and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or tin alloying electrochemical modifiers are used to increase lithium capacity, then capacity is improved, but substantial swelling and shrinkage occur leading to poor cycle life
Solution Approach 1:
The alloying electrochemical modifier particles are encapsulated within a carbon matrix, forming a core-shell structure where the modifier is nested inside the carbon shell. This nesting approach allows the high-capacity modifier to be protected from mechanical degradation during swelling and shrinkage cycles, resolving the contradiction between achieving high lithium capacity and maintaining cycle life.
Solution Approach 2:
A carbon shell is formed around the alloying electrochemical modifier particles through copolymerization and pyrolysis processes. This shell acts as a flexible protective layer that can accommodate the volume changes of the modifier during lithiation and delithiation, preventing structural collapse and maintaining electrode integrity over multiple cycles.
2Reliability
If very small amounts of alloying electrochemical modifier are used in a largely carbon electrode to maintain cycle stability, then cycle life is improved, but desired increase in lithium capacity is not achieved
Solution Approach 1:
The invention changes the protective parameter from 'minimal modifier content' to 'optimized carbon shell thickness'. By controlling the carbon shell formation through copolymerization ratios and pyrolysis conditions, the electrode achieves both high modifier content (for capacity) and adequate protection (for cycle stability), resolving the contradiction between capacity and stability.
Solution Approach 2:
The invention creates a composite material system combining alloying electrochemical modifiers with carbon-containing polymers. This composite structure allows synergistic properties where the modifier provides high capacity and the carbon polymer matrix provides structural stability and protection, enabling both high capacity and cycle stability simultaneously.
3Stability of the object's composition
If known hard carbon materials are used for anodes, then structural stability is achieved, but first cycle efficiency and capacity remain limited
Solution Approach 1:
The invention applies local quality by creating regions of high lithium reactivity at the carbon shell-modifier interface and within the modifier particles, while the bulk carbon matrix maintains structural stability. This local enhancement of lithium storage capability at specific sites increases first cycle efficiency without compromising overall structural integrity.
Solution Approach 2:
The carbon-containing polymer matrix is designed to undergo copolymerization and pyrolysis beforehand to pre-form a protective yet lithium-conductive carbon shell around the modifier particles. This preliminary structuring creates optimal conditions for high first cycle lithium insertion efficiency while maintaining long-term structural 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 composite materials achieve high reversible capacity, first cycle efficiency, and improved power performance, with first cycle insertion and extraction capacities exceeding 700 mAh/g and efficiencies over 70% without ex situ prelithiation, addressing the limitations of traditional anodes.
Implementation Method 1
Silicon, Tin, and other lithium alloying electrochemical modifiers have also been proposed based on their ability to store very large amounts of lithium per unit weight
Implementation Method 2
The carbon anode typically stores lithium between layered graphite sheets through a mechanism called intercalation
Implementation Method 3
copolymerizing polymer precursors with electrochemical modifiers
Implementation Method 4
pyrolyzing to form composite materials with high surface area and tailored pore structures
Data Source
AI summary
The present application is generally directed to composites comprising a hard carbon material and an electrochemical modifier. The composite materials find utility in any number of electrical devices, for example, in lithium ion batteries. Methods for making the disclosed composite materials are also disclosed.