Lithiated Silicon-Graphite Composite Anodes for Volume Change Stability
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Solution Overview
Problem
Silicon-based anode materials for lithium batteries face challenges such as high volume changes during charging/discharging, leading to poor reversibility and rapid capacity drop, as well as irreversible losses due to foreign elements like oxygen, hydrogen, and inorganic carbon, which react with lithium to form electrochemically inactive products.
Innovation Solution
Composite materials comprising lithiated or partially-lithiated graphite or graphene and silicon with particle sizes between 1 μm to 100 μm, combined with lithium powder in specific molar ratios, undergo mechanochemical conversion under inert conditions, followed by a coating process using gaseous or liquid agents to stabilize the surface and reduce reactivity, resulting in an electrochemical rest potential below 2 V against Li/Li+.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as anode material to achieve high lithium absorbing capacity, then capacity is improved, but volume changes cause pulverizing and separation from current arrester
Solution Approach 1:
Silicon particles are embedded within a graphite matrix structure, where the graphite acts as a stable host framework that accommodates silicon's volume expansion. This nested configuration allows silicon to maintain its high capacity function while the graphite outer layer provides structural stability and prevents pulverizing.
Solution Approach 2:
The invention creates a composite material system combining silicon and graphite in specific ratios (1:9 to 9:1 molar ratio). The composite structure leverages silicon's high lithium capacity and graphite's structural stability, allowing the material to achieve both high capacity and good reversibility that neither component could provide alone.
2Ease of manufacture
If foreign elements like oxygen, hydrogen and inorganic carbon are present in silicon, then material is easier to manufacture, but irreversible losses occur during first charge/discharge cycle
Solution Approach 1:
The invention extracts and removes foreign elements (oxygen, hydrogen, inorganic carbon) from the silicon material through purification processes. By taking out these harmful impurities before composite formation, the material achieves low irreversible losses while maintaining ease of manufacture through controlled purification steps.
3Reliability
If particle size of silicon is reduced to submicron range to improve electrochemical properties, then capacity is improved, but manufacturing complexity increases
Solution Approach 1:
The invention segments silicon into fine particles (1-100 μm range) and distributes them uniformly within the graphite matrix. This segmentation approach improves electrochemical performance by reducing particle size while the graphite framework simplifies the overall manufacturing process by providing a ready-made structure to accommodate the segmented silicon particles.
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 exhibit improved stability, reduced reactivity, and enhanced thermal stability, allowing for higher lithium content without self-ignition, and maintain electrochemical activity, making them suitable for high-capacity anode materials in lithium batteries.
Implementation Method 1
a coating layer comprising functional groups or molecular constituents that have reacted with lithium that was available on the composite materials' surfaces
Implementation Method 2
mechanochemically converting the combination in a temperature range of about 0° C. to about 120° C. under inert gas or in a vacuum
Data Source
AI summary
The invention relates to composite materials comprising lithiated or partially-lithiated graphite or graphene, and silicon having particles sizes from about 1 μm to about 100 μm, and that have an electrochemical rest potential less than about 2 V measured against Li/Li+, wherein graphitic material is mixed with silicon powder in a molar ratio of 9:1 to 1:9 and with lithium powder to an amount of the lithium in the composite material in the range of about 10 molar % to 100 molar % of the stochiometrically maximally possible lithium absorption, and to methods for production thereof.