Silicon Suboxide-Graphene Composite for Battery Electrode Stability
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Solution Overview
Problem
Lithium ion batteries face challenges with high irreversible capacity loss and poor cycling stability due to structural changes and large volume expansions in silicon-based negative electrodes, which affect their energy and power density.
Innovation Solution
A composite material comprising processed silicon suboxide and graphitic carbon, with at least a portion of the graphitic carbon in graphene sheets, is developed using high energy mechanical milling to enhance cycling stability and specific capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to increase energy density, then specific capacity is improved, but cycling stability deteriorates due to large volume expansions and structural changes
Solution Approach 1:
The patent applies parameter changes by controlling the oxidation state of silicon to create silicon suboxide (SiOx where 0 < x < 2) with specific compositional parameters. This intermediate oxidation state reduces the volume expansion during lithium alloying compared to pure silicon, while maintaining high capacity. The controlled oxidation parameter resolves the contradiction between high capacity and cycling stability.
Solution Approach 2:
The patent creates a composite material system consisting of silicon suboxide particles embedded in a carbon matrix. This composite structure combines the high capacity benefits of silicon with the structural stability and conductivity of carbon, preventing the volume expansion problems of pure silicon while maintaining high specific capacity through the silicon suboxide component.
2Quantity of substance
If high capacity negative electrode materials are used to increase energy density, then discharge capacity is improved, but irreversible capacity loss increases
Solution Approach 1:
The patent introduces carbon as an intermediary material that mediates between the silicon suboxide and the electrolyte. This carbon layer acts as a protective interface that reduces direct contact between the reactive silicon suboxide and the electrolyte, minimizing side reactions and irreversible capacity loss while allowing lithium ions to pass through for high discharge capacity.
Solution Approach 2:
By controlling the oxidation state parameter of silicon to create suboxide rather than pure silicon or fully oxidized silicon, the patent optimizes the balance between capacity and stability. The specific compositional parameter of silicon suboxide reduces irreversible capacity loss compared to pure silicon while maintaining high discharge capacity.
3Quantity of substance
If silicon-based materials are used to improve energy density, then specific capacity is increased, but volume expansion occurs during lithium intercalation
Solution Approach 1:
The patent changes the compositional parameter of silicon by oxidizing it partially to form silicon suboxide (SiOx with 0 < x < 2). This compositional modification fundamentally changes the volume expansion behavior during lithium alloying, reducing it from the extreme values seen in pure silicon to more manageable levels that maintain structural integrity and enable high specific capacity.
Solution Approach 2:
The carbon-silicon suboxide composite structure accommodates volume changes more effectively than pure silicon. The carbon matrix provides a flexible framework that can absorb and distribute the volume expansion stresses, allowing the silicon suboxide to undergo lithium alloying with reduced net volume expansion and improved 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 material achieves stable cycling performance with a high specific capacity, maintaining 87% of the 5th cycle discharge capacity at the 50th cycle, and supports a discharge rate of C/3, improving the overall energy and power density of lithium ion batteries.
Implementation Method 1
performing high energy mechanical milling of graphite powder with reduced silicon oxide material
Implementation Method 2
at least a portion of the graphitic carbon in graphene sheets
Implementation Method 3
structural changes and anomalously large volume expansions, especially for silicon, that are associated with lithium intercalation/alloying
Data Source
AI summary
Composite silicon based materials are described that are effective active materials for lithium ion batteries. The composite materials comprise processed, e.g., high energy mechanically milled, silicon suboxide and graphitic carbon in which at least a portion of the graphitic carbon is exfoliated into graphene sheets. The composite materials have a relatively large surface area, a high specific capacity against lithium, and good cycling with lithium metal oxide cathode materials. The composite materials can be effectively formed with a two-step high energy mechanical milling process. In the first milling process, silicon suboxide can be milled to form processed silicon suboxide, which may or may not exhibit crystalline silicon x-ray diffraction. In the second milling step, the processed silicon suboxide is milled with graphitic carbon. Composite materials with a high specific capacity and good cycling can be obtained in particular with balancing of the processing conditions.